GLASS FABRICATION AND PRODUCT CONSISTENCY TESTING OF LANTHANIDE BOROSILICATE GLASS FOR PLUTONIUM DISPOSITION

The Department of Energy Office of Environmental Management (DOE/EM) plans to conduct the Plutonium Disposition Project at the Savannah River Site (SRS) in Aiken, SC, to disposition excess weapons-usable plutonium. A plutonium glass waste form is a leading candidate for immobilization of the plutonium for subsequent disposition in a geologic repository. The objectives of this present task were to fabricate plutonium-loaded lanthanide borosilicate (LaBS) Frit B glass and perform testing to provide near-term data that will increase confidence that LaBS glass product is suitable for disposal in the proposed Federal Repository. Specifically, testing was conducted in an effort to provide data to Yucca Mountain Project (YMP) personnel for use in performance assessment calculations. Plutonium containing LaBS glass with the Frit B composition with a 9.5 wt% PuO{sub 2} loading was prepared for testing. Glass was prepared to support glass durability testing via the ASTM Product Consistency Testing (PCT) at Savannah River National Laboratory (SRNL). The glass was characterized with X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) prior to performance testing. This characterization revealed some crystalline PuO{sub 2} inclusions with disk-like morphology present in the as fabricated, quench-cooled glass. A series of PCTs was conducted at SRNL with varying exposed surface area and test durations. Filtered leachates from these tests were analyzed to determine the dissolved concentrations of key elements. The leachate solutions were also ultrafiltered to quantify colloid formation. Leached solids from select PCTs were examined in an attempt to evaluate the Pu and neutron absorber release behavior from the glass and to investigate formation of alteration phases on the glass surface. A series of PCTs was conducted at 90 C in ASTM Type 1 water to compare the Pu LaBS Frit B glass durability to current requirements for High Level Waste (HLW) glass in a geologic repository. The PCT (7-day static test with powdered glass) results on the Pu-containing LaBS Frit B glass at SA/V of {approx} 2000 m{sup -1} showed that the glass was very durable with an average normalized elemental release value for boron of 0.013 g/m{sup 2}. This boron release value is {approx} 640X lower than normalized boron release from current Environmental Assessment (EA) glass used for repository acceptance. The PCT-B (7, 14, 28 and 56-day, static test with powdered glass) normalized elemental releases were similar to the normalized elemental release values from PCT-A testing, indicating that the LaBS Frit B glass is very durable as measured by the PCT. Normalized plutonium releases were essentially the same within the analytical uncertainty of the ICP-MS methods used to quantify plutonium in the 0.45 {micro}m-filtered leachates and ultra-filtered leachates, indicating that colloidal plutonium species do not form under the PCT conditions used in this study

INTERNATIONAL STUDIES OF ENHANCED WASTE LOADING AND IMPROVED MELT RATE FOR HIGH ALUMINA CONCENTRATION NUCLEAR WASTE GLASSES

The goal of this study was to determine the impacts of glass compositions with high aluminum concentrations on melter performance, crystallization and chemical durability for Savannah River Site (SRS) and Hanford waste streams. Glass compositions for Hanford targeted both high aluminum concentrations in waste sludge and a high waste loading in the glass. Compositions for SRS targeted Sludge Batch 5, the next sludge batch to be processed in the Defense Waste Processing Facility (DWPF), which also has a relatively high aluminum concentration. Three frits were selected for combination with the SRS waste to evaluate their impact on melt rate. The glasses were melted in two small-scale test melters at the V. G. Khlopin Radium Institute. The results showed varying degrees of spinel formation in each of the glasses. Some improvements in melt rate were made by tailoring the frit composition for the SRS feeds. All of the Hanford and SRS compositions had acceptable chemical durability

Netec Cold Crucible Induction Melter Demonstration for Srnl With Simulated Sludge Batch 4 Dwpf Waste

Cold Crucible Induction Melter (CCIM) Technology is being considered as a possible next generation melter for the Defense Waste Processing Facility (DWPF). Initial and baseline demonstrations that vitrified a Sludge Batch 4 (SB4) simulant at a waste loading of 50 weight percent (versus about 38 weight percent in the current DWPF Melter) were performed by the Nuclear Engineering and Technology Institute (NETEC) in South Korea via a subcontract from the Washington Savannah River Company (WSRC). This higher waste loading was achieved by using a CCIM which can run at higher glass processing temperatures (1250 C and higher) than the current DWPF Melter (1150 C). Higher waste loadings would result in less canisters being filled and faster waste throughput at the DWPF. The main demonstration objectives were to determine the maximum melt rate/waste throughput for the NETEC CCIM with a Sludge Batch 4 simulant as well as determine the viability of this technology for use in the DWPF

DEFINING A GLASS COMPOSITION ENVELOPE FOR AN IMPURITY VARIABILITY STUDY TO SUPPORT PLUTONIUM DISPOSITION

This study focuses on the development of a composition envelope that describes the solubility of various impurities in the lanthanide borosilicate (LaBS) glass. A series of glass compositions was selected, fabricated and characterized in order to define this envelope. The selection of glass compositions, which is the focus of this report, was based on the projected types and concentrations of impurities expected in the plutonium feed stream. A limited amount of impurity data for the various plutonium sources is available and projections were made through analysis of the available information. These projections were used to define the glass compositions to be fabricated and tested. The results of this glass selection process provided an array of glass compositions to be fabricated and characterized in the laboratory in order to evaluate the solubility of various impurity elements and their effects on crystallization and durability as measured by the Product Consistency Test (PCT). The majority of the glasses will be formulated with hafnium as a surrogate for plutonium to simplify laboratory experiments. Plutonium glass testing will also be implemented for select compositions to validate the results of the surrogate testing. The results of this variability testing will be discussed in a separate report that will provide data to validate the acceptability of the compositional envelope defined here and/or provide additional compositional constraints for the plutonium feed materials

THE U.S. DEPARTMENT OF ENERGY-OFFICE OF ENVIRONMENTAL MANAGEMENT'S INTERNATIONAL PROGRAM

The U.S. Department of Energy's (DOE) Office of Environmental Management (EM) has collaborated with the various international institutes (e.g. Russian Federal Atomic Energy Agency--Rosatom and Ukraine government's Chornobyl Center-International Radioecology Laboratory (CC-IRL)) for many years on radioactive waste management challenges of mutual concern. Currently, EM is cooperating with Rosatom and the Ukraine's CC-IRL to explore issues related to high-level waste and to investigate experience and technologies that could support EM site cleanup needs. EM is currently implementing five collaborative projects with other international institutes on nuclear waste issues: (1) Application of the Cold Crucible Induction Heated Melter to DOE Wastes; SIA Radon, Moscow. (2) Design Improvements to the Cold Crucible Induction Heated Melter; Electrotechnical University, St. Petersburg. (3) Improve Retention of Radionuclides in Cement Type Waste Forms; Khlopin Radium Institute, St. Petersburg. (4) Improved Solubility and Retention of Troublesome Components in SRS and Hanford HLW Glasses; Khlopin Radium Institute, St. Petersburg. (5) Long-term Impacts from Radiation/Contamination within the Chornobyl Exclusion Zone, Chornobyl Center, International Radioecology Laboratory, Ukraine The purpose of this paper is to provide an overview of EM's objectives for participating in cooperative activities with various international institutes. Additionally, this paper presents programmatic and technical information on these activities, and outlines specific technical collaborations currently underway and planned to support DOE's cleanup and closure mission

GLASS FORMULATION DEVELOPMENT TO SUPPORT MELTER TESTING TO DEMONSTRATE ENHANCED HIGH LEVEL WASTE THROUGHPUT

The U.S. Department of Energy (DOE) is currently processing high-level waste (HLW) through a Joule-heated melter (JHM) at the Savannah River Site (SRS) and plans to vitrify HLW and Low activity waste (LAW) at the Hanford Site. Over the past few years at the DWPF, work has concentrated on increasing waste throughput. These efforts are continuing with an emphasis on high alumina content feeds. High alumina feeds have presented specific challenges for the JHM technology regarding the ability to increase waste loading yet still maintain product quality and adequate throughput. Alternatively, vitrification technology innovations are also being investigated as a means to increase waste throughput. The Cold Crucible Induction Melter (CCIM) technology affords the opportunity for higher vitrification process temperatures as compared to the current reference JHM technology. Higher process temperatures may allow for higher waste loading and higher melt rate. Glass formulation testing to support melter demonstration testing was recently completed. This testing was specifically aimed at high alumina concentration wastes. Glass composition property models were utilized as a guide for formulation development. Both CCIM and JHM testing will be conducted so glass formulation testing was targeted at both technologies with a goal to significantly increase waste loading without compromising product quality

VARIABILITY STUDY TO DETERMINE THE SOLUBILITY OF IMPURITIES IN PLUTONIUM-BEARING, LANTHANIDE BOROSILICATE GLASS

This study focuses on the development of a compositional envelope that describes the retention of various impurities in lanthanide borosilicate (LaBS) glass for vitrification and immobilization of excess, defense-related plutonium. A limited amount of impurity data for the various plutonium sources is available and projections were made through analysis of the available information. These projections were used to define types and concentrations of impurities in the LaBS glass compositions to be fabricated and tested. Sixty surrogate glass compositions were developed through a statistically designed approach to cover the anticipated ranges of concentrations for several impurity species expected in the plutonium feeds. An additional four glass compositions containing actual plutonium oxide were selected based on their targeted concentrations of metals and anions. The glasses were fabricated and characterized in the laboratory and shielded cells facility to determine the degree of retention of the impurity components, the impact of the impurities on the durability of each glass, and the degree of crystallization that occurred, both upon quenching and slow cooling. Overall, the LaBS glass system appears to be very tolerant of most of the impurity types and concentrations projected in the plutonium waste stream. For the surrogate glasses, the measured CuO, Ga{sub 2}O{sub 3}, Na{sub 2}O, NiO, and Ta{sub 2}O{sub 5} concentrations fell very close to their target values across the ranges of concentrations targeted in this study for each of these components. The measured CaO and PbO concentrations were consistently higher than the targeted values. The measured Cr{sub 2}O{sub 3} and Fe{sub 2}O{sub 3} concentrations were very close to the targets except for the one highest targeted value for each of these components. A solubility limit may have been approached in this glass system for K{sub 2}O and MgO. The measured Cl{sup -}, F{sup -}, SeO{sub 2} and SO{sub 4}{sup 2-} concentrations were well below their target values for all of the study glasses. This is likely due to volatilization of these species during melting of the glass batch. Note that the degree of volatilization that occurred in this crucible-scale study may differ from the full-scale melter. The measured HfO{sub 2} concentrations were below their target values for all of the surrogate glasses. It is likely that for HfO{sub 2}, the solubility limit in the glass was exceeded and some of the HfO{sub 2} batch material remained in the bottom of the crucibles after pouring the glasses. X-ray diffraction and scanning electron microscopy (SEM) results indicated that some crystalline HfO2 remained in some of the surrogate glasses with the lowest concentration of impurities. No other crystalline phases were identified. The Product Consistency Test (PCT) results showed that all 60 of the surrogate glass compositions tested were very durable, regardless of thermal history, with the highest normalized release for boron being 0.041 g/L. The pH of the leachate solutions was generally lower than that of conventional waste glasses due to the lack of alkali in the LaBS glass, which likely impacted the PCT results. The normalized release rates for the elements measured were generally too small to attempt to correlate the results with the compositions of the test glasses. The Toxicity Characteristic Leaching Procedure results showed that no hazardous metals were leached from the surrogate glasses in any measurable concentration. A plutonium-containing crystalline phase with a cross-shaped morphology was identified via SEM in the glasses fabricated with plutonium oxide. This phase was identified in a previous study of plutonium-bearing LaBS glasses and may provide an opportunity to intentionally crystallize some of the plutonium oxide into a highly insoluble form with an intrinsic neutron absorber. Additional work is necessary to better characterize the influence that this phase has on durability of the glass. The PCT results for the plutonium-containing LaBS glasses with impurities were similar to previous tests conducted on PuO{sub 2}-containing glasses without impurities added. The highest normalized release for boron was 0.02 g/L, which bounded the highest normalized release for plutonium of 0.01 g/L

White Shark Genome Reveals Ancient Elasmobranch Adaptations Associated with Wound Healing and the Maintenance of Genome Stability

The white shark (Carcharodon carcharias; Chondrichthyes, Elasmobranchii) is one of the most publicly recognized marine animals. Here we report the genome sequence of the white shark and comparative evolutionary genomic analyses to the chondrichthyans, whale shark (Elasmobranchii) and elephant shark (Holocephali), as well as various vertebrates. The 4.63-Gbp white shark genome contains 24,520 predicted genes, and has a repeat content of 58.5%. We provide evidence for a history of positive selection and gene-content enrichments regarding important genome stability-related genes and functional categories, particularly so for the two elasmobranchs. We hypothesize that the molecular adaptive emphasis on genome stability in white and whale sharks may reflect the combined selective pressure of large genome sizes, high repeat content, high long-interspersed element retrotransposon representation, large body size, and long lifespans, represented across these two species. Molecular adaptation for wound healing was also evident, with positive selection in key genes involved in the wound-healing process, as well as Gene Ontology enrichments in fundamental wound-healing pathways. Sharks, particularly apex predators such as the white shark, are believed to have an acute sense of smell. However, we found very few olfactory receptor genes, very few trace amine-associated receptors, and extremely low numbers of G protein-coupled receptors. We did however, identify 13 copies of vomeronasal type 2 (V2R) genes in white shark and 10 in whale shark; this, combined with the over 30 V2Rs reported previously for elephant shark, suggests this gene family may underlie the keen odorant reception of chondrichthyans

The Development of a Content Analysis Model for Assessing Students’ Cognitive Learning in Asynchronous Online Discussions

The purpose of this study was to develop and validate a content analysis model for assessing students\u27 cognitive learning in asynchronous online discussions. It adopted a fully mixed methods design, in which qualitative and quantitative methods were employed sequentially for data analysis and interpretation. Specifically, the design was a sequential exploratory (QUAL→ quan) design with priority given to qualitative data and methods. Qualitative data were 800 online postings collected in two online courses. Quantitative data were 803 online postings from the same two courses but from different discussion topics and different weeks. During the qualitative process, a grounded theory approach was adopted to construct a content analysis model based on qualitative data. During the quantitative process, chi-square tests and confirmative factor analysis (CFA) which used online postings as cases or observations and was the first of its kind were performed to test if the new model fit the quantitative data