Hiroto Yokoi

Aerosol, Gas, and Swarf Production during Underwater Cutting of Reactor Core Internals Using Electron Discharge Machining

Secondary products (aerosol, gas and swarf) are released in the work area when cutting nuclear reactor components are underwater during component replacement. We studied the characteristics and behavior of the secondary products produced during cutting of highly radioactive metals using electric discharge machinery (EDM) underwater. The ratio of the weight of the aerosol produced to the melted weight of a workpiece that was cut using EDM, both with a Ag/W alloy electrode and a carbon electrode, was about 1 × 10−3. The aerosol had a high concentration of manganese with a high vapor pressure. The production ratio was expressed as the aerosol production rate (ppm) = −4:6 × 10−2 Tb + 1:4 × 102 (Tb: boiling point (K)). The EDM cutting produced metal vapors which condensed into particles. Air-borne nickel carbonyl was produced during the EDM cutting of nickel and carbon monoxide with a carbon electrode, and a high efficiency particulate air filter and a charcoal filter were used effectively. In the case of a Ag/W electrode, the swarf contained oxide particles of around 20 mm and hydroxide particles with a diameter of around 10 mm. The water clean-up system was able to purify water with over 95% filtration efficiency using a 1 μm pore-pleated filter cartridge.