Recent progress in nuclear data measurement for ADS at IMP

Recent progress in nuclear data measurement for ADS at Institute of Modern Physics is reviewed briefly.Based on the cooler storage ring of the Heavy Ion Research Facility in Lanzhou, nuclear data terminal was established.The nuclear data measurement facility for the ADS spallation target has been constructed, which provides a very important platform for the experimental measurements of spallation reactions. A number of experiments have been conducted in the nuclear data terminal. A Neutron Time-of-Flight(NTOF)spectrometer was developed for the study of neutron production from spallation reactions related to the ADS project.The experiments of 400 MeV/u ~(16)O bombarded on a tungsten target were presented using a NTOF spectrometer.Neutron yields for 250 MeV protons incident on a thick grain-made tungsten target and a thick solid lead target have been measured using the water-bath neutron activation method. Spallation residual productions were studied by bombarding W and Pb targets with a 250 MeV proton beam using the neutron activation method. Benchmarking of evaluated nuclear data libraries was performed for D-T neutrons on ADS relevant materials by using the benchmark experimental facility at the China Institute of Atomic Energy.     

用不同程序模拟计算ADS散裂靶结果的比对(英文)

利用不同的程序对ADS散裂靶进行了模拟计算。用SNSP,SHIELD,DCM\CEM(Dubna Cascade Model\Cascade EvaporationMode)和LAHET等程序计算了长60 cm,直径20 cm的圆柱形铅靶,分别在800,1000,1500 and 2000 MeV的质子轰击下所产生的泄漏中子产额和能谱分布。模拟结果与实验数据进行了比较,对泄漏中子产额而言,SNSP模拟的结果与实验符合较好,SHIELD,DCM\CEM和LAHET计算的泄漏中子能谱分布比较一致。     

Spallation neutron sources: Basics,state of the art,and options for future development

The paper outlines the physics of the spallation reaction and the resulting rules of thumb with respect to neutron yield, heat deposition, and energy distribution. Technical problems and performance expectations are discussed on the basis of two high beam power spallation neutron source projects, namely, the German SNQ Project (not funded) and the Swiss SINQ Project (under construction). Since both of these projects were designed mainly for thermal neutron scattering application, emphasizing the production of a high flux of moderated neutrons, an alternative conceptual design is presented which, while still allowing the extraction of cold and thermal neutron beams, also offers the opportunity of placing samples into positions where the neutron spectrum has changed only very little due to transport in matter. The anisotropy of the high-energy neutron field can be taken advantage of to select, to some extent, how much of the high energy component will be seen by the specimens. No technical design concept exists so far for a spallation neutron source for fusion materials test purposes, and more detailed studies would be required to assess its value and usefulness. However, a source for combined use for different purposes seems to be feasible without too many compromises.     

用LAHET和MCNP程序研究散裂中子靶的中子学性能

利用LAHET和MCNP程序对ADS散裂中子靶进行模拟计算。因靶的基本物理性质随束流和靶形状的变化而改变,所以首先评估了源强和靶的几何形状对靶性质的可能影响,然后计算长1.2m、直径为0.6m的圆柱形液态铅靶在1GeV质子轰击下,靶内中子的产生和泄漏及能量的沉积等。与文献数据、实验数据进行了比较,符合良好。计算结果还表明:源强和几何的选择对中子产生和泄漏可产生较大影响;用液态铅作散裂靶时,中子产额和泄漏额较高,且泄漏能谱在可利用范围内,但能量沉积在靶中的分布极不均匀,这可能给传热带来问题。     

Indirect measurement of inelastic cross section of relativistic protons in Pb target

The inelastic cross section of relativistic protons in Pb was determined indirectly by measuring the neutron distribution along a Lead spallation neutron source. The spallation neutron source was irradiated by 1, 1.5 and 2 GeV protons. The experimental results were obtained using passive methods. By the use of the beam attenuation coefficient, deduced by a fitting procedure of experimental data, the inelastic cross section of protons in Pb was determined.     

On the problem of monitoring the neutron parameters of the fast energy amplifier

The conceptual Fast Energy Amplifier, proposed by Rubbia et al. consists of a combination of a U-233/Th-232 fuelled fast-neutron subcritical facility with a proton accelerator. An intense beam of 1 GeV protons is injected into liquid lead at the core centre and drives the reactor by producing spallation neutrons. The burst of spallation neutrons produced by a single proton alters the basic neutron statistics which are well known for thermal neutrons in conventional nuclear reactors. A short assessment of standard neutron noise analysis methods is made with respect to monitoring neutron parameter data.     

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.     

Neutron production in bombardments of thin and thick W, Hg, Pb targets by 0.4, 0.8, 1.2, 1.8 and 2.5 GeV protons

Neutron experimental data relevant to the design of the target of neutron spallation sources are presented and discussed. The data include the reaction cross-sections for W, Hg and Pb investigated with 0.4, 0.8, 1.2, 1.8 and 2.5 GeV proton beams as well as the neutron production, neutron multiplicity distribution, as determined event per event using a high-efficiency detector. The production as a function of target material is investigated for both thin (with a single reaction) and thick targets (multiple reactions). Comparisons are made with the predictions of a high-energy transport code.     

Material selection for spallation neutron source windows: Application to PDS-XADS and XT-ADS prototypes

High performance neutron sources are being proposed for many scientific and industrial applications, ranging from material studies, hybrid reactors and transmutation of nuclear wastes. In the case of transmutation of nuclear wastes, accelerator driven systems (ADS) are considered as one of the main technical options for such purpose. In ADS a high performance spallation neutron source becomes an essential element for its operation and control. This spallation source must fulfil very challenging nuclear and thermo-mechanical requirements, because of the high neutron rates needed in ADS. The material selection for this key component becomes of paramount importance, particularly the source window that separates the vacuum accelerator tube from the spallation material where the accelerated protons impinge. In this paper, an integral analysis of spallation sources is done, taking as a reference the projects in this field proposal in the framework of European projects. Our analysis and calculations show that titanium and vanadium alloys are more suitable than steel as structural material for an industrial ADS beam window, mostly due to its irradiation damage resistance.     

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.     

多探测器快中子飞行时间谱仪

描述了一台串列加速器HI-13上的多探测器快中子飞行时间谱仪,并与国际上同类谱仪进行了比较。本谱仪主要用于能量大于8 MeV的快中子散射实验、次级中子双微分截面及带电粒子引起的出射中子能谱的测量。简要介绍了谱仪各主要部分(包括零信号拾取筒、氘气体靶、探测器、电子学等)的结构和特性及其在快中子实验中的应用。     

可用一台ADS验证装置的150 MeV固态金属散裂中子靶的性质研究

对可以用于中国“加速器驱动洁净核能系统”的入射质子能量为150MeV,束流为3 mA的固态金属靶进行了研究。采用锥型几何结构作为靶的结构,材料选择钨,靶厚度为3 mm,对“靶-束窗”一体化结构进行了研究。研究了泄露中子产额和中子产额,泄露中子的能谱分布和空间分布,散裂碎片的分布以及能量沉积和辐射损伤。     

Neutron measurements for advanced nuclear systems: The n_TOF project at CERN

A few years ago, the neutron time-of-flight facility n_TOF was built at CERN to address some of the urgent needs of high-accuracy nuclear data for Accelerator Driven Systems and other advanced nuclear energy systems, as well as for nuclear astrophysics and fundamental nuclear physics. Thanks to the characteristics of the neutron beam, and to state-of-the-art detection and acquisition systems, high quality neutron cross-section data have been obtained for a variety of isotopes, many of which radioactive. Following an important upgrade of the spallation target and of the experimental area, a new measurement campaign has started last year. After a brief review of the most important results obtained so far at n_TOF, the new features of the facility are presented, together with the first results on the commissioning of the neutron beam. The plans for future measurements, in particular related to nuclear technology are finally discussed.     

Preliminary design of inner radius of spallation target of an accelerator driven subcritical reactor for waste transmutation (ADS-NWT)

This paper presented preliminary design studies of inner radius of spallation target for lead-bismuth cooled accelerator driven sub-critical reactor, aimed at reducing proton beam current while simultaneously maintaining high Minor Actinides transmutation performance. Lead-bismuth eutectic (LBE) and uranium-free metallic dispersion fuel were used as the coolant and the fuel for this 1000 MWt reactor. By taking Proton Transmutation Support Ratio (PTSR) as an evaluation index, the inner radius of the spallation target was designed for this reference reactor and the optimized design proposal could obtain the higher transmutation performance. The preliminary study found that when the inner radius of the spallation target ran up to a certain value, the spallation neutron yield would have greater influence on the transmutation performance.     

Impact of PHITS spallation models on the neutronics design of an accelerator-driven system

The impact of different spallation models and parametrisation of nucleon–nucleus interactions in the particle transport code PHITS on the nuclear characteristics of an accelerator-driven system (ADS) is investigated. Cut-off neutrons below 20 MeV calculated using the default option of the current spallation model (i.e. Liège intranuclear cascade (INC) model version 4.6, INCL4.6) are found to be 14% less than those calculated by the old spallation model (i.e. Bertini INC model). This decrease increases the proton beam current that drives the 800-MW thermal power and impacts various ADS parameters, including material damage, nuclear heating of the proton beam window and the inventory of spallation products. To validate these options based on the ADS neutronics design, we conduct benchmark calculations of the total and non-elastic cross sections, thick target neutron yields and activation reaction rate distributions. The results suggest that Pearlstein–Niita systematics, which is a default option of the nucleon–nucleus interaction parametrisation, would be the best option and that Bertini INC is better suited for cut-off neutrons than INCL4.6. However, because of the difficulty in making a definite conclusion on the spallation models, we conclude that relatively large uncertainty in the cut-off neutrons, which is the difference between the two spallation models (i.e. 14%), should be considered.     

Verification of Monte Carlo transport codes FLUKA, GEANT4 and SHIELD for radiation protection purposes at relativistic heavy ion accelerators

The crucial problem for radiation shielding design at heavy ion accelerator facilities with beam energies of several GeV/n is the source term problem. Experimental data on double differential neutron yields from thick targets irradiated with high-energy uranium nuclei are lacking. At present there are not many Monte Carlo multipurpose codes that can work with primary high-energy uranium nuclei. These codes use different physical models for simulating nucleus–nucleus reactions. Therefore, verification of the codes with available experimental data is very important for selection of the most reliable code for practical tasks. This paper presents comparisons of the FLUKA, GEANT4 and SHIELD code simulations with experimental data on neutron production at 1 GeV/n ²³⁸U beam interaction with a thick Fe target.     

Conceptual design of an 800 MeV high power proton driver

This paper outlines the conceptual design work of a high power proton cyclotron proposed by the China Institute of Atomic Energy (CIAE) for a spallation neutron source, accelerator driven systems, production of radioactive ion beams, and other applications. For this cyclotron the 100 MeV injection proton beam is currently considered to be provided by the CYCIAE-100 cyclotron, which is under construction at CIAE and will be later replaced by a dedicated injector for beam upgrading. In order to minimize beam losses for high intensity operation, large turn separation at the extraction has first priority. After analyzing of different scenarios, including super conducting designs, a warm magnet solution was chosen. The conceptual design, field calculations, RF cavity simulations, etc. will be presented in the paper.     

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.     

Optimal ion beam,target type and size for accelerator driven systems: Implications to the associated accelerator power

In interactions of different energetic ions with extended targets hydrogen isotopes are the most effective projectiles for the production of spallation neutrons. It is shown that for every target material and incident ion type and energy there is an optimal target size which results in the escape of a maximum number of spallation neutrons from the target. Calculations show that in an ADS, combination of a beam of 1.5 GeV deuteron projectiles and a uranium target results in the highest neutron production rate and therefore highest energy gain. For fast 1.5 GeV d + ²³⁸U ADS with lead or lead–bismuth eutectic moderator, the required ion beam current is only 38% of that for 1 GeV proton projectiles on lead target. It is shown that for a modular ADS with uranium target and output power of 550 MW_th a 1.5 GeV deuteron beam of current 1.8 mA is required, which is easily achievable with today’s technology. For an ADS with k_eff = 0.98 and output power of 2.2 GW_th, the required beam currents for (a) 1 GeV p + Pb and (b) 1.5 GeV d + U systems are 18.5 and 7.1 mA, respectively.     

ADS熔盐散裂靶中子学性能研究

与传统加速器驱动次临界系统（ADS）采用金属靶作为散裂中子靶的设计不同,加速器驱动次临界熔盐堆（AD-MSRs）采用靶堆一体的设计,直接使用燃料熔盐作为散裂中子靶。由于熔盐靶的中子学性能直接影响AD MSRs的能量放大系数、核废物的嬗变和核燃料增殖的效率,所以本研究基于MCNPX程序,详细计算了高能质子轰击氟盐和氯盐两种熔盐靶产生的散裂中子产额、散裂中子能谱、能量沉积分布以及散裂产物等中子学性能,并与液态Pb和铅铋共熔体（LBE）两种液态金属靶进行了对比。计算结果表明,熔盐靶在散裂中子产额上与液态金属靶有一定的差距,但熔盐靶内能量沉积分布的梯度较小,更有利于靶区的热量导出。与液态Pb和LBE靶相比,熔盐靶的散裂产物中包含更多的气体以及高质量数的α发射体核素。