Characterization of simulated corium and zircalloy during laser cutting, applied to Fukushima-Daiichi needs - Archive ouverte HAL
Communication Dans Un Congrès Année : 2019

Characterization of simulated corium and zircalloy during laser cutting, applied to Fukushima-Daiichi needs

Résumé

As part of a partnership between ONET, IRSN and certain CEA sites, research programs are being carried out on corium laser cutting for Fukushima decommissioning operations. Underwater and air cutting trials have been carried out at CEA Saclay with a 7500 W YAG laser on non-uranium corium simulants, VF03 and VF04. Samples of laser cutting spray particles present in the tank, on chamber walls, and on extraction filters were characterized in the LMAC laboratory. To do this, the samples (of water, slag, swabs, or filters) were mineralized using closed or open acidic or basic technical protocols. Their elemental nature was identified after dissolution and ICP/AES chemical analyses, and granulometric analyses were obtained using in situ SEM image analyses. The elemental chemical analyses of various samples from cutting trials enabled the distribution of the different species to be found, most importantly for simulated fission products. Prior to these analyses, corium samples prepared at the CEA Cadarache site had been characterized in order to qualify them before cutting. Each contained about fifteen elements (Hf-Zr-B-Mg-Al-Ca-Cr-Fe-Ni-Sr-Y-Mo-Pd-Sn-Te-Cs-Ba-La-Pr-Nd-Sm-Si). The results enabled the CEA to model contamination distribution in the cutting tank and in the extraction system. To demonstrate that laser cutting does not create a risk of H2 production (through oxidation of unmelted zircalloy in the corium), or at least that this risk remains limited, slag from cutting a zircalloy sample was collected, then examined by SEM EDS and EPMA. The phases formed and their levels of oxidation were determined. They mainly consisted of peripheral β-ZrO2-X and -ZrO2-X phases whose oxygen content was around 20%, and of variable α-Zr core phases with an oxygen content of less than 10%. Zircalloy-4 oxynitridation was also observed, due to the presence of air-borne nitrogen during cutting operations. A cut zircalloy sample was also examined in order to determine the depth of the oxidized zone. The zone thermally-impacted by the laser could be assessed, with a depth of about 400 to 500 µm corresponding to the Z beta structure characteristic of quenched zircalloy-4. The microstructural changes near the cutting zone were clearly identified. Layers formed by a melted zone were identified as having compositions similar to those of slags.
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Dates et versions

hal-02411098 , version 1 (14-12-2019)

Identifiants

  • HAL Id : hal-02411098 , version 1

Citer

C. David, C. Journeau, P. Piluso, V. Testud, Emmanuelle Brackx, et al.. Characterization of simulated corium and zircalloy during laser cutting, applied to Fukushima-Daiichi needs. International Topical Workshop on Fukushima Decommissioning Research FDR2019, May 2019, Naraha, Japan. ⟨hal-02411098⟩
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