bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Near-Field Transport Code Tullgarn and its Use in Performance Assessment
Authors: Sellin Patrik , Kjellbert Nils 
Published: March 2011

ABSTRACTThe near-field radionuclide migration code Tullgarn has been developed for performance assessment purposes. As a part of the PROPER-code package it has been successfully applied in the SKB 91 safety analysis.The features and processes included in the code are:- Radioactive chain decay- Different canister failure mechanisms (copper corrosion from sulphide attack, steel corrosion, internal overpressure and initially defective canisters) - Spent fuel dissolution. The model is based on the assumption that the dissolution rate is proportional to the α-dose rate- Transport calculations are done with a resistance-network model. Tullgarn calculates the stationary release of radionuclides from a defect in the canister through the buffer and out into a fracture in the rock or up to the damaged zone under the deposition tunnel.Tullgarn can be used as a stand-alone model for near-field release calculations or as a submodel in an integrated assessment. In the SKB 91 analysis, Tullgarn gave the source term to the far-field model.
The Importance of Criticality in the Safety Analysis of the Spent-Fuel Waste Container
Authors: Culbreth William G. , Zielinski Paige 
Published: March 2011

ABSTRACTThe storage of high-level spent reactor fuel in a proposed national geologic repository will require the construction of containers to be placed in boreholes drilled into the host rock. Federal regulations require that the fuel be maintained subcritical under normal or accident conditions. This is determined through the calculation of a neutron multiplication factor, keff, that must remain below 0.95. Criticality will play an important role in the container design, the internal configuration of the fuel, and the selection of neutron poisons. An analysis of keff should be a normal step in the conceptualization of new waste container designs. Unlike thermal effects in a proposed repository, criticality will remain a problem long after the 10,000 year lifetime of the facility.
Radionuclide Sorption Modeling Using the Minteqa2 Speciation Code
Authors: Turner David R. , Griffin T. , Dietrich T.B. 
Published: March 2011

ABSTRACTThe MINTEQA2 database has been updated and expanded to include radionuclide data from the most recent release of the EQ3/6 database. Comparison of U(VI)-speciation predicted using the old and new MINTEQA2 databases indicates several significant differences, including the introduction of neutral and anionic species at neutral to alkaline pH. In contrast, comparison of results calculated by EQ3 and MINTEQA2, both using Nuclear Energy Agency (NEA) uranium data, reveals only small differences that are likely due to differences in calculated activity coefficients.With the new database, MINTEQA2 was used to model U(VI)-goethite sorption data from the literature with the Triple-Layer Model (TLM). Values were independently fixed forall but one of the model parameters. The parameter optimization code FITEQL was then used to determine binding constants for mononuclear uranium complexes (UO2(OH)n2−n). The surface complex MOH2-UO2(OH)4− produced a very good fit of the sorption data, which was not significantly improved by the use of two or more surface complexes.
Measurements of Metal Adsorption in Oxide-Clay Mixtures: “Competitive-Additivity” Among Mixture Components
Authors: Tripathi V. S. , Siegel M.D. , Kooner Z. S. 
Published: March 2011

ABSTRACTAn important question concerning the transport of radionuclides from nuclear waste repositories is whether the adsorption of metals by rocks and soils can be predicted from the properties of the constituent minerals. Attempts by previous researchers to use sorption models based on linear adsorption or weighted "sorptive additivity" have met with limited success. In this study, a “competitive-additivity” model based on surface complexation theory was used to model the pH-dependent adsorption of lead by goethite/Ca-montmorillonite mixtures using complexation constants obtained from single sorbent systems. Measurements of lead adsorption by goethite, Ca-montmorillonite, and goethite-Ca-montmorillonite mixtures (and similar studies of copper and zinc adsorption) demonstrate that the two adsorbents compete for adsorption of metals over wide ranges of pH and concentrations of adsorbents and metals. The adsorption behaviors of the mixtures are determined by the relative concentrations of the adsorbents and their respective affinities for the adsorbate metal. Particle-particle interactions such as heterocoagulation of the oxide and clay do not appear to be significant for the majority of the adsorption sites in this system.
Radionuclide Migration Studies on Tonalite
Authors: HÖlttÄ P. , Siitari-KAUPPI M. , Hakanen M. , HautojÄrvi A. 
Published: March 2011

ABSTRACTMigration of water, chloride, sodium, and calcium in tonalite was studied, using dynamic column and static through-diffusion methods. Autoradiography of rocks impregnated with 14C-methylmethacrylate was introduced in order to determine the spatial porosity distribution, as well as to identify and visualize the migration pathways of non-sorbing radionuclides in tonalite matrix at the mm-cm scale. The migration routes of sorbing radionuclides and the sorptive minerals in tonalite were determined by autoradiographic methods, using 45Ca as a tracer. Transport of radionuclides was interpreted, using models for hydrodynamic dispersion with diffusion into the rock matrix. In tonalite, porous minerals were distributed homogeneously in matrix and, therefore, retardation capacity of the rock matrix was found to be high.
Transport Modeling in a Finite Fractured Rock Domain
Authors: Novak Craig F. 
Published: March 2011

ABSTRACTThe Waste Isolation Pilot Plant (WIPP) is a U.S. Department of Energy facility intended to demonstrate the safe disposal of transuranic nuclear waste. The WIPP is located in the thick halite beds of the Salado Formation in the Delaware Basin of southeastern New Mexico. Overlying the repository is the Culebra Dolomite Member of the Rustler Formation, a dolomitic unit containing accessory minerals such as calcite, gypsum, and clays. The Culebra is the predominant continuous water-bearing unit in the area. Part of the scientific demonstration of the safety of WIPP involves understanding and estimating what might happen should the WIPP inadvertently be intruded by exploration boreholes long after the WIPP has been decommissioned. Should such a breach occur, it is possible that dissolved transuranic waste could be transported up a borehole and into the Culebra, through which it could eventually reach the accessible environment. The rates and mechanisms for actinide transport in Culebra Dolomite are being investigated as a component of repository performance assessment.The two primary mechanisms for delaying solute release from a double porosity system are called physical and chemical retardation, both of which retard solute migration relative to bulk water flow. Physical retardation occurs when solutes diffuse out of the advective transport regions (fractures) and into diffusive transport regions (matrix). Results of hydrologic field tests suggest that the Culebra behaves as a double porosity medium. Chemical retardation occurs when chemical interactions between dissolved species and mineral surfaces remove solutes from the aqueous phase. Some fracture surfaces in the Culebra are clay-lined, and, because clays can have a large potential for chemical interactions with solutes (e.g., ion exchange or adsorption), it is possible that fracture linings alone may cause significant retardation of any actinides that could reach the Culebra. This report examines these two features in Culebra transport: delimiting the parameter space where a fully two-dimensional model is needed, and examining the importance of clay linings during transport.Numerical simulations with the FMT (Fracture Matrix Transport) finite difference model in a finite, idealized double porosity system were performed to: 1) delineate parameter values for which a set of two coupled one-dimensional equations is insufficient to describe behavior and a fully two-dimensional representation is needed, 2) compare chemical retardation by ion exchange for fractures with and without a clay lining, and 3) compare physical and chemical retardation by ion exchange as a function of fracture velocity. The simulations differ from others in that the matrix is finite, and thus can become saturated with tracers introduced into the domain. The modeling suggests that the chemical retardation caused by clay linings may not be important in a double porosity system. Over a wide range, a single parameter group essentially determines the complexity of the model.
Direct Determination of Transport Parameters in Repository Materials
Authors: Conca J. L. , Apted M.J. , Arthur R.C. 
Published: March 2011

ABSTRACTA new flow technology has been developed that significantly decreases the time required to obtain transport data on saturated and unsaturated porous/fractured media. This technique is based on open-flow centrifugation and was developed to measure steady-state transport properties in most geologic materials within a matter of hours. Centripetal acceleration does not induce artificial effects in samples i.e., fracturing, collapse of interlayer structures, structural dewatering, compaction, chemical changes, etc., that occur with high-pressure methods. Using this technique, hydraulic conductivities (K) and diffusion coefficients (D) for compacted bentonite and four host rocks have been measured and re-interpreted. Based on these new data, K for compacted bentonite is less than 10−14 m/s, a factor of 1000 lower than previous pressure-gradient measurements, providing further assurance that radionuclide transport through bentonite backfill will be diffusion limited. Measured K for mudstone (1.8 × 10−12 m/s) indicates diffusion-limited far-field transport, while advective transport should occur for granite, basalt, and tuff, with expected matrix diffusion coefficients (correlated to measured D values) of 8.3 × 10−13 and 2.5 × 10−12 m2/s for fractured granite and basalt, respectively.
BNFL Lysimeter Proaramme to Investigate the Leachina of Radlonuclides from Low-Level Radioactive Waste
Authors: Clayton K. , Clegg R. , Holmes R.G.G. , Newton G.W.A. 
Published: March 2011

ABSTRACTBritish Nuclear Fuels ple has initiated an experimental programme to measure the leaching behaviour of radionuclides from various low level radioactive waste (LLW) mareials using Lysimeters. The programme commenced in 1986 and to date 10 lysimeters have been commissioned. These have concentrated on simulating shallow trench conditions but a further programme is now planned to study concrete vault environments. The aim of the study is to provide information on leaching processes as part of the ongoing Drigg Near Field Programme, and also to yield input data for radiological assessment purposes. Towards this end, data have been gained from the lysimeters on basic chemistry, gas generation and radionuclide Release Coefficients. This paper concentrates on one of the lysimeters which has recently been decommissioned and for which interim analytical data are available. Some general comments are given on BNFL's experience using lysimeters and their applicability as a rapid and effective technique for studying near field degradation processes.
Pilot and Field-Scale Uranium Lysimeter Studies at the Oak Ridge Y-12 Plant
Authors: Gates Dianne D. , Francis Chet W. , Laster Lisa M. , Kimmiti Rod 
Published: March 2011

ABSTRACTField- and pilot-scale uranium leaching facilities (lysimeters) have been constructed at the Oak Ridge Y-12 Plant to investigate the rate of uranium (U) leaching and the residual U concentration that can be expected when low level radioactive waste (LLW) is buried in landfills. Current plans are to load three large standard column lysimeters with compacted production trash (blotter, waste wipes, paper etc.) and apply groundwater to the surface of the lysimeters.Several issues had to be addressed before the field lysimeters could be loaded with the LLW. Predominate among these concerns was how to adequately characterize the waste placed in the lysimeters (∼ 10 yd3 waste per lysimeter) and how to effectively collect in situ leachate samples from compacted wasteforms in the absence of soil. Pilot scale studies revealed that monitoring individual bags (30 gal) of LLW with a waste curie monitor would be sufficient to determine the initial U loading and that conventional suction candles would perform adequately within the compacted waste for extended time periods if they are installed properly. In the pilot leaching studies, the highest U concentration (∼ 0.2 mg/l) in the leachate was observed during the first month of leaching, before active biological decomposition processes became dominant making the lysimeter anoxic. After the initial oxic flushing, U concentrations in the leachate became very low (mean = 0.021 mg/l).
Redox Systematics in Model Glass Compositions from West Valley
Authors: Schreiber Henry D. , SCHREIBER Charlotte W. , Ward Cary C. 
Published: March 2011

ABSTRACTAt a processing temperature of 1150°C for model West Valley glass compositions, the prescribed range of oxygen fugacities needed to achieve an [Fe2+]/[Fe3+] of 0.1 to 0.5 is 10−4 to 10−7 atm. Establishment of the Fe2+-Fe0 equilibrium, resulting in metal precipitation from the melt, occurs at oxygen fugacities lower than 10−11 atm at this temperature. The target processing range as defined by the iron redox ratio is equally valid at both lower and higher temperatures (±100°C). Elevations of the concentrations of redox-active components to I wt% Cr2O3, 1 wt% NiO, 1 wt% CuO, 1 wt% CeO2, and 4 wt% Mn2O3 in the waste glass will not affect the redox limits as established by the iron redox ratio of 0.1 to 0.5; these limits provide sufficiently large margins of safety to assure no stabilization of reduced or oxidized forms of these elements.
Conceptual Structure of Performance Assessments Conducted for the Waste Isolation Pilot Plant
Authors: Helton J. C. , Marietta M. G. , Rechard R. P. 
Published: March 2011

ABSTRACTThe Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico is being developed by the U.S. Department of Energy as a disposal facility for trans-uranic waste. In support of this project, Sandia National Laboratories is conducting an ongoing performance assessment (PA) for the WIPP. The ordered triple representation for risk proposed by Kaplan and Garrick is used to provide a clear conceptual structure for this PA. This presentation describes how the preceding representation provides a basis in the WIPP PA for (1) the definition of scenarios and the calculation of scenario probabilities and consequences, (2) the separation of subjective and stochastic uncertainties, (3) the construction of the complementary cumulative distribution functions required in comparisons with the U.S. Environmental Protection Agency's standard for the geologic disposal of radioactive waste (i.e., 40 CFR Part 191, Subpart B), and (4) the performance of uncertainty and sensitivity studies. Results obtained in a preliminary PA for the WIPP completed in December of 1991 are used for illustration.
Uncertainty and Sensitivity Analyses of Groundwater Travel Time in a Two-Dimensional Variably-Saturated Fractured Geologic Medium
Authors: Gureghian A. B. , Sagar B. 
Published: March 2011

ABSTRACTThis paper presents a method for sensitivity and uncertainty analyses of a hypothetical nuclear waste repository located in a layered and fractured unconfined aquifer. Groundwater travel time (GWTlT) has been selected as the performance measure. The repository is located in the unsaturated zone, and the source of aquifer recharge is due solely to steady infiltration impinging uniformly over the surface area that is to be modeled. The equivalent porous media concept is adopted to model the fractured zone in the flow field. The evaluation of pathlines and travel time of water particles in the flow domain is performed based on a Lagrangian concept. The Bubnov-Galerkin finite-element method is employed to solve the primary flow problem (non-linear), the equation of motion, and the adjoint sensitivity equations. The matrix equations are solved with a Gaussian elimination technique using sparse matrix solvers. The sensitivity measure corresponds to the first derivative of the performance measure (GWTT) with respect to the parameters of the system. The uncertainty in the computed GWTT is quantified by using the first-order second-moment (FOSM) approach, a probabilistic method that relies on the mean and variance of the system parameters and the sensitivity of the performance measure with respect to these parameters. A test case corresponding to a layered and fractured, unconfined aquifer is then presented to illustrate the various features of the method.
A Demonstration of Dose Modeling at Yucca Mountain
Authors: Miley Terri B. , Eslinger Paul W. 
Published: March 2011

ABSTRACTThe U. S. Environmental Protection Agency is currently revising the regulatory guidance for high-level nuclear waste disposal. In its draft form, the guidelines contain dose limits. Since this is likely to be the case in the final regulations, it is essential that the U.S. Department of Energy be prepared to calculate site-specific doses for any potential repository location. This year, Pacific Northwest Laboratory (PNL) has made a first attempt to estimate doses for the potential geologic repository at Yucca Mountain, Nevada as part of a preliminary total-systems performance assessment.A set of transport scenarios was defined to assess the cumulative release of radionuclides over 10,000 years under undisturbed and disturbed conditions at Yucca Mountain. Dose estimates were provided for several of the transport scenarios modeled. The exposure scenarios used to estimate dose in this total-systems exercise should not, however, be considered a definitive set of scenarios for determining the risk of the potential repository.Exposure scenarios were defined for waterborne and surface contamination that result from both undisturbed and disturbed performance of the potential repository. The exposure scenarios used for this analysis were designed for the Hanford Site in Washington. The undisturbed performance scenarios for which exposures were modeled are gas-phase release of 14C to the surface and natural breakdown of the waste containers with waterborne release. The disturbed performance scenario for which doses were estimated is exploratory drilling. Both surface and waterborne contamination were considered for the drilling intrusion scenario.
Hot Spot Heating from Impurities and Vacancies in a Crystalline Solid Under Rapid Compression
Authors: Tsai D. H. 
Published: March 2011

AbstractThe role of impurity atoms and vacancy defects in the heating of hot spots in a 2D, fcc, monatomic lattice, subjected to rapid, 1D compression, has been studied by means of molecular dynamics. The interaction potential of the impurity atoms, their mass, and size were allowed to differ from those of the atoms in the host lattice. Several configurations of impurity and vacancy clusters were examined. The mechanisms of heating observed here were similar to those found earlier in a bcc lattice with vacancy defects but without impurities.
Recent Advances in the Thermal Decomposition of Cyclic Nitramines
Authors: Behrens Richard , Bulusu Suryanarayana 
Published: March 2011

AbstractThe effects of physical properties and molecular conformation on the thermal decomposition kinetics of several cyclic nitramines are examined and compared to the decomposition of RDX. The compounds used in the study are: octahydro-1,3,5,7-tetranitro- 1,3,5,7-tetrazocine (HMX), hexahydro-l-nitroso-3,5-dinitro-s-triazine (ONDNTA), 1,3,5- trinitro- 1,3,5-triazacycloheptane (TNCHP), and 2-oxo-1,3,5-trinitro-1,3,5-triazacyclohexane (K6). The decomposition pathways of HMX in the liquid phase are similar to the four parallel decomposition pathways that control the decomposition of RDX in the liquid phase. The products formed during the thermal decomposition of ONDNTA arise from multiple reaction pathways. The identities and temporal behaviors of the ONDNTA decomposition products are discussed. TNCHP is thermally stable in the liquid phase. The decomposition products from TNCHP are formed via multiple reaction pathways. One decomposition pathway for TNCHP is through its mononitroso intermediate. TNCHP does not form a stable product that is analogous to oxy-s-triazine (OST) formed in RDX or the smaller ring fragments formed in the liquid-phase decomposition of HMX. K6 is less thermally stable and the decomposition mechanism is much simpler than that of RDX, HMX and TNCHP. The thermal decomposition of K6 occurs between 150 and 180 °C. The products formed during the decomposition of K6 are mainly CH2O and N2O with minor amounts or HCN, CO, NO, and NO2.
Molecular Dynamics Simulations of Shocks and Detonations in a Model 3D Energetic Crystal with Defects
Authors: Phillips Lee 
Published: March 2011

AbstractWe examine shock induced detonation in a three-dimensional model of a nitromethane crystal. The crystal may contain a defect in the form of a small void. Three regimes are identified: the shock can be weak enough that no chemical bonds are broken; the shock can be so strong that a detonation front is established in the perfect crystal; or the shock can be of intermediate strength, where chemical activity requires the existence of the defect. In all regimes, the defect increases the reaction rate and causes a hot spot to appear.
Overview: High Speed Dynamics and Modelling as It Applies to Energetic Solids
Authors: Covino J. , Finnegan S. A. , Heimdahl O. E. R , Lindfors A. J. , Pringle J. K. 
Published: March 2011

AbstractThis paper discusses experimental techniques and modelling tools used to characterize energetic solids subjected to dynamic deformation and shock. Critical experiments have been designed to study shock response and impact sensitivity of energetic materials. For example, a simplified two dimensional experiment has been developed to study the critical phenomena involved in delayed detonation reactions (XDT). In addition, wedge tests are used to obtain equation-of-state data. Coupled with hydrocodes, these experiments give us an in-depth understanding of the response of energetic materials subjected to shock loading. A coupled methodology using both experimental and modelling tools is presented. Consisting of three parts, it addresses all possible responses to fragment impact. The three parts are: (1) Fragment impact modelling (hydrocodes and empirically based codes); (2) Experiments to obtain accurate data for predicting prompt detonation; and (3) Tests with planar rocket motor models to explore mechanisms related to bum reaction thresholds and degree of violence. This methodology is currently being used in weapon design and munitions hazard assessments.