Part 2 of 3 Parts (Please read Part 1 first)
    Back in the 1980s, the U.S Department of Energy decided that disposal of spent nuclear fuel in boreholes as deep as thirty-two thousand feet was not a preferable alternative to a single national geological repository. Since then, US Nuclear Waste Technical Review Board, the US Nuclear Regulatory Commission, and waste management organizations of Sweden, the United Kingdom, and Canada have studied proposals for borehole disposal at shallower depths between nine thousand feet and sixteen thousand feet. These studies concluded that burial of spent nuclear fuel in boreholes would require decades of research, design and development.
     Even if the results of this development work were successful, there is no guarantee that such borehole disposal would be any safer than a properly sited deep mined single repository. A more recent study found that Deep Isolation’s shallower boreholes at a depth of six thousand five hundred feet would have the same problems as the prior studies. It turns out that suitable borehole disposal sites are actually geographically rare.
    Many borehole problems are related to the limits of the diameter of boreholes drilled by current technology. In general, the exact diameter of a borehole depends on geological variables at specific locations. Usually, the deeper the borehole, the smaller the diameter of the borehole. These limitations have implications in terms of the barrier system that surround the nuclear fuel as well as the ability to fully characterize the geology of a specific site.
     In order to accept spent nuclear fuel canisters with a diagonal cross-section of about twelve inches, the boreholes that Deep Isolation will have to drill will have to be bigger than sixteen inches in diameter. This exceeds the industry standards for boreholes to frack natural gas and oil. This means that the practicality and cost of Deep Isolations borehole approach is still unclear. If it turns out that technical problems with drilling a sixteen-inch diameter borehole can be overcome, there are still problems. The canister walls could only have a thickness of about four tenths of an inch. Plans for a single repository call for canister walls with a thickness of over two inches. Handling thin walled canisters could be dangerous for workers. Possible release of radioactivity in such canisters must be carefully studied.
    Gamma radiation generated by spent nuclear fuel could penetrate a thin canister wall and endanger workers. Thick wall canisters in a mined geological repository will serve to attenuate the gamma radiation where as thin walled canisters in a borehole would have very little shielding capability.
     There is also a problem connected to the sheer number of canisters of spent fuel that must be dealt with. Each canister intended for burial in a single huge repository will be able to handle as many as four fuel assemblies. On the other hand, canisters destined for borehole disposal will only be able to accommodate a single fuel assembly. It will be very difficult to securely and safely insert hundreds of thousands of canisters into hundreds of narrow boreholes. If just one canister was punctured or became stuck in the borehole, there would be significant risk to the workers and the environment.
Please read Part 3 next