WorldWide Drilling Resource

45 WorldWide Drilling Resource ® MARCH 2019 A Horizontal Solution for Nuclear Waste Adapted from Information by Deep Isolation Nuclear waste is composed of dense, compact pellets made of uranium dioxide. It is stored in a fuel assembly made of zirconium alloy, which can hold 22,000-92,000 pellets. After the fission energy in these pellets is spent, the assemblies are removed from the reactor and placed in cooling pools. Over the course of several years, the radioactivity decays to the point where dry storage aboveground is possible. Dry stor- age accounts for nearly one-third of current nuclear waste. It is considered to be in- terim storage, but a licensed location where the waste can be sent for long-term disposal has yet to be constructed or decided. Rather than creating large tunnels, Deep Isolation proposes a solution which in- volves a vertical access borehole extending thousands of feet deep until it is gently turned horizontal. The horizontal part of the borehole will be located in rock which has been stable for millions of years. An upward tilt and a “plumber’s trap” can prevent radioactive material from reaching the vertical portion of the borehole, and reduce dependency on man-made barriers. With this approach, there would be no need for humans to go underground, and sites could be located at or near power plants to minimize transportation of waste. One borehole can store eight years of waste from a boiling water reactor and 33 years of waste from a pressurized water reactor. The unmodified fuel assemblies from the reactor or interim storage will be placed into sealed canisters 8-12 inches in diameter, and 14 feet long. The canisters will be lowered into the vertical borehole, then pushed into the horizontal section using coiled tubing, a stiff cable widely used in the industry. The canister will be unlatched from the tubing, then another canister will be inserted behind it. If ever necessary, the process can be reversed for retrieval of the canisters. By storing nuclear waste in the deep horizontal section, excellent isolation from the surface can be achieved. The repository would be located far below aquifers, and the stable rock formations at such a depth would provide a billion tons of rock between the waste and the surface. The geology also offers natural protection against human intrusion, terrorist attacks, and chain re- actions caused by groundwater intrusion. Furthermore, drilling, placement, and retrieving techniques for the repository are standard and reliable. DIR