In 2000, British Nuclear Fuels Limited (BNFL) commissioned an irradiation program at the United States Department of Energy’s Idaho National Engineering and Environmental Laboratory (INEEL) to assess the effects of extended operating scenarios upon the integrity of Magnox reactor cores. In this program, predictions of thermal and physical effects on these graphite cores were developed using analytical computer models. To benchmark results, experimental graphite assemblies representative of the Magnox graphite were irradiated in the Advanced Test Reactor (ATR). This paper analyzes and contrasts the thermal predictions with those experimental results. These investigations were conducted to extend existing graphite physical property databases for higher radiolytic weight loss (35–50% density reduction) than occur during the economic planning life of these reactors. These data then can be used to make extended life projections regarding the suitable function of the graphite in its various roles of providing the physical structure for the fuel, neutron moderator, medium for instrumentation, and coolant channels. Extended irradiation effects will be obtained with samples of archived, pre-characterized graphite used in the Magnox type reactors. The new Irradiation Test Vehicle (ITV) facility in the ATR contained the experiments and provided the desired irradiation conditions as well as on-line temperature control. The capability to provide both oxidizing and inert gas atmospheres for the graphite specimens was added to the ITV to enable assessment of the individual and combined effects of oxidation and neutron damage to the specimens. In this paper the thermal evaluations (performed to size the control gaps to obtain the desired thermal performance) are contrasted to actual experimental results.

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