Neutronic analysis of deuteron-driven spallation target

Deuteron-driven spallation targets have garnered attention recently because they can provide high-energy neutrons to transmute long-lifetime fission products. I...     

CFD analysis of the HYPER spallation target

KAERI (Korea Atomic Energy Research Institute) is developing an accelerator driven system (ADS) named HYPER (HYbrid Power Extraction Reactor) for a transmutation of long-lived nuclear wastes. One of the challenging tasks for the HYPER system is to design a large spallation target with a beam power of 15–25 MW. The paper focuses on a thermal–hydraulic analysis of the active part of the HYPER target. Computational fluid dynamics (CFD) analysis was performed by using a commercial code CFX 5.7.1. Several advanced turbulence models with different grid structures were applied. The CFX results reveal a significant impact of the turbulence model on the window temperature. Particularly, the k–ε model predicts the lowest window temperature among the five investigated turbulence models.     

Feasibility of uranium spallation target in accelerator-driven system

A feasibility study on natural uranium spallation target in accelerator-driven system (ADS) for minor actinide (MA) transmutation was performed. As a result of comparative study of uranium and lead-bismuth (PbBi) targets in the bare case without blanket surrounding, it was found that uranium target had better neutron generation performance, but limited by the geometrical size due to high neutron absorption in ²³⁸U. In ADS for MA transmutation, uranium used as target instead of PbBi also absorbs neutrons passing the target area.More realistic concept of pin type uranium spallation target cooled by liquid PbBi was considered aiming at enhancing spallation target performance in terms of neutron generation efficiency and operation temperature. The uranium pin target design had nothing better effects on neutron balance of such system than a conventional PbBi target in ADS and it was concluded that uranium target was not suitable for the full-scale ADS.     

Investigation of neutronic parameters of natU spallation target irradiated by low-energy protons

Accelerator-based neutron sources could outstandingly compete with the reactor-based ones, which are widely used for research aims and radioisotope production.Spallation neutron sources are used by many research centers. In this work, the potential of natural uranium spallation target irradiated by low-energy protons for production of an external neutron source was investigated.MCNPX code was used to model the spallation target. The results showed using 30-Me V protons of 100 μA current a neutron flux in order of 10~7n/s cm~2 leaks from an optimized-dimension target. Different physical models available in the computational code do not result in significant relative discrepancies for neutron yield and deposited heat calculations. Water with a velocity of 0.6 m/s can be used as coolant for the spallation target to keep the surface temperature under 100 °C at atmospheric pressure.     

Computational fluid dynamics analysis of spallation target for experimental accelerator-driven transmutation system

One of the key milestones in the roadmap of the European accelerator-driven transmutation system (ADS) is the design and construction of the European experimental ADS (XADS). The window spallation target unit in the lead–bismuth eutectic (LBE) cooled reactor system is one of the basic options considered in the preliminary design study of XADS (PDS-XADS). This paper presents the computational fluid dynamics (CFD) analysis and the main results achieved for this option focusing on the coolability of the window. Steady-state as well as transient behavior, including beam interrupts and three major accident scenarios, has been analyzed using the CFD code CFX 5.6 with an advanced turbulence model. The required boundary conditions were provided by a one-dimensional system code. Based on the CFD analysis, the window geometry was modified in order to achieve sufficient cooling capability of the window under normal operating conditions. The transient behavior of the window temperature under beam trip conditions shows the importance of the beam interrupt duration to the thermal stress load of the window structural material. Further transient analysis of three major accidental scenarios, i.e., beam focusing, loss of heat sink, and beam intensity jump, indicates that the beam focusing accident gives the most serious safety concern. In this case, window failure occurs in less than 1 s after the start of the beam focusing.     

Preliminary physics study of the Lead–Bismuth Eutectic spallation target for China Initiative Accelerator-Driven System

The Lead-Bismuth Eutectic(LBE) spallation target has been considered as one of the two alternatives for the spallation target for China Initiative Accelerator-Driven System.This paper reports the preliminary study on physical feasibility of a U-type LBE target with window.The simulation results based on Monte Carlo transport code MCNPX indicate that the spallation neutron yield is about 2.5 per proton.The maximum spallation neutron flux is observed at about 3 cm below the lowest part of the window.When the LBE target is coupled with the reactor,the reactor neutrons from the fission reaction increased the neutron field significantly.The energy deposition of highenergy protons is the main heat source;the spallation neutrons and reactor neutrons contribute only a small fraction.The maximum energy deposition in the LBE is about 590 W/cm~3 and that in the target window is about319 W/cm~3.To estimate the lifetime of the target window,we have calculated the radiation damages.The maximum displacement production rate in the target window is about10 dpa/FPY.The hydrogen and helium production rates generated during normal operation were also evaluated.By analyzing the residual nucleus in the target during the steady operation,we estimated the accumulated quantities of the extreme radioactivity toxicant ~(210)Po in the LBE target loop.The results would be helpful for the evaluation of the target behavior and will be beneficial to the optimization of the target design work of the experimental facilities.     

Fatigue damage assessment using x-ray diffraction and life prediction methodology

X-ray diffraction line broadening was used to monitor surface damage due to deformation (distortion) that was induced by low cycle fatigue. The integral breadth of selected diffraction peaks was identified as a useful parameter with which to evaluate cumulative fatigue damage. Torsional fatigue tests were conducted on nickel-based Waspaloy material which exhibited planar slip at 1200° F (649°C). X-ray diffraction measurements were taken at 22, 41, 60, and 90% of the life. The data disclosed an increase in breadth with each increment of cycling. The results obtained from line broadening analysis were carefully correlated with observations made on the specimen surface using scanning electron microscopy which showed the progressive distortion occurring in the cycled specimen. The integral breadth, β, was successfully correlated with the applied shear strain to predict the expended fraction of life and hence the remaining cyclic life.     

Radiation damage and lifetime characteristics of the He-EFIT spallation module

The He-EFIT studied under domain DESIGN of the EUROTRANS (FP6) integrated project is a prototype gas cooled accelerator driven subcritical reactor dedicated for transmutation of minor actinides. The paper contains neutronic analysis of the He-EFIT innovative spallation module and aims at the estimation of radiation damage and lifetime characteristics of the target in question.     

Development of microbubble generator for suppression of pressure waves in mercury target of spallation source

A MW-class mercury target for the spallation neutron source is subjected to the pressure waves and cavitation erosion induced by high-intense pulsed-proton beam bombardment. Helium-gas microbubbles injection into mercury is one of the effective techniques to suppress the pressure waves. The microbubble injection technique was developed. The selection test of bubble generators indicated that the bubble generator utilizing swirl flow of liquid (swirl-type bubble-generator) will be suitable from the viewpoint of the produced bubble size. However, when single swirl-type bubble-generator was used in flowing mercury, swirl flow of mercury remains at downstream of the generator. The remaining swirl flow causes the coalescence of bubbles which results in ineffective suppression of pressure waves. To solve this concern, a multi-swirl type bubble-generator, which consists of several single swirl-type bubble-generators arraying in the plane perpendicular to mercury flow direction, was invented. The multi-swirl type bubble-generator was tested in mercury and the geometry was optimized to generate small bubble with low flow resistance based on the test results. It is estimated to generate the microbubbles of 65 μm in radius under the operational condition of the Japanese Spallation Neutron Source mercury target, which is the sufficient size to suppress the pressure waves.     

Neutronic performance of the MEGAPIE spallation target under high power proton beam

The MEGAPIE project, aiming at the construction and operation of a megawatt liquid lead-bismuth spallation target, constitutes the first step in demonstrating the feasibility of liquid heavy metal target technologies as spallation neutron sources. In particular, MEGAPIE is meant to assess the coupling of a high power proton beam with a window-concept heavy liquid metal target. The experiment has been set at the Paul Scherrer Institute (PSI) in Switzerland and, after a 4-month long irradiation, has provided unique data for a better understanding of the behavior of such a target under realistic irradiation conditions. A complex neutron detector has been developed to provide an on-line measurement of the neutron fluency inside the target and close to the proton beam. The detector is based on micrometric fission chambers and activation foils. These two complementary detection techniques have provided a characterization of the neutron flux inside the target for different positions along its axis. Measurements and simulation results presented in this paper aim to provide important recommendations for future accelerator driven systems (ADS) and neutron source developments.     

散裂中子源靶站和中子散射谱仪的概念设计

本文介绍了可应用于多学科应用的散裂中子源(CSNS)靶站和中子散射谱仪概念设计的进展。CSNS靶站将由重水冷却多片钨靶,铍/铁反射体和铁/重混凝土生物屏蔽体组成。采用三个WING型慢化器:水(室温),液体甲烷(100K)和液体氢(20K),设有18个水平中子孔道。MonteCarlo模拟显示优化的靶截面高宽比为1:2.5左右。额定的100kW核功率的质子束轰击后,慢化器处钨靶溢出的脉冲中子通量约为2.4×1016cm?2·s?1。有限元方法计算表明,钨靶体内的总发热量是47kJ/s。即使使用截面较小的钨靶,在通常的水冷速率下,靶体温度也仅略高于90°C。靶体的热应力形变最大不超过0.2mm。根据经济实用原则选择建造粉末衍射仪、小角散射仪、反射仪及直接几何非弹性散射仪等四类有代表性的中子散射谱仪,就能覆盖>80%的中子散射研究领域。     

Numerical design of a 20 MW lead–bismuth spallation target for an accelerator-driven system

A spallation target system is a key component to be developed for an accelerator-driven system (ADS). It is known that a 15–25 MW spallation target is required for the practical size of an ADS. Although there have been some design studies for small power spallation targets, that is, less than 10 MW, designs of high power target systems for ADS are relatively rare. The design of a 20 MW spallation target is very challenging because more than 60% of the beam power is deposited as heat in a small volume of the target system. In the present work, a numerical design study was performed to get optimal design parameters for a 20 MW spallation target for a 1000 MW ADS. The cylindrical beam tube and the hemispherical beam window were adopted in the basic target design concept with 1 GeV proton energy, and the thermal-hydraulic and the structural analyses were performed with the CFX and ANSYS codes. The beam window diameter and thickness were varied to find the optimal parameter set based on the design criteria: maximum lead–bismuth eutectic (LBE) temperature <500 °C, maximum beam window temperature <600 °C, maximum LBE velocity <2 m/s, and the maximum beam window stress <160 MPa. The results of the present study show that a 40 cm wide proton beam with a uniform beam profile should be adopted for the spallation target of 20 MW power. It was found that a 2.5 mm thick beam window is needed to sustain the mechanical load.     

Implementation of an LBE spallation target in an accelerator-driven molten salt subcritical reactor

An accelerator-driven system (ADS) combined with a subcritical molten salt reactor (MSR) is a type of hybrid reactor originally designed to use Th/U (or U/Pu ) fuel cycles. In most accelerator-driven molten salt reactor (AD-MSR) concepts, the salt material is also used as a target for inducing spallation neutrons. Although a neutron source is an important component in the design of ADS, only a few studies have addressed the effects of the neutron spallation source in the AD-MSR. Incidentally, there is no quantitative study on how much the beam power can be reduced by installing a spallation target in a sodium chloride-based fast reactor. We studied the proton and the neutron source efficiencies of an AD-MSR with chloride fuels by considering an Lead Bismuth Eutectic (LBE) spallation target. This LBE target is found to increase the proton source efficiency significantly. The required beam power for an AD-MSR can be reduced by 33 % and 16 % for NaCl-Th/²³³U and NaCl-U/Pu fuels, respectively, relative to the AD-MSR without the LBE spallation target by keeping the same k_eff. The energy gain can be increased up to 1.5 times and 1.2 times for NaCl-Th/²³³U and NaCl-U/Pu fuels, respectively. Thus, incorporating a spallation target module in an AD-MSR can significantly reduce the burden on the accelerator.     

Coupled fluid/structure analyses of the MEGAPIE spallation source target during transients

The paper describes some R&D activities undertaken in support of the design and safe operation of MEGAPIE (MEGAwatt PIlot Experiment) spallation source target, which is scheduled to be irradiated by a proton beam in the SINQ facility at the Paul Scherrer Institute in 2006. The target material is lead bismuth eutectic (LBE), which also acts as the primary coolant. As a consequence of the spallation reactions, about 600 kW of heat would be deposited in the target during operation, and considerable R&D effort is being expended to demonstrate continuing coolability and structural integrity under a variety of operational and abnormal conditions. The paper gives three examples of transient analyses carried out as part of the safety assessment of the target: (1) a beamline trip and recovery; (2) failure of the primary electro-magnetic pump (EMP); (3) failure of the secondary EMP (used to cool the base of the target). The study involves the simultaneous application of a system-analysis code, in our case a version of RELAP5, a computational fluid dynamics (CFD) tool (CFX-4), and a structural analysis code (ABAQUS). The RELAP5 code is used to provide transient boundary conditions for a localized conjugate heat transfer analysis of the lower target region, undertaken using CFD, and includes the feed-back effects arising from the secondary cooling and control systems. A conjugate heat transfer problem is then solved using CFD, which provides time-dependent thermal and flow data within the LBE, together with the thermal and mechanical loads to the target structures. Finally, an in-house interface program is employed to transfer mesh geometry, model topology and (time-dependent) thermal/mechanical data to enable stress analysis of the principal lower-target structural components to be performed. It is demonstrated that none of the transients considered result in critical stress conditions occurring in the target components, but that further operation is not recommended unless both pumps are fully operational.     

散裂中子源(3.7GeV p+Pb)靶散裂研究中Lavsan探测器的应用

利用Lavsan探测器探测了直径8cm，厚20cm的铅靶中散裂反应的分布规律，并利用理论对实验结果进行了模拟解析，同时利用实测的散裂产物在靶区的分布验证了Lavsan探测结果及理论模拟结果。     

Creep-fatigue damage assessment by subsequent fatigue straining

A series of creep-fatigue tests has been conducted with modified 9Cr-1Mo steel at 873 K in a high vacuum environment of 0.1 mPa. In order to investigate the accumulation of creep-fatigue damage, the creep-fatigue test programme includes changes in strain waveform during the test: from creep-fatigue type to fatigue type and from fatigue type to creep-fatigue type. The conventional linear cumulative damage rule for fatigue and/or creep-fatigue damage fails in evaluating the creep-fatigue life under the present complicated strain wave history. The linear summation of the life fraction is smaller than unity when the prior loading is creep-fatigue type and larger than unity when the prior loading is fatigue type. Scanning electron microscope (SEM) observation of the fracture surface was also conducted. In the case where the strain waveform changes from prior creep-fatigue type to subsequent fatigue type, the crack mode changes from transgranular to intergranular with an increase in the prior creep-fatigue loading history. In the case where the strain waveform changes from prior fatigue type to subsequent creep-fatigue type, the primary crack mode is generally intergranular regardless of the prior fatigue loading history.     

Risk-informed assessment of degraded containment vessels

This study couples structural analyses of four typical U.S. nuclear power plant containments with existing probabilistic risk assessment (PRA) models to assess the effects of degradation. This method is used to determine the increase in the early release frequencies (risk) due to postulated cases of corrosion in the steel liners and shells, as well as other forms of degradation.     

Thermal–hydraulic studies related to the design of LBE neutron spallation target for accelerator driven systems

Recently, studies have been taken up in world's leading nuclear research institutes to develop accelerator driven systems (ADS). Our department has earlier proposed a one-way coupled fast-thermal reactor of 750 MW (thermal). This reactor requires current in the range of 1–2 mA for proton beam of 1 GeV. A suitable liquid metal lead bismuth-eutectic (LBE) target based on buoyancy as well as gas driven method has been designed for this reactor earlier. In this paper, detailed thermal analysis in the spallation and window region has been carried out to study the operability of the target from thermo-mechanical point of view. FLUKA and computational fluid dynamics (CFD) codes have been used for this analysis. The results indicate that, the temperatures, thermo-mechanical stresses are within the required values. The detailed analysis of this work is presented in this paper.     

Development of a gas layer to mitigate cavitation damage in liquid mercury spallation targets

Establishment of a gas layer between the flowing liquid and container wall is proposed for mitigating the effects of cavitation in mercury spallation targets. Previous work has shown an order of magnitude decrease in damage for a gas layer developed in a stagnant mercury target for an in-beam experiment. This work is aimed at extending these results to the more complex conditions introduced by a flowing mercury target system. A water-loop has been fabricated to provide initial insights on potential gas injection methods into a flowing liquid. An existing full-scale flow loop designed to simulate the Spallation Neutron Source target system will be used to extend these studies to mercury. A parallel analytical effort is being conducted using computational fluid dynamics (CFD) modeling to provide direction to the experimental effort. Some preliminary simulations of gas injection through a single hole have been completed and show behavior of the models that is qualitatively meaningful.