DOE SAYS SALT, CLAY, CRYSTALLINE ROCK SUITABLE FOR HLW DISPOSAL

By ExchangeMonitor

The Department of Energy’s Office of Nuclear Energy found that high-level waste disposal in salt, clay/shale rocks, and crystalline rock formations could all provide robust long-term isolation for specific wastes, according to a DOE report released yesterday. The report, titled "Evaluation of Options for Permanent Geologic Disposal of Spent Nuclear Fuel and High-Level Radioactive Waste," examined how different geologic disposal options would perform with different waste streams. Notably, it seemed disposal in salt seemed to gather the highest score in terms of performance and cost due to its ability to provide greater flexibility for disposal of heat generating wastes and due to its low cost in comparison to the other two, although the report did say the other two options also rated highly as disposal options.

Ultimately, the decision, the report said, would be a policy decision. “The selection of preferred options will involve policy and programmatic considerations outside the scope of this report, and will be influenced by, and may help inform decisions about, multiple factors that could include future storage and packaging of commercial SNF, treatment and packaging of existing DOE wastes, and progress in repository siting,” the report said. “All of the disposal concepts evaluated in this study have the potential to provide robust long-term isolation for specific wastes. Each of the three mined repository concepts could accommodate essentially all of the identified waste groups, with the exception of untreated sodium-bonded SNF, for which information is insufficient to support evaluation for disposal in any geologic disposal concepts.”

The report also identified deep boreholes as a suitable disposal option for some of the waste although it did not perform as well as the other three mining solutions. The deep boreholes would work nicely with small waste packages and would provide flexibility to the disposal strategy as an additional disposal option, the report said. “Deep borehole disposal concept costs would be comparable (in this range) if all waste forms are included that can feasibly be disposed in deep boreholes,” the report said. “However targeted disposal of select wastes in deep boreholes could provide flexibility with only modest cost increases in conjunction with a mined disposal concept.” The size of the boreholes, though, prevents it from accepting anything larger than a foot in diameter, which would mean more packaging, the report said.

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RadWaste Vol. 7 No. 17
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RadWaste Monitor

Article 6 of 11

May 29, 2014

DOE SAYS SALT, CLAY, CRYSTALLINE ROCK SUITABLE FOR HLW DISPOSAL

By ExchangeMonitor

Jeremy L. Dillon
RW Monitor
5/2/2014

Disposal of high-level waste in salt, clay/shale rocks, and crystalline rock formations could all provide robust long-term isolation for specific wastes, according to a Department of Energy report released this week. The report examines how different geologic disposal options would perform with different waste streams. Notably, it seemed disposal in salt seemed to gather the highest score in terms of performance and cost due to its ability to provide greater flexibility for disposal of heat generating wastes and due to its low cost in comparison to the other two, although the report did say the other two options also rated highly as disposal options. “All of the disposal concepts evaluated in this study have the potential to provide robust long-term isolation for specific wastes. Each of the three mined repository concepts could accommodate essentially all of the identified waste groups, with the exception of untreated sodium-bonded SNF, for which information is insufficient to support evaluation for disposal in any geologic disposal concepts,” the report says.

A DOE spokesperson said that this study would act as a technical foundation to help inform the Department’s decision-making going forward. “In FY14, DOE is doing research and development analysis work that aligns with the recommendations of the Blue Ribbon Commission and supports the Administration strategy,” the DOE spokesperson said. “These activities include laying the groundwork for an integrated waste management system and doing related research and development on storage, transportation and material issues. As part of that effort, the Department evaluated the range of different rock types for disposal concepts and it is intended to be a technical report that will help inform DOE on-going examination of these issues.”

Lack of Water a Benefit of Salt Disposal

From the perspective of a salt repository, the report found that the lack of water and costs compared to the other two options made it an attractive choice. “Disposal in this media provides greater confidence in estimates of long-term performance because it limits radionuclide transport (low permeability) and reduces the reliance on the waste form and waste package lifetimes,” the report says. “The relative lack of water and the high cross-section of chlorine for capture of thermal neutrons make it easier to address criticality concerns. In some cases, it may be appropriate to directly dispose of some untreated waste types, potentially reducing cost and risks associated with waste treatment.” The report also cited the operating experience gained from the Waste Isolation Pilot Plant in Carlsbad, N.M. as another reason to have confidence in the medium.

Heavy Worldwide Interest in Clay Disposal

In addition to salt, both clay and crystalline repositories were workable solutions. The clay option could handle most waste groups, and with much of the world opting for clay disposal, the option has worldwide experience, the report says. Crystalline rocks offer rock strength, which “allows robust openings to be easily maintained providing the potential flexibility of possible ramp access,” the report says. However, crystalline rocks did have some negatives. “However, for fractured crystalline systems, high reliance on clay barriers immediately surrounding the waste package poses additional challenges for high thermal loads that may degrade such barriers,” the report says. “Because of the need for robust performance of the source-term, confidence in system performance may be directly dependent on very conservative thermal management.”

Report Also Looked at Deep Borehole Disposal

The report also identified deep boreholes as a suitable disposal option for some of the waste although it did not perform as well as the other three mining solutions. The deep boreholes would work nicely with small waste packages and would provide flexibility to the disposal strategy as an additional disposal option, the report says. “Deep borehole disposal concept costs would be comparable (in this range) if all waste forms are included that can feasibly be disposed in deep boreholes,” the report says. “However targeted disposal of select wastes in deep boreholes could provide flexibility with only modest cost increases in conjunction with a mined disposal concept.” The size of the boreholes, though, prevents it from accepting anything larger than a foot in diameter, which would mean more packaging, the report says.

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