INFLUENCE OF LOTUS CONCRETE STRUCTURE, BORON-LOADED SHEETS, AND B4C FILTER ON THE INTEGRAL TRITIUM PRODUCTION OF A NATURAL LITHIUM GRAPHITE-REFLECTED BLANKET AND COMPARISON WITH EXPERIMENT

Integral tritium production rate (TPR) measurements are important in c omparisons of calculations to ascertain the suitability of computer co des and cross-section sets used in calculation. At the LOTUS facility, one of the objectives is to make measurements with different types of pure fusion and hybrid blankets and compare the results with calculat ions. Since the concrete cavity housing the blankets is small, it is o f direct relevance to determine the influence of room-reflected neutro ns on the integral TPR and, if possible, to reduce this effect by spec ial absorbers. The effects on the TPR of a stainless steel-natural lit hium-graphite-reflected blanket due to the concrete structure, B4C fil ter, and boron-loaded sheets covering the assembly are studied. Calcul ations are performed by the MCNP Monte Carlo code. Since the room-retu rned component depends strongly on the composition of the concrete and , moreover, does not correspond to a real blanket situation, it is adv isable to compare measurements with calculations for the region where such interference is minimal. A central region measuring 30.15 x 26.25 x 60 cm3 is identified for the purpose of comparison. In addition to calculations for a fully homogenized blanket, the important central bl anket region is considered in the form of rods, and the remaining blan ket as a homogeneous region, to assess the effect of neutron streaming on the TPR of the assembly. An experiment is done by irradiating seve ral Li2CO3 probes positioned in each tube so that the central region o f interest is fully covered. The activity of the probes is measured by the standard liquid scintillation method, and the TPR for the entire region can be derived from the experimental reaction rate data. The co mplete details of the calculational model and the experimental procedu re are provided. Good agreement is found between the calculated and ex perimental TPRs after accounting for various sources of errors. This s uggests that the three-dimensional description of the source and the b lanket arrangement employed for the calculations are quite satisfactor y.