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Development of the concrete wall structure which can drastically reduce radioactive wasteJul. 7, 2008A concrete wall structure with three layers was co-developed by JAEA and Kumagaigumi Co., Ltd. The developed concrete wall structure can be fabricated with low cost. It can effectively shield neutrons and drastically reduce radioactive waste. Neutrons irradiate concrete as a structure in neutron generation facilities such as a nuclear power plant, accelerator facility, etc, and radioactive materials are generated in the concrete. Radiations such as gamma-rays are emitted from the radioactive materials in the concrete, and it requires long cooling time to start maintenance of the facility for radiation dose control of workers. When neutrons irradiate the concrete for the long duration, radioactive materials are accumulated in the concrete. As a result, the concrete has to be treated as radioactive wastes, and it costs a great deal to treat the activated concrete compared with disposal of the concrete as normal industrial waste. Previously the low activation concrete and the boron doped low activation concrete have been developed as the concrete technology to enhance the low activation performance and the shielding performance of the concrete in neutron generation facilities. It has both merits and demerits from various viewpoints including economics perspective to apply these concretes monolithically to the concrete wall. In this study, we developed a concrete wall structure with three layers taking into account the reduction of the radioactive waste, enhancement of the shielding performance and reduction of the cost comprehensively. In the developed concrete wall structure, the low activation concrete, the boron doped low activation concrete and the normal concrete are placed by turns from the neutron source. In order to evaluate the low activation and shielding performances of the developed concrete wall structure, DT neutron irradiation experiments were conducted at FNS in JAEA with the boron doped low activation monolithic concrete, the monolithic normal concrete and the developed concrete wall structure. It was confirmed that the low activation and shielding performances of the developed concrete wall structure were almost the same as those of the boron doped low activation monolithic concrete, and the fabrication cost of the former could be reduced to 1/2 � 1/3 compared with that of the latter. It was also confirmed that radioisotopes produced in the developed concrete wall structure could be reduced to about 1/3 compared with that in the monolithic normal concrete. By using the boron doped low activation layer of the developed concrete wall structure as a mold, its productivity can be enhanced. In addition, it is possible to easily separate highly activated concrete parts from low or no activated concrete parts in decommission of the facility, so the decommissioning cost can be more drastically reduced. In the future, we will apply the developed concrete wall structure to neutron generation facilities such as nuclear power plants, accelerator facilities, cancer therapy facilities, PET facilities, nuclear fusion plants, etc. |
