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ACCESSION NBR:9201020006 DOC.DATE: 91/12/20 NOTARIZED: NOFACIL:50-323 Diablo Canyon Nuclear Power Plant, Unit 2, Pacific Ga

AUTH.NAME AUTHOR AFFILIATIONHUG,M.T. Pacific Gas & Electric Co.RUEGER,G.M. Pacific Gas & Electric Co.

RECIP.NAME RECIPIENT AFFILIATION

DOCKET05000323

SUBJECT: LER 91-002-00:on 910826,determined that Trevitest equipmentfailed during adjustment of main steam safety valve RV-225.Caused by defective cell in battery of Trevitest testrecorder.Maint procedure revised.W/911220 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED: LTR / ENCL I SIZE:TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.NOTES

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EXTERNAL: EG&G BRYCE,J.HNRC PDRNSIC POORE,W.

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3 31 11 1

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PD5 PD

ACRSAEOD/DSP/TPABNRR/DET/ECMB 9HNRR/DLPQ/LHFB10NRR/DOEA/OEABNRR/DST/SELB 8DNRR/DSTJ SQLB+D1REG(~ILERGNG. FILE'1L ST LOBBY WARDNSIC MURPHYgG ~ ANUDOCS FULL TXT

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1 11 11 1

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Pacific Gas and Electric Company 77 Beate Street

San Francisco, CA 94106415I973-4684

Gregory M. Rueger *

Senior Vice President andGeneral Manager

Nuclear Power Generation

December 20, 1991

PG&E Letter No. DCL-91-309

U.S. Nuclear Regulatory CommissionATTN: Document Control DeskWashington, D.C. 20555

Re: Docket No. 50-323, OL-DPR-82Diablo Canyon Unit 2

Licensee Event Report 2-91-002-00 (Voluntary)Potential Hissetting of Hain Steam Line Code Safety Valve due toFailure of Test Equipment

Gentlemen:I

PG&E is submitting the enclosed voluntary Licensee Event Report (LER)concerning a potential missetting of a main steam line code safety valve

- due to a failure of test equipment. This report is being submitted forinformation purposes only as described in item 19 of Supplement 1 toNUREG-1022.

This event has in no way affected the health and safety of the public.

Si,ncerely,

- 4'Fj>~(p~>Gregory H. Rueger

CC: Ann P. HodgdonJohn B. HartinPhilip J.. HorrillHarry RoodHoward J. Wong ;

CPUCDiablo DistributionINPO

DC2-91-HH-N072

Enclosure

5599S/85K/JHA/2246

%ICENSEE EVENT REPORT (LE[

FACIUTY "IAME(IlDIABLO CANYON UNIT 2

PACE 3DOCKET NUMBER 1

0 5 0 0 0 3 2 3 1

TITLE(4I POTENTIAL HISSETTING OF MAIN STEAM LINE CODE SAFETY VALVE DUE TO FAILURE OF TEST

EOUIPHENTEVENT DATE (Sl LER NUMBER (Sl REPORT DATE LTl OTHER FACILITIES 1HVOLVED (B)

MON DAY

08 26 91

SEQUENTIALNIXVIB(R

REVISIONNUMBER

91 — 0 0 2 — 0 0

MON DAY

12 20 91

FACIUTYNAMESDOCKEf NUMBER (Sl

0 5 0 0 0

0 5 0 0 0OPERATINGMODE (9)

THTS REPORT is SVBHIT'fED PURSUANt To THE REQU(REHENTS OF 10 CFRT (11)

POWERLEVEL

0 9 010 CFR

H OTHER VOLUNTARY REPORT

(Specify in Abstract be(OH and in text, NRC Form 366A)

UCENSEE CONTACT FOR TIBS LER 12TELEPHONE NUMBER

HARTIN T. HUG — SENIOR REGULATORY COMPLIANCE ENGINEER

COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN TIES REPORT (13l

AREA CODE

805 545-4005

CAUSE SYSTEM COHPONEN'f MANVFACTVRER

REPORTABLETo NPRDS

CAUSE SYSTEM COMPONENT HANVFAC-TVRER

REPORTABLETo NPADS

SUPPLEMENTAL REPORT EXPECTED (14l

YES (if yes, complete EXPECTED SUBHISSIOR DATE) i X i RO

ABSTRACT (16)

EXPECTEDSUBHISSIOMDATE (15)

MONTH DAY YEAR

This voluntary LER is submitted for informational purposes only as described in Item 19of Supplement 1 to NUREG-1022.

On August 26, 1991, the setpoints for Main Steam Safety Valves (HSSVs) RV-60 and RV-225on main steam line 2-4 were tested using Trevitest equipment. HSSV RV-60 was tested andrequired a normal adjustment to bring it into tolerance. Subsequently, HSSV RV-225 wastested and required an abnormally large adjustment to bring it into tolerance. Becausethis large adjustment was needed, a prompt post-calibration verification was performedon the Trevitest equipment. It was determined that the Trevitest equipment had failedduring the adjustment of RV-225. RV-225 was then declared inoperable. RV-60 was notdeclared inoperable, since the Trevitest failure was judged to have occurred subsequentto adjusting RV-60 (because only normal, minor adjustments had been made to RV-60). On

August 27, 1991, RV-60 was rechecked and lifted at 1105 psi (4 psi above its acceptancecriteria of 1090 psi +/-1%).

The Trevitest equipment failure was due to a defective cell in the battery of theTrevitest test recorder. It could not be determined whether RV-60 lifting out oftolerance on August 27, 1991 was caused by adjusting the setpoint high due to failure ofthe Trevitest equipment, or by normal s'etpoint drift.The corrective action to prevent recurrence was a revision to the applicable maintenanceprocedure to require a post-calibration check of the Trevitest equipment prior totesting another HSSV on the same steamline.

5599S/85K

LICENSEElIENT REPORT (LER) TEXT COIINUATION

FACILITY NAME (1) COCKET NUMSER (2) LER NUMSER 6 PAGE 3

TEXT (17)

DIABLO CANYON UNIT 2 05 0 0 0 3 2 3 91 002 0 0 2 " 8

I; Plant Conditions

Unit 2 was in Hode 1 (Power Operation) at 90'ercent power.

II. Descri tion of Event

Event Summary:

Subsequent to adjusting the setpoints on two Hain Steam Safety Valves(HSSVs)(SB)(RV) using Trevitest equipment, the Trevitest test recorderwas determined to be out of calibration. The first HSSV (RV-60) was notconsidered inoperable (based on valve performance during the adjustments).The second HSSV (RV-225) was determined to be inoperable and the TechnicalSpecification Action Statement was entered for the second HSSV only.

Upon rechecking the setpoints the next day, both HSSVs lifted above theTechnical Specification allowable range. It could not be determined whetherthe first HSSV lifting out of tolerance was caused by adjustin'g the setpointhigh due to failure of the Trevitest equipment, or by normal setpoint drift.Since there is no firm evidence to determine the time of the event (i.e.,when the first HSSV was outside the Technical Specifications), it wasconsidered to occur at the time of discovery per NUREG-1022. Upondiscovery, the first HSSV was reset within four hours in accordance withthe Technical Specifications. This voluntary report is being submitted tosatisfy a commitment to prepare a licensee event report (LER) on the event,as noted in NRC Inspection Reports 50-275/91-24 and 50-323/91-24.

A. Event:

On August 26, 1991, at approximately 0800 PDT, a pre-test calibrationwas performed on the Trevitest equipment used to establish setpoints'n

the HSSVs. No problems were noted.

Technical Specification (TS) 3.7. 1. 1 requires that HSSV setpointsshall be within al% of the nominal setpoint. For RV-60, theacceptance criteria of 1090 psi sl% corresponds to an acceptable rangeof 1079 psi to 1101 psi. For RV-225, the acceptance criteria of1115 psi ~1% corresponds to an acceptable range of 1104 psi to1126 psi. Haintenance Procedure (HP) H-4. 18, "Verification of LiftPoint using Furmanite's Trevitest Equipment for the Hain Steam SafetyValves," requires two consecutive lifts within .the acceptancecriteria.

On August 26, 1991, at approximately 1330-1430 PDT, the setpoint forHSSV RV-60 on main steam line 2-4 was tested using the Trevitestequipment, per procedure HP H-4. 18. A technician employed byFurmanite (the Trevitest equipment vendor) conducted the testing withPG&E supervision. The initial lift (1080 psi) was within the 1090 psia1% tolerance. The second lift was 1064 psi, which was 26 psi low(2.4% below nominal) and indicated that the valve required adjustment.

5599S/85K

FACILITY NAME (I)

LICENSEESIENT REPORT (LER) TEXT COIeNUATION

DOCKET NUMBER (2)SKOVWTNI

NVMWI 'I <

TEXT (17)

DIABLO CANYON UNIT 2 0 5 0 0 0 3 2 3 -91 002 0 0 OF

The valve was adjusted +3 flats (i.e., the 'setpoint adjustment nut onthe valve was turned clockwise three flats of the nut), and respondedin a predictable manner, lifting approximately 20 to 30 psi higherover the next two lifts. (The rule of thumb is to expect a setpointadjustment of approximately 10 to 12 psi per flat.) The as-foundcondition of the NSSVs has historically varied from -2.5X to +10.2% ofnominal (see previous LER 1-88-018-01), and adjustments of. up to fiveflats are considered normal. Therefore, RV-60 requiring this smalladjustment was considered normal.

On August 26, 1991, from approximately 1430 to 1800 PDT, the setpointfor RV-225 was tested. The setpoint appeared to be low and requiredadjustment upwards. Thirteen lifts were eventually required toestablish the setpoint, as the valve did not appear to respondconsistently to the adjustments. The Trevitest equipment indicatedthat the lift setpoint did not increase by the expected 10 to 12 psipe} flat, and a large cumulative adjustment (+13 flats) was eventuallyrequired. This large adjustment, as well as the large number (13) ofadjustments, was considered abnormal. The Trevitest equipmentindicated that the valve finally did lift twice within the acceptancecriteria. However, due to the difficulty in establishing the.setpoint, a prompt post-calibration check was performed on theTrevitest equipment.

On August 26, 1991, at approximately 1800 PDT, the post-calibrationcheck was performed. The test recorder associated with the Trevitestequipment failed completely during the initial post-calibration testtrace. After charging the battery, another trace was completed whichshowed that the equipment was reading approximately 28/o low on itsscale. This would correspond to the Trevitest equipment reading 114psi low.

The identification of this condition brought into question theaccuracy of the setpoint established for RV-225. RV-225 had requireda large positive adjustment, which would be consistent with the testequipment being out of calibration (low) at the time RV-225 was set.In addition, the valve lifts as measured by the Trevitest equipmenthad not appeared to be responding to the setpoint adjustments. On

August 26, 1991, at 1841 PDT, RV-225 was declared inoperable, andAction Statement a for Technical Specification 3.7. 1. 1 was entered.However, the setpoint for RV-60 was believed to be accurate, as only a

small adjustment had been made to RV-60, and RV-60 had responded tothat adjustment as expected.

In accordance with the TS 3.7. 1. 1 action statement, Unit 2 power wasreduced to 80 percent rated thermal power and the power range neutronflux trip high setpoint was reduced to 86 percent rated thermal power.The power range neutron flux trip high setpoint adjustment wascompleted on August 26, 1991, at 2128 PDT.

5599S/85K

LlCENSEE/ENT REPORT (LER) TEXT COlEQUATION

FACILITY RANE (I) DOCKET NUHBER (E) LER NUNBER

RWSONNVMSIR

'AGE 3

TEXT (17)

DIABLO CANYON UNIT 2 05 0 0 0 3 2 3 91 002- 0 0 4 " 8

B.

On August 27, 1991, from approximately 1118 to 1318 PDT, RV-225 wasrechecked with a different Trevitest test recorder. It was determinedthat the initial liftwas 105 psi above the TS 3.7. 1. 1 acceptancecriteria of 1115 psi HX. This was a change of +127 psi (consideredabnormal) from the as-left condition on August 26, 1991. On August27, 1991, at 1318 PDT, rechecking and resetting of RV-225 wascompleted and RV-225 was declared operable.

On August 27, 1991, from approximately 1325 to 1400 PDT,RV-60'as,'echecked

with the second test recorder. The initial lift for RV-60'as

4 psi above the acceptance criteria of 1090 psi HX. This was a'hangeof" +22 psi from the as-left condition on August 26 (slightly

high, but within previous data scatter from lift to lift). RV-60 wasadjusted -IT/3 flats and. satisfactorily retested.

Investigation:

Investigation into this event and the prior test history of the HSSVsdetermined the following:

Setpoint'rift on these valves is a recurring condition thatis currently under investigation. As the normal test frequencyon these= valves is 18 months, PG&E has been investigating driftoccurring over the span of a fuel cycle. However, this

'nvestigationdoes not preclude the possibility 'that some'riftcould occur within, twenty-four hours.

2.

3.

Normal data scatter from lift to lift during the same test, withno adjustments (on the order of several minutes, rather thanseveral months), can show changes even greater than the +22 psichange on RV-60 from the as-left condition on August 26, 1991to the as-found condition on August 27, 1991. Though the liftsetpoints have generally been repeatable to within 1 15 psilift-to-lift(with no adjustments), larger drifts have occurred,going as high as'27 psi from one lift to the next on 'valves ofthis type onsite.

The vendor indicated that the Trevitest equipment failure wasdue to =a failure of the test recorder battery during adjustmentof RV-225, and that RV-60 was not affected.. The battery mayhave had a weak cell or an internal defect, and such a failurewould result in sudden and abrupt failure of the recorder.However, the Trevitest equipment appears to have degraded overtime (rather than an abrupt failure), and may have started todegrade during adjustments to RV-60. The indicated valvesetpoint diverged markedly from the calculated setpoint afterthe first adjustment to RV-225. This divergence could indicatean "abrupt" fai'lure, or could merely be due to the differencesbetween theoretical and actual valve behavior.

5599S/85K

LICENSEI/ENT REPORT (LER) TEXT COINUATION

FACILITY-NAME (1) DOCKET NNIGER (E) LER NIIM8ER

YTAR ski><'MVORAAL,"4<". NUM8OI

REVIQONWueTR

PAGE 3

TEXT (17)

DIABLO CANYON UNIT 2 05 0 0 0 3 2 3 91 00 2 0 0 oF 8

5.

6.

7.

The error in,the Trevitest equipment (approx. 114 psi low)caused RV-225 to be adjusted high (found 127 psi high), butcould not have caused RV-60 to be adjusted high (found only27 psi high), assuming the Trevitest failure was "abrupt"(114 psi error all,at once). In addition, the Trevitestequipment indicated that RV-60 responded to adjustments asexpected, with approximately 10 psi per flat. These factssupport the postulation that the Trevitest equipment did notfail during RV-60 testing and that 'RV-60 was not set aboveits acceptance criteria.

Because RV-60 required an adjustment of +3 flats onAugust 26, 1991, then -IT/3 flats on August 27, 1991, it appearsthat RV-60 was adjusted too high on August 26, 1991. However,as discussed above, there is considerable variance in the actualamount of setpoint change (psi) per flat adjustment.Historically, actual setpoint changes have varied from 9 to17 psi per flat. Therefore, the +3 flat adjustment onAugust 26, 1991 may or may not have caused a lT/3 flat excesson August 27, 1991.

By comparing the calculated as-left setpoints of the valves withthe actual as-found setpoints, the time of the Trevitest failurecould not be determined.

The vendor technician apparently performed' routine "press-to-check" calibration check prior to testing each valve to confirmthat the Trevitest equipment was still in calibration; however,there are no data traces to verify that these checks weresatisfactory. This check, if performed satisfactorily prior toadjusting RV-225, would have verified that the Trevitestequipment was in calibration during the adjustments to RV-60.

C.

In conclusion, there is no firm evidence to determine whether RV-60lifting out of tolerance on August 27, 1991 was caused by eitheradjusting the setpoint high due to failure of the Trevitest equipment,or by setpoint drift. Since there is no firm evidence that theequipment failure caused the HSSV to be out of tolerance, this eventis being reported to the NRC as a voluntary LER.

Inoperable Structures, Components, or Systems that Contributed to theEvent:

D.

RV-225 was declared inoperable due to an out of tolerance setpoint.

Dates and Approximate Times for Najor Occurrences:

1. August 26; 1991, at 0800 PDT: Trevitest equipment was pre-calibrated.

5599S/85K

LICENSEE/ENT REPORT (LER) TEXT COI4UATION

FACILITY NAME (1) DOCKET NUMBER (E) LER NUMBER 6SMVWfW. j: g IISYIQON

NVNSOl );, "c'„'UNSOI

PAGE 3

TEXT (17)

DIABLO CANYON UNIT 2 0 5 0 0 0 3 2 3 91 002- 0 0 6 '

2. August 26, 1991, 1330 - 1430 PDT: Event date - The setpointfor RV-60 was established.

3. August 26, 1991, 1430 — 1800 PDT: The setpoint for RV-225 wasestablished.

4. August 26, 1991, at 1800 PDT:

5. August 26, 1991, at 1840 PDT:

6. August 26, 1991, at 2128 PDT:

7. August 27, 1991, at 1318 PDT:

Discovery date — The testrecorder associated withthe Trevitest equipment wasfound failed.

RV-225 was declaredinoperable.

All high flux trip setpointswere set to 86% power perTS 3.7. 1.1 Action Statementa ~

Rechecking and adjustmentof RV-225 was completed andRV-225 was declaredoperable.

8: August 27, 1991, 1325-1400 PDT: RV-60 was rechecked andreset 1 /3 flats lower.

f. Other Systems or Secondary Functions Affected:

None.

Nethod of Discovery:

The problem was identified during the post-calibration of theTrevitest equipment.

G.

H.

Operators Actions:

None.

Safety System Responses:

None.

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LICENSES/ENT REPORT (LER) TEXT COINUATION

FACiLITY NAME (1) DOCKET NUMBER (E) LER NUMBER 6SEOVTHRAL:?',.;

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DIABLO CANYON UNIT 2 05 0 0 0 3 2 3 91 002 0 0 7 " 8

III. Cause of the Event

A. Immediate Cause:

The immediate cause of the problem was RV-225, and potentially RV-60,lifting above their acceptance criteria due to the Trevitest equipmentfailure.

B. Root Cause:

The Trevitest equipment failure was due to a defective cell in thebatte'ry of the Trevitest test recorder. It could not be determinedwhether RV-60 lifting out of tolerance on August 27, 1991 was causedby adjusting the setpoint high due to failure of the Trevitestequipment, or by normal setpoint drift inherent in the HSSVs.

IV, Anal sis of the Event

There are five code safety valves on each of the four main steam lines. Thevalves provide overpressure protection for each steam generator (SG) andmain steam line.

Safety assessments have been performed for previous instances where severalmain steam line code safety valves lifted outside of their TechnicalSpecification acceptance criteria. (See LER 1-88-018-01 for discussion ofthe previous safety assessments performed by PGE E and Westinghouse for HSSVs

lifting outside the Technical Specification acceptance criteria.) Theassessments concluded that there was no significant impact on the safety ofthe plant. Since th'e prior assessments bound the case where ten HSSVs

lifted at varying points (with'our HSSVs lifting an estimated 6% to 9%

above their setpoints), the assessments bound the current event where onlytwo HSSVs lifted at 1.04% and 10.4% above their setpoints.

Also, according to industry guidance (ASME relief valve standard OM-1), avariance of H% is acceptable for the as-found condition of code safetyvalves in this application. RV-60 would have lifted only 4 psi (0.04%)above the administrative a1% range, well within this accepted K% range.In addition, the actual lift point was also within the graduated band ofsetpoints for the five HSSVs on the steam line. Therefore, RV-60 wouldactually have performed its designed safety function and the safetysignificance of RV-60 lifting out of tolerance was small,

Finally, it should be noted that the design of the HSSVs was determinedassuming that the 10 percent atmospheric steam dump valve on each steam l.inewas non-safety class and conservatively would not be assumed to function.However, the 10 percent atmospheric steam dump valves are now safety relatedvalves, and would be considered to function in the event of an accident torelieve pressure in the SG and the main steam line.

5599S/85K

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LICENSElENT REPORT (LER) TEXT COIEQUATION

FACILITY NAME (I) DOCKEt NUMBER (8)YEAR

LER NUMBER

:YID

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DIABLO CANYON UNIT 2 05 0 0 0 3 2 3 91 002 0 0 8 " 8

V.

Since (1) previous assessments show that there was no significant im'pact on

plant safety, (2) the safety significance of RV-60 lifting 4 psi above itsacceptance criteria was small, and (3) the 10 percent steam dump valves werecapable of providing additional overpressure protection, the healthand safety of the public were not adversely affected by this event.

Corrective Actions

A. Immediate Corrective Actions:

After discovery of the degraded Trevitest equipment, RV-225 wasdeclared inoperable and power was reduced to 80% in accordancewith Technical Specification 3.7. 1. 1 action a.

2. The setpoints for RV-225 and RV-60 were re-established thefollowing day, August 27, 1991.

B. Corrective Actions to Prevent Recurrence:

Haintenance Procedure HP H-4. 18, "Verification of Lift Point usingFurmanite's Trevitest Equipment for the Hain Steam Safety Valves," wasrevised to require a post-calibration check of the Trevitest equipmentprior to testing another HSSV on the same steamline. This procedurerevision was completed on August 29, 1991, prior to resuming testingand adjustment of the other HSSVs.

VI. Additional Information

A,

B.

Failed Components;

None.

Previous LERs on Similar Problems:

LER 1-88.-018-01: "Pressurizer and Hain Steam Line Code Safety ValvesOutside Technical Specification Setpoint ToleranceLimits due to Indeterminate Causes"

This previous LER deals with recurring instances of HSSVs (andpressurizer safety valves) lifting outside of the TS-required el%acceptance band. PG&E is currently still investigating the rootcause, and has not yet finalized corrective actions to preventrecurrence.

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