Postirradiation examination of capsules GF-1, GF-2, and GF-3

The GF-1, GF-2, and GF-3 capsule tests were irradiated in the Siloe reactor at Grenoble, France, between October 31, 1973, and July 25, 1975. High-enriched uranium (HEU) mixed oxide (8Th,U)O2 fissile and ThO2 fertile particles were tested over the following exposure conditions: 3.8 to 11.0 x 1025 n/m2 (E > 29 fJ)/sub HTGR/; 9600 to 11200C time volume average temperature; and mixed oxide (8Th,U)O2 burnup between 5.3 and 11.4% FIMA and ThO2 burnup between 1.1 and 3.6% FIMA. Postirradiation examination of HTGR fuel rods in capsules GF-1, GF-2, and GF-3 showed acceptable structural integrity and irradiation-induced dimensional changes that were consistent with model predictions. Pressure vessel failure levels between different TRISO-coated (8Th,U)O2 fissile particle types showed that the 400-μm-diameter kernel design was more conservative than the 500-μm-diameter designs