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Report No.

Core and fuel design of BWR with multi-axial fuel shuffling

Tasaki, Yudai ; Yamaji, Akifumi*; Amaya, Masaki

In breeding core designs with light water, tight lattice fuel bundle design in which the coolant flow area is small is adopted to prevent the neutron moderating. Additionally, the core often consists of MOX fuel and blanket fuel, which aims to irradiate depleted uranium effectively. In preceding study, the concept of "Multi-axial fuel shuffling" has been proposed for a higher breeding core design of supercritical-water cooled reactor (SCWR), in which the core consists of multiple layers of MOX fuels and blanket fuels with independent fuel shuffling for the upper blanket layer where coolant density is lowest. As a result, the SCWR with multi-axial fuel shuffling has shown improvement of breeding performance. The same principle may be applied to BWR, since the coolant density gets low due to developing void fraction. However, the fuel rod included such a core design has two kinds of fuel pellets, and MOX fuel parts tend to get high power peaking. Therefore, it is necessary to investigate and mitigate the fuel maximum temperature and the shear stress of the boundary between MOX and blanket fuel parts which may occur by the difference of PCMI characteristics of two fuel parts. Moreover, it is possible that the cladding outer diameter change especially in MOX fuel parts may impact on the thermal-hydraulics, because the gap between rods is narrow owing to the tight lattice fuel bundle design. This study has shown the improvement of breeding performance of BWR with multi-axial fuel shuffling, and the fuel design which mitigates the above design issues. The cladding outer diameter change doesn't impact on critical heat flux ratio mostly, but depends on pressure drop of the flow channel. Therefore, this result suggests a design issue with respect to the core flow distribution.



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