This paper proposes a benchmark problem suite for studying the physics of next-generation fuels of light water reactors. The target discharge burnup of the next-generation fuel was set to 70 GWd/t considering the increasing trend in discharge burnup of light water reactor fuels. The UO 2 and MOX fuels are included in the benchmark specifications. The benchmark problem consists of three different geometries: fuel pin cell, PWR fuel assembly and BWR fuel assembly. In the pin cell problem, detailed nuclear characteristics such as burnup dependence of nuclide-wise reactivity were included in the required calculation results to facilitate the study of reactor physics. In the assembly benchmark problems, important parameters for in-core fuel management such as local peaking factors and reactivity coefficients were included in the required results. The benchmark problems provide comprehensive test problems for next-generation light water reactor fuels with extended high burnup. Furthermore, since the pin cell, the PWR assembly and the BWR assembly problems are independent, analyses of the entire benchmark suite is not necessary: e.g., the set of pin cell and PWR fuel assembly problems will be suitable for those in charge of PWR in-core fuel management, and the set of pin cell and BWR fuel assembly problems for those in charge of BWR in-core fuel management.
Effect of the nuclear surface diffuseness on the isoscalar giant monopole resonance is studied with use of a trapezoidal model. It is shown that the nuclear surface diffuseness reduces the resonance energies of light nuclei bringing them to a better agreement with experiment.
In boiling water reactor (BWR) cores, the radial void distribution in fuel bundles is thought to deviate from uniform distribution. The effect of heterogeneity in the subchannel void fraction distribution, caused by the presence of Gd-poisoned and cold surfaces as well as control blades on BWR lattice physics parameters, has been evaluated. The cross-sectional void distributions in each axial plane of a fuel bundle are calculated using the subchannel thermal hydraulics code COBRAG. The rod power distributions to be fed to COBRAG are calculated using either the Monte Carlo code MCNP4C or the fuel lattice code TGBLA. Iterative methods consisting of COBRAG and MCNP4C (or TGBLA) are established. A set of test cases was generated for a typical BWR 8 Â 8 fuel bundle. The results of the coupled MCNP4C and COBRAG method reveal that both Gd rods and control blade increase in worth due to the void heterogeneity, showing a maximum decrease in K 1 of $0:7%Ák=k 1 and $1:5%Ák=k 1 , respectively, at moderator density conditions equivalent to $40% void fraction. With the capability of the coupled TGBLA and COBRAG method to deplete fuel bundles, the acceleration of Gd depletion was evaluated. The impacts on the burnup characteristics of k 1 reached AE0:6%Ák 1 at maximum.
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