Appendix A: RADIATION LEVELS FROM 233U The radiation levels from 233U determine (1) many of the facility requirements for its processing, (2) its transport requirements, and (3) the waste-handling requirements of any 233U product. The material may be either contact-handled (CH) or RH depending upon the radiation level. The historical dividing line between CH and RH is 200 mrem/h at the surface of a container. The radiation levels from 233U, as discussed in Sect. 2, depend upon (1) the impurities in 233U, particularly 232U and its decay products; (2) the age of the 233U since the gamma-emitting decay products have been removed from the 233U and 232U impurity; and (3) other materials with which the 233U is mixed. This appendix provides some additional information on expected radiation levels. A set of calculations was made to determine the radiation dose from a 55-gal (208-L) drum near the surface of the drum. Radiation doses were calculated 1 cm from the drum as an approximation for surface measurements on the drum (to minimize numerical instabilities in radiation calculations). The following assumptions were used. •
Uranium-233 impurity level. The 233U was assumed to have 100 ppm 232U. The 233U inventory has materials with 232U concentrations from a few parts per million to somewhat >100 ppm.
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Uranium-232 age. The primary radiation from 233U in storage is from the 232U decay product, 208 Tl. This decay product emits a 2.6-MeV gamma ray. If the uranium has been purified, the 208 Tl builds up over time and then decays as the 232U decays. The time of maximum radiation levels is 10.3 years after separation of the decay products from the uranium. The radiation calculations herein are for this particular time of maximum radiation.
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Drum characteristics. The drum height is 35 in., the diameter is 24 in., and the wall thickness is 1/16-in. carbon steel. No shielding was incorporated into the drum.
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Uranium chemical form. The uranium is assumed to be U3O8 in the form of a loose powder with a density of 1.5 g/cm3. The drum contains J390 kg of oxide.
If the 233U is isotopically diluted with DU to become non-weapons-usable 233U (1 part 233U with 7.407 parts DU containing 0.2 wt % 235U), the external radiation doses calculated at a distance of 1 cm from the drum will be 141 R/h. The 232U concentration would have to be <0.1 ppm to be CH material (<200 mrem/h). In this specific example, a neutron absorber would have to be added to the drum for criticality control. If the 233U is isotopically diluted with DU to minimize criticality concerns (1 part 233U with 188 parts DU containing 0.2 wt % 235U), the external radiation doses calculated at a distance of 1 cm from the drum will be 6.247 R/h. The 232U concentration would have to be reduced to <3 ppm to reduce the radiation levels to those of CH waste (<200 mrem/h).
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