Surface area considerations for corroding N reactor fuel [report]

A.B. Jr. Johnson, A.L. Pitner
1996 unpublished
An ongoing analysis (Cooper and Johnson) is examining the credibility of a published value for uranium corrosion in oxygenated water as a basis for estimating the area of the corroding K East fuel. Radiation-Induced Porosity Radiation-induced porosity is judged to have a minor effect on true surface area, because burnups on the failed N Reactor fuel are generally 3000 MWd/MT or below. Even on N Reactor fuel with the highest estimated burnups (-7000 MWd/MT), if porosity is significant, it will
more » ... nificant, it will result in a narrow band of pits near the metal surfaces for fuel corroding from the ends, with most of the metal cross section substantially unaffected. Effects of Microcracks Reactions in tight microcracks in the metal are expected to be diffusion-limited; in that case, the cracks would not contribute substantially to true surface area. If the metal is segmented, the area increase could be significant when the segmented metal is exposed to reactants. Microcracks were not observed when a damaged K West fuel element was examined metallographically in a hot cell at a location approximately 12 in. (30 cm) from the damaged end. Cracks also were not observed by Swanson on elements that had survived discharge without breaching the cladding. On the other hand, Swanson (1988) reported that after the cladding was dissolved from a damaged N Reactor fuel element, a jumble of broken pieces was observed, rather than a solid cylinder of uranium. The element had corroded 12 years in water after reactor discharge. Swanson attributed the segmentation to reaction of the partially degraded uranium cylinder with the decladding solution (5M NH,F + 0.45 Ea NH,NO,). The reaction was proposed to involve hydrides that developed in uranium grain boundries. iv
doi:10.2172/251612 fatcat:srzpcnqvnvf37agijb6bqqzh7m