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, 09-11-2006
ERF description: Opening of a disconnector in the 400 kV switchyard to which the unit is connected, caused an arc and a two phase short. As the voltage on the generator bus bars dropped to about 50% of nominal voltage the unit was disconnected from the grid. The excitation of the generators caused an increase in the voltage level on the generator bus bars to about 120%. This overvoltage caused two out of four UPS DC/AC inverters to trip. About 30 seconds later in the sequence, when house load mode of operation on both turbo generators was lost, the trip of the UPS DC/AC inverters implicated that two out of four emergency diesel generators did not start as expected. The switchover to off site auxiliary power was automatic and successful.
Approximately 20 minutes after the initial event, the 500 V diesel bus bars in the affected divisions were manually connceted to the 6 kV system, supplied by the off site auxiliary power, and all electrical systems were thereby operational.

The scram of the reactor was successful, all control rods were inserted as expected. Two valves in the pressure relief system opened because of unwarranted initiation of safety trains. The emergency core cooling system in two out of four trains was however more than sufficient to maintain the reactor level above the core, as there were no additional LOCA. The control room staff had difficulties in supervising the plant properly during the event as many indications and readings were lost due to the loss of power in two trains.

Since there was no real LOCA or any other safety problems associated with the reactor and the core cooling capability was more than adequate, the event is categorized as a level 1 on the INES scale. An increase to level 2 is justified by the common cause failure in the emergency power supply system (failure of two out of four UPS DC/AC inverters).

To remedy the problem in the inverters and rectifiers of the uninterrupted power supply will be modified and a change of power supply of the spreed measurement device on the diesel generators in two divisions will be performed before the unit is allowed to power up again.

ERF rating date: 24-08-2006
ERF contact person: Olle Andersson
ERF address: Forsmarks Kraftgrupp AB, 742 03 Östhammar, Sweden

This map shows a selection of reports from nuclear and radiological incidents stored in the IAEA NEWS-database.
Locations are estimates. Contact us if a location is wrong.
The map shows a maximum of 100 incidents. If hundred incidents or more are within the map, the yellow perimeter indicates from where events are excluded. Drag or zoom the map to explore different areas.

Power Reactor Research Reactor Radwaste Facility Enrichment Facility Radiation Source Irradiation/Accelerator Facility Transportation

Fuel Fabrication Fuel Reprocessing Research Facility Mining/Milling Radioisotope Processing/Handling Facility Other