Attila Validation with Fusion Benchmark Experiments at JAEA/FNS

The three-dimensional S_n code Attila of Transpire, Inc., can use computer-aided-design data as direct geometrical input and can deal with assemblies of complicated geometry without much effort. The International Thermonuclear Experimental Reactor (ITER) organization plans to adopt this code as one of the standard codes for nuclear analyses. However, validation of calculations with this code has not been carried out in detail so far. Thus, we validate this code through analyses of some bulk experiments and streaming experiments with deuterium-tritium neutrons at the Japan Atomic Energy Agency Fusion Neutronics Source. Analyses with the S_n code system DOORS and Monte Carlo code MCNP4C were also carried out for comparison. The agreement between the Attila and DOORS calculations is very good for the bulk experiments. For the streaming experiments Attila requires special treatment (biased angular quadrature sets or last collided source calculation) as well as DOORS in order to obtain similar results as those with MCNP, though Attila consumes much more time than DOORS.