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석수동,전병산,박진호,장현식,장미숙,김성래 (사)한국방사선산업학회 2021 방사선산업학회지 Vol.15 No.4
An effort was made in this paper for the decommissioning purpose of the CANDUplant to review a salient characteristics of the major radiological source terms, which arise fromthe neutron activation of the reactor materials, fission products leaked from fuel cladding andtheir erosion and corrosion products in the primary heat transport system (PHTS) and moderatorsystem of the plant. One of the most important unique features of the CANDU plant is the useof heavy water both as coolant and moderator in contrast to the use of light water in the PWRnuclear plant. As a result, significant amount of tritium and 14C is produced mostly in heavywater during power operation, about 100 times larger than in PWR. Another important featurein terms of decommissioning is that the primary heat transport system is mainly made of carbonsteel (eg., feeder pipes and headers, pumps and shell side of steam generators etc.), while stainlesssteel is used for the reactor vessel and the major part of the reactor coolant system of PWRplants. Due to the flow accelerated corrosion (FAC) on the outlet feeders, a significant amount ofcorrosion product iron as magnetite is transferred from the outlet feeders and accumulated onthe surfaces of the steam generator and inlet feeders. A relevant method is yet to be developedto decontaminate the corrosion products on the PHTS and moderator system of CANDU fordecommissioning purpose. In this paper, the design features and material characteristics of thePHTS and moderator system, which comprise the main sources of radiological source terms,are first briefly described. And then the unique features of the source terms to be considered fordecommissioning are described including; (1) neutron activation of the major reactor componentssuch as pressure tube and calandria tube, reactivity devices and calandria tank, (2) erosion andcorrosion of activated iron products in the PHTS, and (3) production of tritium and 14C in thePHTS and moderator system.