ML20012D012

LER 90-004-00:on 900217,lift Pressures for 6 of 10 Main Steam Safety Valves Found Outside Acceptance Criteria. Caused by Overly Restrictive Operability Criteria.Valves Recalibr & License Amend Submitted to NRC.W/900319 Ltr

ML20012D012
Person / Time
Site:	Fort Calhoun
Issue date:	03/19/1990
From:	Gates W, Voss K OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-004, LER-90-4, LIC-90-0230, LIC-90-230, NUDOCS 9003260293
Download: ML20012D012 (4)

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Omaha Public Power District 1623 Harney Omaha. Nebraska 68102 2247 402/536 4000 March 19,-1990 LIC-90-0230 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Station P1-137 Washington, DC 20555

Reference:

Docket No. 50-285 -

Gentlemen: '

Subject:

Licensee Event Report 90-04 for the Fort Calhoun Station Please find attached Licensee Event Report 90-04 dated March 19, 1990. l Thisreportisbeingsubmittedpursuantto10CFR50.73(a)(2)(ii)(B).

, 'If you should have any questions, please contact me.

l L

Sincerely, I

w. .J h W. G. Gates Division Manager Nuclear Operations

-WGG/ tem Attachment.

L c: R. D. Martin, NRC Regional Administrator q L A. Bournia, NRC Project Manager

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Omaha Public Power District had )reviously completed an analysis concluding that the design pressure for bot 1 the primary and secondary system would still be bounded for setpoint drift of up to five percent on the MSSV's regardless of the Primary Safety Valves' settings. The root cause of this event is therefore overly restrictive operability criteria.

The affected valves were recalibrated and successfully tested. An application for an Amendment to the Facility Operating License was submitted to NRC which will provide wider setpoint tolerances.

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010 012 or 0 l3 TEXT t# mwe ansee e n_ J. war asMeurut 44C Farm W 's/ (1h Overpressure protection at Fort Calhoun Station is ensured by means of Primary SafetyValves(PSV's),MainSteamSafetyValves(MSSV's),andtheReactor ProtectionSystem(RPS). These systems maintain reactor coolant system and secondary side steam generator pressures below 110 percent of their respective design values during a worst-case pressure transient. Technical Specification 2.1.6(3) requires eight of the ten MSSV's to be operable, during power operation, with their lift settings between 1000 psia and 1050 psia with a tolerance of plus or minus one percent of the nominal nameplate setpoint value. This requirement ensures that sufficient relief capacity exists to protect the steam generators from overpressurization resulting from either a loss of main feedwater or a complete loss-of-load without reactor trip.

On February 17, 1990, Fort Calhoun Station Unit No. I was in Mode 3, Hot Shutdown, and preparing to cool down for a scheduled refueling outage. While performing Surveillance Test IC-ST-MS-3002, Main Steam Safety Valves Verification of the Lift Point using Furmanite's Trevitest Equipment, the lift pressures for'six of the ten MSSV's were found outside their respective acceptance criteria.

ThesixvalvesthatfailedtomeetthetestcriteriaareMS-277andMS-291(on SteamGeneratorA)andMS-279,MS-280,MS-281andMS-282(onSteamGenerator B.) All of these valves are Dresser Industries Maxiflow model six inch 1500 psig class relief valves except for MS-291 which is a two and one-half inch 1500 psig class relief valve also manufactured by Dresser Industries.

The setpoints, actual lift pressures observed, and variation percentages for thesevalvesweremeasuredinpoundspersquareinchgauge(psig)valueswhich Liust be converted from the pounds per square inch absolute (psia) values in the Technical Specifications. The measured values were:

Valve Setooint Actual lift point Variation percentaae MS-277 1010 psig 1033 psig +2.3 MS-279 1035 psig 1056 psig +2.0 MS-280 1025 psig 1037 psig +1.2 MS-281 1010 psig 1023 psig +1.3 MS-282 1000 psig 1012 psig +1.2 MS-291 985 psig 1000 psig +1.5 As each valve was discovered out of tolerance, it was recalibrated and retested until it passed two consecutive tests.

The direct cause of this event is safety valve setpoint drift. This drift is not considered to be abnormal for these type valves. The root cause of the event is overly restrictive operability criteria for these valves.

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01 0 013 oF 0l3 Omaha Public Power District (0 PPD) has analyzed the loss of load and the loss '

of feedwater design basis events to support an application for an Amendment to the Facility Operating License (LIC-89-848, dated September 8, 1989) that would, in part, change the drift acceptance criteria for the MSSV's from plus or minus 1 percent to plus 3 percent /minus 2 percent. The results of the analysis show that as long as any of the MSSV actual setpoints do not drift greater than 5 percent above the intended setpoints, the primary and secondary systems will stay below 110 percent of their design pressures (110 percent equals 2750 psia and 1100 psia, respectively) as allowed by ASME Code,Section III, during a worst case pressure transient. This would be valid regardless of ,

the primary safety valve setpoint. Therefore, this event is bounded by this  ;

analysis and the margin of safety was not reduced below that required in the USAR.

The failure of the MSSV's to meet acceptance criteria was reported to NRC pursuant to 10 CFR 50.72(b)(2)(i) on February 17, 1990 with updated information reported on February 18, 1990. Even though six MSSV's were found to be outside the Technical Specification operability criteria, the plant was not in power operation at the time of determination and Technical Specification 2.1.6(3) did not apply. The safety function of the MSSV's was not significantly impaired.

However, it can be assumed that the MSSV setpoints were probably outside the Technical Specification requirements during power operation, so this event is reported as a condition outside the plant design basis.

The immediate corrective action for this event was to recalibrate and retest each valve at the time of discovery. The long term corrective action is approval of a Technical Specification Amendment to increase the allowable setpoint drift for the primary and secondary safety valve setpoints from plus or minus one 3ercent to plus three percent /minus two percent. As noted previously, t11s amendment has been submitted to the NRC.

This is the eighth reportable event in which the MSSV's failed to meet the operabilityrequirementofTechnicalSpecification2.1.6(3). The other seven were LER's88-023, 87-003,85-006, 84-002,82-020, 77-024 and 76-019.

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