Mayak plant is one of the biggest sites dealing with spent nuclear fuel reprocessing, ITAR-TASS reported. The storage facility of the radioactive materials at the Mayak plant is capable to contain up to 400 tonnes of the weapon-grade uranium and plutonium extracted from the nuclear warheads. There are still three big forest fires going on in Chelyabinsk region covering the area of 2.3 thousand ha, ITAR-TASS reported.