Experimental incineration of low level radioactive samples

To determine the volume reduction potential for incineration of radioactivity in low-level radioactive waste, an incineration experiment was performed at the Okayama University Radioisotope Center (OURIC). Solid low- level radioactive samples (LLRS) were prepared for 15 routinely used radionuclides (⁴⁵Ca, ¹²⁵I, ³²P, ³³P, ³⁵S, ⁵⁹Fe, 1²³I, ¹³¹I, ⁶⁷Ga, ^99mTc, ¹¹¹In, ³H, ¹⁴C, ⁵¹Cr, and ²⁰¹Tl). For each radionuclide, incinerated one at a time, the smoke duct radioisotope concentration was less than 1/10 of the regulatory concentration limit (The Japanese law concerning prevention of radiation hazard due to radioisotopes, etc.). The radionuclide-containing combustible and semi-combustible LLRS were incinerated at the AP-150R furnace erected at OURIC, and the distribution of radioactivity inside and outside the furnace was measured. In the experimental incineration of LLRS containing these 15 radionuclides, the fractions released (RF) in the gas phase of the final smoke duct ranged from 0.165 to 0.99. The radioactivities remaining in the incineration residue were ^99mTc, 87%; ⁵⁹Fe, 83.1%; ⁴⁵Ca, 75%; ⁵¹Cr, 62.1%; ³³P, 62.0%; ³²P, 61.1%; ⁶⁷Ga, 57.7%; ³⁵S, 26.0%; ¹¹¹In, 21.1%; ²⁰¹Tl, 16.6%; ¹²³I, 11.9%; ¹³¹I, 8.2%; ¹²⁵I, 2.4%; ¹⁴C, 0.39%; ³H, 0.04%. In the incineration of LLRS containing ³⁵S, the rate of adhesion to the furnace wall was lower at high-temperature (809°C) incineration than at low- temperature (376°C) incineration. For LLRS containing one of the three radioiodines, ¹²³I, ¹²⁵I, or ¹³¹I, no such difference was observed between low (372°C) and high (827°C) temperature incineration (RF varied from 0.82 to 0.94).