05000277/LER-2010-003

LER-2010-003, Laboratory Analysis Identifies Safety Relief Valves and Safety Valve Set Point Deficiencies

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2772010003R00 - NRC Website

Unit Conditions Prior to the Event Unit 2 was in Mode 5 for its 18th Refueling Outage (P2R18) when the event was discovered based on as-found testing from a laboratory from 9/27/10 through 9/30/10. The condition was discovered during routine laboratory as-found testing for Safety Relief Valves (SRVs) and a Safety Valve (SV) removed during the 18th Unit 2 Refueling Outage. There were no other structures, systems or components out of service that contributed to this event.

Description of the Event

Based on information received from 9/27/10 through 9/30/10 from a laboratory performing SRV (EMS: RV) and SV (EIIS: RV) as-found testing, Site Engineering personnel determined that SRV / SV set point deficiencies existed with two SRVs and one SV that were in place during the 18th Unit 2 operating cycle. The three SRVs / SV were removed during the 18th Unit 2 Refueling Outage and were sent to an off-site laboratory for as-found testing and routine refurbishment.

Two SRVs and one SV were determined to have their as-found set points in excess of the Technical Specification allowable ± 1% tolerance. All three valves were within the ASME Code allowable ± 3% tolerance. The three valves' as-found set points were as follows:

% Outside of Technical Required As-Found Specification Set Point Set Point Allowable SRV Serial Number (S/N) (psig) (psig) Tolerance 182 - SRV 1124 - 1146 1154 0.70% 178 - SRV 1134 - 1156 1157 0.09% BL - 1104 - SV 1247 - 1273 1296 1.81% operating cycle.

One of the two SRVs (SRV S/N 182) was also an Automatic Depressurization System (ADS) valve. The set point drift had no impact on the ADS or manual function of the valves.

Cause of the Event

The cause of the three SRVs / SV being outside of their allowable as-found set points is due to set point drift.

Analysis of the Event

There were no actual safety consequences associated with this event.

This report is being submitted pursuant to:

10CFR 50.73(a)(2)(i)(B) — Condition Prohibited by Technical Specifications — Technical Specification Limiting Condition for Operation (LCO) 3.4.3 requires that 11 of the 13 SRVs / SVs be operable during operational Modes 1, 2, and 3. Contrary to this requirement, two SRVs and one SV were found with set points outside of the Technical Specification requirements.

The ASME Boiler and Pressure Vessel Code requires that Reactor Pressure Vessel (EMS:

RCT) be protected from overpressure during upset conditions by self-actuated relief valves. As part of the nuclear pressure relief system, the size and number of SRVs and SVs are selected such that the peak pressure in the nuclear system will not exceed the ASME Code limits for the Reactor Coolant Pressure Boundary. There exists a total of 13 SRVs / SVs installed on the four Main Steam (EllS: SB) Lines. The eleven installed SRVs exhaust steam through discharge lines to a point below the minimum water level in the Suppression Pool. The two installed SVs discharge steam directly to the Drywell. The SRVs and SVs are located on the four main steam lines (EllS: SB) within Primary Containment. The SRVs are 'three-stage' valves consisting of a main valve disc and piston (third stage) operated by a second stage disc and piston displaced by either a first stage pressure-sensing pilot (for overpressure protection) or a pneumatically­ operated mechanical push rod (for the ADS function or for remote-manual operation). The SVs are direct-acting, spring loaded relief valves.

During the Unit 2 Cycle 18 operations, there were no plant transients that required automatic or manual SRV / SV operation. The as-found set points for the three SRVs / SV that tested outside of their Technical Specification allowable range were high. There were a total of six SRVs and one SV removed for testing and replacement during the 18th Refueling Outage. All three SRVs / SV outside of their Technical Specification allowable range were within the ASME Code allowable ± 3% tolerance. An engineering analysis determined one of the three SRVs / SV found outside of its Technical Specification range drifted into the acceptance range of a within the lift pressure range as specified by Tech Specs. One of the two SRVs (SRV S/N 182) was also an Automatic Depressurization System (ADS) valve. The set point drift had no impact on the ADS or manual function of the valves.

The event is not considered to be risk significant.

Corrective Actions

operating cycle.

A change to the PBAPS licensing basis (e.g., extended power uprate) will be pursued to increase SRV / SV set point tolerances.

Previous Similar Occurrences There were three previous LERs identified involving SRVs / SVs exceeding their Technical Specification ± 1% set point requirement. LER 3-07-01 reported three SRVs / SV (two SRVs and one SV) having its as-found set points in excess of the Technical Specification allowable ± 1% tolerance. LER 2-06-02 reported one SV having its as-found set points in excess of the Technical Specification allowable ± 1% tolerance. LER 3-05-04 reported a situation involving four SRVs having their as-found set points in excess of the Technical Specification allowable ± 1% tolerance. The previous SRV / SV as-found set points were all within the ± 3% ASME code allowable set point tolerance. Completed corrective actions addressing set point drift for these previous events involved replacement of the previous SRVs with different SRVs and therefore, would not have been expected to prevent this event.

One of the SRVs / SV reported in this LER (2-10-003) was found in the same location as those previously reported SRVs / SV in LER 2-06-02. However, the serial number of the valve is not the same. During P2R16, the 70A SV was determined to have its as-found set points in excess of the Technical Specification allowable ± 1% tolerance (but well within the ASME Code allowable ± 3% tolerance). The as-found set point was 1.2% higher than the Technical Specification allowable. During P2R18, the 70A SV was determined to have an as-found set point of 1.81% higher than the Technical Specification allowable. Neither of the other two SRVs reported in this LER (2-10-003) were the same as these previously reported in LERs 2-06-02, 3­ 05-04, and 3-07-01.