ML19332E482

LER 89-019-00:on 890927,identified That Closing Torque on Valves May Be Insufficient Against Postulated Worst Case Differential Pressure.Caused by Initial Plant Construction. Mod to Replace Gearing Made to Motor operator.W/891130 Ltr

ML19332E482
Person / Time
Site:	Arkansas Nuclear
Issue date:	11/30/1989
From:	Ewing E, Millar D ARKANSAS POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
2CAN118908, LER-89-019-02, LER-89-19-2, NUDOCS 8912070278
Download: ML19332E482 (5)

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1 e. RMe 3, Box 137 G ihr;wk,4e AR 728N Tel b31 M,4 3100 November 30, 1989-2CAN118998 U.- S. Nuclear Regulatory Commission Document Control Desk Mail' Station P1-137 Washington, D. C. 20555

SUBJECT:

Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6 Licensee Event Report No. 50-368/89-019-00 Gentlemen:

In accordance with 10CFR50.73(a)(2)(1)(B), attached is the subject report concerning the Auxiliary Cooling Water system motor operated isolation valves not being assured of closing against the postulated worst case differential pressure due to an inadequate design of the valve actuators.

Very truly yours,

'E. C. wing General Manager,

' Technical Support and Assessment ECE/DM/sgw attachment cc: Regional Administrator Region IV U. S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, suite 1000 Arlington, TX 76011 INPO Records Center 1500 Circle 75 Parkway Atlanta, GA 30339-3064 a PinJ

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NRC Form 366 U.S. Nuclear Regu*atory Commission  !

.(9 03) Approved OM8 No. 3150-0104 Empires: 8/31/85 L!CENSEE EVENT REPORT (L E R) 1 FACILITY NAME (1) Arkansas Nuclear Onc, Unit Two IDOCKET NUleER (2) IPAGE (3) 10151010101 31 61 Sl110F1014 i TITLE (4) Auxiliary Cooling Water System Motor Operated Isolation valves Were Not Assured of Closing Against '

the Postulated Worst Case Differential Pressure Due to an Inadequate Design of the Valve Actuators i

f EVEN" DATE (5) .ER NLABER (6) REPORT DATl' (7) OTHER FACILITIES INVOLVED (8) i I l l l ioquentiell IRevision. 1 i l Month Day lYear lYear i Number l l Number IMonthi Day lYear i Facility Names I Docken Nmber(s)

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1. 1 i i l i 1 015 0 )l ) 1 01 9 21 71 8 91 81 91**l 01 11 9f**l 01 Of111131018191 015 0 i)l ) I >

OPERA"ING l 1 THIS REPORT 15 $UBMITTED PUR5UANT TO THE REQUIREMENTS OF 10 CFR 5

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L IWDE (9) 15 (Check one or more of the followinn) (11)

POWERI l_ 20.402(b) _l 20.405(c) l l 50.73(a)(2)(iv) I i 73.71(b)

LEVELI l_ 1 20.405(a)(1)(1) I 50.36(c)(1) l_l_ 50.73(a)(2)(v) l[I73.71(c)

(10) 1010101 l 20.405(a)(1)(11) l_ll

_ 50.36(c)(2) l _l 50.73(a)(2)(vii) l_ 1 Other (Specify in l_l 20.405(a)(1)(111) 1J 1 50.73(a)(2)(1) l _l 50.73(a)(2)(viii)(A)l Abstract below and g l_l 20.405(a)(1)(tv)  :

l_l 50.73(a)(2)(11) l_ l 50.73(a)(2)(v111)(8)l in Text, NRC Form i I 20.405(a)(1)(v) I i 50.73(a)(2)(iii) l I 50.73Ja)(2)(*) i 366A)  ;

., JICENSEE CONTACT FOR TH15 LER (12)  !

Name l Teleohone Number -

l Area 1 Dana Miller Nuclear Safety and Licensing Specialist icode l 510111916141-13111010 COMPLITE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (L3) l l l . lReportabiel i l i l (Reportabiel i Causelsysteal Component IManufacturert to NPR05 l ICauselsysteel Component IManufacturert to NPR05 I r 1 1 -l -

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- 1 i l i i i i i i I i 1 1 I I i 1 1 I I I I I i l 1 1 I I I I I SUPPLEMEN" REPORT EXPECTED (14) l EXPECTED (_Monthi Day lYear

. I SUBMISSION I i l l.I Yes (If yes. coselete Expected Submission Date) Ikl No i DATE (15) l I I I I I ABSTRACT (Limit to 1400 spaces, i.e. , approximately fif teen single-space typewritten lines) (16) t, While perfoming a MOVATS engineering review of the design of the t10 redundant motor operated valves (MOV) which isolate Auxiliary Cooling Water (ACW), a non-safety related systes supplied by the Service Water System (SWS), it was identified that the closing torque exerted by the motor operator on the valves may be insufficient to ensure the valves close against the postulated worst case differential pressure. The postulated worst case differential pressure is expected to occur if a shear in the ACW piping were to occur downstream of the valves and the SW5 pumps remain operating. The function ,

of the ACW isolation valves to close in the event of a DBA was evaluated and it was detemined the '

valves would close against the differential pressure expected to occur during a DBA. If a seismic event were to occur and the ACW piping shear, the valves could not be assured of closing, however, the '

redundant loop of SW5 should be available. During initial plant construction, the impact of lower than normal motor operating voltages on the capability of the valve actuator gearing to produce the torque ,

required to close the valve under all postulated conditions was not considered. A modification to

, nplace the gearing was made to the motor operator on each isolation valve. This event is being L: rcported pursuant with.1DCFR50.73(a)(2)(1)(B).

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Form 1062.01B

- NRC Fem 24 U.S. Nuclear Regulatory Commission

'(9-43)' Approved DMB No. 31b0-0104 Expires: 8/31/85

,, LICEN$(( EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1) l DOCKET NUPSER (2) i LfR NUMB (R (6) l PAGE (3)

. l l l 15equentiall IRevisioni Arkansas Nuclear One, Unit Two l l Yearl l Number l l Number l 1015l010101 31 61 81 81 91--I 01 11 91--t 01 0101210Fl014 TEXT (If more space is required, use additional NRC Form 366A's) (17)

A. Plant Status i

At the time of discovery of this condition, Arkansas Nuclear One, Unit Two (AND-2) was in Cold Shutdown (Mode 5) with Reactor Coolant System (RC$) [AB) temperature approximately 121 degrees Fahrenheit and RCS pressure at atmospheric. The seventh refueling outage commenced on September 25, 1989.

B. ' Event Description The Service Water System (SW$) [BI) consists of two redundant independent Seismic Category I loops which furnish water. to Engineered Safety Features (ESF) equipment. The system also supplies the non-safety related Seismic Category II Auxiliary Cooling Water (ACW) [KG) system which supplies water to non-safety related portions of the plant (e.g., turbine generator lube oil coolers, generator stator cooling water system, etc.). The seismic flow paths are normally isolated from each other

- and are isolated from the Seismic Category II ACW system by automatic closure of two redundant motor operated isolation valves upon the initistion of a $4fety Injection Actuation $1gnal ($1AS) or Main Steam Isolation $1gnal (MSIS). The ACW can be supplied with water from either SWS loop during normal operation. See Figure 1.

On September 27, 1989, while performing a MOVAT$ engineering review of the design of the two redundant motor operated valves which isolate ACW from the SWS loop supplying the system, it was identified that the torque required to close the valves under the worst case differential pressure (AP) condition might be greater than the design capability of the valve motor and actuator gearing.

At this time the valves were considered operable pending additional vendor information On October 13, 1989, with additional vendor information, conservative Engineering calculat,ons confirmed this condition and the valves were considered to be inoperable.

C. Safety Significance The potential safety concern of this event relates to the capability to maintain at least one loop of service water available following the occurrence of a postulated design basis event. The ACW system isolation valves are designed to automatically close upon receipt of an SIAS or MSIS which would be generated in the event of en accident such as a LOCA or main steam line break event. This design provision ensures that the non-seismically designed ACW loop is isolated from the seismically designed SW5 loop such that postulated ACW system component failures (active or passive) will not affect the functional capability of the $W5 loop. Under postulated accident conditions a concurrent f ailure of- the ACW piping or an ACW component which could produce a significantly large differential pressure across the ACW isolation valves is not expected to occur. The valves should have been able to function properly and close to isolate the ACW system under these conditions. Therefore, even considering a failure of the redundant SWS loop adequate SW flow should be maintained to one train of ESF equipment during accident conditions.

For occurrences of seismic events the potential safety concern relates to the capability to shut l the plant down and maintain safe shutdown conditions. At least one loop of SW is necessary for safe shutdown equipment. Since the ACW system is not seismically designed, this piping could fail as the result of a seismic event. Under these conditions, maximum differential pressure across the ACW isolation valves could have prevented the valves from closing and rendered the SWS loop aligned to the ACW system inoperable due to flow diversion through the ruptured ACW system.

However, should this occur the redundant SW5 loop should have been available to supply adequate safe shutdown equipment.

D.' Root Cause The criterla that existed during initial plant construction for establishing the design and functional requirements for safety related motor operated valves did not require the impact of lower than nomal motor operating voltages on the capability of the valve actuator gearing to produce the torque required to close the valve under all postulated conditions. As a result of the NRC Bulletin 85-03 and Generic Letter 89-10, reviews of safety related motor operated valves uti11 ring the current guidelines, the subject condition was identified.

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F?rm 1062.019 NRC Fem $HA U.S. Nuclear Regulatory Commission (9-83) Approved OMB No. 3150-0104 Expires: 8/31/86

, LIC[NSEE EVENT REPORT (tER) TEXT CONTINUATION FACILITY NAME (1) lDOCKE1 NUMBER (2) l tfR NUM8(R (6) l PAG [ (3) l l l 15equentia1l lRevisioni Arkansas Nuclear One, Unit Two 1 .

l_Yearl I Number I i Number l 10161010101 31 61 81 el 91--I 01 11 91--t 01 01013lorl014~

TEXT (If more spece is required, use additional NRC Fors $66A's) (17)

E. Basis for Reportability

i. Since it could not be assured the ACW system isolation valves would close under the postulated worst caso differential pressure, the $wS loop to which ACW was aligned was considered to be e inoperable while this condition existed. Therefore, this event is beint reported I pursuant with 10CFR60.73(a)(2)(1)(8), operation prohibited by Technical Specifications.

F. Corrective Actions After identifying that there was inadequate gearing capability in the motor operated ACW header isolation valves, a modification was made to the operator on each of these valves. The actuator gearing on the operators was replaced to ensure valve closure capability against maximum expected differential pressura.

Evaluations were perfomed of other safety related valves in the M0 VATS progree to determine if a similar discrepancy existed. No similar design deficiencies were identified. Therefore, this condition is considered to be an isolated case.

! As a result of the MOVATS program established by engineering in 1986 to evaluate the design and

functional requirements for safety related motor operated valves, design deficiencies related to motor operated valves installed in the plant will be identified and modified to ensure design requirements are satisfied.

C. Additional Information

• Frevious similar events involving motor operated valves not being designed to close under all postulated conditions were identified in LER 50*313/89-002 and 50 313/88 003.

Energy Industry Identification System (E115) codes are identified in the text as (XX).

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NRC Form 366A U.S. Nuclear Regulatory Commission i (9-43). Approved OM8 No. 3150-0104  :

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, LICEN$EE EVENT REPORT (LER) TEXT CONTINUATION ]

., ' FACILITY NAME (1) l DOCKET NWSER (2) l LER Nup6(st (6) l PAGE (3) l l l 15equentiell l Revision! j Arkansas Nuclear One. Unit Two l j. Year i Numbee l Number l <

10151010101 31 61 81 et 9 --I 01 11 91-- 01 0101410F1014 i

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