THECA - a code system for 3-D thermohydraulidc layout of fast reactors

The THECA program system allows the designer to perform the complete 3-D thermal design of a fast reactor core. This means that the whole reactor core is taken into account. THECA consists of 3 principal modules: 1) THELVU for the evaluation of the nominal 3-D power distribution in the reactor core. 2) THESYS for the evaluation of the nominal temperature distribution in the reactor core. 3) THEDRA for the statistical hot spot analysis and design optimization. In this case optimum design means the achievement of maximum power density and coolant temperature rise across the core at given core geometry, neutron flux distribution and hot spot probability. The distributions of the neutron flux and of the fission cross sections as calculated by a diffusion code are elaborated by THECA: then the code delivers as output the power rate distribution and the temperature distribution (obtained considering subchannel mixing, heat exchange among adjacent subassemblies, γ-heating etc.) in a form which can directly be used by further core design computer programs, such as codes for structural calculations, reactivity coefficient calculation and so on. In this way, it is made possible by the THECA program system not only a complete detailled thermal-hydraulic design of a reactor core, but also a useful flow of the very extensive numerical data which are needed for the whole core design. (orig.)