The Disruption of Vessel-Spanning Bubbles in Containers with Sloped Fins

Radioactive sludge was generated in the K-East Basin and K-West Basin fuel storage pools at the Hanford Site while irradiated uranium metal fuel elements from the N Reactor were being stored and packaged. The fuel has been removed from the K Basins. The sludge has been retrieved and loaded into sludge transport and storage containers (STSCs) and transported to T Plant for interim storage. The sludge is composed of a variety of particulate materials and water, including a fraction of reactive uranium metal particles that are a source of hydrogen gas. If a situation occurs where the reactive uranium metal particles settle out at the bottom of a container, previous studies have shown that a vessel-spanning gas layer above the uranium metal particles can develop and can push the overlying layer of sludge upward. The major concern, in addition to the general concern associated with the retention and release of a flammable gas such as hydrogen, is that if a vessel-spanning bubble (VSB) forms in an STSC, it may drive the overlying sludge material to the vents at the top of the container.

A previous study demonstrated that sloped walls on vessels provided an effective approach for disrupting a VSB by creating a release path for gas as a VSB began to rise. Based on the success of sloped-wall vessels, a similar concept is demonstrated here where a sloped fin is placed inside the vessel to create a release path for gas. A key potential advantage of using a sloped fin compared to a vessel with a sloped wall is that a small fin decreases the volume of a vessel available for sludge storage by a very small fraction compared to a cone-shaped vessel.

Experiments were conducted in 5, 10, and 23 in. diameter scaled vessels with a range of simulant shear strengths and fin shapes to determine what fin slope and width were sufficient to disrupt VSBs. Modeling of VSB stability and disruption were also used to support scaling of the results based on the gravity yield parameter (Y_G = τ_s/[ρ_s g D], where τ_s is the shear strength and ρ_s is the density of the simulant, D is the vessel diameter, and g is gravitational acceleration). Results for vessels of different size confirmed scaling with Y_G, though VSBs were shown to be more readily disrupted in progressively larger test vessels, which demonstrated that sloped fins would disrupt VSBs in the larger full-scale STSCs. A T‑shaped fin with a 5-degree slope was selected for use in the full-scale STSCs and 20 STSCs have been loaded with radioactive waste and moved to a temporary storage location.