Analysis of Oxygen Partition Equilibrium within HTGR Low-Enriched UO2 Coated Particles

概要

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To evaluate the temperature- and burnup-dependent intraparticle CO/CO2 pressures for the design of HTGR low-enriched UO2 coated particles, a thermodynamic model has been developed, based on the equilibrium oxygen partition between UO2, carbon oxide gases and fission product oxides. The model takes into account a change in kernel stoichiometry due to temperature change and fuel burnup, and involves oxygen release correlations established by referring to measured CO content data in the literature. The analyses of measured CO contents below 1, 400°C for unirradiated particles show that the 0/U ratio of as-coated particle kernel is 2.00012.001. The 0/U ratio in irra-diated particles has been predicted to range from 2.0001 to 1.999 below 2, 000°C, indicating that the oxygen liberated by fission is consumed nearly all in forming fission product oxides and CO/CO2 gases under normal reactor operating conditions, but at extreme tem-peratures above 2, 000°C the fuel kernel will be reduced to highly hypostoichiometric composition.