ENS 42524
ENS Event | |
|---|---|
09:00 Apr 25, 2006 | |
| Title | Service Water Piping Flooding Concern Impacts Rhr |
| Event Description | At 0500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br /> on April 25, 2006 with the plant in mode 5 and RCS loops filled, Operations declared the 21 and 22 Residual Heat Removal (RHR) pumps inoperable (see IP2-CR-2006-2133). This is reportable under 10 CFR 50.72(b)(3)(v)(B) as an event that at the time of discovery could have prevented the RHR pumps from removing residual heat. Residual heat removal is still available through the steam generators. The pumps were declared inoperable, but remained in operation, after a degraded horizontal section of Service Water (SW) line 405 was identified. SW line 405 is a non-ASME Section XI, non-Class A, seismically supported 24 inch return line routed through the Steam Generator Blowdown (SGBD) Tank room in the Plant Auxiliary Building (PAB) about 15 feet above the floor elevation of 51 feet. The ability of the pipe to withstand a seismic event has not currently been demonstrated. The consequence of a failure of this pipe is the flooding of the SGBD Tank room, cascading water down to the pipe case and then to the 15 foot PAB elevation. Water can drain to the transformer yard through a door at that elevation but the bottom of the RHR pump motors is lower than the door sill.
Compensating actions have been implemented. These include provisions to open the door to the transformer yard with a security guard to monitor the open door, install sand bags at the entrance to the RHR pump room to prevent water entry, and install blocking devices to prevent backflow through the RHR pump room floor drains. A 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> watch is being provided for implementation of these compensatory measures. The watch will have a sump pump should it be necessary for leaks. The RHR pumps were declared operable at 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br />. Corrective action for SWS pipe 405 is being planned. The licensee notified the NRC Resident Inspector.
Indian Point 2 is withdrawing the 8-hour non-emergency notification made on April 25, 2006, at 1231 hours0.0142 days <br />0.342 hours <br />0.00204 weeks <br />4.683955e-4 months <br />. (Log No. 42524). The notification on April 25, 2006, reported an event or condition that could have prevented the Residual Heat Removal pumps from removing residual heat [10CFR54.72{b}(3)(v)(B)]. On April 25, 2006, at approximately 0500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br />, Operations declared the 21 and 22 Residual Heat Removal (RHR) pumps inoperable after a degraded horizontal section of Service Water (SW) line 405 was identified. SW line 405 is a non-ASME Section XI, non-Class A, seismically supported 24 inch return line routed through the Steam Generator Slowdown (SGBD) Tank room in the Plant Auxiliary Building (PAS) about 15 feet above the floor elevation of 51 feet. The ability of the degraded pipe to withstand a seismic event had not been demonstrated. The consequence of a failure of this pipe is the flooding of the SGBD Tank room, cascading water down to the 15 foot PAB elevation where the RHR pumps are located potentially flooding the RHR pump motors. Compensating actions were implemented and the RHR pumps declared operable at 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br />. Subsequently, a detailed engineering calculation was performed that included development of a finite element model of the piping using the SAP 2000 software package. The calculational methodology was based on ASME Section XI, Appendix H, Code Case N-513-1 and was augmented with stress intensity factor solutions from API-579. Stresses resulting from pressure, deadweight, and seismic loads were evaluated and found acceptable demonstrating that the overall structural integrity of the piping is maintained for all loading conditions. Based upon the observed pipe leak rate of approximately 15 gallons per hour (gph), an evaluation of the potential flaw size corresponding to this leak for the lower bound internal pressure was performed. It was concluded that the small stress contribution that would result from seismic loading would cause the flaw to have negligible propagation during a seismic event. Since it was determined that the pipe could support stable flaws much larger than the small flaw that corresponded to the observed leak rate, engineering concluded that the through wall flaws that produced the leakage did not threaten the structural integrity of the pipe. The estimated leakage that could have occurred from the pipe during a seismic event is bounded at 26 gph. Because the 26 gph leakage rate is well within the capacity of the two PAB sump pumps (50 gallons per minute each), there was never any threat to flooding the PAB or a challenge to the operability of the RHR pumps. The licensee notified the NRC Resident Inspector and will be notifying the New York Public Service Commission. Notified R1DO (M. Sykes). |
| Where | |
|---|---|
Indian Point  New York (NRC Region 1) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat | |
| Time - Person (Reporting Time:+3.52 h0.147 days <br />0.021 weeks <br />0.00482 months <br />) | |
| Opened: | Stephen Prussman 12:31 Apr 25, 2006 |
| NRC Officer: | Pete Snyder |
| Last Updated: | Jun 21, 2006 |
| 42524 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Not Critical |
| Scram | No |
| Before | Cold Shutdown (0 %) |
| After | Cold Shutdown (0 %) |