Hasil untuk "Nuclear engineering. Atomic power"

Z. Yu, F. Oneill, M.I. Patino et al.

Pure chromium (Cr) targets were exposed to high-flux deuterium (D) plasmas in the Pisces-RF linear plasma device, and measurements of D retention, release, and erosion were subsequently performed. Post-exposure D retention was quantified using temperature-programmed desorption on Cr targets irradiated by 50 eV ions over a broad range of exposure temperatures (423–873 K) and ion fluences (3×1024–3×1026 m−2). The retained D inventory was observed to decrease rapidly with increased exposure temperature, from approximately ∼7×1020 m−2 at ∼420 K, to then saturate near ∼1020 m−2 for exposure temperatures above ∼550 K. Separately, at fixed exposure temperature (∼450 K), D retention was found to have only a weak dependence on increasing ion fluence. Lastly, the erosion of Cr in D plasma was investigated for ion impact energies in the range 40 ≤ Ei ≤ 250 eV. Erosion was inferred using optical emission spectroscopy (OES) from the ratio of emission lines (Cr I (425.4 nm)/D I (656.1 nm)) measured close to the target. Conversion of the OES yield data to net erosion yield was made with singular ion energy target mass-loss measurements. These net erosion yield data were then further corrected to obtain gross erosion yield by accounting for a re-deposition factor, computed using a simple model. The gross erosion yield is found to be 2–4 times lower than predicted by SDTrimSP, consistent with that typically observed for light-ion sputtering under high-flux plasma conditions.

K. Saito, D. Hwangbo, M. Miyamoto et al.

The release of deuterium (D) atoms from a nanostructure ‘fuzz’ tungsten (W) after a sequential plasma irradiation of helium (He) and D was explored. Thermal desorption spectroscopy revealed that more than 60% of total D amount was already released at >423 K. A sophisticated measurement with an aberration-corrected scanning TEM combined with electron energy-loss spectrometer (STEM-EELS) directly showed the trapping of D atoms into He bubbles after the plasma irradiation and the release of D from the He bubbles at elevated temperature at 423 K. The He bubbles containing D were characterized by (i) relatively large volume and (ii) small He energy-loss shift below 2 eV. It is suggested that the shifts in the energy-loss peaks of He and D could be used as indicators of D absorption within He bubbles.

D. Mazon, G. Vayakis, M. Walsh et al.

This chapter presents the activity conducted by the ITPA topical group (TG) on Diagnostics over about the last 15 years. Following a general introduction of the ITER Diagnostics led by their measurement roles, the document is organized in several subchapters detailing the design support, research and development activity conducted by each of the specialist working groups (WGs) of the TG. Please note that the magnetic diagnostics were supported at the TG without a specific WG. Their status is included in the general introduction. In the following some highlights of the subchapter’s contents are provided. Recent advances in ITER first wall (FW) diagnostics for the measurements of plasma-metallic wall interaction in support of the ITER research plan are reported. An InfraRed imaging Video Bolometer for ITER has been developed and tested on several tokamaks to measure the radiated power loss. A laser-induced breakdown spectroscopy (LIBS) technique which utilizes a pulsed laser beam to ablate locally by forming a crater, will measure local tritium inventory in the FW material. Real-time Residual Gas Analyzers will measure the neutral gas composition in a divertor port and an equatorial port during plasma operation. Due to the full metallic FW environment, the plasma-wall interaction in ITER will face several challenges such as the compromised radiated power and divertor heat flux measurements by reflection. Ray tracing and analysis codes have been developed to eliminate and correct the effects of reflection in the measurements. The characteristics of the reflecting surfaces depending on the roughness and angle of the incidence have been measured by dedicated experiments, and the results were applied to the reflection elimination. For the measurement of the metallic impurity radiation induced by eroded metallic atoms, a vacuum ultraviolet spectrometer has been developed and tested. An extensive thermonuclear diagnostic suite will be required to support the operation of ITER and the planned experimental program for future burning plasma experiments. Due to the harsh environmental conditions, the implementation of diagnostic systems in ITER is a major challenge. These conditions include high levels of neutron and gamma fluxes, neutron heating, particle bombardment. Therefore, the selection and design of diagnostic systems must take into account a number of phenomena previously unseen in diagnostic design. For this reason, the measurement of neutrons and confined or lost fast ions, with particular emphasis on alpha particles, is critical to ITER. The diagnostics associated with these measurements will be important for future plasma-burning experiments at ITER. The high neutron emission and very large plasma size in ITER make neutron diagnostics the main diagnostic method used to measure plasma parameters such as fusion power, fusion power density, ion temperature, energy of fast ions and their spatial distributions in the plasma core. Active spectroscopy techniques are methods where a neutral particle beam is injected into the plasma and information on plasma parameters is extracted from the measurement of line emission resulting from the beam-plasma interaction, either by plasma ions or by beam atoms. Spatial localization is achieved by crossing the beamline and multiple observation lines. The ITER plasma will be a high temperature, moderately dense, fully ionized collisional plasma. The plasma facing surfaces are principally metallic being fashioned from beryllium or tungsten but many other elements, arising from either structural or from operational needs, may enter this plasma. The energy range of the emitted photons range from meV (infra-red) to multi keV (x-rays) and originate from all areas of the plasma volume. The primary role of passive emission diagnostics is to identify what is in the plasma from spectral signatures. Extracting quantitative information from these measurements such as impurity content, ion temperature, rotation, degree of detachment and radiated power depends on calibrated instruments, a physics model of the atomic and molecular processes and plasma transport and an analysis workflow that takes into account environmental effects such as reflections. The particular needs for ITER have prompted a multi-machine, many-year effort to address all these aspects and this chapter reviews the work on diagnostic design, experiments and new analysis techniques. An overview of the laser diagnostics to be implemented on ITER is also provided in this paper. This includes descriptions of the Thomson scattering in the core, edge and divertor regions, polarimetry and interferometry diagnostics used for measuring plasma density and also measurements of helium density in the divertor using Laser Induced Flourescence. Techniques which can allow improvements on current measurements are also addressed in particular expanding poloidal polarimetry measurements to measure field fluctuations and proposed use of dispersion interferometery which has a number of advantages over existing methods. This paper identifies particular areas where further research and testing on existing tokamaks is useful even at this advanced stage to inform the design of diagnostics for ITER. Outstanding areas of concern for the implementation of laser diagnostics, in particular with a view to reliable operation are identified. An overview of the latest developments of microwave diagnostic systems and techniques is given. The primary focus is the contributions for ITER—the next step burning plasma experiment—which is supplemented by describing recent progress of techniques applicable for fusion experiments beyond ITER. The contributions are intentionally kept concise, and are being supplemented by a rich list of references for further studies. Radiation induced effects are receiving continuous and well-deserved attention of the ITER diagnostic community and they are in many cases one of the primary design drivers of the ITER diagnostic systems. The paper summarizes recent progress in this area focusing primarily on the ITER diagnostics but in some cases provides also outlook for the possible solutions for even more demanding radiation environment of fusion reactors beyond ITER. Despite advancements in the area of modeling and simulation of various radiation induced effects, experimental testing in a nuclear environment as close as possible to the target one is still seen as unavoidable for proper qualification of particular diagnostic functional elements. Recent advancement within three diagnostic areas: optical diagnostics, magnetics and bolometers is covered. Encouraging results on qualification of silica glass vacuum window assemblies are presented. In the area of magnetic sensors, progress of irradiation tests performed on ITER in-vessel LTCC inductive sensors is presented with outlook for novel technological approaches to inductive sensors utilizing thick printing and photolithography technologies being highlighted. Summary of advancements in the area of steady state magnetic field sensors based on Hall effect is given. New results of neutron irradiation test of the ITER borosilicate glass inserts for vacuum electrical feedthroughs are summarized finding negligible swelling at target level of neutron fluence. Off-line irradiation tests of fiber optic current sensors for plasma current measurement demonstrated that both for gamma doses up to 5 MGy and a total neutron fluence up to 10 ^15 cm ^−2 , radiation induced changes are still compatible with required measurement accuracy on ITER. The ITER bolometers are given as an example how considering radiation effects may influence the diagnostic design. Finally, outlook for future main R&D directions is outlined. All optical and laser-based diagnostics in ITER will be using mirrors to guide plasma radiation toward detectors, cameras and sensors. In the hostile plasma, radiation and particle environment the optical characteristics of diagnostic mirrors will degrade directly affecting the entire performance of involved diagnostic systems. An assessment of factors affecting mirror performance is provided. Among the prime adverse factors are deposition of plasma impurities, sputtering of mirror surface and steam ingress in the vicinity of mirrors. Within the International Tokamak Physics Activity with active support by ITER central team and domestic agencies, the structured research and development (R&D) program on mitigation of risks for diagnostic mirrors is underway. Within this program the mirror material development, the passive mitigation of mirror degradation by using diagnostic ducts and shutters along with an active mirror recovery program comprising the in-situ mirror cleaning and calibration is underway. Recent developments in diagnostic mirror R&D are described in this Chapter along with an example of their implementation of R&D solutions in ITER Infrared Thermography diagnostic. An assessment of still open engineering and physics questions, considerations on mirror risks during an early phase of ITER operation are given along with an overview of diagnostic mirror evolution in the late ITER operation stage toward the demonstration fusion power plant. Several crucial areas of diagnostic R&D outlined in ITER Research Plan are addressed. The basic control groups in a fusion reactor can be broken-down in five categories: (1) plasma position, magnetic configuration, and plasma current control, (2) profile control and confinement optimization, (3) MHD control and suppression, (4) edge dissipation control, radiation and plasma exhaust control and (5) break-down optimization. These categories are coupled via the physics (a control action in one domain will affect the other domains) and via shared actuators (e.g. ECRH for impurity accumulation avoidance, current density distribution control and MHD suppression). Consequently, a supervisory control system should determine the priority of the various control tasks, their couplings, and the interfaces with the safety and interlock system. For the systematic development of the various controllers taking the complexity of the plasma and the control system into account, a model-based approach is required. A short historical overview is given of the developments in systems and control theory and control engineering with special emphasis on those developments that are most relevant for Nuclear Fusion research and operation. An overview is given of the state of the field of fusion plasma control for the control categories. It will be shown how synthetic diagnostics are being developed in ITER and how they are used in diagnostic design and design validation and how they can be in model-based controller synthesis using relatively simple models. In modern control methods, multiple diagnostics are used to constrain relatively simple models. The constrained models provide an estimate for the state. This opens the route to state controllers, such as model predictive control. A major challenge in nuclear fusion research is the coherent combination of data from heterogeneous diagnostics and modeling codes for machine control and safety as well as physics studies. Measured data from different diagnostics often provide information about the same subset of physical parameters. Additionally, information provided by some diagnostics might be needed for the analysis of other diagnostics. A joint analysis of complementary and redundant data allows, e.g. to improve the reliability of parameter estimation, to increase the spatial and temporal resolution of profiles, to obtain synergistic effects, to consider diagnostics interdependencies and to find and resolve data inconsistencies. Physics-based modeling and parameter relationships provide additional information improving the treatment of ill-posed inversion problems. A coherent combination of all kind of available information within a probabilistic framework allows for improved data analysis results. The concept of integrated data analysis (IDA) in the framework of Bayesian probability theory is outlined and contrasted with conventional data analysis. Components of the probabilistic approach are summarized and specific ingredients beneficial for data analysis at fusion devices are discussed.

赵 正成, 赵 亚楠, 夏 玉博 et al.

氦氙冷却反应堆以氦氙混合气体作为布雷顿循环运行工质，具有循环效率高、功率质量比高和运行可靠等特点，在深空大功率核反应堆电源和无人潜航器核动力等领域具有广阔的应用前景。针对氦氙布雷顿循环系统运行特性，建立了涡轮机、压缩机、紧凑型换热器等氦氙布雷顿循环热力设备仿真模型，开发了氦氙冷却反应堆布雷顿循环运行性能分析仿真工具。以“普罗米修斯”氦氙冷却反应堆布雷顿循环系统为研究对象，分析循环各点参数与各部件性能对系统效率和系统比功的影响。结果表明：系统效率与系统比功均存在最佳压比，循环最高温度越高、最低温度则越低，系统效率与系统比功越大；压力对循环的影响不明显，压力越大，系统效率与系统比功略微减小；回热器总热导率越大，系统效率越大，系统比功不变。

MA Yaolong, ZHANG Zhigang, WEI Xiaodong, LI Hongxing

Liquid sodium leaks and sodium fire accidents are common occurrences during the operation of sodium-cooled fast reactors and pose key and challenging issues in their development. Of the different forms of sodium fire, spray sodium fire has the most severe consequences and is the primary threat to plant safety. The atomization characteristics of liquid sodium are a crucial factor affecting the spray sodium fire. Studying these characteristics through experimental research could provide essential data for simulating and evaluating the safety of spray sodium fires. In this paper, an experimental visualization device that takes into consideration the material characteristics of liquid sodium was designed and constructed. In the experiments, the liquid sodium with varying masses (20-150 g) and temperatures (200-400℃) was injected from nozzles of different shapes (round, oval, sharp crack, rough crack) at different heights (55-85 cm) using high-pressure nitrogen (0.1-0.5 MPa), generating sodium liquid sprays. The experimental phenomenon was noted and recorded. Finally, the sodium spray was collected within a cooling tank filled with liquid paraffin, which caused liquid droplets to solidify into solid sodium particles. The size distributions of the liquid sodium droplets in the spray field were inferred by measuring those of solid sodium particles. The study analyzed the effects of injection pressure, initial sodium mass and temperature, leakage height, and leakage boundary shape on the liquid sodium spray characteristics. It is found that the process of liquid sodium spray can be divided into three stages:the column flow stage, the transition stage and the atomization stage. As the stages develop, the liquid sodium spray angle will progressively rise, reaching its peak during the atomization stage. The raising of leakage height and injection pressure causes increased flow rate of liquid sodium resulting in intensified air disturbance for more atomized sodium flow, leading to a decrease in mass intermediate diameter of the sodium spray. The atomization characteristics of liquid sodium are greatly influenced by the leakage boundary, and the mass intermediate diameter of the spray decreases approximately linearly with the increase of the shape factor of the leakage boundary. Increasing the initial temperature of liquid sodium may lead to a reduction in its surface tension and viscosity, potentially promoting sodium flow atomization. However, such changes are likely to be negligible, thereby limiting the impact of the initial temperature on the atomization characteristics within experimental conditions. The rise in sodium mass would result in an elevation of the liquid level within the crucible, thereby reducing the impact of high-pressure gas on the leakage end in the proximity of the nozzle. Consequently, the intermediate mass diameter of the spray will increase with the initial sodium mass. This research can provide fundamental experimental data for the simulation and safety assessment of spray fires of liquid sodium and can provide technical references for sodium fire prevention and control measures.

Nhan Nguyen Trong Mai, Kyeongwon Kim, Deokjung Lee

STREAM, developed by the Computational Reactor Physics and Experiment laboratory (CORE) of the Ulsan National Institute of Science and Technology (UNIST), is a deterministic neutron- and photon-transport code primarily designed for light water reactor (LWR) analysis. Initially, the photon module in STREAM did not account for fluorescence and bremsstrahlung photons. This article presents recent developments regarding the integration of atomic relaxation and bremsstrahlung models into the existing photon module, thus allowing for the transport of secondary photons. The photon flux and photon heating computed with the newly incorporated models is compared to results obtained with the Monte Carlo code MCS. The incorporation of secondary photons has substantially improved the accuracy of photon flux calculations, particularly in scenarios involving strong gamma emitters. However, it is essential to note that despite the consideration of secondary photon sources, there is no noticeable improvement in the photon heating for LWR problems when compared to the photon heating obtained with the previous version of STREAM.

Kang Wang, Ya Xi, Xiang Zan et al.

A melting failure of W monoblock components of the upper divertor outer target in EAST occurred during the plasma campaigns in 2019. The failure characters and microstructure evolution of the failed W monoblock have been well investigated on one string (W436 string). Near the strike point region where heat flux density is highest, macroscopic cracks and severe surface damage such as dimensional change, melting and solidification are visible in several W monoblocks. At the same time, debonding, melting and migration of Cu/CuCrZr cooling tube components introduced fatal damage to the structure and function. The heat-induced microstructure evolution in the rest part has been examined via hardness tests and metallography. From the heat flux surface to the cooling tube, hardness increased gradually and the recrystallized grains could be found in the region with the highest temperature, while recrystallization grains also appear in some W monoblocks near the cooling tube area. The detailed microstructure has been investigated by metallography and EBSD. Such cases in EAST provide experiences on the extreme condition of accidental loss of coolant or higher discharge power in future devices.

I. V. Melnikov, V. V. Nechitailov, V. G. Beketov et al.

Due to the variety of defects that arise in electrical machines, it is necessary to use more effective methods for monitoring their condition. All over the world research and development of new means and methods for monitoring powerful electrical machines during their operation is underway. Some examples of recent advances are vibration diagnostic methods for assessing the compaction of components inside a transformer, acoustic and electrical systems for monitoring partial discharges, data processing using digital methods, and new sensors for continuous monitoring of gases and moisture in oil, as well as hot spot temperatures. Additionally, thermal imaging testing of power equipment is also an important tool to ensure reliable operation. It is believed that the most effective method is gas chromatographic oil analysis, which can identify most defects in oil-filled equipment. During the operation of powerful electrical machines, the use of existing non-destructive testing methods does not allow a complete assessment of the condition of the main parts of the equipment, as an analysis of damage locations shows, 25% are damage to the core and windings. Effective monitoring of the condition and determination of the performance of transformers is of particular importance, since they are key elements in the operation of nuclear power plants. The paper considers the possibility of using the eddy current testing method; determining a defect in magnetic core steel is based on fixing the unevenness of the magnetic field on the horizontal or vertical planes of a yoke or rod consisting of electrical steel plates. Monitoring and evaluating the functioning of existing equipment, detecting deficiencies in the early stages of their development, when repair costs are still minimal, and preventing emergency failures become a priority. In accordance with the growth rate of detected deficiencies, monitoring is carried out from time to time or continuously, the maximum number of monitored characteristics is achieved when the transformer is fully tested to determine its functionality.

Rudrajit Choudhuri, Ambareesh Ramakrishnan, Amreeta Chatterjee et al.

Generative AI (genAI) tools (e.g., ChatGPT, Copilot) have become ubiquitous in software engineering (SE). As SE educators, it behooves us to understand the consequences of genAI usage among SE students and to create a holistic view of where these tools can be successfully used. Through 16 reflective interviews with SE students, we explored their academic experiences of using genAI tools to complement SE learning and implementations. We uncover the contexts where these tools are helpful and where they pose challenges, along with examining why these challenges arise and how they impact students. We validated our findings through member checking and triangulation with instructors. Our findings provide practical considerations of where and why genAI should (not) be used in the context of supporting SE students.

HAN Xu;YAN Xiaojun;GUO Xiliang;XI Yahui;QIN Xiang;ZHANG Li;GAO Kai;GAO Chao

Recently, cement matrixes become a mainstream solution to address the stabilization of radioactive spent resins. Generally, the cumulative dose of spent resin cemented waste form will reach approximately 106 Gy over a disposal lifetime of 300 years. Due to the organic properties of spent resin, namely producing gas if being irradiated, it inevitably affects the mineral phase of cement waste forms. Therefore, the content and composition of the mineral phase could be key factors determining the performance of cement waste forms. With that in mind, in this paper, the influence of the above factors on ordinary Portland cement (OPC) was explored especially. Specifically, based on the Gibbs free energy minimization principle, the influence of three gases generated by irradiation of waste resin, namely H2, CH4 and CO2, on the mineral phase composition and total volume of ordinary Portland cement was discussed. Thereafter, the evolution of the mineral phase composition of ordinary Portland cement over time was investigated based on the rate of irradiated gas production. In this work, all the experiments were produced by GEMS software based on the thermodynamic Gibbs free energy minimization method. Meanwhile, the formulation for cement solidification of spent resin meets the standard of GB 14569.1-2011. From the experimental results, several important findings were obtained. Firstly, only a small amount of H2 and CH4 reacts with the cement hydration products, which causes the dissolution of the mineral phase with high Ca/Si, while the total volume of the mineral phase is almost invariant. Secondly, in the prior phase, CO2 first reacts with the portlandite in the cement hydration products. After the portlandite dissolute completely, the silicate minerals start to dissolve, forming a system composed of abundant carbonate and a few clay minerals, which decreases the total volume of the mineral phase. Thirdly, during the predicted 160 years, the effects of spent resin irradiation gases on the cemented waste form are consistently dominated by CH4 and H2, while the performance of the cemented waste form is stable. However, the risk of rupture and explosion caused by the accumulation of H2 and CH4 in the waste packaging containers and the risk of radioactive release due to carbonation of the cemented waste form by CO2 should not be overlooked. In summary, the above results reveal the evolution law of degradation of cement solidified body caused by waste resin irradiation gas. The results of this paper provide effective data support for the safety evaluation of waste resin treatment by cement solidified form.

Slim Abid, Ali M. El-Rifaie, Mostafa Elshahed et al.

Multi-area power systems (MAPSs) are highly complex non-linear systems facing a fundamental issue in real-world engineering problems called frequency stability problems (FSP). This paper develops an enhanced slime mold optimization algorithm (ESMOA) to optimize the tuning parameters for a cascaded proportional derivative-proportional integral (PD-PI) controller. The novel ESMOA proposal includes a new system that combines basic SMO, chaotic dynamics, and an elite group. The motion update incorporates the chaotic technique, and the exploitation procedure is enhanced by searching for a select group rather than merely the best solution overall. The proposed cascaded PD-PI controller based on the ESMOA is employed for solving the FSP in MAPSs with two area non-reheat thermal systems to keep the balance between the electrical power load and the generation and provide power system security, reliability, and quality. The proposed cascaded PD-PI controller based on the ESMOA is evaluated using time domain simulation to minimize the integral time-multiplied absolute error (ITAE). It is evaluated in four different test situations with various sets of perturbations. For tuning the cascaded PD-PI controller, the proposed ESMOA is compared to the golden search optimizer (GSO) and circle optimizer (CO), where the proposed ESMOA provides the best performance. Furthermore, the findings of the proposed cascaded PD-PI controller based on the ESMOA outperform previous published PID and PI controllers adjusted using numerous contemporary techniques.

Jochen Stiasny, Baosen Zhang, Spyros Chatzivasileiadis

The dynamic behaviour of a power system can be described by a system of differential-algebraic equations. Time-domain simulations are used to simulate the evolution of these dynamics. They often require the use of small time step sizes and therefore become computationally expensive. To accelerate these simulations, we propose a simulator - PINNSim - that allows to take significantly larger time steps. It is based on Physics-Informed Neural Networks (PINNs) for the solution of the dynamics of single components in the power system. To resolve their interaction we employ a scalable root-finding algorithm. We demonstrate PINNSim on a 9-bus system and show the increased time step size compared to a trapezoidal integration rule. We discuss key characteristics of PINNSim and important steps for developing PINNSim into a fully fledged simulator. As such, it could offer the opportunity for significantly increasing time step sizes and thereby accelerating time-domain simulations.

Kimiaki Kawai

Japan declares in its security policy that US extended nuclear deterrence is “essential”. However, policymakers do not seem to have provided sufficient explanation of the legality and the implications of the use of nuclear weapons, even if they argue that the policy of extended nuclear deterrence is essential. From the perspective of international law, three questions can be identified in examining Japan’s reliance on the US extended nuclear deterrence. The first is what the target would be in an anticipated use of nuclear weapons, a question that relates to policymakers’ understanding of nuclear deterrence. The second is whether the civilian population is a permissible target for belligerent reprisals; this question relates to the legality of countervalue strategy targeting an adversary’s cities and civilians as intolerable punishment. The third is whether countermeasures by a third party on behalf of an attacked state are permissible, a question that relates to the legal basis of Japan’s reliance on the US nuclear capabilities. These questions at the nexus of politics and law have been neither addressed in depth in deliberations in the National Diet of Japan nor examined sufficiently in scholarly research. This article addresses these questions and considers the legal challenges and the implications today that are inherent in Japan’s security policy, which relies on US extended nuclear deterrence.

Tirel Kévin, Kooyman Timothée, Coquelet-Pascal Christine et al.

The link between reactor design studies and scenarios calculations is usually sequential. From a list set of objectives, a reactor design is produced and passed to the scenarist in the form of a numeric irradiation model. This approach assumes that the reactor design is fixed from the scenarist perspective. The method presented in this article proposes to use a flexible reactor model, built with artificial neural networks, that gives the possibility to the scenarist to change a reactor design directly during the scenario calculations. Doing so, the reactor design is no longer an imposed parameter but a tool to find new optimal trajectories. Moreover, this flexible model is able to exploit the historical loaded fuel compositions generated by the scenario calculations in order to monitor the reactor performances over time. In this paper, the flexible reactor model construction is detailed and the interest of such method is highlighted with an application case that consists in the transition from a PWR fleet, similar to the French one, towards a PWR − SFR fleet stabilizing plutonium inventory.

Marc Verriere, Nicolas Schunck, Irene Kim et al.

From the lightest Hydrogen isotopes up to the recently synthesized Oganesson (Z=118), it is estimated that as many as about 3000 atomic nuclei could exist in nature. Most of these nuclei are too short-lived to be occurring on Earth, but they play an essential role in astrophysical events such as supernova explosions or neutron star mergers that are presumed to be at the origin of most heavy elements in the Universe. Understanding the structure, reactions, and decays of nuclei across the entire chart of nuclides is an enormous challenge because of the experimental difficulties in measuring properties of interest in such fleeting objects and the theoretical and computational issues of simulating strongly-interacting quantum many-body systems. Nuclear density functional theory (DFT) is a fully microscopic theoretical framework which has the potential of providing such a quantitatively accurate description of nuclear properties for every nucleus in the chart of nuclides. Thanks to high-performance computing facilities, it has already been successfully applied to predict nuclear masses, global patterns of radioactive decay like $β$ or $γ$ decay, and several aspects of the nuclear fission process such as, e.g., spontaneous fission half-lives. Yet, predictive simulations of nuclear spectroscopy or of nuclear fission, or the quantification of theoretical uncertainties and their propagation to applications, would require several orders of magnitude more calculations than currently possible. However, most of this computational effort would be spent into generating a suitable basis of DFT wavefunctions. Such a task could potentially be considerably accelerated by borrowing tools from the field of machine learning and artificial intelligence. In this paper, we review different approaches to applying supervised and unsupervised learning techniques to nuclear DFT.

Hao Yu, Haoran Wang, Sosuke Kondo et al.

Alumina-forming FeCrAl oxide dispersion strengthened (ODS) ferritic alloys are considered as promising structure materials for the next-generation nuclear reactors. Current work is aimed at investigating Fe ion irradiation effect on the alumina scale formed on FeCrAl ODS ferritic alloy. A single alpha-alumina layer with a thickness of about 0.7 µm was formed on the surface of the alloy by a pre-oxidation process at 1000 °C with 9 h. The pre-oxidized specimen was subsequently irradiated using 6.4 MeV Fe3+ ion beam to 2 dpa at 500 °C. Nanoindentation testing demonstrated that the hardness of the alumina scale decreased after the Fe ion irradiation. Corresponding microstructure characterization was carried out by using electron backscatter diffraction (EBSD) and scanning transmission electron microscopy (STEM). Alumina grain growth and softening in accordance with the Hall-Petch relationship are responsible for the hardness decrease by the Fe ion implantation. Irradiation-induced dissolution of Y-Zr oxide particles in alumina grains as well as the irradiation-induced segregation of reactive elements along the alumina grain boundaries were observed.

Rashina Hoda

Grounded Theory (GT), a sociological research method designed to study social phenomena, is increasingly being used to investigate the human and social aspects of software engineering (SE). However, being written by and for sociologists, GT is often challenging for a majority of SE researchers to understand and apply. Additionally, SE researchers attempting ad hoc adaptations of traditional GT guidelines for modern socio-technical (ST) contexts often struggle in the absence of clear and relevant guidelines to do so, resulting in poor quality studies. To overcome these research community challenges and leverage modern research opportunities, this paper presents Socio-Technical Grounded Theory (STGT) designed to ease application and achieve quality outcomes. It defines what exactly is meant by an ST research context and presents the STGT guidelines that expand GT's philosophical foundations, provide increased clarity and flexibility in its methodological steps and procedures, define possible scope and contexts of application, encourage frequent reporting of a variety of interim, preliminary, and mature outcomes, and introduce nuanced evaluation guidelines for different outcomes. It is hoped that the SE research community and related ST disciplines such as computer science, data science, artificial intelligence, information systems, human computer/robot/AI interaction, human-centered emerging technologies (and increasingly other disciplines being transformed by rapid digitalisation and AI-based augmentation), will benefit from applying STGT to conduct quality research studies and systematically produce rich findings and mature theories with confidence.

Anton S. Lapin, Aleksandr S. Bobryashov, Victor Yu. Blandinsky et al.

For 60 years of its existence, nuclear energy has passed the first stage of its development and has proven that it can become a powerful industry, going beyond the 10% level in the global balance of energy production. Despite this, modern nuclear industry is capable of producing economically acceptable energy only from uranium-235 or plutonium, obtained as a by-product of the use of low enriched uranium for energy production or surplus weapons-grade plutonium. In this case, nuclear energy cannot claim to be a technology that can solve the problems of energy security and sustainable development, since it meets the same economic and ‘geological’ problems as other technologies do, based on the use of exhaustible organic resources. The solution to this problem will require a new generation of reactors to drastically improve fuel-use characteristics. In particular, reactors based on the use of water cooling technology should significantly increase the efficiency of using U-238 in order to reduce the need for natural uranium in a nuclear energy system. To achieve this goal, it will be necessary to transit to a closed nuclear fuel cycle and, therefore, to improve the performance of a light-water reactor system. The paper considers the possibility of using a reactor with a fast-resonance neutron spectrum cooled by supercritical water (SCWR). The SCWR can be effectively used in a closed nuclear fuel cycle, since it makes it possible to use spent fuel and discharge uranium with a small amount of plutonium added. The authors discuss the selected layout of the core with a change in its size as well as the size of the breeding regions (blankets). MOX fuel with an isotopic plutonium content corresponding to that discharged from the VVER-1000 reactor is considered as fuel. For the selected layout, a study was made of the reactor system features. Compared with existing light-water reactors, this reactor type has increased fuel consumption due to its improved efficiency and nuclear fuel breeding rate up to 1 and above.

Geun Hyeong Lee, Hee Reyoung Kim

The geometrical and electromagnetic variables of a rectangular-type magnetohydrodynamic (MHD) circulation system are optimized to solve MHD equations for the active decay heat removal system of a prototype Gen-IV sodium fast reactor. Decay heat must be actively removed from the reactor coolant to prevent the reactor system from exceeding its temperature limit. A rectangular-type MHD circulation system is adopted to remove this heat via an active system that produces developed pressure through the Lorentz force of the circulating sodium. Thus, the rectangular-type MHD circulation system for a circulating loop is modeled with the following specifications: a developed pressure of 2 kPa and flow rate of 0.02 m3/s at a temperature of 499 K. The MHD equations, which consist of momentum and Maxwell's equations, are solved to find the minimum input current satisfying the nominal developed pressure and flow rate according to the change of variables including the magnetic flux density and geometrical variables. The optimization shows that the rectangular-type MHD circulation system requires a current of 3976 A and a magnetic flux density of 0.037 T under the conditions of the active decay heat removal system. Keywords: Magnetohydrodynamics (MHD), Rectangular-type circulation system, Magnetic flux density, Current

C. Subaar, J.K. Amoako, A. Owusu et al.

Magnetic resonance imaging current operating frequencies are above 100 kHz which is converted to heat through resistive tissue losses during imaging. The imaging is coupled with a concurring increase in temperature in patients. Magnetic resonance imaging of the brain has seen a rising clinical request during diagnosis and therefore become imperative that its safety issues be assessed. This study modelled Pennes' classical bio-heat equation using Finite Difference Method (FDM) approach and with the help of MATLAB programming language, predicted three dimensional steady state temperature distributions in patients during magnetic resonance imaging. Sixty-four paediatric patients' referred for (head) brain magnetic resonance imaging scan at 37 Military Hospital and the Diagnostic Center Limited, Ghana, pre-scan and post-scan temperatures were measured at the right tympanic. The numerically steady state temperature distribution during magnetic resonance imaging shows that there is excessive temperature elevation at the skin surface of the patients. The resulting skin heating during magnetic resonance imaging can reach dangerous level which suggests that the ohmic heating of tissue is greatest at the surface and minimal at the center of the patient's brain. Though the experimental results show that patients brain temperature increase after imaging, all measured temperatures were within acceptable safe levels.