ML17313A928

LER 99-004-00:on 990408,PSV Lift Pressures Were Outside of TS Limits.Caused by Lift Pressure Setpoint Drift.Psvs Have Been Tested,Disassembled,Inspected,Reassembled & Certified at Wyle Labs

ML17313A928
Person / Time
Site:	Palo Verde
Issue date:	05/07/1999
From:	Marks D ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:
Shared Package
ML17313A927	List: ML17313A926 ML17313A928
References
LER-99-004, LER-99-4, NUDOCS 9905190030
Download: ML17313A928 (8)

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NRC FORM 366A (6 1996)

U.S. NUCLEAR REGULATORY COMMISSION-LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION DOCKET FACIUTY NAME(1) LER NUMBER (6) PAGE (3)

NUMBER (2)

SEQUENTiAL REVISION NUMBER

'0 NUMBER Palo Verde Nuclear Generating Station Unit 2 05000529 2 OF 4 1999 004 -

TEXT (lfmore spaceis requited, use adChtional copies of NRC Form 366A) (17)

I. REPORTING REQUIREMENT(S):

During the 18 month frequency surveillance testing of the Unit 2 pressurizer safety valves (PSVs)

(EIIS: RV, AB) which was completed on April 8, 1999, the as-found lift pressures for two of the four Unit 2 PSVs were found to be below the Technical Specification limits of+3/-1 percent of design lift pressure.

This LER is being submitted because it is reasonable to assume that the out of tolerance condition existed prior to discovery and may have exceeded Technical Specification (TS) completion times. Therefore, the condition is reportable under 10 CFR 50.73(a)(2)(i)(B).

ln addition, this LER is being submitted pursuant to 10 CFR 50.73 (a)(2)(vii) because it is reasonable to assume that a single cause or mechanism served as a common input to the .

multiple PSV out of tolerance condition in a single system designed to mitigate the consequences of an accident.

II. DESCRIPTION OF STRUCTURE(S), SYSTEM(S) OR COMPONENT(S):

The Unit 2 PSVs were manufactured by Dresser/Consolidated and are Consolidated.31700 series valves designed for nuclear service and certified under Section III, Class 1, of the ASME code for application in nuclear power systems. The PSVs are crossed bonnet maxiflow, spring loaded, direct acting, model no. 31709NA valves. The function of the PSVs is to limit the reactor coolant system (EIIS: AB) pressure to less than the safety limit pressure of 2750 pounds per square inch absolute (psia) for moderate and low frequency events, and to less than the safety limit pressure of 3000 psia for certain very low frequency events.

The PSVs are tested in accordance with TS Surveillance Requirements (SR) 3.4.10.1 and 3.4.11.1, the inservice testing program (IST), and the ASME Code which requires testing of these valves on a five year frequency. However, Arizona Public Service Company (APS) tests the PSVs on a refueling (18 month) basis in accordance with previously specified corrective actions.

TS Limiting Conditions for Operation (LCO) require PSV lift settings to be within+3/-1 percent of the design lift pressure of 2475 psia or 2460 pounds per square inch gauge (psig).

There were no unusual characteristics of the work location (e.g., noise, heat, poor lighting) that contributed to this condition. Other than the PSV degradation described herein, there were no other component or system failures. There were no failures that rendered a train of a safety system inoperable and there were no personnel or procedural errors identified.

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NRG FORM 366A (6-1998)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITYNAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

SEQUENTIAL REVISION NUMBER NUMBER Palo Verde Nuclear Generating Station Unit 2 05000529 3 OF 4 1999 004 00 TEXT (ifmore spaceis required, use eddi5onel copies of NRC Form 366A) ( 7)

III. INITIALPLANT CONDITIONS:

PSV testing occurred at Wyle laboratories on April 7 and April 8, 1999. During this period, Unit 2 was de-fueled in Mode 6 (Refueling) at 0 percent power.

IV. EVENT DESCRIPTION:

On April 8, 1999, Unit 2 PSV set pressure verification testing was completed on the Unit 2 PSVs.

The set pressure veriTication testing revealed that the as-found lift pressures for two of the four Unit 2 PSVs was below the Technical Specification limits of +3/-1 percent of design lift pressure.

The as-found lift setting for RCE-PSV-0201 was 2407 psig or 2.2 percent below the design lift pressure of 2460 psig. Similarly, the as-found lift pressure for Unit 2 RCE-PSV-203 was 2422 psig or 1.5 percent below the design lift pressure of 2460 psig. The as-found lift settings for the other two Unit 2 PSVs were with the TS limit of +3/-1 percent of design lift pressure.

V.SAFETYCONSEQUENCES:

An analysis of the safety consequences of the Unit 2 as-found PSV testing results is being conducted in accordance with PVNGS procedures. This analysis will encompass the effects of the two PSVs which were out of tolerance low, as well as, the effects of four Unit 2 main steam safety valves (MSSVs)(EIIS: RV, SB) which were found to be out of tolerance high prior to Unit 2's eighth refueling outage (reference: LER 50-529/99-002). The analysis of safety consequences will be used to determine if the primary or secondary design peak pressures would have been exceeded under accident conditions. Preliminary analysis results indicate this condition would have no effect on the consequences of UFSAR chapter 15 events and additional safety analysis. Other accident consequences will also be evaluated to determine the effect of the PSV/MSSV as-found condition. If the safety consequence analysis results demonstrate that primary or secondary peak pressures would have been exceeded during accident conditions, or other accident conditions would have been unacceptable as a result of this condition, APS will provide the results in a supplement to this LER.

VI. CAUSE OF THE EVENT:

An evaluation of the as-found PSV lift testing results is being conducted in accordance with the PVNGS corrective action program. Preliminary indications are that the out of tolerance low as-found PSV lifts were the result of setpoint drift If APS determines that the cause was something other than setpoint drift, a supplement to this LER will be submitted.

NRC FORM 366A (6-1996)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION DOCKET FACILITYNAME (1) LER NUMBER (6) PAGE (3)

NUMBER (2)

SEQUENTIAL REVISION NUMBER NUMBER Palo Verde Nuclear Generating Station Unit 2 05000529 4 OF 4 1999 004 - 00 TEXT (ifmore space is required, use additional copies of NRC Form 366'17)

The as-found PSV lift settings is indicative of less than optimum performance rather than equipment failure. The as-found low setpoints do not appear to have adversely affected the PSV's ability to relieve primary system pressure and ensure pressure remains below design limits. However, the analysis of the safety consequences described above (section Vj will be used to determine if the primary or secondary design peak pressures would have been exceeded under accident conditions due to the out of tolerance PSV/MSSV conditions.

VII. CORRECTIVE ACTIONS TO PREVENT RECURRENCE:

The four Unit 2 PSVs had been as-found lift tested, disassembled, inspected, reassembled and certified at Wyle laboratories by April 8, 1999. No discrepancies were noted during the disassembly and inspection of the PSVs. To prevent recurrence, the PSV as-left settings were, to the extent possible, maintained at the higher end of the allowable setpoint band during the certification process at Wyle laboratories. This will allow for a greater setpoint drift between the as-left setting and the low end of the tolerance.

All four Unit 2 PSV installations were completed by April 25, 1999.

Vill. PREVIOUS SIMILAR EVENTS:

Within the last three years, one similar out of tolerance PSV condition was reported in LER 50-528/98-004. The effectiveness of previous corrective actions have reduced the test failure rates of the PSVs, however, as-found out of tolerance conditions continue to periodically occur.

Previous corrective actions increased the testing frequency of the PSVs from five years to 18 months. Previous corrective actions could not have prevented these events because they would not affect the tendency toward setpoint drift exhibited by the PSVs as described in the previous LER.

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