This work aims at evaluating the reliability of the GEANT4(GEometry ANd Tracking 4) Monte Carlo(MC) toolkit in calculating the power deposition on the Megawatt Pilot Experiment(MEGAPIE), the first liquid–metal spalla...This work aims at evaluating the reliability of the GEANT4(GEometry ANd Tracking 4) Monte Carlo(MC) toolkit in calculating the power deposition on the Megawatt Pilot Experiment(MEGAPIE), the first liquid–metal spallation target worldwide. A new choice of codes to study and optimize this target is provided. The evaluation of the GEANT4 toolkit is carried out in comparison with the MCNPX and FLUKA MC codes. The MEGAPIE is an international project led by the Paul Scherrer Institute in Switzerland. It aims to demonstrate the safe operation of an intense neutron source to power the next generation of nuclear reactors, accelerator-driven systems(ADSs). In this study, we used the GEANT4 MC toolkit to calculate the power deposited by fast protons on the MEGAPIE target.The calculation focuses on several structures and regions.The predictions of our calculations were compared and discussed with that of the MCNPX and FLUKA codes,adopted by the MEGAPIE project. The comparison shows that there is a very good agreement between our results and those of the reference codes.展开更多
采用国际开源程序包Geant4,构建高能质子束轰击加速器驱动次临界系统(ADS)散裂靶的物理模型,模拟计算质子轰击液态金属铅、铅-铋合金和汞靶的泄漏中子谱分布,以及计算不同能量质子对应的铅靶泄漏中子产额和轴向积分分布,获得1 Ge V质子...采用国际开源程序包Geant4,构建高能质子束轰击加速器驱动次临界系统(ADS)散裂靶的物理模型,模拟计算质子轰击液态金属铅、铅-铋合金和汞靶的泄漏中子谱分布,以及计算不同能量质子对应的铅靶泄漏中子产额和轴向积分分布,获得1 Ge V质子对应的铅圆柱靶优化参数,考虑入射质子的利用率和整个堆芯的体积质量,优化靶半径范围为16～24 cm,靶高为100 cm,相关研究结果可为(ADS)散裂靶的物理和工程设计提供理论依据。展开更多
In this paper, we study a monitoring method for neutron flux for the spaUation target used in an accelerator driven sub-critical （ADS） system, where a spallation target located vertically at the centre of a sub-crit...In this paper, we study a monitoring method for neutron flux for the spaUation target used in an accelerator driven sub-critical （ADS） system, where a spallation target located vertically at the centre of a sub-critical core is bombarded vertically by high-energy protons from an accelerator. First, by considering the characteristics in the spatial variation of neutron flux from the spallation target, we propose a multi-point measurement technique, i.e. the spallation neutron flux should be measured at multiple vertical locations. To explain why the flux should be measured at multiple locations, we have studied neutron production from a tungsten target bombarded by a 250 MeV-proton beam with Geant4-based Monte Carlo simulations. The simulation results indicate that the neutron flux at the central location is up to three orders of magnitude higher than the flux at lower locations. Secondly, we have developed an effective technique in order to measure the spallation neutron flux with a fission chamber （FC）, by establishing the relation between the fission rate measured by FC and the spallation neutron flux. Since this relation is linear for a FC, a constant calibration factor is used to derive the neutron flux from the measured fission rate. This calibration factor can be extracted from the energy spectra of spallation neutrons. Finally, we have evaluated the proposed calibration method for a FC in the environment of an ADS system. The results indicate that the proposed method functions very well.展开更多
The back-streaming neutrons from the spallation target at CSNS are very intense, and can pose serious damage problems for the devices in the accelerator-target interface region. To tackle the problems, a possible sche...The back-streaming neutrons from the spallation target at CSNS are very intense, and can pose serious damage problems for the devices in the accelerator-target interface region. To tackle the problems, a possible scheme for this region was studied, namely a specially designed optics for the proton beam line produces two beam waists, and two collimators are placed at the two waist positions to maximize the collimation effect of the back-streaming neutrons. Detailed Monte Carlo simulations with the beams in the two different CSNS phases show the effectiveness of the collimation system, and the radiation dose rate decreases largely in the interface section. This can ensure the use of epoxy coils for the last magnets and other devices in the beam transport line with reasonable lifetimes, e.g., thirty years. The design philosophy for such an accelerator-target interface region can also be applicable to other high-power proton beam applications.展开更多
Marinov et al. have detected spontaneous fission events in sources separated from tungsten targets irradiated with 24 GeV protons. These fission events could not be attributed to actinides or to any other known isotop...Marinov et al. have detected spontaneous fission events in sources separated from tungsten targets irradiated with 24 GeV protons. These fission events could not be attributed to actinides or to any other known isotope. Marinov et al. propose that fission events are due to production of element 112 (Eka-Hg) in the tungsten target. We have addressed Marinov’s claim with a new analysis of their data and modern theoretical model calculations of possible interactions. Using data available in the literature the spontaneous fission half-life of the Eka-Hg was estimated to be ~74 days. This is dramatically longer than the half-life obtained for 283112Cn, produced in the fusion of energetic 48Ca ions with 238U. Monte Carlo calculations show that enough Sr isotopes are produced in the tungsten target to make the production of element 112 via fusion of Sr and W feasible;however, if such fusion was possible it had to be deep sub-barrier fusion.展开更多
Deuteron-driven spallation targets have garnered attention recently because they can provide high-energy neutrons to transmute long-lifetime fission products.In this study,the Geant4 toolkit was used to simulate the i...Deuteron-driven spallation targets have garnered attention recently because they can provide high-energy neutrons to transmute long-lifetime fission products.In this study,the Geant4 toolkit was used to simulate the inter-action between a deuteron beam at 500 MeV and a com-posite target composed of alternating lead-bismuth eutectic(LBE)and water.The water was used because it may be employed as a target coolant.The energy spectrum,neu-tron yield,average energy,and total energy of the emitted neutrons were calculated for different thicknesses and thickness ratios between the LBE and water.For a constant target thickness,the neutron yield increases with an increasing thickness ratio of LBE to H 2 O,while the aver-age energy of the emitted neutrons decreases with an increasing in the aforementioned thickness ratio.These two aspects support the use of a pure target,either LBE or water.However,with an increasing LBE-to-H 2 O thickness ratio,the total energy of the emitted neutrons increases and then decreases.This result supports the addition of water into the LBE target.The angular distributions of the emitted neutrons show that the rear of the target is suit-able for loading nuclear waste containing minor actinides and long-lifetime fission products.展开更多
Cooling water is an important part in a Spallation Neutron Source target cooling system, but the unstable vortexes at the exits of the slits between every two tungsten target slices have a negative impact on the stabl...Cooling water is an important part in a Spallation Neutron Source target cooling system, but the unstable vortexes at the exits of the slits between every two tungsten target slices have a negative impact on the stable running of the target system. We apply the field synergy principle for fluid flow to obtain the optimal flow field, which has a uniform velocity distribution without eddy, and then, optimize the geometrical structure of the cooling water flow channel based on the optimal flow field. The results show that when the cooling water flows in the optimized channel, the eddy sizes decrease, the time fluctuations of velocity and pressure almost vanish, and the volume flow rates of the cooling water in each parallel slit are uniform. Therefore, it effectively improves the running stability of the target system with the premise of satisfying the target heat load.展开更多
Measurement of the neutron yield is performed at a primary energy of 400 MeV/u carbons for the Pb target.Water-bath activation-foil method is used in a moderation measurement with Au foils to detect the moderated neut...Measurement of the neutron yield is performed at a primary energy of 400 MeV/u carbons for the Pb target.Water-bath activation-foil method is used in a moderation measurement with Au foils to detect the moderated neutrons. The neutron yield is determined to be 18.4±2.1 per carbon by integrating the neutron flux over the entire water volume. The corresponding simulation values are performed by Geant4 code with three models to compare with the experimental results. The comparison shows that the calculated result with the INCL model is in good agreement with the experimental data.展开更多
文摘This work aims at evaluating the reliability of the GEANT4(GEometry ANd Tracking 4) Monte Carlo(MC) toolkit in calculating the power deposition on the Megawatt Pilot Experiment(MEGAPIE), the first liquid–metal spallation target worldwide. A new choice of codes to study and optimize this target is provided. The evaluation of the GEANT4 toolkit is carried out in comparison with the MCNPX and FLUKA MC codes. The MEGAPIE is an international project led by the Paul Scherrer Institute in Switzerland. It aims to demonstrate the safe operation of an intense neutron source to power the next generation of nuclear reactors, accelerator-driven systems(ADSs). In this study, we used the GEANT4 MC toolkit to calculate the power deposited by fast protons on the MEGAPIE target.The calculation focuses on several structures and regions.The predictions of our calculations were compared and discussed with that of the MCNPX and FLUKA codes,adopted by the MEGAPIE project. The comparison shows that there is a very good agreement between our results and those of the reference codes.
文摘采用国际开源程序包Geant4,构建高能质子束轰击加速器驱动次临界系统(ADS)散裂靶的物理模型,模拟计算质子轰击液态金属铅、铅-铋合金和汞靶的泄漏中子谱分布,以及计算不同能量质子对应的铅靶泄漏中子产额和轴向积分分布,获得1 Ge V质子对应的铅圆柱靶优化参数,考虑入射质子的利用率和整个堆芯的体积质量,优化靶半径范围为16～24 cm,靶高为100 cm,相关研究结果可为(ADS)散裂靶的物理和工程设计提供理论依据。
基金Supported by Strategic Priority Research Program of Chinese Academy of Sciences(XDA03010000 and XDA03030000)the National Natural Science Foundation of China(91426301)
文摘In this paper, we study a monitoring method for neutron flux for the spaUation target used in an accelerator driven sub-critical （ADS） system, where a spallation target located vertically at the centre of a sub-critical core is bombarded vertically by high-energy protons from an accelerator. First, by considering the characteristics in the spatial variation of neutron flux from the spallation target, we propose a multi-point measurement technique, i.e. the spallation neutron flux should be measured at multiple vertical locations. To explain why the flux should be measured at multiple locations, we have studied neutron production from a tungsten target bombarded by a 250 MeV-proton beam with Geant4-based Monte Carlo simulations. The simulation results indicate that the neutron flux at the central location is up to three orders of magnitude higher than the flux at lower locations. Secondly, we have developed an effective technique in order to measure the spallation neutron flux with a fission chamber （FC）, by establishing the relation between the fission rate measured by FC and the spallation neutron flux. Since this relation is linear for a FC, a constant calibration factor is used to derive the neutron flux from the measured fission rate. This calibration factor can be extracted from the energy spectra of spallation neutrons. Finally, we have evaluated the proposed calibration method for a FC in the environment of an ADS system. The results indicate that the proposed method functions very well.
基金Supported by National Natural Science Foundation of China(11235012,10975150)
文摘The back-streaming neutrons from the spallation target at CSNS are very intense, and can pose serious damage problems for the devices in the accelerator-target interface region. To tackle the problems, a possible scheme for this region was studied, namely a specially designed optics for the proton beam line produces two beam waists, and two collimators are placed at the two waist positions to maximize the collimation effect of the back-streaming neutrons. Detailed Monte Carlo simulations with the beams in the two different CSNS phases show the effectiveness of the collimation system, and the radiation dose rate decreases largely in the interface section. This can ensure the use of epoxy coils for the last magnets and other devices in the beam transport line with reasonable lifetimes, e.g., thirty years. The design philosophy for such an accelerator-target interface region can also be applicable to other high-power proton beam applications.
文摘Marinov et al. have detected spontaneous fission events in sources separated from tungsten targets irradiated with 24 GeV protons. These fission events could not be attributed to actinides or to any other known isotope. Marinov et al. propose that fission events are due to production of element 112 (Eka-Hg) in the tungsten target. We have addressed Marinov’s claim with a new analysis of their data and modern theoretical model calculations of possible interactions. Using data available in the literature the spontaneous fission half-life of the Eka-Hg was estimated to be ~74 days. This is dramatically longer than the half-life obtained for 283112Cn, produced in the fusion of energetic 48Ca ions with 238U. Monte Carlo calculations show that enough Sr isotopes are produced in the tungsten target to make the production of element 112 via fusion of Sr and W feasible;however, if such fusion was possible it had to be deep sub-barrier fusion.
基金supported by the National Natural Science Foundation of China(No.11875328).
文摘Deuteron-driven spallation targets have garnered attention recently because they can provide high-energy neutrons to transmute long-lifetime fission products.In this study,the Geant4 toolkit was used to simulate the inter-action between a deuteron beam at 500 MeV and a com-posite target composed of alternating lead-bismuth eutectic(LBE)and water.The water was used because it may be employed as a target coolant.The energy spectrum,neu-tron yield,average energy,and total energy of the emitted neutrons were calculated for different thicknesses and thickness ratios between the LBE and water.For a constant target thickness,the neutron yield increases with an increasing thickness ratio of LBE to H 2 O,while the aver-age energy of the emitted neutrons decreases with an increasing in the aforementioned thickness ratio.These two aspects support the use of a pure target,either LBE or water.However,with an increasing LBE-to-H 2 O thickness ratio,the total energy of the emitted neutrons increases and then decreases.This result supports the addition of water into the LBE target.The angular distributions of the emitted neutrons show that the rear of the target is suit-able for loading nuclear waste containing minor actinides and long-lifetime fission products.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51006060, 51036003)the Foundation for the Author of National Excellent Doctoral Dissertation of China (Grant No.201150)
文摘Cooling water is an important part in a Spallation Neutron Source target cooling system, but the unstable vortexes at the exits of the slits between every two tungsten target slices have a negative impact on the stable running of the target system. We apply the field synergy principle for fluid flow to obtain the optimal flow field, which has a uniform velocity distribution without eddy, and then, optimize the geometrical structure of the cooling water flow channel based on the optimal flow field. The results show that when the cooling water flows in the optimized channel, the eddy sizes decrease, the time fluctuations of velocity and pressure almost vanish, and the volume flow rates of the cooling water in each parallel slit are uniform. Therefore, it effectively improves the running stability of the target system with the premise of satisfying the target heat load.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11575267,11775284,11575289 and 11605258
文摘Measurement of the neutron yield is performed at a primary energy of 400 MeV/u carbons for the Pb target.Water-bath activation-foil method is used in a moderation measurement with Au foils to detect the moderated neutrons. The neutron yield is determined to be 18.4±2.1 per carbon by integrating the neutron flux over the entire water volume. The corresponding simulation values are performed by Geant4 code with three models to compare with the experimental results. The comparison shows that the calculated result with the INCL model is in good agreement with the experimental data.
