A CONCEPT OF PASSIVE SAFETY PRESSURIZED-WATER REACTOR SYSTEM WITH INHERENT MATCHING NATURE OF CORE MEAT GENERATION AND HEAT REMOVAL

The reduction of manpower in operation and maintenance by simplificati on of the system are essential to improve the safety and the economy o f future light water reactors. At the Japan Atomic Energy Research Ins titute (JAERI), a concept of a simplified passive safety reactor syste m JPSR was developed for this purpose and in the concept minimization of developing work and conservation of scale-up capability in design w ere considered. The inherent matching nature of core heat generation a nd heat removal rate is introduced by the core with high reactivity co efficient for moderator density and low reactivity coefficient for fue l temperature (Doppler effect) and once-through steam generators (SGs) . This nature makes the nuclear steam supply system physically-slave f or the steam and energy conversion system by controlling feed water ma ss flow rate. The nature can be obtained by eliminating chemical shim and adopting in-vessel control rod drive mechanism (CRDM) units and a low power density core. In order to simplify the system, a large press urizer, canned pumps, passive residual heat removal systems with air c oolers as a final heat sink and passive coolant injection system are a dopted and the functions of volume and boron concentration control and seal water supply are eliminated from the chemical and volume control system (CVCS). The emergency diesel generators and auxiliary componen t cooling system of ''safety class'' for transferring heat to sea wate r as a final heat sink in emergency are also eliminated. All of system s are built in the containment except for the air coolers of the passi ve residual heat removal system. The analysis of the system revealed t hat the primary coolant expansion in 100% load reduction in 60 s can b e mitigated in the pressurizer without actuating the pressure relief v alves and the pressure in 50% load change in 30s does not exceed the m aximum allowable pressure in accidental conditions in regardless of pr essure regulation.