On the disintegration and acid leaching method for measuring free uranium in HTGR fuel compacts

In order to improve the disintegration and acid leaching method for measuring free uranium in HTGR fuel compacts, a new apparatus was devised and several tests with regard to the acid leaching were made. The apparatus devised was such one which could disintegrate a fuel compact uniformly in nitric acid solution by rotating it. The optimum conditions of disintegration were 3 - 4 A of electric current and 20 h of leaching time in 7 mol/l concentration of the nitric acid solution. The apparatus operated under these conditions made it possible to disintegrate the compact much faster than the conventional method. For chemical analysis of uranium after the leaching, two methods, Arsenazo III and fluorophotometery were examined and the fluorophotometery which was easier way than the former, was found to be applicable for uranium analysis with 14 % of the standard deviation in the measured results. Also made was a study on the uranium contamination source in the fuel compacts, of which results indicated that the major sources were the failed coated particles and contamination during a compact fabrication process. Uranium contaminated in the latter source was inferred to be natural one. (author)