Abstract
This work continues the development of a numerical model to simulate transient tritium transport on the breeder zone (BZ) level for the EU helium-cooled pebble bed (HCPB) concept for DEMO. The basis of the model is the open-source field operation and manipulation framework, OpenFOAM. The key output quantities of the model are the tritium concentration in the purge gas and in the coolant and the tritium inventory inside the BZ structure. New model features are briefly summarized. As a first relevant application a simulation of tritium transport for a single pin out of the KIT HCPB design for DEMO is presented. A variety of scenarios investigates the impact of the permeation regime (diffusion-limited vs. surface-limited), of an additional hydrogen content of 300 Pa H2 in the purge gas, of the released species (HT vs. T2), and of the choice of species-specific rate constants (recombination constant of HT set twice as for H2 and T2). The results indicate that the released species plays a minor role for permeation. Both permeation and inventory show a considerable dependence on a possible hydrogen addition in the purge gas. An enhanced HT recombination constant reduces steel T inventories and, in the diffusion-limited case, also permeation significantly. Scenarios with 80 bar vs. 2 bar purge gas pressure indicate that purge gas volumetric flow is decisive for permeation.
Highlights
Tritium, as one of the two necessary fuels for the currently technically pursued D-T fusion process, will have to be produced inside the fusion plant blanket itself—e.g., starting from lithium making use of the fusion neutrons
The attenuation of nuclear interaction processes with increasing distance from the first wall (FW) and the cooling configuration will result in considerable temperature spreads, tritium generation profiles, and different grades of radiation damage to the structure material (Eurofer-97), as well as to the breeder ceramics (ACB), and neutron multiplier material (Be12 Ti) inside a breeder zone (BZ)
With regard to a leak-tolerant design for DEMO helium-cooled pebble bed (HCPB) it is under discussion to higher than the purge gas mass flow rate
Summary
As one of the two necessary fuels for the currently technically pursued D-T fusion process, will have to be produced inside the fusion plant blanket itself—e.g., starting from lithium making use of the fusion neutrons. For the so-called breeding of tritium, one European concept for DEMO, called the helium-cooled pebble bed (HCPB) uses a pebble bed of an advanced lithium ceramic breeder (ACB), namely Li4 SiO4 with 35%. A breeder blanket typically is built of several identical or at least very similar components. These components represent a practicable level for computational fluid dynamics (CFD) modeling. The attenuation of nuclear interaction processes with increasing distance from the first wall (FW) and the cooling configuration will result in considerable temperature spreads, tritium generation profiles, and different grades of radiation damage to the structure material (Eurofer-97), as well as to the breeder ceramics (ACB), and neutron multiplier material (Be12 Ti) inside a breeder zone (BZ). As a first step in this work the model is applied to tritium transport inside a single pin of the KIT HCPB DEMO pin design
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