THORIUM RBWR PHYSICS

摘要

This paper summarizes several physics phenomena observed while studying Resource-renewable Boiling Water Reactors (RBWR) with thorium fuel. These thorium RBWR cores are based off the Hitachi uranium RBWR cores, which use a tight triangular lattice with an epithermal spectrum to operate on a closed fuel cycle. The self-sustaining design (RBWR-SS) and the TRU-incinerating design (RBWR-TR) deviate from the Hitachi designs by eliminating the internal blanket and the absorbers in the upper reflector, elongating the seed, and using thorium as the primary fertile fuel rather than depleted uranium in order to increase safety margins. The tight lattice spacing and epithermal spectrum lead to several distinctions between typical LWRs and RBWRs. The epithermal spectrum promotes breeding compared to a typical BWR, although the achievable burnup is still much smaller than a fast spectrum reactor. It also leads to strong pin power peaking in the RBWR-SS which necessitates the use of multiple enrichment zones. The axial heterogeneity leads to the cross sections having an axial dependence that is separate from the thermal hydraulic conditions, which necessitates the use of 3-D cross sections.