The IFIN-HH VVR-S nuclear research reactor, which operated between 1957 and 1997, is currently in the decommissioning phase. In the operational history of VVR-S there were two floods with coolant in the pump room (discharge of the 300 m 3 tank into the buffer tank and the pump room) which contaminated the floor and walls. The coolant consists of distilled water containing the following radionuclides: 137 Cs, 60 Co, 152 Eu, 154 Eu, 155 Eu from nuclear fission and the activation of corrosion products. From the Radiological Characterization Report of the structures of the VVR-S nuclear reactor, detailed data regarding the depth of penetration in concrete by using gamma spectrometry for the analysis of samples taken from concrete. During 2014-2016, the systems, equipment and components of the primary circuit and the pump room were decommissioned, followed by the decontamination of the floors and walls. Therefore, the vertical profile of radionuclide penetration into concrete is known for all chamber surfaces.
The project will carry out the necessary measurements for gamma spectrometry analyzes to determine the contamination of the vertical profile by sampling, taking into account the water level of 18 cm in the pump room, the standing time of water in areas before evacuation in 48 hours, the density of the concrete at the floor level and the density of the concrete at the wall level. Thus, spectroscopy measurements of the concrete contamination will be performed, which will be used as input data in the modeling program.
The project will then consist of assessing the migration of radionuclides inside the concrete building of the IFIN-HH VVR-S nuclear research reactor as a result of an unexpected event, in order to safely decommission the reactor. In order to obtain a relevant prediction of the contaminated area, it is essential to use a robust numerical code calibrated using real data. The main aspect is the ability of the numerical code to model diffusion transport in very low porosity media such as concrete.
The concept of the research project is to develop a methodology for assessing the contamination profile and calculating the transport of radionuclides in the pump chamber (chamber 31) and in the chamber below the reactor (chamber 30) from the VVR-S nuclear reactor.