microstructural and thermophysical properties of uo2-mo composite reactor fuels

Abstract

Nuclear fuel performance under normal operating conditions and extreme accident conditions have studied using experimental procedures to investigate the microstructural and thermophysical properties of the fuel. Attention has been drawn to the catastrophic nuclear power station accident at the Fukushima Daiichi in Japan. After the reactor system's failure, efforts are focused on preventing the existing nuclear fuel, uranium dioxide (UO2), and zirconium (Zr), system from melting. Research is required to replace the fuel and clad system with a more robust system that can withstand accidents. With the recognition of associated risks with the current fuel, hence, developing an accident-tolerant fuel (ATF) became a major motivation for research. In this work, Molybdenum (Mo) has been deployed as an additive material in UO2 fuel due to its high thermal conductivity, high boiling point, high melting point, and low thermal neutron absorption cross-section.

The nuclear reactor safety analysis showed that thermal conductivity is an essential property of fuel because it regulates fuel operating temperature and therefore influences the safety of reactor operation. Low thermal conductivity leads to the rapid meltdown at the core of the fuel pellet during the loss of coolant scenario. Apart from thermal conductivity, pellet microstructure and density also played an essential role in fission gas buildup and release, the accumulation of the fission gas in form of voids in the center of fuel pellets. Therefore, three major critical areas of focus have been identified in this research: i) Enhanced thermal conductivity of UO2-Mo composite fuel for high-temperature accident scenarios, ii) Evaluation of the pellet microstructure, grain size, texture, and grain boundary character distribution in UO2-Mo composites, and iii) Optimizing the high densification of the UO2-Mo composite fuel pellets.

One of the limitations of the accident-tolerant fuel has the difficulty of processing dense pellets by the conventional sintering methods. Hence the fabricating of UO2-Mo composite fuels by spark plasma sintering (SPS) was proposed, and the effect of the sintering parameters on the density, microstructure, and thermal conductivity of UO2-Mo composite fuel have established. Finally, a composite fuel of UO2-Mo (micro and nano particles) has been manufactured with enhanced thermal conductivity.