Determination of 232U daughter products released from HTGR fuel during refabrication. Part 2

During the heat treatment step of High Temperature Gas-Cooled Reactor (HTGR) fuel beads, the 233U-loaded fuel beads are exposed to temperatures as high as 17000C. Since 233U fuel beads unavoidably contain a small percentage of 232U, decay products of 232U might be released during the heat treatment step. To avoid shielding requirements, experiments were conducted using 232Th-loaded fuel beads rather than 232U-loaded fuel beads. Decay products of 232U and 232Th are the same after 228Th. Experimental data were obtained by monitoring the 583 and 2614 keV gamma emissions of 208Tl. Computer simulations of the decay process and experimental data were used to infer what relative amount of the daughter products was removed. The carbonization step (300 to 5000C) has an effect on the loss of daughter products in the conversion step. Using uncarbonized fuel beads, approximately 50 percent of 220Rn was removed at 3000C and approximately 20 percent of 220Rn was removed at 2000C. At most, 5 percent of 220Rn was removed from uncarbonized beads at 250C. Marginal 220Rn loss was detected at 1000C using pre-carbonized beads. At 14000C, 92 percent 212Pb, 70 to 90 percent 212Bi, and 0 percent 224Ra losses were observed. At 16000C, 100 percent 212Pb, 80 to 100 percent 212Bi, and 3 to 7 percent 224Ra losses were observed. At 17500C, 100 percent 212Pb, 80 to 100 percent 212Bi, and 62 percent 224Ra losses were observed. At 18000C, 100 percent 212Pb, 80 to 100 percent 212Bi, and 86 percent 224Ra losses were observed