C·E Power Systems Corntius!1c•:i En9,neer1ng inc 1000 F'rc>s~»:>cr Hri! Hoad ~\' nclsor c (_;~1necr1cu! 0609~1

l!Y!!!! POWER .. -..SYSTEMS

George Knighton, Chief Licensing Branch No. l U.S. Nuclear Regulatory Commission Washington, D.C. 20555

lPI 20J/6881 ]11 T PiPX 99297

September 5. l 9R5 LD-85-046

Subject: Informational Report on the Core Operating Limit Supervisory System (COLSS)

Dear Mr. Knighton:

The Core Protection Calcuhtor (CPC) Oversight Co11111ittee, consisting of Arizona IJuclear Power Project, Arkansas Power & Light Company, Louisiana Power & Light Company and Southern California Edison Company, with Combustion Engineering as its technical consultant, met \<lith the NRC staff on November 8, 1984, March 8, 1985, and April 18, 1985 to discuss a program of CPC Modifications and Methodology Improvements scheduled for implementation in 1986 and 1987. In these meetings the NRC indicated t~eir desire for an informational report describing the scope and methodology of COLSS.

The purpose of this letter is to provide the NRC with the requested report !Attachment (A) proprietary and Attachment (B) non-proprietary].

Combustion Engineering is providing this document on behalf of the CPC Oversight Committee. As the NRC staff (Core Performance Branch) requested, this document is being provided for informational purposes only and no ~IRC review is being requested. The attached document is not dpplicable to any individual licensee until referenced by that licensee for use on their docket.

It is requested that any questions you have about the attached document be addressed to the Chairman of the CPC Ovr.rsight Conwnittee, with copies sent to each committee member and C-E. Enclosed is a list of individuals to whom the copies should be sent.

Attachment (A) contains information considered by C-E to be proprietary in nature. As such, we request that it be withheld from public disclosure in accordance with the provisions of 10 CFR 2.790 and that this material be safeguarded. The reasons for the classification of this material as proprietary are delineated in the affidavit provided in Attachment (C).

fAJcL~ IO. C-02.E .fEpfo(t,..~ 5 C<l5

H. P-ooo / c. '1 .J . LO 1lf:o,.J I C 'I

Jb.B LE! I C..lf

E. l:t. C..J?Tl.4 I c.. 'j

Mr. George Knighton September 5, 1985

LD-85-046 Page 2

Since this document is being provided for informdtional purposes only and no review or approval is being requested, Combustion Engineering believes that no fees are to be incurred as a result of this submittal.

Should you have any questions on the contents of this letter, please feel free to contact me or Mr. H. C. Trwin of my staff at (203) 285-5210.

AES: bk s Enclosure cc: G. Hsi i

Very truly yours,

COMBUSTION ENGINEERING, INC.

~ Director Nuclear Licensing

L. Phillips L. Rubenstein

Attachments: (A) CEN-312-P, "Overview Description of the Core Operating Limit Supervisory Sys tern (COL SS)", September 1985: Copies 000001 thru 000009.

(8) CEN-312-NP: Non-proprietary Version of Attachment (A): 9 Copies Attached.

(C) Affidavit Attesting to the Proprietdry IJature of CDJ-312-P.

Correspondence List

Chairman of the COLSS/CPC Overs i gh._!__~omi t_tee

Mr. C. E. OeOeaux Louisiana Power and Light Company P.O. Box 60340 317 Baronne Street Mail Unit 17 New Orleans, Louisiana 70160

r-!~mbers _Qf_ the CPC Ove_~~gh!__~~n.!11_i_!:_tee

Arkansa~ Power -~-Li ght__f_~mp~ny

A. G. Mansell Arkansas Power & Light Company Post Office Box 551 Little Rock, Arkansas 72203

P . F. C raw l ey Arizond Nuclear Power Project Post Office Box 21666 Mail Station 4090 Phoenix, Arizona 85036

Sou_thern _f_C!] i f<?__r:_ni a l_di s_~_']__(:_~_mpan~

E. J. Donovan Southern California Edison Company Room 316 G. 0. 1 Post Office Box 800 Ro~emead, California 91770

Lou s i an a . P o~!-~~_!_gh ~-i=_<?_mp any

F. J. Drulllllond Louisiana Power & Light Company P.O. Box 60340 317 Baronne Street Mai 1 Unit 17 ~Jew Orleans, Lousiana 70160

Combustio~ineering, Inc.

A. E. Scherer Director, Nuclear Licensing Combustion Engineering, Inc. 1000 Prospect Hill Road Post Office Box 500 Windsor, Connecticut 06095

Enclosure to LD-85-046

Combustion Engineering, Inc. State of Connecticut County of Hartford

AFFIDAVIT PURSUANT

TO 10 CFR 2.790

SS.:

I, A. E. Scherer, depose and say that I am the Director, Nuclear Licensing,

of Combustion Engineering, Inc., duly authorized to make this affidavit, and

have reviewed or caused to have reviewed the information which is identified as

proprietary and referenced in the paragraph immediately h•?low. am submitting

''1i s J ff i davit in conformance with the provisions of 10 CFR 2. 790 of the

Commission 1 s regulations for withholding this information.

The information for which proprietary treatment is sought is contained in

the following document:

CEN-312-P, Overview Description of the Core OpPrating Limit Supervisory

System (COLSS), ~eptember 1985.

This document has been appropriately designated as proprietary.

I ~ave personal knowledge of the criteria and procedures utilized by

Combustion Engineering in designating information as a trade secret, privileged

or as confidential commercial or financial information.

Pursuant to the provisions of paragraph (b) (4) of Section 2.790 of the

Commission 1 s regulations, the following is furnished for consideration by the

Commission in determining whether the information sought to be withheld from

public disclosure, included in the above referenced document, should be

withheld.

-2-

1. The ir:",·::,utiun sought to be withhelct from public disclosurt' are the

methods usej i ! OP- l rH1d CETOP-n. <tnd, specific COL SS methods on density

dependent rar· p~aking. vector average tilt, and sensor cross-checking and

replacement, whir .. h is ownect and has been held in confidence by Combustion

Engineering.

2. The information consists of test data or other similar datd concerning

a process, method or component, the application of which results in a

substantial competitive advantage to Combustion Engineering.

3. The information is of a type customarily held in confidence by

Combustion Engineering and not customarily disclosed to the public. Combustion

[ngineering has a rational basis for determining the types of information

customarily held in confidence by it and, in that connection, utilizes a system

to determine when and whether to hold certain types of information in

confidence. The details of th~ aforementioned system were provided to the

Nuclear Regulatory Commission via letter DP-537 from F.M. Stern to Frank

Schroeder dated December 2, 1974. This system was applied in determining that

the subject document herein are proprietary.

4. The information is being transmitted to the Commission in confidence

under the provisions of 10 CFR 2.790 wfth the understanding that it is to be

received in confidence by tht· rmmtission.

5. The information, to the best of my knowledge and belief, is not

available in public sources, and any disclosure to third parties has been made

pursuant to regulatory provisions or proprietary agreements which pro vi de for

maintenance of the information f n confidence.

6. Public disclosure of the information is 11kely to cause substantial

harm to the competitive position of Combustion Engineering because:

-3-

a. A similar product is manufactured and sold by major pressurized

water reactor competitors of Combustion Engineering.

b. Development of this informdtion by C-E required tens of thousands

of manhours and hundreds of thousands of dollars. To the best of my knowledge

and belief a competitor would have to undergo similar expense in generating

equivalent information.

c. In order to acquire such information, a competitor would also

require considerable time and inconvenience in developing similar methods used

in CETOP-1 and CETOP-D, and, specific COLSS methods on density dependent radial

peaking, vector average tilt, and sensor cross-check111:J rnd replilcem1~nt.

d. The information required significant effort and expense to obtain

the licensing approvals necessary for application of the information.

Avoidance of this expense would decrease a competitor's cost in applying the

information and marketing the product to which the information is applicable.

e. The information consists of methods used in CETOP-1 and CETOP-D,

and, specific COLSS methods on density dependent radial peaking, vector average

tilt, and sensor cross-checking and replacement, the application of which

provides a competitive economic advantage. The availability of such

information to competitors would enable them to modify their product to better

compete with Combustion Engineering, take marketing or other actions to improve

their product's position or impair the position of Combustion Engineering's

product, and avoid developing similar data and analyses in support of their

processes, methods or apparatus.

f. In pricing Combustion Engineering's products and services,

significant research, development, engineering, analytical, manufacturing,

licensing, quality assurance and other costs and expenses must be included.

-4-

The ability of Combustion Engineering's competitors to utilize such information

without similar expenditure of resources may enable them to sell at prices

reflecting significantly lower costs.

g. Use of the information by competitors in the interndtional

marketplace would increase their ability to market nuclear steam supply systems

by reducing the costs associated with their technology development. In

addition, disclosure would have an adverse economic impact on Combustion

Engineering's potential for obtaining or maintaining foreign licensees.

Further ~he deponent sayeth not.

Director Nuclear Licensing

Sworn to before me

this ~s\·f\ day of ·,~-\J\S.W'-'* l 1 \ '-r-:3 c~>

\~-~-~~~(Q ___ b_ ___ ~~(( (}:~J:._ -Hotary Public

OVERVIEW DESCRIPTION

OF THE

CORE OPERATING LIMIT SUPERVISORY SYSTEM

(COLSS)

CEN-312-NP

Revision 00-NP

SEPTEMBER, 1985

COMBUSTION ENGINEERING, INC

Nuclear Power Systems

Power Systems Group

Windsor, Connecticut

8509100308 8~§61 PDR ADOCK 0 PDR p

• B) Due to nozzle outside diameter configuration,

the nozzle side cannot be examined. Due to branch connection, the head side of weld cannot be examined (Weld 3. 744).

C) Due to location of lifting lugs and nozzle configuration, 100~ of welds cannot be examined.

ABSTRACT

A nuclear power plant must be maintained within its limiting conditions for

operation as specified in the plant Technical Specifications to assure safe

operation. The Core Operating Limit Supervisory System (COLSS) aids the

operator in maintaining operating margin to limits on linea~ heat rate and

departure from nucleate boiling. To do so, COLSS uses meJsurements of incore

detector signals, CEA positions and plant thennal/hydraulic properties to

detennine the core power distribution and thermal performance.

This report provides a general description of the scope and methodology of the

COLSS algorithms. It is provided solely for information to be tJSed as a

reference during future reviews of submittals on the dockets of C-E supplied

NSSS's that utilize COLSS.

3

Table of Contents

1.0 Introduction and Su1T1Tiary

2.0 COLSS Description

2.1 Purpose of the COLSS System

2.2 Overview of COLSS Operation

2.2.1 System Inputs

2.2.2 Process Measurement Processing

2.2.3 COLSS Calc~lations

2.2.3.1 Volumetric Flow Calculation

2.2.3.2 Core Power Calculation

2.2.3.3 Power Distribution Calculation

2.2.3.4 Secondary Calorimetric Power Calculation

2.2.3.5 Local Power Density Power Operating Limit Calculation

2.2.3.6 Thermal Margin Power Operating Limit Calculation

2.2.3.7 Core Power Margin Calculation

2.2.~ COLSS Outputs

2.3 Description of COLSS Algorithms

4

2.3.1 Reactor Coolant System Volumetric Flow

2.3.2 Primary Calorimetric Power

2.3.3 Turbine Power

2.3.4 Secondary Calorimetric Power

2.3.4.1 Power in Each Steam Generator

2.3.4.2 Power Adjustments from the NSSS

8

10

10

11

12

12

14

15

15

16

J. 7

17

17

18

18

28

29

30

30

31

32

33

2.3.5

2.3.6

Table of Contents (Cont'd)

Plant Power

Core Power Distribution

2.3.6.1 Conversion of Flux to Power

2.3.6.2 Planar Radial Peaking Factors

2.3.6.3 Axial Power Distribution

2.3.6.4 Hot-Pin Integrated Radial and ASI

2.3.6.5 ~zimuthal Tilt

2.3.6.6 Three-0 Power Distribution

2.3.7

2.3.8

2.3.9

2. 3.10

Linear Heat Rate Power Operating Limit

Thermal Margin Power Operating Limit

Thermal Margin Power Operating Limit Update

Core Power Margin

2.4 Uncertainties

2.4.1 Power Measurement Bias

2.4.2 Power Operating Limit Uncertainties

3.0 Constants and Supporting Data

3.1 Basis for Mechanical and Thermal-Hydrau:ic Constants

3.2 Basis for Core Design Constants

5

3. 2 .1

3.2.2

3.2.3

3.2.4

3.2.5

Conversion of Flux to Power Constants

Planar Radial Peaking Factor look-up Tables

Axial Power Distribution Constants

Azimuthal Tilt Calculation Constants

LHR Limit Constants

34

34

35

36

37

38

38

39

40

41

42

43

44

44

45

46

46

42

48

48

49

50

so

Table of Contents (Cont'd)

3.3 Bdsis for DNB Margin Monitoring Constants

3.3.1 Derivation of the[

Flow Analysis

J from the Loss of

3.3.2 Other Events Analyzed to Confirm Adequate Monitoring

3.3.3 COLSS Penalty Factors Applied for CEA Calculat0rs

50

51

52

Inoperable 54

3.4 Basis for Measurement and Calculational Uncertainty Constants 54

3.5 Basis for Constants Supporting On-Line DNB Calculation 56

4.0 Conclusion

5.0 References

6

58

59

[

AOO

ASI

CEA

CHF

COL SS

CPC

CRT

DNB

ONBR

DNB-OPM

DP

F xy

KW/FT

LCO

LHR

LOCA

LOF

NSSS

PDIL

POL

RCP

RCS

RTD

7

GLOSSARY OF TERMS

Anticipated Operational Occurrence

Axial Shape Index

Control Element Assembly

Critical Heat Flux

Core Operating Limit Supervisory System

Core Protection Calculator

Cathode Ray Tube (display)

Departure From Nucleate Boiling

Departure From Nucleate Boiling Ratio

Departure From Nucleate Boiling Overpower Margin

Differential Pressure

Planar Radial Power Peaking Factor

Kilowatts per Foot

Limiting Condition for Operation

Linear Heat Rate

Loss of Coolant Accident

Loss of Flow (event)

Nuclear Steam Supply System

Power Dependent Insertion Limit

Power Operating Limit

Reactor Coolant Pump

Reactor Coolant System

Resistance Temperature Detector

-J

1.0 Introduction and Surrmary

Maintaining a nuclear power plant within its I imiting Conditions fer Operdtion

(LCO) is a necessary condition for safe operation and acceptable trans'2nt

consequences. These LCOs are delineated in the Technical Specifications.

There are many systems in a nuclear power plant that are used to help the

operators maintain the limiting conditions for operation. One such syster

used in C-E supplied NSSSs is the Core Operating Limit Supervisory System

(COLSS). COLSS is a digital computer based on-line monitoring system that is

used to provide information to aid the operator in complying with the Technical

Specifications operating limits on total core power, peak Linear Heat Rate

(LHR), Departure from Nucleate Boiling Ratio (DNBR), Axial Shape Index (ASI),

and azimuthal power tilt. The C-E Standard Technical Specifications discuss

the importance and purpose of these operating limits in the bases for Section

3.2. The system is used at the following plants:

1) Arkansas Nuclear One Unit 2,

2) San Onofre Nuclear Generating Station Units 2 and 3,

3) Waterford Unit 3, and

4) Palo Verde Nuclear Generating Station Units 1, 2, and 3.

COLSS uses input from selected sensors to determine the plant condition and

displays this condition to the operator in a form which allows easy

interpretation of reactor core status. Audible alarms and visual CRT messages

are provided to alert the operator when an operating limit is exceeded. COLSS

is a monitoring system and does not activate any safety equipment, initiate

8

any automatic actions, or provide any direct input to safety systems. The

major calculations performed by COLSS are:

1) Core Power,

2) Core Power Distribution,

3) Margin to Minimum Departure from Nucleate Boiling Ratio,

4) Margin to Linear Heat Rate Limit, and

5) Core Azimuthal Power Tilt Magnitude.

The purpose of this report is to provide a general description of COLSS for

reference during future review of submittals on the dockets of C-E supplied

NSSSs that utilize COLSS. To meet this purpose, the report describes:

1) COLSS monitoring and alarms which aid the operator in maintaining

the appropriate Technical Specification operating limits,

2) sen~or data and its processing for input to COLSS,

3) COLSS algorithm functions, and

4) determination of constants •or use in COLSS.

The accuracy of the information supplied by COLSS to the operator was orig­

inally evaluated in Reference and has been updated in Reference 5. This

subject will not be addressed further in this report.

9

2.0 COLSS Description

2.1 Purpose of the COLSS System

The plant Technical Specifications specify Limiting Conditions for Operation

of plant systems, components, and parameters. Munitoring systems are provided

to assist the operator in meeting these Technical Specification requirements.

COLSS is a monitoring system that assists the p1Jnt operator in maintaining

the Limiting Conditions for Operation (LCD) specified in the following

Technical Specifications:

1) 3.2.1 Linear Heat Rate,

2) 3.2.3 Azimuthal Power Tilt,

3) 3.2.4 DNBR Margin,

4) 3.2.7 Axial Shape Index, and, for some plants,

5) 3.3.3.2 Incore Detector Operability.

An audible alarm and a visual CRT alarm message is initiated whenever any of

the parameters indicated above do not satisfy the LCO conditions required by

the Technical Specifications.

COLSS monitoring is accomplished by performing calculations using incore

detector signals, CEA positions, primary and secondary coolant pressure

measurements, and various temperature measurements and flow measurements to

monitor the following parameters:

10

1) margin to the peak Linear Heat Rate (LHR) limit,

2) margin to the Departure from Nucleate Boiling Ratio (ONBR) 1 in. l t '

3) margin to the licensea total core power,

4) azimuthal tilt, and

5) Axial Shape Index (ASI).

The function of the COLSS in the overall plant monitoring ard protection

system is illustrated in Figure 2-1. The protection function is provided by

the Core Protection Calculators (CPC) which cause a plant trip if necessary to

avoid violation of fuel design limits on LHR or DNBR. The COLSS monitoring

system reviews system behavior and alerts the plant operator to situations

where LHR or DNBR have reached their monitoring limits. In addition, COLSS

alerts the operator when other plant parameters (e.g., azimuthal tilt or axial

shape) are at prespecified limits. The Technical Specifications require

periodic review of specific aspects of the operation of both the monitoring

and protection systems relative to detailed calculations or specific measure­

~ents to verify acceptable cperation and recalibrate as required.

2.2 Overview of COLSS Operation

The COLSS algorithms provide an integrated approach to monitoring those system

parameters important to the evalua~ion of LHR and ONBR. Rather than

restricting each parameter individually, COLSS uses its inputs to simulate the

core power distribution which is then used to directly evaluate the current

LHR and DNBR. From this evaluation, the power margin to the ONBR limit, to

the LHR limit, and to the licensed plant power are determined and compared to

11

alarm setpoints which monitor the requirements of the Technical Specifications.

Additional alarm limits are provided on Axial Shape Index (ASI) and azimuthal

tilt. If an alarm setpoint is violated, an alarm sequence is initiated to

alert the operator to the violation. The functional block diagram of Fig•Jre

2-2 illustrates the overall COLSS algorithm.

2. 2 .1 System Inputs

Table 2-1 provides a typical list of COLSS monitored variables. The specific

number of sensors and the sensor ranges can vary from plant to plant depending

on installed instrumentation. Figure 2-3 shows typical COLSS sensor locations.

All COLSS sensors are sampled at one second intervals except for the CEA

position indications, which are sampled at ten second intervals, and the

incore detectors, which are sampled at two second intervals for some plants.

2.2.2 Process Measurement Processing

The plant computer process cont~ol executive program processes system inputs

for use by COLSS. This processing includes taking the measurements, checking

the values against transducer limits, and conversion of measurements to

engineering units. If a measurement exceeds the associated transducer limits,

it is identified as invalid for use in later algorithms.

Additional measurement validity checking is performed internal to COLSS

[ncluding[ J 12

~This checking will alert the operator to the gradual

deterioration of a sensor.

When data being obtained from a sensor is determined to be invalid, the

operator is informed of the sensor failure by alarm and the data is marked

within COLSS as being invalid. To compensate for invalid data from a

particular sensor,~

13

liUIVlt)U~ I IUI~ tl'illll~tt.KINll

PROPRIETARY INFORMATION

2.2.3 COLSS Calculations

Portions cf the COLSS calculations are performed at one, ten, and thirty

second intervals and are synchronized with data acquisition rates. (e,(:.,

incore instruments are polled at 2 second intervals but used in COLSS power

distribution synthesis at 10 second intervals.) Calculations performed at one

second intervals include:

l) measurement process~ng,

2) reactor vessel volumetric flow calculation,

3) plant power calculation based on:

a) turbine first stage pressure

b) reactor coolant temperature rise across the core

4) update of the DNB power operating limit since the latest detai~ed

calculation, and

5) comparison of the plant pcwer to calculated limits.

Calculations performed at ten second intervals include:

1) axial power distribution synthesis,

2) azimuthal tilt calculat~ons,

14

3) local power density power operating limit calculations, anrl

4) comparison of AS! and azimuthal tilt to al1owe1 limits.

Calculations performed at thirty second intervals include:

I) secondary calorimetric calculations of reactor power, and

2) thermal margin power operating limit calculations.

2.2.3.1 Volumetric Flow Calculation

The volumetric flow for a single pump is based on differential pressure across

the pump, pump rotational speed, and water properties from the measured values

of cold leg temperature and primary system pressure. The total reactor

coolant system flow is derived by summing the individudl pump flows.

2.2.3.2 Core Power Calculation

Core power is determined by an auctioneering process between power values

calculated by a primary side calorimetric and a correlation to turbine first

stage pressure, both of which are calibr?.ted periodica11y to the secondary

side calorimetric. The primary calorimetric power is derived from the

calculated volumetric flow and water properties based on measured valu~s of

cold leg temperature, hot leg temperaturP., and reactor coolant system

pressure. The estimate of reactor power from turbine pressure is based on a

third order polynomial fit to turbine first stage pressure. The secondary

15

* ca 1 orimetri c power is derived from the measured va 1 ues of feed.,.,a ter fl ow ,

feedwater temperature. steam f1 ow, and secondary steam pressure. Appropriate

allowances for energy gains and losses are included.

2.2.3.3 Power Distribution Calculation

Signals from the fixed in-core neutron detectors and signalc from the CEA

pulst counter position indicators supply the input to the power distribution

calculations. The calculations performed include:

1) Determination of planar radial pea~ing factors based on CEAs present

in each axial plane,

2) Calculation of a normalized 40 node axial power distribution and a

3-D power peaking factor for use in the calculation of the LHR power

oper·lting limit,

3) Calculation of a core average axial shape index (ASI),

4) Determination of a 20 node hot channel axial power distribu~ion and

associated integrated radia1 peak for use in the calculat;on of the

thermal margin power operating limit to DNB, and

5) Calculation of azimuthal power tilt.

* Both Feedwater flow and steam flow are determined from differential pressure measurement across known flow restrictions.

16

2.2.3.4 Secondary Calorimetric Power Calculation

Secondary calorimetric power is derived from measurements of steam header

pressure. feedwater flow (as differential pressure), feedwater temperature,

and steam flow (as differential pressure). These inputs are used to perform

an energy balance on each steam generator and then the separate results are

added. Corrections are made to the secondary calorimetric power for energy

additions to and losses from the system, including letdown and charging pump

f1ows, reactor coolant pump heat input, pressurizer heat input, and heat

losses from NSSS components.

2.2.3.5 Linear Heat Rate Power Operating Limit Calculation

The power operating limit is based on the core average ful 1 power linear heat

rate, the linear heat rate limits (historically set by the LOCA), the

calculated 3-D power peaking factor, and the calculated azimuthal tilt. The

LHR limit can be provided as a function of both inlet temperat~re and axial

position.

2.2.3.6 Thermal Margin Power Operating Limit Calculation

The thermal margin power operating limit calculation is based on the same

methods used in the C-E developed thermal margin design computer code (CETOP)

and incorporates the CE-1 Critical Heat Flux (CHF) correlation (see References

2 and 3). This calculation uses measured data from cold leg temperature

sensors and reactor coolant system pressure sensors along with the hot channel

axial power distribution and the primary system volumetric flow calculated

17

previously. The detailed calculation is performed at 30 second intervals and

is updated at one second intervals based on changes in reactor coolant system

pressure, cold leg temperature, reactor coolant volumetric flow rate,

azimuthal tilt, and integrated radial peaking factors to provide the operator

with a smoother response to changes in plant conditions.

2.2.3.7 Core Power Margin Calculation

The core power margin calculation compares the actual power to the thermal

margin and LHR power operating limits (POL) and to the licensed power limit.

Two sets of checks are done. The first set consists of two margin calcu­

lations using the present value of the core power and two POLs. The second

set consists of three margin calcu1ations using running averages of both the

power and the two POLs and includes calculation of the margin to the licensed

power limit. T:-iese latter three margins are called "smoothed" margins. rn

all, five margins are calculated and compared to appropriate limits. The

smallest of the smoothed margins is selected for disp1ay on tne digital panel

meter and the CRT display.

2,? .4 COLSS Outputs

A typical set of ~edicated COLSS outputs to the plant operator are listed in

Table 2-2. These outputs include displays of core power, power operating

limits, the minimum margin to any power operating limit, the COLSS master

alarm, and the azimuthal tilt alarm. The COL~S master alarm is activated when

licensed power is exceeded, when either power operating limit is exceeded, or

when a valid value of plant power or a power operating limit is unavailable.

18

This alarm is also activated when COLSS has been bypassed for testing. Sample

messages that can be displayed on the COLSS alarm CRT are given in Figur~ 2-4.

Additional displays and reports are incorporated in CJLSS to assist the

operator in monitoring the operation of the NSSS and in evaluating COLSS

alarms. These additional outputs are:

19

1) CRT displays of several hundred internal parameters (Figure 2-5

gives a sample of the types of parameters included),

2) a detailed printed report of all inputs and outputs,

3) an axial power distribution plot as illustrated in Figure 2-6,

4) a COLSS Failed Sensor Report listing all sensor inp~ts that have

failed validity checking, and

5) a Test Mode Report to verify correct operation of the COLSS program.

N 0

Measurement

Core volumetric flow

Core power Primary cal orimetr 1 c

Secondary calorimetric

Core power distribution

Reactor coolant pressure

Turbine power

TABLE 2-1

TYPICAL COLSS MONITORED PLANT VARIABLES

Sensors

Reactor coolant pump rotational speed

Reactor coolant pump differential pressure

Cold leg temperature Narrow range Wide range

Hot leg temperature

F eedwa ter fl ow

Steam fl ow tiP

Feedwater t~nperature

Steam pressure

tn-core monitoring system

CEA position

Pressurizer pressure

Turbine first stage steam pressure

Typical Number

2 per pump

2 per pump

1 per cold leg

1 per hot leg

1 per genera tor

1 per generator

1 per generator

1 per generator

44 to 61 incore assemblies with 5 axially stacked detectors each

l per CEA

2 (on pressurizer)

2 (on turbine)

Typical Range & Units

100 - 1200 RPM

0 - 150 PSID

525 - 62:.>F 0 - 600F

525 - 675F

0 780 in water

0 - 660 in water

100 - 500F

850 - 1050 PSIG

NA (power distribu­tion is provided graphically)

0 - 150 inches

1,500-2,500 PSIA

u-l,000 PSIA

TABLE 2-2 TYPICAL DEDICATED COLSS OUTPUTS

TYPICAL UPDATE OUTPUT OUTPUT QUANTITY DI SPLAY RANGE UNITS FREQUENCY TYPE

Plant Power O to 125 " Power l Sec. Analog .'O

Power Operating Limit 0 to 125 CV Power Sec. Ana 1 og "' based on Linear Heat Rate

Power Operating Limit 0 to 125 <¥ Power 1 Sec. Analog ·"' based on Thermal Margin

Minimum Margin to an -50.0 to 125.9 % Power 1 Sec. Digital Operating Limit 4 Di git

Axial Shape Index -.7 to +.7 10 Sec. Analog

Margin alarm close - open 1 Sec. Contact

CPC Azimuthal Tilt alarm close - open 10 Sec. Contact

Tech. Specification close - open 10 Sec. Contact Azimuthal Tilt alarm

Axial Shape Index out close - open 10 Sec. Contact of limits alarm

21

N N

INPUT:

OUTPUT:

WHERE:

WHEN:

FUNCTION:

FIXED IN-CORE CEA POSITIONS SELECTED HOT & COLO LEG TEMPERATURE DETECTOR SIGNALS PRIMARY SYSTEM PRESSURE SECONDARY

PRIMARY COOLANT FLOW PROPERTIES

I I I I

' . • ,, • t •

IN-CORE REACTOR ANALYSIS -----· ENGINEER CDLSS PROGRAM

,L • I • DETAILED l·D POWER MARGIN TO LCD

DISTRIBUTION VERIFICATION OF LIMITS ON: • THERMAL MARGIN COLSS/CPC OUTPUTS •CORE POWER • TILT MAGNITUDE AND STORED CONSTANTS •PEAK LHR • BURNUP DISTRIBUTION • THERMAL MARGIN

• TILT MAGNITUDE

OFF-LINE (ON-SITE OR UTILITY OR C-E ON-LINE (PLANT OR REMOTE COMPUTER) ENGINEERING STAFF CORE MONITORING

COMPUTER )

ONDEMlllO AS NECESSARY SEVERAL TIMES PER MINUTE (AUTOMATICALLY,

PROVIDE DETAILED VERIFY COLSS/CPC PROVIDE INFORMATION CORE INFORMATION RESULTS ANO TO ASSIST OPERATOR IN FOR ANALYSIS AND ACCEPTABILITY OF MAINTAINING CORE INTERPRETATION BY STORED CONSTANTS CONDITIONS WITHIN ENGINEERING STAFF TECH. SPEC. OPERA TING LIMITS

FIGIJAE 2-1 OVERVIEW Of C-E CORE MONITORING AND PROTECTION SYSTEMS

EX·CORE DETECTOR SIGNALS

(3 SEGMENTS)

' ' , , CPC

J,

TRIP SIGNALS BASED ON: •PEAK LHR • THERMAL MARGIN

ON-LINE (CORE PROTECTION CALCULATORS)

SEVERAL TIMES PER SECONO (AUTOMATICALLY)

PROVIDE AUTOMATIC PROTECTION AGAINST EXCEEDING LHR AND DNBR FUEL DESIGN LIMITS

N UJ FEEOWATER TEMP

~ ST

FE

ST

EAll PRESSURE --EDWATER FLOW -.. EAM FLOW .__.

TU PR

Rll•E ht ST AGE _

ESSURE

TH OT

Tc :OLD

R

R

R

:PSPEEO

:P HEAD

:s PRESS

CE .A POSITIOIS

IN -CORE FLUX

-

-.. -.... -... --

-....

~

~ SECONDARY CALORIMETRIC

f+ POWER

i _.... - AUTOMATIC en CALIBRATION Of

TURBINE POWER ¥ TURBINE POWER u ~ .... ANO AT POWER rti w -:c TO SECONDARY u

CALORIMETRIC > ... POWER Q

:; rt- REACTOR COOLANT -t c

> AT POWER a: ,. i. 0 en z

I ..., -en -COO LAU -~ VOLUMETRIC ... r

~ FLOW RATE -- ... -... -..

- - -... FUEL PIN ANO ... COOLANT CHANNEL -- PLANAR RADIALS - CORE POWER l IMIT

rt BASED ON LOCAL .. POWER DENSITY r AZIMUTHAL TILT r+ MAGNITUDE :: AUDIBLE ALARM

NORMALIZED AXIAL ~ POWER DISTRIBUTION

FIGURE £-2 FUNCTIONAL DIAGRAM OF THE CORE OPERATING

LIMIT SUPERVISORY SYSTEM

ALARM/DISPLAY

t COMPARISON ...

CORE POWER LIMIT BASED

ON DNBA

• SELECTION OF

CORE POWER LIMIT -.. ~

LICENSED P )WER LIMIT

N ~

FIGURE 2·3 COLSS SENSOR LOCATIONS

FIRST STAGE PRESSURE

HIGH PRESS.

P~ESSURIZER PRESSURE

STEAM PRESSURE TURBINE STEAM PRESSURE

FEED· ATER

FLOW AP

STEAM FLOW uP

MAIN STEAM LINE 1

PRIP.4ARV COOLANT LINES

TEMPERATURE

LOOP1A

RPM FEEDWATER LINE 1

MOISTURE SEPARATORS

& REHEATERS

NOTE:

PUMP tlP

LOW PRESS. TURBINES

& CONDENSERS

RCP = REACTOR COOLANT PUMP

CONDENSATE PUMPS

MAIN STEAM LINE 2

TEMPERATURE

LOOP 2A I * \.!_A~RPM

UMP T\ .1P. PUMP AP

PRIMARY COOLANT LINES

TEMPERATURE

LOOP28

HEATERS

RPM

PUMP DP

FEEDWATER PUMPS

' I 8

STM. GEN. No. 2

FEEDWATER FLOW ~p

FEEOWATER LINE 2

----\ HEATERS I \

v FEEDWATER TEMPERATURES

FIGURE 2-4

TYPICAL ALARM CRT MESSAGES

Alann 1 Messages

(TIME)

XX:XX:XX ALARM COL SS DNBR POWER LIMIT EXCEEDED

XX:XX:XX ALARM COL SS KW/FT POWER LIMIT EXCEEDED

XX:XX:XX ALARM COL SS LICENSED POWER LIMIT EXCEEDED

XX:XX:XX ALARM COL SS INSTANTANEOUS DNBR POWER LIMIT EXCEEDED

XX:XX:XX ALARM COL SS INSTANTANEOUS KW/FT POWER LIMIT EXCEEDED

XX:XX:XX ALARM COL SS LPL ALARM DURATION EXCEEDED

XX:XX:XX ALARM COL SS DNBR ALARM DURATION EXCEEDED

XX:XX:XX ALARM COL SS KW/FT ALARM DURATION EXCEEDED

ALARM 2 and ALARM 3 Messages

XX:XX:XX

XX:XX:XX

XX:XX:XX

XX:XX:XX

ALARM

ALARM

ALARM

ALARM

Alarm 4 Messages

XX:XX:XX

XX:XX:XX

ALARM

ALARM

Other Alarm Messages

XX:XX:XX

XX:XX:XX

25

ALARM

AL.A.RM

COL SS

COL SS

COL SS

COL SS

COL SS

COL SS

COL SS

COL SS

CPC TILT LIMIT EXCEEDED

TECH SPEC TILT LIMIT EXCEEDED

CPC TILT ALARM DURATION EXCEEDED

TECH SPEC TILT ALARM DURATION EXCEEDED

ASI OUT OF LIMITS

ASI ALARM DURATION EXCEEDED

REMOVED FROM SERVICE

HOT LEG DEVIATION EXCEEDED

FIGURE 2-5

SAMPLE PARAMETERS FOR CRT DISPLAY

·· Parameter Descri2tion Usage Units

I COLSS HOT LEG TEMP-LOOP 1 INPUT DEG F COLSS HOT LEG TEMP LOOP 2 INPUT DEG F COLSS TURB lST STA~E PRES,PR INPUT PSIA COLSS TURB lST STAGE PRES,AL INPUT PSIA COLSS FW OUTLET TEMP, SGl INPUT DEG F COLSS FW OUTLET TEMP, SG2 INPUT DEG F COLSS FEEDWATER FLOW DP,SGl INPUT IN H20 COLSS FEEDWATER FLOW DP,SG2 INPUT IN H20 COLSS SECONDARY STEAM PR,SGl INPUT PSIG COLSS SECONDARY STEAM PR,SG2 INPUT PSIG COLSS STEAM FLOW OP, SGl INPUT IN H20 COLSS STEAM FLOW DP, SG2 INPUT IN H20 CEA REG GRP 1 MINIMUM POS INPUT IN CEA REG GRP 2 MINIMUM POS INPUT IN CEA REG GRP 3 MINIMUM POS INPUT IN CEA REG GRP 4 MINIMUM POS INPUT IN CEA REG GRP 5 MINIMUM POS INPUT IN CEA REG GRP 6 MINIMUM POS INPUT IN CEA REG GRP 1 MINIMUM PCS INPUT IN CEA REG GRP 2 MINIMUM POS INPUT IN CEA S 0 GRP 1 MINIMUM POS INPUT IN CEA S 0 GRP 2 MINIMUM POS INPUT IN CEA REG GRP 1 DEVIATION INPUT IN CEA REG GRP 2 DEVIATION INPUT IN CEA REG GRP 3 DEVIATION INPUT IN CEA REG GRP 4 DEVIATION INPUT IN CEA REG GRP 5 DEVIATION INPUT IN CEA REG GRP 6 DEVIATION INPUT IN CEA P L GRP 1 DEVIATION INPUT IN CEA P L GRP 2 DEVIATION INPUT IN CEA S D GRP 1 DEVIATION INPUT IN CEA S D GRP 2 DEVIATION INPUT IN DET SENSTVTY CORR FLUX INPUT NV*El4 RCP lA SPEED OUTPUT RPM RCP lB SPEED OUTPUT RPM RCP 2A SPEED OUTPUT RPM RCP 28 SPEED OUTPUT RPM RCP IA DIFF PRESS OUTPUT PSID RCP 18 DIFF PRESS OUTPUT PSID RCP 2A DIFF PRESS OUTPUT PSID RCP 28 DIFF PRESS OUTPUT PSID RCS PRESSRZR PRESS OUTPUT PSIA RCS LOOP IA COLD LEG TEMP OUTPUT DEG F RCS LOOP 18 COLD LEG TEMP OUTPUT DEG F RCS LOOP 2A COLD LEG TEMP OUTPUT DEG F RCS LOOP 28 COLD LEG TEMP OUTPUT DEG F

26

N ...... CORE AVERAGE AXIAL POWER SHAPE FROM COLSS

·-----·-----·-----·-..---·-----·-----·-----·-----·-----·-----·-----·-----·-----·~·------· .......... -----·........ . . .. • • • 1.523 .. 1.484 • 1.445 • 1.406 • 1.367 • 1.327 • 1.288 • 1.249 • 1.210 • 1.171 • 1.132 • 1.093 • 1.054 • • 1.015 •

. 976 •

. 937 •

.898 • •

.859 •

. 820 •

. 781 • •

.742 •

.703 •

. 664 •

. 625 • •

. 586 •

. 547 •

.508 •

. 469 ••

. 429 •

. 390 •

. 351 •

.312 •

.213 •

.234 •

. 196 •

.156 •

.117 •

.078 •

.039. .000 •

• PLR1 • PLR2 • REG1• REG2 • REGJ • REG4 • REGS• REG&•

•

• • • • • • • •

• • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• • • • • • • • • ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••

10 ·-----·-----·-----·-----·-----·-----·-----·-----·-----·-----·-----·-----·-----·-----·-----·-----·-----· ....... -·-----·-----·· 5

BOTTOM

15 20 25 30 35 40 45 50 55 60 65 10

CORE HEIGHT. PERCENT

FIGURE 2-6 COLSS POWER DISTRIBUTION PLOT

75 80 85 90 95 100

TOP

2.3 Description of COLSS Algorithms

As discussed in the overview (section 2.2), COLSS performs the following major

calculations:

1) calculation of reactor coolant system volumetric flow rate,

2) calculation of core power based on:

a) reactor coolant temperature rise across the core,

b) turbine first stage pressure, and

c) secondary system calorimetric,

3) calculation of core power distribution parameters including:

a) normalized core average axial power distribution.

b) azimuthal tilt magnitude,

c) hot channel integrated planar radial peaking factors and 3-0

peaking factors, and

4) calculation of power limits based on linear heat rate and on the

departure from nucleate boiling ratio (DNBR).

This section provides additional descriptions of these calculations. This

material is intended to provide a general description of the scope and

methodology implemented in the COLSS algorithms. References are provided, as

appropriate, to more detailed reports.

28

2.3.1 Reactor Coolant System Volumetric Flow

The volumetric flow calculation is performed every second and provides the

flow input needed for the calculation of primary calorimetric power and of the

power operating limit based on DNBR. The flow through each pump is ca1culated

based on sensor inputs of

1) pump rotational speed,

2) pump differential pressure,

3) cold leg temperature, and

4) Reactor Coolant System (RCS) pressure.

Following validity checking of sensor inputs, the specific volume of the water

entering the reactor coolant pumps is determined from cold leg temperature and

RCS pressure. The differential pressure is then converted to pump head and

is adjusted for the fraction of rated pump speed at which the pump is opera-

ting. This result is then used to calcuiate volumetric flow in gallons per

minute based on a polynomial fit to pump speed and the ratio of pump head

divided by the square of the fractional pump speed. The coefficients of this

fit are derived from pump testing. Total flow is then calculated as the sum

* of the flows from each of the four pumps . A normalized vessel volumetric

flow is also calculated.

The volumetric flows are also used to determine the mass flow rate for each

cold leg as the ratio of the volumetric flow rate to the specific volume of

the cold leg water. The total vessel mass flow which is the sum of the flows

through the four cold legs, is provided for operator information.

* allowance is made for core bypass flow in the DNBR calculation

29

2.3.2 Primary Calorimetric Power

The primary calorimetric power calculation is performed every second. This

calculation of power uses the volumetric flow already calculated for each pump

plus sensor inputs of:

1) RCS pressure,

2) cold leg temperature, and

3) hot leg temperature.

The primary calorimetric power calculation begins with the compensation of

each of the four cold leg temperature indications for sensor time response and

plenum mixing time. For each cold leg the compensation uses a digital filter

which is implemented using the present and previous values of cold leg

temperature and the previous value of the compensated cold leg temperature.

The coefficients of this fi1ter are explicitly determined from the time

responses and the period of the calculation.

The enthalpy of the water in each hot leg and cold leg is determined from

polynomial fits to the measured hot leg temperatures, the compensated cold leg

temperatures, and the reactor coolant system pressure. Power is then

calculated from the enthalpy change between the cold and hot legs.

2.3.3 Turbine Power

The turbine power calculation is performed every second. The only measured

input to this calculation is turbine first stage pressure. The calculated

30

power is given by a third order polynomial fit to the turbine pressure. All

coefficients in the fit are determined empirically.

2.3.4 Secondary Calorimetric Power

The secondary calorimetric calculation is performed once per 30 seconds using

input values that are averaged over the previous 10 seconds to reduce the

impact of sensor noise*. The measured inputs to this calculation for each

steam generator are:

1) feedwater flow pressure drop,

2) steam flow pressure drop,

3) feedwater temperature, and

4) secondary steam pressure.

The calculated secondary calorimetric power is the sum of the power

transferred to each steam generator and the energy lost from the system, less

energy additions to the system.

* For the Palo Verde COLSS, secondary calorimetric power itself is averaged

over several calculations rather than using averaged input parameters.

31

2.3.4.1 Power in Each Steam Generator

The power transferred to each steam generator is caiculated from feedwater

enthalpy, feedwater pressure, feedwater mass flow rate, feedwater specific

volume, steam mass flow rate, and steam generator pressure. The calculated

feedwater pressure (performed separately for each feed train) is the secondary

steam pressure corrected for pressure losses from the feed injection point

back to the pressure transducer.

The feeawater specif'~ volume (derived from the feedwater temperature and

pressure using sta,dard water properties) is used to convert the measured

feedwater flow prEssure drop to mass flow for each feed train. A small

temperature correc:ion is provided in this conversion to account for changes

in flow resistance .

The measured se 1 ondary pressure for each steam generator is corrected for

pressure losses uetween the steam generator and the sensor to obtain steam

generator pressure. The steam mass flow rate is calculated as the feedwater

flow minus the blowdown mass flow rate (an input constant).

The power transferred to each steam generator is then calculated as the

difference between enthalpy removal via the steam and blowdown mass flows, and

enthalpy entry via the feedwater mass flow. The quality of both steam flow

and blowdown flow are properly accounted for.

32

2.3.4.2 Power Adjustments from the NSSS

The calculated secondary calorimetric power is adjusted for power losses and

power credits to the NSSS. The power losses are determined from input

constants. On-line measured data is not used directly. The power losses that

are included are:

1) letdown mass flow rate and enthalpy,

2) reactor coolant pump seal cooling mass flow rate and enthalpy,

3) cooling water mass flow rate and enthalpy,

4) mass flow rate of other primary coolant water leaving the system and

its enthalpy,

5) power loss from the pressurizer

6) power loss from primary coolant p;ping,

7) combined power loss from steam generators, and

8) other energy losses from the NSSS.

Similarly, the power credits to the system are also based on input constants.

The power credits that are included are:

1) charging pump mass flow rate and enthalpy,

2) total power input from active reactor coolant pumps,

3) power input from pressurizer heaters,

4) other sources of power input from electrical equipment, and

5) all other power input to the NSSS.

33

The final calculation of secondary calorimetric power is then simply the sum

of the two steam generator powers plus the net NSSS power losses (i.e., total

losses minus total gains).

2.3.5 Plant Power

Both primary calorimetric power and turbine power are calibrated using a

correction factor based on the most r~cently performed secondary calorimetric

calculation of power.~

1 The larger of the two calibrated powers is

selected as plant power for display to the operator, for use in margin

calculations, and for use by the Power Dependent Insertion Limit (PDIL) CEA

Application Program. ~

L ] 2.3.6 Core Power Distr;hution

The major steps in deriving the core power distribution include:

1

1) conversion of incore fluy measurements to assembly relative power by

axial region,

2) determination of planar radial peaking factors from CEA position,

3) synthesis of a core average axial power distribution,

34

4) calculation of azimuthal tilts, and

5) synthesis of a pseudo hot pin power distribution.

2.3.6.1 Conversion of Flux to Power

Using methodology that is essentia11y identical to that used in CECOR

(Reference 4 ), this algorithm converts incore detector compensated neutron

flux to assembly relative power at each incore detector location at 10 second

intervals.

The flux to power conversion uses the incore detector compensated fluxes at

each of the five axial levels of each of the incore detector strings along

with the CEA group positions. The CEA group positions are used to provide an

additive correction to the conversion factor to account for shadowing of a

specific detector by a CEA in the same assembly.

For each string a power dependent correction factor is determined as a linear

function of plant power. The final conversion factor for a string is then the

sum of the CEA shadowing correction plus the product. of the burnup dependent

correction factor and the power dependen~ correction.

The burnup dependent component is calculated daily using the integr~ted power

at a detector 1ocation. This "integration" is done stepwise assuming that the

power has been constant over each 10 second interval. The depletion of fuel

in the vicinity of a given detector 'location is taken to be proportional to

35

the integrated power. The burnup dependent flux to power correction factor is

then given by a polynomial in burnup.

2.3.6.2 Planar Radial Peaking Factors

The appropriate planar radial peaking factors are determined for each axial

node by a table lookup pr0cess based on indicated CEA qroup positions. This

calculation is performed once per ten seconds and is done in two parts.

36

1) Planar radial peaking factor tables are stored for each of the

possible CEA configurations. For each configuration, the table

contains the planar radial peaking factG~

2) Penalty factors are applied to the radial peaking factors based on

the determination of out-of-sequence CEA group insertion and

excessive CEA deviations within any group. A pre-calculated CEA

out-of-sequence penalty multiplier is applied if any out-of-sequence

condition exists.

A secund penalty factor accounts for CEA deviations within a group.

The penalty factor for each CEA group is determined as a piece-wise

linear function of the size of the deviation. The final deviation

penalty factor is the product, over all groups, of the individual

penalty factors. The magnitude of the penalty factor applied

repends on the CEA group in which the deviation is occurring.

2.3.6.3 Axial Power Distribution

A forty node core average axial power distribution is calculated based on

in-core detector power signals using a five mode Fourier series expansion.

This calculation is performed once per ten seconds to provide the power

distribution used in the LHR calculation.

For each of the 5 detector levels, the assembly relative powers calculated

previously (see section 2.3.6.1.) are averaged over all incore locations with

valid signals. These average powers at each level are then normalized to have

a sum of 100%. The normalized detector signals are transformed into five

Fourier series weighting coeffici~nts by evaluating the matrix product of a

prestored "coefficient matrix" and the vector of detector signals. This

prestored matrix depends only on the integral of the five Fourier modes over

the axial length of the incore detectors. The 40 node power distribution is

then constructed by forming the sum. at each axial node. of the Fourier

functions (prestored in an array) times their respective coefficients. The

axial power distribution is normalized so that the average value of the axial

distribution is unity.

37

Once the axial power distribution is available, the core average ASI is

determined as the difference between the lower and the upper half core poher

fractions.

1

2.3.6.4 Hot-Pin Integrated Radial and ASI

A[ ]hot pin power distribution is determined as the product of the axial

power distribution and the planar radial peaking factor for each of thef:_ J nodes. The integrated radial peaking factor is then calculated as the average

of the hot pin power distribution over the[ ]axial nodes. The hot pin ASI is

calculated in the same manner as the core average ASI except for the use of

the hot pin power distribution.

2.3.6.5 Azimuthal Tilt

The core average azimuthal tilt is calculated from the assembly average powers

once per 10 seconds using methodology that is essentially identical to that in

CECOR (Reference 4). The incore detectors are divided into "tilt groups" of

38

four detectors with appropriate symmetry properties. Depending on the olant,

axial detector leoel. ~ ~ there are between nine and twelve tilt groups at each

the signals in opposite

~ For each tilt group,

quadrants are calculated.

the sum and difference of

These sums and differences

and a set of detector location dependent constants are used to calculate an

azimuthal tilt for each group.

The average azimuthal tilt at each level is then calculated as an "arithmetic

average 11 of the magnitude of the individual group tilts at that level. In

some plants,~

The core average azimuthal tilt is calculated by averaging the 5 level tilts

using a weighting factor for each level that is based on the number of valid

sets of detectors at that level. If the calculated azimuthal tilt is higher

than either the Technical Specification limit or the allowance used by tne

Core Protection Calculators (CPCs), then an alarm is initiated.

2.3.6.6 Three-D Power Distribution

The 3-0 power peaking factors are calculated for use in the linear heat rate

power operating limit calculation. The 40 node 3-0 power distribution is then

39

determined as the product of the radial peaking factor (Section 2.3.6.2) and

the value of the 40 node core average axial power distribution (Section

2.3.6.3) at each node. The maximum value of these products is the 3-D power

peaking factor which is made available for operator information.

2.3.7 Linear Heat Rate Power Operating Limit

The core power operating limit based on the Linear H~at Rate (LHR) limit is

calculated once per 10 se~onds. This calculation is used to monitor the LHR

limit normally established by Loss of Coolant Accident (LOCA) considerations.

The linear heat rate is calculated for each of the 40 nodes of the 3-0 power

distribution. This linear heat rate is the product of the normalized power

fraction in the node, the core average linear heat rate at rated power, and

the fraction of core power at which the plant is operating. Correction

factors are applied to account for the azimuthal tilt and modeling

uncertainties.

The power operating limit at each node is calculated as the product of plant

power, a correction factor to account for failed incore detectors, and the LHR

limit divided by the calculated linear heat rate for that node. The minimum

value calculated in this manner is the LHR power operating limit. It is this

value which is compared to the current value of plant power.

40

?.3.8 Thermal Margin Power Operating Limit

The thermal margin power operating limit is based on maintaining the calculated

ONBR above a specified minimum value (based on the CE-1 CHF correlation) and

maintaining the fluid quality below a specified maximum value at the point of

minimum ONBR. The thermal hydraulic model used to evaluate this limit is

based on the C-E proprietary code CEiOP and the CE-1 CHF correlation (see

references 2 and 3). This calculation is performed once per 30 seconds with a

dynamic update provided once per second.

The thermal-hydraulic modeling uses[

41

The calculat~on proceeds in an iterative manner in that an estimate of the

power operating limit (POL) is used to detennine the minirrum DNBR and tf,e

quality at that point. If both the DNBR and the quality are within their

respective limits, the algorithm raises the POL estimate and recalculates the

DNBR and quality. Similarly, if either of DNBR or quality are not within

their limits, the POL is lowered. This iteration continues until it finds the

maximum POL that meets both DNBR and quality limits.

The details of this calculation have been amply described in references 2 and

3 and wi11 not be repeated here. The calculation does incorporate an adjust­

ment~ .~to account for the margin

required for the Loss of Flow event in the re~ultant POL. This adjustment is

discussed further in Section 3.3.

2.3.9 Thermal Margin Power Operating Limit Update

The detailed thermal margin calculation is only performed once per 30 seconds.

An approximate update to the most recent detailed calculation is performed

once a second tc provide the operator vJith a smoother indication of the cure

performance. The updated DNBR power operating limit (POL) is based on cnanges

in several measured and derived parameters including:

1) primary pressure,

2) maximum compensated cold leg t~mperature,

3) core flow rate,

4) integrated radial peaking factor,

42

5) azimuthal tilt,

6) c 7) quality at the node of minimum DNBR,

J 8) most recently calculated power operating limit.

9) POL derivative with respect to quality, and

10) POL derivative with respect to ONBR.

2.3.10 Core Power Margin

The core power margin calculation compares the actual power to the thennal

margin and LHR power operating limits (POL) and to the licensed power limit.

Two sets of checks are done. The first set consists of two margin

calculations using the present value of the core power and the two POLs. The

second set consists of three margin calculations using running averages of

both the power and the two POLs and includes calculation of the margin to the

licensed power limit. These latter three margins are called "smoothed"

margins. In all, five margins are calculated and compared to appropriate

limits. The smallest of the smoothed values is displayed on the digita1 panel

meter and CRT display and is referred to as MARGIN. If any of the 5

calculated margins is less than its respective limit, an alarm is initiated.

Before being used in these comparisons, the calculated power operating limits

are adjl'sted for power measurement biases. These biases are dependent on the

measured power level and on which of the three calculated powers have been

used to determine plant power (see section 2.4.1).

43

2.4 Uncertainties

The calculation of DNB and LHR power operatinJ limits requires numerous

measured inputs and calculated constants. Each of the measured inputs (i.e.,

temperature, pressure, etc.) and the calculated constants (i.e., fuel and

poison rod bow, system parameters, etc.) can have some uncertainty associated

with it. These uncertainties are applied in a conservative fashion to re]uce

the predicted power operating limits to ensure that adverse combinations of

uncertainties do not prevent alarms when limiting conditions for operations

are violated. References l and 5 describe the methods used to determine these

uncertainties.

2. 4. 1 Power Measurement Bias

The accuracy of the power measurement is a function of the frequency of

calibration and the method for determining the present power output. The

secondary calorimetric is the most accurate m~asure of reactor power and

generally has a net uncertainty of less than or equal to 2~ of rated power

near full power increasing to no more than( ]of rated power at low power.

The primary calorimetric and the turbine first stage pressure determinations

of power are less accurate having a typical uncertainty of 3.5~. Biases are

applied to the POLs to account for these uncertainties. All of the bias terms

are calculated as a function of plant power. Before a bias is applied to the

power operating limits, the validity of each of the three methods for deriving

plant power is determined. If the secondary calorimetric calculation is valid

then its bias is chosen since the other powers are periodically calibrated to

44

match it. If the secondary calorimetric is invalid, but either of the other

two power determinations is valid, then an appropriate, larger bias is

applied. The bias term is subtracted from the calculated power operating

limits to obtain the biased power operating limits.

2.4.2 Power Operating Limit Uncertainties

Other uncertainties associated with the calculation of the power operating

limits are accounted for in a conservative fashion in the power operating

limit algorithms by applying additive and/or multiplicative adjustment factors.

The uncertainty factors considered in the generation of these terms for DNBR

and LHR power operating limit calculations are:

45

I) uncertainty in in-core detector signal measurement,

2) uncertainty in Control Element Assembly (CEA) position measurement,

3) uncertainties in temperature, pressure, and flow measurements,

4) uncertainty in verification of tabulated planar radial peaking

factors (F ) using CECOR, xy

5) impact of the COLSS power distribution synthesis on the LHP

algorithms and DNB overpower margin,

6) uncertainty in COLSS DNB-OPM algorithm with respect to design

calculations,

7) computer processing uncertainties,

8) fuel and poison rod bow uncertainties,

9) global axial fuel densification uncertainty, and

10) engineering factors due to manufacturing tolerances.

The generation of these uncertainty terms is discussed briefly in Section 3.4.

A more detailed description can be found in Reference 5.

3.0 Constants and Supporting Data

To support the COLSS a1gorithms, numerous constants based on plant design

characteristics must be generated for incorporation into COLSS. These

constants can be divided into 5 major categories:

1) cons tan ts related to plant mechanical and thermal hydraulic design,

2) constants related to core design,

3) constants related to monitoring margin to limiting conditions for

operation,

4) constants re 1 a ted to measurement and calculational uncertainties,

and

5) constants required to support on~line ONBR calculations.

Each of these areas will be discussed to provide some background into the

basis for the constants in that area. General descriptions of the types of

analysis used to determine the constants will be provided where appropriate.

3.1 Basis for Mechanical and Thermal-Hydraulic Constants

Calculations of the RCS vol~metric flow rate and calibrated power depend on

constants which are based on the NSSS thermal hydraulic and mechanical design.

The volumetric flow calculation is determined by a polynomial fit to measured

values of RCP differential pressure and pump speeds. The constants for this

46

calculation are based on a curve fit of experimental pump characteristic data

obtained from operation of the RCP's in a test loop. RCS rated flow and RCP

rated speed are also used in the flow calculation.

The primary calorimetric power is based on calculated fluid enthalpies and

measured flows, temperatures, and pressures. No significant constants are

required to support a strictly static primary calorimetric power calculation

beyond standard water property tables. However, this calculation includes a

dynamic compensation of variations in cold leg temperatures. The cold leg

temperature compensation depends on the cold leg temperature sensor time

constant and the calculated plenum time constant based on RCS design (sensor

location, flow path, and .·1uw rate). The core rated power is provided as a

data base constant to permit normalization of the calculated power to percent

of rated power.

The secondary calorimetric power is based on measurements of feedwater flow,

steam flow, feedwater temperature, and steam pressure. Most of the constants

used in the power calculation are derived from or confirmed by field data

obtained during power ascension testing. These constants relate feedwater

pressure to secondary steam pressure and steam flow, relate steam generator

pressure to steam header pressure and steam flow, and quantify energy losses

from and credits to the system (including the gain associated with operation

of the RCP's).

The relationship of feedwater mass flow rate to feedwater temperature,

feedwater flow, and feedwater specific volume is based on venturi

47

characteristic test data. The calculated turbine power is based on a

polynomial which is fit to the data obtained during power ascension testing.

3.2 Basis for Core Design Constants

3.2.1 Conversion of Flux to Power Constants

The conversion of the flux signal for each incore detector to relative power

uses correlation coefficients that reflect detector location, local geometry,

and local burnup. These coefficients are the same as those used in the CECOR

off-line power distribution calculation (Reference 4). The System 80 plants

require additional adjustments in those bundles which have both a CEA and an

in-core detector string. Other C-E plants using COLSS do not have CEA's

entering instrumented assemblies anc do not require these adjustments.

3.2.2 Planar Radial Peaking Factor Look-up Tables

Prior to startup, neutron1cs calculations are performed to determine the

maximum expected planar radial peak for each CEA configuration allowed by the

CEA Power Dependent Insertion Limit (PDIL). Detailed calculations are

generally performed for the unrodded core and for CEA configurations containing

only the part length CEAs and the first two lead regulating banks.

Conservative, boundirg values are determined for other configurations including

those which involve insertir;~ of shutdown CEA banks.

48

The maximum radial peak expected is installed in COLSS for each configuration.

During start-up testing. measurements are performed with CECOR to verif; the

peaking factors for the CEA configurations that are permitted at higher

powers. Adjustments to the stored constants are made if appropriate. CECOR

calculations are performed periodically during the cycle to verify the

continued adequacy of the installed constants as required by the Technical

Specifications.

Pen~lty factor constants for CEA banks out of sequence and CEA misalignment

are determined to assure an alarm if the CEA misoperation degrades the margin

below the allowed LCO. These constants are based on analyses using standard

neutronics methods to determine the change in power distribution due to the

CEA misoperation.

An additional, addressable, multiplicative penalty factor on the radial peak

is available to compensate for special circumstances requiring change after

the COLSS constants have been installed.

3.2.3 Axial Power Distribution Constants

The incore detector signals are converted into a 40 node core average power

distribution using two arrays of constants. The first array converts the

planar averages of the incore detector signals to amplitude coefficients of a

Fourier series approximation of the axial power distribution. These constants

depend only on the axial location and the length of the incore detectors, and

on the Fourier modes used. The second array is a tabulation of Fourier mode

49

values at each of the axial locations which are precalculated to reduce the

COLSS calculation time.

3.2.4 Azimuthal Tilt Calculation Constants

The azimuthal tilt calculation requires detector location dependent constants

for each "tilt group" of four detectors and appropriate averaging factors.

These factors are used primarily to account for geometric effects {detector

location) but also include an average radial tilt sensitivity from 3-0

neutronics calculations. CECOR is run at regular intervals to verify the

accuracy of the COLSS azimuthal tilt calculations.

3.2.5 LHR Limit Constants

The maximum allowed steady state LHR limit specified in the Technical

Specifications and monitored by COLSS is typically based on the Loss Of

Coolant Accident (LOCA}. This limit is specified as a function of core inlet

temperature in the COLSS of some plants.

3.3 Basis for DNB Margin Monitoring Constants

The Limiting Conditions for Operation (LCO) in the Technical Specifications

assure that sufficient margin is available to cover the degradation in DNB

margin that can occur during any Anticipated Operational Occurrence (AOO).

Such a margin loss can be caused by an increase in local power or temperature,

by a decrease in core flow or pressure, or by an adverse change in the core

50

power distribution. The margin assured by the LCO is sufficient to cover

continued adverse changes from the time the event begins until either

corrective action is taken or a power reduction caused by a reactor trip

begins to recover margin.

COLSS monitors the marqin required by the LCOs throuqh the use of anf -

~is sufficient to acconmodate AOOs without violating a fuel

design 1 imi t. The[ Ji s defined as a function of AS I to reflect the

sensitivity of the margin loss during some AOO's to the initial axial power

distribution.

Historically, the Loss of Flow (LOF) analysis has determined the acceptable

J This

section provides a brief overview of the types of AOO that could limit the

thermal margin requirement.

3.3.1 Derivation of the~ ., j f ram the Loss of Fl ow Ana 1 ys is

For C-E plants, the Loss of Flow event has historically been the most limiting

with respect to thermal margin. During the few seconds after the pumps begin

51

slowing down and prior to a significant power reduction due to the CEA

insertion, the reduced flow causes a rapid decrease in ONB margin. SevLral

seconds into the event the heat flux/flow combination results in the minimum

ONBR that will be experienced during the transient. The specific time and

value of this minimum is a function of the axial power distribution and the

i ni tia l thermal and hydraulic cond iti ans in the core. r ] ( ]

Numerous power distributions and initial conditions are used to determine the

[ Jover the AS r range of

interest using the HERMITE (Reference 6) or CESEC (Reference 7) transient

codes. The~ ]calculated in this manner is represented in COLSS by a

piece-wise linear function of ASI which bounds the values determined in the

transient cases.

3.3.2 Other Events AnalyzeJ to Confirm Adequate Monitoring

Other AOO's can also result in degradation of thermal margin. If the safety

analysis were to indicate that one or more AOOs require more margin than the

LOF, then the~ ]would be adjusted so that COLSS monitors the larger thermal

margin requirement. Two events that could require more thermal margin than

LOF are the Asynmetric Steam Generator Transient (ASGT) and the CEA Drop.

An Asymmetric Steam Generator Transient may result from the inadvertent

closure of a Main Steam Isolation Valve. The resulting asyrrmetric core inlet

52

temperature distribution results in increased core power peaking on the cold

side. This event is protected by an asymmetric steam generator tr~nsient trip

on cold leg temperature difference (~T) in the CPC, but also requires that

adequate thermal margin be available to cover temperature asyrr.metries that

occur prior to trip actuation. This event is simulated by design transient

codes for different values of the ~T setpoint. The increase in the radial

peak used in the safety analysis is calculated as a function of the temperature

tilt using standard physics methodology.

available margin monitored by COLss[

for the ASGT event or the( Ji s adjusted

The selected ~T setpoint and the

lare shown to be adequate J

to allow for the extra margin.

Plants which include the Core Protection Calculator System as part of the

Reactor Protection System have the capability to accommodate deviated CEAs via

penalty factors generated by the CEA calculators. If a SAFDL violation is

conservatively predicted by the CPCs following ap~lication of the penalty,

then the reactor will trip. If not, operation can continue in accordance with

the Technical Specifications. As a result, COLSS has not been required to

verify that adequate margin has been set aside to cover margin degradation

during a dropped CEA event when the CEA calculators in the CPCs are operable.

Recent modifications in analysis methods on several plants have demonstrated

that the thermal margin assured by the LCOs is sufficient to accommodate a

dropped CEA event. This has eliminated the need for a reactor trip during CEA

insertion events or CEA drops. Thus, comparisons have been made using standard

neutronic methods to assure that the COLSS DNBR-POL calculation using the[ )

is conservative for these events. For these plants, COLSS has been modified

to incorporate [ J 53

3.3.3 COLSS Penalty Factors Applied for CEA Calculators Inoperable

If the CEA calculators of the CPCs are not in operation, automatic trip

protection for CEA deviation events is not provided. Therefore, adequate

margin must be set aside per the Technical Specifications. In the COLSS

calculation, this margin degradation during CEA related transients is accounted

for by an addressable input constant to the DNB calculation. The va1ue of

this constant is determined by simulating the CEA misoperation distortion

factor using neutronics codes.

3.4 Bas1s for Measurement and Calculational Uncertainty Constants

Two uncertainty penalties are calculated for COLSS; one which is used in

calculating the linear heat rate power operating limit and the other which is

used in calculating the DNBR power operating limit.

The LHR adjustment accounts for the composite modeling uncertainty in the

COLSS determination of the 3-D peak and for the various engineering factors.

This modeling error is determined from a set of several thousand comparison

cases between COLSS and design codes covering suitable ranges of power level,

core burnup, CEA position, and primary system fluid properties. The overall

adjustment factor accounts for the effects of fuel rod bow, poison rod bow,

design code modeling uncertainty, COLSS power algorithm uncertainty, CECOR F xy

54

measurement uncertainty, and computer processing uncertainties. In the COLSS

algorithm, this adjustment is applied as a multiplier to the core average

linear heat rate. This has the effect of reducing the linear heat rate power

operating limit.

Similarly, the ONBR adjustment accounts for the composite modeling uncertainty

in the COLSS determination of the hot pin power distribution and power as well

as the~ ~ [ ~This composite modeling error is based on the same set of comparison

cases between COLSS and design codes used for the LHR uncertainty calculation.

The overall adjustment factor includes the effects of fuel rod bow, poison rod

bow, design code modeling uncertainty, CECOR F measurement uncertainty, xy

COLSS DNB algorithm uncertainty, and computer processing uncertainties.

For most COLSS plants, the system uncertainties are combined statistically and

included in the minimum DNBR limit that is established for use with the CE-1

CHF correlation. The uncertainties accounted for include inlet flow

distribution uncertainties, fuel pellet density uncertainties, fuel pellet

enrichment uncertainties, fuel pellet diameter uncertainties, random and

systematic uncertainties in fuel clad diameter, random and systematic

uncertainties in fuel rod pitch, and CHF correlation uncertainties. In the

cases where the statistical combination method is not used, the various listed

uncertainties are accounted for by a multiplicative adjustment to the power

operating limit.

55

Details of the methodology used to determine the measurement and rJ~culational

uncertainties for COLSS can be found in Volume 3 of Reference 5 for the

statistical combination of uncertainties method or in reference 1 for the

alternate methods.

3.5 Basis for Constants Supporting On-Line DNB Calculations

The DNB calculations performed in COLSS use a simplified, faster running

version of the design CETOP code called CETOP-1. Most of the constants used

in CETOP-1 are identical to those in CETOP or are the product of CETOP

constants which are provided to reduce computer calculation time. Three

significant differences exist between CETOP-1 and CETOP to reduce the computer

run time.

56

57

4.0 Conclusion

The preceding discussions have provided an overview of the COLSS program as

used in recent C-E NSSS designs. This system uses measurements of incore

detector signals, CEA positions, and plant thermal-hydraulic properties to

provide an on-line determination of the core power distribution and ther~al

margin performance. The results of these calculations are provided to the

plant operator through various displays to aid him in maintaining the plant

within the Limiting Conditions for Operation as specified in the Technical

Specifications.

58

5. 0 References

*

*

1. "Assessment of the Accuracy of PWR Operating Limits as Determined by the

Core Operating Limits as Determined by the Core Operating Limit

Supervisory System (COLSS)", CENPD-169, July 1975.

2. "CETOP-D Code Structure and Modeling Methods for San Onofre Nuclear

Generating Station Units 2 and 311, CEN-160(S)-NP, September 1981.

3. "C-E Critical Heat Flux - Critical Heat Flux for C-E Fuel Assemblies with

Standard Spacer Grids", Part 1 CENPD-162-A September 1976, Part 2

CENPD-207-A December 1984.

4. 11 INCA/CECOR Power Peaking Uncertainty", CENPD-153, Rev. 1-A, May 1980.

5. "Statistical Combination of Uncertainties - Uncertainty Analysis of

Limiting Conditions for Operation of the San Onofre Generating Station

Units 2 and 311, Part 3, CEN-283(S)-NP, October 1984.

6. "HERMITE - A Multi-dimensional Space Time Kinetics Code for PWR

Transients: CENPD-1°8, March 1976.

7. "CESEC - Digital Simulation of a Combustion Engineering Nuclear Steam

Supply System" Enclosure 1-NP to LD-82-001, January 6, 1982.

* Plant specific references which are intended to be typical of similar references appropriate to other plants

59