X-ray surface and volumetric heat deposition and tritium breeding issues in liquid-protected FW in high power density devices

Innovative concepts are being explored and evaluated in the Advanced Power Extraction (APEX) study to enhance the capability of removing high power de nsity and surface wall load while satisfying all other blanket functional r equirements. The minimum surface and neutron wall load considered is simila r to 1.5 MW/m(2) and 7 MW/m2, respectively, with account taken for peaking factors. Liquid first wall is among the concepts considered in which a flow ing layer is introduced from the sop of the Tokamak. Liquid lithium, Flibe, and Li17Pb83 are among the candidate materials considered. The objectives of the present work are: (a) determination of the spatial range over which X-ray from the plasma deposits its energy across the protective liquid laye r under a realistic spectrum, (b) evaluation of the impact of difference in the neutron moderation among the liquid studied on the volumetric heat dep osition rate across the layer as well the structured blanket behind it, and (c) assessment of the percentage of tritium bred only in the liquid layer relative to the total tritium bred in the entire system. In this paper, it is shown that X-ray deposits its energy over a finite depth in the layer; c ontrary to what have been assumed in previous studies. This assessment give s the correct input source for the thermal hydraulic analysis and leads to a large decrease in the liquid surface temperature. It is shown that: (a) s till high heat deposition rate is attainable at the layer surface due to th e fraction of the Bremsstrahlung spectrum below similar to 80 eV (Li) and s imilar to 200 eV (Flibe) which constitutes only similar to 0.4% of the inci dent spectrum, (b) Flibe is more powerful in moderating neutrons than Li, l eading to a factor of 2-9 reduction in the volumetric heating rate (and the rmal stresses) across the structured blanket, and (c) the fraction of the t otal breeding ratio, TBR, attributed only to the convective layer is simila r to 25% although the liquid layer is only similar to 9% of the layer/blank et length.