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Tritium self-sufficiency is a critical prerequisite for future fusion reactors. The tritium breeding blanket, as the component responsible for in-vessel tritium generation, requires coordinated neutronic and engineering optimization in order to maximize its achievable tritium breeding ratio (TBR). In this work, a high-fidelity 22.5° toroidal sector neutronics model of the China Fusion Engineering Test Reactor (CFETR) equipped with a Helium-Cooled Ceramic Breeder (HCCB) blanket was established. On this basis, we developed a Multi-physics Coupling Intelligent Neutronic Optimization code (MCINO), a two-stage neutronics optimization framework that combines global exploration by simulated annealing with subsequent local refinement. The objective was to maximize the global TBR by optimizing the radial distribution of breeder (Li4SiO4) and neutron multiplier (Be) zones. The optimized design increased the global TBR to approximately 1.193, corresponding to an 8.36% improvement over the initial configuration. The improvement is associated with a more effective radial allocation of breeding and multiplying materials, which enhances neutron moderation, multiplication, and use for tritium production. The optimization workflow was designed to reduce the number of expensive high-fidelity transport recalculations, thereby improving computational efficiency relative to direct brute-force search. Finally, the engineering feasibility of the optimized design was checked through three-dimensional thermal-hydraulic verification, which confirmed that the representative modules remained within their prescribed operating limits. The present work provides an efficient and physically transparent framework for integrated blanket neutronics design and optimization.

A critical challenge for operating fusion burning plasma in high-confinement mode lies in mitigating damage caused by edge-localized modes (ELMs). While impurity seeding has been experimentally validated as a reliable and effective ELM mitigation technique, its underlying physics remains insufficiently understood and requires further clarification. Through nonlinear magnetohydrodynamic simulations, this work reproduces key features of a natural ELM crash and reveals its trigger mechanism. Impurity seeding significantly affects nonlinear ELM dynamics by inducing local and global modifications to the pedestal pressure profile, driving high-n ballooning mode instabilities that govern an ELM crash. Two critical control parameters—impurity density level and poloidal seeding location—are systematically investigated, which play key roles in the timing of ELM crash onset and the resulting energy loss magnitude.

The China Fusion Engineering Test Reactor (CFETR) is the next facility in the Chinese roadmap to realize sustainable-clean fusion energy. Because of the large tritium inventory of the CFETR, safety analyses are necessary. During the current design phase of the CFETR, performing the risk analysis of tritium released into the environment could reveal the design weaknesses and indicate improvements aimed at trtium risk (TR) reduction but also form a part of the licensing process for future CFETR construction and operation. Several CFETR safety analyses using deterministic approaches have been conducted, but relatively few studies based on probabilistic approaches are currently available. In this paper, a probabilistic risk assessment (PRA) model for tritium release into the environment for CFETR was proposed, in which the frequency and the radioactivity of the released tritium in accident sequences are considered. The event tree/fault tree (ET/FT) method was applied to investigate primary factors contributing to the tritium release into the environment and to estimate the frequency of accident sequences. We presented a model for preliminary and rapid assessment of the radioactivity of released tritium in accident sequences and developed a calculation code. The application process and validity of the model were demonstrated through the assessment of TR of the CFETR for selected postulated initiating events.

Self-consistent modeling using the stability, transport, equilibrium, and pedestal (STEP) workflow in the OMFIT integrated modeling framework (predicting pedestal with EPED, core profiles with TGYRO, current profile with ONETWO, and EFIT for equilibrium) suggests ITER and future devices such as China Fusion Engineering Test Reactor (CFETR) Zhuang et al (2019 Nucl. Fusion 59 112010) will benefit from high-density operation (Greenwald limit fraction f g w ≈ 0.7−1.3). Regimes with an operational density near the Greenwald limit will likely need peaked density profiles so that the pedestal density remains below the Greenwald limit. Peaked density profiles can be achieved with the help of pellet injection. A flexible Pellet Ablation Module (PAM), which predicts the density source based on a comprehensive analytical pellet ablation model, has been developed for predicting pellet fueling for transport studies, and has been incorporated into the STEP workflow for predictive modeling. This workflow is applied to DIII-D and finds good agreement with experiments. On ITER the effect of pellet fueling is examined in an advanced inductive scenario, where a fusion gain of up to Q  = 9 is predicted with strong central pellet fueling. On CFETR, with a mid-radius density source, an average of 1.5 × 10 22 electrons s −1 are required to achieve the density and temperature profiles necessary for the 1000 MW advanced scenario with a tritium burn-up fraction of ∼ 3 % .

In-vessel Loss of Coolant Accident (LOCA) is one of the fundamental design-basis accidents that must be considered in the design phase of the China Fusion Engineering Test Reactor (CFETR). If high-temperature coolant leaks into the Vacuum Vessel (VV), a flashing jet is formed, leading to localized pressure and temperature peaks. As the VV serves as a primary barrier for radioactive protection, these peaks may pose significant challenges to its integrity. In this study, a three-dimensional simulation model of the CFETR VV is developed to analyze the evolution of flow, pressure, and temperature fields during an in-vessel LOCA. The study investigates the structural evolution of the highly under-expanded jet and its impact on pressure and temperature dynamics. The results indicate that the pressure at the jet impact surface is significantly higher than at other locations within the VV. Comparisons of temperature and pressure variations at different monitoring points reveal that if the bursting valve is positioned at the furthest location, the pressure at the jet impingement surface may reach the VV’s pressure limit before the VV Pressure Suppression System is activated, as determined using the lumped-parameter analysis method. Additionally, temperature rises caused by gas compression at wave crossings pose challenges to the VV material’s thermal limits. Furthermore, a simulation with a larger breakage size of the First Wall coolant pipes is conducted. The findings show that with increased breakage size, the under-expanded jet evolves more rapidly, pressure inside the VV rises more quickly, and the VV reaches its pressure limit sooner. Moreover, localized temperature spikes exceeding material limits are triggered by the convergence of jet-induced compression waves.

The efficiency of ion cyclotron resonance heating (ICRH) is highly sensitive to plasma composition, indicating that fusion-born alphas, which have already been observed in deuterium-tritium experiments at JET, will have a non-negligible influence in future fusion reactors. This study aims to investigate the impact of alphas on various ICRH scenarios intended for devices similar to the Chinese Fusion Engineering Testing Reactor. An equivalent Maxwellian distribution is employed for a detailed analysis of the potential effects of alphas on ICRH. Preliminary findings indicate that the Doppler broadening mechanism allows alpha particles to absorb ICRH wave energy across a considerably broad spatial area. Furthermore, the relative positioning between the cutoff layer within the plasma and the fundamental resonance layer of alpha particles is crucial for determining absorption. Among the planned ion heating scenarios, alphas are bound to absorb wave energy in both the deuterium minority and three-ion heating scenarios, potentially becoming the dominant absorbers and thereby reducing the heating efficiency for fuel ions. Conversely, the helium-3 minority and second harmonic tritium heating scenarios appear to be less affected by alphas, making them promising candidates for playing a pivotal role in future fusion reactors.

The physics of neoclassical tearing modes (NTMs) is of great concern to tokamak plasma stability and performance, especially in the burning plasma regime. Whereas in many situations the seed events can be clearly identified, such as sawteeth and edge localized modes, the potential seeding mechanism of NTMs due to the resistive tearing instability driven by the impurity radiation cooling still needs more study. Recent NIMROD simulations have demonstrated that local impurity radiation cooling can drive the seed island growth and trigger the subsequent onset of NTM instability. The seed island is mainly driven by the local helical perturbation of the diamagnetic current induced by the perturbed pressure gradient as a result of the impurity radiative cooling on the rational surface. A heuristic closure for the neoclassical viscosity is adopted, and the seed island is further driven by the perturbed bootstrap current induced from the neoclassical electron viscous stress in the extended Ohm’s law. The growth rate of the NTM in simulations is found proportional to the electron neoclassical viscosity, and a theoretical neoclassical driving term is adopted to account for the nonlinear neoclassical island growth in the simulations.

The tritium breeding capacity of fusion blankets is a critical factor in achieving tritium self-sufficiency in fusion reactors. Current designs for tritium production in blankets are based on neutronics simulations, whose accuracy requires experimental validation. This study focuses on the experimental validation of the neutronic design reliability of the supercritical CO2-cooled lithium-lead (COOL) blanket developed for the China fusion engineering test reactor (CFETR). For this purpose, an experimental mock-up was designed and fabricated to replicate the key neutronics characteristics of COOL blanket. The mock-up was irradiated using D–T neutron generator and validated using multiple techniques: tritium production rate (TPR) online monitoring with a miniature back-to-back lithium glass scintillator detector, TPR integral measurement using Li2CO3 pellets analyzed by liquid scintillation counting (LSC), and neutron flux measurement with activation foils (Au, Zr). To enhance accuracy, corrections were applied for lithium-lead (PbLi) segregation based on element analysis and for neutron source intensity based on in-situ depth profiling of tritium in the tritide target. The results show excellent agreement between experiments and simulations, with calculation-to-experimental (C/E) value ranging from 0.96 to 1.11 for TPR measured by lithium-glass scintillator detectors, 0.90–1.09 for TPR by Li2CO3 pellets, and 0.84–1.13 for reaction rates measured by activation foils.

The aim of this work is to analyze the alpha particle transport induced by Alfvén eigenmodes (AEs) based on the latest design of China Fusion Engineering Test Reactor (CFETR). Firstly, the stability of AEs is analyzed in order to understand the physical characteristics of AEs in CFETR with latest design parameters. AEs driven by alpha particles are analyzed using the gyrokinetic ion/fluid electron hybrid code GEM. The transport of alpha particles is investigated using a reduced energetic particle transport model based on the resonance broadened quasi-linear model. GEM results show that AEs with many toroidal mode numbers can be destabilized simultaneously by alpha particles in CFETR, and the toroidal mode number of the most unstable mode is n=8 . It is found that the excitation threshold of the alpha particle central beta for the n=8 mode is substantially below the expected alpha particle beta value of CFETR. All these results indicate that AEs can be driven strongly in CFETR plasmas. Furthermore, simulation results using the reduced transport model show that, due to multiple unstable AEs, the alpha particle density decreases in the core and alpha particles are transported from the core region ( r/a<0.35 ) to the outer region ( r/a>0.35 ). In addition, we find that the minimum value of the safety factor qmin and the central beta value of alpha particle have significant effects on the alpha particle transport, and the AE-induced alpha particle transport level becomes lower with smaller linear growth rates. Finally, it is found that the radial range of the redistributed alpha particle density profile depend on the qmin radial location.

A three-dimensional fluid model of a double-driver negative hydrogen ion source for China Fusion Engineering Test Reactor (CFETR) neutral beam injection is developed. In this model, the magnetic filter field is generated by 16 permanent magnets, which are surrounded by a soft iron. In order to accurately describe the transportation of charged species in the presence of strong magnetic field, both the electron magnetization and ion magnetization are taken into account, and the accuracy of the model has been proved by comparison with experimental data. By employing this model, the spatial distributions of the plasma parameters have been investigated, and three methods are proposed to optimize the symmetry at the bottom of the expansion region of a double-driver source. The results indicate that by adjusting the power of Driver I while keeping the power of Driver II constant, the symmetry of the electron density and negative hydrogen ion density could be improved. Furthermore, the inclusion of partition improves the symmetry of the electron temperature and density but has no impact on the regulation of the negative hydrogen ion density distribution. Finally, the application of magnetic shield can not only improve the symmetry of the electron density and negative hydrogen ion density, but also increase their densities at the bottom of the expansion region.