William C. Buchmiller

Development and Testing of ICV Glasses for Hanford LAW

Preliminary glass compositions for immobilizing Hanford low-activity waste (LAW) by the in-container vitrification (ICV) process were fabricated at crucible- and engineering-scale and tested at Pacific Northwest National Laboratory. This testing showed that glasses with LAW loading of 20 mass% can readily be made and meet all product constraints by a far margin. It was found that the response constraint of the vapor hydration test (VHT) of less than 50 g/(m2•d) alteration rate was the most restrictive constraint placed on LAW glasses. Glasses with over 22 mass% Na2O can be made to meet this constraint along with all other product quality and processability constraints imposed by this process. The results of crucible melts with simulants were scaled-up to engineering scale and also tested with actual (radioactive) LAW. All the results suggest that the baseline glass can be successfully processed by the ICV technology and can meet all the constraints related to product quality.

Laboratory-Scale Melter for Determination of Melting Rate of Waste Glass Feeds

The purpose of this study was to develop the laboratory-scale melter (LSM) as a quick and inexpensive method to determine the processing rate of various waste glass slurry feeds. The LSM uses a 3 or 4 in. diameter-fused quartz crucible with feed and off-gas ports on top. This LSM setup allows cold-cap formation above the molten glass to be directly monitored to obtain a steady-state melting rate of the waste glass feeds. The melting rate data from extensive scaled-melter tests with Hanford Site high-level wastes performed for the Hanford Tank Waste Treatment and Immobilization Plant have been compiled. Preliminary empirical model that expresses the melting rate as a function of bubbling rate and glass yield were developed from the compiled database. The two waste glass feeds with most melter run data were selected for detailed evaluation and model development and for the LSM tests so the melting rates obtained from LSM tests can be compared with those from scaled-melter tests. The present LSM results suggest the LSM setup can be used to determine the glass production rates for the development of new glass compositions or feed makeups that are designed to increase the processing rate of the slurry feeds.

Iron Phosphate Glass as an Alternative Waste-Form for Hanford LAW

Although the current baseline Hanford flowsheet for immobilizing low-activity waste (LAW) assumes borosilicate-based glass, opportunities exist to improve or change this baseline to reduce the current schedule and cost requirements of accomplishing the mission of site cleanup. Development of an alternative glass-forming system can lead to this goal of cost and schedule reduction through enhanced waste loading and higher plant throughput. The purpose of this project is to investigate the iron-phosphate glass system as an alternative for immobilizing Hanford LAW. Previous studies on the iron phosphate glass systems and their potential advantages for immobilizing Hanford LAW have been reviewed and technical uncertainties and data required before implementing this technology have been presented. A team of researchers and engineers from the MO-SCI Corporation, the Pacific Northwest National Laboratory, the Savannah River Technology Center, and the University of Missouri at Rolla has performed a series of tests to address some of the open questions about the potential use of iron phosphate glass for immobilizing Hanford LAW. The results of this team effort are summarized along with recommendations regarding the further laboratory study needs. Additional longer-term testing requirements for implementing the iron phosphate glass-based immobilization process at Hanford are also presented.

The Disruption of Vessel-Spanning Bubbles with Sloped Fins in Flat-Bottom and 2:1 Elliptical-Bottom Vessels

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, and currently, the sludge resides in the KW Basin in large underwater Engineered Containers. The first phase to the Sludge Treatment Project being led by CH2MHILL Plateau Remediation Company (CHPRC) is to retrieve and load the sludge into sludge transport and storage containers (STSCs) and transport the sludge to T Plant for interim storage. The STSCs will be stored inside T Plant cells that are equipped with secondary containment and leak-detection systems. 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. Then it may be released from the container into the cell’s secondary containment system at T Plant. A previous study demonstrated that sloped walls on vessels, both cylindrical coned-shaped vessels and rectangular vessels with rounded ends, 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 investigated 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. The purpose of this study is to quantify the capability of sloped fins to disrupt VSBs and to conduct sufficient tests to estimate the performance of fins in full-scale STSCs. Experiments were conducted with a range of fin shapes to determine what slope and width were sufficient to disrupt VSBs. Additional tests were conducted to demonstrate how the fin performance scales with the sludge layer thickness and the sludge strength, density, and vessel diameter based on the gravity yield parameter, which is a dimensionless ratio of the force necessary to yield the sludge to its weight.( ) Further experiments evaluated the difference between vessels with flat and 2:1 elliptical bottoms and a number of different simulants, including the KW container sludge simulant (complete), which was developed to match actual K-Basin sludge. Testing was conducted in 5-in., 10-in., and 23-in.-diameter vessels to quantify how fin performance is impacted by the size of the test vessel. The most significant results for these scale-up tests are the trend in how behavior changes with vessel size and the results from the 23-in. vessel. The key objective in evaluating fin performance is to determine the conditions that minimize the volume of a VSB when disruption occurs because this reduces the potential for material inside the STSC from being released through vents.

Preparation and Characterization of {sup 238}Pu-Ceramics for Radiation Damage Experiments

As a result of treaty agreements between Russia and the US, portions of their respective plutonium and nuclear weapons stockpiles have been declared excess. In support of the US Department of Energys 1998 decision to pursue immobilization of a portion of the remaining Pu in a titanate-based ceramic, the authors prepared nearly 200 radiation-damage test specimens of five Pu- and {sup 238}Pu-ceramics containing 10 mass% Pu to determine the effects of irradiation from the contained Pu and U on the ceramic. The five Pu-ceramics were (1) phase-pure pyrochlore [ideally, Ca(U, Pu)Ti{sub 2}O{sub 7}], (2) pyrochlore-rich baseline, (3) pyrochlore-rich baseline with impurities, (4) phase-pure zirconolite [ideally Ca(U, Pu)Ti{sub 2}O{sub 7}], and (5) a zirconolite-rich baseline. These ceramics were prepared with either normal weapons-grade Pu, which is predominantly {sup 239}Pu, or {sup 238}Pu. The {sup 238}Pu accelerates the radiation damage relative to the {sup 239}Pu because of its much higher specific activity. The authors were unsuccessful in preparing phase-pure (Pu, U) brannerite, which is the third crystalline phase present in the baseline immobilization form. Since these materials will contain {approximately}10 mass% Pu and about 20 mass% U, radiation damage to the crystalline structure of these materials will occur overtime. As the material becomes damaged from the decay of the Pu and U, it is possible for the material to swell as both the alpha particles and recoiling atoms rupture chemical bonds within the solid. As the material changes density, cracking, perhaps in the form of microcracks, may occur. If cracking occurs in ceramic that has been placed in a repository, the calculated rate of radionuclide release if the can has corroded would increase proportionately to the increase in surface area. To investigate the effects of radiation damage on the five ceramics prepared, the authors are storing the specimens at 20, 125, and 250 C until the {sup 238}Pu specimens become metamict and the damage saturates. They will characterize and test these specimens every 6 months by (1) monitoring the dimensions, (2) monitoring the geometric and pycnometric densities, (3) monitoring the appearance, (4) determining the normalized amount leached during a 3-day, static, 90 C leach test in high purity water, and (5) monitoring the crystal structure with x-ray diffraction crystallography (XRD). In this paper, the authors document the preparation and initial characterization of the materials that were made in this study. The initial XRD characterizations indicate that the phase assemblages appear to be correct with the exception of the {sup 238}Pu-zirconolite baseline material. They made this latter material using too much Pu, so this material contains unreacted PuO{sub 2}. The characterization of the physical properties of these materials found that the densities for all but three materials appear to be > 94% of theoretical, and only a few of the specimens have significant cracking. Those with cracking were the {sup 239}Pu-zirconolite specimens, which were sintered with a heat-up rate of 5 C/min. They sintered the {sup 238}Pu-zirconolite specimens with a heat-up rate of 2.5 C/min and obtained specimens with only minor surface cracking. Elemental releases during the 3-day MCC leach tests show that the normalized elemental releases depend on (1) whether the Pu is {sup 239}Pu or {sup 238}Pu, (2) the material type, and (3) the identity of the constituent. The effect of the Pu isotope in the ceramic is most dramatic for Pu release, with nominally 50 to 100 times more Pu activity released from the {sup 238}Pu specimens. This is unlikely to be an early indicator of radiation damage, because of the short time between specimen preparation and testing. In contrast greater amounts of Mo are released from the {sup 239}Pu specimens. Of the contained constituents, Ca Al, Pu, and U are the species found at relatively higher levels in the leachates.

Preliminary Investigation of Sulfur Loading in Hanford LAW Glass

A preliminary estimate was developed for loading limits for high-sulfur low-activity waste (LAW) feeds that will be vitrified into borosilicate glass at the Hanford Site in the waste-cleanup effort. Previous studies reported in the literature were consulted to provide a basis for the estimate. The examination of previous studies led to questions about sulfur loading in Hanford LAW glass, and scoping tests were performed to help answer these questions. These results of these tests indicated that a formulation approach developed by Vienna and colleagues shows promise for maximizing LAW loading in glass. However, there is a clear need for follow-on work. The potential for significantly lowering the amount of LAW glass produced at Hanford (after the initial phase of processing) because of higher sulfur tolerances may outweigh the cost and effort required to perform the necessary testing.

Hanford Sludge Simulant Selection for Soil Mechanics Property Measurement

The current System Plan for the Hanford Tank Farms uses relaxed buoyant displacement gas release event (BDGRE) controls for deep sludge (i.e., high level waste [HLW]) tanks, which allows the tank farms to use more storage space, i.e., increase the sediment depth, in some of the double-shell tanks (DSTs). The relaxed BDGRE controls are based on preliminary analysis of a gas release model from van Kessel and van Kesteren. Application of the van Kessel and van Kesteren model requires parametric information for the sediment, including the lateral earth pressure at rest and shear modulus. No lateral earth pressure at rest and shear modulus in situ measurements for Hanford sludge are currently available. The two chemical sludge simulants will be used in follow-on work to experimentally measure the van Kessel and van Kesteren model parameters, lateral earth pressure at rest, and shear modulus.

Bulk Vitrification Performance Enhancement: Refractory Lining Protection Against Molten Salt Penetration

Bulk vitrification (BV) is a process that heats a feed material that consists of glass-forming solids and dried low-activity waste (LAW) in a disposable refractory-lined metal box using electrical power supplied through carbon electrodes. The feed is heated to the point that the LAW decomposes and combines with the solids to generate a vitreous waste form. This study supports the BV design and operations by exploring various methods aimed at reducing the quantities of soluble Tc in the castable refractory block portion of the refractory lining, which limits the effectiveness of the final waste form.

The Status of Radiation Damage Experiments

Experiments have been on-going for about two years to determine the effects that radiation damage have on the physical and chemical properties of candidate titanate ceramics for the immobilization of plutonium. We summarize the results of these experiments in this document.

Initial Laboratory-Scale Melter Test Results for Combined Fission Product Waste

This report describes the methods and results used to vitrify a baseline glass, CSLNTM-C-2.5 in support of the AFCI (Advanced Fuel Cycle Initiative) using a Quartz Crucible Scale Melter at the Pacific Northwest National Laboratory. Document number AFCI-WAST-PMO-MI-DV-2009-000184.