Kazuo Adachi and Tadashi Amakawa

Central Research Institute of Electric Power Industry
2-6-1 Nagasaka, Yokosuka-shi, Kanagawa-ken 240-0196, Japan
adachi@criepi.denken.or.jp

Low-level radioactive miscellaneous solid wastes the volume of which must be reduced contain small amounts of nonmetallic materials such as heat insulating materials and burnable materials. When these wastes are fed into a plasma-melting furnace for volume reduction, the voltage of the arc plasma fluctuates if the plasma is a transferred type. This phenomenon is undesirable as it leads to fluctuations in heat power and in some instances, decreases the stability of the arc plasma. We report on the experimental voltage fluctuation data measured in a small plasma-melting furnace. In the case of feeding 200g of SiO2/CaO mixture which are heat insulating materials, the maximum instantaneous arc voltage was 220% of the regular voltage,[1] but in the case of rubber, only 5g was sufficient to increase the instantaneous arc voltage to the same. The increment of instantaneous voltage was almost proportional to the weight of the burnable material such as rubber or wood chips in the experiment as shown in Fig. 2. The fed materials were rapidly decomposed into soot and gases according to the observation by the VCR camera and by gas analysis. The of the soot was proportional to the weight. These decomposed products disturbed the plasma flow and composition and this appears to be a reason for the voltage fluctuation.

(1) K. Adachi, et.al., Proc. 3rdAPCPST, B6-1, 409 (1996)