Second unit of Czech Temelín nuclear power plant back in operation after unplanned outage

The second unit of the Temelín nuclear power plant is back in operation. It had been unexpectedly shut down since 31 January for repairs to a seal in the generator’s internal cooling circuit. The second unit began generating electricity overnight and reached full output in the morning. Marek Sviták, spokesperson for the Temelín plant, told the Czech News Agency.

The plant said the fault affected its non-nuclear section. Engineers replaced one of the four coolers in the generator’s internal system. It was an operational issue that had no impact on the surrounding area or customers; ČEZ secured replacement supplies from other energy sources. The unit’s restart after the cooler was replaced was preceded by several days of equipment inspections.

Since the beginning of the year, the Temelín plant has generated 1.7 terawatt-hours of electricity. The first unit is operating normally.

The turbine-generator sets at the Temelín nuclear power plant are the largest in the Czech Republic. Each of the two generating units has one high-pressure and three low-pressure turbine sections, directly connected to an electric generator with a maximum output of 1125 MWe. The system converts thermal energy into electricity and, through so-called extractions, supplies steam to heat exchangers. Under normal conditions, around 5263 tonnes of steam per hour flow through the steam pipes to the high-pressure section of the steam turbine, at a temperature of 273.6 degrees Celsius and a pressure of 5.8 MPa. The circumferential speed of the blades in the low-pressure sections exceeds twice the speed of sound. Cooling the entire turbine-generator set takes on the order of tens of hours, depending on other conditions.