Many modern PWRs use Integral Fuel Burnable Absorber (IFBA) fuel pellets. These pellets have a very thin (approximately 10 microns thick) layer of ZrB2 on the outer surface which helps reduce reactivity at BOC when higher fuel enrichments are used to extend cycle lengths. This IFBA is very difficult to model using MOC because very few tracks pass through the source regions. Because of this, and how the current FuelPin class is written, we have no computationally reasonable way of modeling IFBA fuel.
To tackle this problem, the FuelPin class should optionally take the IFBA material and thickness, and then if present, use the CylindricalFluxSolver class to perform a 1D annular CP simulation to homogenize the IFBA with the outer most layer of the fuel. The individual spectra of the fuel and IFBA regions from this 1D calculation must be kept for depletion purposes later on. When building the MOC geometry, only this homogenized cross section will be used. This technique is very similar to that mentioned in the Handbook for treating IFBA, and should be fairly computationally efficient while also maintaining decent accuracy (i.e. no need to smear the IFBA throughout the gap or fuel, which can give poor results).
Many modern PWRs use Integral Fuel Burnable Absorber (IFBA) fuel pellets. These pellets have a very thin (approximately 10 microns thick) layer of ZrB2 on the outer surface which helps reduce reactivity at BOC when higher fuel enrichments are used to extend cycle lengths. This IFBA is very difficult to model using MOC because very few tracks pass through the source regions. Because of this, and how the current
FuelPinclass is written, we have no computationally reasonable way of modeling IFBA fuel.To tackle this problem, the
FuelPinclass should optionally take the IFBA material and thickness, and then if present, use theCylindricalFluxSolverclass to perform a 1D annular CP simulation to homogenize the IFBA with the outer most layer of the fuel. The individual spectra of the fuel and IFBA regions from this 1D calculation must be kept for depletion purposes later on. When building the MOC geometry, only this homogenized cross section will be used. This technique is very similar to that mentioned in the Handbook for treating IFBA, and should be fairly computationally efficient while also maintaining decent accuracy (i.e. no need to smear the IFBA throughout the gap or fuel, which can give poor results).