원자력발전소 해체 부지의 방사성오염 분포에 따른 조사설계 오차한계 분석

Abstract

When decommissioning a nuclear power plant, it is necessary to prove that the residualradioactivity is lower than DCGL in order to release the site. If the site is released by mistake, time andresources may be wasted, or it may have a radiological effect on people who use the site in the future. Therefore, for reasonable release of the site, it is necessary to derive the error limit for determiningwhether the radioactivity concentration of the soil sample is appropriate. The purpose of this study is toanalyze the survey design error limit according to radioactive concentration distributions of nuclear powerplant decommissioning site. To achieve the purpose of the study, the source terms, exposure scenario,and input parameters were selected. Each element was selected by domestic and foreign references,and the RESRAD-ONSITE code was used for exposure dose assessment. Source terms were selectedas 14C, 60Co, 63Ni, 90Sr, and 137Cs, and the exposure scenario was selected as a resident farmer scenarioconsidering all ingestion pathways. For input parameters, the domestic soil environment informationsystem and KINS regulation guideline 2.2 were used to select input parameters reflecting the domesticcharacteristics. Based on the selected source term, exposure scenario, and input parameters, we derivedthe soil DCGLw using the RESRAD-ONSITE results and site reuse criteria. Finally, based on the DCGLwand LBGR selected in this study, the gray region according to the change of the distribution of radioactivityconcentration was derived. As results of performing the RESRAD-ONSITE code, 14C, 63Ni, 90Sr, which arebeta emitting nuclides were found to be dominant in exposure dose through ingestion pathways, and 60Co,137Cs, which are gamma emitting nuclides, were dominant in exposure dose by external exposure fromthe surface of the site. As results of deriving the soil DCGLw based on the exposure doses, 63Ni was thelargest value at 5.41×101 Bq g-1, and 60Co was the smallest value at 4.42×10-2 Bq g-1. Finally, as resultsof deriving the values of relative shift based on the standard deviation of radioactivity concentration,LBGR, and DCGLw, it was found that the values of relative shift exceed 3 for all radionuclides. And as thevalues of LBGR were modified, the width of the gray areas were changed to be narrower. Furthermore,it was found that the smaller the standard deviation values of the radioactivity concentration distribution the higher the values of the relative shift in the gray area. As the values of standard deviation decreased,it was expected that the number of samples required in the site survey design will decrease. It is judgedthat the results of this study will be used in deriving the error limit of radioactivity concentration accordingto soil sample measurement when decommissioning a domestic nuclear power plant in the future.,