ML20093N266

Nonproprietary Cpc/Ceac Software Mods for San Onofre Nuclear Generating Station Units 2 & 3. Info Deleted

ML20093N266
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Site:	San Onofre
Issue date:	07/31/1984
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CEN-281(S)-NP, NUDOCS 8408010256
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.. _

CEN- 281 (S)- NP i

?

, CPC/CEAC SOFTWARE MODIFICATIONS '

FOR SAN ONOFRE NUCLEAR GENERATING STATION UNITS No. 2 AND 3 1

' JULY,1984 i

LEGAL NOTICE This report was prepared as an account of work sponsored by Combustion Engineering, Inc. Neither Combustion Engineering nor any person acting on its behalf: $

a. Makes any warranty or representation, express or implied including the warranties of fitness for a particular ,

purpose or merchantability, with respect to the accuracy,

-completeness, or usefulness of the information contained in this response, or that the use of any information, apparatus, method, or process disclosed in this response may not infringe privately owned rights; or-

b. Assumes any liabilities with respect to the use of, or for damages resulting from the use of, any information, apparatus, method or process disclosed in this response.

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TABLE OF CONTENTS

'Section- Title , page No.

1.0 INTRODUCTION

1.1 Report. Scope 1-1 a 1.2 . Report Summary 1-1 1.3 References for Section 1.0 1-3 2.0 SOFTWARE MODIFICATION 2.1 Changes Derived from Implementation of PVNGS 2-1 Cycle 1 Software 2.2 Additional Core Protection Calculator (CPC)

-Algorithm Changes 23 2.3 CPC Addressable Constant Changes 2 13 2.4 Typical Data Base Constants for SONGS Unit 2 2 14 2.5 References for Section 2.0 2 18 e

a iii L1:

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1. 0 - INTRODUCTION 1.1. REPORT SCOPE The Core Protection Calculator (CPC) System developed by Combustion Engineering is a digital mini-computer system which calculates the minimum Departure from Nucleate Boiling Ratio (DNBR) and the peak 6 Local Power Density (LPD) on-line and generates a reactor trip if

.either the minimum DNBR or the peak LPD approaches the appropriate Specified Acceptable Fuel Design Limit. The CPC System has been reviewed by NRC and approved for operation in Arkansas Nuclear One (ANO) Unit 2,Waterford-3,SanOnofreNuclearGeneratingStation (SONGS) Units 2 and 3 and Palo Verde Nuclear Generation Station (PVNGS) Units 1,2and3. The CPC/CEAC software for SONGS Unit 2 and 3 is being modified for operation in Cycle 2. This modification is being made using the PVNGS Cycle 1 CPC/CEAC software (Reference 1.3-3) as a basis since it is the latest NRC approved software. The modification for SONGS Units 2 and 3 Cycle 2 includes algorithm changes derived from the implementation of the PVNGS Cycle 1

~

software as well as other algorithm changes. These changes were made to the CPC System in accordance with the NRC-approved CPC software change procedure (References 1.3-1 and 1.3-2).

This report describes the changes to the SONGS software for Cycle 2.

Changes derived from the implementation of the PVNGS Cycle 1 software are described briefly since they have been approved and implemented previously (Reference 1.3-3) while other changes are described in detail.

n

1. 2 - REPORT

SUMMARY

The modifications to the CPC/CEAC software which will be applicable to Cycle 2 uf SONGS Units 2 and 3 are:

1-1

Modification of the temperature shadowing factor algorithm.

s 1) i

2) Modification of the CPC core power bias algorithm.

3) Improvement to the UPDATE algorithm.

4) Modification of the heat flux distribution extrapolation in e STATIC.

, 5) Addition of new addressable constants.

6) Modification of the four linear heat distributions in STATIC program to account for differences between the hot channel and hot pin relative powers.

7) Upgrade of the non-uniform heating correction factors (FK) in the UPDATE program.

The general format used in describing each software modification contained in this report is a statement of the change, the reason for the change, and a detailed description of the change t including algorithm descriptions in symbolic algebra. This is the.

same format used in Reference 1.3-3.

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a f

1-2

1.3 REFERENCES

FOR SECTION'1.0

1. CEN-39(A)-NP, Revision 02,TheCPCProtectionAlgorithm .

Software Change Procedure December 21, 1978.

2. CEN-39(A)-NP, Supplement 1-NP, Revision 01, January 5,1979.

, 3. Dockets STN-50-470F, Enclosure 1-NP to LD-82-039, CPC/CEAC Software Modifications for System 80, March,1982.

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I 1-3 c.

2.0 SOFTWARE MODIFICATIONS 2.1 CHANGES DERIVED FROM IMPLEMENTATION OF PVNGS CYCLE 1 SOFTWARE Th'e changes in CPC software for SONGS Units 2 and 3 Cycle 2 that hawe been derived from implementation of the PVNGS Cycle I software are described in the following summaries. These changes were

. submitted previously to the NRC (Reference 2.5-1).

, 1. Thenon-uniformheatingcorrectionfactor(,F)intheUPDATE g profr,am was adjusted by the, addition of constants based on the inqualitymarfn.

2. The calculation of the four linear heat rate (LHR) distributions in the STATIC program was modified to account for the difference between the hot channel and hot pin relative powers.

3. The positivogange limit on the CEAC penalty fac';gr

, was shifted from mul<;ipliers,L * - . -

to .

4 .' Algorithms were added to the CPC and CEAC (Control Element Assembly Calculator) for detecting the actuation of a Reactor Power Cutback (RPC) event, for using off-line calculated RPC penalty factors, and for allowing the CPC calculation to more

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closely model core conditions without generating an inadvertent trip in the event of a RPC. Since SONGS Units 2

, and 3 do not have a RPC system, the effect of these algorithms will be nullified through the appropriate data base constants.

5. Addressable constants have been added to the CPC and CEAC to define the duration that the RPC flags can remain set. (For SONGS these addressable constants will be se?. to LJ).

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2. 7. ADDITIONAL CORE PROTECTION CALCULATOR (CPC) ALGORITHM CHANGES 2.2.1 Modification of the Temperature Shadowing Factor Algorithm Change:

' Implement for cycle 2 a the Temperature Shadowing Factor (TSF) on moderator temperature using a inlet mod gator temperature. The slope of the _,

. 1,orrection for tFmpera,tures will i chosen to bound all exp,,,ected TSF datal Including uncertqinties. A ,, , will be used for temperatures . Tire excore

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detector calibratlon procedures will be modifie1 to be cons 1 stent with this determination of the TSF and its use in adjusting the neutron flux power.

Reason:

The temperature shadowing factor (TSF) is used to correct the CPC neutron flux power for decalibration effects resulting from changes in inlet coolant density. A moderator temperature-dependent multiplier is-applied to the neutron flux power calculation to corr u;t excore detector re,s,ponse. In the current algorithm, the TSF is a of,the change in moderator temperature the slope of which is measiTred at start-up. The uncertainty in the measurement of the TSF is currently _ accommodated in the CPC Departure from Nucleate B dling (DNB) and linear Heat Rate (LHR) 6 'overall uncertainty terms .

, This change will allow the TSF uncertainty to be included directly, in the factor itself. This insures a conservative correction for temperature at' moderator temperatures above or below the inlet moderator temperature at which the neutron flux power was calibrated (calibration temperature) while removing unnecessary penalties for uncertainty at the calibration temperature (which is anticipated tn be near nominal conditions).

2-3

Description:

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IM M 2.2.2 Modification of the CPC Core Power Bias Algorithm

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Change:

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Implement to adjust the thermal power and neutro"h flux power level in the CPCs.

2-4

Rea s'on:

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~Where 2.2.3 Improvement to UPDATE Algorithm Change:

The penal,ty on DNBR in UPDATE will be modelled more realistically.

When the Reason: '

The UPDATE algorithm of CPC provides rapid and conservative recalculation of DNBR based upon the detailed DNBR calculation contained in the STATIC algorithm and updated state parameters.

During the CPC overall DNB uncertainty analysis, off-line comparisons of UPDATE and STATIC-predicted DNBRs based on 2-9 L

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7eriod are used to quantify the conservatism. Presently, the UPDATE algorithm of CPC applies a penalty to the updated DNBR at all times.

This change provides greater margin to pre-trip alarms during steady state operation and.is justified by the high accuracy of the UPDATE algorithm for small changes in conditions. The safety margin of the CPC's during transients is preserved by the larger conservative

, penalty factors which are applied when the UPDATE DNBR changes significantly from the STATIC value.

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Description:

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7 Modify the heat flux distribrion extrapolation in STATIC L '"

nodal heat flux distribution values.

P.eason:

For certain CEA configurations, radial peaking factor assignments, and/or radial peaking factor multipliers, it is possible to

Description:

This change is applied in the section of the STATIC program where

" $ m A check is- performed for . If any are detected, e _

2-11

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(4) . node hot pin normalized heat flux distribution 6

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.1. Change-Addressabje_ constant replaces .

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Reason:

Consistent with TSF algorithm change described in section

2.2.1. Descriptitm

2.

Change Addressable constant has been added to the CPC in r~1ation to the core power level'"

-3 Reason:

To implement r w algorithm using and bias terms described in section 2.2.2.

Deseription:

2-13

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TYPICAL DATA BASE CONSTANTS CHA.'iGES FOR SONGS UNIT 2 2.4.1 Data Base Constants for the Temperature Shadowing Factor Algorithm Constants. .

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2.5 : REFERENCES FOR SECTION 2.0 1.. Dockets STN-50-470F, Enclosure 1-NP to LD-82-039, CPC/CEAC Software Modifications for System 80, March,1982.

2. CEN-147(S)-NP, Functional Design Specification for a Core

. Protection Calculator, January 1981.

• 3. CEN-148(S)-NP, Functional Design Specification for a Control Element Assembly Calculator, January 1981.

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