Accelerator-driven Subcritical System Research Articles

Analysis of integrated target in thorium‐based molten salt fast energy amplifier

Conventional neutron targets in accelerator driven subcritical system (ADS) are based on the design using heavy metal like lead and lead-bismuth eutectic (LBE), which generally needs a separated loop for target cooling. In the thorium-based molten salt fast energy amplifier, an integrated target is conceived that the proton beam is directly placed in the chloride/fluoride molten salt core without a separated cooling loop for the target in consideration of the neutron productivity of the liquid molten salt fuel bombarded with the proton. The physical analysis of the spallation target is presented, including the spallation neutron yield, neutron spectrum, spallation products, and energy deposition. Chloride molten salt is a reasonable choice among four kinds of simulated target based on considering about the neutron yield, neutron spectrum, spallation products and energy deposition. The simulation code is the Monte Carlo code MCNP6.1. Besides, evaluation of the target size is presented, and two kinds of the beam tube layout are compared by considering the neutron economy in the system.

Core power control of the ADS based on genetic algorithm tuning PID controller

The accelerator driven subcritical system (ADS) reactor, an accelerator driven transmutation research facility relies on control rod and external neutron source to realize core power regulation. This paper researches the dynamic and control characteristics of the ADS core under the external neutron source disturbance. The state space model of the ADS core with multi-input multi-output is established by linearizing the core nonlinear model with small disturbance. The response characteristics of the ADS core power control under external neutron source strength regulation are simulated by using genetic algorithm tuning proportional-integral-derivative (PID) controller and traditional PID controller. The results show that under different external neutron source relative strength, the effect of genetic algorithm tuning PID controller is better than that of traditional PID controller. The ADS core power can be well controlled by using genetic algorithm tuning PID controller.

Study of Different Seed Fuels with Thorium in Accelerator-Driven Subcritical System

This work aimed to develop accelerator-driven systems (ADSs) with a subcritical thorium assembly for fuel breeding and clean energy utilization by using several seed fuels. The ADS reactor core was loaded with three different fuel types, namely, reprocessed fuel, UN, and UO2 (seed fuel) associated separately with ThO2 fuel (blanket) in a heterogeneous approach. The Monte Carlo code MCNPX 2.7.0 has been employed to calculate neutronic parameters such as the effective multiplication coefficient (Keff), the nuclear fuel evolution during the burnup for every case, and the power fraction from seed and blanket fuels. The results indicate that the utilization of thorium (without any contents of 233U at the beginning of cycle) with reprocessed fuel allowed more 233U production than the UN and UO2 cases but with shorter cycle length. Introducing thorium fuel with the UN into the ADS core presented an efficient method to produce thermal power with the longest cycle length approaching 20 years.

Design of machine protection system for CAFe facility

In an accelerator-driven sub-critical system (ADS), a strong proton beam from a high-power proton accelerator irradiates a spallation target to produce very intense neutrons for driving a reactor. Currently, the China ADS front-end demo linac (CAFe) facility is being built to provide strong beam with the beam intensity of several mAs. This paper reports the machine protection system (MPS) of the CAFe facility, which prevents or minimizes the beam-induced damages or the damages from other sources to the machines in the accelerator. The MPS of CAFe facility works under the framework of experimental physics and industrial control system (EPICS). The developed machine protection system includes fast protection function and slow interlock function, where the fast function is performed by FPGA controller and the slow function is performed by PLC controller. Based on the reports on the status of all relevant subsystems, MPS will either perform an emergency shutdown of the beam or machine or will permit normal operation. When an emergency shutdown of the beam is needed, MPS switches off the ion source or switches on the chopper. In addition to its protective role, MPS will also trace the origin of an emergency shutdown. The developed MPS has played an important role during the commissioning and successful operation of the CAFe facility at the end of 2019.

The PyNE-Based Burnup Analysis Method for Accelerator-Driven Subcritical Systems

To study the burnup features of accelerator-driven subcritical systems (ADSs), simplified transmutation trajectories are imperative to make the simulation process more effective with acceptable precision. This process has long been considered a challenging task since the construction of simplified burnup chains often need complex judgments and experiences. Additionally, the burnup analysis of ADSs requires more specific burnup chains for some important isotopes with minor actinides (MAs) and long-lived fission products (LLFPs) included. However, some general burnup codes lack these chains or pack some particularly important isotopes into a kind of pseudo nuclide. In this context, a PyNE-based burnup module (PyNE-Burn) has been developed to solve the burnup problem in ADSs, where three types of isotopes have been considered to construct the simplified burnup chains and weight-sorted judgment criteria have been proposed to determine which nuclides should be included. Moreover, the scan-mode-method-based high-order differential expression has been employed to substitute the legacy method in solving the linearized burnup chains. Finally, numerical tests have been carried out to demonstrate that the PyNE-Burn module has acceptable accuracy and can be used in dealing with the burnup problem in ADSs.

Development and validation of Burn-up Calculation Code IMPC-Burnup2.0 for accelerator-driven sub-critical system

Fuel depletion analysis is important for the evolutionary behavior of nuclear materials in the reactor. For the accelerator-driven sub-critical system (ADS), the main research focuses on the transmutation of minor actinides (MA) and long-lived fission products (LLFP). To perform nuclide inventory calculation of ADS, a new nuclide point-depletion code IMPC-Depletion has been developed by utilizing Chebyshev Rational Approximation Method (CRAM) and Transmutation Trajectory Analysis method (TTA) to solve the Bateman equation. Besides, a new burnup code system named IMPC-Burnup2.0 which couples the OpenMC neutron transport code and IMPC-Depletion is also developed to perform burnup behavior analysis of ADS sub-critical system. Finally, the decay of Np237 and fixed neutron flux irradiation of 3.4% UO2 are calculated and compared with other reference results to verify IMPC-Depletion. Moreover, IAEA-ADS and OECD/NEA ADS Minor Actinide Burner benchmark are calculated using IMPC-Burnup2.0 to testing the capability for burnup analysis for ADS sub-critical core. Numerical results show that IMPC-Burnup2.0 is reliable when compared with reference values and it can be used to solve burnup problem of ADS.

Structural design on reactor coupled with the spallation target for a lead-based ADS

In the Accelerator Driven Sub-critical System (ADS), the spallation neutron target is a core component connecting accelerator and the reactor, which makes the structure of different from the conventional fission reactor such as PWR and FBR. In the project of the China Initiative Accelerator Driven System (CiADS), the granular flow of the gravity driven Dense Granular flow Target (DGT) is adopted, which is an original spallation target scheme different from the existing international spallation target type. As a new form of target structure, DGT faces new technical challenges in the process of coupling with the reactor, i.e. special attention must be paid for the structure design of the reactor coupled with spallation target so that it can bear both of seismic and thermal loadings. In this paper, the coupling schemes of DGT and reactor are analyzed from engineering feasibility and safety, and the proposal of reactor-target coupling scheme is given. The supporting design and seismic analysis of the “hot pot type” design scheme and “bellows type” design scheme of reactor-target coupling systems for CiADS are carried out. A new damper-based support method is designed: roll-damper support. The calculation results show that the new support method effectively reduces the thermal stress of the container and the target, and realizes the shock absorption function even taking the effect of fluid–structure interaction (FSI) into account. Combining the advantages of the two schemes, a “hybrid type” optimization design scheme is proposed. The seismic calculation of the optimization scheme was completed by the time history analysis method, and then the stress evaluation was carried out. The results show that the “hybrid type” design scheme meets nuclear safety regulations and specifications. The research results can provide guidance for the selection of lead-based ADS reactor- target coupling systems, and propose optimization suggestions and ideas for reactor-target coupling problems.

一种用于C-ADS 低能束流传输线束流强度控制的新型可调限束光阑

A novel adjustable aperture is developed for the low energy beam transport line (LEBT) of the China Accelerator Driven Subcritical System (C-ADS). Two relatively rotating mirror-symmetry cores are adopted for the adjustable aperture to scrape unwanted outer particles, improve the beam quality and reduce the beam losses, and most of all, realize continuously tunable beam current and meet the requirement of round beam. The results of simulation and test show that the unwanted outer particles can be cut away and the beam current can be adjusted continuously online within the range of 0 to 10 mA. This device provides a convenient beam tuning method for the proton linear accelerator, which can satisfy the stable and reliable online operation of C-ADS linear accelerator.

Preliminary neutron study of a thorium-based molten salt energy amplifier

Present designs for molten salt thermal reactors require complex online processing systems, which are technologically challenging, while an accelerator-driven subcritical molten salt system can operate without an online processing system, simplifying the design. Previous designs of accelerator-driven subcritical systems usually required very high-power proton accelerators (> 10 MW). In this research, a proton accelerator is used to drive a thorium-based molten salt fast energy amplifier (TMSFEA) that improves the neutron efficiency of the system. The research results show that TMSFEA can achieve a long-term stable state for more than 30 years with a rated power of 300 MW and a stabilizing effective multiplication factor (keff) without any online processing. In this study, a physical design of an integrated molten salt energy amplifier with an initial energy gain of 117 was accomplished. According to the burn-up calculation, a molten salt energy amplifier with the rated power of 300 MWth should be able to operate continuously for nearly 40 years using a 1 GeV proton beam below 4 mA during the lifetime. By the end of the life cycle, the energy gain can still reach 76, and 233U contributes 70.9% of the total fission rate, which indicates the efficient utilization of the thorium fuel.

Preliminary Study on Transmutation of Plutonium and Minor Actinides in Accelerator Driven System

As a free CO2 emission energy source, nuclear energy can supply the world electricity for very long time, even for thousand years. However, to increase the public acceptance, nuclear spent fuel (high level nuclear waste) should be manage to minimize its radio-toxicity. There are several methods of processing nuclear spent fuel including geological repositories, reprocessing it to be used as fuel again or doing transmutation. In this preliminary study, the nuclear high level waste is transmuted by using an Accelerator Driven Subcritical System (ADS). ADS is a system consisting of a subcritical reactor core and a particle accelerator. Nuclear waste which will be transmuted is plutonium (Pu) and minor actinides (MA). Pu and MA are mixed in the ADS fuel that consists of U-ThO2(NO3)2, PuMA(NO3)4 dan HNO3. Two type of plutonium vectors have been evaluated, those are reactor grade Pu (RGPu) and weapon grade Pu (WGPu). The ADS can maintain it sub-criticality condition for RGPuMA and WGPuMA with the concentration of PuMA-Nitrate are above 62.6 kmol/m3 and 65.6 kmol/m3, respectively.

2 K superfluid helium cryogenic vertical test system for superconducting cavity of ADS Injector I

The accelerator-driven subcritical system (ADS) is the internationally recognized key technology of nuclear waste problem treatment, of which superconducting proton linac is an important part. With the support of the strategic science and technology pilot project of the Chinese Academy of Sciences, the Institute of High Energy Physics of the Chinese Academy of Sciences took the lead in the research of 325 MHz superconducting proton linac, which is called ADS Injector I. The superconducting accelerator part of ADS Injector I mainly consists of 14 spoke-type superconducting cavities with β 0.12. At the same time, the research work of various cavities with different β values and different frequencies is also carried out to lay the technical and technological foundation for ADS main accelerator. The only way to determine whether the superconducting cavity can reach the design target and whether it can be installed into the cryostat is the vertical test at cryogenic. As the only way to test the microwave performance of the superconducting cavity at low temperature, the vertical test can accurately test the acceleration gradient Eacc and the corresponding quality factor Q0 of the superconducting cavity. The design and construction of the superconducting cavity vertical test facility is based on the practical needs of the pilot project and the long-term development of the superconducting accelerator. This paper mainly introduces the design and construction of the cryogenic vertical test system for the superconducting cavity of ADS Injector I, including the system scheme design, process design, heat load analysis, 2 K superfluid helium obtaining method, system commissioning and operation, etc. The static heat leakage at 2 K of the 2 K superfluid helium vertical test system of ADS Injector I is 1.624 W, which has reached the international advanced level. The 2 K superfluid helium vertical test system of ADS Injector I after constructed not only meets the test requirements of ADS pilot project, but also conducts 4 K and 2 K vertical tests for other different types of superconducting cavities and relevant cryogenic experiments.

Development of a long pulsed RF test stand and its applications for performance studies of 1 MW CW klystron

Research and development activities of high power microwave sources for powering RF cavities of Indian Spallation Neutron Source and Accelerator Driven Subcritical Systems are underway at RRCAT. Front end accelerating structures such as Radio Frequency Quadrupoles and Drift Tube Linac demand pulsed RF power up to 1 MW. A 1 MW pulsed RF system based on TH 2089 klystron amplifier at 352.2 MHz with pulse width capability up to 1.5 ms has been developed and tested. A compact 100 kV, 20 A converter type modulator with pulse width capability up to 1.6 ms has been used to energize the klystron of RF test stand. The performance of the klystron in pulsed mode operation has been studied and presented. The variation in the RF output power was measured and it is within ±0.75%. The phase variation of RF output power within the pulse and the pulse to pulse is less than ±2.5°.

Neutronics and thermal-hydraulics coupling analysis in accelerator-driven subcritical system

Accelerator-driven subcritical system (ADS) is a new generation nuclear reactor with various highly coupled physical fields. A typical system is a liquid metal, lead-bismuth eutectic cooled subcritical reactor core coupled to a neutron spallation target. Therefore, ADS simulations require multi-physics coupling among the proton, neutronics, and thermal hydraulics. In this work, GEANT4, RMC, and FLUENT were used to simulate the multi-physics processes in MYRRHA. The GEANT4/RMC was used for the spallation process and the proton-neutron transport calculations, with the power distributions verified against the MCNP6 code with an average difference of about 1.85%. A hybrid RMC/FLUENT coupling scheme was used for the neutronics thermal-hydraulics calculations. The subcritical reactor was simplified using the porous media method for the FLUENT simulations to obtain the coolant temperature and density fields. A temperature-dependent thermal conductivity model used to calculate the temperature filed in typical fuel pellets gave consistent results with the FLUENT predictions within an absolute error of 3 K. The neutronics and thermal-hydraulics coupling took the temperature and the lead-bismuth eutectic density feedback into consideration. Simulations show that thermal-hydraulics feedback has a fairly small effect on the power distribution in the ADS reactor. In this case, the radial power difference between the coupling and coupling-free is within 5%. In addition, the mechanisms of neutronics/thermal-hydraulics are compared for lead-bismuth eutectic cooled reactors and water-cooled reactors. The feedback is much more significant in water-cooled reactors than in the Pb-Bi cooled reactor since the water moderation, and the water density is more sensitive to the temperature.

Commissioning of China ADS demo Linac and baseline design of CiADS project

China Accelerator Driven Subcritical System (C-ADS) program was launched in China in 2011. In the first five-year phase, a 25 MeV demo linac has been successfully built to demonstrate the key technologies of the driven linac. Beam commissioning activities have been carried out to study the high-power beam physics. Followed by the previous phase, China Initiative Accelerator Driven Subcritical System (CiADS) is approved contain a superconducting proton linac with 500 MeV and 5 mA. In this paper, the commissioning results of the demo linac and the beam dynamics design of CiADS linac based on commissioning experiences are presented.

Measurement of Gamma-Ray from Inelastic Neutron Scattering on 56Fe

In nuclear reactors, inelastic neutron scattering is a significant energy-loss mechanism which has deep impacts on designments of nuclear reactor and radiation shielding. Iron is an important material in reactor. However, for the existing nuclear data for iron, there exists an obvious divergence for the inelastic scattering cross sections and the related gamma production sections. Therefore the precise measurements are urgently needed for satisfying the demanding to design new nuclear reactors (fast reactors), Accelerator Driven Subcritical System (ADS), and other nuclear apparatus. In this paper, we report a new system with an array of HPGe detectors, electronics and acquisition system. Experiments had been carried out on three neutron facilities.

Spallation Target Design for Converting the Isfahan MNSR Reactor to an Accelerator Driven Subcritical System

There are many research reactors around the world that have been installed from many years ago and must be decommissioned sooner or later. Most of these reactors were fuelled with high enriched uranium and substantial amount of initial loaded fuel has not been exploited yet. The reactor conversion to an accelerator driven system (ADS) is one of the novel ideas for minor actinide utilization and reducing the spent fuel radio toxicity. The main objective of this study is dedicated to spallation target design in miniature neutron source reactor (MNSR) core conversion to an ADS one. The MNSR is a pool type research reactor, which was developed by China. After more than 25 years, the fuel burn-up could not be compensated more by adding shimming plates. The subcriticality in MNSR reactor was attained by entirely removing the top plate shims as well as control rod and installing the spallation target in interior space of guide thimble. Different state of the art targets such as tungsten, lead, bismuth, and LBE (lead-bismuth eutectic) have been investigated and target neutronic parameters including the spallation yield, neutron energy spectrum, deposited energy and the angular distribution of spallation neutrons were evaluated using MCNPX2.6 code. The results showed that the neutronic performance of tungsten is somewhat greater than its competitors. On the other hand the maximum power density in tungsten is about two times greater than lead and LBE targets.

Simulation of Neutronics of an Accelerator Driven System

Experiments with a big uranium target irradiated by a high-energy proton beam will be carried out at JINR (Dubna, Russia). In this paper, a number of neutronics of this accelerator-driven subcritical system are simulated towards optimizing the experimental conditions. The Geant4-based simulations are performed in the International Sakharov Environmental Institute of Belarusian State University.

Conceptual design and optimization of power generation system for lead-based reactor

The lead-based reactor is one of the key nuclear energy systems for Generation-IV (Gen-IV) and Accelerator Driven Subcritical Systems (ADS). The Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences (INEST, CAS) has taken significant initiative for the design and development of the China Lead-based Reactor (CLEAR) series since 2011. The conventional power generation system has low performance and optimization of main parameter is a challenge when power generation system is connected with lead-based reactor. A new/modified conceptual design of an efficient power generation system with two reheaters has been proposed on the basis of a 400 MWth (thermal power) lead-based reactor with high performance. The analysis results show that the thermal efficiency was influenced by number of reheaters (with bleed-off steam at different positions). The thermal efficiency of Schematic-III (with two reheaters) was 44.3% and higher than Schematic-I and II (one reheater with bleed-off steam from the supply line of the first regenerator and main supply line, respectively). However, key parameters of the power generation system have been optimized to increase the overall performance of Schematic-III. The optimized temperature of feed water at the inlet of the reactor was 360 °C with a flow rate of 237 kg·s−1 and the outlet temperature of the reactor was 558 °C. The efficiency and net power of the plant increased with the part load.

Beam optics design of the superconducting region of the JAEA ADS

The Japan Atomic Energy Agency (JAEA) is proposing an Accelerator Driven Subcritical System (ADS) for the transmutation of the nuclear waste. ADS will consist of a superconducting CW proton linear accelerator of 30 MW and a subcritical nuclear reactor core. The main part of the acceleration will take part in the superconducting region using five types of radio frequency cavities. The ADS operation demands a high intensity and reliability of the beam. Therefore, the beam optics design plays a fundamental role to reduce the beam loss, control emittance growth and beam halo.

Design of the elliptical superconducting cavities for the JAEA ADS

The superconducting CW proton linear accelerator for an Accelerator Driven Subcritical System (ADS) proposed by Japan Atomic Energy Agency (JAEA) employs elliptical cavities for the final acceleration of 180 MeV to 1.5 GeV. Since this energy region implies a changed of β from 0.55 to 1, two cavity models were developed using the geometrical betas of 0.68 and 0.89 to improve the acceleration efficiency. The study of the electromagnetic design was simulated using SUPERFISH (SF) code and python program to do variable scan, the results were benchmarked with CST Microwave Studio program (CST).