Fuel accident performance testing for small HTRs

Leaching behaviour of unirradiated high temperature reactor (HTR) UO2–ThO2 mixed oxides fuel particles

“…Indeed, it has been shown that no radionuclide can be released as long as the coating layers are intact [1,2]. However, if the coatings fails due to mechanical or chemical interactions, the long-term behaviour mainly depends on the chemical stability of fuel kernels.…”

Immobilization of inert TRISO-coated fuel in glass for geological disposal

“…For a HTR power plant (with a thermal output of 200 MJ s À1 ) and below 1620°C the TRISO-particles with SiC were found to ensure a high confinement of fission products [11]. Higher temperatures treatments of TRISOparticles (up to 2100°C) have shown a 4-5 order of magnitude increase in Xe-133, I-131 and Cs-137 release [13,14] due to SiC deterioration. In Japan, TRISO-particles with zirconium carbide (ZrC) showed better confinement properties at high temperature compared to particles with SiC [15].…”

Summary Report on the Volatile Radionuclide and Immobilization Research for FY2011 at PNNL

“…Unlike traditional semiconductor materials, SiC has extremely low thermal diffusivities thereby limiting the migration of impurities. This low diffusivity for impurities is one of the reasons SiC is used as the fission product barrier in tri-structural-isotropic (TRISO) nuclear fuel and its use for this application has been demonstrated at temperatures over 2000 K (Schenk and Nabielek 1991;Schenk et al 1990;Nabielek et al 1990). Because of the low diffusivities for fission products and superior physical and chemical stability of SiC, it is an ideal candidate for immobilization of C, Kr, and Xe and perhaps other fission products, including I 2 .…”