ENS 49312
ENS Event | |
|---|---|
02:52 Aug 28, 2013 | |
| Title | Recirc Pump Runback and Power Reduction |
| Event Description | On August 27, 2013 at 2152 CDT, Monticello Nuclear Generating Plant (MNGP) experienced a runback of [the] 'B' Recirc pump from 87% speed to 71% speed. Operators took action to lock [the] 'B Recirc pump scoop tube. This runback resulted in a power reduction from 100% to 94% RTP [Rated Thermal Power]. With the resultant mismatch between total jet pump flows of the two loops greater than required limits, should a LOCA [Loss of Coolant Accident] occur, the core flow coastdown and resultant core response may not be bounded by the LOCA analyses. It has been determined that this is an unanalyzed condition as defined by 10CFR50.72(b)(3)(ii)(8).
At 0121 CST on August 28, 2013, MNGP completed reducing power to 88% using 'A' Recirc pump to match total jet pump flows and [the plant] is no longer in an unanalyzed condition. The 'B' Recirc scoop tube remains locked pending investigation. The licensee has notified the NRC Resident Inspector.
This is a retraction for ENS 49312: The licensee reviewed the MNGP design basis analysis to determine if the event was bounded. The licensee determined that the Loss of Coolant Accident (LOCA) provides a bounding analysis for this event. The limiting LOCA event for the MNGP as analyzed in accordance with 10CFR50 Appendix K conditions is based upon single failure of the Low Pressure Coolant Injection (LPCI) injection valve, effectively making LPCI inoperable for the event. The large break Design Basis Accident (DBA) with LPCI injection valve failure (which is analytically equivalent to the condition of both LPCI subsystems being inoperable) is the event analyzed for the current Licensing Basis Peak Cladding Temperature (PCT). This analysis bounds the event as a recirculation pump flow mismatch event is less limiting than the LOCA with LPCI injection valve failure analysis. Therefore, this recirculating loop flow mismatched event is less limiting than a previously analyzed event and ENS 49312 may be retracted as an unanalyzed event. The licensee has notified the NRC Resident Inspector. Notified R3DO (Skokowski). |
| Where | |
|---|---|
Monticello  Minnesota (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+2.4 h0.1 days <br />0.0143 weeks <br />0.00329 months <br />) | |
| Opened: | Angel Bray 05:16 Aug 28, 2013 |
| NRC Officer: | John Shoemaker |
| Last Updated: | Oct 13, 2013 |
| 49312 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (94 %) |