ML20028H441

LER 90-001-01:on 900209,Part 21 Rept Received from Gilbert Commonwealth Re Possible Loss of One Train of Chilled Water Sys in Event of High Energy Line Break.Conceptual Design Developed to Reduce Heat Load on coils.W/901231 Ltr

ML20028H441
Person / Time
Site:	Summer
Issue date:	12/27/1990
From:	Higgins W, Skolds J SOUTH CAROLINA ELECTRIC & GAS CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-90 LER-90-001, LER-90-1, NUDOCS 9101070173
Download: ML20028H441 (4)

Text

10CFR50.73

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DEC 311990 Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555 Gentlemen:

Subject:

VIRGIL C. SUMMER NUCLEAR STATION DOCKET NO. 50/395 OPERATING LICENSE NO. NPF-12 LER 90-001, REVISION 1 (ONO 900001)

Attached is Revision 1 to Licensee Event Report No.90-001 for the Virgil C.

Summer Nuclear Station. This report was submitted pursuant to the requirements of 10CFR50.73(a)(2)(v).

Should there be any questions, please call US at your convenience.

Very truly yours, John L. Skolds DCH:JLS: led Attachment c: 0. W. Dixon, Jr. L. J. Montondo E. C. Roberts NRC Resident Inspector R. J. White J. B. Knotts, Jr.

S. D. Ebneter INPO Records Center G. F. Wunder ANI Library General Managers Marsh & McLennan C. A. Price NPCF G. J. Taylor NSRC F. H. Zander RTS (ONO 900010)

1. L. Matlosz File (818.05 & 818.07)

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NUCLEAR EXCELLENCE - A SUMMER TRADITION!

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On Februhry 9, 1990, et approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> Gilbert / Commonwealth, Incorporated (G/C), the Architectural Engineer (AE) for the Virgil C. Summer Nuclear Station, informed the plant of the G/C requirement to report a design deficiency per 10CFR21.

The AE evaluation of the present design had reached the point where it was clear that, in the event of a High Energy Line Break (HELB) in the Intermediate Building (where the chiller units are located), one train of chilled water would be lost and the status of the other train was indeterminate. Since then, the AE has further completed the evaluation and has confirmed that, in the event of an HELB in the Intermediate Building, both chilled water trains would be rendered inoperable. This represents a failure of a safety function as described in 10CFR50.72(b)(2)(iii) and was reported as such by South Carolina Electric & Gas Company (SCE&G).

The 10CFR21 report by G/C indicated the effects of an HELB on the cooling coils that would be exposed to the steam environment were not adequately addressed. Two actions were taken in order to protect the system from the recognized deficiency. The first action provided new guidance on balancing the chiller units such that each chiller is capable of supporting its respective loads during any accident, with the exception of an HELB in the Intermediate Building. The second action isolated the cooling coils, which if exposed to-the steam environment created by an HELB in the Intermediate Building, would have placed excessive heat loads on the chillers.

A conceptual design has been developed which will remove the challenge to the chilled water system by substantially reducing the heat load imparted to selected cooling coils during an HELB in the Intermediate Building. The design and modification implementation will be completed by the end of 1991, i

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NC f erm 3864 ' U $ NUCLE AR R$0VL ATORY COMMi$$lON LICENSEE EVENT REPORT (LER) TEXT CONTINUATION ueaoviooMswo3 m m s o,aes 3on e ACILtiv NAME 11e Duchti NUMet m at Llh WUM8t# 16 PACI (3) taa "tnit' iS*7 Virgil C. Summer Nuclear Station o p lo j o j o l 3l 915 9l0 -

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011 0l2 oF 013 TlKT W ekw, apen e teep.4, one ed@twd kMC Form bl64 's'(116 PLANT IDENTIFICATION:

Westinghouse - Pressurized Water Reactor EQUIPMENT IDENTIFICATION:

Chilled Water System Ells - KM IDENTIFICATION OF EVENT:

A design deficiency reported per 10CFR21 indicated that a single event could preventthefulfillmentofasafetyfunctionasdescribedin10CFR50.73(a)(2)(v).

EVENT DATE:

February 9. 1990, at 1415 EST REPORT DATE:

December 27, 1990 CONDITIONS PRIOR TO EVENT:

Mode 1, 100% power DESCRIPTION OF EVENT:

On February 9, 1990, at approximately.1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> Gilbert / Commonwealth.

Incorporated (G/C), the Architectural Engineer (AE)-for the Virgil C. Summer Nuclear Station, informed the plant of the G/C requirement to report a design deficiency per 10CFR21. The deficiency was identified as a result of an evaluation to resolve a concern expressed by Non-Conformance (NCN) 3645 which was generated by' on-site personnel

.The AE evaluation of the present design had reached the point where it was clear that, in the event of an HELB in the Intermediate Building (where the chiller units are located), one train of chilled water would be lost and the status-of the other '

train was still indeterminate. It is important to note that upon failure of the chilledwatertrain,theComponentCoolingWater(CCW)FumpsandCharging/ Safety Injection (SI) Pumps on the affected train would be rr.ndered inoperable. Since 10CFR21 requires assumption of a single failure, thi:i condition met the criteria for reportability. 10CFR50.72(b)(2)(iii) does not require the assumption of a single failure. but since the status of the other train of chilled water was questionable, SCE&G made the decision to report the results to the NRC per 10CFR50.72(b)(2)(iii). This report was made at 1415 hours0.0164 days <br />0.393 hours <br />0.00234 weeks <br />5.384075e-4 months <br />.

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010l1 l- 0 l1 0l 3 or 0l3 nn a ~, ua. . w . .-- ec w w v e The AE has further completed the evaluation and has confirmed that, in the event of an HELB in the Intermediate Building, both chilled water trains would be ret.dered inoperable.

CAUSE OF EVENT:

The 10CFR21 report by G/C indicated that the previous evaluation of an HELB on the chilled water system addressed the effects of an HELB with respect to the chiller unit itself. However, the effects of an HELB with respect to the heat 1080 on the cooling coils that would be exposed to the steam environment were not adequately addressed.

ANALYSIS OF EVENT:

Since this is an analysis of the condition resulting from an HELB in the Intermediate Building and not the result of an actual event, there has never been  !

an actual challenge of the systems or a compromise of safety to the plant.

IMMEDIATE CORRECTIVE ACTION:

Due to NCN-3645 questioning the adequacy of the design, an interim solution was implemented on January 26, 1990, to alleviate the concern pending an answer of the NCN. This solution performed two actions. The first action provided new guidance on balancing the chiller units such that each chiller is capable of supporting its respective loads during any accident, with the exception of an HELB in'the Intermediate Building. The second action isolated the cooling coils which would be exposed to the steam environment created by an HELB in the Intermediate Building.

Those coils service the Emergency feedwater Pump and the Service Water Booster Pump-areas. It is important to note that the isolation of these coils was verified not to be essential to the affected areas during an accident.

These items were in place when SCE&G was notified of the design deficiency and will remain in place until permanent modifications can be implemented.

ADDITIONAL CORRECTIVE ACTION:

A conceptual design has been developed which will substantially reduce the heat load imparted to selected cooling coils and will remove the challenge to the chilled water system in the event of an HELB in the Intermediate Building. The design and modification impleu ntation will be completed by the end of 1991.

PRIOR OCCURRENCES:

None g, c.w m.

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