05000237/FIN-2011003-06
Finding | |
|---|---|
| Title | Concerns with the Licensing and Design Basis |
| Description | An unresolved item was identified by the inspectors for potential concerns with the licensing and design basis related to a seismic event that causes a dam failure and a loss of offsite power (LOOP). A seismic event that causes a dam failure is a credible event. In a letter to the NRC dated March 31, 1998, (ML073540225), the licensee stated: In a Stability Investigation that was performed by the U.S. Army Corps of Engineers in 1973, the Dresden Lock and Dam was evaluated for earthquakes with a static equivalent horizontal acceleration of 0.05g for the dam and 0.10g for the lock and found to be acceptable. The safe shutdown earthquake (SSE) defined for Dresden Station has a magnitude of 0.2g zero period acceleration (ZPA) horizontal ground acceleration. As described in previous sections of this report, during this scenario, the isolation condensers are the only credited systems available to remove decay heat from both reactors. The inspectors are concerned with the following:
the current licensing bases which relies on non-safety-related components (screen refuse pumps) to mitigate the effects of a credible postulated UFSAR accident; the reliance of one success path to mitigate the consequences of a seismic event which results in a dam failure and a loss of offsite power. Specifically, during this event, the containment cooling service water (CCSW) pumps piping drains to the intake structure due to lower intake water level. Therefore, the CCSW pumps which are designed for containment heat removal and as a support system for the low pressure coolant injection (LPCI) in cold shutdown mode and high pressure coolant injection (HPCI) by means of room cooling, are inoperable. The licensee does not credit the CCSW pumps during this event. The CCSW pumps take suction from bay 13, the same enclosure as the DFPs. If the licensee required CCSW in service, trapped air would need to be rapidly vented from the CCSW piping by cutting into the top of the pipe. This evolution would be performed by two individuals in the Maintenance Department who may not be onsite at the time of the event and may take up to one hour to arrive at the site. In addition, the licensee has not evaluated the capability of the screen refuse pumps to provide enough water to meet the demands of the CCSW pumps and the DFPs; and a seismically qualified method to supply water to the isolation condenser would not be available for about 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. This path entails connecting the discharge of the Unit 2 diesel generator cooling water (DGCW) pump, which is safety-related and draws water at a lower elevation of the intake structure, to the isolation condenser make-up pumps. The Unit 2 DGCW pump would provide make-up water to both Unit 2 and Unit 3 isolation condensers. With no makeup water, the water level in the isolation condenser shell approaches the bottom of the tube bundles in 20 minutes which was viewed as a reasonable length of time allowed for initiating makeup water flow to the shell side of the isolation condenser to minimize water losses from the core. Although the licensee evaluated the potential 5-hour delay and considerably more time is available before the reactor core begins to uncover, the inspectors questioned whether 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> to restore water was reasonable. This issue is unresolved pending further clarification of Dresdens licensing and design basis during a seismic event (URI 05000237/2011003-06; 05000249/2011003-06, Concerns with the Licensing and Design Basis). |
| Site: | Dresden  |
|---|---|
| Report | IR 05000237/2011003 Section 1R07 |
| Date counted | Jun 30, 2011 (2011Q2) |
| Type: | URI: |
| cornerstone | Barrier Integrity |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.07 |
| Inspectors (proximate) | M Bielby M Ring T Go J Draper C Tilton J Corujo-Sandin M Munir R Winter A Dahbur D Melendez-Colon C Phillips C Moore |
| INPO aspect | |
| ' | |
Finding - Dresden - IR 05000237/2011003 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Finding List (Dresden) @ 2011Q2
Self-Identified List (Dresden)
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||