Can a small drilled hole be used to do something that the nuclear industry has been trying to do with a giant repository for decades?’ This question has once again been placed back on the table as a result of the announcement made by Deep Isolation regarding their modeling results. However, this time it is being done as part of a larger engineering-level discussion regarding how the next generation of reactors will solve the biggest problem the nuclear industry has ever faced. In conjunction with Oklo and national lab partners, Deep Isolation has announced the results showing the waste streams produced by this process of electrorefining are compatible with deep borehole disposal, which is several orders of magnitude below a stringent radiological exposure dose requirement in both shale and granitic host rock.
The beauty of this solution is rather than digging a giant repository, this solution uses deep holes to access good rock at great depths below the earth’s surface. This is a technique that has already been used in the oil and gas industry. Deep Isolation’s solution is the use of corrosion-resistant containers in both vertical and curved boreholes. In this solution, the parts of the solution where the radioactive materials will be disposed of could be as long as two miles, spanning the distance between thousands of feet below the ground level and two miles below the ground level. In this solution, the technique is small rather than monumental, rather than one giant national repository. Naturally, this is important because the waste streams are changing.
The most recent validation effort has been related to the ARPA-E program effort related to the recycling of the advanced reactor fuel and the minimization of the waste produced in the nuclear fuel cycle. In this case, it has not necessarily been considered as a replacement for the different ideas related to the repository concept. Instead, it has been considered as a final product related to the residues that are produced by the fuel that comes out of a closed or a partially closed metal fuel cycle that may not be recyclable. The Universal Canister System has been a product that has resulted from a program effort that has taken place over the last three years and has been funded by the ARPA-E program effort.
It has been considered that the canister system that has been produced has the ability to be applicable to different types of advanced reactor waste forms, including the ability to be backward compatible with the existing dry storage and transportation. Perhaps the problem with the product that has resulted from the program effort is that it may not be effective in the area of the waste physics and the repository that has taken place. Instead, it may be effective in the area of the interface that has taken place with the storage, transportation, handling, regulations, and the acceptance criteria that has taken place.
Perhaps one of the most contentious areas that has taken place in the nuclear waste management arena has been the option related to the deep borehole option that has taken place. Perhaps one of the problems that has taken place in the arena has been the idea that perhaps the size of the boreholes that have taken place could influence the design of the canister that has taken place, the shielding of the worker, and perhaps even the strategy that has taken place that has been so dependent upon the geology that has taken place at the site. In fact, one of the issues that is raised in the discussion of the critique of this option in the Bulletin of Atomic Scientists in 2020 is associated with the characterization and the constraints of the canister that can impact this option. It has not gone away just because new modeling makes it a viable option.
In fact, the most ardent supporters of this option have only been able to view it as a viable option by reason of the potential that it has for lessening the footprint of the repository that would be necessary in the mined geology option. In fact, the alternative to the mined geology option is not some trivial excavation project; it is a civil works project that requires the number of shafts, tunnels, spoil, and years necessary to create the repository in the first place. In fact, there has been an academic discussion on the overall question of nuclear waste management that has suggested that perhaps the overall burden on the environment is not the release of the radiation itself, but rather the engineering necessary to put that waste in the ground in the first place.
In that context, it is also true that the latest borehole validation does not really address the waste disposal question and does not remove the legal hurdle that remains between modeling success and deployment in the United States. But it does raise the question that now faces the overall development of the advanced nuclear reactor. Will the development of the reactor itself be able to outpace the development of the waste management solution, or does the waste management solution have to be incorporated into the reactor system in the first place?