Stichting Laka

Event Report Forms (ERFs) are filed to the IAEA. Sometimes there are multiple event reports, updating the rating, the event description. Here you only see the latest event report

ERF send date: Thu, 21-03-1996
ERF description: On 06 Febraury 1996 with the unit operating at 100 percent power; a loss of offsite power (LOOP) and automatic reactor trip occurred as a result of phase-to-ground faults in two phases of the isophase electrical buswork between the main generator and two potential transformers. When these faults occurred simultaneously (one or both believed to be intermittent), a phase-to-phase fault was created causing the LOOP. The LOOP caused the reactor to trip upon loss of the reactor coolant pumps. Prior to this event, one of the two emergency diesel generators (EDG) and its associated electrical equipment were out of service of scheduled maintenance. The available EDG automatically started and loaded to its associated electrical bus. After almost 3 hours into the event, the EDG initially out of service was returned to service and loaded. Electrical power from crossties with unit 1 was established approximately 8 hours after the start of the event.
Following the reactor trip, an automatic reactor safety injection occurred due to low main steam pressure caused by excess steam loads. The injection continued for approximately 30 minutes until terminated by operators. The reactor coolant system was completely filled during safety injection, and overflow caused the pressurizer relief tank rupture disk to fail.
This event involved a challenge to a safety function due to an initiator with a high expected frequency of occurrence (loss of offsite power). Although one of the two EDG and its associated electrical equipment were out of service, plant operation with the remaining EDG was permitted for a limited time by the technical specifications. Thus, safety function availability remained within operational limits and conditions. Additionally, the second EDG was returned to service within approximately 3 hours of the initial event. This event was given a rating of level 1 in accordance with Table II of the INES user's manual. On-site and off-site impact criteria were not relevant for this event.
ERF rating date: 15-02-1996
ERF contact person: R.J. BARRETT
ERF address: United States
ERF affiliation: USNRC, EMERGENCY RESPONSE BRANCH, OFFICE FOR ANALYSIS AND EVALU

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