05000461/FIN-2011003-03
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Finding | |
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| Title | Surveillance Testing of Control Room Ventilation System |
| Description | The inspectors initiated an Unresolved Item pending additional review and resolution of open questions to determine whether the licensee s VC system monthly operability surveillance test procedure contained the appropriate requirements and acceptance limits for intake filtered flow rate from applicable design documents and whether operators appropriately addressed the operability of VC Train A after identifying a degraded condition that could have affected the ability of the system to perform its safety function. The inspectors reviewed the licensee s performance of surveillance testing that was accomplished in accordance with CPS 9070.01, Control Room HVAC Air Filter Package Operability Test Run, Revision 26d. This surveillance test procedure was performed to satisfy TSSRs 3.7.3.1 and 3.7.3.2, which required the licensee to operate each VC subsystem with flow through the makeup filter Y 10 continuous hours with the heater operating and with flow through the recirculation filter for Y 15 minutes, respectively. The surveillance frequency is every 31 days. As described in the Bases for TS 3.7.3, the ability of the VC system to maintain the habitability of the Control Room envelope is an explicit assumption for the safety analyses presented in the UFSAR. The high radiation mode of the VC system is assumed to operate following a design basis accident. The VC system is designed to maintain a habitable environment in the Control Room envelope for a 30-day continuous occupancy after a design basis accident, without exceeding 5 Rem total effective dose equivalent (TEDE) as required by 10 CFR 50, Appendix A, Criterion 19. The UFSAR Chapter 15 accident analyses assumed that for a design basis LOCA, the VC system intake filtered flow rate is 3000 A 10% cubic feet per minute (cfm). During testing of VC Train A on April 1, 2011, an operator noted that the filtered make up flow was oscillating between 2300 and 2880 cfm; however, as stated in Step 8.1.2.h of the test procedure, flow should have been 2700 to 3300 cfm. The operator annotated the test procedure with a note stating that the flow was low and initiated AR 01196342 to have the condition evaluated and corrected. Operators reviewed the acceptance criteria in Section 9.1 of the test procedure and did not find any upper or lower limits for flow rate. Operators noted that the Control Room differential pressure remained positive with the degraded flow condition and, therefore, concluded that VC Train A remained operable and signed off the completed test procedure as satisfactory with no further evaluation. Operators did not request a formal operability evaluation from engineering even though the VC system has a required licensing basis function and the degraded condition could have affected the ability of the system to perform its safety function. During review of the completed surveillance test procedure and AR 01196342, the inspectors questioned: (1) whether VC Train A remained operable with intake filtered flow less than design, and (2) the absence of an appropriate quantitative acceptance criterion for filtered flow rate in the test procedure to assure that the system would be capable of fulfilling its design safety function. The inspectors noted that TSSRs 3.7.3.1 and 3.7.3.2 do not specify upper or lower limits for system intake filtered flow rate, nor do any other VC system TSSRs. Only the administrative program requirement for VC system filter testing in TS 5.5.7 specifies a 3000 cfm intake filtered flow rate, but this testing is performed much less frequently (i.e., every 2 years vice every month). The inspectors reviewed CPS 9866.01, VG/VC HEPA [High Efficiency Particulate Air] Filter Leak Test, Revision 26 and noted that this procedure for system filter testing contained appropriate filtered flow acceptance criteria. Because the UFSAR Chapter 15 LOCA analyses assumes that the VC system intake filtered flow rate is 3000 A 10%, the inspectors determined that system operability would be questionable with system flow not within these limits. For determining the radiological consequences of a design basis LOCA to Control Room operators from external radiation sources, Calculation C-002, Post LOCA Control Room Operator Dose from External Sources, Revision 2, assumes the intake filtered flow rate is at the upper limit of 3300 cfm. The higher value provides a maximum value for iodine buildup in the charcoal bed under normal conditions. For determining the radiological consequences of a design basis LOCA using the alternate source term methodology, Calculation C-020, Reanalysis of Loss of Coolant Accident (LOCA) Using the Alternate Source Term Methodology, Revision 3, assumes the intake filtered flow rate is 2700 cfm. Under this analysis, the lower the flow rate the higher the dose to Control Room operators since less filtered air is being provided to the Control Room envelope. Both of the above calculations support the accident analyses to ensure that post accident dose to Control Room occupants in the event of a LOCA would be less than 5 Rem TEDE. The licensee investigated the low flow condition two weeks later on April 15th and discovered that the VC Train A flow controller was not functioning properly. The flow controller was replaced with a new one and post-maintenance testing was completed satisfactorily. The licensee documented the flow controller problem in AR 012003343 and subsequently performed a past operability evaluation. The licensee s evaluation concluded that the system remained operable with the degraded flow condition because there was sufficient margin in the Control Room post-LOCA dose analysis. The inspectors reviewed the licensee s evaluation and concluded that the results were reasonable. In response to the inspectors questions, the licensee initiated AR 01207896 to review the absence of an appropriate quantitative acceptance criterion for filtered flow rate in the surveillance test procedure. In addition, the licensee initiated AR 01239007 to perform an apparent cause evaluation addressing the timeliness of the formal operability assessment and whether the absence of appropriate acceptance criteria in Section 9.1 of CPS 9070.01 influenced the decision by licensed operators to accept the results of the surveillance test and not request a formal operability evaluation from engineering upon discovery of the degraded condition during testing. At the end of this inspection period, the licensee had just entered this issue into its corrective action program to investigate the cause and to identify appropriate corrective actions. This issue is considered to be an Unresolved Item (URI 05000461/2011003-03, Surveillance Testing of Control Room Ventilation System) pending additional review and resolution of open questions to determine: (1) whether the surveillance test procedure contained the appropriate requirements and acceptance limits for VC system intake filtered flow rate from applicable design documents, and (2) whether operators appropriately addressed the operability of VC Train A after identifying a degraded condition that could have affected the ability of the system to perform its safety function. |
| Site: | Clinton  |
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| Report | IR 05000461/2011003 Section 1R22 |
| Date counted | Jun 30, 2011 (2011Q2) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.22 |
| Inspectors (proximate) | B Kemker D Lords J Cassidy J Draper M Ring R Langstaff S Bell S Mischke V Myerss Mischkea Dunlop B Kemker C Brown D Lords J Cassidy M Jones M Ring R Winter |
| INPO aspect | |
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Finding - Clinton - IR 05000461/2011003 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Clinton) @ 2011Q2
Self-Identified List (Clinton)
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