05000321/LER-2010-001

LER-2010-001, Corrosion Induced Bonding Results in Safety Relief Valve Lift Setpoint Drift

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3212010001R00 - NRC Website

PLANT AND SYSTEM IDENTIFICATION

General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EIIS Code XX).

DESCRIPTION OF EVENT

On March 11, at approximately 1300 EST, Unit 1 was at 0 CMWTh, which is 0.00 percent of rated thermal power (RTP). On that day it was concluded that at the completion of bench testing five Safety Relief Valves (SRVs, EIIS Code SB) experienced setpoint drift that exceeded the allowable plant Technical Specifications (TS) limit which is +/- 3%. The setpoint for each of the eleven SRVs is 1150 +/- 34.5 psig. The following is a tabulation of the test results for the eleven SRVs:

MPL Number Pilot Serial Number As-Found Lift Pressure Percent Drift 1B21-F013A 313 1147 99.7 1B21-F013B 1006 1167 101.5 1B21-F013C 306 1250 108.7 1B21-F013D 304 1165 101.3 1B21-F013E 1007 1205 104.8 1B21-F013F 303 1168 101.6 1B21-F013G 1228 1239 107.7 1B21-F013H 310 1160 100.9 1B21-F013J 1231 1297 112.8 1B21-F013K 1004 1208 105.0 1B21-F013L 1189 1173 102.0 These valves were removed from service during the Spring 2010 refueling outage and replaced with like kind valves that were serviced and tested in accordance with plant procedures.

� PRINTED ON RECYCLED PAPERNRC FORM 366A (9-2007) Per the GE SIL, higher temperature in the pilot area results in higher concentration of steam in that area, which further results in lower concentration of oxygen. The lower concentration of oxygen reduces the amount of corrosion that will occur in the seating area. The as-found condition of the Unit 1 insulation revealed that the insulation was in poor condition, that only one layer of blankets was used, and that the blankets were sagging down around the pilot flange.

REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT

This event is reportable per 50.73(a)(2)(i)(B) because an event occurred which is prohibited by Technical Specifications (TS). Specifically, multiple test failures of the SRVs is defined as reportable in NUREG-1022, Revision 2, dated October 2000, in section 3.2.2, example 3, titled "Multiple Test Failures.

The 11 SRVs, which are located on the four main steam lines within the drywell (EIIS Code NH) between the reactor vessel (EIIS Code AD) and the inboard main steam isolation valves (MSIV EIIS Code SB), are required during Modes 1, 2, and 3 to limit the peak pressure in the nuclear system such that it will not exceed the applicable ASME Boiler and Pressure Vessel Code limits for the reactor coolant pressure boundary. Per TS Surveillance Requirement 3.4.3.1, the valves are tested in accordance with the In-service Testing Program to verify the safety function lift setpoints are within the specified limits. The SRVs must accommodate the most severe pressurization transient which, for the purposes of demonstrating compliance with the ASME Code limit of 1375 psig peak vessel pressure, has been defined as a closure of all MSIVs with a failure of the direct reactor protection system trip from the MSIV position switches; the reactor ultimately shutdowns from a high neutron flux trip. Analysis of this event comparing the as-found bench test results for SRV actuation pressures with previously analyzed lifting pressures for each SRV has demonstrated that the resultant peak pressure was within the ASME Code limit of 1375 psig. The previously analyzed lifting pressures were evaluated and determined to be bounding in comparison to the as-found lift points for this event. Furthermore, the plant TS overpressure safety limit of 1325 psig dome pressure must be met during normal operations and for anticipated operational occurrences (AOOs). The analysis of the as-found test results by comparison with previously analyzed lifting pressures also showed that the resultant dome pressure was within the plant TS Safety Limit.

PRINTED ON RECYCLED PAPERNRC FORM 366A (9-2007) In addition, a non-credited electrical actuation system was installed in 1993 to ensure proper actuation of the SRVs. This system provides a redundant, independent method (i.e., electrical signal) to actuate the SRVs. During the run cycle the redundant electrical system was available. The system was procured to Class 1E environmental and seismic standards, and is deemed highly reliable.

Based on this analysis, it is concluded that this event had no adverse impact on nuclear safety.

CORRECTIVE ACTIONS

All eleven pilot valves have been replaced with refurbished pilot valves.

Each of the eleven pilot disc from the valves removed were replaced with a pilot disc made from Stellite 21 material.

Insulation surrounding each SRV has been upgraded to improve resistance to corrosion induced bonding.

ADDITIONAL INFORMATION

Other Systems Affected: None Failed Components Information:

Master Parts List Number: 1B21-F013 EIIS System Code: SB Manufacturer: Target Rock Reportable to EPIX: Yes Model Number: 7567F Root Cause Code: B Type: Relief Valve EIIS Component Code: RV Manufacturer Code: T020 Commitment Information: This report does not create any new permanent licensing commitments.

Previous Similar Events:

Corrective actions for this event replaced all eleven pilot discs with Stellite 21 material, and improvements were made in the insulation surrounding the SRV's. These actions were taken on Unit 2 therefore they do not directly impact Unit 1 performance. However improvement in the insulation was incorporated into corrective action for the current LER, 1-2010-001.

� PRINTED ON RECYCLED PAPERNRC FORM 366A (9-2007) during the 2008 Unit 1 refueling outage. Industry experience indicates the stellite 21 material to be resistive to corrosion induced bonding. The initial experience for plant Hatch did not follow the industry experience. During the 2008 refuel outage the condition of insulation surrounding the SRV's was not closely controlled.

Corrective action for this LER was replacement of discs with stellite 21 discs. The discs were therefore they do not directly impact Unit 1 performance.

described results from the previous three outages where multiple SRV setpoint drift had occurred. Corrective actions for that LER focused on ensuring proper reporting of SRV setpoint drift was performed.

� PRINTED ON RECYCLED PAPERNRC FORM 366A (9-2007)