Technical Methodology to Evaluate the Decommissioning of the Contaminated Underground Structures Belonging to the VVR-S Nuclear Research Reactor

I. Iorgaa, b, R. Dejua, A.O. Pavelescua, D. Guraua aHoria Hulubei National Institute of Physics and Nuclear Engineering (IFIN-HH), P.O. Box MG-6, RO-077125, Magurele, Romania bFaculty of Physics, University of Bucharest, P.O. Box MG-11, 077125, Bucharest-Magurele, Romania

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Technical methodology to evaluate the decommissioning of the underground pipes connecting the 30 m3 buffer tank of liquid effluents belonging to the Nuclear Reactor VVR-S to the 300 m3 radioactive waste treatment station tanks from the IFIN-HH was made. Type and concentration of radionuclides found in irradiated materials with neutrons depend from nuclides, exposure duration to radiation, the energy and flux of incident neutrons. Internal and external contamination for the technology systems was caused by deposition inside the pipes and equipment of the particulate or soluble compounds circulated by the effluent, and the contamination leaked because of systems maintenance operations or management of radioactive waste. Important radionuclides in decommissioning depend primarily on the type of nuclear facility. For this research reactor in accordance with the approved decommissioning plan and radiological characterization, important radionuclides for underground structures are: Am241, Cs137, Co60, Sr90-Y90 and Eu152. For reactor, the inventory was calculated based on size, weight, irradiated components composition, analyzing trace elements, impurities, and integrated neutron flux and reactor operation history. Thus, the radioactive contents will result based on estimates associated with radiation doses which are then validated through on-site measurements. Internal contamination of irradiated components is estimated based on experimental measurements and correlation factors before a major radionuclide Co60. As results the total level of contamination (Cs137 and Co60) measured during cutting operations was between 11 Bq/cm2 and 75 Bq/cm2. Beta gamma superficial contamination level of outer pipe is close to the background within the error measurements limits.

DOI:10.12693/APhysPolA.134.311 topics: decommissioning, methodology, radioactive effluents, contamination