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| The Japan Atomic Energy Research Institute (JAERI) has continued R&D work on a reduced-moderation water reactor (RMWR), one of a highly advanced nature that potentially can be applied to satisfy various needs as a basic form of technology in energy systems of the future. The feature of the RMWR reactor are effective use of uranium resources, reduction of radioactive waste, deployment of excess plutonium, etc. |
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Advanced Reactor System Laboratory Department of Nuclear Energy System Group Leader Takamichi Iwamura |
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The reactor core characteristics of light water reactors are considered to resemble those of fast breeder reactors (FBR) by their high neutron energy operation resulting from low neutron moderation owing to reduced water (moderator) volume fraction.
This ｔype of light water reactor is called a reduced-moderation water reactor (RMWR). In reduced-moderation water reactors, converting uranium-238 to plutonium-239 by absorbing neutron is accomplished, after which the plutonium generated can be recycled as fuel, thus realizing more effective use of uranium and plutonium multi-recycling, longer-term operation, improved utilization factor and lower periodic inspection cost. In addition, it will contribute to reduced amounts of spent nuclear fuel and radioactive waste by its high-burn function. Designing the core of the reduced-moderation water reactor demands improving core performance, such as the conversion ratio of the amount of new fuel production to that of spent fuel based on safety of operation. Too, while doing this, to secure reactor safety necessitates designing the reactor characteristic for lowering the reactor power naturally, when the volume of void in the reactor core increases owing to the increase of power or reduction of cooling water. Otherwise, there exists the possibility of promoting fission reaction in the core, which can induce a severe adverse incident. It is not easy to cope with conversion ratio improvement and the securing of safety at the same time. Various ideas regarding this include tightening of fuel assembly to improve the conversion ratio and changing the reactor core configuration to secure safety and they have been incorporated into the core's conceptual design. To determine if a high Pu conversion ratio of about 1.0 and reactor safety can be obtained at the same time, the experiments using TCA (Tank Type Critical Assembly) are in preparation. These tests are essential to confirm the feasibility of reduced-moderation water reactors. The series of research activities is called a verification study on the feasibility of RMWR. Following completion of this stage, technical demonstration research will commence, aiming at the commercialization of RMWR around 2020. |
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