Fig. 13-1 Reactor Dismantling Techniques A variety of specially developed techniques are needed for dismantling a reactor. The actual dismantling of JPDR has progressed by applying the techniques developed in JAERI. The figure shows the techniques developed for dismantling the main body of JPDR.

Fig. 13-2 Results of decontamination by the electro-polishing method The contamination level on the inner-surface of stainless steel pipes can be reduced more than three figures by using the electro-polishing method for about twenty minutes.

Fig. 13-3 Results of decontamination of a concrete surface of a building Contaminated concrete from a building was cored. Slices for every 1 mm of depth were prepared. The results of the measurement of sliced concrete samples showed the depth of the contamination was a few mm or, at most, 1 cm.

The lifetime of nuclear power plants now in operation in Japan is estimated to be 30 to 40 years. Therefore, the decommissioning of nuclear reactors will become a matter of great importance early in the twenty-first century. For this coming decommissioning, the Japan Atomic Energy Research Institute (JAERI) has been developing, since 1981, the techniques needed for dismantling nuclear power plants. The techniques developed have been applied to the actual dismantling of the Japan Power Demonstration Reactor (JPDR) to prove their suitability. When dismantling a nuclear power plant, there are three major problems to be resolved as follows: to dismantle the radioactive components efficiently and safely, to remove the radioactivity of contaminated components as much as possible using decontamination techniques, to manage properly the very large volume of wastes produced during dismantling. The dismantling techniques shown in Figure 13-1 have been developed and were applied to the actual dismantling of JPDR. This task progressed effectively, safely, and without any resultant spread of contamination by applying these techniques. For example, the arc saw technique has proved able to cut steel up to 20 cm thick, which corresponds to the material and thickness of the pressure vessel of a power plant. To remove radioactive decontamination, methods employing electro-polishing,chemical immersion using cerium, flowing abrasives, concrete crushing by microwave, and so on, have been developed. Figure 13-2 shows the electro-polishing decontamination method can decrease surface activity of hardware components to less than 10-3 within nearly 20 minutes. Figure 13-3 indicates that activity of contaminated concrete in a building can be adequately reduced by the removal of only a few mm or, at most, 10 mm of the concrete surface. Tests conducted on this demonstration facility have confirmed that the volumetric reduction of large amounts of contaminated metal wastes could be realized effectively by melting and homogenizing.

Reference K. Fujiki, Development programs on decommissioning technology for reactors and fuel cycle facilities in Japan. : Present status and STA's view for advanced technology development.: Decommissioning policies for nuclear facilities. Proc. of an International Seminar. Decommissioning policies for nuclear facilities. Paris (France) 2-4 Oct. 1991. 111 (1992). Dept. of JPDR, JAERI (ed. ), Progress of JPDR Decommissioning Program, Nucl. Eng. 37 (2), p. 14-59 (1991).

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