05000369/FIN-2017003-01
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Finding | |
|---|---|
| Title | Technical Specification (TS) Required Shutdown Due to Reactor Coolant System (RCS) Leakage |
| Description | Inspection Scope On February 23, 2017, McGuire Unit 2 was shut down, as required by Technical Specification (TS) 3.4.13, due to RCS pressure boundary leakage on a Unit 2 safety 12 injection (NI) pipe upstream of the connection to D reactor coolant system (NC) cold leg. The licensee determined that the preliminary cause of the NI pipe leak was thermal fatigue. The inspectors reviewed the LERs for accuracy and completeness and reviewed the associated corrective actions (NCR 2102868) to determine whether they were appropriate . The inspectors also reviewed the LERs and NCRs to identify any licensee performance deficiencies associated with the issue. Licensee Event Reports 05000370/2016- 001 -00 and -01 are closed. Documents reviewed are listed in the attachment. b. Findings Description : On February 20, 2017, the McGuire Unit 2 RCS unidentified leakage increased from 0.01 gallons per minute (gpm) to 0.09 gpm. Concurrently, containment particulate counts increased from 500 to 30,000 counts per minute (cpm) and humidity increased from 8 percent to 12 percent. The licensee also determined unidentified RCS leakage increased to 0.255 gpm on February 22 (dayshift) and 0.303 gpm on February 23 (nightshift). On February 23, 2017, at 1922 hours0.0222 days <br />0.534 hours <br />0.00318 weeks <br />7.31321e-4 months <br />, operators commenced a Unit 2 shutdown upon positive identification of pressure boundary leakage on the NI pipe upstream of the connection to D NC cold leg. Following shutdown, the licensee also discovered a small pinhole pressure boundary leak on the body of valve 2NC -30, the pressurizer spray bypass valve. The leakage from 2NC -30 was a negligible contributor to the total unidentified leakage measured during unit operation. The licensee determined that the cause of the NI pipe leak was thermal fatigue damage caused by NC cross -loop flows. The cause of the 2NC -30 valve leak was a casting flaw attributed to a combination of defects during the manufacturing process that resulted in a through wall pinhole leak in the valve body. The inspectors reviewed the licensees analysis and determined that the licensee had appropriately evaluated the issues. Since the causes were not reasonably within the licensees ability to foresee and correct, the inspectors concluded that there was no performance deficiency associated with the issue. For the purpose of closing the associated licensee event reports and categorizing the associated technical specification violation, a detailed risk evaluation of the RCS pressure boundary leakage condition was performed by a regional senior reactor analyst using the NRC McGuire SPAR probabilistic risk assessment model. The evaluation was performed in accordance with NRC Inspection Manual Chapter 0609 Appendix A. The exposure period was 114 hours0.00132 days <br />0.0317 hours <br />1.884921e-4 weeks <br />4.3377e-5 months <br /> and conditional rupture probability values were taken from EPRI report TR111880. The detailed risk evaluation determined that the condition represented an increase in core damage frequency of <1.0E -6/year, a finding of very low safety significance. McGuire TS 3.4.13 limiting condition for operation (LCO) requires that RCS operational leakage shall be limited to No pressure boundary leakage when in Modes 1 through 4. Action Statement B of TS 3.4.13 requires the plant to be placed in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. The licensee entered Mode 3 on February 24, 2017 , at 0041 hours4.74537e-4 days <br />0.0114 hours <br />6.779101e-5 weeks <br />1.56005e-5 months <br /> and entered Mode 5 on February 24, 2017 , at 1721 hours0.0199 days <br />0.478 hours <br />0.00285 weeks <br />6.548405e-4 months <br />. The licensee made an event notification (EN) to the NRC on February 23, 2017, at 2201 hours0.0255 days <br />0.611 hours <br />0.00364 weeks <br />8.374805e-4 months <br /> (EN 52573) due to a shutdown of the plant required by TS. Enforcement: The McGuire TS 3.4.13 LCO requires that RCS operational leakage shall be limited to No pressure boundary leakage when in Modes 1 through 4. Contrary to the above, McGuire Unit 2 experienced RCS pressure boundary leakage while operating in Mode 1. Although a violation of the TS occurred, the violation was not attributable to 13 equipment failures that were avoidable by reasonable licensee quality assurance measures or management controls, therefore a performance deficiency was not identified. The inspectors utilized the Enforcement Policy examples of Section 6.1, and available risk -informed tools to assess the safety significance of the RCS pressure boundary leakage and related violation. Based on the fact that the leak rate was stable and within the capacity of the charging system and would not impact other systems used to mitigate a loss of coolant accident, the inspectors concluded the safety significance of the violation was very low and consistent with Severity Level IV. Additionally, the risk aspects were discussed and confirmed with a regional senior risk analyst. This issue was documented in the licensees corrective action program as NCR 2102868. The NRC exercised enforcement discretion in Enforcement Action (EA) -2017- 119, in accordance with Section 3.10 of the Enforcement Policy because the violation was not associated with a licensee performance deficiency. Specifically, the violation was not attributable to an equipment failure that was avoidable by reasonable licensee quality assurance measures or management controls and therefore inspectors concluded that there was no performance deficiency associated with the RCS boundary leakage. The violation will not be considered in the assessment process or the NRCs Action Matrix. |
| Site: | McGuire  |
|---|---|
| Report | IR 05000369/2017003 Section 4OA3 |
| Date counted | Sep 30, 2017 (2017Q3) |
| Type: | Violation: Green |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | A Hutto R Cureton J Reece C Scott M Toth F Ehrhardt |
| Violation of: | Technical Specification |
| INPO aspect | |
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