DOE OSTI2016
An outer shield barrier for spent nuclear fuel is being developed in order to improve dry cask performance under mechanical, chemical, and radiological degradation and stresses. The materials proposed for the outer shield barrier are titanium nitride (TiN), a composite oxide layer consisting of ZrO{sub 2}, TiO{sub 2}, and Al{sub 2}O{sub 3}, and a final layer of molybdenum disulfide (MoS{sub 2}). The ultimate aim of this research is to develop a multi component shield material either as multiple layers or a multi material composite that will improve the performance of steel used in long-term storage casks. Two approaches are being examined through this research effort: multilayer and composite. The composition of the oxide layer is crucial to optimizing the shield's properties and performance. At equal oxide compositions the mixture of these specific oxides is commonly known as zirconolite. This material has been shown to provide a water barrier and to provide substantial corrosion resistance to the dry cask. In order to optimize the radiological performance of this layer the compositions of each oxide have been varied and analyzed for chemical, mechanical, and radiological effects on performance. Through the course of this research effort materials performance changes after gamma and neutron exposure as well as gamma and neutron attenuation of the potential shield materials have been measured and correlated to coating composition. As it is particularly difficult to design a novel, five component material with the goal of improving corrosion, wear behavior, heat tolerance, radiation tolerance, and general survivability, it is necessary to understand which coating components contribute to each property enhancement, and which are critical to design and eventual coating survivability. To compliment the experimental research effort, a study of gamma radiation doses using the relevant zirconolite constituent oxides and assorted combinations off all three, ZrO{sub 2}-TiO{sub 2}-Al{sub 2}O{sub 3}, has been conducted in order to gain insight into which, if any, ratios of the three constituent oxides may provide optimal gamma radiation shielding. Analyzing and comparing the oxides to each other it is apparent that the outer shield barrier with no zirconia has the highest absorbed dose rate at 4.88 E6 mrad/hr. The simulations run with no alumina and no titania are remarkably similar in absorbed dose rates. Alumina and titania compositions increase the absorbed dose rate increase. This is to be expected as during these simulations the zirconia composition is decreasing.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗