Inadvertent Intrusion Research Articles

Basis for a research project on marking strategies for a deep geological high-level radioactive waste (HLW) repository in Germany

Abstract. Marking has been considered as an approach for the preservation of information and awareness after the closure of a deep geological repository (DGR) for high-level radioactive waste (HLW). The discussion to use markers to warn people off from – in oversimplified terms – digging into a DGR dates back to the 1980s. Based on the recent recommendations by the Nuclear Energy Agency of the Organization for Economic Co-operation and Development (OECD NEA) regarding the preservation of records, knowledge and memory (RK&M) of DGRs in a systemic approach (NEA, 2019), the Federal Office for the Safety of Nuclear Waste Management (BASE) has identified the need for research regarding relevant aspects of potential future marking strategies in Germany. The first elaborate and sophisticated concept has been developed for the Waste Isolation Pilot Plant (WIPP) in the USA (DOE, 2004). Far from being “one marker”, it is a monumental multi-component system. Internationally, the WIPP concept provided abundant food for thought and inspired a new wave of discussions – not as a design to be copied to other DGRs (the WIPP concept has been developed for this specific DGR at its unique desert location), but as a model for site-specific ambitions to design a marker system that aims in earnest to preserve information and awareness on-site by non-mediated means. In NEA (2019) marking is described as one approach – out of nine – for the preservation of RK&M of DGRs. Marking was found to be focused, in particular, on preserving awareness. However, for a robust system, individual preservation mechanisms should not be planned in isolation, but rather “the components of a systemic RK&M preservation strategy should work together, complement and strengthen each other, act as indexes to each other and thus provide diversity and redundancy with a view to maximising information accessibility, understandability and survivability over the various timescales considered” (NEA, 2019, p. 95). In Germany, there are no regulatory requirements with regards to marking. The Site Selection Act (StandAG, 2017/2023), which sets the regulatory framework for the targeted DGR for HLW, does not mention marking. It mentions, however, two points with specific relevance to RK&M preservation: (1) important data and documents must be permanently stored, and (2) the DGR concept must ensure recoverability of the waste for 500 years after closure, thereby setting a post-closure time frame of specific interest. Against this background, a research project is planned to explore the relevant aspects of potential future marking strategies in Germany. Different types of markers may play different roles. And these roles may again change over time: what are the specifics imposed by the 500-year recoverability requirement? How could surface markers be combined with, e.g., concepts for the re-use of the site or possible added-value projects for the local community? Could off-site markers/monuments play a role? Who would be the stakeholders in a participatory process? With respect to deep geological markers, different questions arise, like the following: could markers within the DGR potentially play a role in recoverability concepts without negatively impacting long-term safety? What dependencies exist on the type of host rock yet to be selected? Could the same markers help warn an inadvertent intruder in the long term? The potential role of markers in a systemic RK&M preservation strategy needs to be investigated by taking other preservation approaches into consideration, too. Which mechanisms could strengthen the efficacy of markers? Which could be strengthened by markers? This presentation will deliver insight into the preliminary studies preceding the planned research project.

Investigation and Modeling of Flight Technical Error (FTE) Associated With UAS Operating With and Without Pilot Guidance

With the increasing interest in the utilization of urban airspace for unmanned aerial system (UAS) operations, be it for cargo delivery or passenger transportation, the future city sky could become quite a crowded place if all those visions become reality. In such case, the question of how close two operations could be conducted while sharing an airspace must be answered to ensure the safe and efficient use of the urban airspace. The lateral separation needed to prevent inadvertent intrusion by neighboring tracks is especially important when designing airspace corridors constrained by the urban landscape. This paper documents a series of flight tests conducted in open fields with the goal of assessing the along-track (longitudinal), cross-track (lateral),and altitude (height) deviation under two different flight conditions: operator guided operation within Visual Line of Sight (VLoS), and the waypoint-guided mission analogous to operating Beyond Visual Line of Sight (BVLoS). The flight test statistics were also compared to the Monte-Carlo based path prediction model that was used in earlier studies for collision prediction. The goal is to determine the Flight Technical Error (FTE) that forms a part of the Total System Error (TSE) for Performance Based Navigation (PBN) of UAS to support the establishment of separation requirements in urban airspace.

Disposal of High-Level Nuclear Waste in Deep Horizontal Drillholes

Spent nuclear fuel and high-level radioactive waste can be disposed in deep horizontal drillholes in sedimentary, metamorphic or igneous rocks. Horizontal drillhole disposal has safety, operational and economic benefits: the repository is deep in the brine-saturated zone far below aquifers in a reducing environment of formations that can be shown to have been isolated from the surface for exceedingly long times; its depth provides safety against inadvertent intrusion, earthquakes and near-surface perturbations; it can be placed close to the reactors and interim storage facilities, minimizing transportation; disposal costs per ton of waste can be kept substantially lower than for mined repositories by its smaller size, reduced infrastructure needs and staged implementation; and, if desired, the waste could be retrieved using “fishing” technology. In the proposed disposal concept, corrosion-resistant canisters containing unmodified fuel assemblies from commercial reactors would be placed end-to-end in up to 50 cm diameter horizontal drillholes, a configuration that reduces mechanical stresses and keeps the temperatures below the boiling point of the brine. Other high-level wastes, such as capsules containing 137Cs and 90Sr, can be disposed in small-diameter horizontal drillholes. We provide an overview of this novel disposal concept and its technology, discuss some of its safety aspects and compare it to mined repositories and the deep vertical borehole disposal concept.

Development and characterization of an ice-selecting pumped counterflow virtual impactor (IS-PCVI) to study ice crystal residuals

Abstract. Separation of particles that play a role in cloud activation and ice nucleation from interstitial aerosols has become necessary to further understand aerosol-cloud interactions. The pumped counterflow virtual impactor (PCVI), which uses a vacuum pump to accelerate the particles and increase their momentum, provides an accessible option for dynamic and inertial separation of cloud elements. However, the use of a traditional PCVI to extract large cloud hydrometeors is difficult mainly due to its small cut-size diameters (< 5 µm). Here, for the first time we describe a development of an ice-selecting PCVI (IS-PCVI) to separate ice in controlled mixed-phase cloud system based on the particle inertia with the cut-off diameter ≥ 10 µm. We also present its laboratory application demonstrating the use of the impactor under a wide range of temperature and humidity conditions. The computational fluid dynamics simulations were initially carried out to guide the design of the IS-PCVI. After fabrication, a series of validation laboratory experiments were performed coupled with the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) expansion cloud simulation chamber. In the AIDA chamber, test aerosol particles were exposed to the ice supersaturation conditions (i.e., RHice > 100 %), where a mixture of droplets and ice crystals was formed during the expansion experiment. In parallel, the flow conditions of the IS-PCVI were actively controlled, such that it separated ice crystals from a mixture of ice crystals and cloud droplets, which were of diameter ≥ 10 µm. These large ice crystals were passed through the heated evaporation section to remove the water content. Afterwards, the residuals were characterized with a suite of online and offline instruments downstream of the IS-PCVI. These results were used to assess the optimized operating parameters of the device in terms of (1) the critical cut-size diameter, (2) the transmission efficiency and (3) the counterflow-to-input flow ratio. Particle losses were characterized by comparing the residual number concentration to the rejected interstitial particle number concentration. Overall results suggest that the IS-PCVI enables inertial separation of particles with a volume-equivalent particle size in the range of ~ 10–30 µm in diameter with small inadvertent intrusion (~ 5 %) of unwanted particles.

Safety Assessment on the Human Intrusion Scenarios of Near Surface Disposal Facility for Low and Very Low Level Radioactive Waste

The second-stage near surface disposal facility for low and very low level radioactive waste`s permanent disposal is to be built. During the institutional control period, the inadvertent intrusion of the general public is limited. But after the institutional control period, the access to the general public is not restricted. Therefore human who has purpose of residence and resource exploration can intrude the disposal facility. In this case, radioactive effects to the intruder should be limited within regulatory dose limits. This study conducted the safety assessment of human intrusion on the second-stage surface disposal facility through drilling and post drilling scenario. Results of drilling and post drilling scenario were satisfied with regulatory dose limits. The result showed that post-drilling scenario was more significant than drilling scenario. According to the human intrusion time and behavior after the closure of the facility, dominant radionuclide contributing to the intruder was different. Sensitivity analyses on the parameters about the human behavior were also satisfied with regulatory dose limits. Especially, manual redistribution factor was the most sensitive parameter on exposure dose. A loading plan of spent filter waste and dry active waste was more effective than a loading plan of spent filter waste and other wastes for the radiological point of view. These results can be expected to provide both robustness and defense in depth for the development of safety case further.

중·저준위 방사성폐기물 천층처분시설에서 시추 후 거주시나리오 평가를 통한 폐쇄 후 제도적 관리기간 연구

처분시설은 폐쇄 후 제도적 관리기간 동안에는 처분 부지로의 일반인의 접근을 제한하며 제도적 관리기간 이후에는 부주의 한 인간침입 시에도 처분시설로 인한 방사선적 영향으로부터 침입자를 보호하도록 설계 되어야 한다. 본 논문에서는 처분시설이 부주의한 침입자에 미칠 수 있는 방사선적 영향을 GENII 프로그램을 사용하여 평가해보았다. 처분고별 적치되는 방사성폐기물의 종류를 달리하여 평가하고 제도적 관리기간 설정에 따른 침입자에 대한 영향도 분석하였다. 평가결과 제도적 관리기간을 두지 않아도 폐필터가 적치된 처분고를 제외하고 모두 성능 목표치를 만족하였다. 하지만 폐필터를 적치한 처분고의 경우 인간침입 평가결과 제도적 관리기간 300년이 되어서야 성능목표치를 만족할 수 있었다. 폐필터와 함께 잡고체 폐기물을 혼합하여 적치하는 경우 제도적 관리기간을 줄일 수 있었으며, 폐필터는 다른 폐기물과 함께 적치하여 제도적 관리기간을 줄이는 것이 필요하다. 폐기물 적치시 방사능을 고려하여 처분고 적치방안을 적절히 수립하는 것이 국부적인 방사능의 최대값을 줄일 수 있어 방사선적 안전성을 확보하며 제도적 관리기간을 단축할 수 있어 바람직하다. The public's access to the disposal facilities should be restricted during the institutional control period. Even after the institutional control period, disposal facilities should be designed to protect radiologically against inadvertent human intruders. This study is to assess the effective dose equivalent to the inadvertent intruder after the institutional control period thorough the GENII. The disposal unit was allocated with different kind of radioactive waste and the effects of the radiation dose to inadvertent intruder were evaluated in accordance with the institutional control period. As a result, even though there is no institutional control period, all were satisfied with the regulatory guide, except for the disposal unit with only spent filter. However, the disposal unit with only spent filter was satisfied with the regulatory guide after the institutional control period of 300 years. But the disposal unit with spent filter mixed with dry active waste could shorten the institutional control period. So the institutional control period can be reduced through the mixing the other waste with spent filter in disposal unit. Therefore, establishing an appropriate plan for the disposal unit with spent filter and other radioactive waste will be effective for radiological safety and reduction of the institutional control period, rather than increasing the institutional control period and spending costs for the maintenance and conservation for the disposal unit with only spent filter.

Planning to 'remember to forget'?

AbstractDisposal in deep geological formations aims to provide isolation of long-lived radioactive waste for hundreds of thousands of years. This raises the question of the long-term governance of the repository throughout its lifetime. In the operational phase the repository is under active regulatory control. Once closed, there will be a phase of passive management control or indirect oversight. This will be followed, at some time in the future, by a period in which there is no oversight. This may be a result of a decision to cease management control or it may occur through loss of records or a change in priorities. The importance of the main exposure scenarios (exposure as a result of the gradual transport of radionuclides in groundwater, transport of radionuclides in gas, and exposure arising from inadvertent intrusion into the repository) are discussed with reference to these different phases. An interesting question is 'How do we minimize the risk of inadvertent intrusion in the far future?' Perhaps it is better to ensure that the repository is forgotten and should we try to plan for this? The different approaches are discussed and the importance of deciding on a strategy at an early stage is emphasized.

Accidental and long-term safety assessment of fission and fusion power reactors

Fusion is seen as a much ‘cleaner’ energy than fission, and a resource for clean energy in the far future. However, being a form of nuclear energy, fusion shares with fission most of its safety problems. This study concerns the assessment of both the short term and the long term hazards associated with fusion, compared with the same figures for fission reactors. Fission data derive from well-known PWR safety assessments, and in particular from the Italian project Progetto Unificato Nucleare (PUN). Fusion data derive from the latest findings of the European Safety and Environmental Assessment of Fusion Power (SEAFP) programme. Concerning inadvertent intrusion in a radioactive waste disposal site and long-term degradation for fusion, this analysis was performed in the frame of the SEAFP studies, while for fission data are taken from typical European waste disposal sites. In all relevant cases, evaluation of associated risks is carried out, with a comparison of the obtained results.

Performance Analysis for Disposal of Mixed Low-Level Waste. II: Results

Ten sites were evaluated as potential locations for disposal of mixed low-level radioactive waste using a simple methodology. Three environmental pathways (water, atmospheric, and inadvertent intruder) were analyzed using generic transport models that were modified for site-specific conditions. The results were summarized by grouping the 58 evaluated radionuclides according to their half-lives and environmental mobility and by their limiting pathway (i.e., the pathway providing the lowest permissible radionuclide concentration in disposed waste of the three evaluated pathways). The results indicate that all evaluated sites have the technical capability for disposal of some radionuclides in the waste. For most radionuclides, the intruder scenarios were more important in determining permissible radionuclide concentrations than the other pathways, particularly for arid sites. For humid sites, if the water pathway is not the most limiting and the permissible radionuclide concentration is high, a more sophisticated and rigorous analysis of the water pathway may not be warranted. However, if the permissible concentration is relatively low, more refined analyses may produce higher permissible concentrations based on additional site characterization data.

Performance Analysis for Disposal of Mixed Low-Level Waste. I: Methodology

A simple methodology has been developed for evaluating the technical capabilities of potential sites for disposal of mixed low-level radioactive waste. The results of the evaluation are expressed as “permissible radionuclide concentrations in disposed waste.” The methodology includes an analysis of three separate pathways: (1) releases of radionuclides to groundwater; (2) releases of potentially volatile radionuclides to the atmosphere; and (3) the consequences of inadvertent intrusion into a disposal facility. For each radionuclide, its limiting permissible concentration in disposed waste is the lowest of the permissible concentrations determined from each of the three pathways. These permissible concentrations in waste at an evaluated site can be used to assess the capability of the site to dispose of waste streams containing multiple radionuclides.

Landscape Permanence and Nuclear Warnings

From the perspective of a human lifetime, the hazards of some nuclear wastes are permanent, so the warnings we place at contaminated nuclear sites must be permanent too. I address questions of how best to provide one hundred centuries of public warning at the first facility for permanent disposal, the Waste Isolation Pilot Plant in New Mexico. Scenarios of intrusion developed to guide the design of warning markers predicted that most of the changes in the area will be social and cultural. Because blatant and permanent markers will increase, not reduce, the probability of inadvertent intrusion, the most appropriate warning is a “landscape of illusion.” Such a landscape needs not permanent surface markers but underground warning devices beneath a soft surface marker. No warning can guarantee deterrence for 10,000 years, however.

Dose and Risk Assessment for Intrusion into Mixed-Waste Disposal Sites

Abstract Sites previously used for disposal of radioactive and hazardous chemical materials have resulted in situations that pose a potential threat to humans from inadvertent intrusion. An example of a generic scenario analysis was developed to demonstrate the evaluation of potential exposure to cleanup workers or members of the public who intrude into buried waste containing both radioactive and hazardous chemical contaminants. The example scenarios consist of a collection of exposure routes (or pathways) with specific modeling assumptions for well drilling and for excavation for building construction. These scenarios are used to conceptually describe potential patterns of human activity during intrusion into mixed-waste disposal sites, assuming that no protective measures are taken. Radiation doses are calculated using the GENII software system and converted to risk using factors from the International Commission on Radiological Protection in Publication 60. The hazard assessment for nonradioactive mat...

Plutonium--its behavior in natural water systems and assimilation by man.

There are a number of factors which must be considered in establishing whether or not the inadvertent intrusion of a sizable amount of plutonium-bearing material into a natural water system may have a significant impact on the health of those individuals who use that system as a drinking water resource. These factors include the chemical form(s) and solubility of plutonium in natural waters, its behavior in relation to natural processes (geochemical and biological), its fate in water treatment systems, and its uptake by man from drinking water. From the results obtained in our investigations of the behavior in natural water systems, it appears that (1) the chemical forms of plutonium dissolved in natural waters are Pu(IV) and Pu(V), (2) the soluble plutonium in many waters is bound to the organic constituents which probably enhances plutonium solubility, (3) the natural process responsible for the removal of plutonium from water is adsorption onto sediments, and (4) in water treatment systems, soluble plutonium is oxidized to the VI state and this form is not removed. From our investigations of gastrointestinal absorption, it appears that the value for f1, the fraction transferred from the gut to blood, is surely greater than 1 X 10(-3) and may be as high as 2 X 10(-1). Consideration of these and other factors indicates that, in the event of an accident, the concentration of plutonium could, in certain small natural water systems, approach and perhaps even exceed, the MPC for plutonium. However, the impact on the health of the affected population would not be inordinately high.

Plutonium-its Behavior in Natural Water Systems and Assimilation by Man

There are a number of factors which must be considered in establishing whether or not the inadvertent intrusion of a sizable amount of plutonium-bearing material into a natural water system may have a significant impact on the health of those individuals who use that system as a drinking water resource. These factors include the chemical forms) and solubility of plutonium in natural waters, its behavior in relation to natural processes (geochemical and biological), its fate in water treatment systems, and its uptake by man from drinking water. From the results obtained in our investigations of the behavior in natural water systems, it appears that (1) the chemical forms of plutonium dissolved in natural waters are Pu(IV) and Pu(V), (2) the soluble plutonium in many waters is bound to the organic constituents which probably enhances plutonium solubility, (3) the natural process responsible for the removal of plutonium from water is adsorption onto sediments, and (4) in water treatment systems, soluble plutonium is oxidized to the VI state and this form is not removed. From our investigations of gastrointestinal absorption, it appears that the value for f1, the fraction transferred from the gut to blood, is surely greater than 1 * 10−3 and may be as high as 2 * 10−1. Consideration of these and other factors indicates that, in the event of an accident, the concentration of plutonium could, in certain small natural water systems, approach and perhaps even exceed, the MPC for plutonium. However, the impact on the health of the affected population would not be inordinately high.