bluuebunny/crossref_metadata_2025_split huggingface dataset:
Remaining Uncertainties in Predicting Long-Term Performance of Nuclear Waste Glass From Experiments
Authors: Grambow B. , Karlsruhe Kernforschungszentrum 
Published: March 2011

ABSTRACTThe current knowledge on the glass dissolution mechanism and the representation of glass dissolution concepts within overall repository performance assessment models are briefly summarized and uncertainties related to mechanism, radionuclide chemistry and parameters are discussed. Understanding of the major glass dissolution processes has been significantly increased in recent years. Long-term glass stability is related to the long-term maintenance of silica saturated conditions. The behavior of individual radionuclides in the presence of a dissolving glass has not been sufficiently and results do not yet allow meaningful predictions. Conservative long-term predictions of glass matrix dissolution as upper limit for radionuclide release can be made with sufficient confidence, however these estimations generally result in a situation were the barrier function of the glass is masked by the efficiency of the geologic barrier. Realistic long-term predictions may show that the borosilicate waste glass contributes to overall repository safety to a much larger extent than indicated by overconservatism. Today realistic predictions remain highly uncertain and much more research work is necessary. In particular the long-term rate under silica saturated conditions needs to be understood and the behavior of individual radionuclides in the presence of a dissolving glass deserves more systematic investigations.
The Lack of Technical Basis for Requiring a Ten Thousand Year Prediction for Nuclear Waste Management
Authors: Ramspott Lawrence D. 
Published: March 2011

ABSTRACTThere is no technical basis for setting a time limit of 10,000 years on the regulated performance of a nuclear waste repository. First, accurate prediction of releases for such periods is not possible. Second, there is nothing unique about 10,000 years. Third, equally toxic materials, which never transform to non-toxic substances by radioactive decay, have less stringent requirements. And fourth, during a 10,000 year time frame, natural disasters will dwarf the worst possible outcomes of repository placement.Analyses could be required to extend as long as doses above current radiation protection guidelines are possible (perhaps several million years), but these results should be recognized as qualitative information rather than evidence of quantitative compliance with exact numerical limits. Concern for what will happen over long times can be addressed for the next several hundred years by maintaining waste retrievability. At that time, uncertainty about future performance should have been reduced significantly.
Objectives and Limitations of Scientific Studies with Reference to the Swedish RD&D Programme 1992 for Handling and Final Disposal of Nuclear Waste
Authors: Sjöblom Rolf , Dverstorp Björn , Wingefors Stig 
Published: March 2011

ABSTRACTThe Swedish Nuclear Power Inspectorate (SKI) has recently concluded its evaluation of the Swedish programme for the development of a system for the management of nuclear waste. The programme was compiled and issued by the Swedish Nuclear Fuel and Waste Management Company (SKB). In this process of programme formulation and review, considerable attention has been paid to the question of how scientific studies should be directed and performed in order to provide the support needed in the programme.When the objectives and limitations of such scientific studies are to be analysed, it is vitally important that the implications of the long timescales and the lack of feedback of post-closure experience are fully understood and adequately dealt with. It must be realised, that simulations will have to be utilized for the systems development work as well as for the assessments of safety. Such performance simulations have to be based on a thorough understanding of the pertinent phenomena as well as on a comprehensive base of experimental data. They must also be based on a good overall perspective that can only be obtained through full performance assessments.Thus, a sound scientific base is needed. The components of this base must be traceable. Moreover, the links must be clearly identified between the knowledge base and the development of the disposal system as well as the performance assessment of such a system. Performance simulations and performance assessments should be utilized, not only as tools to develop a system and to evalute its safety but also to identify areas where further research is required - or unnecessary.The knowledge base will, however, always be limited, and a lack of understanding must also be recognised and adequately dealt with, e.g. by accounting for uncertainties in the performance simulations, by relying on bounding (conservative) assumptions or by robust repository design.Thus, the success of a programme for the handling and disposal of nuclear waste is highly dependent on the strategy applied for the utilization of the scientific knowledge base. The requirements on such a strategy increase considerably when substantial commitments are to be made.
Radiation Defects and Energy Storage in Natural Polycrystalline Rock Salt. Results of an In-Situ Test in the Permian Rock Salt of the Asse
Authors: Gies H. , García Celma A. , de Haas J. B. M. , Pederson L. , Rothfuchs T. 
Published: March 2011

ABSTRACTRadiation damage development and the corresponding energy storage in pure undeformed single crystals have frequently been studied in laboratory experiments, however little is known of irradiation experiments on natural rock salt (polycrystalline, deformed and impure) under geological conditions. The relevance of these parameters to the defect formation was revealed by a joint United States/Federal Republic of Germany in-situ test in the Asse Mine. Natural rock salt was heated and irradiated using Co-60 sources.Calculations of the amount of halite expected to be decomposed by radiolysis during the experiment were performed using the 1985 version of the Jain-Lidiard model. Qualitative agreement between theory and analyses was found for all the performed analyses. Quantitative and qualitative deviations of the natural samples behaviour from that of single undeformed crystals were observed and attributed to the influence of sulfatic admixtures, ‘polycrystallinity’ and strain on radiation damage development and anneal.Special chemical methods, such as iodometric titration and uv-visible spectroscopy were applied in order to measure the hypochlorite ion, which forms in irradiated salt. Composite samples located closest to the Co-60 source averaged 0,4 micromoles neutral chlorine atoms per gram salt, a factor of two more than from other positions. Uv-vis analyses revealed more than a factor of ten greater neutral chlorine concentrations in coloured halite. Similarly, optical absorption measurements indicated a factor of ten difference in sodium metal colloid concentrations.
Radiation Stability of Ceramic Waste Forms Determined by In Situ Electron Microscopy and He Ion Irradiation
Authors: White T.J. , Mitamura H. , Hojou K. , Furuno S. 
Published: March 2011

ABSTRACTThe radiation stability of polyphase titanate ceramic waste forms was studied using analytical transmission electron microscopy, in combination with in situ irradiation by 30 keV He ions, followed by staged annealing. Two experiments were conducted. In the first, a reconnaissance investigation was made of the stabilities of the synthetic minerals hollandite, zirconolite, and perovskite when subjected to a total dose of 1.8 × 1017 He+ cm-2. It was found that all phases amorphized at approximately the same rate, but perovskite recovered its structure more rapidly and at lower temperatures than the other phases. In particular, annealing for 10 minutes at 1000°C was sufficient for perovskite to completely regain its crystallinity, while zirconolite and hollandite were only partially restored by these conditions. In the second experiment, the response of a thin hollandite crystal to irradiation was examined by selected area electron diffraction. At a dose of 1.5 × 1015 He+ cm-2its incommensurate superstructure was disrupted, but even at a dose of 3 × 1016 He cm-2 the hollandite subcell was largely intact. For this dose, total recovery was achieved by annealing for 1 minute at 1000°C.
Effects of Radiation Exposure on SRL 131 Composition Glass in a Steam Environment
Authors: Wronkiewicz D. J. , Bradley C. R. , Bates J. K. , Wang L. M. 
Published: March 2011

ABSTRACTMonoliths of SRL 131 borosilicate glass were irradiated in a saturated air-steam environment, at temperatures of 150°C, to examine the effects of radiation on nuclear waste glass behavior. Half of the tests used actinide and Tc-99 doped glass and were exposed to an external ionizing gamma source, while the remaining glass samples were doped only with uranium and were reacted without any external radiation exposure. The effects of radiation exposure on glass alteration and secondary phase formation were determined by comparing the reaction rates and mineral paragenesis of the two sets of samples.All glass samples readily reacted with the water that condensed on their surfaces, producing two types of smectite clay within the first three days of testing. Additional crystalline phases precipitated on the altered glass surface with increasing reaction times, including zeolites, smectite, calcium and sodium silicates, phosphates, evaporitic salts, and uranyl silicates. Similar phases were produced on both the nonirradiated and irradiated samples; however, the quantity of precipitates was increased and the rate of paragenetic sequence development was accelerated in the latter. After 56 days of testing, the composite smectite layer developed at an average rate of ~0.16 and 0.63 µm/day for the nonirradiated and irradiated samples, respectively. These comparisons indicate that layer development is accelerated approximately four-fold due to the radiation exposure at high glass surface area/liquid volume (SA/V) conditions. This increase apparently occurs in response to the rapid concentration of radiolytic products, including nitric acid, in the thin films of water contacting the sample monoliths.
Immobilization in Ceramic Waste Forms of the Residues From Treatment of Mixed Wastes
Authors: Oversby V. M. , Van Konynenburg R. A. , Glassley W. E. , Curtis P. G. 
Published: March 2011

ABSTRACTThe Environmental Restoration and Waste Management Applied Technology Program at LLNL is developing a Mixed Waste Management Facility to demonstrate treatment technologies that provide an alternative to incineration. As part of that program, we are developing final waste forms using ceramic processing methods for the immobilization of the treatment process residues. The ceramic phase assemblages are based on using Synroc D as a starting point and varying the phase assemblage to accommodate the differences in chemistry between the treatment process residues and the defense waste for which Synroc D was developed. Two basic formulations are used, one for low ash residues resulting from treatment of organic materials contaminated with RCRA metals, and one for high ash residues generated from the treatment of plastics and paper products. Treatment process residues are mixed with ceramic precursor materials, dried, calcined, formed into pellets at room temperature, and sintered at 1150 to 1200°C to produce the final waste form. This paper discusses the chemical composition of the waste streams and waste forms, the phase assemblages that serve as hosts for inorganic waste elements, and the changes in waste form characteristics as a function of variation in process parameters.
Rietveld Analysis of Ceramic Nuclear Waste Forms
Authors: White T.J. , Mitamura H. 
Published: March 2011

ABSTRACTPowder X-ray diffraction patterns were collected from three titanate waste forms - a calcine powder, a prototype ceramic without waste, and a ceramic containing 10 wt% JW-A simulated waste - and interpreted quantitatively using the Rietveld method. The calcine consisted of fluorite, pyrochlore, rutile, and amorphous material. The prototype waste form contained rutile, hollandite, zirconolite and perovskite. The phase constitution of the JW-A ceramic was freudenbergite, loveringite, hollandite, zirconolite, perovskite and baddeleyite. Procedures for the collection of X-ray data are described, as are assumptions inherent in the Rietveld approach. A selection of refined crystal data are presented.
High-Level Waste Glass Compendium; What it Tells us Concerning the Durability of Borosilicate Waste Glass
Authors: Cunnane J. C. , Allison J. M. 
Published: March 2011

ABSTRACTFacilities for vitrification of high-level nuclear waste in the United States are scheduled for startup in the next few years. It is, therefore, appropriate to examine the current scientific basis for understanding the corrosion of high-level waste borosilicate glass for the range of service conditions to which the glass products from these facilities may be exposed. To this end, a document has been prepared which compiles worldwide information on borosilicate waste glass corrosion. Based on the content of this document, the acceptability of canistered waste glass for geological disposal is addressed.Waste glass corrosion in a geologic repository may be due to groundwater and/or water vapor contact. The important processes that determine the glass corrosion kinetics under these conditions are discussed. Testing data together with understanding of the long-term corrosion kinetics are used to estimate radionuclide release rates. These rates are discussed in terms of regulatory performance standards.
Performance of Cementitious Systems in the Repository
Authors: Atkins M. , Damidot D. , Glasser F.P. 
Published: March 2011

ABSTRACTThe behaviour and performance of cement barriers in the repository have been modelled. Since the models employ thermodynamic calculations, an important task is the development of a validated database. This must include phases and aqueous species appropriate to cement and modified cements, containing tly ash and slag. Closed system mineralogy and chemistry are explored as a function of cure duration and thermal excursions. Work has only just begun on open system behaviour: some aspects of reactions with chloride, sulfate and carbonate are described. Future progress depends on database extensions, validation experiments and the coupling of equilibrium and kinetic aspects of reaction.
Ancient Analogues Concerning Stability and Durability of Cementitious Wasteform
Authors: Jiang W. , Roy D.M. 
Published: March 2011

ABSTRACTThe history of cemenütious materials goes back to ancient times. The Greeks and Romans used calcined limestone and later developed pozzolanic cement by grinding together lime and volcanic ash called “pozzolan” which was first found near Port Pozzuoli, Italy. The ancient Chinese used lime-pozzolanic mixes to build the Great Wall. The ancient Egyptians used calcined impure gypsum to build the Great Pyramid of Cheops. The extraordinary stability and durability of these materials has impressed us, when so much dramatically damaged infrastructure restored by using modern portland cement now requires rebuilding. Stability and durability of cementitious materials have attracted intensive research interest and contractors’ concerns, as does immobilization of radioactive and hazardous industrial waste in cementitious materials. Nuclear waste pollution of the environment and an acceptable solution for waste management and disposal constitute among the most important public concerns. The analogy of ancient cementitious materials to modern Portland cement could give us some clues to study their stability and durability. This present study examines selected results of studies of ancient building materials from France, Italy, China, and Egypt, combined with knowledge obtained from the behavior of modern portland cement to evaluate the potential for stability and durability of such materials in nuclear waste forms.
Accelerated Ageing of Blended OPC Cements
Authors: Quilin K.C. , Duerden S.L. , Majumdar A.J. 
Published: March 2011

ABSTRACTAn accelerated experimental technique using high wateπcement ratios has been developed to study the long term hydration of blended cements that may be used in a repository for the disposal of radioactive waste. This technique has been used to investigate the hydration reactions of Ordinary Portland Cement (OPC) blended with ground granulated blastfurnace slag (ggbs) or pulverised fuel ash (pfa). The effects of high sulphate-bearing and high carbonate-bearing ground waters on the compounds formed on hydration were investigated. Solid/solution compositional data were collected during the course of the hydration process for periods up to 2 years. Thomsonite, thaumasite, afwillite and a tobermorite-like phase were found in addition to the expected cement hydration products. The pH of the aqueous solution in contact with 60 pfa:40 OPC blends hydrated at 90°C fell to below 8. This is lower than the value required to inhibit the corrosion of steel canisters in a repository. The pH of the aqueous solution in contact with OPC and 75 ggbs:25 OPC blends remained above 11, although if the ground waters in contact with the OPC/ggbs blends were periodically replaced the pH eventually fell below 10.
Development of Methodology to Evaluate Microbially Influenced Degradation of Cement-Solidified Low-Level Radioactive Waste Forms
Authors: Rogers Robert D. , Hamilton M.A. , Veeh R.H. , Mcconnell J.W. 
Published: March 2011

ABSTRACTBecause of its apparent structural integrity, cement has been widely used in the United States as a binder to solidify Class B and C low-level radioactive waste (LLW). However, the resulting cement preparations are susceptible to failure due to the actions of stress and environment. An environmentally mediated process that could affect cement stability is the action of naturally occurring microorganisms. The U.S. Nuclear Regulatory Commission (NRC), recognizing this eventuality, stated that the effects of microbial action on waste form integrity must be addressed.This paper provides present results from an ongoing program that addresses the effects of microbially influenced degradation (MID) on cement-solidified LLW. Data are provided on the development of an evaluation method using acid-producing bacteria. Results are from work with one type of these bacteria, the sulfur-oxidizing Thiobacillus. This work involved the use of a system in which laboratory- and vendor-manufactured, simulated waste forms were exposed on an intermittent basis to media containing thiobacilli. Testing demonstrated that MID has the potential to severely compromise the structural integrity of ion-exchange resin and evaporator-bottoms waste that is solidified with cement. In addition, it was found that a significant percentage of calcium and other elements were leached from the treated waste forms. Also, the surface pH of the treated specimens decreased to below 2. These conditions apparently contributed to the physical deterioration of simulated waste forms after 60 days of exposure to the thiobacilli.
Modeling of UO2 Aqueous Dissolution Over a Wide Range of Conditions
Authors: Steward Steven A. , Weed Homer C. 
Published: March 2011

ABSTRACTPreviously it was not possible to predict reliably the rate at which spent fuel would react with groundwater because of conflicting data in the literature. The dissolution of the UO2 spent fuel matrix is a necessary step for aqueous release of radioactive fission products. Statistical experimental design was used to plan a set of UO2 dissolution experiments to examine systematically the effects of temperature (25-75°C), dissolved oxygen (0.002-0.2 atm overpressure), pH (8-10) and carbonate (2-200x10-4 molar) concentrations on UO2 dissolution. The average dissolution rate was 4.3 mg/m2/day. The regression fit of the data indicate an Arrhenius type activation energy of -8750 cal/mol·K and a half-power dependence on dissolved oxygen in the simulated groundwater.
The Effect of Fuel Burnup and Dispersed Water Intrusion on the Criticality of Spent High-Level Nuclear Fuel in a Geologic Repository
Authors: Culbreth William G. , Zielinski Paige R. 
Published: March 2011

ABSTRACTStudies of the spent fuel waste package have been conducted through the use of a Monte-Carlo neutron simulation program to determine the ability of the fuel to sustain a chain reaction. These studies have included fuel burnup and the effect of water mists on criticality. Results were compared with previous studies.In many criticality studies of spent fuel waste packages, fresh fuel with an enrichment as high as 4.5% is used as the conservative (worst) case. The actual spent fuel has a certain amount of “burnup” that decreases the concentration of fissile uranium and increases the amount of radionuclides present. The LWR Radiological Data Base from OCRWM has been used to determine the relative radionuclide ratios and KENO 5.a was used to calculate values of the effective multiplication factor, keff.1Spent fuel is not capable of sustaining a chain reaction unless a suitable moderator, such as water, is present. A completely flooded container has been treated as the worst case for criticality. Results of a previous report that demonstrated that keff actually peaked at a water-to-mixture ratio of 13% were analyzed for validity. In the present study, these results did not occur in the SCP waste package container.
Effect of Fluoride on Crystallization in High Calcium and Magnesium Glasses
Authors: Wang E. , Kuang H. , Matlack K.S. , Buechele A.C. , Fu Sabrina S. 
Published: March 2011

ABSTRACTGlasses containing fixed mutual ratios of Al, B, Ca, Fe, Mg, Na, and Si were melted while varying the fluoride content. The effect of fluoride was to suppress the formation of non-fluoride-containing crystals in the composition range from 0 to 11 wt. % F; above 11 wt. % F, the formation of fluoride containing crystals began to define the liquidus temperature. The effect of fluoride on the liquidus temperature was quantified and used to predict the liquidus temperature of melts made from real radioactive wastes. Although the liquidus temperatures of the surrogate and radioactive glasses agreed well, the types of crystals formed differed due to slight compositional differences introduced by the waste stream.