Fig. 7-2 Flow diagram of safety system of JPSR The passive heat removal system consists of residual heat exchangers, a gravity coolant injection pool, and air coolers connected by natural circulation flow lines. The passive coolant injection system consists of accumulators and gravity coolant injection lines.

The conceptual design for the passive safety reactor, JPSR (JAERI Passive Safety Reactor), is ongoing to enhance the safety of the next generation light water reactor. This reactor may be used well into the next century as an alternative energy source that is designed for protection of the environment. The JPSR is a two-loop pressurized water reactor with a 630 MW electrical output. The purpose of the JPSR design is to enhance safety and simplify the reactor system by combining the inherent safety features of the core with passive safety systems. Figure 7-2 shows the safety system of JPSR. The safety design features of JPSR are as follows; The core heat generation rate is physically matched to the heat removal rate of the steam generators. A low power-density core is adopted. OTSG (once-through steam genera tors) are adopted to minimize steam temperature changes while avoiding control rod movement during load- following operation. Passive RHR (residual heat removal) and containment cooling systems using natural circulation are adopted. Passive engineered safety systems actuated by gravity head or nitrogen gas pressure in case of LOCA (loss-of- coolant accident) are adopted. The designs of the following components have been changed to achieve simplification of reactor systems. In-vessel control rod drive mecha nism units are adopted to eliminate the chemical shim control system. A large-volume pressurizer is adopted to retain coolant in the pri mary system during load-following operation. Canned-motor pumps are adopted as primary coolant circulation pumps to eliminate the pump-seal-water feed system. Based on the above features, the auxiliary safety systems such as the emergency diesel generators, many valves and pumps, and the chemical and volume control system (CVCS) can be significantly simplified. As a result, the safety of the reactor system can be significantly enhanced by reducing the number of personnel required for operation and maintenance, and by mitigating the effects of human errors on reactor safety.

Reference Y. Murao, et al., A Concept of Passive Safety Light Water Reactor System Requiring Reduced Maintenance Efforts, ANS Winter Meeting, San Francisco (1993).

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