Development of microwave-enhanced fibre-coupled laser-induced breakdown spectroscopy for nuclear fuel debris screening at Fukushima

Remote sensing is indispensable to decommissioning the post-accident Fukushima Daiichi nuclear power station set to begin in 2021. High radiation levels make containment and reactor vessels inaccessible. Fibre-coupled Laser-induced breakdown spectroscopy (FC-LIBS), with a 50-m long, 800 μm diameter fibre-optic cable has been considered for the pre-analysis of nuclear fuel debris, prior to their processing and secure transport for storage and disposal. Coupling and transmission losses, and radiation effect on fibre core leads to signal deterioration. We present the enhancement of spectral intensity by superposing a 2.45 GHz semiconductor oscillated microwaves (MW) to the induced plasma of FC-LIBS system. The prototype fibre cable used was 1 m long and 800 μm in diameter. Test material for the study was standard aluminium oxide, and a 30 mJ laser output was for seed plasma generation. Using MW energy of 190 mJ per pulse, intensity enhancement of about 1160 times the level of FC-LIBS was achieved. This demonstrates the capability of MW-enhanced FC-LIBS for elemental analysis necessary for screening nuclear fuel debris.