EFFECTS OF IRRADIATION ON STAINLESS STEEL-CLAD UOsup2sup 2 PELLETS IN HELIUM OR CARBON DIOXIDE

Uranium dioxide pellets sealed in Type 316 stainless steel containers with a helium gas were irradiated in helium and in C0/sub 2/ in thermal fluxes or the order of 1 x 10/sup 13/ n/(cm/sup 2/)(sec). Cladding-surface temperatures were reportedly between 1200 and about 1800 F. The hot-cell examination performed by BMI showed that there were no obvious effects of the irradiation on the specimen tested in helium. However, the specimen irradiated in the presence of C0/sub 2/ exhibited severe cladding-CO/sub 2/ reaction and possible central melting of the UO/sub 2/. Although comparisons between pre- and postirradiation data were difficult because of involved fabrication history of the specimens, the tests did further establish the fact that helium is a satisfactory coolant gas for stainless steel cladding material at a temperature of 1200 F. The data obtained from the specimen tested in the presence of C0/sub 2/ indicate that at temperatures in the range of 1600 to 1800 F Type 316 stainless steel is not compatible with C0/sub 2/. (auth

THE EXAMINATION AND EVALUATION OF IRRADIATED THORIUM-11 w/o URANIUM SPECIMENS

Twelve irradiated specimens of thorium -11 wt.% U were examined. The specimens were fabricated by induction melting and casting in graphite and cold swaging to about 42% reduction in area. The irradiations were conducted in the MTR in capsules equipped with thermocouples. Six specimcns were irradiated to burnups ranging from 0.5 to 0.6 total at.% at average central corc temperatures ranging from 1070 to 1250 F. Three spccimens exbibited sevcre swelling or decrepitation and three appeared to be in relatively good condition. The density of these specimens decreased from 4.9 to 9.9%. The remaining six specimens were irradiated to burnups ranging from 0.9 to 1.5 total at.% at average central core temperatures ranging from 970 to 1100 F. These specimens were in relatively good condition, except for three that had swollen sevcrely at one end. Density decreases ranging from 2.4 to 3.8% were determined for these specimens. Swelling of all specimens appeared to be a linear function of burnup to the highest level studied (l.5 total at.%) and at temperatures below about 1100 F. Swelling increased significantly above 1100 F, even at burnups as low as 0.2 at.%. Fission-gas losses averaged about 0.5% for sound specimens after burnups of 1.2 to 3.3 total at.% at around l100 F. These losses were due to diffusion and recoil; cracked specimens exhibited higher losses, Metallographic examination of the specimens indicated that neither thc matrix material nor the fuel material was seriously affected by the irradiation. No evidence of corrosion by the NaK heat-transfer medium was present. (auth