Chemical Reactions of UF 6 With Water on Ingress to Damaged Model 48X 10-Ton Cylinder

Chemistry studies of the effects of water flooding in Model 48X 10-ton UFii storage cylinders, as a result of impact fractures, were conducted to support the Safety Analysis Report for Packaging (SARP) review of the Paducah Tiger Overpack for transportation of those cylinders. The objectives of the study were to determine the maximum amount of water that could be admitted to the interior of such a damaged cylinder, the resulting geometries and chemical compositions from reactions of water with the UFii contents of the cylinder, and the end-state water moderated and reflected configurations for input to nuclear criticality safety analyses. The case identified for analysis was the flooding of the inside of a cylinder, submerged horizontally in 3 ft of water. The flooding was driven by an initial pressure drop of 13 psig, through an assumed fracture (I /32 in wide x 1/2 in deep x 18 in long) in the barrel of the cylinder. During the initial addition of water, transient back pressures occur from the effects of the heats of reaction and solution at the water/UFii interface, with some chugging as more water is added to alternately cool the reaction surface and then heat it again as the added water reacts with more UFii. As the system cools, the process is terrninated by compression of the noncondensable gases when the ullage volume (initially 1.21 x 10^3 L at an assumed pressure of 3 psia) is reduced by a factor of 5. It was deterrnined that the final configuration in the flooded cylinder was a 1.07 x 10^3 L aqueous-phase blanket over a 1.77 x 10^3 L bed of undissolved UFh. The rest of the space in the cylinder consisted of a 2.4 x 10^2 L ullage volume, which was originally 1.21 x 10^3 before the hypothetical flooding event. The conservative upper limit to the (room-temperature) uranium concentration in the aqueous phase was deterrnined to be 330 giL, at HF and H20 mole fractions of0.18 and 0.79, respectively. Density of that aqueous phase was deterrnined to be 1.237 kg!L. These results have not yet been analyzed for their impact on the k-effective of the configuration.