ML20070G662

Interim Deficiency Rept CP-90-08 Re Vol Control Tank Isolation Valve Leakage.Initially Reported on 910104.Mods Evaluated to Correct Deficiency.Supplemental Rept to Be Submitted Prior to Fuel Load

ML20070G662
Person / Time
Site:	Comanche Peak
Issue date:	03/06/1991
From:	William Cahill, Walker R TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CP-90-08, CP-90-8, TXX-91104, NUDOCS 9103120278
Download: ML20070G662 (2)

Text

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= Log # TXX-91104 File # 906.3 .

.'"" 910.4 I Il C C 10110.

Raf, # 10CFR50.55(e);

7UELECTRIC p

NNCTdn , _Harch 6, 1991 j

'U. S. Nuclear Regulatory-Commission Attn: Document Control Desk

' Washington, D.C. 20555

SUBJECT:

- COMANCHE PEAK STEAM ELECTRIC STATION (CPSES), UNIT 2 DOCKET NO.,50-446=

VOLUME CONTROL TANK IS0LATION VALVE LEAKAGE SDAR: CP-90 08 (INTERIM REPORT)

Gentlemen:.

On December 5, 1990, TU Electric orally _ notified the NRC of a deficiency in-which' solenoid-operated isolation ~ valves' leaked excessively in the back-flow direction and would-not isolate the gas-space of the volume control. tank (VCT)

.from the centrifugal charging pump (CCP) suction, during the injection phase of a Less-of Coolant Accident (LOCA). This deficiency was initially discovered by TV. Electric on Unit 1.during evaluation of NRC Information Notice 90 64 and -was reported to the NRC for Unit 1 in Licensee Event Report L '(LER) 90 .035.via-letter logged TXX-90365, dated November 13, 1990. The last l 'r.eport for_ Unit 2 was logged TXX-91003, dated January 4, 1991. After further l evaluation TV' Electric has concluded that this deficiency is' reportable pursuant to-10CFR50.55(e) and the required information follows.

' Des cri pti on -

l A continuour, vent line with. solenoid-operated valves is- provided from the -

suction piping of the-CCP's to the VCT to prevent gas binding of the pumps during: normal Chemical and Volun,e Control System -letdown operations. -The solenoid-operated-valves are closed to prevent a back-flow from the VCT-to the CCP pump suction during theLi_njection phase of a LOCA. A field walkdown in Unit 2 has_ confirmed that in the installed configuration, VCT pressure could unseat-these valves-such that the valves may not' prevent gas backflow.

Safety Imolications During -the injection phase:of a LOCA if the CCPs were taking relatively cold water from the refueling water storage tank and the VCT pressure was at the-high end of the design band.(75 psig), a volume of VCT gas sufficient to : bind one or both pumps could leak past the isolation valves and enter the~ CCP suctions. This could render both pumps inoperable for mitigating'the consequences of the LOCA. Therefore, this deficiency represents a significant deficiency in final design as approved and released for construction such that the design does not conform to the criteria and bases stated in the safety analysis report.

9103120278 910306 }gO I PDR ADOCK 05000446 400 North Olive Street LB. 81 Dallas. Texas 7520! I

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TXX-91104 Page 2 of 2 The root cause-of this deficiency was that the original application and technical review of. the design inputs for the solenoid operated valves was less than adequate. ' Review of all the design conditions applicable to the valves either did not consider all flow conditions or did not consider that these solenold-operated valves were not designed to isolate flow in both directions under anticipated differential pressure conditions.

Corrective Action Various modifications are being evaluated to correct the isolation valve deficiency. A supplemental report will be submitted prior to fuel load i describing the final modification selected.

A review of other'similar solenoid-operated isolation valve-installaticas i showed that the design applications were correct. A review of other venting

. arrangements showed that there were no other such arrangements which could result in similar gas binding. Therefore, this deficiency is determined an isolated event.

Subsequent-to the design oversight (1980), the Westinghouse design concept was included in the Chemical and Volume Control System Design Basis Document to ensure that the criteria are well understood.

A memorandum-describing this deficiency was distributed to Unit I and Unit 2 design engineers. The memorandum discusses the subject solenoid valves, their application, and their design, and reminds design engineers to consider all design 1nformation e,pplicable to the work they are performing as currently required by procedure.

Sincerely.

Y f- '

William J. Cahill, Jr.

By M

• Roger"D. Walker Manager of Nuclear Licensing

, 'JLR/gj h

b c - Mr. R. D. Martin, Region IV E

Resident Inspectors, CPSES (3)

Mr.-M. Fields, NRR

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