Verifying nuclear waste tile-holes using gamma radiation scanning

Nuclear waste management facilities at Chalk River Laboratories (CRL) use below-ground 'tile-holes' to store solid waste from various activities such as medical isotope production. After long periods of isotopic decay, some of the waste has decayed down to low activities, and can be transferred to low-level waste storage facilities. This paper presents a method to verify the radiation level of the waste inside tile-holes by performing gamma radiation scans along the depth of waste storage tile-holes. Such measurements allow for non-invasive verification of tile-hole contents and provide input to the assessment of radiological risk associated with removal of the waste. Using the radiation profile system, the radiation level of the radioactive waste may be identified based on the radiation profile. This information will support planning for possible transfer of this waste to a licensed waste storage facility designed for low level waste, thus freeing storage space for possible tile-hole re-use for more highly radioactive waste. In-house developed small diode-based gamma radiation sensors have been used in these radiation scans. The diode sensors were deployed into verification tubes adjacent to the tile-holes to measure the radiation profile. Over ten tiles holes have been scanned using this technique since 2009. (author)