Core Design and Analysis of Axially Heterogeneous Boiling Water Reactor for Burning Transuranium Elements

The resource-renewable boiling water reactor (RBWR) is an innovative boiling water reactor that has the capability to breed or to burn transuranium elements (TRUs). Core characteristics of the RBWR of the TRU burner type were evaluated by two different core analysis methods. The RBWR core features an axially heterogeneous configuration, which consists of an internal blanket region between two seed regions, to achieve the TRU multi-recycling capability while maintaining a negative void reactivity coefficient. Axial power distribution of the TRU burner core tends to be more heterogeneous because the isotopic composition ratio of fertile TRUs to fissile TRUs becomes larger in the TRU burner-type core than in the breeder-Type core and the seed regions need to be axially shorter than that of the breeder-Type core. Thus core analysis of the TRU burner-type core is more challenging. A conventional diffusion calculation using nuclear constants prepared by two-dimensional lattice calculations was performed by Hitachi, while the calculation using nuclear constants prepared by three-dimensional calculations and axial discontinuity factors was performed by the University of Michigan to provide a more sophisticated treatment of the axial heterogeneity. Both calculations predicted similar axial power distributions except in the region near the boundary between fuel and plenum. Both calculations also predicted negative void reactivity coefficients throughout the operating cycle. Safety analysis was performed by Massachusetts Institute of Technology for the all-pump trip accident, which was identified as the limiting accident for the RBWR design. The analysis showed the peak cladding temperature remains below the safety limit. Detailed fuel cycle analysis by University of California, Berkeley, showed that per electrical power generated, the RBWR is capable of incinerating TRUs at about twice the rate at which they are produced in typical pressurized water reactors

A novel auxetic structure with enhanced impact performance by means of periodic tessellation with variable poisson’s ratio

This study proposes a new approach to designing impact resistant elastomeric structures using innovative bi-dimensional patterns composed of a combination of circular and elliptical voids with variable aspect ratios. Key to the design are discrete sections each with different effective Poisson’s ratios ranging from negative to positive. Cubic samples 80 × 80 × 80 cm in size with different void geometry and effective Poisson’s ratios were fabricated and successively tested under compressive and low-velocity impact loads as a proof-of-concept, showing good agreement with finite element simulations. The numerical comparisons for different porosity levels demonstrated that the variable Poisson’s ratio materials resulted in better impact responses compared to those characterized by a positive (constant) value of the effective Poisson’s ratio. The promising results also show that the variable shape of the voids can lead to a modular trigger of overall effective auxetic behavior, opening up new ways design and use auxetic macro-structures with variable porosity and variable Poisson’s ratio for a wide range of applications and, in particular, for impact and protecting devices