Investigation of polonium decontamination from stainless steel surfaces using the baking method

Polonium contamination on material surfaces has been considered one of the problems in the use of lead-bismuth eutectic (LBE) as a coolant and/or target in nuclear systems. Neutron-irradiated LBE contains polonium and can contaminate material surfaces of the primary loop in nuclear systems. Some methods for removal of polonium from neutron-irradiated LBE have been investigated. In this paper, the theory and the effectiveness of the baking method for polonium decontamination of a material surface contaminated by neutron-irradiated LBE are described. Theoretical investigation of the baking method was performed using Langmuir's equation. The effectiveness of the baking method was investigated by baking experiments using Type 316 stainless steel plates contaminated by neutron-irradiated LBE. The experimental results indicated that the baking method is effective for polonium decontamination when the baking temperature is more than 500 degrees C in a vacuum condition (0.4 Pa). The effective temperature for polonium decontamination of Type 316 plates differed from that of quartz glass plates previously reported. Comparing the experimental results and calculations of the evaporation rate of polonium compound by Langmuir's equation showed that the difference in effective temperatures was due to the different chemical forms of polonium, i.e., elemental polonium and lead polonide.