Mochovce 3 achieves first criticality

Monday, 24 October 2022

Branislav Strýček, CEO and chairman of Slovenské elektrárne, said: "This is a very important milestone in the start-up of the nuclear reactor. It is the moment when the nuclear fuel in the reactor came to life and we are bringing the reactor to life. It should go to full capacity at the beginning of next year."

Commissioning of unit 3 at the plant in the south west of Slovakia began on 9 September with the loading of nuclear fuel over three days, followed by the assembly of the reactor, which ended on 20 September, and tightness and strength tests.

The company said that although a controlled fission chain reaction is now taking place in the reactor, the power is very close to zero, with Martin Mráz, director of the plant, explaining that "the first start-up of the reactor involves complex tests, during which all the characteristics of the reactor's active zone are verified".

The next stage, once the current tests are passed, will see unit 3 switched from physical to energy launch, with heat from the reactor heating water to produce the steam to spin the turbines. With the gradual increase in the power of the reactor, it will be phased into Slovakia's electricity system when it reaches 20%.

During the process of increasing the power of the reactor there are tests carried out and situations - "that the power plant will probably never experience in normal operation" - simulated to ensure safety.

The completion of commissioning will see a 144-hour test run of unit 3 at full capacity. 

Construction of the first two 471 MWe VVER units at the four-unit Mochovce plant started in 1982. Work began on units 3 and 4 in 1986, but stalled in 1992. The first two reactors were completed and came into operation in 1998 and 1999 with a project to complete units 3 and 4 beginning ten years later. Unit 4's schedule has been to follow about one or two years behind unit 3. Each of them will be able to provide 13% of Slovakia's electricity needs when operating at full capacity.

The final design includes many upgrades to safety and security, including increased aircraft impact protection and emergency management measures based on lessons from the Fukushima accident which were incorporated during the project. The Slovak Nuclear Regulatory Authority issued the final authorisation for commissioning of unit 3 of the Mochovce nuclear power plant in August.