Behaviour of VEER-type reactors under some hypothetical accidents

The design safety analysis for standard VVER-440 and VVER-1000 reactors in the USSR has been performed on normal operation, anticipated operational occurrence and postulated accidents. For each initial event, the acceptable limits of damage of the design safety barriers were set up. These limits mainly concern fuel pellets and fuel element claddings, as the damage of the third and fourth design barriers (the pressure boundary of reactor cooling system and the containment) is not allowed in any design initial event. For developing the plan of measures to protect people in hypothetical accidents, the analysis of the events exceeding the design basis accident is required. In this paper, the analysis of the behavior of standard VVER-440 and VVER-1000 reactors in the USSR in hypothetical accidents is reported. The main computer codes used were DINAMIKA-M and TETCH-M. Two types of the hypothetical accidents considered were loss of feedwater and complete loss of electric power supply. The selected scenarios are considered only from the viewpoint of their immediate consequences irrespective of the actual possibility of realization. The DINAMIKA-M model comprises the description of operation of all main components of a nuclear steam supply system. (Kako, I.)