원전 중대사고 분석코드(MELCOR and MACCS)의 불확실성 평가

Abstract

단일호기 리스크에 대한 목표치를 제시하고 있는 2016년 원자력안전법(개정)이 발표됨에 국내원전에 대한 3단계 확률론적 안전성 평가에 대한 연구가 활발히 수행되었다. 또한 후쿠시마 사고 이후 다수기 리스크에 대한 관심도가 증가하며 이에 대한 연구가 진행되고 있다. 그러나 원자력발전소의 중대사고 분석에는 큰 불확실성이 존재함에도 불구하고 국내원전에 대해 도출되는 사고결말에 대한 불확실성 분석에 대한 경험은 전무한 상황이다. 리스크의 불확실성은 사고 빈도에 대한 불확실성과 사고 결말에 대한 불확실성으로 인해 발생한다. 이중 사고 결말에 대한 불확실성은 사고를 모의하고 이로 인한 결과를 계산하는 코드에 의해 주로 발생한다. 이에 본 논문에서는 원자력발전소의 리스크 분석 시 사용되는 중대사고 분석코드인 MELCOR과 MACCS를 바탕으로 사고결말에 대한 불확실성 분석을 수행하였다.

MELCOR 코드의 불확실성은 중대사고 현상에 대한 불확실성 분석을 수행하기 위한 선행연구가 다수 수행되었다. 그러나 원자력발전소 사고결말에 대한 불확실성 분석을 수행하기 위해서는 사고의 현상이 아닌 사고의 결말, 즉 환경으로 방출되는 방사성 물질의 정보에 대한 불확실성 분석이 필요하다. 이를 위해 본 논문에서는 WH600을 참조노형으로 선정하고 선행연구를 토대로 불확실성 변수를 결정하였다. 선정된 불확실성 변수를 이용하여 MELCOR 불확실성 분석을 수행하였다. MELCOR를 통해 도출 할 수 있는 방사선원항 정보 중 리스크 평가에 영향이 클 것으로 판단되는 방출시점과 방출분율에 중점을 두고 분석을 수행하였으며 계산된 값 통계 처리하여 그 결과를 제시하였다.

국내의 경우 MACCS 코드를 통해 계산되는 소외결말에 대한 불확실성 분석이 수행된 경험이 없다. 이에 미국에서 수행된 불확실성 분석 보고서를 바탕으로 변수를 선정하고 국내 원전의 특성과 환경을 고려하여 그 값을 입력하였다. MACCS의 불확실성 분석 기능을 제공하는 WinMACCS를 이용하여 계산을 수행하였다. 분석 결과로는 사고 후 7일 이내에 발생하는 사망확률을 의미하는 초기건강영향과 사고 후 중장기 기간에 발생할 수 있는 암 사망확률을 의미하는 후기건강영향의 인구가중리스크(Population Weighted Risk)를 제시하였다.

본 논문의 평가방법과 그 결과는 국내 원자력 발전소에 대한 리스크의 불확실성을 평가하는데 활용 할 수 있다. 또한 중대사고 리스크 평가가 가지는 불확실성을 정량화하고 이를 제시함으로써 그 결과에 대한 신뢰성을 확보하고 평가 모델을 개선 방향을 수립하는데 활용되어 큰 기여를 할 것으로 전망된다.|Since the 2016 Nuclear Safety Act (Revised), which presents target for single-unit risks, was released, studies on level 3 probabilistic safety assessment for Korean nuclear power plants were actively conducted. In addition, after the Fukushima accident, interest in mult-unit risk has increased. However, although there is great deal of uncertainty in the analysis of severe accident of nuclear power plants, there is no experience in uncertainty analysis of the consequence from Korean nuclear power plant accident. Uncertainty of risk arises from uncertainty about the frequency of accidents and uncertainty about the consequence of accidents. Uncertainty about the consequence is mainly caused by code that simulates the Severe accident. In this paper, uncertainty analysis on consequence was carried out based on MELCOR and MACCS, the major accident analysis codes used in the risk analysis of nuclear power plants.

Uncertainty of the MELCOR code has been studied in a number of previous studies to conduct an uncertainty analysis of severe accidents. However, in order to conduct uncertainty analysis on the risk of nuclear power plant, it is necessary to analyze the uncertainty about the information of radioactive material released into the environment, not the phenomenon. In this paper, WH600 was selected as a reference model and uncertainty variables were determined based on previous studies. MELCOR uncertainty analysis was performed using the selected uncertainty parameters. The analysis was focused on the release timing and release fraction that are considered to have a significant impact on the risk assessment of the source term information derived from MELCOR.

In Korea, no uncertainty analysis has been performed on the off-site consequences calculated through the MACCS code. The variables were selected based on the uncertainty analysis report conducted in the United States, and the values were entered in consideration of the characteristics and environment of Korean domestic nuclear power plants. The calculation was performed using WinMACCS, which provides the uncertainty analysis function of MACCS. As a result of the analysis, Population Weighted Risk was presented as early fatality, which means the probability of death occurring within 7 days after the accident, and cancer fatality, which means the probability of cancer death that can occur in the long-term after the accident.

The analysis method and the results of this paper can be used to assess the uncertainty of risk for Korean nuclear power plants. In addition, by quantifying and presenting the uncertainty of the severe accident risk assessment, it is expected to make a big contribution by securing reliability for the results and establishing the improvement direction of the model.; Since the 2016 Nuclear Safety Act (Revised), which presents target for single-unit risks, was released, studies on level 3 probabilistic safety assessment for Korean nuclear power plants were actively conducted. In addition, after the Fukushima accident, interest in mult-unit risk has increased. However, although there is great deal of uncertainty in the analysis of severe accident of nuclear power plants, there is no experience in uncertainty analysis of the consequence from Korean nuclear power plant accident. Uncertainty of risk arises from uncertainty about the frequency of accidents and uncertainty about the consequence of accidents. Uncertainty about the consequence is mainly caused by code that simulates the Severe accident. In this paper, uncertainty analysis on consequence was carried out based on MELCOR and MACCS, the major accident analysis codes used in the risk analysis of nuclear power plants.

Uncertainty of the MELCOR code has been studied in a number of previous studies to conduct an uncertainty analysis of severe accidents. However, in order to conduct uncertainty analysis on the risk of nuclear power plant, it is necessary to analyze the uncertainty about the information of radioactive material released into the environment, not the phenomenon. In this paper, WH600 was selected as a reference model and uncertainty variables were determined based on previous studies. MELCOR uncertainty analysis was performed using the selected uncertainty parameters. The analysis was focused on the release timing and release fraction that are considered to have a significant impact on the risk assessment of the source term information derived from MELCOR.

In Korea, no uncertainty analysis has been performed on the off-site consequences calculated through the MACCS code. The variables were selected based on the uncertainty analysis report conducted in the United States, and the values were entered in consideration of the characteristics and environment of Korean domestic nuclear power plants. The calculation was performed using WinMACCS, which provides the uncertainty analysis function of MACCS. As a result of the analysis, Population Weighted Risk was presented as early fatality, which means the probability of death occurring within 7 days after the accident, and cancer fatality, which means the probability of cancer death that can occur in the long-term after the accident.

The analysis method and the results of this paper can be used to assess the uncertainty of risk for Korean nuclear power plants. In addition, by quantifying and presenting the uncertainty of the severe accident risk assessment, it is expected to make a big contribution by securing reliability for the results and establishing the improvement direction of the model.