Temelín nuclear plant in Czechia unexpectedly disconnects second unit on Tuesday, technicians carry out checks

The Temelín nuclear power plant unexpectedly disconnected its second unit from the transmission grid on Tuesday. This was done automatically by the so-called flash protection system at one of the four switchyards, plant spokesperson Marek Sviták told ČTK. Electricity supplies were not affected. Technicians are currently inspecting the equipment. Operators are not cooling the reactor down; they are keeping it in the so-called hot state, which is intended to make it easier to reconnect the unit to the transmission grid. They expect to do so this week.

„The brief interruption to generation was caused by the flash protection system at one of the switchyards that transmit electricity for the unit’s equipment being triggered. Operating as designed, it protects the internal electrical network and connected equipment from damage, for example in the event of a short circuit in the non-nuclear part of the plant. Equipment inspections are currently under way, including an overhaul of the switchyard. The timing of the unit’s reconnection will also depend on the results. This should happen by the end of the week,“ Sviták said.

This is the third unplanned disconnection of a Temelín unit from the transmission grid this summer. On 17 July, energy workers disconnected the first unit to inspect and repair a water valve in the system that circulates water between the condensers and cooling towers in the non-nuclear part of the plant. The unit returned to full power the following day. The second unit was unexpectedly disconnected on 30 July because of turbine vibration; technicians then stabilised the turbine during the next scheduled outage on 2 August.

The first unit is operating at full power. The Temelín nuclear power plant has generated 9.4 terawatt-hours of electricity since the start of the year.