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Fusion Science and Technology
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Retrieval of nuclear waste canisters from a borehole
Borehole disposal of spent nuclear fuel (SNF) and high-level waste (HLW) uses off-the-shelf directional drilling technology developed and commercialized by the oil and gas sectors. It is a technology that has been gaining traction in recent years in the nuclear industry. Disposal can be done in one or more boreholes (including an array) drilled into suitable sedimentary, igneous, or metamorphic host rocks. Waste is encapsulated in specialized corrosion-resistant canisters, which are placed end to end in disposal sections of relatively small-diameter boreholes that have been cased and fluid-filled. After emplacement, the vertical access hole is plugged and backfilled as an engineered barrier.
Yuri Igitkhanov, Gerald Kent McCormick, Peter Eckhard Grigull
Fusion Science and Technology | Volume 46 | Number 1 | July 2004 | Pages 101-105
Technical Paper | Stellarators | doi.org/10.13182/FST04-A545
Articles are hosted by Taylor and Francis Online.
A plausible physical explanation of a new advanced high-density H (HDH)-mode operational regime on the W7-AS stellarator is discussed. The HDH regime can be achieved only under a high rate of particle fueling during the starting phase of the discharge. It can be shown that at high enough fueling rates, the density profile grows at the source position, because the relatively weaker diffusivity hinders redistribution of the plasma. This leads to formation of a density gradient at the edge and brings about the radial electric field, which suppresses the plasma turbulence [the edge transport barrier (ETB) formation]. The appearance of the ETB depends on the initial condition, i.e., on the fueling rate, but a steady-state operation depends on the average density value. This critical value can be assessed from the energy and particle balance at the edge, where the transport coefficients depend on the plasma parameters in such a way that bifurcation can occur. The bifurcation occurs between two stable solutions, which are characterized by different values of the particle flux and energy confinement time, reminiscent of the normal confinement and HDH stages. The scaling analysis shows that the threshold average density required for transition increases weakly with power and inverse aspect ratio.