中国实验快堆中子能谱测量实验研究

中子能谱是反应堆的一项重要参数,在快堆中,中子能谱直接决定其增殖与嬗变性能。中国实验快堆是我国第一座钠冷快中子堆,需测量其中子能谱。本文利用活化法在堆芯两个位置进行辐照实验,利用解谱程序处理得到这两个位置的中子能谱。实验结果表明,两个位置的中子能谱与理论计算值基本一致。     

基于中子位置灵敏探测器对点源的三维定位方法研究

使用中子法对密封容器内的放射源进行定位具有重要的现实意义。本研究使用4根矩形分布的中子位置灵敏探测器对探测空间内AmLi源进行定位,首先使用蒙特卡罗方法设计了探测器的慢化屏蔽体;然后设计了延迟电路加到探测器的一端,根据探测器两端探测到中子信号的时间差来确定源y轴（探测器轴向）的位置坐标,并对每个探测器的轴向位置函数进行了刻度;利用探测器围绕密封容器搭建测量空间,使用相邻探测器探测到中子计数率的比值来确定x轴和z轴（另两个方向）的位置坐标并进行了函数刻度。测量时,首先选择计数率最大的探测器来确定源的轴向坐标,再根据与此探测器相邻两根探测器计数率的比值来确定源的另两个方向的坐标,实现了对源的定位。使用该方法测量了点源在探测器空间内的5个不同位置,每个坐标轴上的定位偏差均在1.5 cm之内,并对造成偏差的原因进行了分析。该方法验证了使用中子位置灵敏探测器对放射源进行定位的可行性,并为进一步测量核设施工艺设备内核材料的位置打下了良好的基础。     

CEFR组件替换反应性价值试验测量与计算分析

组件替换反应性价值定义为测量位置组件替换成相应组件时引入的反应性变化。中国实验快堆物理启动试验中组件替换反应性价值测量试验方案中,试验测量了8个典型位置,其中6个位置为燃料组件替换成不锈钢组件,另外两个为不锈钢组件替换成燃料组件。测量结果显示,燃料组件替换反应性价值由内至外依次减少,内圈燃料组件替换反应性价值约-980 pcm,外圈燃料组件替换反应性价值约-470 pcm,补偿棒棒组测量和单根补偿棒测量的结果差别微小。使用CITATION程序对试验方案进行了理论计算,结果表明,计算结果与实验值符合良好,检验了CITATION程序的工程设计实用性。     

环形单针双束流截面测量技术

利用一个三维环形探针对离子束进行旋转扫描，可以同时测量到两个束流截面的大小和位置，估算出二截面附近的聚焦梯度以及束腰的移动。     

俘获探测器转换系数刻度方法研究

本文介绍了一种用于裂变率测量的俘获探测器,研究了俘获探测器转换系数刻度方法。结果表明,特征γ射线刻度方法不受冷却时间的影响,有利于保证转换系数的适用性。在贫化铀装置内两个不同位置用裂变室对两个俘获探测器进行了刻度,两个俘获探测器的转换系数在4%的误差范围内一致。     

132 I半衰期的测量

采用位置接力法和HPGe γ谱仪跟踪测量132I的半衰期.位置之间的交替测量避免了效率刻度,设定每次跟踪测量的真时间相等,简化数据处理,并用平移和迭代两种方法进行数据处理.实验测得132I的半衰期为(2.283±0.002)h,经检验数据可靠.     

MRPC 宇宙线测试技术研究

采用宇宙线测试系统,同时测量两个空间位置对齐的多气隙电阻板室.采用两种不同的事例挑选方法对两个室的性能进行了分析.结果表明,当选取近乎垂直入射的事例时,MRPC的时间分辨、雪崩信号比例等各项性能均得到提高.还研究了pad间串扰对MRPC性能的影响.     

α射线致空气电离的实验研究

利用平行电极板裂变电离室测量技术对α射线致空气电离进行实验研究,探讨电极板间距离和放射源测量位置对测量结果的影响.结果表明,当电极板间距离小于两倍α粒子飞行距离时,测量结果随电极板距离的增大而微弱增大,电离室中放射源的位置对测量结果影响不显著.实验测量的α射线产生的离子对与理论计算结果相吻合.     

快中子小角弹性散射截面测量(英文)

为了研究快中子小角散射,研制了一台位置灵敏探测器。这个探测器主要有由观测液体闪烁体的两个光电倍增管组成,光电倍增管两个信号之间的时间差用来确定光产生的位置,用位置灵敏探测器和伴随粒子方法,从3°～15°角范围,测量了14.7MeV中子在Ti、Nb、Zr、Pb上的弹性散射微分截面,用蒙特卡洛方法对通量衰减、多次散射和有限几何进行了修正。实验结果为核工程设计提供了急需的数据。     

^132Ⅰ半衰期的测量

采用位置接力法和HPGe γ谱仪跟踪测量132I的半衰期.位置之间的交替测量避免了效率刻度,设定每次跟踪测量的真时间相等,简化数据处理,并用平移和迭代两种方法进行数据处理.实验测得132I的半衰期为(2.283±0.002)h,经检验数据可靠.     

共去污单元脉冲萃取柱模型及计算机模拟

在扩散模型的基础上,对共去污单元脉冲萃取柱"切片"数学处理,建立了数学模型,模型中添加了多组分共存分配比计算模块,编写完成了可用于模拟计算共去污单元脉冲萃取柱萃取HNO3、U(Ⅵ)、Pu(Ⅳ)稳态计算程序。利用文献报道的实验数据,对程序进行了验证。结果表明,程序模拟计算的各组分稳态浓度剖面与实测值符合良好,程序可以实现共去污单元多组分共萃的模拟计算。并在此基础上,利用该程序对1A脉冲萃取柱工艺设计进行了初步研究计算。结果表明,脉冲萃取柱的萃取效率与处理料液组分浓度有关,以往一级混合澄清槽等于若干米脉冲柱的设计方法认识有所偏差,应使用计算机模拟方法整体设计脉冲萃取柱。     

Influence of Transverse Magnetic Field on Heat Transport Characteristics of Potassium Heat Pipe

The influence of a transverse magnetic field on the heat transport characteristics of a potassium heat pipe was experimentally studied in the range of field strength 0~0.6 T. The wick was constituted of a multilayer mesh screen, and the adiabatic section, to which the magnetic field was applied, was made up of a concentric double-wall rectangular tube, with the inner wall completely separating the vapor and liquid flows.

The magnetic field was applied perpendicularly to the heat pipe, upon which the axial temperature distribution of the heat pipe was observed to be affected, and the heat transport rate to be reduced with increasing field strength.

The effect of the magnetic field on the heat transport rate is analyzed in terms of the liquid pumping ability of the wick and of the magnetohydrodynamic (MHD) effect on the liquid flow through the wick. The MHD effect on the flow through wick is shown to be expressible by a formula similar to that for flow between parallel plates.

The heat transport rate measured in magnetic field are compared with values calculated assuming that the wick pumping ability was not influenced by the magnetic field but that it was the MHD effect on the liquid flow through the wick that affected the heat transport. The calculated results well explained the experimental data.     

Recovery of neutron-induced damage of SiC by thermal annealing up to 1400 °C

Recovery of the specimen length of neutron-irradiated SiC was observed using a precision dilatometer. The specimens were heated isothermally and isochronally. The accuracy of length measurement at high temperature using the dilatometer was compared with that of length measurement at room temperature using a micrometer. It was clarified that the dilatometer method showed high accuracy and stability. The dilatometer method was applied to observe length recovery by isothermal annealing at 1200 °C of the neutron-irradiated SiC, and at least two recovery rates were clarified.     

Deflection of a liquid metal jet/drop in a tokamak environment

The interaction of a liquid gallium jet with plasma has been investigated in the ISTTOK tokamak. The jet was observed to remain intact during its interaction with plasma, within a certain length beyond which drop formation was observed. Significant deflection of the jet was detected as soon as plasma production was started. Furthermore, a strong dependency of the deflection magnitude on plasma position was observed that could be correlated with plasma potential gradients. As a means to capture and, possibly, quantify this effect, a preliminary magnetohydrodynamic analysis was performed in order to predict the trajectory of a jet that is traveling inside an electromagnetic field. The effect of Lorentz forces, gravity and pressure drop are accounted for in a unidirectional model that assumes a small jet radius in comparison with the trajectory length. The effect of external electric potential gradients on jet deflection was ascertained in conjunction with the importance of electric stresses in modulating the jet speed and radius. Analysis of the results reported in the ISTTOK experiments identifies the process of jet break-up as a capillary instability. The trajectory of the ensuing droplets is modeled and intensification of the deflection process is predicted in the presence of Lorentz forces.     

Divergent impulsive crossflow over packed columnar arrays

A quasi-one-dimensional method was devised for calculating transient, compressible, viscous flows through packet beds and over tube bundles. The method was applied to study the impulsive crossflow of a lithium plasma through an array of liquid jets, a problem that arises in the design of inertial confinement fusion reactors. The jet array was a close-packed annular arrangement with the plasma initially contained within the annular cavity so that the flow was cylindrically divergent. It was found that the crosswise momentum imparted to the jets by the plasma derived mainly from form or profile drag and that skin friction effects were negligible. Plasma drag was estimated to contribute about 20% of the total radial impulse resulting from the pellet microexplosion.     

Mechanism of soft x-ray continuum radiation from low-energy pinch discharges of hydrogen and ultra-low field ignition of solid fuels

EUV continuum radiation(10–30 nm) arising only from very low energy pulsed pinch gas discharges comprising some hydrogen was first observed at Black Light Power, Inc. and reproduced at the Harvard Center for Astrophysics(Cf A). The source was determined to be due to the transition of H to the lower-energy hydrogen or hydrino state H(1/4) whose emission matches that observed wherein alternative sources were eliminated. The identity of the catalyst that accepts 3 · 27.2 eV from the H to cause the H to H(1/4) transition was determined to HOH versus 3H. The mechanism was elucidated using different oxide-coated electrodes that were selective in forming HOH versus plasma forming metal atoms as well as from the intensity profile that was a mismatch for the multi-body reaction required during 3H catalysis. The HOH catalyst was further shown to give EUV radiation of the same nature by igniting a solid fuel comprising a source of H and HOH catalyst by passing a low voltage, high current through the fuel to produce explosive plasma. No chemical reaction can release such high-energy light. No high field existed to form highly ionized ions that could give radiation in this EUV region that persisted even without power input. This plasma source serves as strong evidence for the existence of the transition of H to hydrino H(1/4) by HOH as the catalyst and a corresponding new power source wherein initial extraordinarily brilliant light-emitting prototypes are already producing photovoltaic generated electrical power. The hydrino product of a catalyst reaction of atomic hydrogen was analyzed by multiple spectroscopic techniques. Moreover, the m H catalyst was identified to be active in astronomical sources such as the Sun, stars and interstellar medium wherein the characteristics of hydrino match those of the dark matter of the Universe.     

辐射引发 4-(甲基丙烯酸)2,2,6,6-四甲基哌啶醇酯在聚丙烯上的接枝

利用共辐照法将４（甲基丙烯酸）２，２，６，６四甲基哌啶醇酯（ＴＭＰＭ）接枝共聚在聚丙烯上。研究不同条件对接枝率的影响。研究表明在苯、四氯化碳和石油醚等溶剂中接枝率比在其它溶剂中要高；在氩气中辐照的接枝率比在空气中的高。在苯中，接枝率在１０～６０ｋＧｙ的范围内呈线性增长，大于６０ｋＧｙ出现偏低；在ＣＣｌ４中，接枝率在１０～５０ｋＧｙ的范围内呈线性增长，大于５０ｋＧｙ出现偏低。在０～２．８５ｍｏｌ／Ｌ的浓度范围内接枝率随单体浓度的增加而增加，只有在浓度低于１１４ｍｏｌ／Ｌ时接枝率随浓度增长较快。添加阻聚剂的样品接枝率比不添加阻聚剂的低，在低剂量时相差较大，随着剂量的增大，这种差别越来越小。研究接枝ＴＭＰＭ对聚丙烯耐辐射稳定性能的影响，发现添加接枝共聚物的聚丙烯比添加未接枝的ＴＭＰＭ的聚丙烯更耐辐射。     

钴源辐照室防护屏蔽计算方法的比较研究

采用MCNP(Monte Carlo N particle transport code)程序和经验公式两种方法进行~(60)Co源辐照室的防护屏蔽计算,分析不同方法所得的辐照室外以及迷道内受照剂量率的变化情况。结果表明:从辐射防护最优化、土建经济性及实际测量等角度考虑,经验公式法的贯穿辐射计算结果偏保守;而迷道散射计算中,经验公式法方便省时,尤其是在迷道结构复杂的情况下计算,比MCNP快捷。     

Spatially Dependent Self-Shielding Method with Temperature Distribution for the Two-Dimensional Transport Code PARAGON

The Spatially Dependent Dancoff Method (SDDM) was recently developed to evaluate the power distribution within a fuel rod that has spatial variation of isotopic contents. The method was validated and verified by comparison to Monte Carlo calculations and measurements. However, those evaluations and comparisons were based on the assumption that the temperature distribution within a rod is flat. In this study, an equation used in the SDDM is enhanced in order to more accurately treat the temperature distribution. The enhancement was carried out with the knowledge that a Monte Carlo calculation shows no effect of temperature distribution on spatial flux within a rod. This leads to the cancellation of reaction rate changes due to temperature distribution between inner and outer regions within a rod. The knowledge gained from these evaluations was then applied to the equation used in the SDDM with the temperature distribution. The improved SDDM was validated and verified by comparison to MCNP4C calculations. PARAGON with the improved SDDM is now capable of performing micro-nuclear physics calculations with greater accuracy.     

Experimental study of neutron counting in a zero-power reactor driven by a neutron source inherent in highly enriched uranium fuels

Even a zero-power reactor core containing highly enriched uranium has a weak neutron source inherent in uranium 235, and consequently, a neutron counter placed closely to the core without external neutron source registers a certain counting rate. The study of the counting is very important for zero-power reactor physics experiments with a high precision. In this experimental study, first, at a shutdown state of the UTR-Kinki reactor without start-up neutron source, a pulse height distribution of output signals from a neutron proportional counter was measured to confirm that these signals resulted from neutron detections. At several subcritical states of the UTR, then, the Feynman-α analysis was carried out to confirm that the neutrons detected by the counter must be fission neutrons multiplied by fission chain reactions. The correlation amplitude measured in the Feynman-α analysis was much higher than that measured in a previous drive by start-up source. Further, it was also confirmed that the subcriticality dependence of neutron counting rate followed the source multiplication formula. This feature indicated that the one-point model was very successful in the subcritical range including the shutdown state.