05000317/FIN-2011003-01
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Finding | |
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| Title | Pressure Boundary Leakage Caused by Primary Water Stress Corrosion Cracking |
| Description | On February 27,2011, while Unit 2 was in a refueling outage (Mode 6), Constellation identified (during a bare metal inspection) dry boric acid on pressurizer heater N3 outer sleeve to weld pad J-Groove weld location (not normally accessible by plant personnel during plant operation at power), indicating reactor coolant leakage. Constellation determined that this leakage constituted an RCS pressure boundary leak. Based on both visual inspection and chemical analysis performed during and after the discovery of boric acid at the N3 penetration, it was determined that the leak most likely existed during plant operation. Constellation performed destructive and non-destructive examinations at the weld. The evaluation concluded that the root cause of the crack was primary water stress corrosion cracking. As part of their corrective actions, in accordance with American Society of Mechanical Engineers (ASME) code, Constellation installed a welded plug at the N3 location. Following the repairs, Constellation conducted visual and surface examinations (dye penetrant testing) as well as pressure testing during Mode 3 at normal operating pressure and temperature, with satisfactory results. This LER reported that Calvert Cliffs had been in a condition prohibited by TS 3.4.13.A, which limits pressure boundary leakage during plant operation to zero. The issue is considered within the traditional enforcement process because there was no performance deficiency identified and IMC 0612, Appendix B, lssue Screening, directs disposition of this issue in accordance with the Enforcement Policy. The inspectors used the Enforcement Policy, Section 6.1, Reactor Operations, to evaluate the significance of this violation. The inspectors concluded that the violation was more than minor and best characlerized as Severity Level lV (very low safety significance) because it is similar to Enforcement Policy, Section 6.1, Example d.1. The inspectors conducted an initial significance determination screening using IMC 0609 Attachment 4, Phase 1 - Initial Screening and Characterization of Findings. Using the Initiating Events cornerstone screening criteria in Table 4a, and assuming worst case degradation the inspector concluded a Phase 3 risk evaluation was warranted. A Region I Senior Reactor Analyst performed a Phase 3 qualitative assessment of the observed RCS leakage condition and concluded the risk to core damage was very low (Green). The basis for this qualitative risk determination was that the observed leakage was minimal (quantified as a few drops per minute), well within the capability of the charging system, and the licensee's analysis confirmed that the ASME Code allowable stress limits for the affected penetration were within all design specifications. In addition, the design capability of RCS boundaries and associated piping systems are premised on the leak before break construction and fabrication methodologies and credits periodic in-service inspections to identify and correct potential or actual RCS boundary defects prior to further degradation or catastrophic failure. This issue is of very low safety significance (Green) and was appropriately identified and corrected per the licensee's ongoing inservice inspection program. Because this issue was of very low safety significance and it was not reasonable for Constellation to have foreseen and prevented the leakage, absent a performance deficiency, the NRC has decided to exercise enforcement discretion in accordance with Section 3, Use of Enforcement Discretion, of the NRC Enforcement Policy and has refrained from issuing enforcement action for the violation of TS (EA-11-164). Further, because Constellation's actions did not contribute to this violation, it will not be considered in the assessment process or the NRC's Action Matrix. |
| Site: | Calvert Cliffs  |
|---|---|
| Report | IR 05000317/2011003 Section 4OA3 |
| Date counted | Jun 30, 2011 (2011Q2) |
| Type: | Violation: Green |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | M Orr N Perry R Rolph S Ibarrola S Kennedy E Burket G Dentel K Cronk M Jennerich |
| INPO aspect | |
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Finding - Calvert Cliffs - IR 05000317/2011003 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Calvert Cliffs) @ 2011Q2
Self-Identified List (Calvert Cliffs)
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