Modeling of the Radiation Doses during Dismantling of RBMK-1500 Reactor Pressurized Tanks from Emergency Core Cooling System

Decommissioning of the Ignalina Nuclear Power Plant involves multiple problems. One of them is personnel radiation safety during the performance of dismantling activities. In this paper, modeling results of radiation doses during the dismantling of the pressurized tank from the emergency core cooling system (ECCS PT) of RBMK-1500 reactor are presented. The radiological surveys indicate that the inner surface of the ECCS PT is contaminated with radioactive products of corrosion and sediments due to the radioactive water. The effective doses to the workers have been modeled for different strategies of ECCS PT dismantling. In order to select the optimal personnel radiation safety, the modeling has been performed by the means of computer code “VISIPLAN 3D ALARA Planning tool” developed by SCK CEN (Belgium). The impacts of dismantling tools, shielding types, and extract ventilation flow rate on effective doses during the dismantling of ECCS PT have been analyzed. The total effective personnel doses have been obtained by summarizing the effective personnel doses from various sources of exposure, that is, direct radiation from radioactive equipment, internal radiation due to inhalation of radioactive aerosols, and direct radiation from radioactive aerosols arising during hot cutting in premises. The uncertainty of the collective doses is also presented in this paper. 1. Introduction Ignalina NPP is the only nuclear power plant in Lithuania. Ignalina NPP operated two similar RBMK-1500 units with installed capacity of 1500？MW (each). They were commissioned in 1983 and 1987, and the original design lifetime was projected up to 2010 and 2015, respectively. However, the first unit was shut down at the end of 2004, and the second one was shut down at the end of 2009. The Lithuanian Government approved an immediate decommissioning strategy for the first unit of INPP [1, 2]. Building 117/1, where the emergency core cooling system (ECCS) is installed, is the first dismantling project at Ignalina NPP. After the shutdown of the first unit of INPP, the high pressure part of ECCS pressurized tanks (PT), big diameter pipes, fast acting valves, and the Helium Make-up Station became redundant and were no longer needed for safety or operational purposes and hence could be progressively dismantled. Contamination of internal surfaces of some equipment (big diameter pipes, small pipes, and ECCS PT) that had been in contact with the reactor core cooling water was detected [3]. Nowadays, due to enhancements in computer systems, the dismantling activities are planned using various