EBS Behaviour Immediately After Repository Closure in a Clay Host Rock: The HE-E Experiment (Mont Terri URL)

The evolution of the engineered barrier system (EBS) of geological repositories for radioactive waste has been the subject of many research programmes during the last decade. The emphasis of the research activities was on the elaboration of a detailed understanding of the complex thermo-hydro-mechanical-chemical processes, which are expected to evolve in the early post closure period in the near field. It is important to understand the coupled THM-C processes and their evolution occurring in the EBS during the early post-closure phase so it can be confirmed that the safety functions will be fulfilled. Especially, it needs to be ensured that interactions during the resaturation phase (heat pulse, gas generation, non-uniform water uptake from the host rock) do not affect the performance of the EBS in terms of its safety-relevant parameters (e.g. swelling pressure, hydraulic conductivity, diffusivity). The 7th Framework PEBS project (Long Term Performance of Engineered Barrier Systems) aims at providing in depth process understanding for constraining the conceptual and parametric uncertainties in the context of long-term safety assessment. As part of the PEBS project a series of laboratory and URL experiments are envisaged to describe the EBS behaviour after repository closure when resaturation is taking place. In this paper the very early post-closure period is targeted when the EBS is subjected to high temperatures and unsaturated conditions with a low but increasing moisture content. So far the detailed thermo-hydraulic behaviour of a bentonite EBS in a clay host rock has not been evaluated at a large scale in response to temperatures of up to 140°C at the canister surface, produced by HLW (and spent fuel), as anticipated in some of the designs considered. Furthermore, earlier THM experiments have shown that upscaling of thermal conductivity and its dependency on water content and/or humidity from the laboratory scale to a field scale needs further attention. This early post-closure thermal behaviour will be elucidated by the HE-E experiment, a 1:2 scale heating experiment setup at the Mont Terri rock laboratory, that started in June 2011. It will characterise in detail the thermal conductivity at a large scale in both pure bentonite as well as a bentonite-sand mixture, and in the Opalinus Clay host rock. The HE-E experiment is especially designed as a model validation experiment at the large scale and a modelling programme was launched in parallel to the different experimental steps. Scoping calculations were run to help the experimental design and prediction exercises taking the final design into account are foreseen. Calibration and prediction/validation will follow making use of the obtained THM dataset. This benchmarking of THM process models and codes should enhance confidence in the predictive capability of the recently developed numerical tools. It is the ultimate aim to be able to extrapolate the key parameters that might influence the fulfilment of the safety functions defined for the long term steady state.

Modeling of Alteration Behavior on Blended Cementitious Materials

A “realistic alteration model” is needed for various cementitious materials. Hypothetical settings of mineral composition calculated based on the chemical composition of cement, such as Atkins’s model, have been used to estimate the alteration of cementitious material. However, model estimates for the concentration of certain elements such as Al and S in leachate have been different from experimental values. In a previous study, we created settings for a mineralogical alteration model by taking the initial chemical composition of cementitious materials from analysis results in experiments and applying their ratios to certain hydrated cement minerals, then added settings for secondary generated minerals in order to account for Ca leaching. This study of alteration estimates for ordinary portland cement (OPC) in groundwater showed that the change in Al and S concentrations in simulated leachate approached values for actual leachate[1]. In the present study, we develop an appropriate mineral alteration model for blended cementitious materials and conduct batch-type leaching experiments that use crushed samples of blast furnace slag cement (BFSC), silica cement (SC), and fly ash cement (FAC). The cement blends in these experiments used OPC blended with blast furnace slag of 70 wt.%, silica cement consisting of an amorphous silica fine powder of 20 wt.%, and fly ash of 30 wt.%. De-ionized water was used as the leaching solution. The solid-liquid ratios in the leaching tests were varied in order to simulate the alteration process of cement hydrates. The compositions of leachate and minerals obtained from leaching tests were compared with those obtained from models using hypothetical settings of mineral composition. We also consider an alteration model that corresponds to the diversity of these materials. As a result of applying the conventional OPC model to blended cementitious materials, the estimated Al concentration in the aqueous solution was significantly different from the measured concentration. We therefore propose an improved model that takes better account of Al behavior by using a more reliable initial mineral model for Al concentration in the solution.

An Assessment of the Radiological Impact of Human Intrusion at the UK Low Level Waste Repository (LLWR)

The UK Low Level Waste Repository Ltd submitted an Environmental Safety Case for the disposal of low-level waste (LLW) to the Environment Agency on the 1st of May 2011. The Environmental Safety Case (ESC) presents a complete case for the environmental safety of the Low Level Waste Repository (LLWR) both during operations and in the long term (Cummings et al, in these proceedings). This includes an assessment of the long-term radiological safety of the facility, including an assessment of the potential consequences of human intrusion at the site. The human intrusion assessment is based on a cautiously realistic approach in defining intrusion cases and parameter values. A range of possible human intrusion events was considered based on present-day technologies and credible future uses of the site. This process resulted in the identification of geotechnical investigations, a housing development and a smallholding as requiring quantitative assessment. A particular feature of the site is that, because of its proximity to the coast and in view of expected global sea-level rise, it is vulnerable to coastal erosion. During such erosion, wastes and engineered barrier materials will be exposed, and could become targets for investigation or recovery. Therefore, human intrusion events have been included that are associated with such activities. A radiological assessment model has been developed to analyse the impacts of potential human intrusion at the site. A key feature of the model is the representation of the spatial layout of the disposal site, including the engineered cap design and the large-scale spatial heterogeneity of radionuclide concentrations within the repository. The model has been used to calculate the radiation dose to intruders and to others following intrusion at different times and at different locations across the site, for the each of the selected intrusion events, considering all relevant exposure modes. Potential doses due to radon and its daughters in buildings constructed on excavated spoil from the repository are a particular concern. Options for managing the emplacement of the radium-bearing waste packages with regard to human intrusion have been assessed. These calculations show that a managed waste emplacement strategy can ensure that calculated doses are consistent with regulatory guidance levels.

Adsorption of Cesium Radionuclides by the Composite Sorbents Carbon Fiber/Transition Metals Ferrocyanides

Among various methods of cesium removal from aqueous solutions, sorption using transition metals ferrocyanides is the most efficient method due to extremely high affinity of cesium ions to ferrocyanides. The efficiency of transition metals ferrocyanides application is known to depend on the crystal size being the highest for nanocrystals. Although nanocrystals are difficult to handle in direct application, they can be used in composite materials. In this case two main problems arise: how to control the crystal size of transition metals ferrocyanides and fix them reliably in the supporting matrix. Here we suggest a new route to preparation of composite materials selective to cesium ions using transition metals ferrocyanides stabilized by siloxane-acrylate latexes. The size of transition metals ferrocyanides is controlled by the size of latex particles and their stability is determined by ionization of polyacrylic acid carboxylic groups on the functionalized latex surface. These functionalized particles can be used as precursors in preparation of composite materials by sedimentation and polymerization of latexes on the solid surface of porous matrix, e.g. carbon fibers. Several routes of preparation of carbon fiber based composite materials using functionalized latexes and sorption properties of the obtained materials are discussed. The effect of preparation conditions (method used, carbon fiber polarization potential, concentration of latexes functionalized with transition metals ferrocyanides) on cesium uptake by composite sorbents from solutions of various salinity is reported.

Groundwater Remediation of Hexavalent Chromium Along the Columbia River at the Hanford Site in Washington State, USA

The U.S. Department of Energy Hanford Site, formerly used for nuclear weapons production, encompasses 1500 square kilometers in southeast Washington State along the Columbia River. A principle threat to the river are the groundwater plumes of hexavalent chromium (Cr(VI)), which affect approximately 9.8 square kilometers, and 4.1 kilometers of shoreline. Cleanup goals are to stop Cr(VI) from entering the river by the end of 2012 and remediate the groundwater plumes to the drinking water standards by the end of 2020. Five groundwater pump-and-treat systems are currently in operation for the remediation of Cr(VI). Since the 1990s, over 13.6 billion L of groundwater have been treated; over 1,435 kg of Cr(VI) have been removed. This paper describes the unique aspects of the site, its environmental setting, hydrogeology, groundwater-river interface, riverine hydraulic effects, remediation activities completed to date, a summary of the current and proposed pump-and-treat operations, the in situ redox manipulation barrier, and the effectiveness of passive barriers, resins, and treatability testing results of calcium polysulfide, biostimulation, and electrocoagulation, currently under evaluation.

Mitigation of Sliding Motion of a Cask-Canister by Fluid-Structure Interaction in an Annular Region

The cask-canister system is a coaxial circular cylindrical structure in which several spent fuels are installed. This system is a free-standing structure thus, it is very important to reduce sliding motion for very large seismic excitations. In this study, we propose a mitigation method for sliding motion. Water is installed in an annular region between a cask and a canister. The equations of motion are derived taking fluid-structure interaction into consideration for nonlinear sliding motion analyses. Based on these equations, mitigation effects of sliding motions are studied analytically. Furthermore, a fundamental test model of a cask-canister system is fabricated and shaking table tests are conducted. From the analytical and test results, sliding motion mitigation effects are investigated.

Advanced Simulation Capability for Environmental Management (ASCEM)

The United States Department Energy (DOE) Office of Environmental Management (EM) determined that uniform application of advanced modeling in the subsurface could help reduce the cost and risks associated with its environmental cleanup mission. In response to this determination, the EM Office of Technology Innovation and Development (OTID), Groundwater and Soil Remediation (GW&S) began the program Advanced Simulation Capability for Environmental Management (ASCEM). ASCEM is a state-of-the-art scientific tool and approach for integrating data and scientific understanding to enable prediction of contaminant fate and transport in natural and engineered systems. This initiative supports the reduction of uncertainties and risks associated with EM’s environmental cleanup and closure programs through better understanding and quantifying the subsurface flow and contaminant transport behavior in complex geological systems. This involves the long-term performance of engineered components, including cementitious materials in nuclear waste disposal facilities that may be sources for future contamination of the subsurface. This paper describes the ASCEM tools and approach and the ASCEM programmatic accomplishments completed in 2010 including recent advances and technology transfer.

Set Up of an Environmental Monitoring System, Shchuchye, Russia Technical Assistance

An intergovernmental agreement on cooperation about chemical weapon destruction was signed between France and the Russian federation on 14th February 2006 in the context of a Global Partnership dedicated to preventing catastrophic terrorism and the proliferation of weapons of mass destruction. It came into effect on 25th April 2007 after ratification by both countries. The present demonstrated project was launched as part of this collaboration on the Shchuchye site (Russia – Kurgan Oblast). The project concerned the environmental surveillance system for the Shchuchye site required for the safe operation of the installation used to destroy chemical weapons. The aim was to implement equipments and methods of analysis for very low concentrations of pollutants in the three environmental compartments: air, water and soil. This has been achieved with the help of industry and other organizations in France (Environment/SA for supplies, INERIS and Antea Group) and Russia (ROST Association and EKROS Engineering). This system takes account of the normal operation of the installation as well as incident management. It includes 11 stationary atmospheric measuring stations constructed by Environment/SA and EKROS Engineering including ASTEK dedicated toxic gas detector: “Terminator FOV-1”, 3 mobile atmospheric measuring stations, 2 mobile soil & water measuring stations, 4 sampling cars constructed by Environment/SA and EKROS Engineering, a complete Chemical analysis laboratory which can handle ppb analysis of toxic gases, organics and minerals pollutants, an information collection center and a meteo station which can retrieve, display and archive all the datas or alarm from the stationary and mobile stations. Antea Group has provided a technical expertise and various negotiations during the negotiation phase, the project initiation files & contracts redaction, the project Monitoring and reporting to stakeholders, the REX. Up to 2009, No other site of the world uses such an innovative system. Antea Group worked on this project for 4 years. It successfully began operating in March 2009, before the start of destruction operations, after 15 months of work on the site.

An Innovative Process for Segmenting of Guide Tubes

The purpose of this paper is to describe an innovative process for segmenting PWR Guide Tubes (GT’s) and the service (training and execution) that can be performed successfully and safely. Over time, some utilities are replacing control rod GT’s and store them in temporary disposal facilities. Due to lack of space, as the case for the BCOT (EDF – France / Tricastin), it is sometimes needed to cut and condition them in waste packages for final disposal and waste treatment. Based on its experience, Westinghouse has recently developed a complete solution for cutting and consolidating GT’s. One of the challenges related to such equipment is to consider two routes for the waste management: one for the activated segments and another for the less activated segments. Depending on the regulation and of the storage acceptance criteria’s, the length of the segments has been defined to minimize the volume of highly activated waste and therefore develop a process which is adapted to the size of containers specified by the customer. A model with five cutting operations and generating six segments has been chosen. In order to minimize risks and ensure safety for personnel and facilities, radiological studies were performed for various configurations. All cutting techniques previously used by Westinghouse in similar applications have been evaluated. Underwater mechanical cutting with a band saw has been selected.

Measurement Methodology for Fulfilling of Waste Acceptance Criteria for Low and Intermediate Level Radioactive Waste in Storages

Low and intermediate level radioactive waste must be sorted and treated before it can be sent to radioactive waste storage. The waste must fulfil an extensive amount of acceptance criteria (WAC) to guarantee a safe storage period. NUKEM Technologies has a broad experience with the building and management of radioactive waste treatment facilities and has developed methods and equipment to produce the waste packages and to gather all the required information.