Optimisation of CANFLEX-SCWR bundle through subchannel analysis

A subchannel code ATHAS has been developed to analyze the behavior of CANFLEX®1 bundle. The code includes a relatively large number of correlations for heat transfer, hydraulics resistance, mixing calculations as options and hence is applicable for detailed sensitivity analyses. CANFLEX bundle is appropriate for use in the CANDU®²-SCWR with radial power uniform distribution. The PCST is much lower than the design limit of cladding surface temperature 850°C. The optimization design is preliminary performed, the results show that the bundle can be optimized with modification of geometry and vertical arrangement, the coolant and cladding temperature distribution is more uniform than those before modification and the highest cladding temperature can be reduced to 727°C. The gap effect on heat transfer is also discussed. The gap effect in optimized bundle seems can be neglected.