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Accelerator driven system (ADS) is an advanced nuclear system with high inherent safety feature, which can transmute the nuclear waste including minor actinides (MA) and long-lived fission products (LLFPs) into short-lived fission products. In order to accomplish the neutronic simulation in ADS, a conventional way can be divided into two steps, namely the physical process of proton beam bombarding spallation target (FLUKA) and the neutron transport process in subcritical reactor coupling with a spallation neutron source (OpenMC). However, there are some difficulties in the modeling process for ADS, such as the inconsistent modeling process between FLUKA and OpenMC codes, and the error-prone process of constructing complex geometries. Therefore, it is imperative to build a code system that can convert the CAD modeling files into the input cards of Monte Carlo codes. In this context, a code system named CAD-PSFO (FreeCAD based parsing script for FLUKA and OpenMC) has been developed to solve the modeling conversion problem in ADS, in which basic geometry and boolean logic classes have been established with a mapping relationship to FLUKA and OpenMC codes, and ray-casting technology based iteration method has been proposed to solve the problem of higher-order surfaces in complex geometries. Finally, CAD-PSFO has been verified and validated by comparing with a reference model, two benchmarks, and two simulation tests. [ABSTRACT FROM AUTHOR]

• An unfolding method based on iterative regularization is proposed. • Response functions of the organic scintillator has been simulated with Geant4 code. • The method is applied to neutorn spectrum unfolding of organic scintillation measurement. • Neutron spectrums of the four typical neutron spectrums with large uncertainties are unfolded successfully, such as the mono-energetic DD fusion neutron spectrum, 241Am-Be neutron spectrum, 252Cf neutron spectrum and Gaussian broadened DT fusion neutron spectrum. An iterative regularization method is proposed for neutron spectrum unfolding of the liquid organic scintillator EJ-301. The Arnoldi iteration is used to generate Krylov subspaces. GMRES (Generalized Minimal Residual) combined with Tikhonov regularization is used for neutron spectrum updating. The restart method is applied to speed up the convergence as well as non-negativity constraints. The Monte Carlo code Geant4 is applied to simulate the response functions and PHSs (pulse height spectrums) of the neutron spectrums for unfolding. Four typical neutron spectrums are studied, such as the mono-energetic DD fusion neutron spectrum, 241Am-Be neutron spectrum, 252Cf neutron spectrum and Gaussian broadened DT fusion neutron spectrum. Comparison study between the proposed method and the existing methods is also carried out, such as GRAVEL, MLEM, and direct Tikhonov regularization. Unfolding results with acceptable accuracies are obtained with the proposed method, and the proposed method shows better adaptabilities than the other three methods with both the ideal and simulated PHSs in most cases. [ABSTRACT FROM AUTHOR]

• CAD optimization method is used in converting dense mesh structure to low poly style. • CAD optimization method can provide the intuitive and flexible features. • Neutronics analysis of the FFHR is performed based on CAD optimization method. • Stellarator-type FFHR can keep tritium self-sufficiency and get high breeding ratio. The stellarator plasmas devices have some advantages in steady state operation with less magneto hydrodynamic activities, and the development of stellarator-type FFHR (Fusion-Fission Hybird Reactor) can provide viable energy in the foreseeable future with less requirements to the plasmas technology compared with the pure fusion system. However, the neutronics design of the stellarator-type FFHR has some challenges and difficulties, since the construction of helical structures with large number of high order spline surfaces are the extremely complicated process, and the physical parameters of the complex model have to be changed frequently in the primary design stage, which make the corresponding manual input simulation work into the time consuming and error prone tasks. In this context, the CAD optimization method has been used in converting the dense mesh oriented CAD structure to the low poly style, and the CAD-PSFO code has been employed for the modeling transformation process in Monte Carlo calculation. The thorium resource has been selected as the breeding material for the stellarator-type FFHR, and the polonium and natural abundance of uranium have been used as the seed fuel for the initial loading in order to get the high energy multiplication factor. The OMCB (OpenMC based Burnup code) has been introduced to study the burnup features, and stellarator-type FFHR has been designed as the multi-purposes facility that can keep tritium self-sufficiency and get the high breeding ratio with steady energy output. [ABSTRACT FROM AUTHOR]

• Spallation target and fuel handling system has been developed based on VR platform. • The movement of spallation target has been detailed in the fuel handling process. • The collision detection and the real-time roaming experience have been discussed. • The fuel handling system can cover all the assemblies in subcritical reactor. The China initiative Accelerator Driven subcritical System (CiADS) has already embarked on a plan to be built in south China's Guangdong province for the research purpose of lead–bismuth cooled fast reactor and minor-actinide transmutation technology. In comparison with the other critical reactors, it is difficult to arrange the fuel handling equipment and to make the whole core refueling plan, since there is a proton beam tube in the central of the core and the operating environment is completely opaque. In this context, an innovation design of the spallation target and fuel handling system is proposed in Institute of Modern Physics, Chinese Academy of Sciences (IMPCAS) based on an immersive Virtual Reality (VR) platform, which can fulfill the loading and refueling procedure without mutual collisions, and provide the real-time roaming experience as in the real world. Detailed information of the handling system have been introduced including the optimized logical structure in consideration of the movement of spallation target for the fuel handling process, the principle of collision detection based on the fast ray-casting technology, the real-time roaming experience with feedback control in refueling procedure, and the reliability assessment and sequential optimization for the above process. The spallation target and fuel handling system can cover all the assemblies in subcritical reactor and provide a powerful tool for the frequently updated engineering design of the CiADS project. [ABSTRACT FROM AUTHOR]

• The structure and models of the subchannel code are described. • Critical validation with experience is carried out and discussed. • The relevant calculation results of CiADS are analyzed in detail. The lead bismuth eutectic (LBE) cooled fast reactor fuel assemblies in China Initiative Accelerator Driven subcritical System (CiADS) are supported by wire spacers, and the sub-channel code is a significant analysis method to evaluate the thermal–hydraulic behavior of fuel assemblies. In this study, a sub-channel analysis code for LBE coolant is developed, in which the pressure drop model, turbulent mixing model, and heat transfer model based on LBE are added and applied. Besides, the heat transfer experience of the 61-pin fuel assembly and other sub-channel codes are chosen to verify. Finally, the full-scale simulation of CiADS fuel assembly is calculated. The results show that the thermal–hydraulic parameters of CiADS meet the design criterion. The optimized range of pitch to diameter ratio is 1.133–1.145 according to the thermal–hydraulic analysis. It is recommended to use 37-pin bundle for the numerical simulation simplification of full-scale rod bundles. [ABSTRACT FROM AUTHOR]

• The power optimization control strategy for CiADS project has been developed. • Logical structure of PID controller has been established for power control process. • QEA has been employed to deal with CiADS power optimization control strategy. • Performance of optimization method has been verified in predefined scenarios. The power optimization control strategy for China initiative Accelerator Driven subcritical System (CiADS), which focuses on the study of dynamic features and the stable operation of coupling nuclear system, is one of the most important research topics for the current engineering stage that is expected to be completed in the year 2025. However, the traditional way in handling the power control problem was carried out by specialists with transcendental knowledge and experiences, which has been believed as the high labor intensity and the brute force trial-and-error process. In this context, the Quantum Evolutionary Algorithm (QEA) has been employed to deal with the CiADS power optimization control strategy in order to fulfill the adaptive searching procedure continuously and automatically. The manipulation of proton beam intensity has been used as the main control approach, and the physical model in describing the dynamic characteristics of power control system has been constructed in coupling the lumped parameter method and the point reactor kinetics method. In addition, the logical structure of Proportional Integral Derivative (PID) controller has been established for the power control process, and the QEA has been adopted to obtain the suitable set of parameters in the PID controller. Finally, the performance of the optimization method has been verified in the predefined control scenarios, and all the numerical results show that the control method has the applicability and feasibility in solving the CiADS power control problems. [ABSTRACT FROM AUTHOR]

• Genetic algorithm has been used for the temperature control of DGT system in CiADS. • The control approaches of beam intensity and granular speed have been introduced. • Logical structure of PID temperature controller for DGT system has been established. • Evolution of parameters in genetic algorithm based controller has been discussed. The DGT (Dense Granular spallation Target) is the crucial component in CiADS (China initiative Accelerator Driven subcritical System), which is the important device in connecting the high power accelerator and the subcritical reactor. In order to keep the stable and reliable running of the coupling system, the temperature control of the DGT should be carefully studied and optimized, where the gravity driven tungsten alloy granules are considered as the spallation target material and the corresponding coolant, and the working temperature in normal operation condition should be controlled around the pre-setting value without bringing the large perturbation. Two kinds of control approaches have been adopted in this research in adjusting the temperature inside the DGT, which are the intensity of proton beam and the flow speed of tungsten alloy granules. Therefore, the simulation method and the PID (Proportional Integral Derivative) controller have been established based on the cooperation of two approaches in order to better adapt to the temperature control of the DGT. Moreover, the genetic algorithm has been employed to select and optimize the key parameters in PID controller for the purpose of substituting the experiential selection in traditional manually iterative process. Finally, the temperature control system has been evaluated based on the reference control scenarios, and all the simulation results demonstrate that the optimized method has applicability and feasibility in the temperature control of the spallation target system. [ABSTRACT FROM AUTHOR]