Spallation particles can be utilized in different fields such as neutron scattering studies, external source for burning spent fuel as well as running subcritical reactors. Accelerator driven subcritical system (ADS) has been considered as an advanced nuclear waste transmutation facility with inherent safety feature. In this paper, the neutronic performance of the spallation target with the proton beam variation was investigated. Monte Carlo code FLUKA has been used to calculate neutronic parameters including: spallation neutron flux and energy deposition. As the beam position is shifted towards the positive direction of the Y-axis, the neutron flux and energy deposition increased significantly along the positive direction of the Y-axis, while the flux and energy deposition in the opposite direction decreased. Such a change may lead to a sharp increase of the neutron flux of fuel components near the beam target in subcritical reactor. But as the beam shifts further and further, the neutron flux in the positive direction declines compared to the previous data. The calculation and analyzing the data obtained from proton beam variation shows that it has a great influence on the physical properties of the neutron spallation target.

Spallation particles can be utilized in different fields such as neutron scattering studies, external source for burning spent fuel as well as running subcritical reactors. Accelerator driven subcritical system (ADS) has been considered as an advanced nuclear waste transmutation facility with inherent safety feature. In this paper, the neutronic performance of the spallation target with the proton beam variation was investigated. Monte Carlo code FLUKA has been used to calculate neutronic parameters including: spallation neutron flux and energy deposition. As the beam position is shifted towards the positive direction of the Y-axis, the neutron flux and energy deposition increased significantly along the positive direction of the Y-axis, while the flux and energy deposition in the opposite direction decreased. Such a change may lead to a sharp increase of the neutron flux of fuel components near the beam target in subcritical reactor. But as the beam shifts further and further, the neutron flux in the positive direction declines compared to the previous data. The calculation and analyzing the data obtained from proton beam variation shows that it has a great influence on the physical properties of the neutron spallation target.

The use of liquid metal alloy as a coolant in nuclear systems receives more and more attention in recent years, such as Dual-functional Lithium Lead Test Blanket Module (DFLL-TBM) for ITER, Lead-bismuth spallation target for accelerator driven sub-critical system (ADS) and Lead-alloy-cooled fast reactor (LFR). A system safety analysis code is an important tool for the liquid metal nuclear system safety analysis. In order to analyze some of the basis accidents, there is the need to simulate the mixing of liquid metal and noncondensable gas. While the current system safety code RELAP/SCDAPSIM/MOD4.0 which was initially designed to predict the behavior of light water reactor systems is incapable of modeling the mixture of liquid metal fluids and noncondensable gas. This paper first briefly introduce the two-fluid model in RELAP5/MOD4.0 and the reason for its incapability of modeling liquid metal in contact with a non-condensable gas. Then, a solution to solve the problem and the modification of the RELAP5/MOD4.0 code is proposed. Last, several typical problems in DFLL-TBM system were simulated and the results demonstrate the feasibility and validity of the modified RELAP5/MOD4.0 in modeling the mixing of liquid metal and non-condensable gas. The modified code provides a powerful tool for liquid metal nuclear system designs and safety analysis.

Accelerator driven subcritical system (ADS) has been considered as an advanced nuclear waste transmutation facility with inherent safety feature. Nowadays, Institute of Modern Physics, Chinese Academy of Science (IMPCAS) has made a plan to research and develop ADS, which project was formally approved by the National Development and Reform Commission at the end of 2015. In order to pursue high transmutation rate of Minor Actinide (MA), a new concept design of the lead-bismuth cooled ADS is proposed in present work, in which a gravity-driven dense granular flow spallation target has been designed to substitute the traditional solid or liquid heavy metal spallation target. Sensitive parameters of the spallation target have been investigated, such as the radius and axial position of the spallation target, the size of heavy metal grains, the granular filling rate, the spallation neutron yield, and the distribution of neutron source. Furthermore, an optimized design of sub-critical reactor has been proposed with three zone loading pattern as a consequence of eliminating the power peak factor, which thermal power is 10MW with the operation cycle 600 EFPD. Finally, some important physical parameters in the coupling depletion system have been studied, including the effective multiplication factor k-eff, subcritical multiplication factor k-s, the change of beam current, time-dependent void and Doppler effect, fraction of effective delayed neutron, and the transmutation supporting ratio.

A new neutronics and thermal-hydraulics coupled code named ARTAP is developed to analyze the steady-state and transient characteristics of accelerator driven subcritical system (ADS) in this paper. Monte Carlo simulations for spallation neutron source and deterministic calculations for the subcritical core are performed in the steady-state analysis module. The ADS core is divided into a number of nodes both along the reactor axis and the fuel pellet radius for the calculation of spatial temperature distributions. The power iteration method is adopted to solve the coupled neutronics and thermal-hydraulics problems. The transient analysis module consists of space-time neutron kinetics model and thermal-hydraulics dynamic model, which is calculated by using numerical differentiation formulas (NDFs) method. The new code is verified by comparing its predictions for both the steady-state and transient cases of the OECD/NEA ADS benchmark. Results of numerical simulations indicate that ARTAP is reliable and efficient to be applied for the ADS analysis.

In recent years, the morphological characteristics and stabilization methods of free interface in liquid windowless target become hot research topics in accelerator driven subcritical system (ADS). Based on the structure design of a certain windowless spallation target, CFX program was used to simulate and analyze its free interface character. The method of k-ε turbulence model, Cavitation model and VOF method were used to study the flow characteristic of liquid lead-bismuth alloy (LBE) with cavitation phase change and to analyze the free interface morphology characteristics of coolant in the target area. It is concluded that the target region form two stable free interfaces when fluid outlet pressure is in the range of 10000–40000Pa and fluid entrance velocity is in the range of 0.5–1.2m/s. The flow field near the free interface structure is complex. The vortex region appears, and the disorders in the vortex flow pattern leads to fluctuation of the free interface. After establishing stable free interface morphology, the heat transfer characteristics of windowless target was further analyzed.

In ESS, a 5 MW proton beam will hit a helium cooled tungsten target to generate neutrons by spallation. For the purpose of investigating various aspects of cooling with helium, an experimental system has been constructed at Lund University, Department of Energy Sciences. A helium flow of 3 g/s is circulated in a closed loop with pre-heater, cooler, filters and a test vessel. The vessel has windows for measurements and is designed for 10 bar and above 400 °C. In the test vessel, a tube forms a helium jet of up to 150 m/s onto a coin shaped material sample. One purpose of the system is to investigate erosion of sample surfaces. Drilling and attaching equipment to the surface had to be avoided, so the setup has been benchmarked and the comparison was used to tune a CFD model. Then the model is used to assess the conditions in the experiments. The setup, as well as the tests and calculations, are described and it is concluded that the temperature and velocity estimates are sufficient for the experiments to be performed.

The Chinese Spallation Neutron Source (CSNS) is the national major scientific equipment, which will be completed around 2018. The moderator is the core of the CSNS parts, and CSNS uses three types of moderator to meet the requirements of different neutron wavelength and pulse shapes, and the structure and flow field of Decoupled Poisoned Hydrogen Moderator (DPHM) is the most complicated. Currently, Computational Fluid Dynamics (CFD) is the primary tool for thermal design of DPHM to ensure the reliability of calculation result and precision of the engineering requirements. In the current work, three-dimensional simulation of fluid-solid conjugate heat transfer and flow for container pipe, poisoned plate and moderator material were carried out, by compiling corresponding UDF program for ANSYS FLUENT to describe the non-uniform heat source distribution accurately. Thermal-Hydraulic behaviors such as pressure disturbance, pressure rise and temperature distribution cooling capacity are investigated.

The implementation of the Generation IV nuclear reactors and a spallation target of the accelerated driven system (ADS) concerning to the use of liquid lead-bismuth eutectic (LBE) alloy. The liquid LBE alloy should be fully characterized and especially its physical properties should be completely known to make sure the nuclear safety. Differential scanning calorimetry (DSC) experiments were employed on LBE alloy at a temperature range of room temperature (RT) to 500°C to detect the structure phase transition and obtain the thermal effect of LBE alloy. The results of DSC curves showed that there existed two remarkable thermal signal events at the melting points zones of Pb and Bi during the melting process tested with a scan rate of 2°C/min. Even though the scan rate was increased to 5°C/min, the DSC signal still exhibited the changes of curve slop at the element melting point zone. Just this interesting DSC thermal signal change phenomenon around 300°C contributed to the relationship with the explanation on the severe embrittlement of T91 steel induced by liquid LBE alloy. The results suggest that there existed effective critical size and form of chemical clusters in liquid LBE alloy worked actively on the embrittlement of T91 Steel.

An accelerator driven sub-critical (ADS) system consists of an accelerator, a sub-critical reactor, and a spallation target located at the centre of the reactor core. In this paper, we report the conceptual design of the control system for ADS system, which will integrate two big nuclear facilities, an accelerator and a reactor, into an overall system for the first time in the world. Because varied expectations on redundancy, diversity, availability, reliability, communication speed and latency are required for both accelerator and reactor, at least six systems have been designed for an ADS system, i.e. a main control system, three protection systems, a timing system, and a data archiving system. The main control system is designed to monitor and control the overall ADS system. In order to exactly couple the high-energy beam from the accelerator to the spallation target located in the reactor, many instrumentations are required in the main control system, such as instrumentations for beam monitoring and beam switching-off, instrumentations for ex-core neutron monitoring, instrumentations for in-core temperature and neutron monitoring, instrumentations for monitoring and controlling several cooling loops, and Instrumentations for control rod system. In order to enhance the safety of the ADS system during the operation, three protection systems, a reactor protection system, an accelerator’s machine protection system and a personnel protection system, have been designed. Independent network is used for each system. Furthermore, both redundant network and hardwired communication are used in each protection system to provide extremely reliable communication link. Finally, the communication network with parallel redundancy protocol has been studied for the main control system. In comparison with a network without redundancy, the parallel redundancy protocol can improve dramatically the reliability of a communication network by up to forty thousand times.

In this paper, we study the electronics in the instrumentation and control (I&C) systems for an accelerator driven sub-critical (ADS) system, where a target located at the centre of a sub-critical reactor core is bombarded by the protons from an accelerator. In comparison with a commercial reactor used in nuclear industry, more control electronics are required to exactly couple the high-energy beam from the accelerator to the spallation target in the reactor core. There is a strong drive to utilize standard commercial-off-the-shelf devices to minimize cost and development time. In order to improve the reliability of I&C systems, redundancy architecture has been considered by adding more electronic devices. In comparison with I&C system without redundancy, the dual redundancy architecture improves the reliability of the system by 20000 times. Then, we study the potential application of electronics devices, such as the preamplifiers for detectors, in the reactor building by shielding them with shielding materials. Since the most effective neutrons in creating radiation damages are those fast neutrons with the energy of more than 0.1 MeV, we have proposed a sandwich shielding method to reduce the neutron-induced radiation effects, in which the first and third layers are made of polyethylene and the second layer is made of heavy metal, e.g. tungsten. Simulation results with GEANT4 code have indicated that the shielding with a 30 cm-thick sandwich can increase the expected lifetime of electronics by 1258 times, and can reduce the soft errors caused by single event upsets by 5400 times.

In ESS, a pulsed proton beam of 5 MW mean power will hit a tungsten target to generate neutrons by spallation. The pulses are 2.86 ms long and occur with 14 Hz; the power within a pulse is 125 MW. Only centimeters from the target, the neutrons are moderated by liquid hydrogen in aluminium vessels. The deposited power heats the surrounding structures and fluids which are circulated and cooled. The hydrogen is operating at 15 bar and average temperature between 17 and 21 K, i.e. above the critical pressure 12.8 bar, but below the critical temperature 32.9 K. During the pulses, the peak heat deposition in the aluminium is 15 W/cm 3 and in the hydrogen 4 W/cm 3 . If the cooling of the aluminium is neglected during one pulse, the temperature increases to 34 K. That is above the critical temperature, where physical properties change strongly with temperature. Therefore the conjugate heat transfer has to be investigated in detail. This work includes 1D principal transient calculations of a general configuration as well as CFD simulations of the heating and cooling of a specific design. The 1D calculations are performed using GNU/Octave and the CFD using ANSYS/CFX. It is concluded that with an inlet temperature of 17 K, the wall temperature can be kept below the critical temperature in the general configuration and sufficient cooling can be ensured in the investigated specific design.

To support the feasibility and the deployment of LFRs one of the main issues to be solved is the reliability of structural materials to be exposed to liquid metal coolant. Particularly the Liquid Metal Embrittlement (LME) of steels is of interest for nuclear reactors and spallation sources projects because structural materials for these systems are selected according to their corrosion resistance, irradiation embrittlement and compatibility with the coolant. This study was performed in the framework of MYRRHA project, a new-generation sub-critical reactor (based on the Accelerator Driving System concept) that uses Lead-Bismuth Eutectic (LBE) as coolant. LME phenomenon has been investigated by performing theoretical and experimental activity profiting and basing on the results obtained for the T91 m/f steel in contact with LBE. This paper first reviews the model of Kamdar: weak points and contradictions are highlighted. From an experimental point of view to verify the occurrence of LME, Slow Strain Rate Tensile tests were performed on the AISI 316L in LBE environment at SCK-CEN laboratories. Besides, a fracture surface analysis was carried out together with a microstructural analysis by using that Scanning Electron Microscopy. This was done in order to confirm the results obtained by the mechanical tests and to look for impurities in the metallic matrix. These impurities are an interesting feature in case of high scatter in the results. Indeed one of the difficulties was the opacity and conductivity of the medium. The methodological approach and the procedure are also duly described along with preliminary results.

The Accelerator Driven System (ADS) is a kind of nuclear reactor which can burn minor actinide waste products from conventional reactors with inherent safety. Because of the characteristics of a sub-critical reaction process, the fission chain reaction is maintained by additional neutrons generated by protons in spallation target. In this paper, a helium-cooled solid target is designed for a 10MW helium-cooled prismatic-type experimental ADS. The spallation material tungsten is modeled into the honeycomb structure, and high pressure helium flow in honeycomb holes remove heat deposited by the proton beam in the target. Since the complexity of geometry, if analysis the target with CFD code the computing time is unacceptable. Thus, a simple mathematical method was developed to solve the heat transfer problem in honeycomb structure, which avoids fine grid and the turbulent simulation, and gets a solution quickly. In order to analyze the transient characteristics of spallation target cooling system, a equivalent RELAP5 model for target and a RELAP5 model for cooling system are established. Results obtained indicate that the peak temperature in the target is lower than the limiting value under operating state and blockage condition as well as three typical transients with protected.

For the project of the Chinese Initiative Accelerator Driven Sub-critical system (CIADS), the Lead-Bismuth-Eutectic (LBE) spallation target is one of the two alternatives, which has high good thermal performance, mature technology, and other advantages. The physical design of the spallation target determines the neutron yield and the utilization of the neuron source, as well as the performance of the sub-critical reactor and other key issues. Based on the Monte Carlo program MCNPX, we did the preliminary design of spallation target coupled with the reactor with a k eff about 0.95. The energy deposition density distribution of the target and the window were calculated. In the mean time, the neutron flux density, the neutron energy spectrum, and the power amplification factors were calculated. By changing the positions of the target, the radii of the beam pipe and the thickness of target, we studied the variation of the neutronic parameters mainly mentioned above. The energy deposition density distribution was used as the heat source of the thermal-hydraulics analyses. From the neutronic parameters, we found that to get the maximum power amplification factor, the target window should be put at the positions 11.4 cm above the center of the core. Actually, when the target was put above the center of the core, from 0cm to 22cm, the maximum differences of the power amplification factor is less than 4.0%, which means the position will have little influences in this range. When the target window was put at the center, increasing of the window’s thickness will lead the decreasing of the power amplification factor. The enlargement of the beam pipe radii will decrease the maximum that the amplification factors can reach. Meanwhile, the increasing of the beam radii will enlarge the power amplification factor slightly. The physics analysis of the LBE target coupled with the reactor can give more information to the optimization of the target structure and the sub-critical reactor for CIADS.

The conceptual design and basic engineering of a multipurpose ADS for R&D, named Chinese Initiative Accelerator Driven System (CIADS), have been carried out by Chinese Academy of Science. A lead-bismuth eutectic (LBE) spallation target with beam window is an alternative for the CIADS. In this work, by using the code system ANSYS, the static structure analysis of the spallation target beam window at the initial state was performed parametrically in conjunction with the thermal hydraulics to check the design compliance with the stress and the buckling design criteria. The static structure analysis of the target window was presented under the conditions of different window thicknesses, proton beam intensities and beam spot diameters. The results showed that all the parameters investigated in this work which meet the needs of thermal hydraulics design also compliance with the stress and the buckling design criteria. Also, the results were used to select the thickness of the beam window to maximize the engineering margins. More work will be done in the future for the structural analysis of target operating with certain dosage irradiated by the neutrons and the protons.

In ADS reactor which choose LBE (Lead-Bismuth Eutectic) as coolant and spallation target. While SGTR (Steam Generator Tube Rupture) accident occur, water in secondary side will inject to LBE in primary coolant, and flow with LBE. The code of FLUENT will be used, steam is looked as particle, and standard k - ε model is used to predict turbulence variation of continuous phase in core. The DPM (Discrete Phase Model) will be used to track the trajectory of the particles. The distribution of steam in core will be obtained, which will verify the safety of reactor. The results show that the steam flowing across the core with LBE, might accumulate in some position and cause a surge of power. At the same time, the aggregation of steam at the channel might lead to a steam plug, and hinder the flow of the coolant in core, then core overheating might occur. Last but not least, local accumulation of water vapor may accelerate the corrosion of stainless steel material in core.

Accelerator Driven Systems (ADS) are subcritical nuclear reactor cores driven by external spallation neutron source. These systems are currently under investigation to be used as minor actinide burners and also as transmuters of long lived fission products. The subcriticality level plays an important rule in the control of the system. Low subcriticality level more source dominant is the system. In this paper one analyzes two transients to analyze the feedback effect on power of the Accelerator Driven Systems, since they cover a wide range of temperature variations. These operational transients are a beam interruption in power and a startup one, when the ADS are powered up from zero power to power operation. Numerical results shown that ADS can not reach the nominal operation temperatures if the systems operate next to critical ones. In a beam interruption transient systems are not affected if operated as critical ones.

The steady-state phase distribution and the structural parameters have been taken as the input for the nuclear physics calculation in the ADS windowless spallation target. The distribution of the extreme large power density of the heat load is imported back as the source term in the energy equation. Then temperature distribution is obtained based on the flow process and heat transfer. The preliminary results show that the temperature distribution reaches the steady-state and its shape is like the broken wings of the butterfly. This is very important for the further design and optimization of the ADS windowless spallation target. So the two-way coupling simulation of the heat transfer process is successfully performed between the computational fluid dynamics and the nuclear physics simulation.

Pursuing a high minor actinide (MA) transmutation rate, this paper proposes a neutronics concept design of lead-bismuth (LBE) cooled accelerator-driven system (ADS) with burnup reactivity swing less than 1% and proton beam current smaller than 17mA. After a comparison with other types of fuels, Uranium-free metallic dispersion fuel (TRU-10Zr)-Zr* is selected to obtain a harder neutron spectrum to transmute MA. With a MA initial loading, the suitable proportion of initial Plutonium to transuranium element (TRU) is found around 33% to make sure that the burnup reactivity swing is less than 1%. The location of the spallation target is optimized to guarantee high external spallation neutron source efficiency and to lower proton beam current. For the subcritical system, initial effective multiplication factor is 0.97, and the thermal power is 1000 MW. For the accelerator, proton with energy of 1.5GeV and a parabolic spatial profile is provided by proton linac. It is demonstrated by the numerical results that the transmutation rate of MA is about 28% after 600 effective full power days (EFPD) while the support ratio for LWR units with the same power is about 46.