Radiation safety assessment of a worker for the treatment facilities of the mixed spent resin from heavy water reactor

Abstract

The treatment facility for mixed spent resin at Wolsong CANDU nuclear power plant involves potential radiation exposure risks to workers during operation. This study established realistic normal and accident scenarios in advance to ensure long term and stable operation of the treatment facility to be installed, and provided the number of operations, time, and methods for conducting a radiation safety assessment. The primary components of the treatment facility include 1 kW and 9 kW scale beta-nuclide removal unit. This research evaluated shielding safety of the beta-nuclide removal units, analyzed worker doses during waste transport before and after treatment and examined exposure during injection, assessed doses under the leakage scenario of radioactive airborne particulates and maintenance operations. The study established realistic operational scenarios through empirical experiments and quantitatively analyzed both external and internal dose rates of workers. Using the VISIPLAN 4.0 code, the external dose rates of radionuclides contained in the mixed spent resin were evaluated, and internal dose rates were calculated considering the facility volume, breathing rate, and working time. For the shielding safety evaluation, lead and water shields of varying thickness were applied, and increasing shielding thickness consistently reduced spatial dose rates. The before treatment scenario assumed normal operation without leakage, while the after treatment scenario evaluated worker doses by accounting for the production of 5 kg of spent resin and 0.5 kg of combined zeolite and activated carbon. The injection scenario involved lifting the reactor lid and loading 2 kg of mixed spent resin into the facility. The leakage scenario of radioactive airborne particulates, the analysis considered a 20 % generation of radioactive airborne particulates relative to the unit volume for both the 1 kW and 9 kW scale beta-nuclide removal unit. And the maintenance scenario simulated pipe replacement based on an actual blockage incident. Therefore, this study conservatively assessed radiation safety by presenting work methods based on an annual dose of 20 mSv. Mixed spent resin treatment facility is currently in the pre-installation stage, during which various feasibility and performance verifications are being conducted. Accordingly, presenting measures to maintain radiological protection for workers during future operation will provide essential baseline data for securing the long-term safe operation of the facility.