Diffusion of Plutonium in Compacted, Brine-Saturated Bentonite

1984 ◽  
Vol 44 ◽  
Author(s):  
E. J. Nowak
Keyword(s):  
Radioactive Waste ◽  
Packing Density ◽  
Solution Chemistry ◽  
Lithostatic Pressure ◽  
Release Rates ◽  
Rock Types ◽  
Diffusion Studies ◽  
Engineered Barriers ◽  
Radionuclide Release ◽  
Wyoming Bentonite

AbstractDiffusivities were measured for plutonium in brine-saturated compacted Wyoming bentonite. Complexities of the solution chemistry and retardation of transuranics necessitate diffusion studies under conditions that are specific for repository host rock types in this case salt. Diffusivity values in the range of 10−15 to 10−14 m2/s were obtained for bentonite at a packing density of 1800 kg/m3. That density was obtained by compaction at 15 i0Pa, a typical lithostatic pressure in a repository in salt at 650 m depth. Even a 0.05 m (2 inch) thick bentonite-containing engineered barrier could decrease radionuclide release rates by approximately 4 orders-of-magnitude if the diffusivity for that radionuclide were in the observed range of 10−15 to 10−14 m2/s. These results confirm the effectiveness of uncompacted bentonite-containing materials as engineered barriers for radioactive waste isolation.

Fast/Instant Radionuclide Release: Effects inherent to the experiment

2014 ◽  
Vol 1665 ◽  
pp. 233-243
Author(s):  
B. Kienzler ◽  
A. Loida ◽  
E. González-Robles ◽  
N. Müller ◽  
V. Metz
Keyword(s):  
Nuclear Fuel ◽  
Spent Nuclear Fuel ◽  
Fission Products ◽  
Solution Chemistry ◽  
Release Rates ◽  
Radionuclide Sorption ◽  
Series Of Experiments ◽  
Radionuclide Release

ABSTRACTThe release of radionuclides measured during washing cycles of spent nuclear fuel samples in a series of experiments using different solutions are analyzed with respect to the fission products Cs, Sr, and Tc and the actinides U, Pu, and Am. Based on the concentrations of the dissolved radionuclides, their release rates are evaluated in terms of fraction of inventory in the aquatic phase per day. The application of this information on the fast/instant radionuclide release fraction (IRF) is discussed and following issues are addressed: Duration of the wash steps, solution chemistry, and radionuclide sorption onto surface of the experimental vessels. Data for the IRF are given and the correlation between the mobilization of the various elements is analyzed.

Long-Term Prediction of Radionuclide Release From Borehole Type Repositories

2003 ◽  
Author(s):  
L. B. Prozorov ◽  
S. A. Korneva
Keyword(s):  
Radioactive Waste ◽  
Safety Assessment ◽  
Radiation Safety ◽  
Large Diameter ◽  
Development Program ◽  
Safety Standards ◽  
Engineered Barriers ◽  
Radionuclide Release ◽  
Long Term Prediction

As part of a development program for radioactive waste management, two test boreholes have been constructed at the MosNPO “Radon” Site to evaluate the conditions of LILW storage in such facilities, to observe the behaviour of engineered barriers as a function of time, the ability of the system to contain radionuclides and to test the reliability of a monitoring system. To obtain a licence for operation of such boreholes, MosNPO “Radon” specialists have prepared a package of documents, including a “Report on Safety Assessment of LILW Storage in Large Diameter Boreholes” [1]. On the basis of radiation safety standards and requirements being in force in Russian Federation, a range of possible accidents and emergencies during the operational period has been considered in this study. In this paper, the authors present results of a long term safety assessment of LILW disposal in the boreholes, performed within the framework of the above mentioned report.

The Assessment of the Performance of the Engineered Barriers in a Repository for the Disposal of Low- and Intermediate-Level Radioactive Waste

1991 ◽  
Vol 257 ◽  
Author(s):  
A. Atkinson ◽  
A.W. Harris ◽  
C.C. Naish ◽  
S.M. Sharland ◽  
A.C. Smith
Keyword(s):  
Radioactive Waste ◽  
Intermediate Level ◽  
Uniform Corrosion ◽  
Short Term ◽  
Deep Underground ◽  
Ph Conditions ◽  
Engineered Barriers ◽  
Intermediate Level Radioactive Waste ◽  
Radionuclide Release ◽  
Modelling Approach

ABSTRACTCurrent plans for the disposal of low- and intermediate-level radioactive waste in the U.K. comprise emplacement of steel or concrete containers of waste in a deep underground repository where they will be surrounded by a cementitious backfill. Research is in progress to assess the effectiveness of steel and concrete as barriers to radionuclide release from the repository. A joint experimental and modelling approach is used. Studies of the transport properties of dissolved radionuclides and gases through concrete, and the ability of the concrete to control the pH in the repository are described. Localised and uniform corrosion of carbon and stainless steels are investigated in the high pH conditions of the repository. The research shows that engineered barriers of concrete and steel can provide useful physical containment in the short term and contribute to chemical containment for hundreds of thousands of years.

Influence of Cracks in Cementitious Engineered Barriers in a Near-Surface Disposal System: Assessment Analysis of the Belgian Case

2013 ◽  
Author(s):  
Janez Perko ◽  
Suresh C. Seetharam ◽  
Diederik Jacques ◽  
Dirk Mallants ◽  
Wim Cool ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Safety Assessment ◽  
Total System ◽  
Near Surface ◽  
Disposal Facility ◽  
The Matrix ◽  
Flow Through ◽  
System Assessment ◽  
Engineered Barriers ◽  
Radionuclide Release

In large cement-based structures such as a near surface disposal facility for radioactive waste voids and cracks are inevitable. However, the pattern and nature of cracks are very difficult to predict reliably. Cracks facilitate preferential water flow through the facility because their saturated hydraulic conductivity is generally higher than the conductivity of the cementitious matrix. Moreover, sorption within the crack is expected to be lower than in the matrix and hence cracks in engineered barriers can act as a bypass for radionuclides. Consequently, understanding the effects of crack characteristics on contaminant fluxes from the facility is of utmost importance in a safety assessment. In this paper we numerically studied radionuclide leaching from a crack-containing cementitious containment system. First, the effect of cracks on radionuclide fluxes is assessed for a single repository component which contains a radionuclide source (i.e. conditioned radwaste). These analyses reveal the influence of cracks on radionuclide release from the source. The second set of calculations deals with the safety assessment results for the planned near-surface disposal facility for low-level radioactive waste in Dessel (Belgium); our focus is on the analysis of total system behaviour in regards to release of radionuclide fluxes from the facility. Simulation results are interpreted through a complementary safety indicator (radiotoxicity flux). We discuss the possible consequences from different scenarios of cracks and voids.

scholarly journals About this title - Multiple Roles of Clays in Radioactive Waste Confinement

10.1144/sp482 ◽  
2019 ◽  
Vol 482 (1) ◽  
pp. NP-NP
Keyword(s):  
Radioactive Waste ◽  
Water Movement ◽  
Spatial Scales ◽  
Multiple Roles ◽  
Retention Capacity ◽  
Chemical Contaminants ◽  
Geological Disposal ◽  
Special Publication ◽  
Sealing Capacity ◽  
Engineered Barriers

This Special Publication highlights the importance of clays and clayey material, and their multiple roles, in many national geological disposal facilities for higher activity radioactive wastes. Clays can be both the disposal facility host rock and part of its intrinsic engineered barriers, and may be present in the surrounding geological environment. Clays possess various characteristics that make them high-quality barriers to the migration of radionuclides and chemical contaminants, e.g. very little water movement, diffusive transport, retention capacity, self-sealing capacity, stability over millions of years, homogeneity and lateral continuity.The 20 papers presented in this Special Publication cover a range of topics related to clays in radioactive waste confinement. Aspects of clay characterization and behaviour at various temporal and spatial scales relevant to the confinement of radionuclides in clay are discussed, from phenomenological processes to the overall understanding of the performance and safety of geological disposal facilities.

Integrated Testing of the Srl-165 Glass Waste Form

1986 ◽  
Vol 84 ◽  
Author(s):  
D.L. Phinney ◽  
F.J. Ryerson ◽  
V.M. Oversby ◽  
W.A. Lanford ◽  
R.D. Aines ◽  
...  
Keyword(s):  
Mass Balance ◽  
High Surface ◽  
High Energy ◽  
Leach Solution ◽  
Solution Chemistry ◽  
Waste Form ◽  
Depth Of Penetration ◽  
Glass Waste ◽  
Integrated Testing ◽  
Radionuclide Release

AbstractIntegrated testing of the important components of a glass waste form waste package has been performed in order to gain a better understanding of the processes of radionuclide release and transport in the near field environment. Based upon an interpretation of the depth of penetration of hydrogen in reacted SRL-165 glass we have modeled the radionuclide release from the glass as a combined process of (1) the diffusive exchange of alkalis and boron in the glass for hydrogen species in the solution (D=10−16 cm2/s) and (2) surface dissolution. Surface dissolution controls the release of components not exchanged by diffusion and takes place at a rate of 1.5-3.0 μm/yr. Subsequent to release the radionuclides may remain in the leach solution, diffuse into the tuff, or precipitate as secondary phases. Precipitation is particularly important for plutonium and americium. Diffusive transport of radionuclides through the tuff takes place at an extremely slow rate, D=10−16 cm2/s. As such, the mass of radionuclides incorporated in the tuff by diffusion during the tests is inconsequential relative to that in the leach solution (with the exception of plutonium) and can be ignored in mass balance calculations. Mass balance calculations based upon the release of radionuclides by surface dissolution of the glass waste form are in good agreement with observed solution chemistry when allowances are made for a pulse of dissolution early in the tests. This pulse may be due to either the rapid dissolution of high-energy surface features early in the inLegrated tests, or an initially high surface dissolution rate that decreases with time as silica saturation is approached [1], or a combination of the two.

Determination of the characteristics of crystalline rocks by field experiments: a review

1986 ◽  
Vol 319 (1545) ◽  
pp. 139-156 ◽  
Keyword(s):  
Radioactive Waste ◽  
Field Experiments ◽  
The United States ◽  
Crystalline Rocks ◽  
Granitic Rocks ◽  
Rock Types ◽  
Basement Rocks ◽  
Deep Boreholes ◽  
High Level ◽  
Underground Research Laboratory

Crystalline rocks, particularly granitic rocks and basalts, are one of the principal rock types under consideration as a potential host rock for a high-level radioactive waste repository. Permeability in such rocks is related to discontinuities of various scales, and the quantification and prediction of groundwater flow within both the fractures and the intact rock between the fractures is the major goal of field experiments. The Canadian Underground Research Laboratory is unique in that the hydrogeological conditions within a large volume of rock surrounding the experimental shaft are being monitored before, during and after excavation and the results compared with model predictions. In Switzerland twelve deep boreholes are being drilled to over 1000 m to investigate crystalline basement rocks beneath a cover of sediments. The Stripa Mine in Sweden has hosted a major experimental programme including heater tests to stimulate the thermal effect of radioactive waste and hydrogeological tests at various scales down to individual fractures. The United States of America, the United Kingdom, France and Finland have also embarked on major experimental programmes. Continuing research is needed, with an emphasis on field experiments and research in underground rooms, to provide the data on which detailed risk assessments can be based.

scholarly journals Multiple roles of clays in radioactive waste confinement – introduction

2019 ◽  
Vol 482 (1) ◽  
pp. 1-9
Author(s):  
Simon Norris
Keyword(s):  
Radioactive Waste ◽  
Integrated Approach ◽  
Multiple Roles ◽  
Chemical Contaminants ◽  
Geological Disposal ◽  
Clayey Material ◽  
Engineered Barriers ◽  
Host Rocks ◽  
Term Management

AbstractGeological disposal provides the safe long-term management solution for higher-activity radioactive waste. The development of a repository (or geological disposal facility) requires a systematic and integrated approach, taking into account the characteristics of the waste to be emplaced, the enclosing engineered barriers, and the host rock and its geological setting.Clays and clayey material are important in the development of many national geological disposal systems. Clays exhibit many interesting properties, and are proposed both as host rocks and as material for engineered barriers. Whatever their use, clays present various characteristics that make them high-quality barriers to the migration of radionuclides and chemical contaminants. As host rocks, clays are, in addition, hydrogeologically, geochemically and mechanically stable over geological timescales (i.e. millions of years).

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