Kozloduy NPP units 5&6

Daniel Genov

Ageing management of Buried and

Underground Piping and Tanks at NPPs

Technical Meeting 621-I2-TM-47031

IAEA / EPRI, Charlotte 13-15.10.2014

1

Agenda

1. Kozloduy NPP Plc - Introduction

2. Buried / Underground Piping

3. Underground Tanks

4. Plant Life Extension (PLEX)

5. Ageing Management

6. Summary

2

Kozloduy NPP Plc

• Units 5&6 in operation – Design: VVER-1000 V-320

– Rated output power: 2000 MWe

– Plant design life: 30 years

• Unit 5: – Commissioned: 1987

– End of original design life: 2017

• Unit 6: – Commissioned: 1991

– End of original design life: 2021

• Comprehensive Modernization Program (MP) – Time frame: 1998-2008

– Total budget: over 500M EUR.

– Over 200 measures implemented • The MP is based on the issued by IAEA document: “Safety Issues and

Their Ranking for VVER-1000 model 320 NPPs”

– First stage of PLEX

• Plant Life Extension project of units 5&6 undergoing

KNPP MP measures

3

Buried / Underground Piping

Simplified Scheme

Sp

ray P

on

ds (

x6)

5DGS

6DGS

Turbine

Hall - 5

Turbine

Hall - 6 Circu

latin

g W

ate

r

Sta

tio

n (

CW

S)

3,4

6RB

5RB

Cavity Pumping Houses (CPH) (x6)

Pressure Piping - QF Redundant Piping

Drain Piping - QF Additional water CPH

Additional water CWS External fire protection ring

*RB – Reactor Building

4

• QF – Essential Service Water System

Buried / Underground Piping

Piping of system QF

• Drain piping between Reactor

Building and Spray Ponds

• Pressure piping between Spray

Ponds and DGS

• Pressure piping between Diesel

Generator Station and Reactor

Building

Cross-section of piping

5

• Design data and и Normative requirements

– Overview of system QF: • Assure the operation of the Safety Systems. Conduct the heat from

primary circuit during accident and normal operation conditions.

• 1st seismic category (determined by NP-031-01*)

– In accordance with IAEA Safety Guide 50-SG-D15

(now NS-G-1.6)

– Materials: steel pipes with diameters DN600,800,1000,1200

• Base metal: Стомана 20 (Carbon steel 1020) by technical specifications TU 14-3-808-78**, TU 14-3-190-82**

• Corrosion-proof coating

*Gosatomnadzor – Russian regulatory body

**Russian codes and standards

Buried / Underground Piping

Piping of system QF

6

• Operational condition and current status

– Laying method

• filled up in a trench on a sand bed

• laid in reinforced concrete channel

– Design pressure and temperature

• Pressure pipes:

– temperature: 120C to 450C (550C to 700C during accident

conditions)

– pressure: 0,46 Mpa

• Drain (gravity) pipes:

– temperature: 50C to 330C

– pressure: 0,2 Mpa

– Design flowrate: 3000 m3/h

Buried / Underground Piping

Piping of system QF

7

• Plant life management (PLiM)

– Seismic qualification • Measure 21241 of Modernization Program

• Seismic resistance of Maximal Design Earthquake is

verified (0.2g Peak Ground Acceleration)

– Ageing management measures

• Monitoring level of corrosion through technical means without

excavation

– Visual inspections by remote TV camera

– Water chemistry upgrade

– Repairs: 1 significant repair reported • Replaced 8 m part of pressure pipe with DN1000

• leakage in result of heavy corrosion

• Base metal break is detected as well as past compromised section of

waterproof coating around metal ruptures

• Cause: mechanical damage during improper lay down of piping

Buried / Underground Piping

Piping of system QF

8

• Water chemistry

– Program to “Corrective treatment of ESWS consumers through

spray pond water”

– Targets:

• incrustation free operational condition of equipment

• inhibition of corrosion process

• control of microbiological contamination

• Chemical reagents

– Depositrol BL-5300; Depositrol PY-5200; Spectrus BD-1501E;

Spectrus OX-1201; Spectrus NX-1167

• Instrumentation and Control System

– Monitoring of parameters such as: pH, temperature, rate of

corrosion, electrical conductivity, degree of concentration

• Output: Decreased rate of metal corrosion below prescribed rate of

0,1 mm per year

Buried / Underground Piping

Piping of system QF

9

• Data by 1st channel of QF system

Rate of corrosion

mm

/ye

ar

measured norm

Replacement of

sensor

Buried / Underground Piping

Piping of system QF

10

• Description – Part of Service Water System - VB

– System of normal operation • In accordance with the Technological manual for safe operation of

units 5 and 6 of NPP Kozloduy

– Design steel pipelines • High rate of corrosion and repair events

• Redundant piping is installed

• Redundant piping of PEHD – piping layout follows design ones

– pressure pipe, filled up in a trench on a sand bad

– operational parameters are in full compliance with design piping • Fluid velocity is within 3 m/s

– Specification • Diameters: 400х23,7; 280х16,6

• Standard: EN 12201

• Material: PE100 SDR17

• Design criteria: material strength according to ISO 9080

Buried Piping

Piping of additional water by Circulating Water Station

11

• Seismic classification of the redundant piping

• Unavailability of Codes and Standards for Polyethylene

Pipes for Nuclear Power Plants during design and

construction

• The redundant piping is not approved by regulatory

body as independent element

• Design requirements are selected by

– ASME B31.1-1995 Appendix VII, Nonmandatory

Procedures for the Design of Restrained Underground

Piping

– Piping is designed for half of Maximal Design

Earthquake (0,1 g Peak Ground Acceleration)

Buried Piping

Piping of additional water by Circulating Water Station

12

• Description

– Backup water supply to Spray Ponds for recover of water losses due to

evaporation, drift, filtrations, etc.

– Backup water supply of auxiliary buildings and systems

– Pressure pipes, filled up in a trench on a sand bad

– Especially required by regulatory body

• Plant project of 2001

– Piping is classified as safety relevant

– Classified as 3th safety class

• according to 50-SG-D1 (now SSG-30)

– Classified as 1st seismic category

• According to 50-SG-D15 (now NS-G-1.6)

Buried Piping

Piping of additional water by Cavity Pumping Houses

13

• Ageing mechanisms

– PLEX report

• Critical component: pressure pipeline between the CPH and SP

• Damages and flaws: heavy corrosion of visible sections

• Ageing mechanism: general corrosion

• Index: COR01

• Current status

– Pipeline operation conditions: exposure to nonaggressive ground waters

with unstable level due to the direct interconnection between ground

waters and Danuve Rive waters

– The mode of the pipeline continuous wetting and drying adversely affects

the corrosion process developing in the pipeline metal

– Virtually the pipeline is near the end of its design life. A decision for

replacement with PEHD is under consideration.

Buried Piping

Piping of additional water by Cavity Pumping Houses

14

• Description: supply of suficient quantity of water at required pressure to

building and rooms where fire extinguishing system exist. The main

consumers are as follows:

– Reactor Building, Turbine Hall

– Auxiliary Building

– OSK – combined auxiliary building

– Oil-petrol storage facility

• Water source: CWS 3,4 (Danube river)

• Pipe specification:

– 90% (6532 m) of total length of the ring is comprised of pipes with

diameters within range of DN200 do DN300

– Spirally welded steel pipes (such as system QF)

• Carbon steel type ВСт3 по BDS2592 1971

• Laying method:

– In most part the pipeline is laid down into U-shaped channel with

reinforced concrete roof slab. Channel depth vary within 0,9 to 2,5 m.

– Construction and Commissioning : 1982-1984

Underground Piping

External fire protection ring

15

• Cross-section view

1 Dense bituminous concrete

2 Porous bituminous concrete

3 Concrete covering кл.В30

4 Padding paper

5 Sand

6 Gravel

7 Consolidated loess soil

1 2

3

4

5

6

7

fire protection pipe

reinforced concrete chanel

with roof slab

Underground Piping

External fire protection ring

16

• Operational experience: – There are 15 cases of unscheduled repairs for a period of

7 years ( 2012)

– Damaged corrosion protection

• mainly during construction period

– Technical solution

• Project for replacement with PEHD pipes with analogous

hydraulic characteristics

• New PEHD pipeline

– PEHD 100, PN1,6 Mpa; Diameters 110 to 355 mm

• BDS, EN 12201-1:2005, 12201-2:2005, 12201-3:2005

– Laying method: excavation-free technology

• Project is approved by Regulatory Body (Bulgarian Nuclear

Regulatory Agency)

Underground Piping

External fire protection ring

Petrol tanks in DGS

3x100m3: QC15,25,35B01

• per unit

17

Underground tanks Overview

100м3

Oil tanks in DGS

2x25m3 QD16B01 – Emergency oil

purge tank

2x5m3 QD17B01 – Drainage tank

25м3 5м3

The structure is made of monolithic reinforced concrete B20 and reinforcement steel A-I

and A-III. The steel liner placed on the innner surface has a thickness of 3 mm.

The structure is made of monolithic reinforced concrete B20 and reinforcement steel A-

I. The steel liner placed on the innner surface has a thickness of 3 mm.

18

Underground tanks

Condition evaluation

• Measure 21241

– Within the Modernization Program the seismic resistance of the

safety-related and important to operation structures has been

checked and upgrading measures developed

– Performed 2002-2004

– Underground tanks for oil and petrol

• Seismic calculation performed with the software product

STARDYNE – “Structural Analysis Systems”

• Maximum Design Earthquake resistance verified (0,2g)

• PLEX

– Ageing management

• Ultrasonic thikness measurement (steel liner)

• Visual inspection (inner volume and overgrade parts)

• Waterproof coating repair

• Two layer corrosion protection of inner surface – “Tankguard

Storage” protection used (phenol-epoxid coating)

– thickness measurement: callipers “Mititoyo”

19

Ageing Management

Plant Life Extension Project

• Operating licenses of units 5 and 6

– require assessment of the actual condition of the Systems Structures and

Componentws

– undertaking

• “Comprehensive assessment of the actual condition and residual lifetime

analysis of Kozloduy of SSC” – completed

• Program of Kozloduy NPP Units 5&6 “Preparation for Extended Lifetime”

- undergoing

• Underground Piping

– System QF (essential service water – closed loop chemically treated water)

• Corrosion rate monitoring and early leak detection

• Special chemical treatment

• Replacement if necessary

– System VB (service water – Danube river water)

• Condition monitoring of the design piping (Maitanance&Repair) until

• Independent operation of newly installed redundant PEHD piping

– Need regulatory body approval

– Seismic qualification concerns

20

Ageing Management

Plant Life Extension Project

• Underground Piping

– System UK (backup water by artesian wells)

• Replacement with PEHD piping

– Need regulatory body approval

– Seismic qualification concerns

• Underground Tanks

– System QC (petrol) and UN (oil)

• seismic qualification

• corrosion protection monitoring

21

Ageing mechanisms PLEX Project

• General corrosion

– Description

• General surface corrosive damage of metal during contact

with an electric conductive solution

– Critical elements

• Invisible underground parts of pipelines

• Inner and outer surface

– Damages, defects

• Loss of integrity of pipes insulation and leakages

• Pitting

• Change of size

– Ageing mechanisms

• Steel pipes corrosion

22

Summary

Comprehensive MP, PLEX and PLiM

Replacement, R&M, Monitoring

PEHD piping alternative

Seismic Qualification

Regulatory body concerns PNEG-7-008-89 do not address non-metalic materials

NUREG-1793 Supplement 2 express uncertainty about PEHD

23

Kozloduy NPP Plc

Thank you for your attention!!!