Flexible Operations Technical Advisory Group · Fuel integrity investigations Chemistry, Low Level...

© 2016 Electric Power Research Institute, Inc. All rights reserved.

Sherry Bernhoft

Senior Program Manager

Nuclear Power Council

Wednesday, August 31, 2016

Flexible Operations

Technical Advisory GroupIntroduction and Project

Summaries

081716 R.1

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EPRI’S PRIMARY

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YOUR ROLE AT EPRI

ADVISORY MEETINGS

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Agenda

Flexible Operations TAG

Meeting Holder: Sherry Bernhoft

Room Location: Roosevelt Ballroom, Salon IV

Wednesday, August 31, 2016

Time Topic Lead

8:00 am Welcome and Introductions S. Bernhoft, EPRI

8:45 am Fuel Integrity under flexible operations S. Yagnik, EPRI

9:15 amBalance of Plant Impacts and Site Readiness Review Visits

D. Ziebell, EPRI

10:00 am Morning Break All

10:15 am Exelon Operating Experience Report T. Wojcik, Exelon

11:00 amINL Integrated Nuclear- Renewable Energy Systems Feasibility Study

S. Bragg-Sitton, INL

11:30 am Case Studies for Flow Accelerated CorrosionR. Wolfe, EPRI

11:45 amSteam Generator Primary to Secondary Leakage GLs

H. Cothron, EPRI

12:00 pmLunch - Waldorf Astoria Ballroom (Mezzanine Level)

All

Time Topic Lead

1:00 pm Crud Transport Studies – PWR & BWR D. Wells, EPRI

1:30 pm PWR Water Chemistry J. McElrath, EPRI

2:00 pm BWR Water Chemistry S. Garcia, EPRI

2:30 pm Radiation Safety: Source Term ImpactsP. Tran, EPRI

C. Gregorich, EPRI

3:00 pm Afternoon Break All

3:15 pm Primary Side Impacts – Study Results D. Steininger, EPRI

4:00 pm Round Table and Stakeholder Input All

4:45 pm Summary and Action Item Review

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EPRI Flexible Operations Program

Purpose:

Proactively identify, understand, research and define management strategies to mitigate potential impacts of plant flexible operations

Actively engage all key stakeholders

Share Operating Experience

Completed:

Gap Matrix

Transition reference guideline published 2014

Secondary-side vulnerability assessment published 2014

Supplemental program funded for 2105-2017

EPRI Project Team of SMEs

Developing project plans and budget for 2018 – 2020 program extension

Columbia Generating Station

Economic Dispatch June 2008

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NPP Flexible Operations TAG - Membership

Members:

Westinghouse

Mitsubishi Heavy Industries

AREVA

GE Hitachi

Nuscale – new 2016

CANDU Owners Group

UNESA – A.E. Industria Electria

Emirates Nuclear Energy Corporation

Southern Nuclear Operating Co.

Electricite de France S.A.

Nebraska Public Power District

Exelon Corporation

Pinnacle West Capital Corporation

Pacific Gas & Electric Co.

Participants as Stakeholders:

US DOE (INL)

INPO

IAEA

NEI

PWROG

BWROG

NEIL – new 2016

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Funding Status – NPP Sector Flexible Operations

Supplemental for 2015-2017:

– Three year project commitment

– $40k/year for EPRI members

– $50k/year for non-members (vendors)

– $610k total/ year

Base:

– $600k in 2016

– $600k in 2017

Budget for 2018 – 2020

– Under development

Total research projects of $1.2M/ year

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What We Learned …. Flexible Operations is Possible

“Approach to Transition NPPs to Flexible Plant Operations” (#3002002612 January 2014)

Need to establish protocol with the ISO/TSO

Plant modifications maybe needed

Challenges at end-of-cycle

Xe transients

Li-control band

Volume of waste water generated

Protection of secondary components

Accident and transient analysis

Changes are needed to operating procedures, and maintenance programs

Training needs to be a part of the plan

Flexible Operations is possible … but what are the

impacts?

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How NPPs Can Be Flexible – i.e. Help with Grid Variability

Need to change the paradigm on how NPP

Flexible Operations can help with grid

variability

– NPPs will not respond the same as fossil

plants!

Two options:

– Pre-planned and maneuvered by the control

room operator

– Frequency control by ISO/TSO within a pre-

determined band (International mostly)

Three pre-planned ‘bounding’ cases for the

studies:

– High renewable integration

– Extended low power operation

– Response to grid transient

High renewable integration

Be available on a daily basis for a pre-planned

100-80-100 power cycle

Example – days with low demand and high

solar

Extended low power operations

Pre-planned extended operations at ~50%

power with scheduled maintenance activities

Example – high hydro in the spring, or low

demand in the winter

Response to grid transients

Up to 5%/minute power change 100-30-100

due to grid conditions

Research question – can this be done with

existing design and how frequently

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Priorities for 2015 - 2017

Operating Experience (OE) exchange and readiness reviews for

transition to flexible operations

Fuel integrity investigations

Chemistry, Low Level Waste and Radiation Management guideline

reviews

Impacts on balance of plant, data collection and guidance

recommendations

Impacts assessment on primary side (NSSS)

Updated Gap Matrix for 2018 – 2020 project prioritization

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Project Status Summary

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OE Exchange and Readiness Reviews

Operating Experience reports are presented at each TAG

– EDF

– Bruce Power

– Columbia Station

– Exelon

– Germany OE (presented by AREVA)

Facilitated focused group to support readiness reviews – Dave Ziebell

– Small group for flexibility readiness information exchanges and challenge reviews being formed

– Completed site readiness reviews:

Diablo Canyon (Palo Verde participated)

Quad Cities

Bryon

BYR01V_U0921

99.894

PC

11/24/2015 12:00:00 AM10/5/2015 12:00:00 AM 50.04 days

U1 Economic Dispatch

50

60

70

80

90

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Support for site readiness reviews and data collection

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Fuel Integrity

Fuel Integrity – Suresh Yagnik

– Operational recommendation to ensure fuel integrity under Flexible Plant Operations

– Phenomena Identification and Ranking Table (PIRT) with fuel vendors and industry SMEs–

completed August 2015

– Work with fuel vendors to use their codes to assess impact of flexible operations

– Technical Report: Findings of the PIRT - August 2016

– Technical Report: Update of vendor code work - TBD

Crud deposits and transport studies – Dan Wells (PWR) and Aylin Kucuk (BWR)

– Crud deposition on fuel has led to cladding failure (CILC) and other operating challenges such

as channel distortion for the BWRs

– Collected and reviewed existing data on power histories and chemistry changes

– Modeling to evaluate the impact of crud redistribution under flexible operations

– Technical Report: Impact of Flexible Operations on Crud Transport for PWRs - October 2016

– Technical Report: Impact of Flexible Operations on Crud Transport for BWRs - 2017

Crud-Induced Localized

Corrosion (CILC) Failures

Pellet Clad Interactions

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Integrity of PWR Control Rods – New

Considerations for control rod usage during flexible

operations:

– Increase inspections and monitoring of control rod

condition

– Variable operations result in absorber swelling

behavior leading to mechanical life limits (MEOL)

Tip swelling leading to clad cracking and/or fretting

wear

– Burnup of dominant Ag, In and Cd isotopes leading to

nuclear life limits (NEOL) and reactivity (worth) control

issues

Project co-funded with Fuel Reliability Program

(FRP) for 2017 & 2018

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Chemistry and Radiation Safety

Radiation Safety – Phung Tran

– Conduct gap assessment and investigate potential impacts:

Source Term and Radiation Fields – Carola Gregorich

Radiation Protection and Worker Dose – Donald Cool

Effluents (Gaseous and Liquid) – Karen Kim

Radioactive Waste – Karen Kim

– Technical Report: Flexible Operations Impact on Source Term – 2017

– Technical Report: Flexible Operations Impact on Radioactive Waste and Effluents – 2018

– Technical Report: Flexible Operations on Radiation Protection – 2018 (if funded)

Chemistry – Susan Garcia (BWR) and Joel McElrath (PWR)

– Understand the impacts on Water Chemistry GLs

– Impacts have been identified:

Corrosion product transport and control parameters

Maintaining boron-lithium controls

Chemical injection system demands

– Collected and reviewed chemistry data during periods of cycling

– Technical Report: Gap Assessment of impacts on PWR Water Chemistry – Nov 2016

– Technical Report: Gap Assessment of impacts on BWR Water Chemistry – Nov 2016

Minimizing Dose

Reducing Radiation

Fields

Accurate Reporting

Optimized Waste

Storage

EPRI

Chemistry Program

Minimizing material

degradation, improving

asset protection, and

reducing source term

Auxiliary

Chemistry

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Balance of Plant and FAC Program Impacts

Secondary Side/BOP System Impacts – David Ziebell

– Completed site visits: Columbia, Bruce, Diablo Canyon, Quad Cities, Bryon

– Technical Report: Summary of lessons learned and recommendations – 2017

– Technical Report: Impact of FPO on large pumps and seals – 2018 (if funded)

– Technical Report: Impact of FPO on maintenance and operations of rad waste process equipment – 2019 (if funded)

– Technical Report: OE update – 2020 (if funded)

Flow Accelerated Corrosion – Ryan Wolfe

– Completed case studies for 1 PWR and 1 BWR

– Review data and heat balances for varying power levels

– Conclusions:

There is some variability in the FAC wear rates for two phased systems (e.g. Extraction Steam) due to changes in quality

FAC susceptibility may be affected due to changes in temperature and quality

Previously excluded lines may become susceptible during FPO

Inspection selection should consider susceptibility changes and changing FAC wear rates as a result of FPO.

– Technical Report: FAC Case Studies - 2017

– Technical Report: Impact on susceptible but not modeled lines – 2018 (if funded)

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Primary Side (NSSS) Impacts

Primary Side NSSS Impacts – David Steininger and Kyle Amberge

– Assessing the impacts on primary side components due to flexible operations

– Westinghouse (PWR) draft report completed

– GEH (BWR) in progress

– Project started in 2016 to further quantify the impacts PWR core internals (MRP-227 impacts)

– Technical Report: PWR Load Following Impacts August 2016

– Technical Report: BWR Load Following Impacts September 2016

– Technical Report: PWR Core internals impacts - 2017

Steam Generator Impacts – Brent Capell

– Assessing the impacts on SGs

– Operating Experience data collection and analysis

– Technical Report: Impact on Secondary-to-Primary Leakage GL due to flexible operations – 2017

– Technical Report: FPO impact on secondary side crud and iron transport – 2018 (if funded)

– Technical Report: FPO impact on SG integrity GLs and alternate repair criterion – 2019 (if funded)

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EPRI Cross Sector Work

Cross-sector coordination – Mike Carravagio

– Changing mission profile working group - Generation

– Flexible Operations TAG - Nuclear

– Share OE across the sectors – David Ziebell

Support DOE project using REGEN (an economic

modeling tool) to answer the question “How much

flexibility will be required”

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Integrated Hybrid Systems

Technology Innovation proposal for 2017

– Feasibility study for an hybrid integrated

energy system with existing NPP

– Collaboration with INL (DOE funded) and

NREL

– Use electrical power during periods of low

demand

– High potential projects are desalinization and

hydrogen production

Applicable to existing plants and new builds

– Andrew Sowder

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Together…Shaping the Future of Electricity

Suresh Yagnik

Technical Executive

Flexible Operations Technical Advisory

Group

August 31, 2016

Fuel Integrity Under Flexible

Operations

PIRT Process (Completed)

&

Future Plans

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Key question:

How will this work without increasing risk of fuel failures?

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Presentation Outline

Update on PIRT process (completed)

– Recap from last TAG meeting

Future plans

– Validation and analysis of fuel behavior under FPO

Concluding Remarks

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Recap from the last TAG meeting

Expert Panel consisting of fuel-suppliers, utilities, and INPO

convened

PIRT process completed

– Focus : Identify and rank fuel behavior (phenomena) that arise in

transitioning from Baseload to FPO

Recommendations from PIRT Expert Panel presented

– Ranked phenomena tabled

– Direct expert response to the questions posed to the panel

Report written-up, reviewed, and comments addressed

– To be published

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What is PIRT?

Phenomena Identification and Ranking Table (PIRT)

– A structured process to identify and rank phenomena and assess

their importance. In this case,

Phenomena = Various behavior regimes and characteristics

that impact fuel performance under FPO

Considerations under the phenomena may have varying

degrees of

– Complexities

– Knowledge and prior experience base

PIRT process has been used by NRC

– To evaluate (e.g., LOCA, RIA, concrete degradation)

– Typically, with ~ 8-10 Expert Panelists participating

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PIRT Process – Evaluation Criteria

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Recap (cont’d)

All levels of fuel phenomena considered in terms of power changes:

– How fast? (Rate)

– How much? (Depth)

– How long? (Duration)

– How often? (Frequency: Daily, Weekly, Seasonal)

Fuel Pellet Fuel Cladding

Fuel Rod Fuel Assembly

Safety and Core Design Core Monitoring

RCCA/Control Blade CRDM and drive mechanisms

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Recap (cont’d)

PIRT report completed:

– “An Assessment of Fuel Performance Requirements for Baseload

Nuclear Power Plants Transitioning to Flexible Power Operations”,

EPRI-3002009087 (2016).

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Future Plans: Part 1—Validation/Benchmarking

Fuel performance analyses using FP codes

– All fuel suppliers, EDF, and EPRI have their own codes

– Validated for base load operatons but not rigorously for FPO

Approach:

– Continue collaboration of the PIRT group organizations

– Analyze and benchmark results from a test-reactor experiment which emulated

FPO type of power changes

Fuel rod segment response monitored/measured (e.g., rod outer diameter)

PIE performed

EPRI FRP had acquired such data from prior EDF test programs completed in France

– DÉCOR (1994)

– RECOR (1998)

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More about DÉCOR and RECOR (for analysis work in 2016-17)

DÉCOR (1994)

– In-situ measurement of the cladding strain of fuel test rods in Siloé

under PWR conditions

During steady state and power changes

– Capable of measuring fuel-cladding hard contact during power

change accurately

RECOR (1998)

– In-situ measurements of the impact of pellet fragmentation and

relocation on test rods submitted to typical load follow power profile

– Performed on a fresh fuel rod of perfectly known characteristics

and dimensions to analyze pellet cracking and relocation

– Typical data show cladding creep and ridging in cladding at mid-

pellet and inter-pellet locations

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Typical RECOR data (published)

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Future Plans: Part 1—Validation/Benchmarking (cont’d)

Approach (cont’d)

– Evaluate and synthesize all analysis results as a collaborative

group exercise, while respecting proprietary information and

independence

– Participants draw their own conclusions whether any behavioral

models in the codes need to be improved under FPO

If so to be pursued independently by each Participant

Precedences of such approach exist in the ‘fuel world’ (e.g.,

NFIR, OECD programs)

Benefits:

– Unique validation case study made available to industry wide

stakeholders

– Technical exchanges among fuel performance experts provide

insights to all

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Analysis Details

– Evaluation based on an EDF simulated fuel rod irradiation

17x17 design, full length rod

Power history contains two periods of irradiation:

– 1) An initial steady state irradiation at ~ 20 kW/m to ~ 11

GWd/tU

– 2) A second period with three ramps reaching 35.5 kW/m at ~

12 GWd/tU burnup. Followed by a period of reduced power

operation (at 25kW/m)

Starting at ~ 13 GW/tU and held for ~ 2 wks (350 hrs) before

returning to full power (35.5 kW/m)

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Post analyses data evaluations

– Primary parameters of comparison will include:

Fuel/cladding gap thickness

Cladding deformation (diametral strains)

Cladding peak hoop stress

– These values will compared over time to assess the effects of rod

deconditioning and response to the extended period of reduced

power operation.

– Other fuel performance parameters will also be noted… such as

rod internal pressure, void volume, FGR release, rod elongation,

etc.

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Example of fuel rod response… cladding OD

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Have approached all fuel suppliers of FPO program and

EDF

– All agree in principle

– Implementation being pursued at present

Next steps…

– Convene a kick-off Webcast

– Share experimental details and power histories

– Allow time for Participants to complete their own analyses

– Synthesize results

– Convene a live meeting (1-2 days) to discuss results and draw

conclusions

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Have approached all fuel suppliers of FPO program and

EDF

– All agree in principle

– Implementation being pursued at present

Details, details…

– Convene a kick-off Webcast

– Share experimental details and power histories

– Allow time for Participants to complete their own analyses

– Synthesize results

– Convene a live meeting (1-2 days) to discuss results and draw

conclusions

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Future Plans: Part 2—Sensitivity Analyses

Perform sensitivity analysis around parameters in daily,

weekly, and seasonal scenarios of FPO

Key issues to be examined are:

– The effects of length, depth, and frequency of reduced power

operation on fuel rod deconditioning

– Identification of operational ranges to mitigate or limit PCI rod

failure susceptibility

– The definition of a simulation-based “safe operational envelope” for

FPO

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David Ziebell

Senior Technical Leader


Committee

August 31, 2016

Balance of Plant Impacts

& Readiness Review Visits

080516

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Content

Project Status and Evolution

Preliminary Results for Discussion

Going Forward – Opportunities to Get Involved

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2017: Summary of BOP Impacts Findings and

Insights from Applying EPRI’s Approach to

Transitioning to Flexible Plant Operations

Planned Deliverables

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Balance of Plant (BOP) Impacts

Assess impacts of flexible operations on secondary

plant components with supporting industry data

Flexible Plant Operations Assessment and

Management Matrix, Published Oct 2014

(3002004360)

– Expert panel process

– Systematic evaluation to identify potential

vulnerabilities and management strategies

Initial Research Phase: Validate the matrix

and develop recommended actions

Status: Still seeking more plants, expanding to

include Readiness Review Visits to gain more

experience/data and provide support of utility

decision-making process Generation Sector also affected…

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Mission Profiles Working Group Liaison

Many dozens of issues across the SME

groups

Above are some drivers in the Generation

sector

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Deliverables

Database– Warehouse of all issues

– Living database

Database potentially used to develop:– Self-Assessment tool

Systematic approach for assessing which issues to address

– Progressive Layup tool

Extending shutdown period, process for ensuring equipment preservation

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Preliminary Results

Energy Northwest – Columbia: October 12-13, 2015

Bruce Power – Bruce A and B: October 15-16, 2015

PG&E – Diablo Canyon: April 13-14, 2016

Exelon – Quad Cities: April 25-27, 2016

Exelon – Clinton: April 28, 2016

Exelon – Byron: May 23-25, 2016

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Columbia – single BWR 5

Resonances– Main Turbine vibration at a high reduced power level

– Condensate Booster Pumps

Leaks after transients– Digital Electro-Hydraulic turbine controls

– Steam Leaks

– Turbine Driven Reactor Feedwater Pump Seals

– Hotwell (Condensate) Pumps

Operational issues related to transients– Errors – two-stage MSRs, 4C drain cooler

– Operator Burdens – TDRFW Seal Injection, Hotwell pumps, H2 and Airside Generator Seal Oil Coolers

Physical issues related to transients/reduced power– 4 point drain coolers move into the sweet spot temperature for FAC

– Thermal transients on Exciter Diodes

– Condenser erosion from TDRFW miniflow

Potential success story on MOV/AOV valve packing

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Bruce Power – 8 CANDU

“Maintenance Campaigns in the condenser have increased due to SBG.”– increased cracking in the Condenser Steam Dump Valve (CSDV) headers

– atypical erosion patterns adjacent to lower portion of CSDV header

– parts fall off CSDV headers, damage tubes

Resonances– Unit 1 turbine only – dynamic balance not yet done

– Old style CSDV – replacing them all: 24 valves

– Turbine engineers walk down all systems, find/fix vibrating things

Operational issues related to transients– Generator H2 cooler imbalance at reduced output

– Increased duty cycles on many valves throughout secondary plant, no concern yet other than CSDVs

Physical issues related to reduce power– Increased MIC in H2 Coolers in winter with stagnant flow due to TCV closure

– Steam Pipe struts/hangars between Governor valves and HP Turbine Steam Chest

– Evaluating turbine blade flutter with increased backpressure (Siemens 13.9 Turbine Tech Bulletin)

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Diablo Canyon – 2 Westinghouse PWR

Operational issues:

– Chemical Injection Pumps loose suction when

shifting from vendor-provided skid to the in-house

pumps; in-house pumps loose suction creating a chemistry

transient

– They used to have problems with feed water heater level controls,

but no longer.

They are certain iron transport increases as a result of any

transient.

LP turbine seal rubbing during deep load reductions caused

by uneven heating in the condenser fixed. They beefed up

the design of the seal so that if a rub occurs, the seals are

not rapidly degraded.

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Quad Cities – Two BWR 3

Advanced Nuclear Dispatch begun 3/1/16

– 2002-2005 EPU 820 MWe to 980 Mwe (17%)

– Finding/fixing emerging issues during load ramps is difficult for stations that maneuver on short notice or have limited access due to ALARA

Small-bore piping vibration-induced failures

– MS Instrumentation lines, Booster pump seal injection lines

FW Heater Train Trips on load reductions for turbine valve tests

– Flash tank level controller AOV air leak is proximate cause, FW Heater Tuning Team formed to improve resiliency

Condensate Booster Pumps shuttle at a specific power reduction

– Complex cause, current economic risk management guidance is: set maneuvering floor above that level.

Vacuum changes flex the main turbine bearing supports

– Once rubbed a bearing edge at a deep load reduction – treated as minor issue.

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Byron – 2 Westinghouse PWR

HIT Approach used to guide utility through rapid initiation of FPO

– Charter with success criteria, Multi-discipline team, actions trackedin CAP, team closed out with right to re-start if needed

Steam Driven Feedwater Pump Controls need special handling during load reduction to avoid severe resonance

Several swing check valves replaced with nozzle check design

Operational impact on AOP for Condenser tube leak

Useful management practices: CAP tracking code “ECD”; reviewed system monitoring plans,

Weak/under-designed components being addressed

– CD pump impellers and seals, cooling tower, increased check valve inspections, MSR normal and emergency drain valves

Some design features advantageous

– Stainless H2 coolers; Stiffening ring in end windings limits effects of temperature differences across machine, heater drain controls well tuned, MSR and heater drain pumps started at low power and auto controls work well to 100%; cycle isolation design is efficient;

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A Few Points of Interest

A CSDV failed closed during 300 MWe SBG due to condenser spray interlock issue…

– New, or previously rare failure mode / event initiator

– AOP interactions may need more imaginative review

Maintenance practices must be near-perfect so that the small things are resilient for FPO

– Bolted joints, valve and pump packing/seals, calibration and tuning control systems, alignment, balancing, etc.

Some components may be under-designed for new demands

– Bruce CSDVs, small-bore piping vibration susceptibility

Some over-designed components may need scrutiny due to demands of reduced power combined with cold weather

– oversized transformers staged for EPU

14


Broad conclusions

Similarity of BOP issues across plant designs

– Importance of quality maintenance and calibration practices

– Small bore piping and other sensitivities to vibration

– Pumps running in parallel (shuttling at particular flowrates for motor

driven pumps or resonance bands in steam driven/variable speed

pumps); further EPRI effort planned

– Importance of cooling system controls (some still manual, others

lack requisite complexity)

Validity of training operators and technicians

– Valve packing, calibration of heater level controls, sequence of

operating steam driven pumps during ramps

– Cold weather operations may warrant additional scrutiny

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Value of this effort

Consensus requires being skeptical of claims that

“this is unique to me” and

“everybody should do this because when I was a wee

engineer, we found _________”

EPRI is well positioned to collaborate with a variety of utilities

to help guide a cost effective approach to understanding and

managing the phenomena/risks associated with increased

FPO.

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Readiness Review Visits available

Two way street:

– EPRI project/program gains more data, we share insights

– Address the approach to transitioning to FPO – customizable

across the program

17


Next Step: How can you participate?

Site impact of participating may be as low as a few person-days of Engineering staff time for a site visit, with several one-on-one interviews

Benefits:

– Sustained Equipment Reliability

– Use EPRI’s guided process of capturing the data instead of re-invent a process

– Fastest benchmarking with other participating utilities

– Direct advice to the project regarding priorities for recommendations

– Support for your internal deep-dive into FPO

Reduced power for UHS?

Power Uprate?

Coast down?

Reduced power for safety margin?

Contemplated economic dispatch?

Or, will you in the near future be doing these things?

ANSWER: Contact Sherry or David!

18



1


Exelon Operating Experience Report

“Presentation Placeholder”*Materials will be added on (TBD)

1


INL Integrated Nuclear –

Renewable Energy System Feasibility

“Presentation Placeholder”*Materials will be added on (TBD)


Ryan Wolfe

Principal Technical Leader, Engineering Programs

Flexible Operations

Technical Advisory Group Meeting

August 31, 2016

080216

Flow Accelerated Corrosion (FAC)

Flexible Operations Case Study

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Background

FAC Flexible Operations Case Study

FAC can affect personnel safety and equipment reliability.

Flexible Power Operations (FPO) will affect FAC susceptibility and degradation

rates through changes primarily in:

– Temperatures

– Steam Quality

– Mass flow rates

Experience with power uprates is plant and location-specific.

– The increase in FAC rate can be 2X the power level increase.

3


FAC Flexible Operations Case Study

Objectives

NSAC-202L* recommends evaluating the changes to operating conditions and heat balance diagrams using Predictive Plant Models (e.g., CHECWORKS™ SFA).

Case Study will document changes in FAC rates for different locations at target power levels of 75%, 50%, and 25%.

Results for a typical PWR and BWR will be published in 2017.

*Recommendations for an Effective Flow-Accelerated Corrosion Program (NSAC-202L-R4). EPRI, Palo Alto, CA: 2013. 3002000563.

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FAC Case Study Methodology

Develop CHECWORKS™ Steam Feedwater Application (SFA) 4.1 Test Models

Perform CHECWORKS™ SFA 4.1 Water Chemistry and Wear Rate Analysis

Perform CHECWORKS™ SFA 4.1 Wear Rate Analysis Comparison

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FAC Case Study Tasks

Test Model Development

– Two Plant Types (4-loop Westinghouse PWR & BWR-3)

– 4 Different Power Levels (100%, 75%, 50%, 25%)

– Power Level, Steam Cycle, and Component Level Data Populated

– Carbon Steel Material

Water Chemistry & Wear Rate Analysis

– Constant Chemistry

– Sampling of Lines

Single Phase

Two Phase

Flashing Flow

Wear Rate Analysis Comparison, to review differences in:

– Temperature

– Quality

– Mass Flow Rate

– Wear Rate

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Preliminary Results

Temperature (as a % of 100%)

Generally, temperature decreases as power

decreases.

One exception, PWR LP Extraction Steam,

decreases at the 75% power level but increases

through the 50% and 25% power levels.

FAC susceptibility may be affected by changes

in temperature (i.e., lines which drop below 200°F during FPO).

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Preliminary Results

Steam Quality

Generally, Quality decreases as power decreases.

Notable Exceptions:– Quality is 0% for Feedwater, Condensate, HP Heater

Drain U/S CV and LP Heater Drain U/S CV.

– PWR LP Extraction Steam steadily increases to superheated through the 50% and 25% power levels.

– BWR HP and LP Extraction Steam increases.

FAC susceptibility may be affected by changes in quality (i.e., lines which become superheated).

Decreasing

Quality

8


Preliminary Results

Mass Flow Rate (as a % of 100%)

Mass Flow Rate decreased as power

decreased. ☺

Generally decreased by more than the power

level percentage difference for all lines (e.g. HP

Extraction flow rate decreases by 40% from the

100% to the 75% power level).

9


Preliminary Results

Average Wear Rates (as a % of 100%)

Generally, Wear Rates decrease as power decreases.

Notable Exceptions:

– Single Phase: Temperatures approaching peak susceptibility at 300°F (150°C)

– Two Phase: Wetter extraction steam lines

Depending on conditions, changes in chemistry and flow rate may also increase

the wear rate.

10


Preliminary Conclusions

Generally, FPO leads to decreased FAC wear rates in most systems which are

traditionally modeled using CHECWORKS™ SFA (Condensate, Feedwater,

Heater Drains, etc.)

There is some variability in the FAC wear rates for two phased systems (e.g.

Extraction Steam) due to changes in quality as a result of FPO.

FAC susceptibility may be affected by FPO due to changes in temperature and

quality.

Previously excluded lines may become susceptible during FPO.

Inspection selection should consider susceptibility changes and changing FAC

wear rates as a result of FPO.

11


Additional Considerations

Effects of configuration changes (plant and cycle-specific)

Effects of chemistry changes (pH and oxygen)

Method for modeling in CHECWORKSTM: to be incorporated into

Version 4.2 in December 2017

Impacts of Flexible Operations on Erosion locations and rates

Impacts of Flexible Operations on Susceptible Non-Modeled (SNM)

guidance and piping (targeted to start in 2017)

12




Helen Cothron, SGMP, Program Manager

Brent Capell, SGMP, Senior Technical Leader

Flexible Operations Technical Advisory Group

081016

Steam Generator Flexible

Operations Projects

2© 2016 Electric Power Research Institute, Inc. All rights reserved.

SGMP Flexible Operations IssuesConsideration of the Effects of Flexible Operations on Primary-to-Secondary Leak

Monitoring

• Leakage quantification (current focus)

– Effect of flexible operations on assumptions made in quantifying leakage

– Effect of flexible operations on measurement accuracy/uncertainty

– Assessment of available operating experience

• Probability of tube rupture under flexible operations – Slow Growing Crack (SCC)

– Building on EPRI 3002007607

• SGMP: Correlating Primary-to-Secondary Leakage with Probability of Burst (June 2016)

• Verify calculations for full power operations are bounding

• Probability of tube rupture under flexible operations – Other Mechanisms (e.g. Fatigue Cracks)

– Review of inputs to current assessment for hidden assumptions regarding power level

– Gap assessment to identify any areas that need further research or analysis

Supports next PSL

Guidelines Revision


Formally Reviewing Current BasesCurrent Methods (per PSL Guidelines) Use a Mass Balance on a Primary Species

• Mass balance allows quantification

of leak from one primary side

measurement and one secondary

side measurement

• All methods used at plants utilize

simplifying assumptions

• Assessing validity of assumptions

for flexible operations

• Assessing effect of flexible

operations on measurement

accuracy/uncertainty

Simplified BOP Model

,

, , ,

1

SG SG Leak

Leak RCS FW FW Steam Steam Leak BD SG Leak SG SG Leak

dV A

dt

F A F A F A F A V An


2017 and 2018 Proposed Projects (1 of 2)

• Integrity Assessment Guidelines

(IA GLs)

– Review IA GLs to determine if

changes are needed or would

be useful for performing

assessments

– Review licensing basis for

select Alternate Repair

Criterion (ARC) (e.g., W*, H*)

Integrity Assessment Guidelines Rev 4, 3002007571


2017 and 2018 Proposed Projects (2 of 2)

• Secondary Side Deposit Management Impacts

– Fe transport to SGs is important for effect

on performance and integrity

– Utilize work from Chemistry program to

determine how much change in Fe

transport occurs with flexible operations

– Perform analysis to determine if significant

impacts to life cycle maintenance

operations (e.g. will frequency of chemical

cleanings need to be increased)

Effect of chemical cleaning on SG

performance

© 2016 Electric Power Research Institute, Inc. All rights reserved.© 2015 Electric Power Research Institute, Inc. All rights reserved.

Dan WellsProgram Manager, Chemistry, [email protected]

Aylin Kucuk (BWR Crud)Principle Technical Leader, [email protected]

Dennis HusseySr. Technical Leader, [email protected]

FPO Technical Advisory Group Meeting31 August 2016

Impact of Flexible Power

Operations on Fuel Crud

August 17, 2016, Rev. 1

mailto:[email protected]



2


Flexible Power Operations and Water Chemistry

Minimizing Dose

Reducing Radiation

Fields

Accurate Reporting

Optimized Waste

Storage

EPRI

Chemistry Program

Minimizing material

degradation, improving

asset protection, and

reducing source term

Auxiliary

Chemistry

Water Treatment System

• Increased demand water production

• Equipment Reliability

Water Chemistry Guidelines

• BWRVIP-190 Impacts

• PWR Primary Water Chemistry

• PWR Secondary Water Chemistry

Chemical Injection Systems

• Secondary chemistry injection

systems

• Additional maintenance

Auxiliary Cooling Water System

• Turbine Plant Cooling Water, Component

Cooling Water, etc

• Impact on cycling

Fuel Crud and Corrosion Guidelines

• Fuel Reliability Guidelines: PWR Fuel Crud and Corrosion

• Boron-induced Offset Anomaly (BOA) Risk Assessment Tool (for PWRs)

• Fuel Reliability Guidelines: BWR Fuel Crud and Corrosion

• CORAL BWR Fuel Crud Risk Assessment Tool

Documents and Products being evaluated

Plant systems to consider

3


Impact of Flexible Power Operation on

BWR Fuel Crudding Risk

EPRI Lead: Aylin Kucuk, [email protected]

Project starting in 2016


4


EPRI BWR Chemistry and Fuels Guidelines

• All three guidelines include closely related guidance

• The focus of this project is to assess the BWR Fuel Cladding Corrosion and Crud Guidelines for

its applicability of flexible operations

5


BWR Experiences with Frequent Power Cycling BWRs are more readily adaptable to FPO

– Control blade movements throughout the reactor cycle quite common

– Power reductions of 100% → ~50% → 100% can be accommodated, with smaller drops easier through flow control and virtually unrestricted ramp rates

– Reconditioning may be required for extended time at low power.

– Generally, the user follows the fuel supplier’s guidelines.

Recent examples of ELPO (Extended Low Power Operation) followed by return to normal power without fuel failures

– Columbia Cycle 22: Load drop events of 15% and 75% per user’s request

– Fitzpatrick Cycle 21: Similar magnitude load drops, with even more frequent power cycling

– Fermi-2 Cycle 16: Load drops of 30% + power cycling between 70% and 0% with several intervals of ELPO

– Several BWRs reduced power during summer months due to environmental concerns

Hope Creek, Browns Ferry

Need to evaluate available operating experience and include in the BWR C/C Guidelines

6


BWR Crud/Corrosion and Channel Distortion IssuesCrud Issues

Autocatalytic Corrosion

– Thick tenacious crud deposition led

to fuel failures

Crud/oxide Spallation

– Results in an increased risk of fuel

failures

Cladding Corrosion Issues

Shadow Corrosion

– Forms localized thick corrosion

layer on Zircaloy fuel cladding at

contact points and close

proximity regions to Inconel

spacers

– Resulted fuel failures before

Channel Distortion

Channel distortion may result

in severe control blade

interference and inoperable

control blades

Distortion is driven by;

– Fluence gradient across the

channels

– Shadow corrosion due to control

blade exposure early in life

Fuel rods under Inconel Spacers

7


BWR Crud/Corrosion and Channel Distortion

Considerations for Flexible Operations

Crud in BWR core redistributes depending on the water chemistry regime

changes and rod power changes

– As power is cycled in the FlexOp mode, crud is released from fuel surface and may re-

deposited on high power rods

– What is the impact of flexible operations on crud re-distribution?

Severe crud and oxide spallation is a risk to fuel performance

– May result hydride localization in cladding, which may result fuel failures

– Do multiple power cycles increase frequency of crud/oxide spallation?

Frequent use of control blades during flexible operation, may increase control

blade exposure of channels

– Does it increase shadow corrosion and possibly shadow corrosion induced bow on channels?

8


Project Objectives and TasksObjectives Assess the impact of flexible operations on guidance and technologies available to utilities for

assessing risk for BWR fuel crud and corrosion as well as channel distortion and include them in the next revision of BWR guidelines.

Tasks Collect the existing BWR power history, chemistry changes and OE for cycles of FlexOp.

Review BWR Fuel Cladding Corrosion and Crud Guidelines for its applicability to flexible power operations

Evaluate the impact of FlexOp to crud redistribution by using CORAL risk assessment tool

– Identify gaps and define workscope to enhance CORAL capabilities to assess crud induced fuel performance issues under these conditions

Assess the impact of FlexOp to channel control blade exposures to determine if additional distortion monitoring is needed

Deliverable Describe the BWR fuel cladding corrosion and crud risk as well as channel distortion risk due to

flexible operation and needed changes in the next revision of BWR Fuel Cladding and Corrosion & Crud Guidelines

– Final report at the end of 2017

9



PWR Fuel Crudding Risk

EPRI Lead: Dan Wells, [email protected]

Lead Transition in 2016 to Dennis Hussey, [email protected]

October 2016 publication being finalized



10


Background on Crudding Issues and Guidance

Crud deposition on PWR fuel has led

to cladding failure (CILC) and

operating challenges (CIPS)

Current generation cycles are

designed for long duration, high

capacity factor operation

– Most plants have uprated in last 10 years

– More efficient core designs concentrate

power production, can increase crud

deposition

– Current guidance for crud management is

operating experience (OE) based

Also developed over the last 10 years

OE is from Base Load operation

Crud-Induced Localized

Corrosion (CILC)

Failures

Crud-Induced Power

Shifts (CIPS) Issues

11


Task Overview

Assess impact of Flexible Operations on guidance and technology

available to utilities for assessing crud formation risks on PWR fuel

Specific tasks (2015-2016):

1. Review existing PWR cores and crud data for cycles operated

flexibly (including extended down powers, multiple trips, etc.)

2. Review PWR Fuel Cladding and Corrosion & Crud Guidelines,

Rev. 1 and PWR Primary Water Chemistry Guidelines, Rev. 7*

control and monitoring guidance for applicability to Flexible

Operations Based on review, develop work scope to clarify or enhance fuel reliability related guidance

3. Model crud generation in a PWR planning to/has operated

flexibly using the current EPRI crudding risk assessment code Identify items to enhance capability to assess CILC/CIPS risk with Flexible Operation

*See J. McElrath section of presentation

12


Task 1

Review of Operating Experience



13


Review of Operating ExperienceStrategy

Identify units based on knowledge of individual events/practices

– EDF

– SONGS

– Millstone

Review EPRI PWR CMA Database

– Review 1700+ recent cycles

– Rank by relevance

– Review details for top ranked cycles

Note this review is being used for all PWR Chemistry/Crud Projects

ANO 1, Cycle 23

5E-08

5E-07

5E-06

5E-05

0.0005

0.005

0.05

0.5

0

20

40

60

80

100

0 100 200 300 400 500 600 700 800

Co

-xx

-T (

μC

i/m

L)

% P

ow

er

Days Since the Beginning of the Cycle

Power Co-58-T Co-60-T

No Discernable

Changes in Trends

Impact of sampling unknown

14


Additional Data Needed for AssessmentRequested for Assessment of Recent Events High Frequency During Transients

Power trend

Temperature trends (hot and cold leg)

Flow rates

– Loops

– Letdown

– Makeup

– Spray

Boron concentration

Corrosion product measurements

– Transition metals (Ni, Fe, Cr)

– Radioisotopes (Co-58, Co-60, Mn-54, Cr-51,

Fe-59)

Proxies for corrosion product measurements

– Letdown line radiation monitor

Control Rod positions

Core design info

– BOA decks if available

Chemistry program data

– pH program

– Zinc program

Other events

– CIPS, leakers, etc.

Critical gap in high frequency data. If a

downpower is anticipated, extra efforts to

collect these data would be highly beneficial.Active collaboration with Exelon Byron

units is underway

15


Example Analysis of Additional DataMcGuire 2, Cycle 13 (Preliminary)

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

0

20

40

60

80

100

5/20/99 7/9/99 8/28/99 10/17/99 12/6/99 1/25/00 3/15/00 5/4/00 6/23/00

Co

-58

(µ

Ci/

mL)

Po

we

r (%

) o

r LD

HX

Do

se R

ate

(m

Re

m/h

r)

Power

LD HX DR

LDHX Exp Fit

Co-58 HL1

-15

-10

-5

0

5

10

15

0

20

40

60

80

100

8/28/99 10/7/99 11/16/99 12/26/99 2/4/00 3/15/00

LDH

X D

ose

Rat

e D

evia

tio

n f

rom

Tre

nd

(m

Re

m/h

r)

Po

we

r (%

) o

r LD

HX

Do

se R

ate

(m

Re

m/h

r)

Power

LDHX Exp Fit

Co-58 not frequent enough

Long-term trend in proxy measure Detrending reveals effect of downpowers

Additional cycles with “enhanced” data are needed

16


Tasks 2 and 3

Risk Assessment Tool and Guidelines Gap Identification



17


Anticipated Crudding Impacts and Concerns for Flexible Operations

There are two main anticipated impacts from routine use of the flexible operation scenarios:

1. Changes to the core design and to the 3-D power distributions from both:

Partial power operation More extensive use of Control

Rods during power maneuvers

2. The changes to the crud release and re-deposition mechanics from the stop-start cycling of subcooled nucleate boiling (SNB) in the fuel

Possibility of small SNB areas will be maintained in the core during periods of high crud mobility

– Significant crud-induced localized corrosion (CILC) concern – can lead to fuel failures

Release of fuel crud during power reductions and Re-deposition during and following completion of the maneuver

– Both a crud-induced power shift (CIPS) and CILC concern

18


Methods for Modeling Crudding Risk in Flex Ops cycleBOA Version 3.1

Two methods available in BOA to model a

power reduction

A. Use a BOA input to specify core power

change– All locations and elevations adjusted

together – scaled

– No local effects from Control Rod insertion

B. Model the power reductions with the

neutronics code– Includes detailed effects from method used to

reduce power

Current analysis considered three cases:

1. Predicted core power distributions, all full

power operation, “Base Load, Nominal”

2. Predicted core power distributions with the

BOA input power reduction, “BOA Reduced

Power”

3. Predicted core power distributions at full

power with additional predicted 3-D power

distributions during the power reductions,

“Core Follow, Neutronics”

Standard BOA analysis uses predicted 3-D core power distribution from

a neutronic code as input

– Operating data are typically not available – Risk Prediction Tool

19


M2C13 BOA* Results – Mass Evaporation

Mass Evaporation results (Core SNB Rate and

Area) best show the effect of reduced power

operation

Both reduced power inputs show the

anticipated SNB decreases, but response is

very method dependent

– “BOA Reduced Power” method

underestimates the decrease in SNB area and

rate

Likely not an issue for short term (days)

reductions, but significant for extended

power reduction periods (week or longer)

Concern is small SNB area and non-zero

SNB rate will accelerate local crud

deposition

*BOA Version 3.1 (3002000831)

Planned frequent or extended power reductions require neutronic modeling

20


M2C13 BOA* Results – Crud Inventory

Crud inventory response (Core Crud Mass and

Maximum Core Crud Thickness) reacts as

expected

Core Crud Mass decreases, Maximum Crud

Thickness increases

– Increase for M2C13 is small and acceptable,

HOWEVER

BOA calculations are 1/4th assembly

radial mesh, local fuel rod deposit will be

thicker

BOA V3.1 does not model any short term

crud release and redistribution effect

*BOA Version 3.1 (3002000831)

Improved modeling of crud mobility with reduced power could compound the CILC risk concern

21


BOA CIPS Risk AssessmentM2C13 BOA* Analysis

CIPS Risk is evaluated relative to total

deposited boron in the core

– Westinghouse 4-loop plant – threshold is 0.3 -

0.33 lbm boron

– “Nominal” result was under CIPS threshold

CIPS risk reduced for “Core Follow” case in

M2C13

– Lower Core Crud Mass, MOC Crud Thickness,

and slightly lower Core SNB rate contributes

For this operating scenario, CIPS risk

reduced by Flex Ops, but may not be the

case for all

– Cycle specific analysis will be necessary

*BOA Version 3.1 (3002000831)

22


Risk Assessment – Initial Conclusions and Next StepsBOA Analysis

Initial Conclusions

Current models suggest flexible operation

scenarios could increase CILC and fuel

failure risk

– Small SNB areas for extended time with

increased circulating crud inventory

Flexible operation scenarios may reduce

CIPS risk for a cycle, but cycle specific

analysis required

Planned power reductions for extended time

periods should be modeled in the neutronics

code and subsequently analyzed in BOA

– Allows for explicit modeling of effect of 3-D

power changes during the maneuver

Continuing Work and Next Steps

Review all modeling equations and

assumptions for reduce power operation

– Assumptions based on base load operation

Model other plants operating flexibly

– Validation of M2C13 observations

Application of BOA to Flex Ops (Likely Fuel

Reliability Program Work)

– If the models are applicable

Develop standard method for risk

assessment in Flex Ops cycle

– If models need updated

Develop technical basis for updates

23


Fuel Clad Corrosion and Crud Guideline, Rev 1, Volume 1 – Guidance*

C/C Guidelines, Rev. 1 reviewed for possible impacts from

the 3 planned Flexible Operations scenarios

– Existing PWR crud guidance is almost exclusively based on OE

from the early 1990’s through 2014

During this period, the vast majority of OE is from Base Load

operation

– Only cycle with extended partial power operation was Callaway

Cycle 9 (sever CIPS cycle)

– Operated the last half of the cycle at 70% power to mitigate CIPS

*3002002795

24


Proposed PWR C/C Guideline Modifications (1/3)Table 1-2 – Summary of Mandatory and Needed Guidance Elements

Guidance includes a list of actions to mitigate crudding issues

One Mandatory (must do) item - utilities include a CILC risk assessment as part of the core design process for each cycle – Clearly unchanged by the migration to flexible operation scenarios

Needed category (must do, but alternatives acceptable), 2nd item in Managing Core Design states:

“Minimize locally high steaming rates on small surface areas” – Included relative to fuel assembly grid design changes and local peaking next to a guide

tube

– The same result will be a large concern for Flex Ops but from a completely different source not currently considered

The discussion of and considerations for Flex Ops effects needs to be included

25


Proposed PWR C/C Guideline Modifications (2/3)Table 1-2 – Summary of Mandatory and Needed Guidance Elements

Two additional items to support flexible power operation

1. New Needed item in Managing Core Design Utilities should use the risk assessment process presented in this Guideline (see

Section 2.3) or another acceptable method to evaluate CIPS and CILC risk for changes from Base Load to planned cycle Load Follow/Flexible Operation scenarios

– Flex Ops will change the core design as well as the local 3-D power distribution during the maneuvers. Both affect mass evaporation/crud deposition.

– Analysis should include both power distribution and core boundary condition changes, timing and frequency of planned maneuvers

2. Additional Needed item in Plant Operations Maximize letdown purification flow during flexible operation maneuvers and for at least

72 hours after return to full power

– The only external core crud removal capability, should be maxed out when crud mobility is high

26


Proposed PWR C/C Guideline Modifications (3/3)Table 2-1 – Plant Parameter Change, Impact, and Evaluation Methods

Table 2-1 provides a change management approach for evaluating

risk for PWR crudding issues

– Each “change” is provided with a threshold and assessment methodology

– Flex Ops evaluation added to Fuel Design and Core Management

Change Parameter Threshold for Additional Assessment Assessment

Fuel Design and Core

Management

Change to loading pattern

Increase in the number of face-adjacent feed assemblies (non-mixing vane assembly

designs) Levels III and IV

Increase in the number of face-adjacent feed assemblies (mixing vane assembly designs)

beyond the unit experience base Level III

Significant change (increase or decrease) in the number of feed assemblies beyond the

unit experience base Level III

Change from Base Load to planned Load Follow / Flexible Operation for the cycle

Level III

Flex Ops should be evaluated with

Level III (BOA-type) tool to address

synergistic effects of steaming rate

and crud inventory

27


Impact of Flex Ops on PWR Fuel Crud

Review of PWR Operation– Review has been completed of several cycles of reduce power operation

– Sampling frequency has limited most analysis – analysis of enhanced data is underway

– Report to be published in October 2016

PWR Fuel Cladding Corrosion and Crud Guidelines– Proposed changes have been developed, but

– A technical basis needs to be developed to support thresholds for significant flexible operation (threshold for additional analysis of crudding risk)

Scope developed in 2016 – potential FRP work

PWR Crudding Risk Assessment Tools– Capability of modeling flexible operations exist, but validity is unclear – work underway

– A method for applying available risk assessment tools is likely needed

A bounding operational plan (cycle specific) may need to be identified prior to performing CILC and CIPS assessments

Identified change will be evaluated for inclusion in future PWR C/C Guidelines revisions

© 2016 Electric Power Research Institute, Inc. All rights reserved.© 2015 Electric Power Research Institute, Inc. All rights reserved.

Susan Garcia (BWR)Principle Technical Leader, [email protected]

Joel McElrath (PWR)Principle Technical Leader, [email protected]

Dan Wells, PhDProgram Manager, Chemistry, [email protected]

FPO Technical Advisory Group Meeting31 August 2016

Impact of Flexible Power

Operations on Chemistry

15 August 2016




29


Chemistry Impacts for PWRs of Flexible Power

Operations

EPRI Lead: Joel McElrath, [email protected]


30


Overview

Three parallel investigation paths undertaken to evaluate

actual and theoretical effects of flexible operations on

chemistry parameters and the PWR Primary and Secondary

Water Chemistry Guidelines

– Actual experience with intended flexible operations

– Actual effects evaluated using data analysis and statistical

techniques on CMA* data from plants with cycles that mimic the

flexible operations regimes identified for the flexible operations

projects

– Theoretical effects identified from an assessment of the chemistry

mechanisms for parameters identified in the Guidelines documents.

* EPRI PWR Chemistry Monitoring and Assessment Database

31


Review of Operating ExperienceStrategy

Review EPRI PWR CMA Database

– Review 1770 recent cycles

– Rank for detailed review

– Review details for top ranked cyclesMillstone

32


Review of Operating Experience

# Start End Start End First Day DaysAverage

% Power

Arkansas Nuclear One 1 23 4/17/2010 10/16/2011 4/25/2011 5/13/2011 373 19 46.0



Asco 2 20 6/29/2010 11/12/2011 3/9/2011 3/11/2011 253 3 36.1

Asco 2 20 6/29/2010 11/12/2011 8/27/2011 9/18/2011 424 23 88.7

Byron 1 18 4/17/2011 9/10/2012 6/27/2012 7/10/2012 437 40 84.5

Byron 2 17 10/10/2011 4/8/2013 6/28/2012 7/31/2012 262 34 87.8

Byron 2 17 10/10/2011 4/8/2013 8/14/2012 8/16/2012 309 3 91.8

Byron 2 17 10/10/2011 4/8/2013 8/23/2012 8/27/2012 318 5 91.2

Crystal River 3 14 11/5/2003 10/29/2005 12/9/2003 12/11/2003 34 3 74.5

Crystal River 3 14 11/5/2003 10/29/2005 4/18/2005 5/2/2005 530 15 68.8

Crystal River 3 14 11/5/2003 10/29/2005 6/17/2005 6/20/2005 590 4 87.1

Crystal River 3 15 12/10/2005 11/3/2007 12/24/2005 12/28/2005 14 5 82.0

Crystal River 3 15 12/10/2005 11/3/2007 9/30/2006 10/4/2006 294 5 85.0

Crystal River 3 15 12/10/2005 11/3/2007 2/18/2007 2/21/2007 435 4 60.8

Crystal River 3 16 12/7/2007 9/26/2009 1/29/2009 2/1/2009 419 4 58.3

DC Cook 1 23 4/9/2010 9/21/2011 5/3/2010 5/15/2010 24 13 57.3

DC Cook 1 23 4/9/2010 9/21/2011 12/13/2010 12/15/2010 248 3 74.1

DC Cook 1 23 4/9/2010 9/21/2011 3/11/2011 3/19/2011 336 9 59.9

DC Cook 1 24 10/26/2011 3/27/2013 11/26/2011 12/5/2011 31 10 59.1

San Onofre 3 14 12/11/2006 10/13/2008 1/21/2007 1/23/2007 41 3 65.0

San Onofre 3 14 12/11/2006 10/13/2008 2/4/2008 2/7/2008 420 4 68.0

San Onofre 3 14 12/11/2006 10/13/2008 5/14/2008 5/29/2008 520 16 80.0

San Onofre 3 14 12/11/2006 10/13/2008 8/15/2008 8/17/2008 613 3 65.0

San Onofre 3 15 12/18/2008 10/10/2010 3/5/2010 4/30/2010 442 57 56.2

Sizewell B 7 11/15/2003 3/25/2005 4/19/2004 6/16/2004 156 59 51.4

Cycle

Unit

Reduced Power Period

CMA-Based Assessments

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

-0.002

-0.0015

-0.001

-0.0005

0

0.0005

0.001

0 50 100 150 200 250 300 350 400 450

Cs-1

34

-T in

(μ

Ci/

ml)

Cs-1

34

-T (

μC

i/c

m)


Detrended Cs-134-T

Cs-134-T

Trend

De-Trending (example)

33


Summary of FindingsPrimary Chemistry (1/2)

Increase Decrease Increase Decrease

Control Chloride RCS 12 1 0 0 0

Control Dissolved Oxygen RCS 5

Control Fluoride RCS 14 0 0 0 1*

Control Hydrogen RCS 13 0 0 0 1

Control Sulfate RCS 6

Diagnostic Ammonia RCS 3

Diagnostic Corrosion Products RCS 8 1 0 0 0

Diagnostic Cesium Isotopes RCS 5 1 3 0 0

Diagnostic Iodine Isotopes RCS 22 0 13 0 0

Parameter Type Parameter Location

No Effect

No Effect

No Effect

During Reduced

Power Period

After Reduced

Power PeriodTotal

Cases

34


Summary of FindingsPrimary Chemistry (2/2)


Diagnostic Iron RCS 2

Diagnostic Nickel RCS 1

Diagnostic Zinc RCS 6 0 2 0 0

Diagnostic Krypton Isotopes RCS 13 0 3 0 0

Diagnostic Sodium Isotopes RCS 3 0 1 0 0

Diagnostic Specific Conductivity RCS 4 1 0 0 0

Diagnostic Xenon Isotopes RCS 4 0 1 0 0

Diagnostic Tritium RCS

Diagnostic Zn-65 RCS 1 0 1 0 0

Diagnostic Zr-95 RCS 4 0 1 0 0


No Effect

Insufficient Data

During Reduced

Power Period

After Reduced

Power PeriodTotal

Cases

No Effect

35


Summary of FindingsSecondary Chemistry (1/2)


Control Chloride Feedwater

Control Dissolved Oxygen Feedwater 10 0 2 0 1

Control Hydrazine Feedwater 6 1 0 0 0

Control Iron Feedwater

Control Sodium Feedwater

Control Sulfate Feedwater 2 1 0 0 0

Diagnostic pH Feedwater 8 2 1 0 0


Insufficient Data

During Reduced

Power Period

After Reduced

Power PeriodTotal

Cases

Insufficient Data

Insufficient Data

36


Summary of FindingsSecondary Chemistry (2/2)


Control Cation Conductivity Blowdown 13

Control Chloride Blowdown 8 0 1 0 0

Control Dispersants Blowdown 1

Control Fluoride Blowdown 14

Control Silica Blowdown 1

Control Sodium Blowdown 9 0 1 0 0

Control Sulfate Blowdown 8 0 1 0 0

Diagnostic Boron (Boric Acid) Blowdown 1 0 1 0 1

Diagnostic pH Blowdown 4 0 1 0 0

Diagnostic Specific Conductivity Blowdown 4

Control and Diagnostic pH Condensate 4 3 0 0 0

Control and Diagnostic Dissolved Oxygen Condensate 8 2 0 0 0


No Effect

No Effect

No Effect

During Reduced

Power Period

After Reduced

Power PeriodTotal

Cases

No Effect

No Effect

37


0.0001

0.001

0.01

0.1

1

10

0

20

40

60

80

100

0 100 200 300 400 500

Co

-58-T

(u

Ci/

ml)

Po

we

r

Days Since Beginning of Cycle

Flexible Power Normal Power Flexible Co-58-T Normal Co-58-T

Cycle ComparisonByron Cycles 17 and 18 – Co-58

Differences between

flexible and normal

behavior are more

difficult to see with

other variables

38


Cycle ComparisonSizewell Cycles 7 and 8 – Secondary Sulfate

0

5

10

15

20

25

30

35

0

20

40

60

80

100

0 50 100 150 200 250 300 350 400 450

SO

4 (

pp

b)

% P

ow

er


Flexible Power Normal Power Flexible SO4 Normal SO4

No notable increase in

sulfate concentration

during flexible period

Increase in

sulfate

concentration

during mid-cycle

shutdown.

39


PWR Water Chemistry Guidelines Gap

Assessment

Chemistry Impacts for PWRs of Flexible Power Operations

40


Assess Potential Impact(s) Upon the Guidelines

Primary Water Chemistry Guidelines

– pH control

– Hydrogen control

– Dissolved oxygen (plants without oxygen

control on makeup water)

– Zinc control

Secondary Water Chemistry Guidelines

– FW iron control

– FW hydrazine/amine control

– SG hideout return impact

41


Guidelines Assessment

Available literature and the PWR Primary and Secondary

Water Chemistry Guidelines were reviewed to identify

possible effects of flexible operations on chemistry

parameters.

Additionally, gaps were identified between the existing

guidance and the guidance that would be beneficial for

plants operating flexibly.

The preliminary identification of these gaps and potential

effects is intended to facilitate discussion among interested

parties.

42


Identified Gaps in GuidanceTiming of Applicability

The main gap identified is a specification of chemistry guidelines during flexible operations.

The current Guidelines only address full-power operation, startup, and shutdown.

Parameters that apply during full-power operation should generally also apply during periods of reduced power operation.

The current Guidelines have exceptions for short periods. These would dramatically increase as a proportion of the cycle for flexible operations cycles (e.g., primary lithium control is not required until xenon equilibrium, which might never occur in a plant making frequent power adjustments).

Interim guidance about the applicability of the Guidelines during periods of flexible operations could address this requirement until the Guidelines are next revised.

43


Flexible Operation and Primary Chemistry

If boron is used to maintain reduced power operation:

– In order to meet lithium concentration and pH limits during flexible operations, they must be monitored closely and adjustments must be made accordingly. Depending on the timing of the flexible operations within the cycle, maintaining the desired pH within the established lithium control band may be challenging.

– More coolant boron dilution will need to be performed to reduce the boron concentration to return to full power operation, and more boron will need to be added to increase the boron concentration to reduce power.

In all cases of reduced power operation:

– The coolant temperature may change slightly, which could affect pHT and the solubility of nickel ferrites. The temperature change is expected to be small, so these effects are likely to be negligible.

– Changes in the boiling patterns could affect crud distribution on the fuel (addressed in Flexible Operations – Fuel project)

44


Flexible Operation and Secondary Chemistry

The secondary side flow rates are typically decreased during power reductions.

– Chemical additive concentrations will fluctuate more than was typical in the current experience base, especially for units on condensate polishers, unless additional action is taken to modulate chemical addition with power. The effects of increased hydrazine, oxygen, pH, and PAA transients have not been evaluated.

Steam quality can be affected by reduced power operation.

– At least two utilities have recently identified impurity transients that were related to moisture carryover in parts of the system that are typically exposed only to steam.

Boiling characteristics in the steam generators may change.

– This could affect the spatial distribution of species deposition within the SGs.

45


ConclusionsGeneric Guidelines Issues

Guidelines currently based on full power operation

Assumes plants at 100% or will return there ASAP

Example issue:

– Some Primary Chemistry GL elements are tied to xenon equilibrium

– This may not be a practical criterion if plants are operating flexibly

46


ConclusionsPrimary GLs - Consideration by Next Review Committee

Increase frequency for some parameters

– Boron

– Gamma isotopes and suspended solids

Include discussion of effects of Flex Ops on technical

evaluations

May need to adjust lithium control bands

– Effects of additional lithium exposure may need to be considered

Draft report under review

47


ConclusionsSecondary GL – Considerations by Next Review Committee

The secondary side flow rates are typically decreased during power reductions.

– Additive concentrations may fluctuate more than was typical in the current experience base or may require more intervention to prevent such fluctuations

Steam quality can be affected by reduced power operation.

– Changes in wetting condition may mobilize impurities

– Turbine wash is one well known example of this phenomenon

Flow rates, qualities, and temperatures will change

– Partitioning of pH control agents could change, resulting in slightly higher iron transport

Boiling characteristics in the SG may change.

– Could affect the spatial distribution of deposition within the SGs

48


Status and Overall Conclusions

Main analysis and review work completed

– Draft report to EPRI by 9/15

Small task on a detailed case study still in progress

Main conclusions

– No major barriers

– Recommendations for consideration by Guidelines committees

– Some potential additional chemistry “costs”

Entrance into Action Levels during transients

Enhanced monitoring during transients

Additional work load to control additive concentrations

Loss of chemistry optimization

49


Chemistry Impacts for BWRs of Flexible Power

Operations – Update

EPRI Lead: Susan Garcia, [email protected]


50


NPP Flexible Operation and Chemistry Impacts

BWR Work scope Summary:

Collect and compile industry OE (Columbia, Quad Cities, others)

Identify potential changes in BWR plant operating conditions

• Assess impacts on plant chemistry

Identify known operational strategies to counter adverse effects

of flexible operations on plant chemistry

Identify chemistry issues and knowledge gaps to control chemistry

for IGSCC mitigation, flow assisted corrosion, fuel reliability

and radiation field control under flexible operations

– Document evaluation results, 2016 EPRI Technical Report

(will be: 3002008064)

51


Number of Down-Powers per BWR Plant

0

10

20

30

40

50

60

70

80

1 3 5 7 9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49N

um

ber

of

Do

wn

Po

wers

Plant

Downpowers take place at many BWRs for various reasons

EPRI Chemistry Monitoring and

Assessment (CMA) database

provides a source of historic power

data

– Data starts ~1990s

– Number of down-powers per

plant ranged from 1 to 71

– Longest down-power was 327

days and shortest was <1 day

Observations

– Short duration power

reductions likely under-reported

– Frequent daily down-powers at

Columbia in 2008 were not

captured

52


BWR Plant Chemistry Comparisons

Columbia – 2012 Operation

Limit power reductions to 65-85% power to minimize the impact to operations

– Typically done by lowering core flow and control rod manipulations

All systems remain in service during power changes

All condensate and feedwater pumps remain in service during down power

Feedwater heaters are taken off line as needed when power is reduced

RWCU flow does not change

– Chemistry Control

HWC remains in auto (H2 injection rate is lowered with feedwater flow)

Passive zinc skid flow can change but flow is only adjusted as feedwater zinc analysis indicates

Chemistry sampling frequencies unchanged unless there is a limit exceeded

Quad Cities – 2008 and 2013

Limit power reductions to about 13% (125

MWe) per unit.

– Can be typically done by lowering core flow

Avoids the need for cycling any major pumps

(condensate, feedwater)

RWCU flow did not change

– Chemistry Control

HWC remains in auto (H2 injection rate is

lowered with feedwater flow)

Passive zinc skid flow did not change

No additional chemistry sampling required by

Tech Specs or chemistry procedures for the

power change

53


Columbia Flex Ops Chemistry – 2012 (85% power)

• Columbia observed some increases in anions during periods of frequent cycling of power, while Quad did not

Columbia – Anion Concentrations over Time

Different plants respond differently; impact of sampling unknown

Quad Cities 2 – Anion Concentrations over Time

See August 2015 FPO TAG presentation for more information

54


Enhanced Online Monitoring of Anionic Species in BWRs and PWRs

Project cofounded by Chemistry and FlexOps Program

Background/Need

Chemistry Guidelines require (more) frequent analysis of ionic species

such as chloride and sulfate

Current grab sampling process increases technician radiation dose and

the potential for sample contamination

Current analytical techniques are time consuming…many require hours for

results

Accuracy and precision of current techniques is limited for some water

streams (sub-ppb concentrations difficult to attain)

Overall Project Objectives

• Provide more immediate indication of out-of-specification conditions or

adverse trends, allowing for more timely corrective actions

• Improve the accuracy and precision of results

• Maintain ALARA goals and optimize chemistry technician workloads

Lab on a Chip

http://en.wikipedia.org/wiki/File:Glass-microreactor-chip-micronit.jpg

http://en.wikipedia.org/wiki/File:Glass-microreactor-chip-micronit.jpg

55


Microchip Capillary Electrophoresis (MCE)

• Prototype unit manufactured by Mettler Toledo (MT)

• Cost Sharing for Equipment/Support

• MT to cover overhead costs for on-site engineering

support during demonstrations

• Reduced cost for equipment

• MT to cover reagent costs

• Equipment Requirements

• Appx. 20” x 24” footprint, 36” tall

• Requires DI water, 15 amp 120 VAC power, floor drain

• 1/16” sample line

• ~10 mls/min sample flow

• Estimate of 14 L/day to radwaste

• Demonstration sites: Quad Cities (BWR) and Byron (PWR)

• Both sites practice Flexible Operations

Selected for 2016 Demonstrations…

56


Operational Strategies to Counter Adverse Effects of Flex Ops on

BWR Plant Chemistry…and Gaps

Strategies to Counter Adverse Effects

– Condensate Treatment System

– RWCU System

– Hydrogen Injection

– Feedwater Oxygen Injection

– DZO Addition

– OLNC Applications

Potential Gaps Identified:

– Is increased monitoring (or online monitoring) needed?

– Should plant procedures be revised to reflect operational considerations?

– What is minimum flow through condensate treatment vessels to avoid/limit removal from service?

– Are MMS flow adjustments required at reduced power to match original hydrodynamic design of simulating core shroud OD velocities at core mid-plane elevation?

– Is there a potential for increased noble metal wear due to frequent cycling of core flow?

– Will frequent cycling/throttling of process valves with Stellite® increase elemental cobalt source term?

– Is there a potential for an increase in foreign material ingress (including chemicals) due to increased component maintenance?

57


BWR Flexible Operations Summary and Next Steps

Chemistry programs for SCC mitigation, fuel reliability, and radiation field control must adapt for flexible power operations.– Optimization of all BWR chemistry processes (OLNC, HWC, Zinc, condensate

treatment, etc.) must consider flexible power operations

– BWRVIP-190, Rev.1 guidance must consider the impact of flexible power operations for several key areas:

Action Levels, Good Practice guidance

Sampling frequencies

– Equipment limitations

– Available plant resources

– Could benefit from EPRI Chemistry project on improving the capability of online instrumentation (funding will be provided)

EPRI-FPO Technical Report in 2016

Identified changes will be evaluated for inclusion in future BWR WC Guidelines revisions

58



59


Primary Side Example

Raw Data De-Trended Data

0

20

40

60

80

100

0

2

4

6

8

10

12

14

16

18

20

0 100 200 300 400 500 600

Po

wer

(%)

Cl (p

pb

)


Cl

Trend

Power

0

20

40

60

80

100

-150

-100

-50

0

50

100

150

0 100 200 300 400 500 600

Po

wer

(%)

Perc

en

t C

han

ge f

rom

Cl Tre

nd

(%

)


Percentage Deviation from Cl Trend

Power

60


Secondary Side Example

Raw Data De-Trended Data

0

10

20

30

40

50

60

70

80

90

100

0

5

10

15

20

25

30

35

40

0 100 200 300 400 500

Po

wer

(%)

DO

(p

pb

)


DO

Trend

Power

0

10

20

30

40

50

60

70

80

90

100

-500

0

500

1000

1500

2000

2500

0 100 200 300 400 500

Po

wer

(%)

Perc

en

t C

han

ge f

rom

DO

Tre

nd

(%

)


% Deviation from Trend

Power


Phung Tran – Program Manager

Carola Gregorich – Principal Technical Leader

Flexible Operations TAG

August 31, 2016

Impacts of Flexible

Operations on Radiation

SafetySource Term Evaluation

August 15, 2016

2


Impacts to Radiation Safety from Cycling Power (Flexible

Operations)

• Material corrosion behavior

• Primary chemistry

• Fuel crud behavior

Corrosion Product Behavior

• Inventory and mobility of activated corrosion products radiation field generation

Radiological Source Term (funded)

• Increased liquid radwaste volumes solid radwaste

• Release of effluents to environment

Effluents and Radwaste (funded)

• Increased monitoring

• Increased exposure

RP and Occupational Exposure (unfunded)

Cycling reactor power may introduce changes that could impact radiation safety programs

3


Phase 1: Assess the Impact of Flexible Operations

on Source Term/Radiation Fields (2016-2017)

Identify knowledge gaps and challenges to source term and radiation field generation:

– Survey component reliability, corrosion behavior, operational practices, and radiation fields in BWRs and PWRs that have executed load following (e.g. Columbia, Byron, Quad Cities)

Hot spots

Isotopic data

Plant radiation field monitoring

– Review global experiences

– Leverage ongoing work from BWR and PWR chemistry and Fuel Reliability

C. Gregorich

4


Phase 2: Assess Impact of Flexible Operations on

Effluents (Gaseous, Liquid) and Radwaste (2017-

2018)Assess impacts to gaseous and liquid effluents by

collecting data and OE:

– Generation of liquid and gaseous radwaste

– Volume, activity concentration, isotopic composition of radwaste generated

– Capacity of gaseous and liquid radwaste systems

– Frequency and volume of releases (continuous or batch)

Assess impacts on amount and characteristics of wet solid waste generation, packaging, transport, and disposal

K. Kim

5


Phase 3: Assess Impact of Load Following on Radiation

Protection and Occupational Exposure (unfunded)

Assess impacts on radiation protection

programs, measurements, and controls

– Leverage results from Phase 1, Phase 2, and

other Flex Ops project results (e.g. inspection)

– Area radiation monitoring needs

– Radiological controls (e.g. area access, needs for

radiation field minimization – flushing, shielding)

– Impacts to collective radiation exposure (CRE)

(due to increased on-line work, inspection

requirements, radwaste handling)

D. Cool

6


Radiation Field & Source Term Reduction

Are a Team Sport – and Essential for efficient Flexible Operations.

7


Phase 1: Assess the Impact of Flexible Operations on

Source Term/Radiation Fields (2016-2017)

Why Team?

– Coordination of processes in flexing power levels

Why Essential?

– Source term is driven by corrosion, erosion, wear and

activation of the products released to coolant

– Flexing power equates to many and frequent changes

Increasing valve operations

Coolant flow and temperature (thermohydraulic)

Neutron and gamma fields

How will flexible operation practices impact source term?

8


BWR Observation – Extended Operation at Lower Power

Dose rates measured at BWR

Radiation Level Assessment

and Control (BRAC) program

monitoring points at the

reactor recirculation system

(RRS) were twice as high

after a cycle with extended

low power operation

Chemistry program changes

were implemented in the cycle

prior

– First time noble metal injection

– Lower hydrogen injection rates

What change in operational practices caused dose rates to increase? _

9


BWR Observation – Frequent/Seasonal Down Power

What change in operational practices caused dose rates to increase? _

RRS BRAC dose rates

steadily increased following

cycles with frequent down

power transients

Chemistry program

changes were implemented

in the third cycle

– noble metal injection

practice changed

from classical noble

metals chemistry

application (NMCA) to

On-Line NobleChem™

(OLNC)

10


BWR Observation – Frequent/Seasonal Down Powers

Operational monitoring practices assist in identifying gaps. _

Power transients occur at

minute/hour notice

Soluble/Insoluble Co-60

data are reported weekly

11


Phase 1 Scope: Assess the Impact of Flexible Operations on Source Term/Radiation Fields (2016-2017)

2016 – Focus on BWR Fleet

– Identify source term origins of high susceptibility

– Identify parameter that allow to adequately judge the impact

– Assess data availability and needs

– Initiate data collection

2017 – Complete BWR and Evaluate PWR

– BWR fleet evaluation

Corrosion mass balance vs. selected parameter (activated species, dose rate at certain locations)

– PWR fleet evaluation – equivalent to BWR evaluation

Objective – _

Develop data-based understanding of flexible operations impact on radiation field, _

Identify gaps in data and knowledge. _

12


Deliverables

Phase 1 - Evaluation of Source Term Impacts:

– Assessment of Flexible Operations on Radiation Field Generation

for BWRs and PWRs (4Q 2017)

Phase 2 – Evaluation of Impacts to Effluents and Radwaste:

– Assessment of Flexible Operations on Liquid and Solid Radwaste

Programs in BWRs and PWRs (2Q 2018)

– Assessment of Flexible Operations on Gaseous Effluents in BWRs

and PWRs (4Q 2018)

13




David Steininger

Senior Technical Executive


Group

August 31, 2016

Flex Ops Status, Effect

on Primary System

Materials

08/10/2016

2


Project Goal and Status

Assess the impact of load following transients on reactor

coolant system components and piping

– Qualitative assessment only, i.e., no detailed calculations

– The project is intended to establish the present design/licensing

basis of a PWR, its possible modifications, constraints if load

following becomes the operating norm

Westinghouse final report published

General Electric final report in EPRI publishing process

3


Design Transients and Load Following Transient

– Defined two situations for investigation:

Step 1: Power range for load change is limited to (100% -

80%) Pr at a rate of 1% Pr/min to 2% Pr/min, such that

effects on systems are easily identified; showing

insignificant component impact

– Plants benefit in the near term.

Step 2:The unit shall drop load from 100% Pr to a minimum

load of 30% Pr (the lowest power level from which minimal

plant actions are needed to rise to 100% pr) at a rate of 5%

Pr/min, hold at 30% load for 6 hours, then rise to 100% Pr

at 5% Pr/min.

4


Areas Addressed

US plants were designed for load following, but not used this way. Predominately

for past 40 years, they have been base loaded plants and a lot of plant changes

may have occurred over this time.

– What was in original design basis and what is presently in a plant’s licensing

basis that allows a certain number of load following transients?

Provide reactor coolant temperatures (Thot and Tcold) for given load following

transients.

– Identify components that are significantly affected by the thermal transient including aux

systems

For plants with an approved license renewal period, how did they meet the

environmentally assisted fatigue (EAF) requirements of the NRC?

How does the more severe load following transient (100% - 30% power

maneuver) affect reactor pressure vessel internals?

5


PWR Results (Westinghouse and CE)

Westinghouse has provided graphs of RCS temperatures for the a load following

maneuver

– Simple linear equations provided for Thot, Tcold, Tavg

750

850

950

1050

1150

1250

0 20 40 60 80 100

Ste

am G

en

era

tor

Ou

tle

t P

ress

ure

, PSI

A

Thermal Power, %

Varibility of Steam Generator Outlet Pressure vs Thermal Power For the

Westinghouse and CE Fleets

Plant F

Plant C

Plant A

Plant B

Plant D

Plant E

525

550

575

600

625

0 10 20 30 40 50 60 70 80 90 100

Tem

pe

ratu

re, °

F

Thermal Power, %

Westinghouse Fleet Temperature vs Thermal

Power

InletTemperature

AverageTemperature

OutletTemperature

6


Original Design Basis (W/CE)

Plants were sold with the capability for load following (i.e.,

100%-15% load maneuver)

– Plants operated as base loaded plants for almost 40 years

Did not use up the original allocation of load following transients

– FSAR’s clearly show this with the specification of the allowable

number of load following transients for 40 years

FSAR’s have been updated for license renewal

– Maintained same load following transient design point

– Number of transients modified if needed

7


Environmentally Assisted Fatigue (W/CE)

Concern that overly conservative NRC requirements for EAF (NUREG 6909) would significantly limit the number of allowable load following transients for certain components

– NRC requires certain locations to be evaluated (NUREG 6260)

Reactor Vessel Shell and Lower Head

Reactor Vessel Inlet and Outlet Nozzles

Surge Line

Charging Nozzle

Safety Injection Nozzle

Residual Heat Removal System Class 1 Piping

Also, investigated effect on RCS auxiliary systems

8


Environmentally Assisted Fatigue (W/CE), con’t

A plant’s current licensing basis bounds the newly defined load following transient in terms of their number allowed

– License Renewal Period covered

– Daily load following transient assumed in original design (100%-15%)

– NUREG 6909 requirements are met

May have required more complex stress analysis at some locations

Most auxiliary systems are connected to the primary loop cold leg

– RHR is isolated

Cold leg coolant temperature during the load following transient does not change by a significant degree (see earlier graph)

Little effect from EAF

9


RPV Internals (W/CE)

Reactor internals is the sensitive component for fatigue

associated with the load following transient

– Limiting component in W design is the baffle bolt; barrel bolts less

– CE does not have an issue because of welded design

10


Effect on RPV Internals (W/CE)

Bolt is loaded primarily in shear from the load following

transient

L and R are critical design characteristics relative to fatigue

of the bolt

– The temperature change causing a significant increase in the

shear load is not the coolant temperature change, but the

gamma heating change that results in a significant temperature

change for the baffle/former configuration

11


Effect on RPV Internals (W/CE), con’t

Increase in bolt shank radius, bolt length and material choice

lowers fatigue cracking susceptibility

– Later series of W plants using 316SS incorporate this design

change

Low leakage loading patterns (LLLP) for the core help

mitigate gamma heating affects to the internals

– Majority of plants have implemented LLLP

The lower power value (e.g., 80% or 30%) of the load

following transient is critical in evaluation of bolt fatigue

– 100% to 80% power appears to show little impact

– 100% to 30% is problematic

12


Summary (W/CE)

W and CE plants may load follow in the future and their

current licensing basis (original or updated) covers load

following

W plants may have accelerated ageing issues associated

with RPV internals

– Temperature induced changes

Dominated by gamma heating

Baffle bolts appear to be the critically affected component

CE plants have welded internals and former plates are not

connected to barrel

– Doesn’t appear to have a fatigue issue

13


Summary (W/CE), con’t

If load following is implemented today, W load following

plants should perform plant specific analysis for the internals

to quantitatively evaluate the effect of fatigue from a series

of expected load following transients

Environmentally assisted fatigue (EAF) was not evaluated

for its impact on fatigue of internals in this project. It needs to

be a quantitative analysis.

– EAF will only probably make things worse

– Regulatory Guide 1.207 does not specify that EAF must be

evaluated for its affect on reactor internals (internals not a pressure

boundary)

– NRC will probably not impose EAF evaluation on Internals

14



Some plant in their license renewal application did fatigue evaluations for the RPV internals because such analysis was part of their original design basis

– This was required by NRC in their review of the application

– Not clear how many plants fall in this category

MRP 227 (Internals Inspection and Assessment GL) is applicable only to base loaded plants

– Plant specific analysis may be required prior to entering License Renewal period and possibly even before the original design life

– MRP is contracting Westinghouse to perform same analysis as that supporting MRP 227, but with fatigue of internals due to flexible operations taken specifically into account

– IASCC of bolts will probably be the limiting degradation mechanism

15



Plants thinking of going into SLR should consider transient

counting during their license renewal period

– Suspect that fatigue margins (e.g., expected load following

transient number, complex stress analysis, etc) have been used up

in license renewal applications if the plants load followed during the

license renewal period

16


BWR Results

BWR has an inherent capability to vary power efficiently with

relatively small changes in operating pressure and

temperature

– Change recirculation flow

Decreasing flow results in more steam, less neutron moderation,

less fission and therefore less power

EPRI specification of power reduction to 80% for extended

period well within design capability

EPRI specification of a 70% power reduction goes beyond

original design specification (50% power reduction)

– Can’t fully cover by recirculation flow control; must use control rod

insertion

– Specification limit of 40% reduction in recirculation flow

17


BWR Results

70% power reduction would result in some systems,

specifically recirculation and fuel capability, needing

additional margins and/or mitigation

– Flow decreases to minimum recirculation flow pump speed

– Minimum flow control valve position

– Frequent and more extended operation with control rod

suppression, as well as faster power changes challenges the fuel

– Other various component issues identified (e.g., level control)

Feedwater nozzle thermal sleeve (e.g., triple piston design)

leakage causing material fatigue becomes problematic for

60 year operation

Plant specific analysis of issues recommended using the

results of this investigation as a guideline before performing

flexible operations

18



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