Synthesis and Characterization of CeO₂-Based Simulated Fuel Containing CsI

Abstract

　Following the accident at the Fukushima Daiichi Nuclear Power Plant in 2011, radioactive nuclides caused serious contamination. In particular, cesium (Cs) and iodine (I) are the most important fission products (FPs) because they are easily released due to their high vapor pressure. However, their release behavior from nuclear fuels during the accident has not been clarified. Understanding such behavior can contribute to improving the accuracy of the source term evaluation. Simulated nuclear fuels containing non-radioactive FPs can be used in laboratory experiments to understand such behavior. However, simulated nuclear fuels containing Cs and I are difficult to synthesize because of their high volatility. Here, cerium dioxide (CeO₂)-based simulated fuels containing cesium iodide (CsI) are synthesized by spark plasma sintering, allowing us to obtain bulk samples rapidly at low temperatures compared with those of conventional sintering methods. CeO₂ is used to simulate uranium dioxide (UO₂) owing to its similar chemical and physical properties to those of UO₂. The obtained simulated fuels are characterized by X-ray diffraction and scanning electron microscopy/energy dispersive X-ray spectrometry. CsI is confirmed to exist as small precipitates almost uniformly distributed throughout the CeO₂ matrix. The optimized conditions to synthesize the simulated fuels are proposed.