ML18039A204

LER 97-008-00:on 971104,main Steam Safety/Relief Valves Exceeded TS Setpoint Limit.Caused by Pilot Valve Disc/Seat Bonding.Replaced All 13 Unit 2 Main Steam SRV Pilot Cartridges

ML18039A204
Person / Time
Site:	Browns Ferry
Issue date:	12/03/1997
From:	Hsieh C TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML18039A203	List: ML18039A202 ML18039A204
References
LER-97-008-02, LER-97-8-2, NUDOCS 9712110186
Download: ML18039A204 (12)

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NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150<104 (4-95) EXPIRES 04/30/96 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS MANDATORY INFORMATION COLLECTION REQUEST:

50.0 HRS. REPORTED LESSONS LEARNED ARE LICENSEE EVENT REPORT (LER) INCORPORATED INTO THE UCENSING PROCESS AND FED BACK TO INDUSTRY. FORWARD COMMENTS REGARDING (See reverse for required number of BURDEN ESTIMATE TO THE INFORMATIONAND RECORDS digits/characters for each block) MANAGEMENT BRANCH (TW F33). U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 205554)001, FACILITYNAME (I) COCKET NUMSER (S) PAGE (S)

Browns Ferry Nuclear (BFN) Plant Unit 2 05000260 1 OF 6 Tl'TLE (a)

Main Steam Safety/Relief Valves Exceeded the Technical Specifications Required Setpoint Umit as a Result of Pilot Valve Disc/Seat Bonding EVENT DATE (5) LER NUMBER 6) REPORT DATE (7) OTHER FACILITIES INVOLVED (6)

FACILITYNAME DOCKET NUM8ER SEQUENTIAL REVISION MONTH DAY YEAR MONTH DAY YEAR NUMBER NUMBER NA FACIUTY NAME 11 04 97 97 008 00 12 97 NA OPERATING THIS REPORT IS SUBMITTED PURS UANT TO THE REQUIREMENTS OF 10 CFR g: (Chock ono or moro) (11 MODE (9) 20.2201(b) 20.2203(a)(2)(v) 50.73(a)(2)(l)(B) 50.73(a)(2)(viii) 20.2203(a)(1) 20.2203(a)(3)(l) 50.73(a) (2) (il) 50.73(a)(2)(x)

POWER 100 LEVEL (10) 20.2203(a)(2)(l) 20.2203(a)(3)(ii) 50.73(a)(2)(ill) 73.71 20.2203(a)(2)(ii) 20.2203(a)(4) 50.73(a) (2)(iv) OTHER 50.36(c) (1) 50.73(a)(2)(v) Spec(fv In Abstract below 20.2203(a)(2)(iii) or ln NRC Form 366A 20.2203(a)(2)(iv) 50.36(c) (2) 50.73(a)(2)(vli)

LICENSEE CONTACT FOR THIS LER (12)

TELEPHONE IIUMSER (Ioorrrde Area Code)

Clare S. Hsieh, Licensing Engineer (205) 729-7854 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT MANUFACTURER REPORTABLE CAUSE SYSTEM COMPONENT MANUFACTURER REPORTABLETO NPRDS TO NPRDS SB ~ RV T020 Y SUPPLEMENTAL REPORT EXPECTED (14) MONTH DAY YEAR EXPECTED YES SUBMISSION X NO DATE (15)

(If yes, complete EXPECTED SUBMISSION DATE).

ABSTRACT (Limit to 1400 spaces, I.e., approximately 15 s(ngle-spaced typavnitten lines) (16)

On November 4, 1997, with Unit 2 at 100 percent power following the'Unit 2 cycle 9 refueling outage, Unit 3 operating at 100 percent power, and Unit 1 shutdown and defueled, Wyle Laboratories notified TVA that 5 of the 13 Unit 2 main steam safety/relief valves (SRV) pilot cartridges removed during the Unit 2 cycle 9 refueling outage failed the setpoint tolerance bench tests. Wyle Laboratories'ests discovered that the SRVs's-found setpoints were outside the TS setpoint tolerance of+/-11 psi. This condition is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by the plant's technical specifications (TS). The cause was SRV pilot disc/seat bonding attributed to corrosion at the two-stage,SRV pilot disc/seat interface. This resulted in drifting of the SRV setpoints. The Unit 2 SRV pilot cartridges were installed during the Unit 2 forced outage (October 29-November 3, 1996). Setpoint drift is a generic concern experienced by utilities using Target Rock Two-Stage SRVs (Model No. 7567F) in boiling water reactors and is being investigated by the Boiling Water Reactors Owners Group (BWROG) SRV Drift Fix Development Committee and the manufacturer. TVA will continue to participate in the BWROG's evaluation of the long-term solution for the SRV setpoint drift problem. During the Unit 2, cycle 9 outage, SRV pressure switches were installed to minimize the effects of setpoint drift. In addition, TVA will continue to evaluate other possible solutions. Previous.LERs for failed SRV testing included: 260/87005, 259/88053, 260/93003, 260/95003, 260/96004, 260/96008, and 296/97003.

'T)7i2i i0i86 'T)7i20S PDR ADQCK 05000260 8 PDR 4

i NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (4-95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME DOCKET LER NUMBER PAGE (

NUMBER NUMBER Browns Ferry Unit 2 05000260 2 of 6 97 -- 008 -- 00 TEXT (I more space s reqinre, use a iiiona copies o orm (17)

X. PLANT CONDXTXONS At the time of the discovery of this condition, Unit 2 was at 100 percent power following a refueling outage, Unit 3 was operating at 100 percent power, and Unit 1 was shutdown and defueled.

ZX. DESCRXPTXON OF EVENT Event On November 4, 1997, Wyle Laboratories notified TVA that of the 13 main steam [SB] safety/relief valves (SRV) [RV) pilot cartridges tested at their laboratory in Huntsville, Alabama, five failed the setpoint tolerance bench tests. The'RV steam pilot cartridges were previously removed from the unit 2 main SRVs (Target Rock Two-Stage SRV Model No. 7567F) during the unit 2 cycle 9 refueling outage and shipped to Wyle Laboratories for tests. The pilot cartridges were installed during the unit 2 forced outage (October 30-November 3, 1996).

Altogether, Wyle Laboratories tested five SRV pilot platinum-stellite and eight stellite disc cartridges. One platinum-stellite and four stellite cartridges failed the 'as found outside tolerance bench tests. The setpoints were found'etpoint the technical specifications (TS) tolerance of +/- 11 pounds per square inch (psi) (approximately 1 percent). See Table 1 for specific SRV pilot cartridge test results.

The above condition is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by the plant's TS.

B. Xno erable Structures Co onents or S stems that Contributed to the Event:

None.

Dates and A roximate Times of Ma'or Occurrences:

October 30-November 3, 1996 Unit 2 in forced outage. Pilot cartridges installed in unit 2 main steam SRVs.

September 27, 1997 Unit 2 entered cycle 9 refueling outage.

October 8-15, 1997 Pilot cartridges removed from main steam SRVs and shipped to Wyle Laboratories for tests.

NRC FORM 366A (4-95)

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NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (4-95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATEON FACZLITX NAME (1 DOCKET PAGE NUMBER NUMBER Browns Ferry Unit 2 05000260 3 of 6 97 -- 008 00 TEXT more space s require, use a iuona copies o C orm (17)

October 19, 1997 Unit 2 completed cycle 9 refueling outage.

November 4, 1997 Wyle Laboratories notified TVA of the SRV pilot cartridges test results.

D. Other S stems or Seconda Functions Affected:

None.

E. Method'f Discove This condition was identified during valve bench testing at Wyle Laboratories in Huntsville, Alabama.

F. erator Actions:

None.

G. Safet S stem Res onses:

None, CAUSE OF THE EVENT A. Immediate Cause:

The immediate cause was SRV pilot disc/seat bonding resulting in the SRV setpoints deviating outside the TS setpoint tolerance of

+/- 11 psi.

B. Root Cause:

Four of the five failed SRV pilot cartridges opened above the TS setpoint tolerance of +11 psi. The cause was SRV pilot disc/seat bonding which was attributed to corrosion at the two-stage SRV pilot disc/seat interface. Thepressure corrosion bonding resulted in an increase in the valve opening due to the need fox additional opening force above the setpoint value. As a result of this bonding, the SRV setpoints drifted above the TS setpoint limit.

One SRV pilot cartridge opened below the setpoint tolerance of

-11 psi (cartridge 1070 opened at -21 psi below its setpoint).

TVA believes the low opening pressure was due to leakage which may have caused the valve to drift below its

'inservice'alve NRC FORM 366A (4-95)

i NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION

(~5)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATZON FACILITY NAME (1) DOCKET PAGE (

NUMBER NUMBER Browns Ferry Unit 2 05000260 4 of 6 97 -- 008 -- 00 TEXT ( snore space is requir ~ use ad itiona copies o orrn (17) setpoint tolerance. TVA will examine cartridge 1070 later in more detail after it is disassembled, and any corrective action needed to fix this problem is tracked by the TVA corzective action program.

IV. ANALYSIS OF THE EVENT There aze 13 SRVs on the main steam piping. The valves are designed to perform the safety/relief function for the primary reactor system boundary by opening at a sensed pressure of 1105, 1115 or 1125 psig.

The safety/relief function of the SRVs is to limit primary reactor system pressure to less than 1375 psig in the event of a pressurization transient resulting from a turbine trip or a main steam isolation valve closure. The failures of the four SRVs (from approximately +1.17 to +6.31 percent above their setpoint pressure) would not have resulted in exceeding the TS safety limit during any abnormal operational transient. Additionally, in this event one SRV pilot valve cartridge (valve cartridge 1070) opened below its setpoint limit at -21 psi (approximately -1.88 percent)'. Valve opening before reaching the setpoint tolerance would result in no adverse effects on the TS safety limit of the primary reactor system pressure during analyzed transients.

ASSESSMENT OF THE SAFETY CONSEQUENCES TVA performed a limiting pressurization transient analysis for unit 2 cycle 6 assuming a spectrum of main steam SRV failures and setpoint dr'ifts. The analysis concluded that even if four main steam SRVs completely fail to open and the remainder operate at ten percent above setpoint, the primary reactor system pressure would not exceed the TS safety limit of 1375 psig. Considering the conservative inputs to this analysis and the low sensitivity of the pressurization transient to cycle-by-cycle loading differences, the SRV failures in this unit 2 event would not have resulted in exceeding the TS safety limit during operational transients. Thus, the plant and public safety would not have been adversely affected and safety of plant personnel was not compromised.

VI. CORRECTIVE ACT1ONS A. Immediate Corrective Actions:

Prior to the unit 2 restart, TVA replaced all 13 unit 2 main steam SRV pilot cartridges. The SRV pilot cartridges were replaced with the newly certified cartridges which had previously been removed from other units.

The cartridges removed from unit 2 will later be refurbished, retested and recertified with their setpoint within TS requirements, NRC FORM 366A (4-95)

i' NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (4.95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACZLZTX NAME 1 DOCKET PAGE (

NUMBER NUMBER Browns Ferry Unit 2 05000260 5 of 6 97 -- 008 -- 00 TEXT ( more space s requ rod, use a niona copies o N orm (17)

B. Corrective Actions to Prevent Recurrence:

During the Unit 2, cycle 9 refueling outage, a modification was implemented that installed pressure switches to activate SRVs.

The pressure switches ensure the initiation of any SRV should fail to open at its setpoint; thus, minimizing the effects of it setpoint drift. In addition, TVA has requested a TS change which raises the setpoint limits from +/- 11 psi (approximately +/- 1 percent) to +/- 3 percent which corresponds to the inputs currently used in the Unit 2 and 3 cycle-specific core reload analyses. This change will provide added margin for SRV tests.

SRV setpoint drift is a generic concern experienced by utilities using this brand of SRVs in boiling water reactors and is being investigated by the BWROG's SRV Drift Fix Development Committee and the manufacturer. TVA will continue to participate in the BWROG's evaluation of the long-term solution for the SRV setpoint drift problem. Long-term corrective actions associated with this pxoblem are being tracked by the TVA corrective action program.

VZZ. ADDZTZONAL INFORMATION A. Failed Co onents:

Target Rock, Two-Stage SRVs Model No. 7567F.

B. Previous LERs on Similar Events:

There have been several previous LERs written concerning main steam SRV setpoint drift due to pilot valve disc/seat corrosion bonding (LERs 260/87005, 259/88053, 260/93003, 260/95003, 260/96004r 260/96008r and 296/97003) ~ However, none of the corzective actions in previous LERs would have precluded this event.

TVA had previously implemented the BWROG recommendation of replacing SRV pilot cartridges with cartridges that have a 0.3 percent platinum alloyed stellite pilot disc. The platinum-stellite disc did not correct the SRV setpoint drift problem (see LERs 260/96004 and 260/96008). During the unit 2 cycle 9 refueling outage, TVA installed redundant pressure transmitters/switches to control the opening of the SRVs.

In addition, TVA will continue to evaluate other possible solutions and to participate in the BWROG's evaluation of the long-term solution of the SRV setpoint drift problem.

VIII . COMMITMENTS None.

NRC FORM 366A (4-95)

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LICENSEE EVENT REPORT (LER)

TEXT CONTXNUATION FACILITX HAMS DOCKET PAGE NUMBER NUMBER Browns Ferry Unit 2 05000260 6 of 6 97 -- 008 00 TExT ( moro space s required, use a iuooa copies o C orm (17)

Table SRV AS-FOUND TEST RESULTS Five (5) of the following thirteen (13) Unit 2 main steam SRVs failed to meet the required TS setpoint tolerance (+/-

failed SRV pilot cartridges is shown in bold type.

ll psi). The information for the Valve Pilot Disc Nameplate As-Found Pressure Percent Cartridge Composition Setpoint Actuation Difference Difference Serial Number Pressure Pressure (psig) ()

(S/N) (psig) (psig) 1060 stellite 1105 1101 -0. 36 1234 stellite 1105 1139 +34 +3.08 1069 platinum 1105 1095 -10 -0.90 1022 platinum 1105 1105 0.00 1079 platinum 1115 1128 +13 +1. 17 1021 platinum 1115 1123 +0.72 1240 stellite 1115 -0.36 1070 stellite 1115 1094 -21 -1. 88 1071 stellite 1125 1136 +11 +0. 98 1026 platinum 1125 1124 -0. 09 1078 stellite 1125 1131 +0.53 1233 stellite 1125 1196 +71 +6.31 1064 stellite 1125 1153 +28 +2.49 Energy Industry Identification System (E1ZS) system and component codes are identified in the text with brackets (e.g., [XX] ) .

NRC FORM 366A (4-95)

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