Explosive Freeze Pipe Cutting at the McArthur River Uranium Mine

摘要

The McArthur River uranium mine in Saskatchewan, Canada is the world's largest high-gradeuranium mine. It has employed a freeze-wall system consisting of multiple freeze pipes to control thelarge quantities of water encountered during mining.Raise boring is the mining method employed at McArthur River mine. Mining has advanced to thepoint that the raise-bore machines are encountering freeze pipes that were part of de-commissionedfreeze-walls. Cutting through the freeze pipes with the raise-bore machines is a difficult, timeconsumingprocess that can also damage the equipment. Explosive freeze-pipe cutting was proposedas a means to expedite this process.Several challenges existed with this explosive cutting: 1) each freeze pipe consisted of multipleconcentric steel pipes with cement grout between the pipes, and, 2) the location prevented any accessto the outside of the pipes. Thus, the explosive charges had to be placed on the inside of the centerpipe and had to be capable of shattering all of the concentric pipes over a specified distance. Theexplosive charges were created by assembling a number of pentolite boosters and thus exhibited noshaped-charge effects.Prior to the field trials of this system, hydro-code computer simulations that accurately treated theexplosive system and its interaction with the concentrically layered freeze pipes were created. Thesesimulations indicated that the explosive design would be sufficient to shatter the multiple pipingsystems with interstitial cement.A field trial at the mine, incorporating the explosive design developed, demonstrated that the pipescould be consistently cut at specified locations to clear them for the raise-bore machines.