원전 해체 시 ALARA를 고려한 대형구조물 절단 시나리오 구축 연구

Abstract

There are 26 nuclear power plants in South Korea, of which 24 are currently in operation, excluding Kori Unit 1 and Wolseong Unit 1, which have been shut down permanently. Dismantling a nuclear power plant involves several steps, such as cutting, decontamination, disposal, and treatment. Cutting is performed close to the target structure as workers risk being overexposed. Typical large-scale structures, such as nuclear reactors, steam generators, pressurizers constructed with metals, and bio-shields, are representative concrete materials. Regarding pressurizers and bio-shields, studies on worker exposure management and cutting scenarios are relatively insufficient compared to other large-scale structures. Nuclear power plant decommissioning in these circumstances may cause unnecessary exposure of workers and increase secondary waste generation. In this study, a pressurizer and a bio-shield were selected as representative structures, and a cutting scenario was established. The radioactive waste disposal drum specifications were considered a basic construction condition. The bioshield was constructed by dividing the methodology for hot to cold and cold to hot and the application/nonapplication to abrasive decontamination situations. For the scenario evaluation, VISIPLAN, which includes cases applied to the dismantling of BR-3 and BR-2, was used. Among the conditions considered in the evaluation, the cutting time was the five-year interval from the period of permanent suspension to 30 years after the previous planned permanent suspension. The time point of 8.5 years was also considered. It is impossible to specify the cutting speed for each cutting technology, as various variables depend on the output and specifications of the machine. Therefore, it was divided into a pressurizer and a bio-shield based on the material, and the speed range was designated and applied to the evaluation. First, the pressurizer was set to 10cm/min intervals from 10 to 100cm/min, and the bio-shield was set to 1m2/hr intervals from 1 to 10m2/hr. This range results from extensive collection and analysis of cutting speed data for each cutting technology. The evaluation results of this study are intended to be presented as valuable data to establish ALARA-based cutting methods and consider applicable cutting methods for cutting large structures during dismantling.