05000528/FIN-2011005-04
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Finding | |
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| Title | Assumption that Low Pressure Injection Pump fails to trip on a Recirculation Actuation Signal not Included in Analysis. |
| Description | During a TI 2515/177 inspection, inspectors reviewed the licensees analysis that determined the required refueling water tank transfer volume after a recirculation actuation signal. Inspectors asked why the licensee had not analyzed for the failure of a low pressure safety injection (LPSI) pump to trip off at a recirculation actuation signal (RAS). Inspectors were concerned that the failure of a LPSI pump to trip off at a RAS could potentially result in a greater than previously calculated drain down rate of the refueling water tank; therefore, a greater transfer volume would be required to prevent air entrainment in the emergency core cooling system. The licensee provided the inspectors a license amendment request, dated November 30, 2009, which, among other changes, discusses the basis for not evaluating the single failure of a LPSI pump to trip off at a RAS. The license amendment request documents that the subject single failure is bounded by the previously analyzed single failure (failure of an engineered safety features train to realign to the containment sump at a RAS) for the following reasons: 1. The emergency operating procedures, for loss-of-coolant accident recovery, direct the operators early in the event, to stop one of the redundant containment spray pumps; thereby maintaining containment pressure high enough, but within limits, to significantly reduce the range of loss-of-coolant accident break sizes where air entrainment remains a potential concern. 2. The failure of a LPSI pump to trip off on a RAS, within the limited range of break sizes where air entrainment is a concern, is considered to have a low probability of occurrence. 3. All of the operating crews tested at the licensees simulator demonstrated that initiation of refueling water tank discharge valve closure could be completed even within the reduced time that would be available if the refueling water tank pump down rate included the LPSI pump operating at its maximum flow rate. 4. Per the emergency operating procedures, the first step after a RAS is to ensure that the LPSI pumps are stopped. Inspectors informed the licensee that the basis provided in the license amendment request may not be adequate to satisfy the requirements of 10 CFR Part 50, Appendix B, Criterion III, Design Control, which states that design control measures shall provide for verifying or checking the adequacy of design, such as by the performance of design reviews, by the use of alternate or simplified calculational methods, or by the performance of a suitable testing program. In compliance with 10 CFR Part 50, Appendix A, Criterion 35, Emergency Core Cooling, Section 3.1.31 of the licensees updated final safety analysis report states The system [safety injection system] design includes provisions to assure that the required safety functions are accomplished with either onsite or offsite electrical power system operation, assuming a single failure (qualified as described below) of any component. Inspectors informed the licensee of the following, with respect to the basis for not performing the analysis: 5. The licensees assertions that containment pressure would be maintained high enough to reduce the range of loss-of coolant accident break sizes where air entrainment is a concern, that the task of closing the refueling water tank discharge valves could be completed more quickly if the refueling water tank pump down rate included the operation of one LPSI pump, and that the first step in the emergency operating procedures after a RAS is to ensure that the LPSI pumps are stopped are all qualitative statements and do not verify that the refueling water tank would not be drained down further than previously analyzed. 6. The deterministic requirements of Criterion III, to verify the adequacy of design, assuming a potentially more limiting single failure than previously analyzed, cannot be met with a probabilistic approach. The licensee provided inspectors with the safety evaluation report issued by the Office of Nuclear Reactor Regulation (dated November 24, 2010) that approved the subject license amendment request. The licensee told inspectors that because the Office of Nuclear Reactor Regulation had approved of the license amendment request, without taking exception to the licensees basis for not analyzing for the subject potentially more limiting single failure, they were in compliance with regulatory requirements. Inspectors were concerned that by not performing the single failure analysis, the licensee did not meet the requirements of Criterion III. Inspectors contacted a representative in the Office of Nuclear Reactor Regulation to obtain clarification on the intent of the safety evaluation approval, but the guidance received during the on-site portion of the inspection was inconclusive. Because more information is necessary to resolve this issue, it is considered an unresolved item pending further NRC review. Inspectors concluded that further discussions with the Office of Nuclear Reactor Regulation were required to determine whether or not the licensee was required to perform the subject single failure analysis and whether the failure to perform the analysis constitutes a violation of NRC requirements. |
| Site: | Palo Verde  |
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| Report | IR 05000528/2011005 Section 4OA5 |
| Date counted | Dec 31, 2011 (2011Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | |
| Inspectors (proximate) | N Greene D You T Skaggs -Ryan L Ricketson R Lantz M Brown M Davis B Parks M Baquera I Anchondo D Reinertl Ricketson G Guerra R Lantz M Brown B Baca D Allen J Melfi B Parks A Fairbanks E Uribe M Baquera D Reinert S Hedger |
| INPO aspect | |
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Finding - Palo Verde - IR 05000528/2011005 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Palo Verde) @ 2011Q4
Self-Identified List (Palo Verde)
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