Experiments for airborne dispersion ratio of radionuclides during plasma arc cutting were carried out in a contamination control enclosure, using stored radioactive metal wastes arising from the decommissioning activities of Japan Power Demonstration Reactor, which was a boiling water type reactor. Neutron induced-activated piping and surface contaminated piping were segmented into pieces using air plasma arc cutting, using a current power was 100A. In addition, similar experiments for contaminated piping of the Advanced Thermal Reactor, Fugen were carried out. As a result, dispersion ratios for activated piping were 0.2 to 0.7% of Co-60 and 0.4% of Ni-63 under the condition with a covered cap on the head. And those for surface contaminated piping were from 18 to 23%. In addition, those for vertically segmented piping which simulated flat plate were from 34 to 43%. There was no difference of dispersion ratios between stainless steel and carbon steel base materials. All values obtained were smaller than the Handbook recommended value of 70% for contaminated materials. Filtering collection efficiencies of the coarse dust filter were approximately 40% for activated piping and approximately 55 to 80% for surface contaminated piping. However there was no effect for collection of aerosols smaller than 1 μm. Size distribution analysis indicated a greater concentration of radionuclides in particles smaller than 0.1μm when compared with larger particles. In addition, there was a tendency that the Ni-63 was concentrated to the particles smaller than 0.3 μm compared with the Co-60. The results support data obtained in the previous studies using non-radioactive materials.

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