Burnup characteristics and performance of boron nitride and boron coated urania and urania-gadolinia fuels

In this research the burnup performance of (1) boron nitride (BN) and (2) boron nitride-boron (B), hybrid coated urania (UO₂) and urania-gadolinia (Gd₂O₃) fuels were studied. The behavior of fuel burnup, depletion of BN and B, the effect of coating thickness and also Gd₂O₃ content on the burnup performances of the fuels were found by using the code WIMS-D/5 for pressurized water reactor (PWR) and boiling water reactor (BWR) fuel assemblies. The optimum thickness ratio of B to BN was found as 4 and their thicknesses were chosen as 4 and 1 μm, respectively. Based on this observation, calculations were performed for the standard fuel assemblies with and without burnable poison and similar assemblies with BN-B hybrid coating with the desired BN-B thicknesses. Results are discussed to make an assessment of the effect of such hybrid coating on fuel cycle characteristics.