Qualification of the pressure compensator system for the management of accidents with complete loss of long power supply from vver power plant

Abstract

Developing effective accident management strategies with complete loss of long-term power supply at nuclear power plants requires the qualification of existing and promising passive safety systems that do not require power supply. One of the approaches to solving this problem is to qualify the system of pressure compensator for accidents with complete loss of long-term power supply. The original method of qualification of the system of pressure compensator for the conditions of accidents with complete loss of long-term power supply is presented, taking into account the significant dynamics of thermo-hydraulic processes in the reactor. As a result of the computational modeling of the developed method of qualification of the pressure compensator system for the conditions of failure with complete loss of long power supply, it is established that the effective action of the pressure compensator system to maintain the required level of coolant in the reactor is carried out up to 900 s from the beginning of the emergency process. At 2000 seconds from the start of the emergency process, the pressure in the pressure compensator increases to the maximum permissible values and there is an automatic opening of the safety valves of the pulse-relief device of the pressure compensator. Within the developed method defines the criteria, conditions and consequences of occurrence of water hammers due to overflow of the pressure compensator coolant, transonic modes of flow of two-phase flow in the flowing part of the pressure compensator relief valves and unacceptably accelerated closure of the safety valves at the maximum steam. The obtained criteria, conditions and consequences of water hammers in the pressure compensator system are in good agreement with the known experimental data. As a result of the calculated analysis it is established that in the process of an accident with a complete loss of long-term power supply, water hammers may occur due to the overflow of the volume of the pressure compensator when opening the safety valves and the transonic modes of flow of the two-phase flow in the flow part of the valve. An effective measure to prevent water hammers in the pressure compensator system is to increase the hydrodynamic resistance at the top of the pressure compensator by installing remote grilles. Qualified alternative passive safety systems that provide effective accident management with complete loss of long-term power supply with 900 seconds of start of the emergency process.