Radiation safety evaluation of workers on aerosol generated during radioactive waste processing in hot cell facility

The permanent shutdown of the Kori Unit 1 nuclear power plant (NPP) required a decommissioning process, which generated an uncertain amount of radioactive waste containing nuclides produced by unidentified impurities. Radiation safety evaluations were conducted on workers to confirm the emission source and dose evaluation during the cutting of the pressure vessel and core barrel made of carbon steel and stainless steel in hot cell facility. Analysis of the decommissioning waste of the pressurized water reactor (PWR), the treated pressure vessel, and the core barrel in the hot cell facility was essential. In addition, the Monte Carlo N-Particle (MCNP) transport code was used to evaluate the exposure dose affecting workers in the event of an accidental ventilation failure, broken lead glass window, and normal operations at the hot cell facility during the processing of the radioactive waste. The exposure dose in the case of accidental ventilation failure was evaluated as 2,950 times the exposure dose during normal operation, and that due to a broken lead glass window was evaluated as a further 140 times. Therefore, it was found that the exposure dose of broken lead glass accident was 4.12E + 05 times greater than the exposure dose during normal operation. Accordingly, the emission concentration of the dominant nuclides (3H, 14C, 55Fe, 59Ni, 60Co, and 63Ni) of the airborne source term was detected using a high-efficiency particulate air filter with an efficiency of 99.97%, which satisfies the emission management standard of Nuclear Safety Commission Notice No. 2016-16. Based on these results, the emission control of airborne source terms can be evaluated when decommissioning radioactive waste in a hot cell facility using the standard radiation protection methods.