A simulation study of thermal breeding of tritium at low temperatures in a D-T fusion reactor blanket

Results are reported for tritium production rate (TPR) and tritium breeding ratio (TBR) in a 20-cm-thick bare lithium slab, at temperatures 100, 150, 200 and 300 K. The multigroup diffusion equation is solved as an eigenvalue problem for a completely thermalized source. The spatial variation of TPR has been estimated in the above-mentioned temperature range. It is observed that as the temperature is lowered the values of TPR show a considerable increase at distances very close to the source plane, whereas it falls rapidly at later distances for low temperatures. Variation of TBR with thickness of the breeding region at the aforesaid temperatures, shows saturation regions at various thicknesses. This thickness is seen to decrease as the temperature is lowered or the concentration of 6Li nuclei is enhanced. The effects of enrichments of 6Li nuclei on the value of TBR has also been assessed. The calculation shows that with increase in concentration of 6Li nuclei, the TBR value after an initial rise attains a constant value. It is also seen that TBR saturates at lower concentration of 6Li nuclei as the temperature is lowered. For the above-mentioned temperature range, TBR values show an exponential decay with increase in temperature. It is interesting to observe here, that even in a simple bare lithium slab the optimal value of TBR (1.05) is attainable at a temperature below about 180 K.