Aerosol Characterization During Heating and Mechanical Cutting of Simulated Uranium Containing Debris: the URASOL Project in the Framework of Fukushima Daiichi Fuel Debris Removal
Résumé
One of the important challenges for the decommissioning of the damaged reactors of the Fukushima Daiichi Nuclear Power Station (1F) is the fuel debris retrieval. The generation and dispersion of radioactive aerosols during the cutting operations of fuel debris pose a significant radiation and health risk during the decommissioning process. Quantitative assessments of potential contamination with radioactive aerosols are fundamental to the development of a safety case for the decommissioning of 1F. Detailed studies on the generation of aerosols during cutting processes of inactive fuel debris simulants by various tools have been performed [1, 2, 3, 4, 5], underlining the influence of each cutting tool and its operating conditions, the chemical composition of cut materials, and the environmental conditions of the dismantling, such as in air for dry or wet conditions and underwater conditions. The size distribution, morphology and composition of particles released during cutting are equally significant when predicting their transport and deposition behavior through numerical simulations and assessing their radioactivity. Furthermore, quantitative characterization of radioactive aerosols is essential to develop and optimize technologies to capture and mitigate particulate contaminants dissemination. In this context, the URASOL project (abbreviation for “Particle generation test using simulated uranium containing debris”, a word coined from URAnium and aeroSOL), which is undertaken by a French consortium consisting of ONET Technologies, CEA, and IRSN for JAEA/CLADS, is dedicated to acquire basic scientific data on the generation and characteristics of radioactive aerosols from the thermal or mechanical processing of fuel debris simulant [6]. Heating process undertaken in the VITAE (acronym for VITi-AErosols) facility simulates some representative conditions of thermal cutting by laser [7]. For mechanical cutting, the core boring technique is implemented in the FUJISAN facility. Fuel debris simulants have been developed for inactive and active trials [8]. The aerosols are characterized in terms of mass concentration, real time number concentration, mass size distribution, morphology, and chemical properties. The chemical characterization aims at identifying potential radioactive particles released and the associated size distribution, both of which are important information for assessing possible safety and radioprotection measures during the fuel debris retrieval operations at 1F.