A METHOD FOR RADIOACTIVE CONTAINMENT DURING BIOLOGICAL INACTIVATION OF RADIOACTIVE-BIOMEDICAL MIXED WASTE

Abstract

A waste coffin that can contain the radioactive component of a radioactive-biomedical mixed waste while the biological component of the waste is inactivated was designed, fabricated, and validated. Bacillus stearothermophilus spore indicator strips were used to validate the biological inactivation through autoclaving of a given biomedical waste mixture. Repeated successful experiments indicated that a ninety minute autoclave sterilization cycle with the addition of no extra water was adequate to effect biological inactivation of the biomedical waste. All experiments validated that any radioactivity placed within the coffin could be contained during the autoclaving process. Any volatilization of radionuclides was contained within the coffin or adsorbed onto a charcoal filter column attached to the coffin. Experiments were performed using varying activities of three common radionuclides used in research at the National Cancer Institute-Frederick Cancer Research and Development Center (NCI-FCRDC). Radioisotopes used in this study were ³H, ³⁵S, and ¹²⁵1. A comparison of relative volatilities of the three radionuclides was also documented. Contrary to what was expected, the ¹²⁵1 was the least volatile of the three radionuclides. For a given activity placed in the biomedical waste coffin, approximately ten fold the activity of ³H and one hundred fold the activity of ³⁵S was volatilized as compared with that of the ¹²⁵1.Specific problems with this process were encountered. One was the design of an appropriate clamping mechanism, and the other was the bending of the stainless steel during the autoclaving process. A remedy was found for both of these problems. C clamps were attached to the corners of the coffin before the coffin was the autoclaved. This afforded a better seal of the coffin during the process. Finally, the coffin had to be physically reshaped after each couple of experiments to assure a good seal during the process.