Optimization of Deep Borehole Systems for HLW Disposal
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
This is the final report on a project to update and improve the conceptual design of deep boreholes for high level nuclear waste disposal. The effort was concentrated on application to intact US legacy LWR fuel assemblies, but conducted in a way in which straightforward extension to other waste forms, host rock types and countries was preserved. The reference fuel design version consists of a vertical borehole drilled into granitic bedrock, with the uppermost kilometer serving as a caprock zone containing a diverse and redundant series of plugs. There follows a one to two kilometer waste canister emplacement zone having a hole diameter of approximately 40-50 cm. Individual holes are spaced 200-300 m apart to form a repository field. The choice of verticality and the use of a graphite based mud as filler between the waste canisters and the borehole wall liner was strongly influenced by the expectation that retrievability would continue to be emphasized in US and worldwide repository regulatory criteria. An advanced version was scoped out using zinc alloy cast in place to fill void space inside a disposal canister and its encapsulated fuel assembly. This excludes water and greatly improves both crush resistance and thermal conductivity. However the simpler option of using a sand fill was found adequate and is recommended for near-term use. Thermal-hydraulic modeling of the low permeability and porosity host rock and its small (≤ 1%) saline water content showed that vertical convection induced by the waste’s decay heat should not transport nuclides from the emplacement zone up to the biosphere atop the caprock. First order economic analysis indicated that borehole repositories should be cost-competitive with shallower mined repositories. It is concluded that proceeding with plans to drill a demonstration borehole to confirm expectations, and to carry out priority experiments, such as retention and replenishment of in-hole water is in order.
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
- Sponsoring Organization:
- USDOE Office of Nuclear Energy (NE)
- DOE Contract Number:
- AC07-05ID14517
- OSTI ID:
- 1223390
- Report Number(s):
- 12-3298; 12-3298; TRN: US1500823
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
HIGH-LEVEL RADIOACTIVE WASTES
THERMAL HYDRAULICS
GRAPHITE
THERMAL CONDUCTIVITY
CONTAINERS
CONVECTION
ZONES
ECONOMIC ANALYSIS
FUEL ASSEMBLIES
ZINC ALLOYS
COMPARATIVE EVALUATIONS
BOREHOLES
DESIGN
MINES
OPTIMIZATION
POSITIONING
AFTER-HEAT
RADIONUCLIDE MIGRATION
FILLERS
LINERS
SAND
SIMULATION
RADIOACTIVE WASTE DISPOSAL
DEPTH 1-3 KM
GRANITES