## 5 Conclusions  
The preliminary DCGLs for the soil of the Wolsong NPP site, which is a pressurized heavy water reactor, were derived in this study according to the methodology suggested by the MARSSIM. The decommissioning cases of overseas NPPs such as Rancho Seco and Zion NPPs were considered, and various literature was referred to as well for the evaluation. The target radionuclides for calculating the DCGL were selected based on the data of radionuclides identified in the pressure tube specimens of Wolsong Unit 1 that have been reported in the literature. The input parameters were selected considering the site-specific variables of the Wolsong NPP site and employed in the RESRAD-ONSITE code. In addition, input data such as distribution coefficients were derived and applied to simulate the migration and retardation behavior of radionuclides using the JAEA-SDB [9]. Consequently, the DCGLs for the Wolsong NPP site soil with respect to the resident scenario were preliminarily derived by using the input parameter database built in the present work. A comparison of the results with that of previous studies showed that they were relatively consistent with each other. To preliminarily derive the year for site release for unrestricted reuse, the inventory of 14 target radionuclides was set to 0.037 Bq\(\cdot\)g\({}^{-1}\) (1 pCi\(\cdot\)g\({}^{-1}\)) in the contaminated zone, and their total exposure dose was calculated accordingly. The result showed that the exposure dose of 0.1 mSv\(\cdot\)year\({}^{-1}\) for site reuse was satisfied at 4.07 years after the decommissioning of the Wolsong NPP and the final investigation of the site condition. Furthermore, as a result of sensitivity analysis to identify input parameters that affect the calculation of the year for site release for unrestricted reuse, the density of contaminated zone, evapotranspiration coefficient, and external gamma shielding factor were found to be major sensitivity parameters. These parameters were evaluated to have a significant impact on the external radiation pathway by radionuclide numbers remaining in the contaminated zone. As the first study that evaluated the DCGL for the pressurized heavy water reactor, Wolsong NPP, the input parameter database and calculation model developed in the present work are expected to be useful as a preliminary study that can be referenced when decommissioning heavy water reactors in South Korea in the future. Furthermore, it is foreseen that the economic and efficient site release standards for pressurized heavy water reactors can be established through the derivation of further reliable exposure dose results if the uncertainties in radionuclide inventory, hydrogeological parameters, and other input parameters are reduced through practical experiments on soil samples in the NPP site, along with additional field surveys in the future. For example, previous research work has confirmed the considerable relationship between the distribution coefficient and exposure dose results in the safety assessment model of nuclear waste repositories [33]. In the former investigation, a relatively increased distribution coefficient provided a remarkably delayed release rate of radionuclides owing to the enhanced retention capacity of geologic barriers and presented a relatively delayed peak time and decreased peak value of exposure dose. Since the distribution coefficient is an element-specific and conditional parameter, depending on various hydro-geochemical conditions, securing more precise distribution coefficient data for various radionuclides through a practical field test is expected to provide a significant contribution to further reliable model calculation. Conceptualization, J.-Y.L. and C.-G.K.; methodology, J.-Y.L. and S.A.; software, C.-G.K.; validation, J.-Y.L. and S.A.; formal analysis, J.-Y.L. ; investigation, C.-G.K.; resources, J.-Y.L. ; data curation, J.-Y.L. and [PERSON]-G.K.; writing--original draft preparation, C.-G.K.; writing--review and editing, [PERSON]-Y.L. ; visualization, J.-Y.L. ; supervision, J.-Y.L.