05000315/LER-1999-018, :on 990629,determined That Valve Yokes May Yield Under Combined Stress of Seismic Event & Static,Valve Closed,Stem Thrust.Caused by Inadequate Design of Associated Movs.Operability Determinations Were Performed for Valves

:on 990629,determined That Valve Yokes May Yield Under Combined Stress of Seismic Event & Static,Valve Closed,Stem Thrust.Caused by Inadequate Design of Associated Movs.Operability Determinations Were Performed for Valves

ML17326A074
Person / Time
Site:	Cook
Issue date:	07/29/1999
From:	Berry L INDIANA MICHIGAN POWER CO.
To:
Shared Package
ML17326A073	List: 05000315/LER-1999-018, :on 990629,determined That Valve Yokes May Yield Under Combined Stress of Seismic Event & Static,Valve Closed,Stem Thrust.Caused by Inadequate Design of Associated Movs.Operability Determinations Were Performed for Valves
References
LER-99-018, NUDOCS 9908060217
Download: ML17326A074 (8)

LER-1999-018, on 990629,determined That Valve Yokes May Yield Under Combined Stress of Seismic Event & Static,Valve Closed,Stem Thrust.Caused by Inadequate Design of Associated Movs.Operability Determinations Were Performed for Valves

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(x)
3151999018R00 - NRC Website

text

NRC FORM 366 U.S. NUCLEAR REGULA COMMISSION (6-1998)

LICENSEE EVENT REPORT (LER)

(See reverse for required number of digits/characters for each block)

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If an information cogection does not display a currently valrd OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the Information collection.

FACIUTYNAME (1)

Cook Nuclear Plant Unit 1 DOCKET NUMBER I2) 05000-315 PAGE (3) 1 OF 4

TITLE(4)

Refueling Water Storage Tank Suction Motor Operated Valves Inoperable Due to Inadequate Design EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED(8)

MONTH DAY YEAR YEAR 1999 SEQUENTIAL NUMBER REVISION NUMBER MONTH DAY YEAR FACILITYNAME Cook Nuclear Plant Unit 2 FACIUIYNAME DOCKET NUMBER 05000-316 DOCKET NUMBER OPERATING MODE (9)

POWER LEVEL (10)

THIS REPORT IS SUBMITTE 20.2201 (b) 20.2203(a) (1) 20.2203(a)(2)(i) 20.2203(a)(2)(ii) 20.2203(a) (2)(iii) 20.2203(a)(2)(iv)

D PURSUANT TO THE REQU 20.2203(a)(2)(v) 20.2203(a)(3)(I) 2O.2203(a) (3)(ii) 20.2203(a)(4) 50.36(c) (1) 50.36(c) (2)

IREMENTS OF 10 CFR g: (Check 50.73(a)(2)(i) 50.73(a) (2)(ii) 50.73(a) (2)(iii) 50.73(a) (2)(iv) 50.73(a)(2)(v) 50.73(a)(2)(vii) one or more)

(11) 50.73(a)(2)(viii) 50.73(a)(2)(x) 73.71 or tn NRC Form 366A OTHER Specify In Abstract below LICENSEE CONTACT FOR THIS LER Lyle R. Berry, Regulatory Compliance Engineer (12)

TELEPHONE NUMBER(Indude Area Code)

(616) 465-5901 X1623 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DES CRIBED IN THIS REPORT (13)

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE TO EPIX

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE TO EPIX

'r)9080602 PDR ADO17'90729, CK 050003i5 PDR I '(I SUPPLEMENTAL REPORT EXPECTED 14 X

YEs (If yos, complete EXPECTED SUBMISSION DATE).

NO EXPECTED MONTH 12 DAY 31 1999 ABSTRACT (Limitto 1400 spaces, i.e., approximatoiy 15 single-spaced typewritten lines) (16)

On June 29,1999, during a review of a stress calculation for the Refueling Water Storage Tank (RWST) motor-operated (MOV) suction valves to the centrifugal charging pumps (CCPs), it was determined that the valve yokes may yield under the combined stress of a seismic event and the static, valve closed, stem thrust.

Based upon discussions with Engineering personnel, Operations declared the MOVs inoperable at 1540 hours0.0178 days <br />0.428 hours <br />0.00255 weeks <br />5.8597e-4 months <br />, June 29,1999.

Since these MOVs were considered to be incapable of opening during a postulated seismic

event, this condition is reportable pursuant to the requirements of 10CFR50.73(a)(2)(ii) as an event that resulted in the nuclear power plant being in a condition that was outside the design basis of the plant.

Technical Specifications (TS) require one boron injection path from the RWST to the Reactor Coolant System (RCS) to be operable in Modes 5-6 and two boron injection flow paths in Modes 1-4.

Since these valves were determined to be inoperable in those

modes, this condition is also reportable pursuant to the requirements of 10CFR50.73(a)(2)(i) as an operation or condition prohibited by TS. The apparent cause for this event was inadequate design of the MOVs. This event is applicable to both Units.

Compensatory action for the RWST to CCP MOVs for both Units has been taken via a temporary modification to restore operability in anticipation of changing from Mode 5 to Mode 6 to allow removal of fuel from the vessel.

Evaluation of the extent of this condition has identified that a change in the method of calculating torque/thrust available from the actuator, initiated by Limitorque Technical Update 98-01, may also impact the operability of the RWST to CCP suction MOVs and other Limitorque MOVs. Operability determinations were performed for those valves required for core offload and reload to establish operability in Modes 5 and 6.

Necessary corrective actions or analyses to establish operability for safety-related Limitorque MOVs in Modes 1-4'will be performed prior to entering Mode 4.

Based upon the proceduralized capability to establish an ECCS boration flowpath, should the RWST to CCP suction MOVs fail to open on demand, this event had minimal impact on the health and safety of the public.

R ORM 366 (6-1996)

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I IjU.S. NUCLEAR R TORY COMMISSION I6-1999)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACIUTYNAME (1)

I DocKET I2)

LER NUMBER I6)

PAGE I3)

Cook Nuclear Plant Unit 1 05000-315 YEAR 1999 SEQUENTIAL NUMBER 018 REVISION NUMBER 00 2

OF 4

TEXT /Ifmore spaceis required, use additional copies ofNRC Form 366A/ (17)

Conditions Prior To Event

Unit 1 was in Mode 5, Cold Shutdown Unit 2 was in Mode 5, Cold Shutdown Descri tion Of The Event On June 29,1999, during a review of a stress calculation for the Refueling Water Storage Tank (RWST) motor-operated (MOV)suction isolation valves (BQ/ISV) to the centrifugal charging pumps (CCPs), it was determined that the valve yokes may yield under the combined stress of a seismic event and the static, valve closed, stem thrust.

A preliminary MOV weak-link calculation for 2-IMO-910 and 2-IMO-911 was performed by Altran Corporation to include stem thrust as an additional load on the valve yoke, since this had not been addressed in previous calculations.

These calculations indicate the valves cannot be considered operable ifthe MOVs are closed with seating thrusts exceeding designated closing thrust values.

The Altran analyses indicate the electrically closed valves may not successfully maintain valve yoke structural integrity during a seismic event.

Based upon discussions with Engineering personnel, the Operations Shift Manager declared the MOVs inoperable at 1540 hours0.0178 days <br />0.428 hours <br />0.00255 weeks <br />5.8597e-4 months <br />. This event is applicable to both Units.

Evaluation of the extent of this condition has identified that a change in the method of calculating torque/thrust available from the actuator to open or close Limotorque MOVs, initiated by Limitorque Technical Update 98-01, may also impact the operability of the RWST to CCP suction MOVs and other Limitorque MOVs.

Cause Of The Event

The apparent cause of this event was inadequate design of the associated MOVs. A contributing causal factor was the failure of the MOV Program to adequately address industry information for applicability at D.C. Cook. The significance of MOV actuator toads on the seismic capability of MOVs 1/2-IMO-910, and 1/2-IMO-911 in the closed position was not identified and resolved in a timely manner.

Anal sis ofthe Event Since the RWST to CCP suction MOVs were considered to be incapable of opening during a postulated seismic event, this was determined to be reportable pursuant to the requirements of 10CFR50.73(a)(2)(ii) as an event that resulted in the nuclear power plant being in a condition that was outside the design basis of the plant.

Technical Specifications (TS) require one boron injection path from the RWST to the Reactor Coolant System (RCS) to be operable in Modes 5-6 and two boron injection flow paths in Modes 1-4.

Since these valves were determined to be inoperable in those modes, this condition is also reportable pursuant to the requirements of 10CFR50.73(a)(2)(i) as an operation or condition prohibited by TS.

The RWST to CCP suction isolation valves are normally closed 8-inch valves arranged in a parallel configuration in the supply piping from the RWST to the charging pump suction header.

The safety function of these valves is to open on a Volume Control Tank (VCT) LOW-LOWlevel signal or on a safety injection signal to provide an ECCS boration flowpath to the RCS. These valves can be remotely opened and closed during normal and emergency conditions.

From a structural standpoint, the capability of the RWST to CCP suction MOV yokes to withstand simultaneous seismic loading combined with the actuator induced thrust and torque operating loads cannot be shown to meet operability criteria.

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'bU.S. NUCLEAR REGULATORY COMMISSION (6-1999)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION LER NUMBER (6)

PAGE (3) 3 OF 4

DOCKET (2) 05000-315 FACIUTYNAME (1)

Cook Nuclear Plant Unit 1 SEQUENTIAL NUMBER REVISION NUMBER YEAR 1999 018 00 TEXT iifmore spaceis required, use additionai copies of IVRCForm 366A/ (17)

This combination of actuator operating loads with seismic loads would occur if a postulated design basis seismic event were to occur with the MOV in a closed position. With the MOV in the open position (but not power back-seated),

actuator operating loads are such that the valve yoke structure has the capability to withstand the seismic loading alone.

Therefore, if the valve were open during a seismic event, the ability of the valve to close during or after the event would not be compromised.

With the MOV in the closed position (normal operating condition), actuator loads combined with the postulated seismic loads may have prevented opening of the valve in response to a Sl signal resulting in failure to align the CCP to the RWST.

During power operation, CCP suction is supplied from the VCT through the normally open MOVs 1/2-QMO-451 and 1/2-QMO-452.

MOVs 1/2-QMO-451 and 1/2-QMO-452 automatically close once RWST to CCP suction MOVs (1/2-IMO-910, and 1/2-IMO-911) complete opening.

The volume in the VCT is not sufficient to satisfy Sl requirements, nor does it contain sufficient borated water, which is required to control reactivity changes in the Reactor Coolant System (RCS).

If the RWST to CCP suction MOVs for each Unit both failed to open upon receipt of a safety-injection (Sl) signal, the normal design flow path for borated water from the RWST to the RCS would not be available.

In the event of a small break loss of coolant accident (SBLOCA) without Sl, CCP suction from the VCT will be the source of borated makeup.

The Emergency Operating Procedures (EOPs) require the operator to verify at least one CCP is running and control charging flowfrom the VCT as necessary to maintain pressurizer level.

For a SBLOCA with Sl, or a large break LOCA (LBLOCA),the EOPs require verification that Sl is actuated and that the RWST to CCP suction MOVs open.

Plant operator(s) would be dispatched to attempt to manually open the valves ifthey did not open.

The Safety Injection pumps also provide borated water from the RWST to the RCS.

If the flowpath from RWST via the charging pumps cannot be manually'established, Sl pump flow is verified (or established, ifthe pumps are not running and/or appropriate valves are not aligned) once the requisite lower RCS pressure of 1630 psig is achieved.

Therefore, regardless of the size of the break, a boration flowpath can be established.

Based upon the proceduralized capability to establish an ECCS boration fiowpath, this event had minimal impact on the health and safety of the public.

CORRECTIVE ACTIONS

Operability determinations were performed for those valves required for core offload and reload to establish operability in Modes 5 and 6.

Necessary corrective actions or analyses to establish operability for safety-related Limitorque MOVs in Modes 1-4 willbe performed prior to entering Mode 4.

This condition was discovered as a part of the programmatic review of safety related MOVs for design, testing, and potential operability concerns in support of the closure of outstanding Generic Letter 89-10 Program issues.

This review of the MOV Program is scheduled for completion by December 1, 1999.

Resolution of identified deficiencies will be addressed and tracked to completion via the Corrective Action Program.

Significant changes to the cause of event, extent of condition, safety significance or corrective actions, identified during the review, will be addressed in a supplement to this LER.Upon discovery of the identified condition, the RWST to CCP suction MOVs were declared inoperable.

A temporary modification was completed to lower the torque/thrust settings for the RWST to CCP suction MOVs on Unit 2 and Unit 1, in anticipation of changing from Mode 5 to Mode 6 to allow removal of fuel from the vessel.

These temporary modifications were completed and the boration flowpath from the RWST to RCS declared operable on July 8, 1999 and July 11, 1999, for Unit 2 and Unit 1, respectively.

A permanent modification will be made to the RWST to CCP suction MOVs for both Units to replace the valve yokes with different yokes capable of withstanding the combined loads associated with actuator closure and a seismic event prior to Mode 4.

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I JU.S. NUCLEAR REGULATORY COMMISSION (6.1999)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACIUTYNAME(1)

Cook Nuclear Plant Unit 1 DOCKET (2) 05000-315

'EAR LER NUMBER (6)

SEQUENTIAL REVISION NUMBER NUMBER PAGE (3) 4 OF 4

1999 018 00 TEXT (Ifmore space is required, use additional copies ofIVRCForm 366AJ (17)

As part of the Cook Nuclear Plant Restart Plan, a Programmatic Readiness Review will be performed to assess the MOV Program and address improvements necessary to support the restart effort and establish a basis for continued improvement in CNP performance beyond plant restart.

SIMILAREVENTS 315/96-006-00 315/98-059-00 0

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