Management of sorption data to support radioactive waste disposal

The geological disposal of higher activity radioactive wastes is internationally accepted as a safe, permanent solution. Work to implement this solution is progressing in many countries, involving national and international programmes that bring together technical, social, scientific and engineering considerations to advance subject matter understanding, enhance experience and broaden knowledge bases. This Special Publication collates research outputs from site investigations, advances in technology, experimental studies and modelling activities relevant to radioactive waste disposal. The sixteen papers report research undertaken on a variety of topics, including knowledge management, engineered barrier design and geological investigation studies, as well as contributions that consider how disposed waste and multiple barriers of geological disposal facilities evolve on prolonged timescales. The papers reflect the breadth and depth of scientific research activities contributing to radioactive waste disposal.

19 - Application of knowledge management systems for safe geological disposal of radioactive waste

자연유사연구는 방사성폐기물의 지하 처분에서 안전성평가를 포함하는 다중의 안전성 확보를 요구하는 safety case에서 중요한 역할을 담당하고 있다. 본 연구에서는 해외의 자연유사연구 동향을 조사하여, 처분장 재료물질들과 핵종이동 및 지연과 관련된 자연유사연구 결과들을 연구주제별로 정리하고, 주요 연구결과와 문제점, 결과의 활용성 등에 초점을 두고 분석하였다. 아울러 국내에서 수행된 자연유사연구 결과들을 우라늄 광상 연구, 암반을 이용한 연구, 지하수를 이용한 연구, 고고학적 유물을 이용한 연구 등으로 분류하고, 그 주요 결과들을 정리하였다. 지난 수 십 년 동안 수행되어 온 방대한 양의 자연유사연구 결과들이 존재하지만, 처분안전성 평가와 safety case 개발에 적극적으로 활용되지 못하였다. 따라서 본 연구에서는 자연유사연구 결과의 활용방법을 정리하고, 활용성을 증진하기 위한 방법론을 검토하였다. 방사성폐기물 처분장에 대한 안전성 평가의 신뢰성을 증진하고 검증하기 위해서는 자연유사연구의 수행은 필수적이다. 따라서 자연유사연구 결과들을 safety case 개발에 활용하기 위해서는 자연유사 정보 데이터베이스의 구축과 함께 활용방법론이 개발되어야 할 필요가 있다. Natural analogue studies play an important role in the safety case which requires multiple lines of evidence including the safety assessment for the geological disposal of radioactive wastes. In this study, foreign status of natural analogue studies was investigated by summarizing natural analogue results according to the research topics related with repository materials and radionuclide migration and retardation. Main results, issues, and applicability of the foreign natural analogue studies were also analyzed. The results of domestic natural analogue studies were classified into studies using uranium ore bodies, rocks, groundwaters, and archeological artifacts, respectively, and their main results were summarized. There are massive materials for natural analogue studies which have been carried out during last several decades but they have not been actively applied to the safety assessment and safety case development for the radioactive waster disposal. Thus, in this study, applicable methods of natural analogues were summarized and a methodology for improving their applicability was examined. Natural analogue study is apparently necessary to improve and illustrate the reliability of safety assessment for a radioactive waste repository. Therefore, it is necessary to develop a methodology and construct a natural analogue information database for the application of the results from natural analogue studies to safety case development.

A major concern in the geological containment of radioactive wastes is the speed of movement of radionuclides from the repository, after their eventual leaching and release, into the geosphere and finally into the biosphere. Radionuclide sorption onto the host rock is an important retarding mechanism. Experimental evidence shows that the presence of microbes in this environment influences the sorption capabilities of the host rock. Their presence can decrease the amount of retardation of137Cs, a common radionuclide in radioactive waste, by the solid phase. Sorption methods and data analysis procedures are presented and the implications for radioactive waste disposal assessments are discussed.

Guidelines for thermodynamic sorption modelling in the context of radioactive waste disposal

The Royal Society of Chemistry, the Geological Society, the Institution of Civil Engineers, the Nuclear Institute, the Institution of Chemical Engineers, the Royal Academy of Engineering and the Mineralogical Society organized a wide-ranging conference themed around the geological disposal of radioactive waste from 18th–20th October 2011 at the Burleigh Court Conference Centre, Loughborough University, Loughborough, UK. One of its principal objectives was to showcase and publish research relevant to radioactive waste storage and disposal. The event was supported by the Nuclear Decommissioning Authority (NDA) and the Energy Generation and Supply Knowledge Transfer Network (KTN) for the Nuclear Sector, and kindly sponsored by AMEC and the National Nuclear Laboratory (NNL). The conference brought together scientists, engineers and other interested specialists to discuss the chemical, biological, geological, hydrological, materials, engineering and other scientific and technological challenges associated with the long-term management of radioactive waste in the UK. The scientific committee peer-reviewed all abstracts received prior to the conference, and determined those best for oral and poster presentation. Papers presented in this issue of Mineralogical Magazine were subsequently subjected to a detailed and independent peer-review process. The organizing committee consisted of Nick Evans (chair), Loughborough University; Katherine Morris, The University of Manchester; Neil Smart and Gordon Turner, Nuclear Decommissioning Authority; Nic Bilham, Geological Society; Glen Owen, Institution of Civil Engineers; Claire Gallery-Strong, Nuclear Institute; Sam Shaw, Mineralogical Society; Steve Lancaster, Royal Society of Chemistry; Richard Ploszek, Royal Academy of Engineering; and Richard Shaw, British Geological Survey. The organizing committee would like to place on record its thanks to the sponsors (see back cover) and exhibitors. The conference was organized in thematic sessions and this volume is presented in the same manner. Each of the sections begins with a peer-reviewed paper from the NDA outlining its view on the state-of-the-art in …

Uranium is typically the most abundant radionuclide by mass in radioactive wastes and is a significant component of effluent streams at nuclear facilities. Actinide(IV) (An(IV)) colloids formed via various pathways, including corrosion of spent nuclear fuel, have the potential to greatly enhance the mobility of poorly soluble An(IV) forms, including uranium. This is particularly important in conditions relevant to decommissioning of nuclear facilities and the geological disposal of radioactive waste. Previous studies have suggested that silicate could stabilize U(IV) colloids. Here the formation, composition, and structure of U(IV)-silicate colloids under the alkaline conditions relevant to spent nuclear fuel storage and disposal were investigated using a range of state of the art techniques. The colloids are formed across a range of pH conditions (9-10.5) and silicate concentrations (2-4 mM) and have a primary particle size 1-10 nm, also forming suspended aggregates <220 nm. X-ray absorption spectroscopy, ultrafiltration, and scanning transmission electron microscopy confirm the particles are U(IV)-silicates. Additional evidence from X-ray diffraction and pair distribution function data suggests the primary particles are composed of a UO2-rich core and a U-silicate shell. U(IV)-silicate colloids formation correlates with the formation of U(OH)3(H3SiO4)32- complexes in solution indicating they are likely particle precursors. Finally, these colloids form under a range of conditions relevant to nuclear fuel storage and geological disposal of radioactive waste and represent a potential pathway for U mobility in these systems.

Some types of radioactive waste remain hazardous for thousands of years. Disposal of this long-lived waste in stable geological formation is the best thinkable solution according to the current state of technology and science. This is done by placing packages with radioactive waste in an underground facility, hundreds of metres below the land surface. After closure of a facility, isolation of the waste and containment of the radionuclides are achieved by a disposal system consisting of engineered barriers, the geological formation and surrounding rock formations. This geological disposal of radioactive waste has been studied in the Netherlands for more than four decades. Permian and Triassic rock salt formations are investigated since a facility can be constructed in this rock and its ultralow permeability ensures containment of radionuclides. Upward movement of salt (diapirism) and dissolution due to groundwater flow (subrosion), however, can disrupt the key aspects of rock salt. These natural processes are studied to assess the likelihood of radionuclides from the waste to enter the biosphere. The suitable disposal depth is determined by considering plausible natural processes, such as climate change (including ice ages) that in the future may interfere with underground disposal sites. Paleogene clay formations are an alternative rock type for the disposal of radioactive waste. New techniques have become available to construct underground facilities in these low-permeability argillaceous sediments. Emphasis is now put on obtaining freshly cored material at suitable disposal depths to gain further knowledge on the geotechnical properties of these clays.

Diffusion and sorption of radionuclides in potential host rocks are key processes controlling the safe geological disposal of radioactive waste. To set reliable parameters of diffusion and sorption relevant to safety assessment, it is necessary to understand these processes under laboratory and in situ conditions, and to confirm the consistency or the relationship of these parameters (D e and K d ) between both conditions. This paper focused on comparative experiments and modeling of diffusion and sorption of Cs for both in situ and laboratory conditions in siliceous mudstone in the 350 m Gallery at the Horonobe Underground Research Laboratory (URL) in northern Hokkaido, Japan. The D e values for Cs were consistent between in situ and laboratory results, indicating typical cation excess and porewater salinity effects. The effect of the diffusion direction, parallel or perpendicular to the bedding plane was not significant. The K d values for Cs were also consistent between in situ and laboratory results, indicating the porewater salinity effect. The clay-based modeling approach, which accounts for the major contributions of clay minerals through cation excess diffusion by electrostatic interaction at the clay surface, and the component additive cation exchange reactions, could interpret the diffusion and sorption behaviors of Cs under different salinity conditions and for both in situ and laboratory conditions.

The option of disposing of radioactive waste deep underground has been studied in Belgium by SCK CEN since the 1970s. This led in 1980 to the construction of the HADES underground research laboratory (URL) in a clay formation, the Boom Clay, at a depth of 225 m under the premises of SCK CEN in Mol. Over the last four decades, many in situ experiments have been conducted in the HADES URL. These have made a significant contribution to ONDRAF/NIRAS’ research, development and demonstration (RD&amp;D) efforts demonstrating that disposal in Boom Clay can offer a safe solution for the long-term management of high-level and/or long-lived radioactive waste. Moreover, the construction of the HADES URL itself is a demonstration that shafts and galleries can be constructed in clay at that depth. However, the HADES URL did not only contribute to the Belgian programme. Many of the in situ experiments have been part of international research and the laboratory has provided valuable input to the research programmes of other URLs, such as the Meuse/Haute-Marne URL in France and the Mont Terri rock laboratory in Switzerland. This paper gives a brief overview of the main contributions of the HADES URL to both national and international research into geological disposal.

ABSTRACT: The groundwater flow in rock fractures and the chemical dissolution of rock minerals, which are greatly affected by the confining pressure and temperature, are important issues in the geological disposal of radioactive waste and geothermal studies. In order to investigate the long-term deformation and permeability of rock fractures, the authors conducted long-term permeability tests using a granite specimen with a single split fracture, with parameters of confining pressure and temperature. The saturated specimen was subjected to confining pressure of 3 MPa at 20°C for more than six months, and then the temperature was raised to 60°C. Microfocus X-ray computed tomography (CT) images were taken at predetermined times. The results showed that the CT values inside the fracture rapidly increased with time for 60 days at 20°C and 3 MPa, and then became stable. However, after the temperature was raised to 60°C, the CT values started to increase again. This evolution in the CT values implies pressure solution at the fracture interface due to the long-term confining pressure and temperature. 1. INTRODUCTION The groundwater flow in rock fractures and the chemical dissolution of rock minerals, which are greatly affected by the confining pressure and temperature, are important issues in studies on the geological disposal of radioactive waste (Tsang et al. 2012; Watson et al. 2018), enhanced geothermal systems (EGS) (Pruess 2006; Gerber and Marechal 2012), and petroleum extraction (Chen and Spiro 1994; Gan et al., 2009). In order to investigate the long-term deformation and permeability of rock fractures, the authors conducted long-term permeability tests using a granite specimen with a single split fracture, with parameters of confining pressure and temperature (Song et al. 2021). The saturated specimen was subjected to confining pressure of 3 MPa at 20°C for more than six months, and then the temperature was raised to 60°C. The results revealed that the permeability measured in the short-term tests showed reversible behavior and a dependence on the applied confining pressure and temperature. In contrast, the permeability measured in the long-term tests displayed irreversible behavior and an irregular change under constant confining pressure. In the experiment, microfocus X-ray computed tomography (CT) images were taken at predetermined times to observe the changes in the internal fracture structure.

The investigation of sprayed clay technology has been underway at the Josef Underground Laboratory for a number of years. This technology was developed principally with respect to the backfilling of shafts and galleries in deep repositories providing access to disposal wells containing high-level long-lived radioactive waste. At present research is being focused on the use of this technology to fill the space between the spent fuel container and the wall of the disposal well. This paper describes experience gained from the various stages of the research including the selection of a suitable spray material and the testing and modification of the equipment employed and presents the results of a selection of shot clay mixture tests. ARTICLE INFO

In France, it is planned to manage high-level radioactive waste via deep geological disposal. The carbon steel overpacks containing the waste will face corrosion processes specific to the unusual environment of the disposal. To protect these overpacks against corrosion, the use of metallic sacrificial coatings was considered as a possible solution. Therefore, the corrosion behavior of thermally sprayed Zn and Zn-15wt.%Al coatings (500 µm thick) was studied in a solution simulating the specific environment of the disposal. Galvanic corrosion experiments were performed with a coated steel electrode connected to a bare steel one, which simulated a coating defect. First, it was observed that the Zn coating had lost its sacrificial properties after ~2 months of coupling. XRD and µ-Raman analysis carried out after the experiment demonstrated that the coating was covered with a protective hemimorphite (Zn4Si2O7(OH)2·H2O)-rich layer. In contrast, the Zn-15wt.%Al coating kept its sacrificial properties all along the 6-month experiment. It proved to be covered with a layer mainly composed of Zn and Zn-Al hydroxysulfates, which did not contain hemimorphite. However, SEM cross-sectional observations showed that the electrolyte had seeped into the coating and had even reached the steel surface. This infiltration led to the oxidation of the splats inside the coating, even close to the steel surface, and induced a large swelling of the coating. Its thickness was increased by 50%.

It is important to consider the closure of cracks and pores in rock for radioactive waste disposal and carbon capture and storage to maintain or decrease the permeability of rock. In this study, we investigated the precipitation of calcium compounds on the rock surface in calcium hydroxide solution to consider whether sealing of pores and cracks is possible and accelerated or not. It was found that the precipitation of calcium compounds occurred on rock surfaces. Additionally, we found that the closure of cracks and pores in rock occurred from the P-wave velocity measurement and observation by the scanning electron microscope. Since the closure of cracks and pores can decrease the permeability in rock, it is concluded that the precipitation of calcium compounds on rock is useful for the geological disposal of radioactive wastes and carbon capture and storage.

Use of replicated Latin hypercube sampling to estimate sampling variance in uncertainty and sensitivity analysis results for the geologic disposal of radioactive waste