Fusion energy conversion in magnetically confined plasma reactors

The use of liquid walls for fusion reactors could help solve problems associated with material erosion from high plasma heat-loads and neutronic activation of structures. A key issue analyzed here is the influx of impurity ions to the core plasma from the vapor of liquid side-walls. Numerical 2D transport simulations are performed for a slab geometry which approximates the edge region of a reactor-size tokamak. Both lithium vapor (from Li or SnLi walls) and fluorine vapor (from Flibe walls) are considered for hydrogen edge-plasmas in the high- and low-recycling regimes. It is found that the minimum influx is from lithium with a low-recycling hydrogen plasma, and the maximum influx occurs for fluorine with a high-recycling hydrogen plasma.

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Interactions between Liquid-Wall Vapor and Edge Plasmas

As candidate blanket concepts for a U.S. advanced reactor power plant design, with consideration of the time frame for ITER development, we assessed first wall and blanket design concepts based on the use of reduced activation ferritic steel as structural material and liquid breeder as the coolant and tritium breeder. The liquid breeder choice includes the conventional molten salt Li 2 BeF 4 and the low melting point molten salts such as LiBeF 3 and LiNaBeF 4 (FLiNaBe). Both self-cooled and dual coolant molten salt options were evaluated. We have also included the dual coolant lead-eutectic Pb-17Li design in our assessment. We take advantage of the molten salt low electrical and thermal conductivity to minimize impacts from the MHD effect and the heat losses from the breeder to the actively cooled steel structure. For the Pb-17Li breeder we employ flow channel inserts of SiC f /SiC composite with low electrical and thermal conductivity to perform respective insulation functions. We performed preliminary assessments of these design options in the areas of neutronics, thermal-hydraulics, safety, and power conversion system. Status of the R&D items of selected high performance blanket concepts is reported. Results from this study will form the technical basis for the formulation of the U.S. ITER test module program and corresponding test plan.

http://www.fusion.ucla.edu/neil/Publications/AssessmentOfFirstWallAndBlanket.pdf

Assessment of First Wall and Blanket Options with the Use of Liquid Breeder

Three-dimensional analysis has been made using the MCNP Monte Carlo code and ENDF/B-VI nuclear data. The nuclear characteristics of a fusion-fission hybrid reactor such as tritium breeding ratio, energy multiplication factor, fissile fuel breeding, first wall radiation damage, and heat deposition have been investigated in a liquid first wall, blanket, and shield for the various mixture compositions of molten salt and heavy metals for blanket layer thicknesses of 20, 30, 40, and 50 cm. The neutron flux load at the first wall is assumed to be 10 MW/ m 2 . The flowing molten salt wall is composed of flibe (Li 2 BeF 4 ) as the main constituent with increased mole fractions of heavy metals, 2 to 10% ThF 4 and UF 4 . In terms of all parameters, the mixtures with UF 4 show better performance than the mixtures with ThF 4 . The atomic displacement and the helium, tritium production rates remain well below the presumable limits for all mixture compositions of molten salt and heavy metals and thicknesses of the blanket.

Three-Dimensional Neutronic Calculations for the Fusion Breeder APEX Reactor

Safety assessment of two advanced ferritic steel molten salt blanket design concepts

As part of work in the US on free flowing liquid surfaces facing the plasma, we are studying issues of integrating a liquid surface divertor into a configuration based upon an advanced tokamak (ARIES-RS) with the flow of the liquid first wall of molten salt Flinabe (Li, Na, Be fluorides) continuing to become the divertor. We present the design and thermal performance and issues in design integration such as the interactions with the plasma edge. Sn and Sn-Li have also been considered, although the complicated 3-D MHD flows cannot yet be fully modeled.

/pdf/liquid-surface-divertor-designs-for-fusion-reactors-3sbcze32jz.pdf

Liquid surface divertor designs for fusion reactors

The APEX study is investigating the use of free flowing liquid surfaces to form the inner surface of the chamber around a fusion plasma. We present a design for the chamber of a 3840 MW fusion reactor based on the configuration for the chamber and magnets from ARIES-RS but with a fast flowing molten salt of mixed Be, Li and Na fluorides for the first wall and divertor and molten salt blanket with a ferritic steel structure. Our design analysis includes strong radiation from the core and edge plasma, (liquid) MHD effects on the weakly conducting molten salt, a recycling first wall stream that enables a high efficiency thermal conversion, and evaluations of breeding, neutronics, tritium recovery and safety.

/pdf/a-fusion-chamber-design-with-a-liquid-first-wall-and-4cnnv8eg3d.pdf

B.E. Nelson

Papers

Liquid surface divertor designs for fusion reactors

A fusion chamber design with a liquid first wall and divertor