NL7602753A - Underground storage system for solidified radioactive waste - comprises deep boreholes in rock salt with leakage collectors - Google Patents

Abstract

Solidified high-level reprocessing waste is brought under cover and stored in canisters, in a min. of holes drilled to a great depth in a rock salt fault through the top layer and the water holding strata above it. This ensures that the fissile waste is stored under conditions making the optimal use of the heat buffer capacity of the whole rock salt mass. A very limited number of shafts and a set of passages through the salt fault give access to working chambers from which very deep holes are bored for the fissile waste, using a drilling mud comprising a satd. soln of salt weighted with a suspension of clay. The drilling mud is maintained in the borehole until the canisters are lowered in, and the mud forced out during the filling operation, is collected and inspected. When filled the hole is plugged with a radiation screening stopper. An overflow line passes through this; a weighted safety valve being fitted, and any fluid expelled by the flow through the salt is collected and subjected to a process of adsorption and adsorption for the radionuclides and a solidifying process for the mud itself. The drilling mud allows the boring of deeper holes in the face of their tendency to converve due to the high pressure prevailing. The mud is kept in the hole to impede convergence until the canisters have been lowered in, and that remaining helps towards a better distribution of the heat generated by the waste into the rock salt mass.