Mitigation of Hydrogen Gas Generation from the Reaction of Uranium Metal with Water in K Basin Sludge and Sludge Waste Forms

Abstract

Sludge formed and reposing in the K East (KE) and K West (KW) fuel storage basins on the Hanford Site has been a subject of concern since extended storage of metallic fuel from the N Reactor began in the 1980s. Although the last of the fuel was removed from the basins in 2004 and transport of sludge from the KE Basin to the KW Basin was completed in 2007, sludge still remains in the KW Basin stored in engineered containers. Sludge will be recovered from the engineered containers into Sludge Transport and Storage Containers and stored at an interim storage location on the Central Plateau. The stored sludge ultimately will be processed for disposal to the Waste Isolation Pilot Plant (WIPP) as remote-handled transuranic waste. However, before the sludge can go to WIPP, it must be processed and packaged into WIPP-acceptable forms. The presence of uranium metal fuel particles in the sludge poses problems to these operations because uranium metal reacts with water to form flammable hydrogen gas.Activities surrounding the storage, transport, treatment, and disposition of the K Basin sludge are currently administered under the Sludge Treatment Project (STP) managed by CH2M Hill Plateau Remediation Company (CHPRC) operating under contract to the U.S. Department of Energy. Investigative studies in this report were conducted by Pacific Northwest National Laboratory (PNNL) under contract to CHPRC for the STP.The reaction of uranium metal with water to form diatomic hydrogen gas (H 2 ) and uranium dioxide or uraninite (UO 2 ) proceeds by way of uranium hydride (UH 3 ). Mechanistic studies show that hydrogen radicals (H) and UH 3 serve as intermediates in the reaction of uranium metal with water to produce H 2 and UO 2 . Because H 2 is flammable, its release into the gas phase above K Basin sludge during sludge storage, processing, immobilization, shipment, and disposal is a concern to operational safety. PNNL conducted literature reviews and laboratory studies to identify methods that could be used to decrease the rate of H 2 gas generation from uranium metal corrosion in water present in sludge (Sinkov et al. 2010). Four means to decrease the H 2 evolution rate were identified for further experimental consideration:1. decreased temperature 2. reactant isolation (separation of the uranium metal from the water) 3. corrosion inhibition 4. hydrogen scavenging.The effect of decreased temperature could be inferred based on the known published rates of uranium metal reaction with water (Delegard and Schmidt 2009). Of the remaining three approaches, hydrogen scavenging appeared to be the most promising for laboratory testing, but experimental effort into reactant isolation and corrosion inhibition was also conducted and reported.Laboratory testing identified nitrate, NO 3 -, and nitrite, NO 2 -(added as their sodium salts) to be the most promising agents to minimize H 2 generation in prospective K Basin sludge operations because of their demonstrated high-attenuation factors, decreasing hydrogen generation rates hundreds-to thousan...

Flotation using sodium dodecyl sulphate and sodium lauroyl isethionate for rapid dewatering of Mg(OH)2 radwaste suspensions

“…To accelerate dewatering, there is current research into the application of polymeric occulants to enhance suspension zonal settling rates, which have been shown to signicantly decrease residence times in thickening operations. [11][12][13][14][15] However, these processes have a number of drawbacks, in terms of their modication to waste structure and related downstream issues. 1 In particular, the resultant fractal nature of these polymeric ocs can increase settled bed volumes, which may reduce the solid waste capacity of intermediate level waste containers for nal geological disposal.…”