Conference Proceedings Paper
ERBIA-LOADED CANDU FUEL FOR MINIMIZATION OF THE COOLANT VOID REACTIVITY
13th International Conference on CANDU Fuel - 2016 Aug. 15-18
W. Kim (Korea Advanced Institute of Science and Technology)
M.A. Motalab (Korea Advanced Institute of Science and Technology)
Y. Kim (Korea Advanced Institute of Science and Technology)
To improve the inherent safety of the CANDU6 reactor, the coolant void reactivity (CVR) should be minimized. This work is concerned with minimization of the coolant void reactivity of a CANDU6 reactor loaded with natural U CANFLEX fuel. In spite of improved thermal margin and lowered fuel temperature, CANFLEX fuel is known to slightly increase the coolant void reactivity the standard 37-element fuel bundle. In this work, a burnable absorber of Er2O3 (erbia) is used to minimize the CVR of CANDU6 reactor. Erbia is directly admixed with the UO2 fuel as is utilized in the PWR applications. The allowable range of erbia loading in UO2 pellet is reviewed in terms of the fuel thermal conductivity. The optimal loading of erbia is investigated through lattice-based analysis and its impacts of on the lattice characteristics are discussed. In particular, both the fuel Doppler effect and coolant void reactivity are evaluated for the lattice. For a more reliable analysis, a 3-D equilibrium core is determined by using the standard time-average methods for erbia-loaded CANDU6 cores by using an in-house code system. The core analysis is based on a hybrid two-step method in which the lattice analysis is performed by the Serpent Monte Carlo code and the 3-D core analysis is performed by a diffusion theory code named COREDAX. To compensate for the negative reactivity due to the erbia loading, some of the adjuster rods are removed to increase the fuel discharge burnup. Both partial and complete removal of the adjuster rods are considered in this study. For the derived equilibrium cores, the core performances are evaluated in terms of the fuel burnup, power profile. Also safety parameters including the CVR are also evaluated for the equilibrium core conditions. In this work, safety parameters of the 3-D cores are compared with those obtained with simple lattice-based analysis.
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