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: Mon, 13-06-1994
ERF description: Salem Unit 1 was operating at 73% power when excessive marsh grass/debris in the Delaware river caused some of the main condenser circulating water pumps to trip off due to high differential pressure. Operators manually initiated a power reduction to 7% power which, upon going below 10%, automatically re-instated the low power trip setpoints of 25%. The operator subsequently withdrew rods to restore RCS (reactor coolant system) temperature to its normal band. This resulted in a power increase to 25% and an automatic reactor trip.
Immediately thereafter, an automatic safety injection occurred on a high steam flow coincident with low RCS temperature signal. The steam line high steam flow bistables actuated on a short duration pressure pulse which was generated when the turbine stop valves closed in response to the reactor trip. The pressure pulse was not of sufficient duration to actuate both trains of the safety injection logic. As a result, several automatic actions associated with a full safety injection did not occur, including:
- two of the four main steam isolation valves failed to close
- the main feedwater isolation valves failed to close
- the main feed pumps failed to trip,
operators manually completed these actions.
A second safety injection later occurred on low pressurizer pressure. The pressure reduction was due to the cooldown of the RCS when two steam generator safety relief valves lifted. The two safety injections resulted in the pressurizer filling, and discharging to the PRT (pressurizer relief tank) via the power operated relief valves. The PRT rupture disc blew, as designed, to prevent overpressurization of the tank. Essentially no water was discharged from the PRT due to the blown rupture disc.
Operators subsequently re-established the pressurizer bubble and performed an orderly cooldown of the plant to cold shutdown. The unit has remained shutdown for repairs while the event was being investigated, and is preparing for restart.
ERF rating date: 16-05-1994
ERF contact person: KEN BROCKMAN
ERF address: WASHINGTON, DC 20555, United States
ERF affiliation: USNRC

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