05000483/FIN-2010002-03
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Finding | |
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| Title | Failure to Maintain an Adequate Ultimate Heat Sink Thermal Performance Analysis |
| Description | The NRC identified a noncited violation of 10 CFR Part 50, Appendix B, Criterion III, Design Control, after AmerenUE failed to provide adequate design control measures for verifying the adequacy of the ultimate heat sink thermal performance analysis evaluating the impact of heat rejected during a large break loss of coolant accident. The thermal performance analysis, most recently revised in 2007, did not account for a potential single active failure of each trains motor-operated valve designed to redirect the essential service water return flow up and over the tower fill material. With further analysis the licensee determined that a compensatory measure implementing a more restrictive initial operating range based on pond volume and initial temperature would ensure that the ultimate heat sink pond will not exceed its maximum temperature of 92.3 degrees Fahrenheit during a design basis accident. Corrective actions were being developed using Callaway Action Request 201001813. This finding was determined to be greater than minor because it impacted the Mitigating Systems Cornerstone attribute of design control and affected the cornerstone objective to ensure the availability, reliability, and capability of systems that respond to initiating events to prevent undesirable consequences. A resident inspector performed the initial significance determination for the inoperable essential service water system, under certain conditions, using the NRC Inspection Manual 0609, Attachment 0609.04, Phase 1 Initial Screening and Characterization of Findings. The finding screened to a Phase 2 significance determination because it involved the potential inoperability of both trains of essential service water for greater than the technical specification allowed outage time. A Region IV senior reactor analyst performed a Phase 2 significance determination and found that the finding was potentially greater than green. The senior reactor analyst then performed a bounding Phase 3 significance determination and found the finding to be of very low safety significance (Green). The dominant core damage sequences included a medium break loss of coolant accident concurrent with the failure of essential service water system cooling tower bypass valves. The finding was mitigated because the motor operated valves remained functional throughout the year, which minimized the frequencies for the scenarios of interest. This finding was determined to not have a crosscutting aspect as the calculation of record was not reflective of current licensee performance |
| Site: | Callaway  |
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| Report | IR 05000483/2010002 Section 1R15 |
| Date counted | Mar 31, 2010 (2010Q1) |
| Type: | NCV: Green |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.15 |
| Inspectors (proximate) | D Dumbacher P Elkmann G Replogle G Miller J Groom |
| INPO aspect | |
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Finding - Callaway - IR 05000483/2010002 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Callaway) @ 2010Q1
Self-Identified List (Callaway)
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