Very small amount of U-232 is included in UO3 powder reprocessed from spent fuel. Bi-212 and Tl-208 (those are) the daughter nuclides of U-232 are the major gamma sources and they increase the gamma dose rate on the surface of UO3 storage container. So, it is necessary to pay attention to the exposure doses of workers. In fact, the surface gamma dose of the container is increasing in Tokai Reprocessing Plant of JAEA. Therefore, UO3 samples were taken from the storage containers and the properties were investigated. Relation between the Bi-212 and Tl-208 contents and the surface gamma dose of the storage container was clearly observed, however their calculated doses were 30–50% of the measured ones. Water content of UO3 powder was also investigated and it was kept 0.2wt% or less for over 20 years.

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