05000461/FIN-2014007-01
Finding | |
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| Title | Interpretation of Requirements for Multiple Spurious Operations |
| Description | Based on discussions with the licensee, the inspectors identified several differences in interpretation of requirements between the inspectors and the licensee with respect to the requirements for addressing multiple spurious operations (MSOs). Requirement for Addressing Multiple Spurious Operations: The licensee expressed the belief that addressing MSOs was a voluntary effort on their part versus a requirement. Although the licensee had expended resources to address MSOs, the licensee had not updated their licensing basis documents, such as their SSD analysis, to reflect the procedure changes and modifications implemented to meet the intent of Nuclear Energy Institute (NEI) 00-01, Guidance for Post-Fire Safe Shutdown Circuit Analysis, Revision 2.
Applicability of Appendix R to MSOs: The licensee presented the view that the references to hot shorts (plural) in 10 CFR Part 50, Appendix R, Sections III.G and III.L, were only in sections of Appendix R, which pertained to the SSD train, i.e., the train to be free of fire damage. The inspectors noted that the sections with the references to hot shorts (plural) also included associated non-safety circuits that could prevent operation or cause mal-operation of systems necessary to achieve and maintain hot shutdown. As such, the inspectors considered MSOs as required to be addressed. Licensing Basis Applicability for MSOs: The inspectors noted that although Clinton Power Station is a post-1979 plant, the licensee committed to meeting Appendix R or providing equivalent protection as discussed in Section 9.5.8 of NUREG-0853, Supplement 1. In addition, Section 9.5.1 of the Updated Safety Analysis Report (USAR) noted that the licensee committed to meet Section III.G of 10 CFR Part 50, Appendix R with exceptions identified in their SSD analysis. Except for two sets of redundant valves in series, the licensee did not take any exceptions to Appendix R with respect to MSOs. The licensee presented the view that no general exceptions to MSOs were taken at the time of licensing because the common understanding was MSOs were not a consideration except as identified in Generic Letter 81-12, Fire Protection Rule for high-low pressure interfaces. Number of MSOs to be evaluated: The licensee performed evaluation Engineering Change (EC) 383786, MSO Scenario 5a Additional Components Load onto Credited EDG, revision 1, to address emergency diesel generator (EDG) loading. Although the licensee evaluated 4 kiloVolt loads, the licensee chose not to evaluate 480 Volt (V) loads. The licensee cited NEI 00-01, Section 4.4.3.4, as a basis for excluding 480V loads from their review. In discussions with the licensee, the inspectors identified two interpretation issues as discussed below. The inspectors requested the licensee to perform a qualitative analysis to gauge the significance of excluding the 480V loads. In response, the licensee reviewed 480V loads greater than 30 horsepower (HP) which had not already been accounted for in the load profile. Seven such additional loads were identified which totaled 300 HP. The potential 300 HP in additional loads was within the margin for the peak ratings of the EDGs. The licensee also noted that the load profile used reflected loss-of-offsite power (LOOP) combined with loss-of-coolant accident (LOCA) loads which was a more demanding load profile than LOOP only loads which would be expected in the event of a fire. With respect to the NEI 00-01 guidance, the interpretation issues were: Extent of Endorsement of NEI 00-01 Chapter 4: Regulatory Guide 1.189, Fire Protection for Nuclear Power Plants, Revision 2, states that The approach outlined in Chapter 4 of NEI 00-01, which relies on the Expert Panel Process and the Generic List of Multiple Spurious Operations contained in Appendix G to that document, provides an acceptable methodology for the identification of multiple spurious actuations that may affect safe-shutdown success path SSCs. The inspectors view was that the endorsement was limited to use of the expert panel process and the list of MSOs in Appendix G of NEI 00-01 for guidance. The licensees view was that the entire chapter had been endorsed by the NRC as the NRC had not taken any exceptions. Limiting Analysis of Multiple Spurious Operations to Four Components: In both Section 3.5.1.2 and Section 4.4.3.4, NEI 00-01 states: ... if the combined MSOs involve more than a total of four components or if the MSO scenario requires consideration of sequentially selected cable faults of a prescribed type, at a prescribed time, in a prescribed sequence in order for the postulated MSO combination to occur, then this is considered to be beyond the required design basis for MSOs. The inspectors considered the statements made with respect to limiting consideration of MSOs to four components to be in the context of considering MSOs from a combination of multiple MSO scenarios. The inspectors view was that the limitation of the number of MSOs to four components was not applicable within a single scenario. The licensees point of view was that it was acceptable to limit the review of MSOs to a maximum of four components within a single MSO scenario as well as combinations of MSO scenarios. The inspectors were concerned because the limitation of four components was an arbitrary number of components with no technical basis to support the number four. Excluding review of more than four components could result in failing to address adverse component actuation scenarios which could compromise the SSD of a plant during a fire. Determination of SSD Path Components: High pressure core spray (HPCS) was credited for inventory control in the event of a fire in the west portion of containment. Section III.L of Appendix R to 10 CFR Part 50 and Section 5.1 of Regulatory Guide 1.189, Revision 2, identified the reactor coolant make-up function (i.e., inventory control) as one of the functions necessary to meet post-fire safe-shutdown performance goals. Section 3.1 of NEI 00-01, Revision 2, also identified inventory control as a function required for post-fire safe shutdown. As such, the HPCS system was a system required for hot shutdown (sometimes referred to as a Green Box system) versus a system characterized as important to safety (i.e., an Orange Box system). However, Section 3.2.2 of USAR, Appendix F, identified that cable damage due to a fire in the west portion of containment could cause spurious actuation of HPCS due to impacts upon the HPCS initiation logic. In the event of inadvertent HPCS operation, operators would be directed by procedure to place the HPCS pump control switch in the stop position to prevent reactor vessel overfill. Placing the HPCS pump control switch in the stop position would prevent automatic initiation of the HPCS system in addition to preventing spurious operation. Manual operation of HPCS from the control room would be required to maintain inventory control. The use of manual actions would normally be considered acceptable for a system characterized as important to safe shutdown (i.e., Orange Box) but not acceptable for a system required for hot shutdown (i.e., Green Box). The inspectors considered crediting the placement of the pump control switch in the off position to be operating outside the normal functioning of the system and to not represent a train free of fire damage. Although the inspectors acknowledged that the automatic feature of HPCS may not explicitly be needed to provide inventory control, the inspectors questioned why the automatic feature was not characterized as a required for hot shutdown component (i.e., a Green Box component) and protected accordingly. The licensees position was that only manual operation of the pump was credited for safe shutdown and automatic operation of the pump was unnecessary. The licenseenoted that Section 3.3.1.1.4.1 of NEI 00-01 stated The automatic ignition logics for the credited post-fire safe shutdown systems are generally not required to support safe shutdown. Typically, each system can be controlled manually by operator actuation in the main control room or emergency control station. While this statement is true, in general, and certainly applicable for important to safe shutdown functions, it does not address the adequate protection for functions of a required for safe shutdown system that do not manually operate the system, but do adversely affect its safe shutdown function. These interpretation issues are considered an unresolved item (URI) pending furtherconsideration of the above interpretations. (URI 05000461/2014007-01, Interpretation of Requirements for Multiple Spurious Operations). |
| Site: | Clinton  |
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| Report | IR 05000461/2014007 Section 1R05 |
| Date counted | Mar 31, 2014 (2014Q1) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.05 |
| Inspectors (proximate) | D Oliver R Daley R Langstaff R Wintera Shaikhd Szwarc J Corujo-Sandin J Robbins R Daley |
| INPO aspect | |
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Finding - Clinton - IR 05000461/2014007 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Clinton) @ 2014Q1
Self-Identified List (Clinton)
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