05000395/FIN-2012005-04
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Finding | |
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| Title | Failure to Consider the Risk Impact of Time to Core Boil with Reactor Vessel Upper Internals Installed and Cavity Level is Greater than Reactor Vessel Flange |
| Description | A URI was identified by the inspectors for a PD associated with a failure to modify the computer program for time to core boiling during conditions where reactor vessel upper internals are installed, reactor vessel head is removed, and the reactor cavity is at greater than reactor vessel flange level in addition to the impact on the refueling outage qualitative risk assessment. On October 23, 2012, the licensee initiated CR-12-04757 in response to inspector concerns that the program which calculates time to core boiling did not account for installation of reactor vessel upper internals when reactor cavity level was increased above the reactor vessel flange and the corresponding impact on the licensees risk assessment. The inspectors noted that on October 21, 2012, when reactor cavity fill operations began at approximately 0135 hours0.00156 days <br />0.0375 hours <br />2.232143e-4 weeks <br />5.13675e-5 months <br />, the qualitative risk assessment was shifted from Yellow to Green and the time to core boil was moved from approximately 22 minutes (level at 9 inches below flange) to 2.1 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> (level at approximately 6 feet above flange. At a reactor cavity level of greater than 23 feet above the flange with upper internals installed the time to core boil was identified as approximately 7.44 hours5.092593e-4 days <br />0.0122 hours <br />7.275132e-5 weeks <br />1.6742e-5 months <br />. The upper internals were removed at approximately 1644 hours0.019 days <br />0.457 hours <br />0.00272 weeks <br />6.25542e-4 months <br /> on October 22, 2012. The inspectors noted that procedure SSP-004, Outage Safety Review Guidelines, Revision 3, definition for a high risk evolution states in part, Considerations for establishing High Risk Evolutions (HREs) include equipment availability, inventory, and time to boil. The inspectors also noted that SSP-004 did not appear to adequately address the impact of upper internals installation on time to core boiling. Section 7.1.3, Inventory Control Guidelines, states in part, During Lowered or Reduced Inventory operations, boiling and potential core uncoverage can occur in a relatively short time period (less than one hour). However, there is no discussion on time to core boil and any potential core uncoverage with the reactor cavity greater than flange level and upper internals installed. The inspectors also noted that industry guidance stated that the most effective way to reduce outage risk or core damage probability is to minimize the duration of the highest risk periods consisting of loops not filled, internals installed, and the core not off-loaded. The inspectors did, however, note that SSP-004 required both trains of RHR operable while the upper internals are installed. Pending completion of additional evaluations in determining if the PD is more than minor, this is identified as URI 05000395/2012005-04, Failure to Consider the Risk Impact of Time to Core Boil With Reactor Vessel Upper Internals Installed and Cavity Level is Greater Than Reactor Vessel Flange |
| Site: | Summer  |
|---|---|
| Report | IR 05000395/2012005 Section 1R13 |
| Date counted | Dec 31, 2012 (2012Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.13 |
| Inspectors (proximate) | E Coffman G Mccoy J Reecee Coffmane Lea G Mccoy J Laughlin J Reece M Coursey R Hamilton R Williams |
| INPO aspect | |
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Finding - Summer - IR 05000395/2012005 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Summer) @ 2012Q4
Self-Identified List (Summer)
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