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| Entered date | Event description | |
|---|---|---|
| ENS 44508 | 21 September 2008 02:13:00 | On Saturday, September 20, 2008, Monticello Nuclear Generating Plant (MNGP) experienced an actuation of the following systems: Reactor Protection System (with the reactor shutdown), Containment Isolation, and Emergency Diesel Generators. The apparent cause of the actuation was a pressure pulse in the reference leg of a Reactor level instrument that resulted when a CRD (Control Rod Drive) pump was started without the reference leg backfill system isolated from the CRD system. This notification is being made in accordance with 10CFR50.72(b)(3)(iv)(A). Due to the containment isolation, shutdown cooling was lost for approximately 90 minutes. Initial reactor temperature was ~95 degrees when the isolation occurred. When shutdown cooling was restored, reactor temperature had increased to ~120 degrees. The Emergency Diesel Generators started but did not load. The diesels have been restored to normal standby status. The licensee has notified the NRC Resident Inspector. |