The German nuclear plant Kruemmel (KKK) is unlikely to be restarted until April or May 2010, according to operator Vattenfall. The company has decided to buy two new transformers, following a failure on 4 July caused an automatic shutdown at the plant. It will take until spring 2010 to receive and install them. The 4 July incident is the second transformer-related shut down in a week for the 1346MWe BWR, which was coming out of a two-year maintenance and repair outage.
On 4 July, a short circuit in this device forced the plant while operating at a power of about 1200 MW to be quickly shut down automatically which again led to a severe power cut in the Hamburg area, though only for a few milliseconds. This led to an electricity fall out for about 1500 of the 1750 traffic lights in the city and also all 14 water supply works had to be shut off from electricity supply, so that about 100,000 citizens had no water. Resulting oscillations in the water supply system resulted in 16 breaks of water supply pipes.
As an event which has to be announced to the supervising authority the failure belongs to the category N (for normal) and is also below the seven steps of the international scale which means INES zero. Nevertheless the incident has attracted the public’s attention, as the ministry for social affairs as Schleswig-Holstein licence authority was only informed after the local police at Geesthacht had been informed.
The head of Vattenfall Europe Nuclear Energy GmbH, Michael Züfle, strongly apologised for failing to inform the regulator directly, and promised that similar mistakes would be excluded in the future.
Although this second transformer was tested while the first one, which exploded two years ago, was replaced, the reason for the new incident has not yet been found. First results of the investigation of the incident have shown that a planned supervision device for the transformer had not been installed before startup of the plant. As a consequence of this omission the plant manager Hans-Dieter Lucht has resigned; his successor is Walther Stubbe.
During the automatic shutdown all 205 control rods were inserted hydraulically. However one of the rods had an electrical fault. Also, the cooling of the reactor water purification system failed and was, therefore, not available for about four hours. This system was, however, not needed during the incident. Finally, radioactivity in the reactor water indicated one probably defect fuel element which has to be found and inspected.
On 16 June, KKK management informed the licence authority that the plant was ready for a new startup. After the ministry gave its consent on 19 June, the station started up the same day and reached full power on the night of 23/24 June. Then on 1 July, the turbine went into an automatic shut down due to the failure of a plant supply transformer. That day, the plant had to be separated from the grid and the reactor power was, therefore, reduced to a low level. At 19.15 the plant was re-connected to the grid and operated at a reduced power of 700 MW. On 2 July the cause of the first problem was found: a valve at the pressure compensation tank of the transformer was set incorrectly. On Friday 3 July the transformer was operational again so that the power could be increased, only to fail with much worse consequences the next day.
