Unit 3 of the Zaporozhiya nuclear power plant tripped on 28 November, but posed no threat to the environment or public and is expected to return to normal operation on 5 December.
The six-unit Zaporozhiya plant (Image: Energoatom)
Energoatom, the country’s state-owned nuclear power plant operator, said today that the unit had disconnected from the grid automatically as “protection against internal damage to the generator.”
The short circuit was caused by damage to the “winding voltage section of the auxiliary transformer and switch block transformer,” it added. The unit was transferred to a cold state.
Ukraine’s energy minister Volodymyr Demchishin said earlier today that the short circuit at unit 3 had led to a drop in electricity production, but stressed that the problem had occurred in the electricity transmission system and not in the reactor. “There is no threat … there are no problems with the reactor,” Demchishin said at a briefing to local media, following inaccurate reports there had been an accident at the plant.
Energoatom issued a statement in response to “misinformation” distributed by some media about the incident at unit 3.
The unit “was disconnected from the grid as protection against inner generator damage. The incident occurred at 19:24 on 28 November and was caused by damage of the house load voltage transformer coil that led to disconnection of the house load transformer and unit transformer breakers,” it said. “The specified event does not refer either to nuclear or [any] other type of accident and is classified as ‘failure in NPP unit operation’, according to regulatory documents. Work to restore power supply of the unit is well underway according to the emergency work order.”
The incident had no radiological consequences and a preliminary assessment indicated that it was “below scale,” or Level 0 on the International Nuclear Event Scale (INES), Energoatom said.
Work is underway to restore the auxiliary power supply unit, and the reactor is expected to return to normal service on 5 December.
With an installed capacity of 6000 MWe, the six unit Zaporozhiya nuclear power plant is the biggest electricity generating station in Europe and accounts for half of all nuclear power generated in Ukraine and 22% of the country’s entire electricity production. The six units were commissioned between 1984 and 1995.
Like the scales that describe earthquakes or major storms, each of the INES scale’s seven levels is designed to be ten times more severe than the one before. After below-scale deviations with no safety significance, there are three levels of incidents, then four levels of accidents.
The State Nuclear Regulatory Inspectorate of Ukraine (SNRC) said that radiation levels at the site of the Zaporozhiya plant remain within the limits of normal plant operation and that its physical protection systems are operating “in normal mode”.
Twelve of Ukraine’s 15 nuclear power reactors are in operation. Zaporozhiya 3, Khmelnitsky 1 and Zaporozhiya 1 are undergoing scheduled maintenance work until, respectively, 5 December, 15 December and 30 December, SNRC said.
Source: World Nuclear News