Calvin H. Delegard

Corrosion of uranium and its low content Zr, Nb, and Ru alloys in aqueous solutions

Corrosion of uranium and its alloys with low content (0.5–5.0 at %) of Zr, Nb, and Ru in water and bicarbonate aqueous solutions is studied; the effect of hydrogen peroxide, the main product of radiation processes, on the corrosion rate is elucidated. The rate of the primary corrosion process U +(2 +n)H2O=UO2·nH2O+ 2H2↑ is measured by electrochemical methods in anaerobic and aerobic conditions for uranium metal and its alloys containing 0.5 to 5.0 at % of Zr, Nb, and Ru. It is shown that the corrosion rates for the alloys are lower than that of reactor-grade uranium; however, the difference is rather close to the measurement error. The corrosion mechanism is studied; U(III) is shown to be rather unstable in neutral solutions when uranium(III) hydroxide is precipitated and no significant amount of U(III) and UH3 is present among the products of the metallic uranium corrosion in water. The kinetics of the second corrosion stage U(IV) + O2→U(VI) is studied by spectrophotometric method. It is shown that the reaction of U(IV) oxidation by atmospheric oxygen is similar in weakly acid solutions (pH 1.5–4.0) and in bicarbonate media: in particular, it has an induction period for uranium (IV) accumulation, after which the reaction accelerates; it is formally a first-order reaction with respect to uranium. The reaction mechanisms differ in the two media: in weakly acid solutions, after the appearance of U(VI), the reproportionation reaction proceeds; thus formed U(V) interacts with O2 faster than U(IV). In the bicarbonate medium, the acceleration of the reaction is due to the formation of a [U(IV)ΣU(VI)] complex whose reactivity is higher than that of uranium (IV). In the absence of bicarbonate, of great importance is the formation of a copolymer of U(IV) and U(VI), which at pH≥4 prevents formation of U(V). It is shown that on the introduction of hydrogen peroxide to aqueous solutions, the metallic uranium surface becomes transpassive, which increases the rate of corrosion process by at least an order of magnitude,. The introducing of oxidants and platinum mesh lowers the hydrogen accumulation at 120–150°C and, hence, the hydrogen-explosion danger of the uranium-water-corrosion-products system. Methods of deposition of metal oxide (Tc, Ru, Mo, W) films onto uranium surfaces by immersing uranium metal into Tc(VII), Ru(VI), or Mo and W heteropoly compound solutions are studied.

Evaluation and Recommendation of Waste Form and Packaging for Disposition of the K East Basin North Loadout Pit Sludge

This report discusses the recommendation from the Pacific Northwest National Laboratory (PNNL) to Fluor Hanford regarding the treatment of the Hanford K East Basin North Loadout Pit (KE NLOP) sludge to produce contact handled transuranic waste (CH-TRU) for disposal at the Waste Isolation Pilot Plant (WIPP). The recommendation was supported in part by chemical and radiochemical characterization analyses (provided in this report) performed on a sample of KE NLOP sludge.

Final Report - Gas Generation Testing of Uranium Metal in Simulated K Basin Sludge and in Grouted Sludge Waste Forms

The Waste Isolation Pilot Plant (WIPP) is being considered for the disposal of K Basin sludge as RH-TRU. Because the hydrogen gas concentration in the 55-gallon RH-TRU sealed drums to be transported to WIPP is limited by flammability safety, the number of containers and shipments likely will be driven by the rate of hydrogen generated by the uranium metal-water reaction (U + 2 H{sub 2}O {yields} UO{sub 2} + 2 H{sub 2}) in combination with the hydrogen generated from water and organic radiolysis. Gas generation testing was conducted with uranium metal particles of known surface area, in simulated K West (KW) Basin canister sludge and immobilized in candidate grout solidification matrices. This study evaluated potential for Portland cement and magnesium phosphate grouts to inhibit the reaction of water with uranium metal in the sludge and thereby permit higher sludge loading to the disposed waste form. The best of the grouted waste forms decreased the uranium metal-water reaction by a factor of four.

Assessment of K Basin Sludge Volume Expansion Resulting from Uranium Corrosion During Storage

K Basin sludge contains metallic uranium and uranium oxides that will corrode and hydrate during storage. The end-state (final) corrosion products will have a lower particle density and a higher void fraction (or volume fraction of sludge occupied by water) than the starting-state sludge at the beginning of storage. As the particle density and void fraction change, the volume occupied by a given mass of sludge will also change. The purpose of this report is to quantify how the various types and sources of K Basin sludge will react and volumetrically expand (or contract) between the time the sludge is first loaded into the storage containers (starting state) and the time all major volume-changing reactions have been completed (end state). The results from this report will be used in design and safety basis calculations for sludge management systems and will be incorporated into the sludge technical basis documents.

Disposition Options for Hanford Site K-Basin Spent Nuclear Fuel Sludge

This report provides summary-level information about a group of options that have been identified for the disposition of spent-nuclear-fuel sludge in the K-Basins at the Hanford Site. These options are representative of the range of likely candidates that may be considered for disposition of the sludge. The product of each treatment option would be treated sludge that would meet waste acceptance requirements for disposal as transuranic (TRU) waste at the Waste Isolation Pilot Plant (WIPP).

Behavior of plutonium(V) in alkaline media

Abstract In alkaline solutions with NaOH concentration below 8 M, Pu(V) has been found to be unstable, disproportionating to form Pu(IV) hydrous oxide precipitate and dissolved Pu(VI). Sorption of Pu(V) on the freshly precipitating Pu(IV) hydrous oxide and partial reduction of Pu(VI) by water α-radiolysis products complicate disproportionation of Pu(V). Disproportionation and reproportionation equilibrium constants were measured in the range 4–8 M NaOH. The yield of disproportionation and reproportionation reaction products increase with temperature and sharply fall with NaOH concentration.

Mechanical Properties of K Basin Sludge Constituents and Their Surrogates

A survey of the technical literature was performed to summarize the mechanical properties of inorganic components in K Basins sludge. The components included gibbsite, ferrihydrite, lepidocrocite and goethite, hematite, quartz, anorthite, calcite, basalt, Zircaloy, aluminum, and, in particular, irradiated uranium metal and uranium dioxide. Review of the technical literature showed that information on the hardness of uranium metal at irradiation exposures similar to those experienced by the N Reactor fuel present in the K Basins (typically up to 3000 MWd/t) were not available. Measurements therefore were performed to determine the hardness of coupons taken from three irradiated N Reactor uranium metal fuel elements taken from K Basins. Hardness values averaged 30 {+-} 8 Rockwell C units, similar to values previously reported for uranium irradiated to {approx}1200 MWd/t. The physical properties of candidate uranium metal and uranium dioxide surrogates were gathered and compared. Surrogates having properties closest to those of irradiated uranium metal appear to be alloys of tungsten. The surrogate for uranium dioxide, present both as particles and agglomerates in actual K Basin sludge, likely requires two materials. Cerium oxide, CeO2, was identified as a surrogate of the smaller UO2 particles while steel grit was identified for the UO2 agglomerates.

Validation Testing of the Nitric Acid Dissolution Step Within the K Basin Sludge Pretreatment Process

The work described in this report involved comprehensive bench-scale testing of nitric acid (HNO{sub 3}) dissolution of actual sludge materials from the Hanford K East (KE) Basin to confirm the baseline chemical pretreatment process. In addition, process monitoring and material balance information was collected to support the development and refinement of process flow diagrams. The testing was performed by Pacific Northwest National Laboratory (PNNL)for the US Department of Energys Office of Spent Fuel Stabilization (EM-67) and Numatec Hanford Corporation (NHC) to assist in the development of the K Basin Sludge Pretreatment Process. The baseline chemical pretreatment process for K Basin sludge is nitric acid dissolution of all particulate material passing a 1/4-in. screen. The acid-insoluble fraction (residual solids) will be stabilized (possibly by chemical leaching/rinsing and grouting), packaged, and transferred to the Hanford Environmental Restoration Disposal Facility (ERDF). The liquid fraction is to be diluted with depleted uranium for uranium criticality safety and iron nitrate for plutonium criticality safety, and neutralized with sodium hydroxide. The liquid fraction and associated precipitates are to be stored in the Hanford Tank Waste Remediation Systems (TWRS) pending vitrification. It is expected that most of the polychlorinated biphenyls (PCBs), associated with some K Basin sludges, will remain with the residual solids for ultimate disposal to ERDF. Filtration and precipitation during the neutralization step will further remove trace quantities of PCBs within the liquid fraction. The purpose of the work discussed in this report was to examine the dissolution behavior of actual KE Basin sludge materials at baseline flowsheet conditions and validate the.dissolution process step through bench-scale testing. The progress of the dissolution was evaluated by measuring the solution electrical conductivity and concentrations of key species in the dissolver solutions as a function of reaction (dissolution) time, by analyzing offgas generation rate and composition, and by analyzing intermittent and final acid-insoluble solids at the end of the dissolution. The testing was conducted in a system designed to assess parameters that can influence sludge dissolution and provide information that can be used to determine operating conditions for the actual system.

Independent Review of Tank 241-AY-101 Fitness for Service

Video inspections in the annulus of Hanford double-shell waste storage tank 241-AY-101 in 2001 and earlier showed rust over large areas of the primary and secondary tank walls. These observations led to extensive on-destructive inspections and analyses to determine the extent and severity of the corrosion and correction of several operational deficiencies that contributed to the problem. PNNL has performed an independent review of the accumulated evidence from these efforts to determine whether unacceptable conditions were corrected and the current condition of the tank meets or exceeds technical and operational requirements. The findings of this review are the subject of this report. The conclusion is that AY-101 is fit for service without restriction subject to several recommendations for further inspections and analyses.

Characteristics of KE Basin Sludge Samples Archived in the RPL - 2007

Samples of sludge were collected from the K East fuel storage basin (KE Basin) floor, contiguous pits (Weasel Pit, North Load Out Pit, Dummy Elevator Pit, and Tech View Pit), and fuel storage canisters between 1995 and 2003 for chemical and radionuclide concentration analysis, physical property determination, and chemical process testing work. Because of the value of the sludge in this testing and because of the cost of obtaining additional fresh samples, an ongoing program of sludge preservation has taken place with the goals to track the sludge identities and preserve, as well as possible, the sludge composition by keeping the sludge in sealed jars and maintaining water coverage on the sludge consistent with the controlling Fluor Hanford (FH) Sampling and Analysis plans and FH contracts with the Pacific Northwest National Laboratory (PNNL). This work was originally initiated to provide material for planned hydrothermal treatment testing in accordance with the test plan for the Sludge Treatment Project (STP) corrosion process chemistry follow on testing (Delegard et al. 2007). Although most of the planned hydrothermal testing was canceled in July 2007 (as described in the forward of Delegard et al. 2007), sample consolidation and characterization was continued to identify a set of well-characterized sludge samples that are suited to support evolving STP initiatives. The work described in the letter was performed by the PNNL under the direction of the Sludge Treatment Project, managed by Fluor Hanford.