Removal of tile holes containing intermediate level radioactive waste by steel and concrete encapsulation

During the mid-seventies, intermediate level radioactive waste, mainly in the form of ion exchange (IX) columns and filters from the Douglas Point Nuclear Reactor were stored in 23 in-ground Tile Holes at the Radioactive Waste Operations Site no.1 (RWOS1) at the Bruce Power Site. Use of this site was discontinued in 1976 and water quality in the groundwater system has been monitored since then. The presence of moderately elevated tritium concentrations in one of the perimeter groundwater monitoring wells prompted several investigations. These have inferred one or more of the Tile Holes as the source. It was decided to remove the Tile Holes to prevent further leakage. Investigations were conducted during 2000 to determine the present state of the Tile Holes. The results showed radiation fields up to 0.2 Sv/hr at 5 cm and soil with moderate to significant radioactive contamination at the base of four of the Tile Holes. In order to minimize contamination spread and worker dose, it was decided to encapsulate the Tile Holes in steel and concrete prior to removal. This paper describes the methodology and results of a pilot project during 2001 in which one Tile Hole was successfully encapsulated and removed. The other 22 Tile Holes will be removed during the spring and summer of 2002. (author)