ENS 43139
ENS Event | |
|---|---|
18:50 Feb 2, 2007 | |
| Title | Low Pressure Injection (Lpi) Net Positive Suction Head Flow Requirements Not Met for Certain Accident Sequences |
| Event Description | At 1350 hours0.0156 days <br />0.375 hours <br />0.00223 weeks <br />5.13675e-4 months <br /> on February 2, 2007, with the plant at 100% power, it was determined [that] the low pressure injection (LPI) system net positive suction head calculation does not account for the additional flow through the failed LPI pump recirculation line during certain accident scenarios. The additional flow is upstream of the flow element used by control room operators to throttle system flow to maintain net positive suction head flow requirements. The additional flow could result in net positive suction head below required design limits. The system design is not affected in events where both LPI trains perform as designed.
Emergency operating procedures direct control room operators to open the LPI system discharge flow cross-connect line isolation valves, if accessible, following a LPI pump failure. Operators are then directed to throttle system flow through the operable LPI pump to maintain proceduralized values. These values are designed to provide sufficient design flow and maintain pump NPSH. During a simulator training scenario, operators identified when the discharge cross-connect line isolation valves were opened, the idle Building Spray train indicated flow. Follow-up investigation identified the increased flow was due to back flow through the failed LPI pump minimum flow recirculation line. This additional flow is upstream of the flow element used by operators to maintain adequate net positive suction head for the operable LPI pump. The additional flow could result in not meeting NPSH design requirements. The licensee entered the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Technical Specification limiting condition for operation (LCO) for one inoperable LPI train. The licensee is revising calculations and emergency operating procedures to account for the additional flow. This condition is reportable in accordance with 10CFR 50.72(b)(3)(ii) and (b)(3)(v) as an unanalyzed condition, and a condition that could have prevented the fulfillment of the safety function of the LPI system to mitigate the consequences of an accident, respectively. The NRC Resident Inspector was notified of this event by the licensee.
The purpose of this report is to retract the ENS report made on February 2, 2007 at 2105 hours0.0244 days <br />0.585 hours <br />0.00348 weeks <br />8.009525e-4 months <br /> ( ENS #43139) under 10CFR50.72(b)(3)(ii) and (b)(3)(v) as an unanalyzed condition, and a condition that could have prevented the fulfillment of the safety function of the Low Pressure Injection (LPI) system to mitigate the consequences of an accident, respectively. The initial report was made when it was determined that the LPI system net positive suction head (NPSH) calculation does not account for the additional flow through the LPI pump recirculation line during certain accident scenarios. The additional flow could result in net positive suction head below required design limits. Due to this condition, it was not certain if the LPI system could have met its design basis requirements. The licensee entered the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Technical Specification limiting condition for operation (LCO) for one inoperable LPI train. The LCO was exited on February 3, 2007 at 9:25PM following implementation of a procedure change that accounted for the additional flow and ensured that adequate NPSH was maintained. A subsequent engineering evaluation has determined that sufficient LPI pump NPSH would have been available to perform its design basis function prior to the procedure change. The engineering evaluation shows that the LPI pumps remained capable of performing their design basis functions based on the following three independent assessments: 1) the LPI pumps would have operated well beyond their mission time without significant cavitation damage at the available NPSH 2) proceduralized operator actions would have throttled flow to restore required NPSH if signs of cavitation occurred 3) an evaluation using realistic Reactor Building pressures showed that sufficient NPSH would exist. The licensee notified the NRC Resident Inspector. Notified R1DO (Hott) |
| Where | |
|---|---|
Three Mile Island  Pennsylvania (NRC Region 1) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+2.25 h0.0938 days <br />0.0134 weeks <br />0.00308 months <br />) | |
| Opened: | Stuart Brantley 21:05 Feb 2, 2007 |
| NRC Officer: | Bill Huffman |
| Last Updated: | Mar 14, 2007 |
| 43139 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Three Mile Island with 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
WEEKMONTHYEARENS 531062017-12-06T14:58:0006 December 2017 14:58:00
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