Unplanned Outage of Unit 1 at NPP Temelin

Drop-out of the main coolant pump at Unit 1 at Temelin NPP occurred on June 2nd 2006 at 0.20 a.m. because of improper function of pressure measurement on seal of one of four main coolant pumps. Afterwards, the power level was automatically decreased to 50% of nominal power, the software card was changed and main coolant pump was put in into operation again.

At this moment, this event is classified as “below INES level” by the operator.

In reaction to drop-out of the main coolant pump, the limitation system was activated and one of the safety clusters group was inserted into the active core. During this process, improper signalisation of lower positions of clusters was identified and investigated. The final decision was adopted to prepare a new set of tests and measurements of dropping time of clusters.

At this moment, this event is classified as INES 0 by the operator. The State Office for Nuclear Safety (SÚJB) continues in its evaluations and inspections, the results will be announced later.