ML20235U431

Turbine Bypass Valve Out-of-Svc Evaluation Summary. Related Info Encl

ML20235U431
Person / Time
Site:	Cooper
Issue date:	09/23/1987
From:	Cornwell K, Lee T, Sozzi G GENERAL ELECTRIC CO.
To:
Shared Package
ML20235U383	List: ML20235U379 ML20235U393 ML20235U409 ML20235U422 ML20235U431
References
CNSS876103, DRF-B21-00378, DRF-B21-378, NUDOCS 8710140088
Download: ML20235U431 (3)

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GENERALvO ELECTRIC COOPER NUCLEAR STATION TURBINE BYPASS VALVE OUT-OF SERVICE EVALUATION

SUMMARY

DRF B21-00378 September 23, 1987 i fluid Cooper Nuclear Station (CNS) recently discovered a hydraulic It was 1 leak associated with one of the three turbine bypass valves.

subsequently determined that the leak could be isolated by closure of j

the high pressure hydraulic fluid isolation valve. It is desirable to continue operating CNS, with one turbine bypass valve disabled,General Therefore, until a time when the repairs can more. conveniently be made.-

Electric performed an evaluation to determine the potential increase in the CPR with one bypass valve inoperable ,

currently, the limiting cycle 11 fuel thermal limits (Option B) are dictated by the feedwater controller failure maximum demcud (WCF)- ,

event. The calculated minimum critical power ratio (MCPR) for this event at end of cycle (EOC) is 1,23 and the corresponding technical specification limit is 1.25 (i.e., a margin of 0.02 exists to the  ;

technical specification limit to allow for 10CFR50.59 evaluations of the cycle specific limits). The WCF Disabling transient is analyzed assuming all >J three bypass valves are operable. one of the bypass valves l

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may increase the calculated CPR for the WCF event.

In order to ensure Nebraska Public Power District (NPPD) could i continue to operate CNS efficiently with one bypass valve disabled, bounding, conservative core nuclear parameters were utilized toThe evaluate plant the operation of CNS throu5h the end - of fuel cycle 11.

initial conditions were assumed, consistent with the cycle 11 reload licensing evaluation, to correspond to 105% of rated steam flow, The 1

calculated fuel thermal response for the WCF event with one bypass ij valve inoperable resulted in a calculated MCPR of.1.26 (Option B currently in force for cycle 11).

This represents an increase of 0.01 in MCPR (Option B) over the current EOC Technical Specification Limit.

Although not used for the current cycle, the limiting transient for i the Option A MCPR limits, as determined by the cycle 11 reload licensing This evaluation. is the load rejection without bypass (LRNBP) event.

transient, with an Option A MCPR of 1.33, is unaffected by disabling one bypass valve. since the bypass function is assumed to fail. The calculated Option A MCPR limit for the WCF event with one bypass valve inoperable was determined to be 1.33. This is . equivalent to the i

limiting Option A MCPR obtained in the_ reload A licensing evaluation for MCPR for cycle 11 is the LPJiBP event. Therefore, the Option unaffected by disabling one bypass valve. ,

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COOPER NUCLEAR STATION TURBINE BYPASS VALVE OUT-OF-SERVICE EVALUATION

SUMMARY

(PaSe 2)

In. summary,-limitin5 the operating CPRs above 1.26.for Option B and 1.33 for Option A will ensure that the safety limit MCPR of 1.07 will not be violated while operating with one bypass valve out-of service considerin5 any of the abnormal transient events previously analyzed for CNC.

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1-4 Prepared by: . Awff K.'F. Cornwelf.' Senior Engineer

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Application Engineering Services Reviewed by: .

/ C. Lee, tenior EnB i "**Y-Licensing and Consulting Services

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Approved by: M C(L.Sozzi/Managr*

Application Engineerin5 Services l' -

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' CNSS87'61,03 l e Enclosure 7 ,,

Page 1 of 3 -

September 23, 1987 SPECIAL ORDER 87-04 REV. 1 i MCPR LIMIT WITH TWO BYPASS VALVE OPERATION i

Due to operation with only two bypass valves in service, procedural MCPR limits are replaced with an operational limit, at full flow, of greater ,

than or equal to 1.26. Please reference the attached General Electric i

provided, "CNS Turbine Bypass Valve ~Out Of Service Evaluation Summary",

for the particular details associated with this MCPR limit revision. )

This new limit will be input into the process computer and will, thus, result in no change to MFLCPR limit as enforced by Surveillance Procedure 6.2.4.1 (in accordance with Technical Specifications).

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/ GENERAL $. ELECTRIC C COOPER NUCLEAR STATION

'IURBINE BYPASS VALVE OUT OF-SERVICE EVALUATION SUM.%RY DRF B21-00378 September 23, 1967 Cooper Nuclear Station (CNS) recently discovered a hydraulic fluid leak associated with one of the three turbine . bypass valves. It was subsequently determined that the leak could be isolated by closure of the high pressure hydraulic fluid isolation valve. It is desirable to continue operating CNS, with one-turbine bypass valve disabled, until a time when the repairs can more conveniently be made. Therefore, General Electric performed an evaluation to determine the potential increase in the CPR with. one bypass valve inoperable.

Currently, the limiting cycle 11 fuel thermal limits (Option B) are dictated by the feedwater controller failure - maximum demand (WCF) event. The calculated minimum critical power ratio (MCPR) for this event at end-of-cycle (EOC) is 1.23 and the corresponding technical specification limit is 1.25 (i.e., a margin of 0.02 exists to the technical specification limit to allow for 10CFR50.59 evaluations of the .!

C cycle specific limits). The FWCF transient is analyzed assuming all l three bypass valves'are operable. Disabling one of the bypass valves l 1

may increase the calculated CPR for the WCF event.

4 In order to ensure Nebraska Public Power District (NPPD) _ could continue to operate CNS efficiently with one bypass valve disabled, bounding, conservative core nuclear parameters were utilized to evaluate the operation of CNS thrcush the end. of fuel cycle .11. The plant initial conditions were assumed, consistent with the cycle 11 reload licensing evaluation, to correspond to 105% of rated steam flow. The calculated fuel thermal response for the WCF event with one bypass 4 valve inoperable resulted in a calculated MCPR of 1.26 (Option B' -

currently in force for cycle 11). This represents an increase of 0.01. i in MCPR (Option B) over the current EOC Technical Specification Limit.

Although not used for the current cycle, the limiting transient for the Option A MCPR limits, as determined by the cycle 11 reload licensing  ;

evaluation, is the load rejection without bypass (LRNBP) ovent. This transient, with an Option A MCPR of 1.33, is unaffected by disablin5 one bypass valve, since the bypass function is assumed to fail. The

- . calculated Option A MCPR limit for the WCF event with one bypass valve inoperable was determined to be 1.33. This is equivalent to the limiting Option A MCPR obtained in the reload licensing evaluation for the LRNBP event. Therefore, the Option A MCPR for cycle 11 is unaffected by disabling one bypass valve.

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Page:3 of 3 COOPER IWCLEAR STATION TURBINE BYPASS VALVE OUT-OF-SERVICE EVALUATION

SUMMARY

(Pa50 2)

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In summary, linittin5 the operating CFRs above 1.26 for Option B and 1.33 for option A vill ensure- that the safety' limit MCPR of 1.07 will; not be violated while operating with one bypass valve out-of service considerin5 any of the abnormal transient events previously analyzed for .

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Prepared by: , hff

' K.F. Cornwell",' Senior Engineer- -

Application Engineering Services l

Reviewed by:

A C. Lee, Senior Engineer i

l Licensing and Consulting Services I

' I Approved by: ~

C(L. Sozzi,' Mana@r' Application Engineerin5 Services

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