Fukushima Daiichi fuel debris simulant materials for the development of cutting and collection technologies

International audienceCutting fuel debris (solidified corium) is an important issue for the decommissioning of Fukushima Daiichi Nuclear Power Station. The main reasons for developing and using fuel debris simulants are presented. The relative merits of the various types of materials (stainless steel, zirconium, sintered alumina-zirconia, cast fused zirconia, metal+zirconia, melted inactive simulants, prototypic fuel debris simulant, irradiated fuel debris simulant) that can be used to simulate fuel debris cutting have been assessed against criteria relevant for the cutting technique itself (hardness, melting temperature, elastic modulus, toughness, heterogeneity) as well as relevant to (radioactive) aerosol and combustible gas generation. It appears that simplified simulants can be used for the development of fuel debris cutting techniques but have some limitations in terms of representativity so that melted inactive fuel debris simulant must be used to assess the cutting performance. Concerning combustible gas generation, zirconium plates will provide an upper bound in term of underwater generation of hydrogen. Finally, for aerosol and dust generation, it appears that non-radioactive simulant cannot correctly represent the aerosol formation during cutting. Prototypic fuel debris simulant, using depleted uranium and natural isotopic composition for the fission product elements are the best available option for determination of cutting secondary outlet

Aerosol characterization and particle scrubbing efficiency of underwater operations during laser cutting of steel components for dismantling of nuclear facilities

International audienceThe goal of this article is to provide results on aerosol particles emissions of a laser Nd:YAG cutting technique used for the decommissioning of nuclear facilities. In particular, the study aims at characterizing the aerosol emitted during the cutting of steel specimens of different thicknesses and to study particulate emissions for cuts in air and under water. To do so, we calculate the emitted aerosol mass per unit area of cut. Overall, it was found that the mass of aerosol per unit area of cut by laser cutting decreases when the laser power and cutting speed increase. We also examine the performance of the height of the water column above the cut on the particle collection efficiency. We found that the driving phenomenon for particle collection is the scrubbing of particles by bubbles present in the water column. When cuts are realized under water, the production of aerosol particles mass per unit area of cut is reduced by a factor of 10 and limited below 70 g m–2. © Taiwan Association for Aerosol Research

Analysis of aerosol emission and dispersion during the laser cutting of fukushima fuel debris simulants

International audienceThe general context of the article is related to demonstrate the feasibility of the use of the laser cutting technique for the fuel debris retrieval on the damaged reactors of Fukushima Dai-ichi. IRSN is involved in a project lead by ONET with CEA, to bring relevant elements to analyze the risk occurred by the dispersion of aerosols emitted by the dismantling operations. Results regarding the aerosols source term characterization emitted during laser cutting of non-radioactive fuel debris simulants were acquired during experiments undertaken on the DELIA cutting laser platform from CEA. IRSN realized aerosol sampling, aerosol size distribution measurement and CFD calculation of aerosol transport and wall deposition. The evaluations performed will enable the Japanese teams responsible for extracting corium from the damaged reactors of Fukushima Dai-ichi to define the best strategies to implement containment, and ultimately to limit the dissemination of radionuclides in the environment

Analysis of aerosol emission and dispersion during the laser cutting of fukushima fuel debris simulants

International audienceThe general context of the article is related to demonstrate the feasibility of the use of the laser cutting technique for the fuel debris retrieval on the damaged reactors of Fukushima Dai-ichi. IRSN is involved in a project lead by ONET with CEA, to bring relevant elements to analyze the risk occurred by the dispersion of aerosols emitted by the dismantling operations. Results regarding the aerosols source term characterization emitted during laser cutting of non-radioactive fuel debris simulants were acquired during experiments undertaken on the DELIA cutting laser platform from CEA. IRSN realized aerosol sampling, aerosol size distribution measurement and CFD calculation of aerosol transport and wall deposition. The evaluations performed will enable the Japanese teams responsible for extracting corium from the damaged reactors of Fukushima Dai-ichi to define the best strategies to implement containment, and ultimately to limit the dissemination of radionuclides in the environment

Analysis of aerosol emission and dispersion during the laser cutting of fukushima fuel debris simulants

International audienceThe general context of the article is related to demonstrate the feasibility of the use of the laser cutting technique for the fuel debris retrieval on the damaged reactors of Fukushima Dai-ichi. IRSN is involved in a project lead by ONET with CEA, to bring relevant elements to analyze the risk occurred by the dispersion of aerosols emitted by the dismantling operations. Results regarding the aerosols source term characterization emitted during laser cutting of non-radioactive fuel debris simulants were acquired during experiments undertaken on the DELIA cutting laser platform from CEA. IRSN realized aerosol sampling, aerosol size distribution measurement and CFD calculation of aerosol transport and wall deposition. The evaluations performed will enable the Japanese teams responsible for extracting corium from the damaged reactors of Fukushima Dai-ichi to define the best strategies to implement containment, and ultimately to limit the dissemination of radionuclides in the environment

Deep gouging development of deep blind kerf laser cutting technology for FUKUSHIMA fuel debris retrieval

International audienceAs a part of international calls for projects for Fukushima for fuels debris retrieval (Request For Proposal (RFP) for Conceptual Study of Innovative Approach for Fuel Debris Retrieval and Feasibility Study of Essential Technologies), the Japanese government is funding projects led by industrial companies it has selected. In this frame and since 2014, CEA, in collaboration with ONET Technologies and IRSN has performed several assessments on laser cutting process feasibility and performances for dismantling and FUKUSHIMA fuel debris retrieval. The applicability of laser process cutting to corium has been assessed under several conditions, namely in air, under water, in through-thickness-cutting conditions and gouging conditions. Indeed, in through-thickness conditions a fibre laser beam affects the work piece surface with sufficient energy to melt the material, which is ejected through the kerf from a gas-jet coaxial to the laser beam. When the piece is too thick or when it lays on a support which can not be cut, molten material can not be ejected through the kerf in the laser beam direction and special tools and cutting strategies must be employed. Specific tools and strategies have been developed, optimized (e.g. in terms of robustness and reliability) and implemented at CEA in order to adapt laser cutting process to FUKUSHIMA fuel debris retrieval specificities. This paper presents proposed solutions and main cutting results obtained in conditions representative of in site conditions deep gouging (more than 40 mm thickness in one pass), edge or bulk (in the middle of the work piece) start/stop cutting, not plane surface (relief variation) cutting, sensitivity to position, inclination

Deep gouging development of deep blind kerf laser cutting technology for FUKUSHIMA fuel debris retrieval

International audienceAs a part of international calls for projects for Fukushima for fuels debris retrieval (Request For Proposal (RFP) for Conceptual Study of Innovative Approach for Fuel Debris Retrieval and Feasibility Study of Essential Technologies), the Japanese government is funding projects led by industrial companies it has selected. In this frame and since 2014, CEA, in collaboration with ONET Technologies and IRSN has performed several assessments on laser cutting process feasibility and performances for dismantling and FUKUSHIMA fuel debris retrieval. The applicability of laser process cutting to corium has been assessed under several conditions, namely in air, under water, in through-thickness-cutting conditions and gouging conditions. Indeed, in through-thickness conditions a fibre laser beam affects the work piece surface with sufficient energy to melt the material, which is ejected through the kerf from a gas-jet coaxial to the laser beam. When the piece is too thick or when it lays on a support which can not be cut, molten material can not be ejected through the kerf in the laser beam direction and special tools and cutting strategies must be employed. Specific tools and strategies have been developed, optimized (e.g. in terms of robustness and reliability) and implemented at CEA in order to adapt laser cutting process to FUKUSHIMA fuel debris retrieval specificities. This paper presents proposed solutions and main cutting results obtained in conditions representative of in site conditions deep gouging (more than 40 mm thickness in one pass), edge or bulk (in the middle of the work piece) start/stop cutting, not plane surface (relief variation) cutting, sensitivity to position, inclination

Fabrication et découpe laser de simulants des débris de corium de l'accident de Fukushima Dai-ichi

National audienceUn consortium français (COMEX Nucleaire/ONET Technologies + CEA et IRSN) a été sélectionné dans le cadre d'appels d'offre japonais relatif au démantèlement de Fukushima Daiichi afin d’étudier la faisabilité d'une découpe laser du corium.On a pour ce faire, selectionné des blocs de simulants de corium, issus des etudes passées du CEA pour la sûreté des réacteurs a eau pressurisée a l'aide du four a arc plasma VULCANO, et fabrique de nouveaux échantillons simulants grace a un chauffage par induction, avec une composition issue de calculs des accidents graves de Fukushima Daiichi. Les temperatures de liquidus de ces melanges varient entre 1700 et 3000 K selon les compositions, principalement en fonction de la fraction de produits de decomposition du béton. Le CEA a aussi developpé et validé une tête de découpe laser pour la découpe d'acier lors du démantèlement des installations nucléaires. Des essais ont montre la faisabilité de la découpe laser tant sur des échantillons simulants que sur de la zircone electro-fondue. Ces résultats encourageants ont été obtenus, non seulement sur des debris céramique denses ou poreux mais aussi sur des échantillons contenant des inclusions métalliques (acier, zirconium) qui sont généralement difficile a couper avec les outils traditionnels

Deep UV excited muscle cell autofluorescence varies with the fibre type

International audienceThe rat skeletal muscle consists of four pure types of muscle cells called type I, type IIA, type IIX and type IIB, and their hybrids in different proportions. They differ in their contraction speeds and metabolic pathways. The intracellular composition is adapted to the fibre function and therefore to fibre types. Given that small differences in composition are likely to alter the optical properties of the cells, we studied the impact of the cell type on the fluorescence response following excitation in the deep UV region. Rat soleus and extensor digitorum longus (EDL) muscle fibres, previously identified based on their cell types by immunohistofluorescence analysis, were analyzed by synchrotron fluorescence microspectroscopy on stain-free serial muscle cross-sections. Muscle fibres excited at 275 nm showed differences in the fluorescence emission intensity among fibre types at 302, 325, 346 and 410 nm. The 410/325 ratio decreased significantly with contractile and metabolic features in EDL muscle, in the order of I \\textgreater IIA \\textgreater IIX \\textgreater IIB fibres (p \\textless 0.01). Compared to type I fibres, the 346/302 ratio of IIA fibres decreased significantly in both EDL and soleus muscles (p \\textless 0.01). This study highlights the usefulness of autofluorescence spectral signals to characterize histological cross-sections of muscle fibres with no staining chemicals