Nuclear Waste Disposal Facility Research Articles

A synthesis of approaches for modelling coupled thermal–hydraulic–mechanical–chemical processes in a single novaculite fracture experiment

The geological formation immediately surrounding a nuclear waste disposal facility has the potential to undergo a complex set of physical and chemical processes starting from construction and conti ...

Development of approaches for modelling coupled thermal–hydraulic–mechanical–chemical processes in single granite fracture experiments

The geological formation immediately surrounding a nuclear waste disposal facility has the potential to undergo a complex set of physical and chemical processes starting from construction and continuing many years after closure. The DECOVALEX project (DEvelopment of COupled models and their VALidation against EXperiments) was established and maintained by a variety of waste management organizations, regulators and research organizations to help improve capabilities in experimental interpretation, numerical modelling and blind prediction of complex coupled systems. In the present round of DECOVALEX (D-2015), one component of Task C1 has considered the detailed experimental work of Yasuhara et al. (Appl Geochem 26:2074–2088, 2011), wherein three natural fractures in Mizunami granite are subject to variable fluid flows, mechanical confining pressure and different applied temperatures. This paper presents a synthesis of the completed work of six separate research teams, building on work considering a single synthetic fracture in novaculite. A range of approaches are presented including full geochemical reactive transport modelling and 2D and 3D high-resolution coupled thermo–hydro–mechanical–chemical (THMC) models. The work shows that reasonable fits can be obtained to the experimental data using a variety of approaches, but considerable uncertainty remains as to the relative importance of competing process sets. The work also illustrates that a good understanding of fracture topography, interaction with the granite matrix, a good understanding of the geochemistry and the associated multi-scale THMC process behaviours is a necessary pre-cursor to considering predictive models of such a system.

Comparative modelling of laboratory experiments for the hydro-mechanical behaviour of a compacted bentonite–sand mixture

A comparative modelling exercise involving several independent teams from the DECOVALEX-2015 project is presented in this paper. The exercise is based on various laboratory experiments that have been carried out in the framework of a French research programme called SEALEX and conducted by the IRSN. The programme focuses on the long-term performance of swelling clay-based sealing systems that provide an important contribution to the safety of underground nuclear waste disposal facilities. A number of materials are being considered in the sealing systems; the current work focuses on a 70/30 MX80 bentonite–sand mixture compacted at dry densities between 1.67 and 1.97 Mg/m3. The improved understanding of the full set of hydro-mechanical processes affecting the behaviour of an in situ sealing system requires both experiments ranging from small-scale laboratory tests to full-scale field emplacement studies and coupled hydro-mechanical models that are able to explain the observations in the experiments. The approach was to build models of increasing complexity starting for the simplest laboratory experiments and building towards the full-scale in situ experiments. Following this approach, two sets of small-scale laboratory experiments have been performed and modelled. The first set of experiments involves characterizing the hydro-mechanical behaviour of the bentonite–sand mixture by means of (1) water retention tests under both constant volume and free swell conditions, (2) infiltration test under constant volume condition, and (3) swelling and compression tests under suction control conditions. The second, more complex, experiment is a 1/10th scale mock-up of a larger-scale in situ experiment. Modelling of the full-scale experiment is described in a companion paper. A number of independent teams have worked towards modelling these experiments using different conceptual models, codes, and input parameters. Their results are compared and discussed. This exercise has enabled an improved modelling of the bentonite–sand mixture behaviour, in particular accounting for the dependence of its retention curve on the dry density. Moreover, it has shown the importance of the technological voids on the short-term behaviour of the sealing system.

The solubility of nickel and its migration through the cementitious backfill of a geological disposal facility for nuclear waste

This work describes the solubility of nickel under the alkaline conditions anticipated in the near field of a cementitious repository for intermediate level nuclear waste. The measured solubility of Ni in 95%-saturated Ca(OH)2 solution is similar to values obtained in water equilibrated with a bespoke cementitious backfill material, on the order of 5×10−7M. Solubility in 0.02M NaOH is one order of magnitude lower. For all solutions, the solubility limiting phase is Ni(OH)2; powder X-ray diffraction and scanning transmission electron microscopy indicate that differences in crystallinity are the likely cause of the lower solubility observed in NaOH. The presence of cellulose degradation products causes an increase in the solubility of Ni by approximately one order of magnitude. The organic compounds significantly increase the rate of Ni transport under advective conditions and show measurable diffusive transport through intact monoliths of the cementitious backfill material.

Fracture Mechanics Modelling of an In Situ Concrete Spalling Experiment

During the operation of nuclear waste disposal facilities, some sprayed concrete reinforced underground spaces will be in use for approximately 100 years. During this time of use, the local stress regime will be altered by the radioactive decay heat. The change in the stress state will impose high demands on sprayed concrete, as it may suffer stress damage or lose its adhesion to the rock surface. It is also unclear what kind of support pressure the sprayed concrete layer will apply to the rock. To investigate this, an in situ experiment is planned in the ONKALO underground rock characterization facility at Olkiluoto, Finland. A vertical experimental hole will be concreted, and the surrounding rock mass will be instrumented with heat sources, in order to simulate an increase in the surrounding stress field. The experiment is instrumented with an acoustic emission system for the observation of rock failure and temperature, as well as strain gauges to observe the thermo-mechanical interactive behaviour of the concrete and rock at several levels, in both rock and concrete. A thermo-mechanical fracture mechanics study is necessary for the prediction of the damage before the experiment, in order to plan the experiment and instrumentation, and for generating a proper prediction/outcome study due to the special nature of the in situ experiment. The prediction of acoustic emission patterns is made by Fracod 2D and the model later compared to the actual observed acoustic emissions. The fracture mechanics model will be compared to a COMSOL Multiphysics 3D model to study the geometrical effects along the hole axis.

Das Planungsrecht der Energiewende

The turnaround in energy policy has had a great impact on the electricity infrastructure in Germany. New sources of renewable energy need to be developed, electricity networks modified and expanded, and the question answered concerning the disposal of the old nuclear power plants and their waste. Meeting this challenge involves various political and legal areas. On the legal side, the legislature plans to use valued instruments to manage the relocation of renewable energies, and it has made legislative changes in some areas to strengthen these instruments. In order to carry out the integration of renewable energies into the network, Germany is going one step further in terms of the methods that it uses: as well as the well-known array of planning instruments available, it has decided to adopt special laws to subject the planned energy highways which are intended to extend across the Federal Republic to a special regime, so that they can be built as quickly as possible. Finally, the legislature intends to rely entirely on a legal solution with regard to the search for a suitable nuclear waste disposal facility, with the site selection law (Standortsauswahlgesetz) having been put in place to meet this particular challenge. The task of my contribution here is to demonstrate the different facets of the solutions adopted. In doing so, I shall not only describe the legal structures, but also sometimes point to their strengths and weaknesses.

Evaluation of the US DOE's conceptual model of hydrothermal activity at Yucca Mountain, Nevada

Abstract. A unique conceptual model describing the conductive heating of rocks in the thick unsaturated zone of Yucca Mountain, Nevada by a silicic pluton emplaced several kilometers away is accepted by the US Department of Energy (DOE) as an explanation of the elevated depositional temperatures measured in fluid inclusions in secondary fluorite and calcite. Acceptance of this model allowed the DOE to keep from considering hydrothermal activity in the performance assessment of the proposed high-level nuclear waste disposal facility. The evaluation presented in this paper shows that no computational modeling results have yet produced a satisfactory match with the empirical benchmark data, specifically with age and fluid inclusion data that indicate high temperatures (up to ca. 80 °C) in the unsaturated zone of Yucca Mountain. Auxiliary sub-models complementing the DOE model, as well as observations at a natural analog site, have also been evaluated. Summarily, the model cannot be considered as validated. Due to the lack of validation, the reliance on this model must be discontinued and the appropriateness of decisions which rely on this model must be re-evaluated.

Redox processes in the safety case of deep geological repositories of radioactive wastes. Contribution of the European RECOSY Collaborative Project

Redox processes influence key geochemical characteristics controlling radionuclide behaviour in the near and far field of a nuclear waste repository. A sound understanding of redox related processes is therefore of high importance for developing a Safety Case, the collection of scientific, technical, administrative and managerial arguments and evidence in support of the safety of a disposal facility. This manuscript presents the contribution of the specific research on redox processes achieved within the EURATOM Collaborative Project RECOSY (REdox phenomena COntrolling SYstems) to the Safety Case of nuclear waste disposal facilities. Main objectives of RECOSY were related to the improved understanding of redox phenomena controlling the long-term release or retention of radionuclides in nuclear waste disposal and providing tools to apply the results to Performance Assessment and the Safety Case. The research developed during the project covered aspects of the near-field and the far-field aspects of the repository, including studies relevant for the rock formations considered in Europe as suitable for hosting an underground repository for radioactive wastes. It is the intention of this paper to highlight in which way the results obtained from RECOSY can feed the scientific process understanding needed for the stepwise development of the Safety Case associated with deep geological disposal of radioactive wastes.

Experimental investigations of the creep–damage–rupture behaviour of rock salt

The creep–damage behaviour of rock salt, especially in the tertiary creep phase has been rarely investigated. The creep–damage–rupture characteristics of rock salt are studied in this paper by applying Wang's creep–damage model, the experimental results of the triaxial destructive creep–damage tests using quasi-static loading on rock salt specimens are presented, complete creep–damage curves are obtained, and the evolution laws of deformation and damage of rock salt in the primary (transitional), secondary (steady-state) and tertiary (accelerating) phases are deduced. The long-term behaviour of dilatancy of rock salt is investigated according to the dilatancy boundary theory and an approximate long-term dilatancy boundary range is obtained. Finally, the long-term strength of rock salt is evaluated for the test samples. The used model proves to conform well to the test data, including in the tertiary creep–damage phase; it can be suitable for the assessment of collapse, cracking, rupture and other long-term failures, and hence for theoretical basis of design in the underground engineering of gas and oil storage cavern, nuclear waste disposal and other facilities in salt deposit.

電気的促進試験による放射性廃棄物セメント固化体の溶脱挙動の評価

セシウムあるいはストロンチウムを含む放射性廃棄物固化処理体を模擬したセメント硬化体に対し、長期間にわたる溶脱現象に伴う物性変化に関する情報を短期間で取得することを目的とした電気的促進試験を用いて、放射性廃棄物セメント固化体の溶脱挙動を評価した。さらに、浸漬試験（拡散現象）による溶脱挙動と比較することにより、実際の溶脱現象との差異について検討し、変質評価手法としての電気的促進法の適用性について考察した。浸漬試験に比べて電気的促進試験における硝酸セシウムならびにカルシウムアルミネート相の溶脱と同時に、空隙が粗となり連続性の高い空隙構造を形成する現象が著しく速くなることを確認することができた。

Mineral Synthesis in Si–Al–Ca Systems and Their Iodide Sorption Capacity under Alkaline Conditions

The release of anionic nuclides such as 129I from underground nuclear waste disposals is of great environmental concern due to its long half-life and high mobility in alkaline environments. The leachability of iodide is largely dependent on the sorption capacity of various Ca-bearing minerals such as ettringite, hydrocalumite, and calcium silicate hydrate (C-S-H) which are common hydration products of cement materials. Moreover, the pore water chemistry of cement materials is dominated by Si, Al, and Ca during the initial stage of weathering, and the ratios of the ions present vary much depending on the source materials. Examining the mineral phases generated in Si–Al–Ca systems with respect to different ratios of Si, Al, and Ca and their interaction with iodide is important to better understand the sorption behavior of iodide in nuclear waste disposal facilities. In this study, the mineral synthesis in Si–Al–Ca systems was conducted under alkaline conditions at ambient temperature, and the sorption behavior of iodide with the mineral phases was investigated during and after the mineral formation. The results showed that portlandite, C-S-H, stratlingite (CASH), hydrocalumite, gibbsite, and amorphous compounds were precipitated from the systems, depending on the Si, Al, and Ca ratios. The Kd values of iodide were greatly affected by the Ca content and relatively high Ca-containing phases such as hydrocalumite, C-S-H, CASH, and portlandite showed high iodide retention capacity. Hence, ensuring the formation of these secondary minerals by modification of the chemical composition of cement materials could assist in safety design of nuclear waste disposals.

Equilibrium Partial Pressure of CO2 in the Callovo-Oxfordian Argillite as a Function of Relative Humidity

Understanding the behavior of a clay mineral-rich rock submitted to different physical-chemical perturbations is important for assessing the safety of nuclear waste disposal facilities in the corresponding geological formations. In this work we studied the effect of rock desaturation on the CO2 partial pressure signature of the Callovo-Oxfordian argillite. This integrated study, which combines experiments and geochemical modeling, points out the primary role of capillary forces on the chemical equilibria. In particular, it was possible to model, without any fitting parameters, the experimental decrease of pCO2 as a function of decreasing water content in the argillite. Moreover, this application to a complex natural system is an example of confirmation of the theoretical concepts of geochemistry in capillary contexts and is promising for dealing with other natural and industrial systems.

Paul A. Witherspoon (1919–2012)

The hydrologic community lost one of its most charismatic leaders with the death of Paul Witherspoon on 10 February 2012, in Berkeley, Calif. He passed away from complications brought on by his long battle with Parkinson's disease. He was 93. Paul was a dynamic and influential research leader in hydrogeology for more than 50 years. Working from his base at the University of California, Berkeley (UC Berkeley), and later from the Lawrence Berkeley National Laboratory (LBNL), he made significant contributions to the understanding of the flow of fluids in porous media and fractured rock, and he applied his findings to a diverse set of societally important issues, including the development of geothermal energy, use of underground gas storage, and siting and design of nuclear waste disposal facilities. In all these spheres of interest he emphasized the need to marry theoretical studies and field testing. He was especially passionate about the need for large‐scale, in situ, underground experiments to guide and corroborate the predictions of theoretically based numerical models.

“Because We've Got History Here”: Nuclear Waste, Cooperative Siting, and the Relational Geography of a Complex Issue

This paper takes as its focus recent developments in UK radioactive waste management policy and, through a relational reading of siting conflicts, stresses the need to locate, historically, controversy that takes place in the present. In particular, I argue that temporally distant actors and events, which remain culturally very salient, are critical in shaping the pathway of contentious planning processes. Here I trace the space—time relations that configure the (possible) siting of a Geological Disposal Facility (GDF) for higher activity nuclear waste, through a cooperative process of volunteerism, as a matter of concern for publics in West Cumbria. The history, economy, and culture of West Cumbria is intimately connected with the nuclear industry—and, at the time of writing, the region represents the only area of England and Wales for which there are recorded expressions of interest in hosting a GDF. The paper demonstrates that controversy centred on the spatial ordering of the siting process by government—a politics that was rooted in the area's history with nuclear waste—and the actors and events that had structured this past. In this regard, I argue for a geographical reading of siting controversy that acknowledges the agency of the absent, and the play of distant others in configuring a public politics of the present.

Development and analysis of a dynamic compartment model to predict carbon-14 behavior in rice paddy field for dose assessment of atmospheric release

Abstract Carbon-14 is one of the critical radionuclides for the dose estimation from nuclear fuel reprocessing plants and nuclear waste disposal facilities. To assess the impact on public health caused by carbon-14 released from these nuclear facilities in Japan, a reasonable estimation of internal dose from the rice ingestion is necessary because rice is a staple food. Therefore, we are developing a dynamic compartment model to predict carbon-14 behavior in atmosphere – paddy soil – rice plant system and carbon-14 concentration in rice by using a migration prediction code, MOGRA. In this model, growing curves of “leaf and stem part” and “ear part” of a rice plant were fitted to sigmoid curves. The transfer coefficients between the compartments were estimated by using sub-models and parameters which describe transfer mechanisms of carbon in a rice paddy field, such as photosynthesis, translocation and respiration in a rice plant. A validation study of the model, carried out with “Rice Scenario” presented by the IAEA EMRAS (Environmental Modelling for RAdiation Safety) project, showed that the developed model can be practically used to predict the carbon-14 concentration in rice. The model was also applied for hypothetical releases of carbon-14 from nuclear fuel reprocessing plant. In addition, parameter sensitivity analyses were carried out to select critical parameters.

Qualification of a truly distributed fiber optic technique for strain and temperature measurements in concrete structures

Structural health monitoring is a key factor in life cycle management of infrastructures. Truly distributed fiber optic sensors are able to provide relevant information on large structures, such as nuclear power plants or nuclear waste disposal facilities. The sensing chain includes an optoelectronic unit and a sensing cable made of one or more optical fibers. A new instrument based on Optical Frequency Domain Reflectometry (OFDR), enables to perform temperature and strain measurements with a centimeter scale spatial resolution over hundred of meters and with a level of precision equal to 1 μ strain and 0.1 °C. Several sensing cables are designed with different materials targeting to last for decades, either embedded in the concrete or attached to the surface of the structure. They must ensure an optimal transfer of temperature and strain from the concrete matrix to the optical fiber. Based on the European guide FD CEN/TR 14748 “Non-destructive testing – Methodology for qualification of non-destructive tests”, a qualification method was developed. Tests were carried out using various sensing cables embedded in the volume or fixed to the surface of plain concrete specimens and representative-scale reinforced concrete structural elements. Measurements were performed with an OFDR instrument, while mechanical solicitations were imposed to the concrete element. Preliminary experiments seem very promising since measurements performed with distributed sensing systems are found comparable to values obtained with conventional sensors used in civil engineering and with the Strength of Materials Modelling. Moreover, the distributed sensing system makes it possible to detect and localize cracks appearing in concrete during the mechanical loading.

Reversing Nuclear Opposition: Evolving Public Acceptance of a Permanent Nuclear Waste Disposal Facility

Nuclear facilities have long been seen as the top of the list of locally unwanted land uses (LULUs), with nuclear waste repositories generating the greatest opposition. Focusing on the case of the Waste Isolation Pilot Plant (WIPP) in southern New Mexico, we test competing hypotheses concerning the sources of opposition and support for siting the facility, including demographics, proximity, political ideology, and partisanship, and the unfolding policy process over time. This study tracks the changes of risk perception and acceptance of WIPP over a decade, using measures taken from 35 statewide surveys of New Mexico citizens spanning an 11-year period from fall 1990 to summer 2001. This time span includes periods before and after WIPP became operational. We find that acceptance of WIPP is greater among those whose residences are closest to the WIPP facility. Surprisingly, and contrary to expectations drawn from the broader literature, acceptance is also greater among those who live closest to the nuclear waste transportation route. We also find that ideology, partisanship, government approval, and broader environmental concerns influence support for WIPP acceptance. Finally, the sequence of procedural steps taken toward formal approval of WIPP by government agencies proved to be important to gaining public acceptance, the most significant being the opening of the WIPP facility itself.

In-situ FTIR analyses of bentonite under high-pressure

The stability of bentonite is of particular interest for containment barriers in nuclear waste disposal facilities. However, very little is known about the stability of montmorillonite (the major component of bentonite) under high-pressure (HP) conditions. The objective of this work is to investigate the stability of montmorillonite under HP conditions, using a sample of bentonite in which the major component is a dioctahedral calcium montmorillonite. This montmorillonite was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray fluorescence (XRF), specific surface area (SA), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). HP experiments up to 7.7GPa at room temperature (RT) were performed using toroidal chambers (TC). The samples were characterized by XRD after the HP processing. In-situ FTIR analyses were performed in the samples inside a diamond anvil cell (DAC) up to 8GPa (dispersed in KBr) and up to 13GPa (pure bentonite). In-situ FTIR measurements inside the DAC showed that montmorillonite was stable despite a reversible deformation in the Si–O bond and did not lose water up to 13GPa. XRD analysis of the samples processed at 8GPa at RT inside the TC showed no marked modification in the (001) reflections and b-parameter (060) reflections of montmorillonite induced by high pressure. The obtained results indicated that montmorillonite remained stable under high pressure conditions.

The Impacts of Information Cascade on Residents' Collective Preference: The Case of Nuclear Waste Disposal Facility Sites

The Impacts of Information Cascade on Residents' Collective Preference: The Case of Nuclear Waste Disposal Facility Sites

Assessment of Concrete Cracking at Nuclear Waste Disposal Facilities via Fiber Optic Sensors

AbstractFiber optic sensors offer a novel approach to monitoring of fractures in concrete waste disposal vaults and offer the possibility of determining the quantity, width and location of the cracks as they form. Fiber optics can directly detect cracks if they form within the path of a fiber optic as well as monitor secondary indicators of cracking such as temperature changes and strain. When cracks form in concrete waste disposal vaults they can fill with water which has a high heat capacity, this enables cracks to be observed by monitoring temperature variations near the crack. An analytical solution for heat transfer is applied to estimate the propagation of temperature waves around cracks. It is demonstrated that discharge rates through the concrete which are less than 10-5 m3/m-s do not produce a meaningful temperature wave through the concrete. Fractures in the concrete must be larger than 0.07 cm to produce a measurable result and temperature sensors must be located within 0.5 meters of a crack to detect a change in temperature produced by seasonal groundwater flow through a crack. A distributed system of fiber optic sensors may be embedded in the concrete vault and used to monitor crack formation, temperature variations and strain.