방사성폐기물 자체처분을 위한 RESRAD코드 민감도 분석 및 안전성 평가

Abstract

방사성폐기물 자체처분 시 원자력관계사업자는 원자력안전법에 따라 방사성폐기물 자체처분계획서를 원자력안전위원회(이하 “원안위”라 한다.)에 제출하여야 한다. 자체처분계획서에는 원안위 고시 제2020-6호「방사성폐기물 분류 및 자체처분 기준에 관한 규정」에 따라 핵종별 허용농도 또는 허용선량이 만족함을 입증하기 위한 자체처분 안전성을 평가하여 기술하고 그 타당성을 설명하여야 한다. 국내의 매립대상 폐기물 자체처분 안전성평가는 미국 DOE(Department of Energy)의 ANL(Argonne National Laboratory)에서 개발한 RESRAD 전산프로그램이 가장 많이 활용되고 있으며, 매립장의 부지 특성인자는 RESRAD 기본값과 KINS/RR-144「방사성폐기물 규제해제 요건 개발」에 근거한 대푯값을 채택하여 평가가 이루어지고 있다. 그러나 입력인자의 기술적 판단 근거가 부족하여 대푯값 선정이 어렵고, 동일한 종류의 폐기물 평가 시에도 입력인자 적용에 차이를 보이고 있다. 이는 국내 부지 특성인자 확보의 어려움과 규제요건 입증의 용이성에 초점을 맞춘 보수적인 입력인자 선택이 주요 요인이며, 그 결과 예상피폭선량 과대평가로 자체처분에 미치는 영향이 매우 크다. 따라서 본 연구에서는 자체처분 적합성 및 안전성 확보를 위해 매립대상 폐기물의 선량평가 주요 인자의 특성과 민감도 분석을 통해 자체처분을 효율적으로 수행하기 위한 입력인자를 고찰하였다.|Radioactive waste is a by-product that is unavoidably generated in the process of using nuclear power and radioactive materials, and is classified into high, medium, low, ultra-low and deregulated waste according to the level of activity. Radioactive waste above the ultra-low level is finally disposed of in a permanent disposal method, and clearance level wastes with an extremely low level of radioactivity is classified as waste subject to clearance, and nuclear-related business operators can dispose of it by incineration, landfill, or recycling. For domestic clearance, the waste generated during operation of nuclear power plants has been continuously disposed since 1995 after the first disposal of NaF by KNFC. In 2017, the dismantling of Kori unit 1, the first nuclear power plant in Korea, was confirmed, and permanent suspension of 14 nuclear power plants by 2033 was realized, and it is expected that the generation of radioactive waste subject to clearance of wastes due to nuclear power plant decommissioning will steadily increase in the future. . In particular, The importance of securing a landfill for safe disposal of self-disposable waste and safety evaluation is emphasized because it is expected that a large amount of waste to be landfilled such as concrete and soil will be generated during the dismantling of nuclear-related facilities and site restoration. When evaluating the safety of clearance of wastes subject to landfill, the estimated dose to residents is evaluated using the RESRAD computer program developed by ANL(Argonne National Laboratory) of the US Department of Energy (DOE). Most of the input factors of RESRAD are evaluated by adopting the program default values ​​and representative values ​​based on KINS/RR-144 (2002). However, it is difficult to select a representative value due to the lack of the basis for technical judgment of the input factor, and there are differences in the application of the input factor even when evaluating the dose of the same type of waste. The main factor is the selection of conservative input factors focusing on the difficulty of securing domestic site characteristic factors and the ease of verification of regulatory requirements, and as a result, the impact on clearance by overestimating the expected exposure dose is very large. In this study, in order to secure the suitability and safety of clearance of waste to be landfilled, input factors for efficient clearance were considered through the characteristics and sensitivity analysis of the input variables of the RESRAD, and the latest literature and reports were reviewed to be overly conservative. Excluding assumptions and applying practical values. In addition, in order to evaluate the dose evaluation age group appropriately in accordance with the regulatory guidelines, an intake factor and a dose conversion factor (DCF) were applied for each of the six age groups, and the results were compared and evaluated by additionally performing the single-age group evaluation, the existing method. Finally, the exposure dose of the age group showing the maximum value among the results of the dose evaluation of the six age groups was adopted, and it was judged that it was suitable for the regulatory standards. As a result of analyzing the effectiveness and sensitivity of the RESRAD-ONSITE input factor in this study, it was confirmed that the evaluation was somewhat conservative due to some different conditions from the domestic environment. In the future, by developing and discovering practical input factors reflecting domestic conditions, securing safety, and performing evaluations tailored to the characteristics of each waste, it will be possible to more accurately predict the expected radiation dose. Based on this, it is expected to increase confidence in the deregulation to promote self-disposal, and to minimize the occurrence of radioactive waste drums, resulting in significant economic effects from reducing disposal costs.