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The size of deep boreholes suitable for disposal of radioactive wastes can be increased through an innovative combination of blind shaft and oilfield drilling technologies. This would enable deep borehole disposal (DBD) of the UK's high-level waste (HLW), which is being packaged in containers hitherto considered too large for DBD and destined for a deep geological repository (DGR/GDF). DBD could advance, by over 40 years, disposal of this waste, avoid expensive replacement of ageing storage facilities and reduce the size and cost of the DGR/GDF by up to 70%. A generic reference design is presented for the boreholes and a route proposed for DBD of the UK's HLW in between seven and ten boreholes on a site smaller than three football pitches. Following location and approval of a suitable site, disposal could be completed in under 10 years using currently available technology. Estimates are presented that show the entire programme, including a non-active demonstration borehole, could be undertaken for less than £744 million (at today's prices); a saving of over £8.5 billion on the estimated cost of the proposed DGR/GDF. Implementing DBD of the UK's HLW could begin now and should be reconsidered as a matter of urgency.

Around the world, deep borehole disposal is being evaluated for intermediate-level waste (ILW), high-level waste (HLW), spent nuclear fuel (SNF), separated plutonium waste and some very high specific activity fission product waste. In Australia, long-lived ILW from research reactors and radiopharmaceutical production represents the principal waste stream that requires deep geologic disposal. Whilst the Australian government has not yet made a decision on its preferred strategy for ILW disposal, deep borehole disposal of small volumes of ILW would be a more cost-effective and modular solution compared to a conventional geologic disposal facility (GDF). CSIRO, ANSTO and SANDIA have created an international partnership to execute a full-scale borehole research, development and demonstration (RD&D) project in Australia. The project will demonstrate the technical feasibility of the long-term safety of borehole disposal in deep geological formations. The execution of this project could also demonstrate options for nuclear waste disposal that would reduce proliferation risks, potentially up to the termination of compliance with international safeguards requirements. The RD&D includes demonstration of surface handling and waste/seal emplacement capabilities, basic research on foundational science areas, and full-scale field testing in both a deep characterization borehole and a larger-diameter (0.7 m or 27.5 inch) 2000 m deep demonstration borehole. The multi-barrier system designed for such a deep disposal borehole concept places much less reliance on engineered barriers at the disposal zone to achieve safety as compared to a conventional GDF. It rather relies on geological features for waste containment. The concept being explored uses disposal containers with primary waste packages, such as vitrified waste canisters, inside; to be both cost effective and fit for purpose, such a container could have a mild steel-based structural component with copper coating. A critical review of six coating technologies showed that cold spray has the greatest advantages, such as minimal porosity and compressive residual stress. The RD&D has delivered novel enabling tools that assist with site screening, borehole design and post-closure safety assessments. For instance, an automated geological fault mapping and meshing tool was developed that assists with ranking the suitability of potential disposal sites based on proximity to faults. New codes were developed for better representation of fault zones in 2D/3D numerical flow and transport models, while also being more efficient to execute. Post-closure safety assessments tested the sensitivity of long-term safety with respect to disposal depth, rock permeability and sorption. Heat transport calculations explored the sensitivity of temperature evolution within the borehole to parameters such as heat load, borehole depth, geothermal gradients and rock thermal conductivity. For verification of host rock tightness while also demonstrating the absence of recent groundwater, a new noble gas analytical facility has been established for measuring rare noble gases in mineral fluid inclusions as indicators of very old pore fluids.

Various versions of deep borehole nuclear waste disposal have been proposed in the past in which effective sealing of a borehole after waste emplacement is generally required. In a high temperature disposal mode, the sealing function will be fulfilled by melting the ambient granitic rock with waste decay heat or an external heating source, creating a melt that will encapsulate waste containers or plug a portion of the borehole above a stack of the containers. However, there are certain drawbacks associated with natural materials, such as high melting temperatures, inefficient consolidation, slow crystallization kinetics, the resulting sealing materials generally being porous with low mechanical strength, insufficient adhesion to waste container surface, and lack of flexibility for engineering controls. In this study, we showed that natural granitic materials can be purposefully engineered through chemical modifications to enhance the sealing capability of the materials for deep borehole disposal. The present work systematically explores the effect of chemical modification and crystallinity (amorphous vs. crystalline) on the melting and crystallization processes of a granitic rock system. The approach can be applied to modify granites excavated from different geological sites. Several engineered granitic materials have been explored which possess significantly lower processing and densification temperatures than natural granites. Those new materials consolidate more efficiently by viscous flow and accelerated recrystallization without compromising their mechanical integrity and properties.

The concept of deep borehole disposal (DBD) for high-level nuclear wastes has been around for about 40 years. Now, the Department of Energy (DOE) in the United States (U.S.) is re-examining this concept through recent studies at Sandia National Laboratory and a field test. With DBD, nuclear waste will be emplaced in boreholes at depths of 3 to 5 km in crystalline basement rocks. Thinking is that these settings will provide nearly intact rock and fluid density stratification, which together should act as a robust geologic barrier, requiring only minimal performance from the engineered components. The Nuclear Waste Technical Review Board (NWTRB) has raised concerns that the deep subsurface is more complicated, leading to science, engineering, and safety issues. However, given time and resources, DBD will evolve substantially in the ability to drill deep holes and make measurements there. A leap forward in technology for drilling could lead to other exciting geological applications. Possible innovations might include deep robotic mining, deep energy production, or crustal sequestration of CO2, and new ideas for nuclear waste disposal. Novel technologies could be explored by Korean geologists through simple proof-of-concept experiments and technology demonstrations.

Cementitious grouts are being developed for use as sealing and support matrices (SSMs) in deep borehole disposal (DBD) where temperatures do not exceed 190 °C. They will seal radioactive waste containers into the bottom 2 km of holes drilled up to 5 km deep into the crystalline basement. The temperature and pressure is likely to be similar to those in hydrocarbon and geothermal energy wells, where grout placement and durability are affected. This paper reviews the potential cementing systems suitable for this application and explains why a single solution of a formulation of Class G oil well cement, silica flour, water, fluid loss additive, and retarding admixture has been selected. This type of formulation has been used extensively for over 100 years in well cementing. It should provide the short-term performance and durability required for an SSM, maintaining the seal around the waste packages within the disposal zone long after the boreholes are sealed back to the surface, and thus augmenting the safety case for DBD.

Post-closure performance assessment (PA) calculations suggest that deep borehole disposal of cesium (Cs)/strontium (Sr) capsules, a U.S. Department of Energy (DOE) waste form (WF), is safe, resulting in no releases to the biosphere over 10,000,000 years when the waste is placed in a 3&ndash, 5 km deep waste disposal zone. The same is true when a hypothetical breach of a stuck waste package (WP) is assumed to occur at much shallower depths penetrated by through-going fractures. Cs and Sr retardation in the host rock is a key control over movement. Calculated borehole performance would be even stronger if credit was taken for the presence of the WP.

원자력발전소에서 전기를 생산하고 난 후 발생하는 사용후핵연료 또는 이들 사용후핵연료의 재처리/재활용 공정으로부터발생하는 고준위폐기물은 인간환경으로부터 안전하게 장기간 격리시켜야 한다. 최근 심부시추공 굴착기술의 획기적인 발전으로 인하여, 방사성폐기물의 심부시추공 처분기술에 대한 연구가 의미 있게 진행되고 있다. 본 논문에서는 이러한 심부시추공을 활용하여 고준위 방사성폐기물을 지하 3~5 km 심도에 격리시키는 심부시추공 처분기술의 국내 적용 가능성을 분석하기 위하여 국내 심부 지하환경 특성에 대하여 예비분석 하였다 이를 위하여, 미국 및 유럽권 국가 연구사례와 기술개발 현황을 검토하고, 실제 국내의 심부 지질조건을 검토하기 위하여 고지열 분포지역에 개발 중인 지열 탐사공을 대상으로 3~4 km 심도까지의 암석, 지온 등 특성 자료를 수집, 분석하였다. 결정질 암반 심도 및 지온경사 등 분석 결과와 국내 발생 사용후핵연료를 바탕으로 심부시추공 처분시스템 구성요소인 처분용기, 밀봉시스템 등에 대하여 예비단계의 개념을 제안하였다.

In the very deep borehole (VDH) concept for high level radioactive waste disposal, the combined usage of clay and concrete provides an attractive way of achieving both high strength and low permeability required for sealing the various sections of the hole. The concrete is required for mechanical stability where water-bearing fracture zones are intersected, whereas the clay effectively seals sections in stable rock masses. As both the clay and concrete may be exposed to temperatures in the range of 60–150 °C in various parts of the hole, there is a need to address the stability of these materials under thermally enhanced aqueous conditions. In this pilot study, a new type of organic-free, low pH concrete based on granulated blast furnace slag is tested, which is hardened and altered under hydrothermal conditions in the laboratory. The results presented show that both adequate compressive strength (up to ∼9 MPa) and low hydraulic conductivity (down to ∼5.6 × 10−10) is attained at elevated temperatures ranging up to 150 °C, indicating that clay-concrete sealing can be a successful method used to prevent radionuclides from migrating vertically up through the borehole repository.

Geological disposal of HLW and spent nuclear fuel (SNF) in very deep boreholes is a concept whose time has come. The alternative – disposal in a mined, engineered repository is beset with difficulties not least of which are the constraints placed upon the engineered barriers by the high thermal loading. The deep borehole concept offers a potentially safer, faster and more cost-effective solution. Despite this, international interest has been slow to materialize, largely due to perceived problems with retrievability and uncertainty about the ability to drill accurate vertical holes with diameters greater than 0.5 m to a depth of 4-5 km. The closure of Yucca Mountain and the subsequent recommendations of the Blue Ribbon Commission have lead to a renewed interest in deep borehole disposal (DBD) and the US DoE has commissioned Sandia National Labs, working with industrial and academic partners (including the University of Sheffield), to undertake a program of R&D leading to a demonstration borehole being drilled somewhere in the continental USA by 2016.In this paper, we focus on some of the key safety and engineering features of DBD including methods of sealing the boreholes, sealing and support matrices for the waste packages. Numerical modeling has, and continues to play, a significant role in expanding and validating the DBD concept. We report on progress in the use of modeling in the above contexts, paying particular attention to constraints on the engineering materials resulting from high heat loading.

Deep borehole disposal (or DBD) is now seen as a viable alternative to the (comparatively shallow) geologically repository concept for disposal of high level waste and spent nuclear fuel. Based on existing oil and geothermal well technologies, we report details of investigations into cementitious grouts as sealing/support matrices (SSMs) for waste disposal scenarios in the DBD process where temperatures at the waste package surface do not exceed ∼190ºC. Grouts based on Class G oil well cements, partially replaced with silica flour, are being developed, and the use of retarding admixtures is being investigated experimentally. Sodium gluconate appears to provide sufficient retardation and setting characteristics to be considered for this application and also provides an increase in grout fluidity. The quantity of sodium gluconate required in the grout to ensure fluidity for 4 hours at 90, 120 and 140°C is 0.05, 0.25 and 0.25 % by weight of cement respectively. A phosphonate admixture only appears to provide desirable retardation properties at 90°C. The presence of either retarder does not affect the composition of the hardened cement paste over 14 days curing and the phases formed are durable under conditions of high temperature and pressure.

Geosciences 7(3), 58 (2017). doi:10.3390/geosciences7030058, Published by MDPI, Basel

This Special Issue of the Energies Journal on Deep Borehole Disposal of Nuclear Waste has delivered a timely update on the science and technology of borehole disposal and the types of radioactive wastes it could potentially accommodate. The Special Issue papers discuss (i) circumstances under which a national waste management programme might wish to consider deep borehole disposal; (ii) a status report of deep borehole disposal options in Germany; (iii) the analysis of corrosion performance of engineered barrier systems; (iv) a review of the potential cementing systems suitable for deep borehole disposal; (v) the thermal evolution around heat-generating waste for a wide range of material properties and disposal configurations; (vi) a geochemical analysis of deep brines focussed on fluid-rock interactions; (vii) post-closure performance assessment calculations for deep borehole disposal of Cs/Sr capsules and an example safety case for (viii) horizontal and (ix) vertical deep borehole disposal of nuclear wastes.

This paper focuses on the improvement of the longevity and robustness of materials for sealing and plugging the upper portion of a deep borehole used for permanent isolation of high-level nuclear waste. Analytical models of porous and laminar flows show that even when materials have low intrinsic permeability, micron-sized cracks and gaps between the plug and rock (formed via chemical reaction, shrinkage, osmotic consolidation, etc.) significantly diminish the plug’s sealing properties. On this basis, materials such as asphalt, traditional cements, and pure bentonite—which crack or shrink under certain conditions—are unfavorable. An ongoing test program has formulated expanding cement mixtures containing MgO to prevent such bypass flow. Furthermore, these findings support using stable, malleable, and low-permeability plug material (k ≤ 10-16 m2), such as a crushed rock (70%) and bentonite (30%) mixture. Alternative clays such as sepiolite could be blended with the bentonite to further reduce the p...

The United States is in need of a new and more adaptive long-term strategy for spent nuclear fuel. In this communication, we outline the fundamental reasons why deep borehole disposal should receive more detailed investigation, alongside traditional shallow mined repositories. This potential solution is supported by advancing drilling technologies and an improving understanding of extremely long fluid residence times in deep bedrock. Radionuclide isolation is supported by verifiable and stable geologic barriers such as long transport distances to aquifers, low permeability, and reducing chemical conditions. The modular nature of implementing deep borehole disposal could offer unique programmatic and economic advantages. Experience with a pilot borehole program will be required to confirm the feasibility of drilling and emplacement operations, and key chemical and hydraulic conditions.

(Received November 14, 2013 / Revised January 13, 2014 / Approved January 28, 2014)If the spent fuels or the high-level radioactive wastes can be disposed of in the depth of 3~5 km and more stable rock for-mation, it has several advantages. For example, (1)significant fluid flow through basement rock is prevented, in part, by low permeability, poorly connected transport pathways, and (2)overburden self-sealing. (3)Deep fluids also resist vertical movement because they are density stratified and reducing conditions will sharply limit solubility of most dose-critical radionuclides at the depth. Finally, (4) high ionic strengths of deep fluids will prevent colloidal transport. Therefore, as an alternative disposal concept to the deep geological disposal concept(DGD), very deep borehole disposal(DBD) technology is under consideration in number of countries in terms of its outstanding safety and cost effectiveness. In this paper, for the preliminary applicability analyses of the DBD system for the spent fuels or high level wastes, the DBD concepts which have been developed by some countries according to the rapid advance in the development of drilling technology were reviewed. To do this, the general concept of DBD system was checked and the study cases of foreign countries were described and analyzed. These results will be used as an input for the analyses of applicability for DBD in Korea.사용후핵연료를 포함하는 고준위 방사성폐기물을 지질학적 조건이 안정적인 지하 3~5 km의 심도에 처분할 수 있다면 다음과 같은 많은 장점이 있는 것으로 평가되고 있다. 즉, (1)암반 수리전도도가 매우 낮아 지하수가 생태계까지 도달하는데 속도가 현저히 감소되며, (2)상부층 두께로 인하여 생태계와의 이격거리 확보에 유리하고, (3)지하수가 환원상태이므로 핵종의 용해도가 매우 낮을 뿐만 아니라 (4)오랜 연령의 지하수에서는 핵종이 흡착된 콜로이드 생성과 이동이 극히 제한된다는 점이다. 이와 관련하여 심부시추공 처분(Deep Borehole Disposal) 연구는 심층 처분(Deep Geological Disposal) 시스템에 대한 이상적인 처분 대안기술로서 꾸준하게 진행되어 왔다. 본 논문에서는 최근 심부 시추기술이 비약적으로 발전됨에 따라 의미있게 연구가 진행되고 있는 심부시추공 처분시스템을 국내 적용하기 위한 초기 단계로서 해외의 심부시추공 처분시스템 기술개발 사례를 분석하였다. 이를 통하여 심부시추공 처분에 대한 일반적인 개념과 심부시추공 처분시스템 개념을 도출한 연구사례를 국가별로 정리하였다. 이들 분석결과는 향후 심부시추공 처분기술의 국내 적용을 위한 입력자료로서 유용하게 활용될 수 있을 것이다.Keywords: Spent fuels, High-level radioactive wastes, Deep geological disposal(DGD), Deep borehole disposal(DBD), Safety, Alternative Technology 중심단어: 사용후핵연료, 고준위폐기물, 심층처분, 심부시추공처분, 안전성, 대안기술 *

In recent years, geological disposal of radioactive waste has focused on placement of high- and intermediate-level wastes in mined underground caverns at depths of 500–800 m. Notwithstanding the billions of dollars spent to date on this approach, the difficulty of finding suitable sites and demonstrating to the public and regulators that a robust safety case can be developed has frustrated attempts to implement disposal programmes in several countries, and no disposal facility for spent nuclear fuel exists anywhere. The concept of deep borehole disposal was first considered in the 1950s, but was rejected as it was believed to be beyond existing drilling capabilities. Improvements in drilling and associated technologies and advances in sealing methods have prompted a re-examination of this option for the disposal of high-level radioactive wastes, including spent fuel and plutonium. Since the 1950s, studies of deep boreholes have involved minimal investment. However, deep borehole disposal offers a potentially safer, more secure, cost-effective and environmentally sound solution for the long-term management of high-level radioactive waste than mined repositories. Potentially it could accommodate most of the world's spent fuel inventory. This paper discusses the concept, the status of existing supporting equipment and technologies and the challenges that remain.

The safety case for deep borehole disposal of nuclear wastes contains a safety strategy, an assessment basis, and a safety assessment. The safety strategy includes strategies for management, siting and design, and assessment. The assessment basis considers site selection, pre-closure, and post-closure, which includes waste and engineered barriers, the geosphere/natural barriers, and the biosphere and surface environment. The safety assessment entails a pre-closure safety analysis, a post-closure performance assessment, and confidence enhancement analyses. This paper outlines the assessment basis and safety assessment aspects of a deep borehole disposal safety case. The safety case presented here is specific to deep borehole disposal of Cs and Sr capsules, but is generally applicable to other waste forms, such as spent nuclear fuel. The safety assessments for pre-closure and post-closure are briefly summarized from other sources; key issues for confidence enhancement are described in greater detail. These confidence enhancement analyses require building the technical basis for geologically old, reducing, highly saline brines at the depth of waste emplacement, and using reactive-transport codes to predict their movement in post-closure. The development and emplacement of borehole seals above the waste emplacement zone is also important to confidence enhancement.

사용후핵연료의 지층처분의 대안으로 심부시추공을 설치하여 지하 3-5 km 구간에 사용후핵연료를 처분하는 개념이 여러나라에서 제시된 바 있다. 특히 미국 샌디아국립연구소의 최근 연구 결과를 분석하고, 국내 적용을 위한 한국형 캐니스터 디자인과 심부시추공 디자인 개념을 처분 소요 면적과 함께 제시하였다. 【As an alternative of the spent fuel disposal in a geologic repository, a deep borehole disposal concept for disposal at the section of 3 - 5km deep in a borehole has been proposed in several countries. In this paper, the latest reports of Sandia National Laboratories on the borehole disposal researches are analyzed. For implementation of this disposal concept in Korea, a conceptual design of spent fuel disposal canister and a modified deep borehole concept are suggested along with a required disposal area.】

The United States Department of Energy (US DOE) is conducting research and development (R&D) activities under the Used Fuel Disposition Campaign (UFDC) to support storage, transportation, and disposal of used nuclear fuel (UNF) and wastes generated by existing and future nuclear fuel cycles. R&D activities are ongoing at nine national laboratories, and are divided into storage, transportation and disposal. Storage R&D focuses on closing technical gaps related to extended storage of UNF. Transportation R&D focuses on ensuring transporta- bility of UNF following extended storage, and addressing data gaps regarding nuclear fuel integrity, retrievabili- ty, and demonstration of subcriticality. Disposal R&D focuses on identifying geologic disposal options and addressing technical challenges for generic disposal concepts in mined repositories in salt, clay/shale, and granitic rocks, and deep borehole disposal. UFDC R&D goals include increasing confidence in the robustness of generic disposal concepts, reducing generic sources of uncertainty that may impact the viability of disposal con- cepts, and developing science and engineering tools to support the selection, characterization, and licensing of a repository. The US DOE has also initiated activities in the Nuclear Fuel Storage and Transportation (NFST) Planning Project to facilitate the development of an interim storage facility and to support transportation infra- structure in the near term.

Radioactive waste disposal in deep boreholes may be more “ready” than disposal in mined geologic repositories since humans have greater experience operating small deep holes (i.e., boreholes) than big shallow holes (i.e., mines). There are millions of precedents for constructing >2 km deep boreholes and several hundred precedents for disposing long-lived wastes in boreholes. Borehole disposal is likely to be faster, cheaper, and more flexible than mined disposal, while also offering greater long-term isolation. Isolation would rely on the great depth, water density gradients, and reducing conditions to prevent vertical movement of waste up the borehole.

The heat outputs of higher burn up spent fuels (SF) create problems for disposal in mined repositories, including needs for reduced container loadings and extended pre-disposal cooling. An alternative that is less temperature sensitive is deep borehole disposal (DBD) which offers safety, cost, security and other potential benefits and could be implemented relatively quickly using currently available deep-drilling technology. We have modified our previously proposed version of DBD to be more appropriate for higher burn-up fuels by using smaller (0.36 m diameter) stainless steel containers, a smaller (0.56 m diameter) borehole, and different support matrices. We present the results of new heat-flow modelling for DBD of UO2 and MOX SF with burn ups of 55 and 65 GWd/t showing how temperatures evolve, especially on the outer surface of the containers. Consequences for the performance of the support matrices and the disposal concept are discussed. The thermal modelling indicates DBD is a viable option for higher burn-up SF and could be a practical disposal route for many combinations of fuel types, burn ups, ages and container loadings. Further, the results suggest that DBD of complete fuel assemblies, a desirable option, would be feasible and require much shorter pre-disposal cooling than necessary for disposal in mined repositories.

Acoustic emission (AE) signals resulting from the melting and solidification of natural granite were monitored and analysed. The experimental work was conducted in laboratory conditions simulating very deep borehole disposal (DBD) of high level wastes such as sealed radioactive sources (SRS) or spent nuclear fuel (SNF). The cumulative number of signals, their durations and frequencies were the main characteristics of the monitored processes. The recorded AE could be associated with the complex changes in volume and shape of the constituent minerals associated with solid–liquid and solid–solid phase transformations within the granite. AE from the granite was also studied in part by monitoring phase transformation on heating and cooling of quartz.

As an alternative of the high-level radioactive waste disposal in the subsurface repository, a deep borehole disposal is reviewed by several nuclear advanced countries. In this study, the state of the art on the borehole disposal researches was reviewed, and the possibility of borehole disposal in Korean peninsula was discussed. In the deep borehole disposal concept radioactive waste is disposed at the section of 3 - 5km depth in a deep borehole, and it has known that it has advantages in performance and cost due to the layered structure of deep groundwater and small surface disposal facility. The results show that it is necessary to acquisite data on deep geologic conditions of Korean peninsula, and to research the engineering barrier system, numerical modeling tools and disposal techniques for deep borehole disposal.

A nuclear fission-based energy system is described that is capable of supplying the energy needs of all of human civilization for a full range of human energy use scenarios, including both very high rates of energy use and strikingly-large amounts of total energy-utilized. To achieve such “planetary scale sustainability”, this nuclear energy system integrates three nascent technologies: uranium extraction from seawater, manifestly safe breeder reactors, and deep borehole disposal of nuclear waste. In addition to these technological components, it also possesses the sociopolitical quality of manifest safety, which involves engineering to a very high degree of safety in a straightforward manner, while concurrently making the safety characteristics of the resulting nuclear systems continually manifest to society as a whole. Near-term aspects of this nuclear system are outlined, and representative parameters given for a system of global scale capable of supplying energy to a planetary population of 10 billion people at a per capita level enjoyed by contemporary Americans, i.e., of a type which might be seen a half-century hence. In addition to being sustainable from a resource standpoint, the described nuclear system is also sustainable with respect to environmental and human health impacts, including those resulting from severe accidents.

Deep (4–5 km) boreholes are emerging as a safe, secure, environmentally sound and potentially cost-effective option for disposal of high-level radioactive wastes, including plutonium. One reason this option has not been widely accepted for spent fuel is because stacking the containers in a borehole could create load stresses threatening their integrity with potential for releasing highly mobile radionuclides like 129I before the borehole is filled and sealed. This problem can be overcome by using novel high-density support matrices deployed as fine metal shot along with the containers. Temperature distributions in and around the disposal are modelled to show how decay heat from the fuel can melt the shot within weeks of disposal to give a dense liquid in which the containers are almost weightless. Finally, within a few decades, this liquid will cool and solidify, entombing the waste containers in a base metal sarcophagus sealed into the host rock.

Waste actinides, including plutonium, present a long-term management problem and a serious security issue. Immobilisation in mineral or ceramic waste forms for interim storage is a widely proposed first step. The safest, most secure geological disposal for Pu is in very deep boreholes and we propose that the key step to combination of these immobilisation and disposal concepts is encapsulation of the waste form in cylinders of recrystallized granite. We discuss the underpinning science, focusing on experimental work, and consider implementation. Finally, we present and discuss analyses of zircon, UO2 and Ce-doped cubic zirconia from high pressure and temperature experiments in granitic melts that demonstrate the viability of this solution and that actinides can be isolated from the environment for millions, maybe hundreds of millions, of years.