METHOD FOR RESTRAINING SHIFT OF RADIOACTIVE NITROGEN TO GASEOUS PHASE IN PRIMARY COOLING WATER SYSTEM OF DIRECT CYCLE TYPE REACTOR

摘要

PURPOSE:To enable the shift of radioactive nitrogen to a gaseous phase to be restrained, and reduce the dose rate of a turbine system by adding a reagent having high capability of forming complex ions with ammonia to primary cooling water. CONSTITUTION:In a feed water system at the downstream side of a condenser 15, a reducing agent, for example, nitrogen is supplied from a reducing agent filling system 16 to a line between a condensate demineralizing unit 10 and a feed water pump 21, thereby reducing the concentration of dissolved oxygen in a primary cooling system. On the other hand, a reagent filling system 23 is provided in a recirculation system comprising a recirculation pump 6 and a reactor water purifying system 8, and concurrently with the filling of the reagent from the system 16, a reagent having the high capability of forming a complex with ammonia is supplied from the system 23 to the downstream outlet of a purifying system 8. According to this construction, the reagent is dissolved in the liquid phases of a reactor core 1, a mixing plenum 4, a downcomer 5 and a lower plenum 7. Consequently, the gaseous phase shift amount of radioactive nitrogen generated in the core 1 can be restrained, and the radiation dose of a main steam piping and the turbine system can be reduced.