05000387/LER-2012-003
| Telephone Number (Include Area Code) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded |
| Initial Reporting | |
| ENS 47812 | 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded |
| 3872012003R01 - NRC Website | |
On April 6, 2012, during the Susquehanna Unit 1 17th Refueling and Inspection Outage (R10), it was determined that the as-found minimum pathway Secondary Containment Bypass Leakage (SCBL) Technical Specification (TS) limit was exceeded during the regularly scheduled Local Leak Rate Testing (LLRT). At the time the limit was exceeded, a LLRT was being performed on the Unit 1 'A' Feedwater (FW) Line Penetration X-9A. Of the three containment isolation valves in this FW line, two of the valves (141F010A and HV141F032A) failed to pressurize during testing. This required the leakage from valve 141818A, the remaining valve in the Unit 1 'A' FW line, to be used as the as-found minimum pathway leakage SCBL result. The leakage from the tested 141818A valve was determined to be 2,855 standard cubic centimeters per minute (sccm). When the 2,855 sccm leakage was added to the combined as-found minimum pathway SCBL calculation (which included 3,893 sccm carryover from 2010 from the Containment Spray penetration X-39B valves), it contributed to the total as-found minimum pathway leakage exceeding the TS limit of 7,079 sccm (15 scfh).
TS Surveillance Requirement 3.6.1.3.11 states, "Verify the combined leakage rate for all secondary containment bypass leakage paths is less than or equal to 15 scfh when pressurized to greater than or equal to Pa." In accordance with 10 CFR 50.72(b)(3)(ii)(A), on April 6, 2012, ENS notification (# 47812) was made to the NRC for a degraded or unanalyzed condition. This condition is also reportable under 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TSs because the total as-found minimum pathway SCBL leakage rate of 7,185 sccm exceeded the TS limit of 7,079 sccm.
CAUSE OF THE EVENT
Direct Cause:
The direct cause of the excessive leakage through the 141818A valve was due to a galled disc stud and minor seat wear. This excessive leakage, in combination with the carryover leakage from the containment spray penetration X-39A/B and X-17 valves (3,893 sccm) during the 2010 Unit 1 16th RIO, resulted in the TS SCBL limit being exceeded in 2012.
Root Causes:
Following initial evaluation of this event and subsequent submittal of the LER, a root cause analysis was performed.
The analysis identified the following root causes:
o Station Engineering management and supervision had not exercised technical authority over the Appendix J Program to prevent SCBL LLRT failures.
- The Leak Rate Test Program procedure did not establish "maintenance limits" for as-found and as-left SCBL LLRT test results for each valve.
1 The purpose of the primary containment isolation valves is to limit fission product release during and following postulated Design Basis Accidents. The SCBL TS value is established to limit the release of radioactive materials outside of secondary containment to ensure offsite and main control room doses remain within NRC regulatory limits. No event occurred during the SCBL testing or during any other plant condition over the past operating cycle that would have challenged the regulatory limits. As such, this event did not impact the health and safety of the public.
Potential Consequences Analysis has concluded that during a postulated design basis accident, the increase in dose related to the elevated SCBL leaks rate would not have exceeded NRC regulatory limits.
CORRECTIVE ACTIONS
Completed Actions
- Maintenance was performed on the Unit 1 'A' Feedwater Line Penetration X-9A valve 141818A. The disc stud was repaired and the soft seat was replaced. This reduced the as-left valve leakage from 2,855 sccm to 415 sccm.
- A modification was completed during the 2012 Unit 1 17R10 which replaced the containment isolation valves for Containment Spray penetrations X-39A/B and X-17, as SCBL barriers, with smaller isolation valves in the Condensate Transfer and Residual Heat Removal (RHR) to Liquid Radwaste lines. This modification reduced the Containment Spray penetration X-39B leakage input from 3,893 sccm to 415 sccm, gaining significant margin.
- The Conduct of Station Engineering procedure was revised to include the Technical Conscience obligation statement from INPO 10-005, Principles for Maintaining an Effective Technical Conscience.
- The Leakage Rate Testing Program procedure has been revised to establish administrative maintenance limits for as-found and as-left SCBL LLRT results for each valve. These administrative maintenance limits identify when as-found corrective maintenance needs to be performed as well as what as-left limit must be achieved prior to returning the valve back to service after maintenance.
Planned Corrective Actions
A Unit 2 modification to replace the containment isolation valves for Containment Spray penetrations X-39A/B and X-17 as SCBL barriers with smaller isolation valves in the Condensate Transfer and RHR to Liquid Radwaste lines is planned for the next Unit 2 RIO.
- With the Unit 1 modification to replace the containment isolation valves for containment spray complete as noted above (although not included in the as-found SCBL calculation for Unit 1 17R10), the next step is to address the performance of the feedwater check valves. Condition Reports are in the SSES corrective action program to address these valves which could have future impact on SCBL.
ADDITIONAL INFORMATION
Failed Component Information:
Component: 141818A; 24-inch Advanseal check valve Model: None Manufacturer: Anchor Darling Valve Co.
Previous Similar Events:
- LER 2010-001-00, Docket No. 387/ License No. NPF-14