1,721,038 research outputs found
Application of the TRANSURANUS code for the fuel pin design process of the ALFRED reactor
No full textThe Advanced Lead Fast Reactor European Demonstrator (ALFRED) is the 300 MWth pool-type reactor aimed at proving the feasibility of the design concept adopted for the European Lead-cooled Fast Reactor(ELFR) of Generation-IV, whose preliminary design has been proposed within the LEADER (Lead Cooled European Advanced Demonstration Reactor) EURATOM Project.
In the frame of investigating different options to optimize the conceptual fuel pin design of ALFRED, the fuel performance analysis of the reactor core is carried out by means of the TRANSURANUS code, which is presented in this paper. Results of the average and the hottest reactor conditions are discussed concerning both fuel and cladding performance on the basis of indicative design limits. A sensitivity analysis is performed in order to assess the impact of models and parameters affected by a larger uncertainty, and to identify a “worst case” scenario. This strategy allows identifying some design parameters which could be modified to improve the fuel pin behaviour, in order to gain benefits mainly in terms of maximum fuel temperature. The results of the present work are useful for giving feedback to the conceptual design of the ALFRED reactor and, in perspective, to improve the safety-by-design characteristics of the LFR systems
Analysis of transient fission gas behaviour in oxide fuel using BISON and TRANSURANUS
Full text linkThe modelling of fission gas behaviour is a crucial aspect of nuclear fuel performance analysis in view of the related effects on the thermo-mechanical performance of the fuel rod, which can be particularly significant during transients. In particular, experimental observations indicate that substantial fission gas release (FGR) can occur on a small time scale during transients (burst release). To accurately reproduce the rapid kinetics of the burst release process in fuel performance calculations, a model that accounts for non-diffusional mechanisms such as fuel micro-cracking is needed. In this work, we present and assess a model for transient fission gas behaviour in oxide fuel, which is applied as an extension of conventional diffusion-based models to introduce the burst release effect. The concept and governing equations of the model are presented, and the sensitivity of results to the newly introduced parameters is evaluated through an analytic sensitivity analysis. The model is assessed for application to integral fuel rod analysis by implementation in two structurally different fuel performance codes: BISON (multi-dimensional finite element code) and TRANSURANUS (1.5D code). Model assessment is based on the analysis of 19 light water reactor fuel rod irradiation experiments from the OECD/NEA IFPE (International Fuel Performance Experiments) database, all of which are simulated with both codes. The results point out an improvement in both the quantitative predictions of integral fuel rod FGR and the qualitative representation of the FGR kinetics with the transient model relative to the canonical, purely diffusion-based models of the codes. The overall quantitative improvement of the integral FGR predictions in the two codes is comparable. Moreover, calculated radial profiles of xenon concentration after irradiation are investigated and compared to experimental data, illustrating the underlying representation of the physical mechanisms of burst release
A semi-empirical model for the formation and depletion of the high burnup structure in UO2
No full textIn the rim zone of UO2 nuclear fuel pellets, the combination of high burnup and low temperature drives a microstructural change, leading to the formation of the high burnup structure (HBS). In this work, we propose a semi-empirical model to describe the formation of the HBS, which embraces the polygonisation/recrystallization process and the depletion of intra-granular fission gas, describing them as inherently related. For this purpose, we performed grain-size measurements on samples at radial positions in which the restructuring was incomplete. Based on these new experimental data, we infer an exponential reduction of the average grain size with local effective burnup, paired with a simultaneous depletion of intra-granular fission gas driven by diffusion. The comparison with currently used models indicates the applicability of the herein developed model within integral fuel performance codes
Modelling of Burst Release in Oxide Fuel and Application to the Transuranus Code
No full textThe substantial release of fission gas during temperature transients (burst release) can be critical during operational reactor transients and (design-basis) accidents. A purely diffusion-based model cannot explain the rapid kinetics of the process. In this work, we present a model for transient fission gas release in oxide fuel. This model arises from experimental observations relative to both in-reactor irradiation and post-irradiation annealing of UO2 fuel. In particular, micrographs demonstrate the presence of grain-face separations (micro-cracks) in transient-tested fuel, thus indicating that a basic mechanism of burst release is micro-cracking. The presented model extends a previously developed diffusion-based model, introducing the effect of micro-cracking. This is interpreted as a reduction of the grain-face gas inventory and storing capacity during transients. The process is modelled through an empirical temperature-dependent function based on the experimentally observed characteristics of gas release during both heating and cooling transients. The model also includes an irradiation-induced micro-crack healing process, which gradually restores the original grain-face gas storing capacity. This process is described by means of an empirical burnup-dependent function. The resulting extended model (diffusion-based fission gas behaviour together with transient release) is overall semi-empirical, but the burst release capability notably preserves the continuity in time and space as well as the consistent coupling of the calculated fission gas release and swelling. The new model was originally implemented in the fuel performance code BISON. In this work, we implemented the model in the TRANSURANUS fuel performance code, and applied it to the simulation of some light water reactors fuel rod irradiation experiments of the OECD/NEA International Fuel Performance Experiments database. The results point out a representation of the kinetics of burst release consistent with experimental evidence
Greenspace: Towards a Systematic, Global and Innovative Evaluation of the Environmental Impact of Space Activities for a Safe and Sustainable Space Environment
No full textESA has recently decided, through the Clean Space program, to begin a systematic assessment of the environmental impact of its activities. The reasons lie in the increasing environmental awareness, in the emanation of new and stricter regulations on industrial processes and in the fact that the impact of space activities has never been methodically evaluated. The present work has been developed in this frame: its goals are to define the idea of sustainability for space activities, to develop innovative methods to evaluate their impact and to propose a more environmentally-friendly design solution to mitigate their effects in one of the many stages of their life cycle. The first task was carried out starting from the definition of sustainability given by Gro Brundtland and performed by adding sustainability drivers related to space waste, further divided into the subdrivers room availability and risk of collisions. Moreover, a distinction between absolute green technologies and relative green technologies has been proposed. As for the second objective, the eMergy approach, holistic and simpler than LCA methods, was adapted from ecology and used to identify the critical subsystem of a space launcher. The criticality analysis shifted the focus on the propellants, which were further analyzed through a specifically tailored qualitative method, Fuel Life Environmental Cycle Assessment (FLECA). The use of this method led to the identification of the hydrogen production for Ariane launchers as one of the most significant environmental hotspots. Six alternatives to mitigate the carbon dioxide emissions caused by the hydrogen-producing plant were proposed. After a preliminary evaluation of their effectiveness, a Multi-Criteria Decision Analysis (MCDA) method, TOPSIS, was applied to find the optimal solution, considering also the criteria of adaptability to the plant, maturity of the technology and cost. The production of hydrogen from biomass-derived methanol, paired with carbon capture, turned out to be the best option, mainly because of the significant reduction in specific CO2 emissions it generates. In conclusion, the present work has given new perspectives and new insights on the evaluation of the environmental impact of space activities, in order to create a safe and sustainable space environment. The adopted method is systematic, global and multidisciplinary: rigorous definitions have been given and framed in the scientific literature, launches are not seen as singular events, but as occurrences that have extended influence in space and time, and frontier developments from other fields of engineering have been adapted to the space field
PolyPole-1: An accurate numerical algorithm for intra-granular fission gas release
No full textThe transport of fission gas from within the fuel grains to the grain boundaries (intra-granular fission gas release) is a fundamental controlling mechanism of fission gas release and gaseous swelling in nuclear fuel. Hence, accurate numerical solution of the corresponding mathematical problem needs to be included in fission gas behaviour models used in fuel performance codes. Under the assumption of equilibrium between trapping and resolution, the process can be described mathematically by a single diffusion equation for the gas atom concentration in a grain. In this paper, we propose a new numerical algorithm (PolyPole-1) to efficiently solve the fission gas diffusion equation in time-varying conditions. The PolyPole-1 algorithm is based on the analytic modal solution of the diffusion equation for constant conditions, combined with polynomial corrective terms that embody the information on the deviation from constant conditions. The new algorithm is verified by comparing the results to a finite difference solution over a large number of randomly generated operation histories. Furthermore, comparison to state-of-the-art algorithms used in fuel performance codes demonstrates that the accuracy of PolyPole-1 is superior to other algorithms, with similar computational effort. Finally, the concept of PolyPole-1 may be extended to the solution of the general problem of intra-granular fission gas diffusion during non-equilibrium trapping and resolution, which will be the subject of future work
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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