05000282/LER-2009-001
| Prairie Island Nuclear Generating Plant | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 2822009001R00 - NRC Website | |
On January 14, 2009, during a review of Prairie Island Nuclear Generating Plant's (PINGP) safe shutdown compliance assessment, it was discovered that the loss of the instrument air' (IA) system due to a fire in either fire area 31 or 32 had not been fully analyzed with respect to the clarifications made in Regulatory Issue Summary (RIS) 2006-10, Regulatory Expectations with Appendix R Paragraph III.G.2 Operator Manual Actions. Upon a loss of IA, the safeguards chilled water system is supported by a safety related backup compressed air system that relies on the use of manual operator actions to ensure that an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> air supply is always available. However, RIS 2006-10 provides clarification that operator manual actions are not compliant with the intent of 10 CFR 50 Appendix R Paragraph III.G.2.
EVENT ANALYSIS
Fire area 31 contains the two train B auxiliary feedwater2 (AFW) pumps and one IA compressor whereas fire area 32 contains the two train A AFW pumps and two IA compressors. A fire in either fire area 31 or 32 would only affect one train of AFW, but could potentially cause the loss of the IA system. Engineering calculation GEN-PI-052, Revision 3B credits the IA system with providing compressed air to the pressurizer power operated relief valves (PORVs), steam generator PORVs, and the safeguards chilled water system. Upon a loss of IA, the pressurizer and steam generator PORVs fail in the desired configuration (closed) for hot shutdown.
The safeguards chillers on the other hand, require compressed air to perform their safety function in the event of a fire such that hot shutdown can be accomplished as required by 10 CFR 50, Appendix R. The IA system is the primary source of that compressed air and is necessary to maintain operability of the safeguards chillers. The PINGP Appendix R compliance strategy for a fire in either fire area 31 or 32 considered that the IA compressors could be damaged due to fire, but did not address the effect on the chilled water system. The safeguards chiller units rely on two safety related backup compressed air cylinders that are installed to provide at least 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> of compressed air. PINGP operators monitor the air pressure of the compressed air cylinders and replace them if the combined pressures drop below what is required to provide a 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> air supply.
10 CFR 50 Appendix R, Paragraph III.G.2 requires one train of equipment necessary to achieve and maintain hot shutdown be unaffected by a fire. It is required to maintain hot shutdown until repairs to achieve and maintain cold shutdown are completed within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Because the operator manual actions to replace the compressed air cylinders would need to be performed within that 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> period, it is not in compliance with 10 CFR 50 Appendix R as clarified by RIS 2006-10. Accordingly, this is being reported as an unanalyzed condition as required by 10 CFR 50.73(a)(2)(ii)(B) because the IA system — required for the safeguards chillers — lacks a fire barrier to ensure a compressed air supply is provided to the chillers in the event of a fire. This condition was previously reported to the NRC as an unanalyzed condition in accordance with 10 CFR 50.72(b)(3)(ii)(B) on January 14, 2009.
ENS Component Identifier: BA ' EllS Component Identifier: LE 2 U.S. NUCLEAR REGULATORY COMMISSIONNRC FORM 366A LICENSEE EVENT REPORT (LER)(9-2007)
CONTINUATION SHEET
SAFETY SIGNIFICANCE
In the event of a fire in one of the affected fire areas causing a loss of the IA system, the manual operator actions — while not compliant with Appendix R — would have allowed the safe shutdown of either unit. Therefore, this event did not impact the health and safety of the public, and the safety significance of this event is considered minimal. Due to no actual loss of safety function occurring as a result of the as-found condition, this event is not reportable per 10 CFR 50.73(a)(2)(v).
CAUSE
The cause of this event is the result of misinterpretation of the regulations governing licensees' safe shutdown capability. While Appendix R, paragraph III.G.2 does not list operator manual actions as a means of ensuring that one of the redundant trains is free of fire damage, it does not expressly prohibit the use of operator manual actions either. In 2006 the NRC's issuance of RIS 2006-10, Regulatory Expectations with Appendix R Paragraph III.G.2 Operator Manual Actions, clarified the intent of Paragraph III.G.2 of Appendix R as not allowing operator manual actions as a means to ensure that one of the redundant trains is free of fire damage.
PINGP made an initial event notification for non-compliant operator manual actions in response to RIS 2006-10 on June 4th, 2007.
CORRECTIVE ACTIONS
The PINGP fire protection program requires an hourly fire patrol for all inoperable fire barriers or an alternate compensatory measure that is more effective than an hourly fire patrol. If utilized as a compensatory measure, operator manual actions can provide a more effective compensatory measure than hourly fire patrols. Operator manual actions are allowed to be used as compensatory measures provided the stipulated actions are feasible and reliable. While not acceptable as a compliance strategy for Appendix R, manual operator actions currently in place are preferable, as an alternate compensatory measure, to the hourly fire patrols that are stipulated by the PINGP fire protection program.
PINGP is also transitioning to NFPA 805, Performance-Based Standard for Fire Protection for Light Water Reactor Electric Generating Plants, which allows the licensee to quantify the fire area risk provided it is realistic and accurate. Under NFPA 805 the use of operator actions is one of the factors that can be considered to lower the overall risk presented by a fire in that area. PINGP's licensee amendment request (LAR) to implement NFPA 805 — expected to be submitted in the fourth quarter of 2010 — will describe how PINGP intends to meet the requirements for the new fire protection program.
unanalyzed condition in fire area 29 due to noncompliance with Appendix R in the use of operator manual actions. An extent of condition review at that time identified a number of additional fire areas that were non-compliant. The lack of fire barriers in fire areas 31 and 32 was not identified at that time because it was not included in the fire protection or Appendix R programs. The compressed air cylinders were installed to meet design basis requirements, not specifically for fire protection requirements.