Radioactive Waste Disposal Facility Research Articles

Parametric analyses of diffusion of activated sources in disposal forms

The primary objective of a low-level radioactive waste disposal facility is to isolate low-level radioactive waste from the public and the environment until the radionuclides in the waste have decayed to levels at which the hazard is negligible. Two fundamental concerns must be addressed when attempting to isolate low-level waste in a disposal facility on land. The first concern is isolating the waste from water, or hydrologic isolation. The second is preventing movement of the radionuclides out of the disposal facility, or radionuclide migration. Particularly, we have investigated here the latter scenario. Empirical curves describing the progression of the altered zone are obtained and they are used to define the correspondent altered thickness in the numerical calculations for a cement sample. Subsequent numerical analyses of diffusion of activated sources in waste disposals are considered for cemented containers. The adopted DAMAGE code takes into account a mass conservation equation and the linear momentum balance equation for the multiphase material. The mathematical model is based on the theory developed by Bazant for concretes and geomaterials; the fluid phases are considered as a unique mixture interacting with a solid phase. Short- and long-term diffusion analyses are performed for different characteristics of the grout and the results are presented in terms of radionuclides concentration. Indications on the minimum grout thicknesses able to resist to radioactive fluxes up to 1000 years are given.

Modeling of leaching from cementitious materials used in underground environment

The purpose of this research is to evaluate the long-term durability of engineered barrier materials used in underground radioactive waste disposal facilities. Radioactive waste repositories are constructed in crystalline rocks, sedimentary rocks, or clay, which are natural barrier materials, using bentonite and/or cementitious materials as additional engineered barriers in those natural barriers. These engineered barriers are required to inhibit leakage of radionuclides for a long period of more than 1000 or 10,000 years. This necessitates the actual evaluation of long-term durability and quantitative evaluation of the interactions of each of these barrier materials. Cementitious materials are considered to come in contact with underground water or bentonite and release alkali components, which may degrade their performance. Furthermore, there is apprehension that the properties of bentonite may be altered due to the effect of alkaline components included in cementitious materials. In view of the above, the estimation of changes with time of various components that leach out of cementitious materials is considered to be important for evaluating the long-term performance of engineered barriers. The authors firstly carried out leaching experiments considering temperature effects to construct a solubility equilibrium model of cement hydrate. Next, leaching of calcium from concrete was modeled using this solubility model and an advection–diffusion model. Furthermore, the degradation due to leaching of actual structures, from 34 to 104 years old, was studied, and it was observed that a degradation of 100 mm maximum occurs over a period of 100 years. The calculated results of the proposed model showed very good agreement with the results of studies on actual structures. Finally, the effects of various factors on the degradation rate were evaluated numerically using this model. In addition, a simple evaluation of the degradation of bentonite was also performed.

Modelling the interaction of hyperalkaline fluids with simplified rock mineral assemblages

Designs for geological disposal facilities for radioactive wastes often envisage the extensive use of cementitious materials. After closure, the repository will saturate with groundwater and cement porewater will migrate into the geosphere to form an alkaline (pH 12.5–13) plume. This plume will react with the components of the surrounding host rock leading to mineralogical, chemical and physical changes which will be complex in nature. Coupled computer models of geochemistry and hydrogeological transport will be needed to scope these changes. In the recent past, a series of laboratory column experiments were carried out by the British Geological Survey in order to test the capabilities of coupled models to predict the evolution of outflow fluid compositions and product solids. These experiments reacted single minerals (i.e., quartz, albite, calcite and muscovite/quartz) and potential host rock lithologies (i.e., Borrowdale Volcanic Group fault rock, Äspö granite and Wellenberg marl) with cement pore fluids. The objectives of the present work were to develop the understanding of these experiments and to improve simulations of the data by computer models. To this end, a systematic approach was adopted in which dissolution rates for individual minerals were calibrated to the results of the single mineral columns and the resulting parameter values applied to the more complex columns. It was found that for the systems studied, reasonable agreement between the experimental data and the calculated results could be obtained. However, the calibrated dissolution rate constants used in the models first vary between experiments by up to half an order of magnitude and secondly differ from literature values by up to one order of magnitude, with the calibrated values being generally slower than those found in the literature.

空気カプセル輸送を用いた地層処分場の総合輸送システム(NP4 核燃料サイクル・バックエンド技術)

The pneumatic capsule pipeline transportation is a method to transport various materials by utilizing differential pneumatic pressure. It has advantages over conventional methods (e.g., vertical transport using a lift in a shaft) in terms of safety and economical efficiency when it is applied to the deep radioactive waste disposal facilities (Hane, et al., 2002). In this paper, focusing attention on the safety and efficiency of transportation, we propose a concept of the comprehensive transportation system for the high-level radioactive wastes disposal facilities. By introducing a curved pipe section to the pipeline system, we show the applicability and practicability of the system for the facility by analytical study.

The Uptake and Distribution of Buried Radionuclides by Pocket Gophers (Thomomys bottae)

Material Disposal Area G (Area G) at the Los Alamos National Laboratory is a low-level radioactive waste disposal facility. The noticeably high activity of pocket gophers on closed waste burial sites of various types at Area G resulted in the need to understand possible interactions between gophers and radioactive waste. Fossorial animals can influence the fate of contaminants by directly burrowing into waste trenches, pushing contaminated soil to the surface, or through indirect mechanisms such as consumption of contaminant-laden vegetation or the ingestion of soil. In our study, pocket gophers, mound soil, surface soil, and vegetation were collected at Area G and at offsite reference locations. The samples were analyzed for 241Am, 238Pu, 239Pu, 3H, and total U. It did not appear that gophers were responsible for any upward transport of radionuclides. Concentrations of 241Am, 238Pu, 239Pu, and 3H in some gophers, soil, and vegetation were higher than at reference sites; however, only 3H in gopher carcasses at only one of five sites within Area G was higher than a conservative ecological screening level.

Canada's Low-level Radioactive Waste Disposal Problem: Voluntarism Reconsidered

Voluntary siting methods are no more successful than conventional regulatory or market-based methods in siting new low-level radioactive waste (LLRW) disposal facilities. The promise of voluntarism, I argue, is diminished by the excessively local conception of public participation that typically informs voluntary siting attempts. This is evident in Canada's search for an LLRW disposal facility in Ontario. Placing strong boundaries around municipalities for purposes of public participation violates two key conditions of democratic siting policy - maximising social inclusiveness and ensuring a large unit of review. Selecting a larger unit of public deliberation would have permitted a more socially inclusive participatory analysis of the political, economic and social implications of managing radioactive wastes. A regional approach to LLRW management can therefore provide a more just and democratic framework for resolving siting disputes that jointly involve neighbouring communities.

Development of a solution method for the differential equations arising in the biosphere module of the BNFL's suite of codes MONDRIAN

British Nuclear Fuels plc owns and operates the near-surface Drigg disposal facility for low level radioactive waste. The long-term performance of the site is modelled by a suite of computer codes called MONDRIAN. One of the modules of MONDRIAN deals with the transport of radionuclides through the environment, and this paper reports on the current status of this module (BIOS). We derive the basic set of working equations from first principles and show clearly how the approximate nature of the final equations is arrived at. This is done by an averaging process leading to compartments, in and out of which radionuclides, solids and water can flow. The equations allow radioactive decay chains and an arbitrary number of compartments. There is also the facility to deal with changes in the rate coefficients, thereby simulating different environmental states. It is also possible to include the creation of new compartments arising as a consequence of climatic variations. In addition to developing a new differential equation solver which is now incorporated in the BIOS module of MONDRIAN, we have demonstrated the relative efficiency of this in comparison with a previously employed differential equation solver and have compared the benefits with an alternative approach that restricted the solution to the case which required all the retardation factors to be equal. The comparison is based upon a 31 compartment biosphere model with an eight member radionuclide decay chain. Verification against the probabilistic assessment code MASCOT is also reported to further increase confidence.

Modelling the interaction of bentonite with hyperalkaline fluids

Many designs for geological disposal facilities for radioactive and toxic wastes envisage the use of cement together with bentonite clay as engineered barriers. However, there are concerns that the mineralogical composition of the bentonite will not be stable under the hyperalkaline pore fluid conditions (pH > 12) typical of cement and its properties will degrade over long time periods. The possible extent of reaction between bentonite and cement pore fluids was simulated using the reaction-transport model, PRECIP. Key minerals in the bentonite (Na-montmorillonite, analcite, chalcedony, quartz, calcite) were allowed to dissolve and precipitate using kinetic (time-dependent) reaction mechanisms. Simulations were carried out with different model variants investigating the effects of: temperature (25 and 70 °C); cement pore fluid composition; dissolution mechanism of montmorillonite; rates of growth of product minerals; solubilities of product minerals; and aqueous speciation of Si at high pH. Simulations were run for a maximum of 3.2 ka. The results of all simulations showed complex fronts of mineral dissolution and growth, driven by the relative rates of these processes for different minerals. Calcium silicate hydrate (CSH) minerals formed closest to the cement-bentonite boundary, whereas zeolites and sheet silicates formed further away. Some growth of primary bentonite minerals (analcite, chalcedony, calcite and montmorillonite) was observed under certain conditions. Most alteration was associated with the fluid of highest pH, which showed total removal of primary bentonite minerals up to 60 cm from the contact with cement after ∼1 ka. The maximum porosity increase observed was up to 80–90% over a narrow zone 1–2 cm wide, close to the cement pore fluid- bentonite contact. All simulations (except that with alternative aqueous speciation data for Si) showed total filling of porosity a few cms beyond this interface with the cement, which occurred after a maximum of 3.2 ka. Porosity occlusion was principally a function of the growth of CSH minerals such as tobermorite. There was very little difference in the alteration attained using different model variants, suggesting that bentonite alteration was not sensitive to the changes in parameters under the conditions studied, so that transport of pore fluid through the bentonite governed the amount of alteration predicted. Principal remaining uncertainties associated with the modelling relate to assumptions concerning the evolution of surface areas of minerals with time, and the synergy between changing porosity and fluid flow/diffusion.

366. 高レベル放射性廃棄物処分地選定の社会的受容性を高めるための課題に関する考察

366. 高レベル放射性廃棄物処分地選定の社会的受容性を高めるための課題に関する考察

Analcime reactions at 25–90°C in hyperalkaline fluids

AbstractExtensive use of cement and concrete is envisaged in the construction of geological disposal facilities for radioactive wastes. The hyperalkaline porefluids typical of groundwaters that have reacted with these materials have the potential to react chemically with other engineered barrier components such as bentonite, potentially degrading their performance. Analcime, NaAlSi2O6.H2O, has been identified from previous modelling and experimental studies as a potential alteration product of bentonite.Laboratory experiments to investigate the stability of analcime under hyperalkaline porefluid conditions have been performed. Experiments used both batch and fluidized bed equipment at 25, 50, 70 and 90°C in K-based pH buffer solutions, both under- and over-saturated with respect to analcime. Results from dissolution experiments demonstrate that release of Na was greatly enhanced (by up to a factor of thirty) over that for Si and Al, particularly at pH 10 and 11. However, enhanced release of both Na and Al occurred in the batch experiments at pH 12–13. Near stoichiometric dissolution was observed in fluidized bed experiments under steady-state conditions at 70°C. Sodium was removed from the analcime structure by ion exchange for K, without involving dissolution and re-precipitation of the analcime framework. Scanning electron microscopy of reacted analcime grains showed that some grains had pronounced cracks parallel to original cleavage traces. These cracks were a result of volume decrease due to the substitution of K for Na ions and water molecules in the analcime structure to form leucite, KAlSi2O6.Synthesis of the dissolution data shows that the rate of dissolution increased with increasing temperature in the range 25–70°C and with pH at each temperature. Absolute rates of dissolution ranged from 10−10 mol m−2 s−1 at pH 9.5 at 25°C to 10−7 mol m−2 s−1 a pH 12 at 70 and 90°C. The rate of dissolution at any temperature was pH-dependent, such that the rate could be described by k (aH+)n, where k is the rate constant and n is −0.3 at 25°C, −0.4 at 50°C, −0.6 at 70°C and −0.7 at 90°C. Attempts to measure the growth rate of analcime in supersaturated solutions at 70 and 90°C were unsuccessful, although a limiting rate at 70°C, pH 10 was calculated to be 4 × 10−11 mol m−2 s−1, roughly 100× less than the rate of dissolution under the same conditions.These results imply that any trace amounts of analcime in bentonite will be converted to leucite by reaction with cement fluids with a high K/Na ratio. In some instances, leucite may thus incorporate K+ in preference to other phases (e.g. illite, K-feldspar) during alteration of bentonite by cement porefluids.

Analysis of the Financial Assurance Plan in the License Application for a Low-Level Radioactive Waste Disposal Facility

Our purpose is to evaluate efficiency of financial assurance plan in license application' submitted by American Ecology Corporation (AEC) to site, design, and build a new technological facility in Boyd County, Nebraska, for disposal of low-level radioactive waste (LLRW). Efficiency means ability to accomplish desired effects. Thus, efficiency considerations begin with social beliefs and ethics in order to know what is desirable. Ethics can be considered a system of guidance designed to assist in living within a society.... That we must live together installs positive requirement of doing good for one (Anderson and Englehardt 2001, 6-7). Humans in a social system are immersed in obligation to one another (8). Ethics seeks to resolve problems of what is harm and what is help and to unravel complexities of moral choice (9). In a socioeconomic system, choices and decisions are about organizational actions. Action is behavior under governance of some larger understanding. . (9). For sodality, a is immersed in obligations, rules, and requirements which force decision makers to determine ethical actions. This requires decision makers to complete efficiency evaluations in order to make judgments based on criteria drawn from social beliefs. As court stated in Ohio v. Interior, efficiency means the result that achieves greatest value to society (1989). The efficiency criteria applied here

Performance assessment models for low level radioactive waste disposal facilities: A review

The statutory role of performance assessment of radioactive waste disposal facilities is a technical analysis to evaluate the prospective performance of a disposal site with respect to regulatory compliance. The areas that are covered by performance assessment range from the characterization of the waste and site to estimation of any potential dose to the public due to release of radionuclides over long periods of time (typically thousands of years). In developing new disposal sites, performance assessment has also been used as a screening tool for determining site suitability, a guide in site characterization, as well as a final technical analysis for license application. This paper provides a review of the current status of performance assessment models in the U.S. for civilian low-level radioactive waste (LLW) disposal facilities.

Estimating the Optimal Scale of Public Investments: The Case of Low-Level Radioactive Waste Disposal Facilities

This paper addresses the regulatory problem of estimating the optimal scale of public capital investments, such as regional low-level radioactive waste (LLRW) disposal facilities and sports stadiums, when regulators can require information disclosures from firms. I evaluate the efficacy of the Illinois LLRW mandatory forecast disclosure rule against an estimated ARIMA model of LLRW volume disposed over the 1985–1995 period; the ARIMA model is shown to be more accurate. I conclude with an ARIMA model forecast of lifecycle volumetric capacity of a proposed LLRW disposal facility in Illinois.

Myth-Making, Moral Communities, and Policy Failure in Solving the Radioactive Waste Problem

Nineteen years after the passage of the Low-Level Radioactive Waste Policy Act (1980) and fifteen years since significant amendments were made to the policy, no state or regional compact has yet opened a new low-level radioactive waste (LLRW) disposal facility. While active siting efforts are currently being pursued in several states, this study focuses on the stagnation of the Southwest Compact's siting process at Ward Valley, CA, to illustrate how a social constructionist perspective can clarify our understanding of public and stakeholder reactions. From a series of key informant interviews and an extensive analysis of secondary materials, we describe the formation of ''moral communities'' of opponents and proponents whose position statements have been constructed on antithetical ''high principles.'' We find that these contrapositions are becoming increasingly divergent, resulting in a highly charged technical and emotional battle to win over public and policymaker opinion that leaves little hope of finding a compromise solution acceptable to both sides.

Total System Performance Assessment for Waste Disposal Using a Logic Tree Approach

The Electric Power Research Institute (EPRI) has sponsored the development of a model to assess the long‐term, overall “performance” of the candidate spent fuel and high‐level radioactive waste (HLW) disposal facility at Yucca Mountain, Nevada. The model simulates the processes that lead to HLW container corrosion, HLW mobilization from the spent fuel, and transport by groundwater, and contaminated groundwater usage by future hypothetical individuals leading to radiation doses to those individuals. The model must incorporate a multitude of complex, coupled processes across a variety of technical disciplines. Furthermore, because of the very long time frames involved in the modeling effort (>104 years), the relative lack of directly applicable data, and many uncertainties and variabilities in those data, a probabilistic approach to model development was necessary. The developers of the model chose a logic tree approach to represent uncertainties in both conceptual models and model parameter values. The developers felt the logic tree approach was the most appropriate. This paper discusses the value and use of logic trees applied to assessing the uncertainties in HLW disposal, the components of the model, and a few of the results of that model. The paper concludes with a comparison of logic trees and Monte Carlo approaches.

Comments on the Legal Admissibility of a Performance Assessment for a Radioactive Waste Disposal Facility

We were invited by the Editor of Risk Analysis to comment on the legal admissibility of the performance assessment conducted for the Waste Isolation Pilot Plant (WIPP) in 1996.(1) This invitation was extended because of work we have conducted regarding the admissibility as evidence in legal proceedings of risk assessments and the results thereof.(2,3) With the advent of ‘‘risk-based’’ decision making and ‘‘risk-informed’’ decision making in environmental management, the legal admissibility of the underlying risk assessment becomes a key issue if the affected environmental decision is challenged within the legal framework. For that reason, we undertook the studies in Refs. 2 and 3. We have examined the tests and criteria to which a court of law may subject risk assessment and their results to determine whether or not they can be admitted as evidence. We have discovered that those tests and criteria are different, and generally stricter, that the standards of scientific acceptability to which we are accustomed. We have also found that, in general, risk assessment practitioners are seldom aware of the admissibility standards for technical and scientific data as evidence. Consequently, those standards are not usually factored in when designing and conducting risk assessments. We reviewed Ref. 1 from the point of view of the legal admissibility of the performance assessment methodology. We were not able to draw specific conclusions on the legal admissibility of the performance assessment methodology for two reasons. First, the level of detail in the information that would had to be examined is far more than could be reasonably included in a journal publication, and this is indeed

Probabilistic safety assessment model for near surface radioactive waste disposal facilities

A probabilistic safety assessment model has been developed for assessing the performance of near surface disposal facilities for low-level radioactive waste. Two modes of disposal such as single dump and multiple dump are considered in the model. The model is composed of four components: source term, repository failure, geosphere transport and radiological assessment. The source term contains low-level radioactive waste equivalent to 50 GWe.y energy production (1 GWe.y=3.2×10 16 J of electrical energy production) either disposed at an instant or distributed over 50 years. The endpoints of assessment are expressed as radioactivity release rate, radionuclide concentration in ground water, radiation dose to a member of the critical group through drinking water pathway and total risk to critical group due to disposal practice. Sensitivity analysis is carried out to identify the critical parameters, which have maximum effect on the assessment endpoints. Uncertainty analysis, based on random selection of all main parameters, is also carried out to identify the effect of overall variation of parameters used in the model in relation to a reference level. The reference level delivers a maximum annual effective dose of 1.2×10 −2 mSv to a member of the critical group after about 1.25×10 2 years of disposal mostly from 129I, the long-lived and less sorbing radionuclide. The corresponding risk to the public due to the disposal practice (9.0×10 −7 y −1) is found to be lower than that due to natural background radiation. The most critical parameters as indicated by the sensitivity analysis are the distribution coefficient of radionuclides, seepage velocity in the unsaturated zone between the facility and the water table, dispersivity in ground water and thickness of the unsaturated zone. The uncertainty analysis shows that 129I is the critical radionuclide delivering maximum dose in most cases though it constitutes a low percentage in the low-level radioactive waste inventory. The annual effective doses derived from the uncertainty analysis fall in a log normal distribution with a geometric mean of 3.6×10 −2±3.9 mSv and the most probable annual effective dose to a member of the critical group works out to be 2.8×10 −4 mSv.

Experimental simulation of the alkaline disturbed zone around a cementitious radioactive waste repository: numerical modelling and column experiments

Abstract One approach to describe the migration of an alkaline plume from the cementitious engineered barriers of a geological disposal facility for radioactive wastes is to employ coupled chemistry and flow computer models. Although evidence from natural systems is useful to constrain reaction mechanisms and minerals to be incorporated into such models, time-dependent information is generally lacking. A series of laboratory column experiments has been conducted in order to test the capabilities of two of the currently available, coupled models to predict product solids and output fluid compositions with time. The coupled models PRECIP and CHEQMATE were used to provide predictive calculations based upon known experimental parameters and data available from the literature. The predictions did not replicate all the variations in mineralogy observed in the experiments, primarily due to restrictions in the availability of kinetic and thermdynamic data for the range of secondary phases of interest. However, the model predictions did reproduce the general variation of secondary phases with time and distance along the columns.

Lead and Lead-Based Alloys as Waste Matrix Materials

AbstractMetals and alloys with relatively low melting temperatures such as lead and lead-based alloys are considered in Russia as prospective matrices for encapsulation of spent nuclear fuel in containers in preparation for final disposal in underground repositories. Now lead and leadbased alloys are being used for conditioning spent sealed radioactive sources at radioactive waste disposal facilities.

Total system performance assessment for waste disposal using a logic tree approach.

The Electric Power Research Institute (EPRI) has sponsored the development of a model to assess the long-term, overall "performance" of the candidate spent fuel and high-level radioactive waste (HLW) disposal facility at Yucca Mountain, Nevada. The model simulates the processes that lead to HLW container corrosion, HLW mobilization from the spent fuel, and transport by groundwater, and contaminated groundwater usage by future hypothetical individuals leading to radiation doses to those individuals. The model must incorporate a multitude of complex, coupled processes across a variety of technical disciplines. Furthermore, because of the very long time frames involved in the modeling effort (>> 10(4) years), the relative lack of directly applicable data, and many uncertainties and variabilities in those data, a probabilistic approach to model development was necessary. The developers of the model chose a logic tree approach to represent uncertainties in both conceptual models and model parameter values. The developers felt the logic tree approach was the most appropriate. This paper discusses the value and use of logic trees applied to assessing the uncertainties in HLW disposal, the components of the model, and a few of the results of that model. The paper concludes with a comparison of logic trees and Monte Carlo approaches.