Abstract
We use the Serpent Monte Carlo code to produce total and partial albedo boundary conditions that can be used to model the Loviisa NPP VVER-440 core with the nodal neutronics tools of Fortum. The albedo generation process is described in detail. The dependence of the generated albedos on boron content and water density is investigated and a clear distinction is noted in water density dependence between regions containing mostly water and those containing mostly structural materials. The Serpent generated albedos are currently used in production calculations for modeling the Loviisa reactors at Fortum.
Highlights
Reflector modelling is a necessary part of core level nodal calculations as it provides a boundary condition for the neutronics solution in the active core
We describe the use of the continuous energy Monte Carlo particle transport code Serpent 2 [1] for evaluating the axial and radial albedos for a VVER-440 type reactor core
In analyzing the dependence of the total albedos on state variables, we focus on radial reflector nodes R4 and R5
Summary
Reflector modelling is a necessary part of core level nodal calculations as it provides a boundary condition for the neutronics solution in the active core. Various approaches for reflector modelling exist, from a full nodal solution in the reflector to simplified pre-calculated boundary conditions applied at the core–reflector interface. One approach is the use of an albedo boundary condition, where the reflector is represented using an albedo matrix formulation that allows the calculation of the core-returning neutron current distribution based on the core-exiting neutron current distribution. As an example of production level calculations, Serpent is used to generate the albedo boundary conditions needed for modelling the Loviisa NPP VVER-440 reactor core with the nodal neutronics tools of Fortum (HEXBU-3D [2] and Apros ∗ [3]). The albedos are generated as functions of coolant temperature (and density) and boron content and the dependence of the albedos on these state variables is discussed
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