共查询到20条相似文献,搜索用时 238 毫秒
1.
2.
3.
利用缓发中子计数法对235U-239Pu混合物中235U和239Pu含量的快速测定进行了初步研究。在中国原子能科学研究院30 kW微型反应堆(简称微堆)垂直孔道辐照235U、239Pu以及235U-239Pu混合物样品30 s,冷却2 s,用缓发中子探测器测量100 s,得出235U和239Pu的探测限分别为0.14和0.18 μg;探测器效率为0.015 0±0.001 0;当235U和239Pu质量比m(235U)/m(239Pu)=1.2时,235U、239Pu含量计算值与标称值的相对偏差分别为0.8%和6.9%。 相似文献
4.
自然界中236U与238U原子个数比约10-14,不同反应堆类型及核燃料辐照情况辐照后的核材料中236U与238U原子个数比不同,一般为天然236U与238U原子个数比的107~1011倍。通过测量环境样品中的236U与238U原子个数比可探知取样点附近进行过的辐照活动、环境污染的来源及对应核燃料的燃耗。本研究使用配制的模拟样品,建立了多接收电感耦合等离子质谱(MC-ICP-MS)技术测定236U与238U原子个数比的方法以及估算核燃料燃耗的工作方案,并与其他燃耗计算方法比较,燃耗的相对偏差约10%。 相似文献
5.
232U是燃料元件制造中需严格控制的铀同位素,为此,需建立一种准确的测量方法。本工作建立了一种α谱仪和质谱法相结合测定铀产品中232U含量的新方法。采用质谱法测量234U、235U、236U与238U的同位素丰度比,α谱仪测量232U的活度和234U、235U、236U、238U的总活度,即可计算出铀产品中232U的浓度。对于232U含量为1.118 ng/g的样品,16次测定数据的相对标准偏差为3.43%,证明该测量方法有效,可应用于实际样品的分析测定。 相似文献
6.
由于238U裂变反应率在中国实验快堆(CEFR)中是一非常关键的指标参数,因此,在CEFR的首次物理启动工作中对其进行了实验测量。在实验过程中,利用高贫化的UO2(235U-0.002%)直接进行了238U裂变反应率的绝对测量;利用国产贫铀片(235U-0.335%)、高浓铀片(235U-90%)组合方式间接进行了238U裂变反应率的测量。给出两种方法与理论值的对比和轴向及径向的相对分布。本实验为238U裂变反应率测量提出一新的选择方案,并验证了其可靠性。 相似文献
7.
本文基于最小二乘不确定度传递方法,建立235U中子裂变核反应截面模型依赖型与非模型依赖型协方差评价体系。通过针对实验测量较丰富的中子反应总截面、辐射俘获、(n,2n)等核反应实验数据不确定度源项分析,为协方差评价提供实验基础,并给出对应核反应截面的非模型依赖型协方差评价数据。通过开展快中子能区235U核反应理论模型参数灵敏度计算与分析,导出实验测量缺乏的核反应截面模型依赖型协方差评价数据。经上述系统评价,所得协方差数据与核反应截面中心值研究过程自洽、物理合理,并按国际标准ENDF-6格式输出,便于核工程用户使用。 相似文献
8.
用HPGe γ能谱法绝对测量了0.57、1.0和1.5 MeV中子诱发235U裂变产物99Mo的产额,使用双裂变室测量了样品辐照过程中的裂变率,应用MCNP ⅣB模拟了铀样品中的中子能谱,并讨论了非主中子的各种来源对产额数据的影响。得到99Mo在0.57、1.0和1.5 MeV的产额分别为6.61%、6.62%和6.28%。本工作与美国阿贡实验室的结果有15%以上的相对偏差,主要是由引用的衰变数据不同引起。对阿贡实验室数据进行校正后,本工作与阿贡实验室数据的相对偏差处于实验不确定度范围内。 相似文献
9.
10.
核数据不确定性分析影响着反应堆安全,在反应堆堆芯物理计算过程中具有重要意义。利用SCALE6.1程序包中KENO模块建立反应堆模拟评估和验证基准BEAVRS(Benchmark for Evaluation and Validation of Reactor Simulations)第一循环热态零功率堆芯物理模型,采用TSUNAMI-3D模块开展keff的敏感性与不确定性分析,分析了不同燃料富集度、不同温度对keff敏感性与不确定性的影响。结果表明:核数据不确定性导致BEAVRS模型的keff总的不确定性为0.501 6%;235U的平均裂变中子数敏感性导致keff的敏感性系数最大(0.926 58);对keff不确定性贡献最大的是238U(n,γ)反应截面,为0.298 14%;在燃料富集度降低、温度上升时,238U(n,γ)反应截面不确定性会导致keff的不确定性增大。因此,在开展反应堆... 相似文献
11.
12.
Xianggao Wang Shan Jiang Ming He Wei Wang Guozhu He Jie Gong Shaoyong Wu 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2010,268(13):2295-2299
236U is a long-lived radioactive isotope which is produced principally by thermal neutron capture on 235U. 236U may be potentially applied in geological research and nuclear safeguards. Accelerator mass spectrometry is presently the most sensitive technique for the measurement of 236U and a measurement method for long-lived heavy ion 236U has been developed. The set-up uses a dedicated injector and the newly proposed 208Pb16 molecular ions for the simulation of 236U ion transport. A sensitivity of lower than 10−10 has been achieved for the isotopic ratio 236U/238U in present work. 相似文献
13.
Bency John 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(12):1379-1381
It is possible that discrete-resonances in slow-neutron reactions can be induced in inverse-kinematics when an ion-beam of reactant-nuclei of right kinetic energy is made to pass through a column of thermal-neutrons. A scheme for effective cross-section calculation in this type of reactions has been discussed. Effective cross-sections have been calculated for the lowest 17 large s-wave resonances in 238U+n and 239U+n capture-reactions, induced by low energy ion-beams of 238U and 239U, respectively. Use of ion-beams in this manner will facilitate online-separation of transmuted-isotopes and this may be a useful feature for future nuclear energy technology. 相似文献
14.
Hani Negm Hideaki Ohgaki Izuru Daito Takehito Hayakawa Heishun Zen Toshiteru Kii 《Journal of Nuclear Science and Technology》2013,50(6):811-820
The dependence of the nuclear resonance fluorescence (NRF) yield on the target thickness was studied. To this end, an NRF experiment was performed on 238U using a laser Compton back-scattering (LCS) γ-ray beam at the High Intensity γ-ray Source facility at Duke University. Various thicknesses of depleted uranium targets were irradiated by an LCS γ-ray beam with an incident beam energy of ~2.475 MeV. The scattering NRF γ-rays were measured using an High-purity Germanium (HPGe) detector array positioned at scattering angles of 90° relative to the incident γ-beam. An analytical model for the NRF reaction yield (NRF RY model) is introduced to interpret the experimental data. Additionally, a Monte Carlo simulation using GEANT4 was performed to simulate the NRF interaction for a wide range of target thicknesses of the 238U. The measured NRF yield shows the saturation behavior. The results of both of the simulation and the analytical model can reproduce the saturation curve of the scattering NRF yield of 238U against the target thickness. In addition, we propose a method to deduce the precise integral cross section of the NRF reaction by fitting the NRF yield dependency on the target thickness without any absolute measurements. 相似文献
15.
S.E. Agbemava B.J.B. Nyarko J.J. Fletcher R.B.M. Sogbadji E. Mensimah M. Asamoah 《Annals of Nuclear Energy》2011
While there are growing demands for the nuclear data at higher energy regions than keV for up-to-date scientific and technological development, accurate capture cross sections at thermal energy are still needed. The thermal neutron capture cross sections for the reactions 127I(n,γ)128I, 152Sm(n,γ)153Sm,154Sm(n,γ)155Sm, and 238U(n,γ)239U were determined by the method of foil activation using 55Mn(n,γ)56Mn as a reference reaction. The experimental samples with and without a Cd cover were irradiated in an isotropic neutron field of a 20 Ci 241Am–Be neutron source facility. A high purity Ge detector was used to measure the induced gamma-rays from the samples and the monitor. The thermal neutron capture cross sections of the reactions 127I(n,γ)128I, 152Sm(n,γ)153Sm, 154Sm(n,γ)155Sm, and 238U(n,γ)239U were deduced from the analysis of obtained gamma-ray spectra. The thermal neutron capture cross section values for 127I(n,γ)128I, 152Sm(n,γ)153Sm, 154Sm(n,γ)155Sm, and 238U(n,γ)239U reactions are (5.93 ± 0.52), (207.3 ± 9.4), (7.7 ± 0.3), and (2.79 ± 0.09) barns respectively. The obtained results have been discussed and compared with the available experimental data and were found to be in agreement with each other. 相似文献
16.
The yields of more than fifteen fission products have been carefully measured using radiochemical techniques, for 235U(n,f), 239Pu(n,f) in a thermal spectrum, for 233U(n,f), 235U(n,f), and 239Pu(n,f) reactions in a fission neutron spectrum, and for 233U(n,f), 235U(n,f), 238U(n,f), and 239Pu(n,f) for 14.7 MeV monoenergetic neutrons. Irradiations were performed at the EL3 reactor, at the Caliban and Prospero critical assemblies, and at the Lancelot electrostatic accelerator in CEA-Valduc. Fissions were counted in thin deposits using fission ionization chambers. The number of fission products of each species were measured by gamma spectrometry of co-located thick deposits. 相似文献
17.
叙述了水泥反射体中D-D中子源反射中子测量实验原理。测量了无反射体、有反射体、本底三种状态下中子引发235U(包镉)、238U产生的裂变率。并根据裂变率得到实验装置下水泥反射体对中子的反射系数。对反射系数随角度变化趋势进行了分析。 相似文献
18.
Primary study on holdup measurement of ^235U in pipe using γ-ray spectrometry and Monte Carlo simulation 总被引:1,自引:0,他引:1
WU Lun-Qiang WEI Meng-Fu ZHANG Lian-Ping YANG Suo-Long 《核技术(英文版)》2006,17(4):241-244
The pipe holdup measurement is very important for decommissioning nuclear facilities and nuclear-material control and accounting. The absolute detection efficiencies (εsp) of full-energy γ rays peak under different source density distribution function have been simulated using the Monte Carlo (MC) software, and the counting rates (no) of the characteristic γ rays have been measured using the γ spectrometer followed by the calculation of the holdup. The holdup is affected by the energy of γ rays, distance at which they are detected, pipe material, thickness, and source distribution of pipe, especially source distribution at a short distance. The comparative test of ^235U reference materials on the inner wall of Fe and A1 pipes (the total mass of ^235U is 44.6 mg and 222.8 mg, respectively) have been accomplished using this method. The determined result of ^235U is 43.2mg (U0.95rel=5.4%) and 216.2mg (U0.95rel= 3.2%), respectively, which are in accordance with the reference values. 相似文献
19.
The thermal-neutron-induced fission cross-section of 238U was measured at an intense and very clean thermal-neutron beam of the Grenoble high-flux reactor. The best 238U sample material used contained only 12 ppb of 235U. The fission fragments were detected with surface barrier detectors. Relative to a thermal fission cross-section of 587.6 barn for 235U, a value of (11 ± 2) μbarn was obtained for the 238U fission cross-section. By comparing this result with 238U(n, f) measurements in the resonance region, the existence of a negative resonance or resonances in 239U is demonstrated. 相似文献
20.
Christof Vockenhuber Marcus ChristlCornelia Hofmann Johannes LachnerArnold Milenko Müller Hans-Arno Synal 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(24):3199-3203
The performance of the compact ETH-TANDY system for accelerator mass spectrometry measurements of 236U is presented. Despite the low ion energies of around 1.2 MeV we can demonstrate a background level that is comparable to larger facilities. The careful ion-optical design of the high-energy spectrometer leads to a high suppression of neighboring isotopes sufficient to measure samples with isotopic ratios of 236U/238U > 10-11 the ion chamber only, as demonstrated by systematic investigations with different slit settings and time-of-flight measurements. Additionally, a high overall efficiency is achieved due to a high transmission through the accelerator. 相似文献