05000275/FIN-2012003-05
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Finding | |
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| Title | Control Room Habitability Operability Issues |
| Description | Technical Specification 3.7.10, Control Room Ventilation System (CRVS), required the licensee to maintain two independent and redundant control room ventilation trains and the control room envelope operable. The specified safety function of each control room ventilation train, in conjunction with the control room envelope, was to maintain operator dose below 5 rem equivalent. Technical Specification 5.5.19, Control Room Envelope Habitability Program, and Surveillance Requirement 3.7.10.5 required the licensee to perform control room envelope in-leakage testing in accordance with Positions C.1 and C.2 of Regulatory Guide 1.197, Demonstrating Control Room Envelope Integrity at Nuclear Power Reactors. These positions required the in-leakage test to be performed in the most limiting configuration for operator dose, consistent with the plant design and licensing basis. In November 2011, the licensee completed testing in accordance with Surveillance Requirement 3.7.10.5. During the test, the licensee concluded that control room envelope in-leakage was greater than the in-leakage assumed in the licensing basis accident analysis. The licensee declared the control room envelope inoperable and applied Technical Specification 3.7.10, Actions B.1, B.2, and B.3. Action B.3 allowed continued reactor operation up to 90 days provided that the licensee implemented mitigating actions per Actions B.1 and B.2 to ensure control room envelope occupant exposures would not exceed limits. PG&E conducted additional in-leakage testing using alternate system alignments. The licensee observed that unfiltered in-leakage was reduced to an acceptable value in an alternate alignment with one control room ventilation system train plus one control room ventilation system booster fan from the opposite train in operation. The licensee subsequently established mitigating actions/compensatory measures to maintain a control room ventilation system booster fan from the opposite train available and declared the control room envelope operable. The inspectors were concerned that the licensees operability determination was inconsistent with NRC inspection guidance contained in Regulatory Issue Summary 2005-20, Operability Determinations & Functionality Assessments for Resolution of Degraded or Nonconforming Conditions Adverse to Quality or Safety. While the results from the alternate alignment in-leakage test demonstrated that control room occupant exposures would not exceed limits, satisfying the requirements for Technical Specification Action B.3, the system alignment for this testing did not appear to satisfy either Technical Specification 5.5.19 or Surveillance Requirement 3.7.10.5. These requirements were not satisfied because the testing was did not use the most limiting configuration for operator dose. Technical Specification Surveillance Requirement 3.0.1 stated that the failure to meet a surveillance requirement, whether the failure was experienced during the performance of the surveillance or between performances of the surveillance, was a failure to meet the Technical Specification Limiting Condition for Operation. On January 3, 2011, PG&E submitted Licensee Event Report (LER) 1-2011-008-00 Diablo Canyon Power Plant - Control Room Ventilation System Design Vulnerability. The licensee reported the failure of the control room envelope as an unanalyzed condition. However, the licensee did not report the failed surveillance test as a condition prohibited by technical specifications. Title 10 CFR 50.73 required the licensee to make a 60 day report to the NRC following discovery of a condition prohibited by technical specifications. These issues are considered unresolved pending NRC review of current and past control room habitability system operability, Unresolved Item: 05000275; 323/2012003-05 Control Room Habitability Operability Issues. |
| Site: | Diablo Canyon  |
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| Report | IR 05000275/2012003 Section 1R15 |
| Date counted | Jun 30, 2012 (2012Q2) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.15 |
| Inspectors (proximate) | L Ricketson M Peck L Willoughby N O 'Keefe N Greene N Makrisg Guerra P Elkmann L Willoughby N O 'Keefe T Hipschman G Warnick N Hernandez L Micewski D Yo |
| INPO aspect | |
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Finding - Diablo Canyon - IR 05000275/2012003 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Diablo Canyon) @ 2012Q2
Self-Identified List (Diablo Canyon)
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