Development of laser remote spectroscopy for onsite and in-situ analysis of nuclear fuel debris under severe environment

Wakaida, Ikuo  ; Akaoka, Katsuaki ; Miyabe, Masabumi   ; Oba, Hironori  ; Saeki, Morihisa; Ito, Chikara   ; Oba, Masaki ; Kato, Masaaki

In the decommissioning of "Fukushima Daiichi Atomic Power Plant", it will be difficult work by the extremely high radioactivity from fission products and meltdown nuclear fuel debris. Technical innovations and some breakthrough will be indispensable for a safety accomplishment of this work. For the basic R&D on the decommissioning, Japan Atomic Energy Agency has opened the new research center "Collaborative Laboratories for Advanced Decommissioning Science". The development of onsite and in-situ analysis of fuel debris is one of the most important for the planning and working of the decommissioning. Quick, easy, non-contact, no-preparation, direct and remote analysis technique by Laser Induced Breakdown Spectroscopy (LIBS) based on radiation resistant optical fiber will be now under developing. Pulsed Nd:YAG laser will be propagated though an optical fiber and focused on the sample. Plasma emission produced by the laser on the surface of the sample is collected by the same focusing lens, propagated through the same optical fiber and put into the spectrometer. Elemental identification and the composition are evaluated by specific atomic emission line and its intensity. Under strong irradiation condition; dose rate of 10 kGy/h and after total dose of 2 MGy, radiation resistant optical fiber had good transmission, no damage by laser light propagation, and had good performance for plasma emission spectroscopy. In addition, we have successfully observed and identified the specific spectra of Zr and U from the simulated sample of molten debris made by sintered oxide of Zr and U which is the raw materials of the fuel assembly. Quantitative analysis of the composition ratio of Zr/U has been also evaluated from the intensity ratio of specific emission lines.