05000277/LER-2012-001
| Docket Number Sequential Revmonth Day Year Year Month Day Year 05000Number No. | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 2772012001R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 2 was defueled to support its 19th Refueling Outage (P2R19) when the event was discovered on 9/25/12 based on as-found testing data from a testing laboratory. The condition was discovered during routine laboratory as-found testing for Safety Relief Valves (SRVs) and a Safety Valve (SV) removed during the 19th Unit 2 Refueling Outage. There were no other structures, systems or components out of service that contributed to this event.
Description of the Event
On 9/25/12, Site Engineering personnel determined that SRV / SV setpoint deficiencies existed with six SRVs and one SV that were in place during the 19th Unit 2 operating cycle. This was based on information received from a laboratory performing SRV (EMS: RV) and SV (EMS: RV) as-found testing, The seven SRVs / SV were removed during the 19th Unit 2 Refueling Outage and were sent to an off-site laboratory for as-found testing and routine refurbishment. Six SRVs and one SV were determined to have their as-found setpoints outside of the Technical Specification (TS) allowable ± 1°/0 tolerance. All six SRVs were within the ASME Code allowable ± 3% tolerance. The one SV outside of its TS allowable setpoint range also exceeded the ASME Code allowable ± 3% tolerance. The seven valves' as-found setpoints were as follows:
Required TS As-Found % Outside of TS Type ID S/N Setpoint (psig) Setpolnt (psig) Nominal Setpoint SRV 71A 24 1143 - 1167 1121 -2.94% SRV 71D 16 1124 - 1146 1118 -1.50% SRV 71E 81 1124 - 1146 1103 -2.82% SRV 71F 19 1124 - 1146 1116 -1.67% SRV 71G 82 1134 - 1156 1127 -1.57% SRV 71H 17 1134 - 1156 1111 -2.97% SV 70B BL-1095 1247 - 1273 1303 +3.41% operating cycle.
Two of the six SRVs (SRV S/N 24 and S/N 82) were also Automatic Depressurization System (ADS) valves. The setpoint drift had no impact on the ADS or manual function of the valves.
Cause of the Event
The cause of the SRVs / SV being outside of their allowable as-found setpoints is due to setpoint drift.
Additional evaluations of the cause(s) of the SRVs / SV setpoint deficiencies are being performed in accordance with the site Corrective Action Program.
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, six SRVs and one SV were found with setpoints outside of the Technical Specification setpoint requirements.
10CFR 50.73(a)(2)(vii) — Common Cause Failure of Multiple Trains being Inoperable - Six SRVs and one SV were considered inoperable as a result of exceeding their allowable setpoint range based on laboratory testing. Therefore, this occurrence is considered as a common cause failure of multiple independent trains being inoperable.
The ASME Boiler and Pressure Vessel Code requires that the Reactor Pressure Vessel (EllS:
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-stag& 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.
Analysis of the Event, continued There were a total of seven SRVs and one SV initially removed for testing and replacement during the 19th Refueling Outage. Technical Specification Limiting Condition for Operation 3.4.3 requires 11 of the 13 total SRVs / SVs to be operable to provide the reactor coolant system overpressure safety function. The safety function of any combination of 11 SRVs and SVs are required to satisfy the assumptions of the safety analyses. During the Unit 2 Cycle 19 operations, there were no plant transients that required automatic or manual SRV / SV operation.T The as-found setpoints for the six SRVs that tested outside of their Technical Specification allowable range were low. However, all six SRVs outside of their Technical Specification allowable setpoint range were within the ASME Code allowable ± 3% tolerance.
Because the SRV as-found set points were on the low side, there was no loss of the TS 3.4.3 overpressure safety function for these valves. The one SV outside of its TS allowable range also exceeded the ASME Code allowable ± 3% tolerance. Since only 11 of the 13 SRVs / SVs are required to be operable, the 70B SV did not impact the TS 3.4.3 safety function. Two of the six SRVs (SRV S/N 82 and S/N 24) were also Automatic Depressurization System (ADS) valves. The setpoint 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. Since the 70B SV exceeded the ± 3% SV tolerance, the other SV (70A) was removed and sent for laboratory testing in accordance with the ASME code. The 70A SV was replaced with a refurbished SV for the 20th Unit 2 operating cycle.
A licensing change to revise the SRV / SV set point tolerance to ± 3% is planned to be submitted to the NRC in 2013.
Other actions will be pursued, as necessary, to address causes determined in accordance with the site Corrective Action Program.
Previous Similar Occurrences There were four previous LERs identified involving SRVs / SVs exceeding their Technical Specification ± 1% setpoint requirement. LER 2-10-03 reported two SRVs and one SV having their as-found setpoints in excess of the TS allowable ± 1% tolerance. LER 3-07-01 reported two SRVs and one SV having their as-found setpoints in excess of the TS allowable ± 1% tolerance. LER 2-06-02 reported one SV having its as-found setpoints in excess of the TS allowable ± 1% tolerance. LER 3-05-04 reported a situation involving four SRVs having their as-found setpoints in excess of the TS allowable ± 1% tolerance.
Previous Similar Occurrences, continued The previous SRV / SV as-found setpoints were all within the ± 3% ASME code allowable setpoint tolerance. Completed corrective actions addressing setpoint 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. The corrective action discussed in LER 2-10-03 to revise the TS to change the SRV/SV tolerance from ± 113/0 to ± 3% is not yet complete. The TS change request is expected to be submitted in 2013.