2016 Volume 5 Issue 2 Pages 57-58
In the Rokkasho Reprocessing Plant in Japan, spent fuel produced in nuclear power plants is reprocessed and many radiation monitors are situated within the plant. There are risks of internal exposure of workers from alpha radiation emitting nuclides treated in the reprocessing plant; therefore, the air inhaled by the workers needs to be continuously monitored via radiological equipment. Alpha radiation airborne dust monitors collect aerosols from the air and continuously measure alpha radiation emitted from radionuclides using a solid-state detector (SSD). During the maintenance of the reprocessing plantʼs ventilation system when the ventilation time is less than that during normal operational periods, the concentrations of natural radioactive materials which emit alpha radiation in the air, increase, resulting in an increase indication of the alpha radiation airborne dust monitors. This study aims to determine how the influence of natural radioactive materials on the alpha radiation airborne dust monitors can be reduced. Therefore, we have obtained and evaluated the measurement data of the energy spectra of natural radioactive nuclides within the reprocessing plant and the energy characteristics of radiation sources. The results show that the alpha radiation airborne dust monitors possess some sensitivity to the beta radiation as well, which can reduce the counts of the dust monitors to alpha radiation by beta radiation counts. The use of this approach has highlighted the necessity to resolve certain technical problems such as using the correct dust monitor settings that consider the differences between individual alpha radiation airborne dust monitors and time delay to the radiation equilibrium of radon progeny.
