New technical solutions for the design of NPP passive safety systems

The paper describes the new principle of passive NPP safety systems designing, in which the natural circulation of working fluid or gas is replaced by forced circulation in order to increase it’s capacity. The energy required by the system is converted from the emergency process itself, which this system resists when performing a given safety function. The goal is to expand the variety and capacity of passive NPP safety systems in order to optimize and reduce costs of NPP power units with various types of reactors while increasing the safety level. The proposed technical solutions are based on the use of direct non-mechanical conversion of the energy, comprised in emergency process, to electricity, and then to mechanical energy of hydraulic machine for working medium moving in a forced circulation mode. To demonstrate the proposed principles, the following technical solutions have been considered: • new passive electrochemical hydrogen recombiner for NPPs with light water reactors. Application of new techniques allowed increasing the performance by weight of the recommended hydrogen simultaneously with increasing the hydrogen torch threshold, as well as other important characteristics; • passive emergency core cooling system for heavy liquid metal cooled reactors. Application of new techniques allowed increasing the core remove heat capacity in order to scale down the main equipment; • passive system for in-vessel core melt retention of Pressurized Water Reactors of high thermal capacity (more than 3000 MWe). Application of new techniques allowed increasing the system thermal capacity in order to be able to apply to high thermal power reactors like VVER-1000 and more.