Cooling conditions of the reactor of the Beloyarsk nuclear power station first unit during shutdown of the station and depressurization of the evaporative circuit

An analysis of the dynamics of the processes in the case of emergency situations with shutdown of the station and depressurization of the circulatory circuit allow the conditions of heat removal in the core to be determined in these regimes (reserves up to limiting power, fuel element temperature), and recommendations to be formulated for the assurance of the safe operation of the AMB-200 reactor, which has two main (MCP) and two emergency (ECP) circulatory pumps in each of the two circulation loops [I]. The investigation of an emergency situation associated with total shutdown of the facility is an essential part of the work carried out for substantiating the safety of the Beloyarsk nuclear power stations. In the computational investigations of this emergency, the results of which are presented below, experimental data on the switchlng-off of the MCP in the Beloyarsk nuclear power station (Fig. i) and data on a mechanical breakdown of the turbogenerator used for powering the electric motors of the circulator pumps were used. In the case of triggering of the scram system, the experimental data on the transit time of the signal to the equipment and to the control and safety system logic were used. Experiments on tripping the MCP were conducted at a power of 35-45% of the nominal. Before the start of each experiment, stabilization of the thermotechnical parameters of the reactor and the unit as a whole was carried out for 15-30 min, and loop oscillographs were prepared, having recorded on photographic film the variation of the coolant flow rate and other characteristics of the power generating unit (power, reactivity). After stabilization, the physical and thermotechnical parameters of the unit were recorded and then the MCP were switched off [2] simultaneously with the start of closure of the slide valve at the pump outlet. As a result of this, the flow rate in the circuit changed abruptly over 2-3 sec. In order to ensure nuclear safety and to prevent functioning of the scram system, simultaneously with switching off the MCP, two rods of the standby automatic regulator, operated in the manual regulation regime were inserted to a specified depth in the core [2].