Be-reflectors of the former research reactor Saphir: how to condition hazardous and toxic radioactive waste

After 36 years in operation the former research reactor SAPHIR was decommissioned on December 23rd 1993. After removing the spent fuel, the highest activity was contained in the BeO-reflectors. Twenty reflectors were used; ten of BeO, in total 65.1 kg, and ten of Be-metal, in total 60.78 kg. Both types are in aluminum housings. The highest activation was built up in the Be-metal reflectors. The activity was calculated using the program ORIGEN resulting in 573 TBq 3H and 240 GBq 60Co for the Be-metal reflectors and 181 TBq 3H and 21 GBq 60Co for the BeO (December 1995). The corresponding dose rates due to the 60Co were 4.64 Sv/h and 0.4 Sv/h from the Be-metal and BeO reflectors respectively. Due to the intrinsic toxicity, the high dose rate and the high 3H content, the following principles had to be followed: The reflectors should be conditioned without any additional dismantling; Due to the high 3H content the reflectors should be sealed in gas tight welded steel cans; The reflectors should be dried before welding to avoid corrosion; The void between the can and the reflector should be filled with quartz sand; The surface of the damaged BeO-reflectors should be sealed to avoid contamination from toxic BeO-dust; The dose rate should be reduced by using a shielded container; The volume should be minimized due to high costs of interim and final storage. These goals were achieved by sealing the dried reflectors in square section steel cans using a welding robot (type MOTOMAN SK6) in a shielded hot cell. The 20 cans were placed in a MOSAIK container Type II-15 U, using a steel grid to position the cans correctly. This container is stored in the Swiss Federal Interim Storage Facility to await the Swiss final repository. (author)