Dismantling Of Nuclear Facilities Research Articles

Proposed Detection Limits for Radioactivity Concentrations in Water in the Decommissioning and Dismantling of Nuclear Facilities

The Dismantling and Decommissioning (D&D) of nuclear facilities poses several challenges for radioactivity measurement laboratories involved in environmental radiation monitoring plans. One of them is the definition of the detection limits to be achieved for the radionuclides analysis in different samples. The detection limits should be set in such a way that the obtained concentration values for each radionuclide are easily discriminated from certain maximum activity concentration levels. These maximum activity concentration levels are usually set in view of the respective dose contributions from each radionuclide. There are some national legislations that settle detection limits for drinking water. However, there is no regulation containing detection limits for groundwater or surface water. In this way, different institutions or companies require very different detection limits for radioactivity concentration assessment in those types of water associated with D&D activities. In this work, we focus on the detection limits required for the D&D activities in rainwater, surface water and groundwater. We propose detection limits obtained by applying the WHO methodology for maximum activity concentration levels and compare with those requested by radioactive waste management agencies and regulatory bodies. Some real cases where our proposal allows identification of events are analysed and conclusions are extracted.

Optimizing radiation exposure in dynamic radioactive environments: Dynamic ACO-RRT* path planning algorithm

Abstract Radioactive environments are often dynamic for various reasons, such as the dismantling of nuclear facilities, leakage of radiation sources, and nuclear accidents. Path planning in a dynamic radioactive environment is one of the important issues in radiation protection for nuclear facility workers. In traditional dynamic optimal path planning, there are phenomena, in which the optimal path is not found within the allowable time or the quality of the path searched within the allowable time is low. To solve this problem, we propose a hybrid algorithm that combines meta-heuristic and sample-based algorithms, called dynamic ant colony optimization-rapidly exploring random tree star (ACO-RRT*). A low-level grid optimal path consisting of grid vertices is obtained by the ACO algorithm, and then it is further refined by the RRT* algorithm. At every instant of environmental change, the vertices of the grid optimal path are divided into vertices with and without samples, and new samples are generated only around vertices without samples. Sampling optimization is performed only around the grid optimal path using new samples and already existing samples. Simulations in a virtual radioactive environment showed that the proposed algorithm reduces computational costs and improves the quality of the optimal path compared to traditional algorithms.

Wet sieving and magnetic separation for the treatment of radioactive secondary waste produced from waterjet abrasive suspension cutting

Abstract. Dismantling of reactor pressure vessels and their built-in components is an enormous challenge in the deconstruction of a nuclear power plant. Due to the years of exposure to neutron radiation, the activated components can only be dismantled and packaged remotely. For reasons of radiation protection, preference is given to techniques that can be used underwater due to the shielding effect. A cutting method that meets these requirements is the waterjet abrasive suspension cutting technique (WAS). The cutting tool is capable of slicing metallic internals and other materials using a pure jet of water mixed with an abrasive substance at high velocity and pressure. The process offers numerous technical advantages, but it has a major disadvantage in producing secondary waste. Due to the addition of the abrasive substance, the WAS process produces a waste mixture of inactive abrasive particles and radioactive steel particles (activated by neutron radiation) during the dismantling of steel components in nuclear facilities. Since the steel particles are radioactive when the reactor pressure vessel (RPV) and its internals are dismantled, this particle mixture currently has to be disposed of as radioactive waste. This leads to a doubling of the radioactive waste. Despite the technical advantages, the WAS process used for cutting purposes is a severely disadvantage from an economic point of view, considering the significant disposal costs of the radioactive waste. The research project NaMaSK (wet sieving and magnetic separation of grain mixtures to minimise secondary waste in the dismantling of nuclear facilities), funded by the German Federal Ministry of Education and Research (BMBF), aims to separate the two fractions (abrasive and steel particles) with the help of magnetic separation and wet sieving. For this purpose, a prototype separation system MaSK (magnetic separation of grain mixtures to minimise secondary waste in the dismantling of nuclear facilities) with a magnetic filter and sieve has already been built and tested, and it can separate up to 98 % of the steel particles from the mixture. The separation process aimed to reduce the total amount of secondary waste by reusing abrasive particles for further WAS cutting. In the new test plant NaMaSK, the mode of operation will be converted from a batch process to continuous operation to highlight the economic aspect of the separation process. In this regard, an efficient design of the sieve structure and magnetic filter, followed by process optimisation, will be implemented. These new developments and the first results will be presented at the conference.

A State-of-the-Art Review of Radioactive Decontamination Technologies: Facing the Upcoming Wave of Decommissioning and Dismantling of Nuclear Facilities

The average share of nuclear energy in electricity production is expected to increase under the background of the global pursuit towards carbon neutrality. Conjugating with its rapid development, the wave of decommissioning and dismantling (D&D) of nuclear facilities is coming. The surface decontamination is a prerequisite to D&D, which will make it easier and reduce the volume of radioactive wastes. However, there are no comprehensive studies on the decontamination methods, which is not helpful for the sustainable development of nuclear energy and environment protection. Therefore, in this work, the current status and future trends of global energy and nuclear energy are first analyzed. Then, various decontamination approaches are comparatively studied, including cleaning mechanisms, application subjects, and intrinsic advantages and disadvantages. Finally, the criteria and factors for selecting a decontamination process, the challenges, and future studies are directed. Among the mechanical methods, laser-based cleaning is high-speed, having automation ability, and thus is promising, although it creates a dust and airborne contaminant hazard. In further studies, factors such as selecting a proper laser facility, optimizing operating parameters, and designing a high-efficiency dust collection system could be studied. Regarding the chemical method, chemical gels are good for decontaminating complex shapes and vertical and overhead surfaces. In addition, they can enhance other decon agents’ efficiency by improving contact time. However, the formulation of colloidal gels is complex and no gel type is useful for all contaminants. Therefore, novel and versatile gels need be developed to enlarge their application field. Combining various decontamination methods will often have better results and thus a reasonable and effective combination of these decontamination methods has become the main direction.

Mobile attachment for automated crack milling

Abstract. In the dismantling of nuclear facilities, the decontamination and remote-controlled crushing of reinforced concrete is a central point. The main objective is to selectively remove the contaminated material in order to feed the remaining material, which in relation to the overall system or overall mass, represents the predominant part of the normal recycling cycle. For the surface decontamination of the upper millimeters, several methods are available that are constantly being optimized and further developed. However, there is a great need for research in the demolition and selective deep removal of reinforced concrete, e.g. in the case of cracks or eruptions into which contamination could penetrate, or the removal of metallic fixtures. The production of freely measurable surface geometries is a constant objective (Edelmann et al., 2018). The German “Defined removal of highly reinforced concrete” (DefAhS) research project was funded by the German Federal Ministry of Education and Research (BMBF) from October 2013 to the end of March 2018. In the course of the project, a new combination tool consisting of indexable inserts and impact lamellas was developed. With this method it is possible to remove highly reinforced concrete in one operation. The following property right could be granted: “Device for removing building material” (DE102015114122B3). Within the research project, concrete, reinforcement and fixtures (dowels, rails, anchor plates, pipe penetrations) could be successfully cut. It could also be shown that it is possible to remove several layers of steel reinforcement within a concrete matrix. The “Mobile attachment for automated crack milling” (MAARISS) research project has been running since November 2020. The hybrid milling technology developed in DefAhS is intended to form the basis for the milling drum used in MAARISS. The aim in MAARISS is, among other things, a new development of the extraction system directly on the removal unit and an automation system for use in a nuclear facility. Cracks are to be automatically milled over in order to enable subsequent clearance measurement by the staff on site. The physically very strenuous work of crack uncovering should be reduced to just one operator in a safe environment. The construction of a scaffold should be completely dispensed with and existing transport technology (forklift or lifting platform) should be used.

Explanations for the development of a novel universally inside pipe separator for dismantling (contaminated) pipelines

Abstract. During the operation and dismantling of nuclear facilities, individual pipelines must always be removed due to leaks because of the end of their maximum service life or the dismantling of the plant. In practice, this activity, which at first glance appears simple, is associated with many challenges due to limited space or the fact that the pipelines run through walls, despite various solutions that are available on the market. Therefore, the aim of the joint research project “RoTre” (Development of a novel universally inside pipe separator for dismantling contaminated pipelines) between KIT, Siempelkamp NIS Ingenieurgesellschaft mbH and RWE Nuclear GmbH is the development of an innovative and competitive inside pipe separator for use in decommissioning and dismantling of nuclear facilities with a wide range of applications for various pipe diameters, wall strengths and materials (Fig. 1). An amendment will be the forward cleaning, whereby metal chips or other components can be captured continuously. Besides the dismantling in areas which are difficult to access, such as pipelines set in concrete or pipelines that cannot be drilled over their full length, dismantling should be possible in air and under water. After application, the system can be decontaminated. In order to separate pipes made out of different materials with various wall thicknesses, the development of a universally applicable test stand is planned in order to achieve the scientific work objectives. Among other things, it should be determined whether a sawing or an abrasive cutting process is more suitable for cutting inside pipes. Building on this, the parameters of the separation process are tested in a parameter study to achieve the smallest possible process forces with a universal applicability. Relevant parameters are the geometry parameters of the cutting unit like the saw tooth shape, the composition of the cutting wheel, as well as the process parameters in the form of infeed, cutting speed and tool speed. The cutting quality achieved by the different tools with the setting of the machine parameters is also an evaluation criterion for the selection of the cutting process.

Training needs assessment: identification of competence fields for the dismantling of nuclear power plants

Abstract. The dismantling of nuclear facilities is a continuous process of change encompassing the complete site. Thereby, the focus changes from a stable and standardized operational phase to a situation characterized by constant changes in the facility as well as in the facility organization. Thus, employees and managers are confronted with a markedly changed working environment: processes and methods must be continuously re-evaluated and adapted, qualification requirements change or shift and new interfaces emerge. Furthermore, compared to the operational phase, the regulatory depth is reduced, decisions must be made faster and more flexible and the mode of operation changes from hierarchically organized routine standard operational procedures to an efficiency-orientated project-based mode of operation with limited resources at the same time. To make dismantling efficient and safe, this change should be actively managed by a change project in terms of the human technology organization approach (MTO approach, Strohm and Ulich, 1999). Against this background, our BMBF-funded collaboration project (“Die Kompetenzen von Führungskräften und MitarbeiterInnen für den Rückbau stärken – Rückbaukompetenzen”; funding number 15S9426A) aims to identify the dismantling-related requirement changes and the associated competence shifts as well as to develop and support the changed roles of managers and employees by scientifically based training (Goldstein and Ford, 2002; IAEA, 1998). Thereby, seminar-based training (knowledge-based and demonstration-based, e.g., Sitzmann and Weinhardt, 2019) will be complemented by exercise-based and experience-based training (Cannon-Bowers and Bowers, 2010) with multimodal mixed reality applications, which allow experience-based learning with the help of virtual reality-based representations (via data glasses, tablet or PC) and can be adapted to the individual usage and learning style preferences of the trainees. The training will be developed and implemented in cooperation with our project partner GfS (Gesellschaft für Simulatorschulung mbH). After project completion, the GfS will provide the training to nuclear power plant operators and, if necessary, develop them so that a sustainable contribution to the preservation of the specialized knowledge in the nuclear energy sector is achieved. To identify the needs for dismantling-relevant training objectives and competencies in the first step, a document analysis (safety alerts and monthly reports from our project partner PreussenElektra GmbH and over 500 reportable incidents from 28 nuclear power plants from 2012–2020), as well as 10 expert interviews, were conducted. The document analysis was used to investigate the incidents for (1) differences between operational phase and decommission, (2) differences in events between in-house and contractor personnel and to identify the incidents with the highest frequencies. The objective of the expert interviews was the qualitative context analysis as well as the identification of dismantling-relevant competence fields. The analysis allowed us to identify nine dismantling-related competence fields for employees and managers and a further three specifically for managers. These 12 competence fields will be discussed and defined in more detail in further interviews with approximately 20 managers and 30 employees. Based on these findings, training objectives will be formulated and training content designed. The presentation outlines the analysis described above as well as the identified fields of competence and sketches the further procedure of the collaborative project.

Aerosol release fraction by concrete scarifying operations and its implications on the dismantling of nuclear facilities

The sanitation of concrete structures through dismantling of nuclear buildings is complicated by the radiological threat associated with the airborne release of fine dust. This is the reason why the aerosol release fraction (ARF) associated with mechanical removal of concrete structure containing radioactivity needs to be accurately evaluated to implement efficient radiological survey and containment techniques. We characterize experimentally the ARF resulting from milling operations on a standard non-radioactive concrete slab in a confined experimental chamber using an industrial scarifying machine. Our results reveal a significant production of fine aerosol particles with a mass median aerodynamic diameter close to 4 μm and which mineralogical composition is dominated by calcium and silica compounds. The ARF measured when a vacuum suction device is used to confine the dust production close to the source is on the order of 5 × 10−4; the maximum ARF estimated when no suction device is used is on the order of 0.5. As the study is focused on non-radioactive concrete, transposition of aerosol characteristics investigated in this study to assess radioactive airborne release is only relevant for in-depth neutron activation on elemental compounds of concrete.

Improvement of cutting performance for thick stainless steel plates by step-like cutting speed increase in high-power fiber laser cutting

A study was conducted to improve the cutting performance of a 60-mm thick stainless steel plate using a 6-kW fiber laser. Two techniques for improving the initial cutting performance were evaluated by preheating the work piece with a waiting time and step-like cutting speed increase. Both techniques showed improved cutting results compared to constant speed cutting. Among them, the method with a step-like cutting speed increase showed the better result in terms of cutting performance. As a result, a 60-mm thick stainless steel plate was cut at a maximum cutting speed of 72 mm/min with a preheating cutting speed of 24 mm/min. In order to confirm the effect of preheating, an additional experiment was performed to measure the temperature variation during the cutting process. Through this experiment, preheating temperature conditions were found to allow the specimen to be cut. It is expected that the results of this work will contribute to improving the cutting performance of thick metal structures in various industrial fields, as well as the dismantling of nuclear facilities using lasers in the future.

Les nouveaux procédés de décontamination des effluents liquides et des solides du nucléaire

Les nouveaux procédés de décontamination des effluents liquides et des solides du nucléaire

Aspects of operational radiation protection during dismantling of nuclear facilities relevant for the estimation of internal doses

Operational radiation protection of workers during the dismantling of nuclear facilities is based on the same radiation protection principles as that applied in its exploitation period with the objective of ensuring proper implementation of the as-low-as-reasonably-achievable (ALARA) principle. These principles are: prior determination of the nature and magnitude of radiological risk; classification of workplaces and workers depending on the risks; implementation of control measures; monitoring of zones and working conditions, including, if necessary, individual monitoring. From the experiences and the lessons learned during the dismantling processes carried out in Spain, several important aspects in the practical implementation of these principles that directly influence and ensure an adequate prevention of exposures and the estimation of internal doses are pointed out, with special emphasis on the estimation of internal doses due to transuranic intakes.

Decommissioning strategy selection

Abstract At the end of their useful life nuclear facilities have to be decommissioned. The strategy selection on how to decommission a facility is a highly important decision at the very beginning of decommissioning planning. Basically, a facility may be subject to (a) immediate dismantling; (b) deferred dismantling after a period of “safe enclosure” or (c) entombment where a facility is turned into a near surface disposal facility. The first two strategies are normally applied. The third one may be accepted in countries without significant nuclear activities and hence without disposal facilities for radioactive waste. A large number of factors has to be taken into account when a decision on the decommissioning strategy is being made. Many of the factors cannot be quantified. They may be qualitative or subject to public opinion which may change with time. At present, a trend can be observed towards immediate dismantling of nuclear facilities, mainly because it is associated with less uncertainty, less local impact, a better public acceptance, and the availability of operational expertise and know how. A detailed evaluation of the various factors relevant to strategy selection and a few examples showing the situation regarding decommissioning strategy in a number of selected countries are presented in the following article.

Decommissioning technologies, including recent developments and special features of the dismantling of nuclear research and prototype facilities

Abstract A variety of technologies is available for the decontamination and dismantling of nuclear facilities. All over the world, these technologies as well as conditioning processes of decommissioning waste are further developed. So far, they have been mainly applied to the dismantling of research and prototype facilities. Dismantling of reactors of higher power has started with the nuclear power plants of Greifswald and Würgassen among others. The present paper shall present the state of the art of decontamination and dismantling techniques as well as of post-treatment processes of radioactive decommissioning waste. From the technical point of view, the most complex step is the remote dismantling of activated and highly contaminated components. The prototype facilities of Forschungszentrum Karlsruhe, which are currently being dismantled, cover all types of plants. Their status of dismantling and the experience gained from using decommissioning technologies that are also suited for power facilities shall be illustrated. Further developments and adaptations of individual techniques, e. g. thermal and mechanical cutting methods, as well as of the complete systems technology, including carrier system, manipulator system, and tools, are reasonable and indispensable for managing the variety of dismantling tasks and, not least, for reducing their operation times and costs of use.