Study of core melting process for 7.4 per cent failure using the MARCH-2 code

The analysis of severe accidents regarded as out of design basic accident events is described. These accident types can occur in the case of some level of safety feature inoperability. Calculations were done for the response of 7.4% blowdown in the water-cooled reactor system of WWER-440 type by the computer program MARCH-2 implemented at the International Atomic Energy Agency. The analysis covers the entire accident sequence from the time of the initiating accident event through the stages of core uncovering, heating up of the fuels, partial or total melting of the reactor core and reaching of the core debris in the reactor cavity. (author)