Tritium breeding capability of water cooled ceramic breeder blanket with different container designs

Highlights: • Tritium breeding capability of a WCCB blanket with different container designs was evaluated. • Tritium breeding ratio was assessed by using MCNP5.1.60 and FENDL-2.1. • A considerable amount of neutron was captured by the container. • Neutron capture by the container can be mitigated by applying the envelope. • Envelope effects were visible in all blankets irrespective of the blanket design. -- Abstract: Water cooled ceramic breeder (WCCB) blankets have been regarded as a primary concept in Japan. We investigated the tritium breeding capability of a WCCB blanket with a cylindrical structure, an advantageous shape for withstanding high coolant pressure, in this study. The breeding area in the blanket was modeled as a homogeneous mixture or heterogeneous structures. Nuclear analyses with Monte Carlo method were conducted for evaluating the tritium breeding ratio (TBR) of the blanket. The neutron balance of the blanket was analyzed to elucidate the mechanism related to the increase in TBR when an additional thin breeding layer (envelope) was applied to the blanket. The neutron multiplication in (n, 2n) reaction increased concomitantly with increase of the beryllium volume ratio. However, numerous neutrons were not used efficiently for tritium production, but were captured by the container, which was made of the reduced activation ferritic martensitic steel, F82H. Capture by the container can be reduced by introducing an envelope. The effect of the envelope was considerable when modeling the internal structure such as U-shaped pipes in the breeding area. The envelope was also applied to a blanket with different container designs. An increase in TBR was shown irrespective of blanket design. The envelope effect was remarkable when it was difficult to achieve the internal configuration, which was equivalent to the homogeneous mixture in the breeding area.