Design research on a Reduced-Moderation Water Reactor (RMWR) is being performed, aiming at such benefits as the effective utilization of uranium resources, the high burn-up and the long operation cycle, and the multiple recycling of plutonium. Such a reactor concept can be realized by utilizing neutrons with high energy generated under reduced water (i.e., moderator) fraction in the core.
In this design, various ideas such as the tight-lattice fuel rod configuration, the short core design, and the internal blankets for neutron absorption, have been introduced to increase as much as possible the conversion ratio from fertile material of uranium-238 to the fissile material of plutonium-239, as well as to attain the automatic core power reduction characteristic even if the core power increases and generates bubbles, i.e., a negative void reactivity coefficient. As a result, some design concepts with various benefits have been obtained. One is a boiling water reactor (BWR) type concept as shown in Fig. 8-1 with a conversion ratio of more than 1.0; this means that more fissile material than consumed can be produced in the core. Another is a pressurized water reactor (PWR) type concept as shown in Fig. 8-2 with the feasibility for the multiple recycling of plutonium, which is not possible with the recently planned plutonium utilization in thermal reactors. A BWR-type concept is also proposed as shown in Fig. 8-3 with the feasibility for an increase of plant factor and the reduction of spent fuel generation, by the longer operation cycle and the higher burn-up through the characteristic of a high conversion ratio to fissile material.
The research will be continued to complete the RMWR design and to conduct the reactor physics and the thermal hydraulic experiments for the confirmation of the validity of design and safety, aiming at a realization of RMWR to challenge the limits of light water reactor technology and to flexibly cope with a possible future change in the energy situation. |
