Evaluation of DCGLs and RSSI Process for Kori Unit-1 Decommissioning Based on MARSSIM

Abstract

The Kori Unit-1, which is the first Pressurized Water Reactor (PWR) in South Korea, was permanently shut down on June 19, 2017 and started decommissioning. Kori Unit-1 has been completed to the historical site assessment (HSA), which is a non-radiological survey conducted by examining the site operating history and worker interviews. Radiological survey of Kori Unit-1 will be carried out as decommissioning phase proceeds actively. However, since South Korea has not been established guideline related to radiological survey on decommissioning sites, it will be necessary to establish manual and regulation for the radiological survey in future. In this paper, Multi-Agency Radiation survey and site investigation (MARSSIM), which is the guidelines of U.S. for radiological survey on decommissioning sites and decommissioning sites release was introduce as well as preliminary DCGLW calculation and application of RSSI process protocol was carried out to provide considerations for actual execution of radiological survey in Kori Unit-1 decommissioning. The preliminary DCGLW of Kori Unit-1 was calculated considering the resident farmer scenario to enable conservative calculation, by using the habit data of a 1-y-old-infant, 10-y-old child, and adult who live around the Kori Unit-1 as a human receptors. The direct measurement and scanning of two hotspot scenarios were performed for evaluating mutual effect of hotspot size, concentration, and scan speed in actual application of Radiation Survey and Site Investigation (RSSI) process protocol. First scenario is a hotspot present in survey unit that does not comply with release criterion (high-concentration, homogeneous distribution) and second scenario is a hotspot present in survey unit that complies with release criterion (low-concentration, non-homogeneous distribution).