Thermal analysis of ceramic nuclear fuels for the HPLWR

Abstract

The High Performance Light Water Reactor (HPLWR) is one of the most promising designs of the Super-Critical Water Reactor (SCWR). The use of uranium nitride (UN) and uranium carbide (UC), as alternative nuclear fuels for the SCWR, offer the advantage of high thermal conductivity compared to uranium dioxide (UO2). For the analysis of these alternative nuclear fuels in SCWRs, some important design features must be considered. One of them is the porosity; the nuclear fuel is manufactured with different porosity values, as high as 20%, to reduce its hardness and swelling, influencing its thermal conductivity. Another issue is related to the chemical reactivity of UN and UC with water and nickel, which forces the use of coatings for fuel pellets. In this paper, a preliminary thermal-hydraulic analysis, using CFD codes, of the HPLWR fuel assembly, focused on the thermal behavior of ceramic fuel, was carried out. The use of UN coated with zirconium carbide layers and UC coated with titanium nitride layers were analyzed. The impact of porosity induced changes in fuel temperature profiles was analyzed. The radial and axial fuel temperature distributions were obtained for all cases. It was found that the maximum temperature values obtained using UN and UC, both coated and uncoated, were lower than those obtained with UO2. It was found that the porosity changes on the proposed fuels have a small influence on the maximum fuel temperature.