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DOE OSTI2019

Progress in Deep Geologic Disposal Safety Assessment in the U.S. since 2010

The Spent Fuel and Waste Science and Technology (SFWST) Campaign of the U.S. Department of Energy (DOE) Office of Nuclear Energy (NE), Office of Spent Fuel & Waste Disposition (SFWD) is conducting research and development (R&D) on geologic disposal of spent nuclear fuel (SNF) and high-level nuclear waste (HLW). Two high priorities for SFWST disposal R&D are design concept development and disposal system modeling (DOE 2011, Table 6). These priorities are directly addressed in the SFWST Geologic Disposal Safety Assessment (GDSA) work package, which is charged with developing a disposal system modeling and analysis capability for evaluating disposal system performance for nuclear waste in geologic media.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Development of a backfill material for LILW and HLW disposal galleries in the current Belgian geological disposal concept - 15374

In Belgium, it is planned to dispose of long-lived and high-level waste in an underground facility. After disposal of the waste, the galleries will be backfilled to provide stability to the galleries and to limit the amount of voids in the repository. To achieve those goals, the backfill material has to have a good flowability, a negligible bleeding, and a limited shrinkage. A limited grain size is also required to allow the injection of the backfill material. Despite the fact that the backfill supports the gallery lining, its strength must be low enough to enable the retrieval of the waste packages. The backfill material has to be chemically compatible with the Boom Clay and the waste packages. This means that it should not unduly perturb the clay or disposal packages. The thermal conductivity of the backfill material in the galleries containing high-level and thus heat-generating waste must be high enough to allow sufficient dissipation of the decay heat into the surrounding clay. Based on these objectives, material requirements were specified and the development of a backfill mixture was carried out. Initially, the mix composition was optimized in the laboratory. Thereafter, the backfill process of a gallery section was simulated. The investigations illustrate that this mixture can be transported via pipelines through the shaft and drifts and would fill completely the backfill sections in the galleries. Measurements of the porosity, the pore solution composition, the thermal material properties, and the strength illustrate the compliancies with the requirements and the feasibility of backfilling the disposal galleries. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Advances in Geologic Disposal System Modeling and Application to Crystalline Rock

The Used Fuel Disposition Campaign (UFDC) of the U.S. Department of Energy (DOE) Office of Nuclear Energy (NE), Office of Fuel Cycle Technology (OFCT) is conducting research and development (R&D) on geologic disposal of used nuclear fuel (UNF) and high-level nuclear waste (HLW). Two of the high priorities for UFDC disposal R&D are design concept development and disposal system modeling (DOE 2011). These priorities are directly addressed in the UFDC Generic Disposal Systems Analysis (GDSA) work package, which is charged with developing a disposal system modeling and analysis capability for evaluating disposal system performance for nuclear waste in geologic media (e.g., salt, granite, clay, and deep borehole disposal). This report describes specific GDSA activities in fiscal year 2016 (FY 2016) toward the development of the enhanced disposal system modeling and analysis capability for geologic disposal of nuclear waste. The GDSA framework employs the PFLOTRAN thermal-hydrologic-chemical multi-physics code and the Dakota uncertainty sampling and propagation code. Each code is designed for massively-parallel processing in a high-performance computing (HPC) environment. Multi-physics representations in PFLOTRAN are used to simulate various coupled processes including heat flow, fluid flow, waste dissolution, radionuclide release, radionuclide decay and ingrowth, precipitation and dissolution of secondary phases, and radionuclide transport through engineered barriers and natural geologic barriers to the biosphere. Dakota is used to generate sets of representative realizations and to analyze parameter sensitivity.

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DOE OSTI2016

Update on implementing geological disposal in the UK - 16266

For more than 60 years, Britain has been accumulating radioactive waste which is currently stored safely at over 20 sites around the country. Radioactive Waste Management (RWM) is responsible for making this waste even safer by disposing of it securely for the long term in a GDF. This paper provides an update on the implementation of the process for siting a Geological Disposal Facility (GDF) in the United Kingdom (UK) and the role of RWM as the developer in its implementation. The UK Government favours an approach for selecting a GDF site that is based on working in partnership with communities. In early 2013 when there were no longer any communities participating in the site selection process, the UK Government embarked upon a review to consider what lessons could be learned. Informed by this review the UK Government published in July 2014 a renewed approach to implementing geological disposal based on working with interested communities. The first two years of the programme comprises of initial actions overseen by Government recognising the need to provide additional information before the siting process is formally launched in 2017. (authors)

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DOE OSTI2012

EC MoDeRn Project: In-situ Demonstration of Innovative Monitoring Technologies for Geological Disposal - 12053

Monitoring to provide information on the evolution of geological disposal presents several challenges. The 4-year, euros M 5, EC MoDeRn Project (http://www.modern-fp7.eu/), which commenced in 2009, addresses monitoring processes, state-of-the-art technology and innovative research and development of monitoring techniques. This paper discusses some of the key drivers for the development of innovative monitoring techniques and provides outlines of the demonstration programmes being conducted within MoDeRn. The aim is to develop these innovative monitoring techniques and to demonstrate them under realistic conditions present in underground laboratories. These demonstration projects, applying a range of different monitoring techniques, are being carried out at underground research facilities in different geological environments at HADES URL in Belgium (plastic clay), Bure in France (indurated clay) and at Grimsel Test Site (granite) in Switzerland. These are either built upon existing infrastructure (EC ESDRED Low pH shotcrete and TEM experiments at Grimsel; and PRACLAY experiment and underground galleries in HADES) or will be attached to infrastructure that is being developed and financed by resources outside of this project (mock-up disposal cell in Bure). At Grimsel Test Site, cross-hole and hole-to-tunnel seismic methods are being employed as a means to monitor induced changes in an artificially saturated bentonite wall confined behind a shotcrete plug. Recognising the limitations for travel-time tomography for monitoring a disposal cell, full waveform inversion techniques are being employed to enhance the capacity to monitor remote from the excavation. At the same Grimsel location, an investigation will be conducted of the potential for using a high frequency wireless (HFW) sensor network embedded within the barrier system; this will include the possibility of providing energy remotely to isolated sensors. At the HADES URL, the monitoring programme will utilise the PRACLAY gallery equipped to simulate a disposal gallery for heat-generating high-level waste evaluating fibre-optic based sensing techniques, including distributed sensing for thermal distribution and long-term reliability in harsh conditions. It also includes the potential to improve the treatment of signals from micro-seismic monitoring to enable enhanced understanding of the evolution around the gallery following its excavation due to ventilation, saturation and heating, and to image a water-bearing concretion layer. HADES URL will also be used to test wireless techniques to transmit monitoring data from the underground to the surface. The main focus of this contribution is to evaluate magneto-inductive data transmission; and to optimise energy usage. At the Bure underground facility in France, monitoring systems have been developed and will be embedded into the steel liner for the mock-up high-level waste disposal tunnel. The aim of this programme is to establish the capacity to conduct integrated monitoring activities inside the disposal cell, on the cell liner and in the near-field and to assess the capability of the monitoring to withstand construction and liner emplacement procedures. These projects, which are supported by focused development and testing of the monitoring systems, will allow the testing of both the effectiveness of these techniques applied to disposal situations and to understand the limits of these monitoring technologies. This approach should also enhance the confidence of key stakeholders in the ability to understand/confirm the changes occurring within a disposal cell. In addition, remote or 'non-intrusive' monitoring technologies are evaluated to provide a means of enhancing understanding of what is occurring in an isolated disposal cell. The projects also test solutions for embedded monitoring systems in challenging (risk of damage) situations. The outputs from this work will lead to improved understanding of these state-of-the-art techniques and allow focused development of those techniques beneficial to future monitoring programmes. It is also planned, as part of the MoDeRn programme of stakeholder engagement to show some of these monitoring demonstrations to lay stakeholders in order to receive their feed-back on the approach taken and their views on the value of this work. This feedback will help improve our understanding of how this work and future work on monitoring can be more effectively communicated. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

French Geological Disposal Project: From Siting to Permitting - 19018

The future 'Cigeo' geological repository will be located in eastern France, at the border between the Meuse and Haute-Marne. Research has been carried out in this area since the 1990's, leading to the identification of a zone within the Paris basin whose geological characteristics make it suitable for the deep geological disposal of high- and intermediate-level long-lived radioactive waste, as well as a smaller zone of approximately 250 km{sup 2} (proposed in 2005) within which the characteristics of the host layer are very similar to those observed in the Underground Research Laboratory (URL). In 2010, based on additional surveys, a zone of approximately 30 km{sup 2} called ZIRA, in which the industrial underground facility would be constructed was defined. The repository structures within the ZIRA will be located at a depth of 525 metres. Half the surface area of the ZIRA is located in a wooded area, the other half being situated in grassland or farmland. All the subsequent design studies (preliminary and detailed) of Cigeo as well as the preparation of the licensing files (to be submitted in 2020) were conducted on the basis on this precise siting. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Optimization of Backfill Material Transport for the Future Belgian Geological Disposal Facility - 19071

In Belgium, long-lived, low- and intermediate level waste (B waste) will be conditioned in concrete monoliths B and high-level waste (C waste) in so-called Supercontainers (SC). It is planned to dispose of the waste packages in a Geological Disposal Facility (GDF). The B and C waste shall be disposed of each in one emplacement field at a depth between 200 m and 600 m below the surface. Two access galleries run through each field and connect the disposal galleries with a central shaft and support zone. After the emplacement of a specified number of waste packages, a stepwise backfilling of the voids is planned in order to stabilize the galleries, to limit the amount of voids, and to ensure a favourable chemical environment. Taking into account the objectives of backfilling and the specific material properties of the waste packages two mortars were developed to backfill the disposal galleries. In particular, for reasons of safety at work, the mortars should be hydraulically pumped through pipelines. Accordingly, in any case, it is necessary to operate storage facilities of the raw materials, a mix plant and a pump. The raw materials are foreseen to be supplied by trucks from external producers. Due to this fact, the better accessibility of the plants and with the aim of minimizing noise and dust emissions and the space for technical systems in the GDF, it is advisable to install the technical equipment above ground outside the GDF control area. However, the feasibility of this basic concept depends on the processing time of the backfill materials and the capacity of the transport system. Thus, although short transport times can theoretically be realized if pipelines with a small cross sections are chosen, in this case the required power of the pump increases significantly. If no suitable configuration can be found, the distance of the mixing and pumping system to the backfill segment has to be shortened. In this case a pneumatic conveyor system would have to be installed to transport the solids to a mix plant and pumping unit located in the underground galleries to be able to meet the desired backfill rates. In order to identify the optimum solution, the decision criteria and the advantages and disadvantages of existing and planned transport systems were evaluated. The investigations showed that it is technically feasible to pump the backfill material from above ground into the disposal galleries. As failures of the backfill system would result in interruptions of the general disposal operation, a redundant pump and pipeline system was developed. The two lines can be operated separately or simultaneously in order to realize high flow rates needed for the backfilling of segments far from the shaft. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

A Methodology for defining intermediate level waste package characteristics that ensure criticality safety in a geological disposal facility - 14599

Radioactive Waste Management (RWM) is responsible for implementing geological disposal of the UK's higher activity radioactive wastes. These wastes include fissile nuclides and, therefore, demonstration of the criticality safety of the wastes under disposal conditions forms an important component of RWM's disposal system safety case. The basis for ensuring criticality safety of intermediate level waste (ILW) packages is to specify controls on the fissile material content of individual packages through the application of deterministic criticality safety assessments (CSAs). The approach is defined and controlled through RWM's Disposability Assessment process, which aims to ensure that: criticality is prevented during waste package transport to a GDF; the risk of criticality is tolerable and as low as reasonably practicable (ALARP) during GDF operations; and the likelihood and consequences of criticality arising from the evolution of waste packages after GDF closure are low. The most restrictive phase determines the package fissile material limit and, until now, in many cases the GDF post-closure phase has provided the most restrictive limit. Currently, the GDF post-closure limits are derived deterministically using highly stylised and conservative assumptions about fissile material accumulations occurring on very long timescales into the future. RWM, waste producers and regulators do not currently consider this approach to be yielding an appropriate balance of risk. Therefore, RWM is modifying the process for setting fissile material limits on ILW packages by making use of the outcomes of its recent research projects to establish the likelihood of post-closure criticality in a GDF and the consequences of hypothetical post-closure criticality events (presented in companion papers). This paper presents the revised methodology, which is based on the requirement that criticality in a GDF can be demonstrated to be of low and tolerable consequences with regard the performance of a GDF. A probabilistic 'low-likelihood package envelope' is proposed that establishes the packaging and disposal facility conditions under which post-closure criticality is considered to be of low likelihood and low consequence. The bounding conditions for establishing the extent of the package envelope have been evaluated through application of the methodologies and models developed in RWM's Likelihood of Criticality research project. It is expected that the vast majority of ILW packages would meet the package envelope requirements. The methodology also allows the use of other options, such as deterministic CSAs, for waste packages that fall outside the low-likelihood package envelope. (authors)

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DOE OSTI2018

Global Review of Site Suitability Conditions for the Geological Disposal of Radioactive Waste - 18136

The long-term safety of radioactive waste disposal is based on two key principles: (i) containment of the waste until the radioactivity has decreased to negligible levels, and (ii) the isolation of the waste packages in stable conditions that are conducive to maintaining the integrity of the containment for as long as required. In this paper, we review disposal site suitability criteria based on international best practices from geological disposal studies in crystalline and argillaceous rocks. Adopting social acceptability criteria in addition to safety-related criteria has been shown to be pivotal in obtaining community support. The reviewed criteria may be used as a guide to develop future site selection criteria for disposal of Australian intermediate level waste streams that are incompatible with surface disposal. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Backfilling of Geological Disposal Facilities - Development of Optimized Backfill Material - 18146

In Belgium, low- and intermediate-level waste (B-waste) will be conditioned in concrete monoliths and high-level waste (C-waste) in so-called Super-containers (SCs). The Belgian radioactive waste management program has focused on the disposal of these waste types in two emplacement fields of a geological disposal facility (GDF). When the disposal waste packages (DWP) have been emplaced, backfilling of the galleries is supposed to be carried out in order to stabilize the galleries, to reduce voids, to guarantee a favourable chemical milieu with regard to the retention of the radionuclides, to minimize a possible gas pressure build-up, to dissipate radioactive decay heat and to enable good conditions for a potential retrieval of the DWP. The current reference solution is to mix the backfill at the surface and then to pump the mixture through pipeline distribution systems into the underground structures. The catalogue of backfill material requirements comprises common, but also different requirements due to the characteristics of the B and C waste packages and differences in the backfilling systems. It was found that two backfill material recipes have to be developed. Different requirements, such as high porosity (low strength and low gas threshold pressure) and high thermal conductivity have contrary consequences for the material. In addition, during backfill production quality variations of the raw materials that influence the backfill material properties can occur. Different lengths of the delivery pipeline may require adjustments of the material composition. In order to consider the practical experiences of backfill material production, one focus of the development programs was to identify compositional ranges that guarantee the respective material property. A combination of the individual 'conformity fields' results in optimal solutions for the standard operating conditions as well as a compositional range that guarantees compliance with the required material specifications. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Advances in Geologic Disposal System Modeling and Shale Reference Cases

The Spent Fuel and Waste Science and Technology (SFWST) Campaign of the U.S. Department of Energy (DOE) Office of Nuclear Energy (NE), Office of Fuel Cycle Technology (OFCT) is conducting research and development (R&D) on geologic disposal of spent nuclear fuel (SNF) and high level nuclear waste (HLW). Two high priorities for SFWST disposal R&D are design concept development and disposal system modeling (DOE 2011, Table 6). These priorities are directly addressed in the SFWST Generic Disposal Systems Analysis (GDSA) work package, which is charged with developing a disposal system modeling and analysis capability for evaluating disposal system performance for nuclear waste in geologic media (e.g., salt, granite, shale, and deep borehole disposal).

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2013

An integrated approach to geological disposal of UK wastes containing carbon-14

Carbon-14 is a key radionuclide in the assessment of the safety of a geological disposal facility for radioactive waste because of the calculated assessment of the radiological consequences of gaseous carbon-14 bearing species [i]. It may be that such calculations are based on overly conservative assumptions and that better understanding could lead to considerably reduced assessment of the radiological consequences from these wastes. Alternatively, it may be possible to mitigate the impact of these wastes through alternative treatment, packaging or design options. The Radioactive Waste Management Directorate of the UK's Nuclear Decommissioning Authority (NDA RWMD) has established an integrated project team in which the partners are working together to develop a holistic approach to carbon-14 management in the disposal system [ii]. For a waste stream containing carbon-14 to be an issue: There must be a significant inventory of carbon-14 in the waste stream; and That waste stream has to generate carbon-14 bearing gas; and a bulk gas phase has to entrain the carbon-14 bearing gas: and these gases must migrate through the engineered barriers in significant quantities; and these gases must migrate through the overlying geological environment (either as a distinct gas phase or as dissolved gas); and these gases must interact with materials in the biosphere (i.e. plants) in a manner that leads to significant doses and risks to exposed groups or potentially exposed groups. The project team has developed and used this 'and' approach to structure and prioritise the technical work and break the problem down in a manageable way. We have also used it to develop our approach to considering alternative treatment, packaging and design options. For example, it may be possible to pre-treat some wastes to remove some of the inventory or to segregate other wastes so that they are removed from any bulk gas phase which might facilitate migration through the geosphere. Initially, the project team has undertaken a six month programme of work to examine the current understanding of these aspects and has captured this in the Phase 1 report [ii], in a modelling basis spreadsheet and in scoping assessments, which help us better understand the potential significance of carbon-14. Using the current modelling basis, but ignoring any potential benefits from the geosphere in retarding or preventing gas from reaching the surface, the calculated release of carbon- 14 is dominated by: corrosion of irradiated reactive metals (in the operational and early post-closure time frame); corrosion of irradiated stainless steel and leaching of irradiated graphite (in the longer term). The Phase 1 work has shown that there is considerable scope for reducing the calculated radiological consequence for these wastes and a roadmap has been developed for a second Phase of work. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Draft Geologic Disposal Requirements Basis for STAD Specification

This document provides the basis for requirements in the current version of Performance Specification for Standardized Transportation, Aging, and Disposal Canister Systems, (FCRD-NFST-2014-0000579) that are driven by storage and geologic disposal considerations. Performance requirements for the Standardized Transportation, Aging, and Disposal (STAD) canister are given in Section 3.1 of that report. Here, the requirements are reviewed and the rationale for each provided. Note that, while FCRD-NFST-2014-0000579 provides performance specifications for other components of the STAD storage system (e.g. storage overpack, transfer and transportation casks, and others), these have no impact on the canister performance during disposal, and are not discussed here.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2012

Development of Wireless Data Transmission System for the Monitoring in Geological Disposal of Radioactive Waste - 12063

The authors have been developing a wireless data transmission system to monitor the performance of a geological disposal system for radioactive waste. The system's concepts, advantages, and a recent development focused on reducing transmitter size to suit narrow spaces such as bentonite buffers and boreholes. A wireless transmitter with a built-in temperature sensor and a connector for external sensors has been developed, measuring 130 mm in length and 50 mm in diameter. The capability of the transmitter was confirmed by transmission tests on the ground and in a bentonite block. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2013

Radioactive waste management: the relation between geological disposal and advanced nuclear technologies

Throughout this paper we aim to scope the most pregnant themes, issues and research questions concerning the relation between geological disposal and advanced nuclear technologies in the broad context of radioactive waste management. Especially from a socio-technical point of view the mutual impacts, divergences and complementarities between both strategies seem to have received limited dedicated examination up until today. Specific attention is paid to the main arguments that seem to underpin both research streams, related to how the issue of radioactive waste is contextualized and which problems and solutions are consequently identified and proposed. Ultimately we aim to encourage scientifically integer communication and constructive dialogue between both fields, to investigate the common possibilities of enhancing radioactive waste management as a whole. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

The role of international collaboration in the United States geologic disposal research program

Abstract. More than a decade ago, the United States disposal program discontinued all research activities focused on the unsaturated fractured tuff formation at Yucca Mountain as the geologic disposal site for spent fuel and high-level radioactive waste. A new research and development (R&D) program was initiated to provide a sound technical basis for alternative disposal options across clay, crystalline, and salt rocks. The goals of this broad program were (and still are) to (1) increase confidence in the robustness of generic disposal concepts, (2) develop the science and engineering tools needed to support disposal concept implementation, and (3) conduct R&D on the direct disposal of existing dual-purpose (storage and transportation) canisters. Recognizing the benefits of international collaboration toward the common goal of safely and efficiently managing the back end of the nuclear fuel cycle, the program emphasized international cooperation as an effective strategy for sharing information and knowledge. In a multi-laboratory effort coordinated by Lawrence Berkeley National Laboratory, the United States Department of Energy (DOE) program established formal and informal cooperation partnerships with several international initiatives and institutions and developed a number of collaborative R&D activities in important research areas, such as engineered barrier integrity, near-field perturbations, radionuclide transport, performance assessment, and methods for characterization and monitoring of engineered and natural barriers. This presentation gives an overview of these R&D activities, with a specific focus on activities that improve our current understanding of the coupled thermal–hydrological–mechanical–chemical (THMC) processes occurring in engineered and natural barriers. We start with a brief review of selected international collaboration initiatives and then describe a few specific collaboration projects. We focus specifically on such studies that use experimental data sets provided by international research cooperation for joint modeling work to increase confidence in performance-relevant predictions of coupled processes. Overall, the focus on international collaboration has allowed deep engagement of US researchers with the international waste management R&D community in terms of best practices, new scientific advances, state-of-the-art simulation tools, new monitoring and performance confirmation approaches, and lessons learned. The joint R&D with international researchers, worldwide sharing of knowledge and experience, and access to relevant data and experiments from a variety of host rocks have helped our researchers to significantly improve their understanding of the current technical basis for disposal in a range of potential host rock environments. International collaboration also provides ample opportunity for training and educating junior staff that are well suited to move the United States disposal research program forward into the next decades, a promising avenue for developing a next-generation workforce of disposal scientists.

Birkholzer, Jens T.↗