05000282/FIN-2015002-05
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Finding | |
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Title | Licensee-Identified Violation |
Description | Title 10 CFR Part 50, Appendix R, requires, in part, that safe shutdown equipment and systems for each fire area shall be known to be isolated from associated non-safety circuits in the fire area so that hot shorts, open circuits, or shorts to ground in the circuit will not prevent operation of the safe shutdown equipment. The isolation of these associated circuits from the safe shutdown equipment shall be such that a postulated fire involving the associated circuits will not prevent safe shutdown. On August 8, 2014, the licensee identified an Appendix R non-compliance in that the emergency bearing oil pumps were not properly isolated (fuse protected) from safe shutdown equipment, in accordance with 10 CFR Part 50, Appendix R. As a result, an overload condition in the emergency bearing oil pump circuitry could result in a fire that damages other cabling and prevents the licensee from achieving safe shutdown following a fire. The inspectors reviewed this issue and determined that the improper fuse protection was part of the initial plant design. Specifically, the design philosophy in the late 1960s was to maximize the reliability and availability of the emergency bearing oil pumps to protect the main turbines. The potential impact that this design philosophy had on fire protection of safe shutdown equipment was also not recognized as 10 CFR 50, Appendix R, did not exist until the early 1980s. The licensee documented this issue in CAP 1442220. The licensee also implemented hourly fire watches in the impacted fire areas to ensure that any potential fires were identified prior to it impacting safe shutdown capability. Section 9.1 of the NRC Enforcement Policy allows the NRC to exercise enforcement discretion for certain fire protection related non-compliances identified as a result of a licensees transition to the new risk-informed, performance-based fire protection approach included in 10 CFR 50.48(c) and for certain existing non-compliances that reasonably may be resolved by compliance with 10 CFR 50.48(c) as long as certain criteria are met. This risk-informed, performance-based approach is referred to as NFPA 805, Performance-Based Standard for Fire Protection for Light Water Reactor Electric Generating Plants. In 2005, the licensee submitted a letter of intent to transition to 10 CFR 50.48(c). This licensee submitted a license amendment request to the NRC for review and approval in September 2012. The inspectors reviewed the remaining criteria included in Section 9.1 of the NRC Enforcement Policy and concluded that the licensee had met the criteria. Specifically, the licensee entered the noncompliance into the CAP as CAP 1442220, implemented compensatory fire watches in the area and the noncompliance was not willful. In addition, this issue would not have been identified under normal surveillance or quality assurance activities. Lastly, a regional SRA reviewed an analysis performed by the licensee to show that the risk of the condition was less than high safety significance (i.e., less than red). The licensee identified the cable routing for the six cables of concern (three for each unit) and the fire scenarios where an initial fire could cause a secondary fire in a separate fire area due to the inadequate fusing of the emergency bearing oil pumps. The licensees evaluation assumed that a secondary fire would be limited to the cable tray that contained the faulted cable and would not propagate beyond that tray. The licensee cited NFPA 805 FAQ13005, Close-out of Fire Probabilistic Risk Assessment Frequently Asked Question 13005 on Cable Fires Special Cases: Self-Ignited and Caused by Welding and Cutting, that provided similar guidance for self-ignited cable fires as the basis for the assumption. The SRA consulted with NRC Headquarters staff and concluded that the FAQ guidance did not specifically apply to cable fires resulting from inadequate fusing. However, there currently is no available method for estimating the likelihood and extent of a secondary cable fire caused by inadequate fusing. Given the lack of an acceptable method, the SRA also performed a walk down of the control cable routing to observe the potential for secondary fires to impact additional targets. In all cases, there did not appear to be a significant potential for a secondary fire to damage additional targets beyond the cable tray of interest. The licensee provided other reasons why secondary fire damage would be limited, such as existing fire detection and suppression systems and the fact that the cables are thermoset rather than thermoplastic material. The SRA determined that the likelihood of significant secondary fire spread for these particular scenarios was low. The licensee also determined that some scenarios did not impact any unique targets. For those scenarios, there was no change in risk due to the inadequate fusing. For scenarios that did have the potential for additional target damage from a secondary fire, the licensee calculated the change in risk of this condition. The change in risk was determined to be less than 1E4/yr. The dominant fire scenarios involved a fire starting in the fire area 18 with a secondary fire propagating to either Fire Area 58, 31, or 32. Because each of the criteria listed in Section 9.1 of the NRC Enforcement Policy was met, the NRC concluded that enforcement discretion should be granted for this issue. No enforcement action will be documented unless the licensee fails to address this non-compliance after completing their transition activities. |
Site: | Prairie Island |
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Report | IR 05000282/2015002 Section 4OA7 |
Date counted | Jun 30, 2015 (2015Q2) |
Type: | NCV: Green |
cornerstone | Mitigating Systems |
Identified by: | Licensee-identified |
Inspection Procedure: | |
Inspectors (proximate) | A Shaikh J Corujo-Sandin K Riemer K Stoedter L Haeg L Kozak M Jeffers M Phalen N Feliz-Adomo P Laflamme |
Violation of: | 10 CFR 50.48 10 CFR 50 Appendix R |
INPO aspect | |
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Finding - Prairie Island - IR 05000282/2015002 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Prairie Island) @ 2015Q2
Self-Identified List (Prairie Island)
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