05000278/LER-2013-001
| Peach Bottom Atomic Power Station Unit 3 | |
| Event date: | 17-9-1155 |
|---|---|
| Report date: | 6-7-1121 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 2782013001R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 3 was defueled to support its 19th Refueling Outage (P3R19) when the event was discovered on 10/01/13 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) (EIIS:
RV) and a Safety Valve (SV)(EIIS: RV) removed during the 19th Unit 3 Refueling Outage. There were no other structures, systems or components out of service that contributed to this event.
Description of the Event
In accordance with Technical Specification (TS) Surveillance Requirement 3.4.3.1 and ASME Refueling Outage and were sent to an off-site laboratory for as-found testing and routine refurbishment. On 10/01/13, based on laboratory results, Site Engineering personnel determined that setpoint deficiencies existed with four SRVs and one SV that were in place during the 19th Unit 3 operating cycle. The four SRVs and one SV were determined to have their as-found setpoints outside of the TS allowable ± 1% tolerance. All relief valves were within the ASME Code allowable ± 3% tolerance. The five valves' as-found setpoints were as follows:
Nominal Required TS As-Found % Outside of TS Type ID S/N Setpoint Setpoint (psig) Setpoint (psig) Nominal Setpoint (psig) SRV 71B 179 1155 1143 - 1167 1121 -2.94% SRV 71D 85 1135 1124-1146 1149 +1.23% SRV 71G 77 1145 1134 - 1156 1127 -1.57% SRV 71K 22 1155 1143 - 1167 1137 -1.58% SV 70A BL-1103 1260 1247 - 1273 1275 +1.19% operating cycle.
Three of the four SRVs (71B, 71G and 71K) 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. Current relief valve design characteristics are challenged by a setpoint tolerance of ±1% for the given application over a two year cycle.
Any additional causes of the event identified during valve refurbishment will be evaluated and documented 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 installed SRVs / SVs be operable during operational Modes 1, 2, and 3. Contrary to this requirement, four 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 — Four 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 (EIIS:
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 relief valves installed on the four Main Steam (ENS: 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 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.
NRC FORM 7.46A (10-2010) I NRC FORM 366A LICENSEE EVENT REPORT (LER) U.S. NUCLEAR REGULATORY COMMISSION (10-2010)
CONTINUATION SHEET
1. FACIUTY NAME 2. DOCKET 6. LER NUMBER 3. PAGE 13 - 001 - 00 Analysis of the Event, continued TS Limiting Condition for Operation 3.4.3 requires any 11 of the 13 total SRVs / SVs to be operable. Operability is based on verifying the safety function lift setpoints of the valves to be within +/-1% of the nominal setpoint as specified in TS surveillance requirement 3.4.3.1. The current safety analysis for overpressure protection is based on a lift setpoint 3% above the nominal setpoint. Since there were no as-found results greater than 3% above the nominal setpoint, the P3R19 test results are bounded by the current analysis and there are no impacts on any safety analysis.
Three of the four SRVs (71B, 71G and 71K) were also Automatic Depressurization system (ADS) valves. The ADS reduces the reactor pressure in the event of certain accident conditions. If needed, the ADS function for the SRVs is actuated automatically at lower than the setpoint pressure and is independent of the relief pressure setpoint. As a result, the setpoint drift had no impact on the ADS function of the valves.
During the Unit 3 Cycle 19 operations, there were no plant transients that required automatic or manual SRV / SV operation.
The event is not considered to be risk significant.
Corrective Actions
operating cycle.
A TS change request to revise the SRV / SV set point tolerance to ±3% was submitted to the NRC in June 2013. This change has been recommended by the Boiling Water Reactors Owners Group (BWROG), accepted by the NRC, and implemented by a majority of other BWRs in the US.
Other actions will be pursued, as necessary, to address causes determined in accordance with the site Corrective Action Program.
Previous Similar Occurrences There were five previous LERs identified involving SRVs / SVs exceeding their Technical Specification ± 1% setpoint requirement. LER 2-12-001 reported six SRVs and one SV having their as-found setpoints in excess of the TS allowable ±1% tolerance. LER 2-10-003 reported two SRVs and one SV having their as-found setpoints in excess of the TS allowable ±1% tolerance. LER 3-07-001 reported two SRVs and one SV having their as-found setpoints in excess of the TS allowable ±1% tolerance. LER 2-06-002 reported one SV having its as-found setpoints in excess of the TS allowable ±1% tolerance. LER 3-05-004 reported a situation NRC FORM 1643A (10 20101 t FACILITY NAME 2. DOCKET 6. LER NUMBER 3. PAGE 13 - 001 - 00 Previous Similar Occurrences. continued involving four SRVs having their as-found setpoints in excess of the TS allowable *1% tolerance.
The previous SRV / SV as-found setpoints were all within the t3% ASME code allowable setpoint tolerance except for one SV with a setpoint 3.41% high, as documented in LER 2-12- 001. 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 2-12-001 to revise the TS to change the SRV/SV tolerance from *1% to ±3% is not yet complete. The TS change request is expected to be approved and implemented in 2014.