Abstract
At the first step of the assessment of dust dispersion data during cutting fuel debris of Fukushima Daiichi Nuclear Power Station, dust dispersion data during cutting cold simulants with four cutting methods under dry condition were obtained against wide range of operating parameters. This presentation summarizes the dry cutting tests with chisel and core boring.
The tests were conducted by measuring the generated floating aerosols with particle size analyzers (Welas2000 and/or ELPI+). Since amount of aerosol generation is not sufficient for measuring in large casings, dry cutting tests with core boring and chisel were carried out within small area such as an acryl box of roughly 30cm cubic. The inlets of the particle size analyzers were inserted close to the cutting position so that the aerosols were sucked without dilution by the air flow. With a correction to same flow condition according to computational analysis, the measured data for dry cutting with four different cutting methods were compared each other. The detail and result of each cutting test are summarized as following.
The chisel tests were conducted using both Φ30mm flat and point chisels of Makita with an electric hammer of Makita HM1511 after modification to allow changing the beating frequency at 500-950 bpm. The applied static load ranged 600-800 N including the weight of the hammer. As for test results, the peak diameter of the dispersed particles was around 10μm, similarly to disk cutter. The maximum Airborne Release Fraction (ARF) for various kinds of simulants reached tens of percent for zircon and several percent for porous alumina and mortar due to small mass defect of chisel cutting.
The core boring tests were conducted using Φ76mm impregnated core bits of Asahi Diamond with the rotation speed of 60-600 rpm. The applied load ranged 1-6 kN. The mass defect was estimated by the weight loss of the simulant or the volume of the generated ditch. As for test results, the peak diameter of dispersed particles was in the range of 10-30μm. The ARF for mortar and porous alumina were less than 1%, and that for other simulants ranged less than 10%.
