The European Journal of Physics N (EPJ-N)
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Design and experimental assessment of an innovative vacuum end-effector for irradiated graphite handling
No full textThe decommissioning of graphite-moderated nuclear reactors presents considerable obstacles, primarily due to the handling of large volume of irradiated graphite that must be safely extracted and managed. In response to these difficulties, this work focuses on the design and validation of a novel vacuum-based system specifically engineered for the brick-by-brick retrieval of graphite components during reactor decommissioning. The proposed solution aims to overcome limitations of earlier methods, particularly those related to graphite cracking and the generation of secondary waste. The system developed is a proprietary end-effector that enhances suction-based lifting, achieving up to seventeen times increase in lifting power compared to existing industrial counterparts. This design has undergone testing and experimental trials under diverse operating conditions, replicating the handling of Magnox graphite blocks. The system’s capabilities were assessed using key performance indicators such as lifting strength, safety margin, and adaptability under different operational scenarios. Results demonstrated a safety factor of 7 and the capability to lift damaged and broken blocks. The system also proved effective under less-than-ideal airflow conditions, maintaining high safety standards and demonstrating its robustness for real-world decommissioning tasks
Adaptive adjoint-based population-control methods for kinetic simulations in TRIPOLI-4
No full textTime-dependent Monte Carlo simulations for reactor kinetics applications require special variance-reduction and population-control techniques in order to efficiently cope with the typically huge imbalance between the respective time scales and population sizes of neutrons and precursors. Building upon the legacy implementation of the algorithms devoted to kinetics in the Monte Carlo code TRIPOLI-4, in this work we propose an adaptive adjoint-based population-control method that considerably improves the behaviour of time-dependent simulations. Thanks to a time-dependent importance-sampling scheme, based on the solution of the adjoint point-kinetics equations, neutron and precursor weights are continuously adjusted, which paves the way towards the simulation of previously unattainable reactor transients involving long times and large reactivity excursions. The computational effectiveness of the newly developed method is evaluated in terms of Figure of Merit (FoM) over a set of time-dependent scenarios encompassing the Flattop-Pu, SPERT III E-core and CROCUS benchmarks
Research on the safety of heavy-liquid-metal-cooled reactors
No full textSince the fifth edition, dating 1998 to 2002, the Euratom Framework Programmes have supported numerous collaborative projects dealing with the research and development of the heavy liquid metal technology. In this 20+ year's context of outstanding scoring, LESTO – the latest project recently launched – is taking the baton from PASCAL, about to conclude, with ANSELMUS bridging the gap in between. Both PASCAL and LESTO address (on complementary and synergic topics) key safety-related aspects of the technology, sharing the same foundational approach: advancing on the two pillars of experimental testing and software simulation. The two projects also share the focus on ALFRED and MYRRHA, the two heavy-liquid-metal-cooled reactors included in the strategic roadmap of the European Sustainable Nuclear Industrial Initiative. Thanks to the results generated by the two projects, a significant contribution will be delivered to the substantiation of evidences requested for the licensing of ALFRED and MYRRHA and, in perspective, for that of future heavy-liquid-metal-cooled nuclear systems
The Euratom PULSAR project
No full textPULSAR (PU-238-coupLed dynamic power system for SpAce exploRation and beyond) was a research and innovation project funded by the European Commission between 2022 and 2024. The aim of this project was to establish building blocks for the development of Radioisotope Power Systems (RPS) fueled by Pu-238 with European technologies and standards. Radioisotope Power Systems (RPS) is a key enabling technology for exploration of locations hidden from the sun for prolongated periods, or of deep space, where the sun cannot deliver sufficient power to spacecrafts. This project has brought together leading stakeholders in the field of space and nuclear. PULSAR consortium includes nine partners: Tractebel (coordinator), SCK CEN, CEA, JRC, Airbus DS, ArianeGroup, UBFC, INCOTEC and ARTTIC. The paper provides a presentation of the project, the organization of the different work packages between partners, the objectives and the achievements obtained. Future prospect and expected challenges are presented based on the hypothesis assumed in PULSAR
Advancing sustainability and innovation in waste management and decommissioning within the Euratom HARPERS project
No full textThe HARPERS (HARmonised PracticEs, Regulations and Standards in waste management and decommissioning Harpers [
New model developments for fuel supply strategies in molten salt reactors: Application to the REM depletion code
No full textIn recent years, a particular family of molten salt reactors (MSRs) – those designed to burn plutonium and minor actinides – has attracted considerable interest from research institutions and companies, including CNRS and Orano. NRS/LPSC Grenoble has been studying and optimising MSRs since the early 2000s, within which framework the in-house precision-driven material evolution REM code was developed. Depletion simulation of burner MSRs has led to the development of new methods for supply management and the addition of additional constraint parameters to the REM code. These developments make it possible to introduce physico-chemical constraints into the analysis of this kind of reactor, enabling more precise studies. Examples include controlling the alkali or alkaline-earth fraction, or regulating the salt volume either by adjusting the supply or by adding a dynamic expansion tank. This paper presents new perspectives that led to work on the numerical stabilization of the system, which helped smooth out reactor characteristics such as reactivity and fuel supply. This, in turn, opened the way to new supply strategies, e.g., by considering separate supplies for each chemical species or for individual elements. Finally, results are presented showing that, in the case of an extraction scheme with actinide reinjection, element-based supplies better satisfy mass balance requirements than species-based supplies. Conversely, in schemes without reinjection, the opposite trend is observed. Considering these strategies, while taking into account chemical constraints such as element valency and salt electroneutrality, could lead to the development of a new model for material extraction
The Geant4 software toolkit evolution over the past decade
No full textGeant4 is an open software toolkit for the Monte-Carlo simulation of particle transport in matter. It is used in many domains, like high energy and nuclear physics, medical and space science, as well as homeland security and material science. Started 30 years ago, it is still subject to very active developments. This paper presents the developments in Geant4 over the past 10 years, covering the kernel, physics models, and software aspects. It also discusses ongoing R&D projects
Convergence of Monte Carlo algorithms for power reactor noise
No full textPower reactor noise refers to the small periodical variations of the neutron flux in nuclear reactor cores, induced by various perturbations. A prominent example is the vibration of fuel assemblies due to fluid-structure interactions. Although noise is generally an unwanted phenomenon, its analysis is useful for core monitoring. In this respect, several state-of-the-art deterministic or Monte Carlo solvers have been developed to solve the equations describing neutron noise. In this paper, we investigate the convergence properties of Monte Carlo methods for neutron noise analysis, within the orthodox linearization approximation. For this purpose, we establish a theoretical framework for complex-weighted Monte Carlo games and we show that convergence of such algorithms can be assessed using two sets of eigenvalues. In order to substantiate our findings, we examine a few relevant benchmark configurations for noise problems
ASSAS project, Artificial intelligence for Simulation of Severe AccidentS; Simulator development and Isotopic Source Term proposals
No full textNuclear Power Plant simulators play a central role in the training of nuclear operators. However, most simulators worldwide only cover Design Basis Accident, excluding the management of Severe Accidents. The need for a realistic training on such situations has been strengthened by the deployment of post-Fukushima safety improvements, which include different improvements to better mitigate severe accidents. The European project ASSAS (Artificial intelligence for Simulation of Severe Accidents) aims to address this gap by developing a proof-of-concept for a severe accident simulator. The prototype will feature a basic principles generic Pressurized Water Reactor, whose Graphical User Interface will be developed by Tecnatom-Westinghouse.
In addition to being a demonstrator for more complex industrial simulators, this basic-principles simulator is intended to support education and training activities on severe accident phenomenology. Reaching this objective required to address several competing constraints: representing the complexity of severe accidents without overwhelming the user with information, showing a large variety of phenomenology and operating situations with a limited number of systems and scenarios, running the simulation accurately in real time, etc. The proposed characteristics of the simulator to reach a compromise are presented in the first part of the article.
Besides, the description of the Source Term (ST) released by the accident appeared to need special attention, because of the complexity of its chemical and isotopic composition, which can drastically influence the radiological consequences of the accident. The second part of the article proposes a synthetic description of the source term, considered appropriate for training but also for a fast and still accurate assessment of accident consequences. This last feature opens the way for the use of the simulator to support emergency preparedness and response, possibly with Artificial Intelligence models.
This paper summarizes the work developed by Tecnatom-Westinghouse as leading WP6: Interfacing ASTEC with the simulation environment, of Project ASSAS funded by EU-EURATOM (g. a. no. 101059682) along the first-year project. It includes the development of the Simulator Specifications and Interface, the selected systems included in the scope and the scenarios to be considered as well as the definition of the Graphical User Interface and the main criteria used to fit to the targets of the project. Then, the paper focuses on the discussion on the proposals made to define the potential isotopic composition for the source term estimates, fitting to the main objectives of the project, as they are the education, the training, or the training for the surrogate models defined by the IA methodology, and how these targets impose restrictions to the isotopic characteristics of the ST used but keeping the major simulator features. Even though it is out of the current scope of the project, it has also been considered the potential use of the simulator for emergency preparedness and response training and consequence assessments to be properly founded for the future evolution of the simulator