黄土包气带水分运移的现场研究

本文主要介绍在核素迁移试验现场进行的黄土包气带水分运移研究的方法和主要结果。包气带水分运移试验场建有一座 9.0 m深的负压计观测竖井和二个 2 8.0 m深的中子仪测管。分别采用 WM- 1型负压计系统和 IHiii型土壤中子水分仪测量黄土剖面的基质势和含水量。一组负压计和中子仪测管在天然条件下测量 ,连续观测 2年多 ,用于水分运移特征研究 ;另一组测量停止淹灌后的水分再分配过程 ,连续观测 7个月 ,用于非饱和渗透系数测定。结果表明 :(1)降雨入渗主要影响深度、蒸发影响深度在 1.0 m以上 ;(2 )水分运移可分为 4个带 :1.0 m深度以上为强交替带 ,含水量、水势和水势梯度随时间变化快、变幅大 ,液态水的运移比较明显 ;1.0～ 7.2 m深度上为含水量和水势随时间变化小的弱交替带 ,除黄土颗粒大小变化较大的深度处 ,一般来说 ,水势梯度方向单向向下 ,其中 :含水量和水势在 1.0～ 1.6 m深度上随时间变化较大 ,液态水的运移也比较明显 ;在 5.0～ 7.2 m深度上 ,水分变化很小 ,基本趋于稳定状态 ,液态水的运移很不明显 ,微弱的热水汽扩散显现出来 ;在 7.2～ 2 3.0 m深度上 ,含水量除在黄土 -古土壤 -钙质结核层组合交界处有变化外 ,其余则基本保持与黄土颗粒大小变化相对应的稳定状态 ,为水分运移的传递带 ;2 3.     

黄土包气带水分运移的现场研究

本文主要介绍在核素迁移试验现场进行的黄土包气带水分运移研究的方法和主要结果.包气带水分运移试验场建有一座9.0m深的负压计观测竖井和二个28.0m深的中子仪测管.分别采用WM-1型负压计系统和IHiii型土壤中子水分仪测量黄土剖面的基质势和含水量.一组负压计和中子仪测管在天然条件下测量,连续观测2年多,用于水分运移特征研究;另一组测量停止淹灌后的水分再分配过程,连续观测7个月,用于非饱和渗透系数测定.结果表明: (1)降雨入渗主要影响深度、蒸发影响深度在1.0m以上; (2)水分运移可分为4个带:1.0m深度以上为强交替带,含水量、水势和水势梯度随时间变化快、变幅大,液态水的运移比较明显;1.0～7.2m深度上为含水量和水势随时间变化小的弱交替带,除黄土颗粒大小变化较大的深度处,一般来说,水势梯度方向单向向下,其中:含水量和水势在1.0～1.6m深度上随时间变化较大,液态水的运移也比较明显;在5.0～7.2m深度上,水分变化很小,基本趋于稳定状态,液态水的运移很不明显,微弱的热水汽扩散显现出来;在7.2～23.0m深度上,含水量除在黄土-古土壤-钙质结核层组合交界处有变化外,其余则基本保持与黄土颗粒大小变化相对应的稳定状态,为水分运移的传递带;23.0～28.0m深度上为毛管水带; (3)在0.4～2.4m深度上,当体积含水量θ为0.18～0.41时,非饱和渗透系数K(cm/d)为3.6×10-3～23.4,拟合得到K与θ的经验关系式:K＝2.81×105θ10.51,它可适用于含水量在此范围内的马兰黄土上段; (4)在水分运移的基本稳定带(5.0～7.2m深度),应用达西方程并采取年平均方法,估算得到年降雨入渗补给量不到1cm; (5)在半干旱黄土地区,热水汽的扩散也可能是地下水的一种补给方式.     

中子水分仪的刻度与评价(英文)

研究了中子水分仪校正曲线的各种影响因素,包括土壤类型、质地、容重及土层深度等。当土壤容积含水量为15～45％时,校正曲线近似为一直线,其他因素只改变直线的截距或斜率。土壤中有否植物生长对校正曲线也稍有影响。测量表土层(<20cm)水分时测量误差较大。中子法与取土称重法的相对误差小于8％,但中子法具有不扰动土壤、快速简便及无滞后现象等优点。     

中子水分仪的刻度与评价

研究了中子水分仪校正曲线的各种影响因素,包括土壤类型、质地、容重及土层深度等。当土壤容积含水量为15～45％时,校正曲线近似为一直线,其他因素只改变直线的截距或斜率。土壤中有否植物生长对校正曲线也稍有影响。测量表土层(<20cm)水分时测量误差较大。中子法与取土称重法的相对误差小于8％,但中子法具有不扰动土壤、快速简便及无滞后现象等优点。     

平面型硅快中子剂量探测器初步研究

介绍了平面型硅快中子剂量探测器,初步探索了探测器的中子剂量响应与PN结长和结宽的关系。基于239Pu-Be中子辐射实验结果,可以得出探测器电压随中子剂量线性变化的结论。对探测器等效电阻进行了计算,给出了测试电流为1~10 mA时平面型硅快中子剂量探测器的电流、电压和中子剂量的关系式。     

IAE—Ⅱ型中子水分仪在半湿润沙地中的应用研究

ＩＡＥ－Ⅱ型中子水分仪测定半湿润沙地中土壤含水量较重量法方便、快速且误差较小。但在测量过程中，不同物质间的界面和安装中子管时产生的空隙对中子测水仪的测量精度有较大影响。在中子测水仪测量数值的方差分析中，标定方差对沙地的测量值带来较大的偏差。     

闪烁光纤在快中子辐照下部分特性的蒙特卡罗模拟

采用蒙特卡罗方法对闪烁光纤在快中子辐照下的特性进行了研究。利用Geant4模拟计算得到了快中子照射下,闪烁光纤中的能量沉积效率与光纤长度、半径及入射中子能量的变化曲线,同时对量子效率随上述参数的变化关系进行了模拟分析。研究结果表明选择合适尺寸的闪烁光纤和入射中子能量对于快中子成像技术具有重要的意义,并为实际测量工作中的参数选择提供了的理论指导。     

一个聚乙烯长计数管效率的刻度

长计数管是一种简便而可靠的快中子探测器。由于它有探测效率高,探测效率随中子能量的变化缓慢,以及易于甄别γ射线本底等优点而被广泛用做快中子通量测量的次级标准。     

近临界系统中子倍增时间行为的实验测量

为确定近临界系统内中子倍增因子随时间的变化与系统的反应性的关系,为反应堆启动提供参考,实验测量了中心中子在1个快中子临界装置3个次临界状态的中子倍增的时间行为,在反应性ρ=-2.27×10^-3和-4.79×10^-4的两个次临界状态下,阶跃加入反应性,分别等待180和450s后,中子密度（正比于中子倍增因子）才达到稳定值。与单群缓发中子假设计算的变化曲线比较表明,实验测量的中子倍增因子的变化比理论预估的变化快。即使如此,在反应堆启动中,仍需考虑中子倍增的延迟,以便推算正确的反应性。     

热中子测小样品水分

用插入型中子水分计不能测量小样品和低水分。雷诺兹曾提到用中子透射和散射法可测含氢量。塞缪尔用快中子减速透射法测食品水分,但要用较强的中子源(10~8n/s),考虑到水的热中子截面大,所以我们研究了用热中子测小样品水分的方法。     

Variation of environmental neutron flux with altitude and depthof both water and soil

Applying the extreme low-level y-ray spectroscopic analysis the environmental neutron flux is measured using different moderator construction and environment through the reaction ^197Au (n, γ) ^198Au- The contribution of thermal and resonance neutrons is separated using the cadmium difference technique, while fast neutrons are measured by the paraffin moderator. The results of altitude dependence of the neutron flux are discussed. The thermal neutron flux near the surface of sea water is less than its value at 100 cm over ground near sea water, while the value over the surfaces of fresh water is higher than that near the surface of sea water. Also the thermal neutron flux at 5 cm soil depth increases, then decreases to its original value at 10 cm depth and still constant until 25 cm, then decreases rapidly to reach 27% of its original value at 60 cm depth. The soil compositions, corresponding neutron temperatures and effective absorption cross sections of earth are the most effective factors on the equilibrium region of thermal neutrons in the ground.     

裂变率测量中的杂质影响及其消除方法

核裂变法是通过测量中子进行裂变率测量的重要方法．常用于热中子测量的裂变室有２３５Ｕ裂变室和２３９Ｐｕ裂变室，快中子测量可以用２３８Ｕ、２３２Ｔｈ和２３７Ｎｐ等裂变室．通常用于裂变室的可裂变核素是采用同位素分离方法或人工方法得到的，其中含有少量其他核素杂质．实验测量表明，少量能发生热裂变的杂质对快中子的测量有很大影响。利用热裂变修正方法和裂变室包镉方法可以消除这种影响。     

Development of on-line reactivity meter for nuclear reactors

An online reactivity meter which has been developed for continuous monitoring of reactivity in the Pakistan Research Reactor-1 (PARR-1) is described. The theory of the kinetic technique of measuring reactivity, used by the meter, is described. The meter itself consists of hardware and software for online acquisition of neutron flux signals from plant instrumentation channels and high-level Fortran-77 real-time programming for the computation of reactivity by the solution of neuron kinetic equation. The PDP-11/23 plant computer is used to monitor the plant reactor with the time sharing of its regular data logging function. For the PARR-2 reactor the reactivity meter has been implemented with an IBM PC/AT personal computer. The response of both reactivity meters is fast enough to monitor safety-related reactivity and power excursions in the two reactors. The results of various reactivity measurements are described. The proper choice and location of nuclear detectors and system calibration are discussed     

MTS5露点仪在HTR-10气体采样分析系统中的应用

讨论了对10MW高温气冷堆一回路高纯氦气进行湿度监测的仪器的特点,并介绍了利用氧化铝电容式水分析仪对氦气中的湿度进行在线监测的使用情况。在数年的使用中,仪器测量结果满足反应堆运行要求,需指出的是,该仪器还存在工作过程中发生漂移的特点,所以,欲提高仪器测量的准确性,就必须对该仪器进行定期标定。     

External corrosion of cladding in PWRs

In-reactor corrosion of Zircaloy is strongly influenced by the fast neutron flux and water chemistry of the primary coolant. Under typical PWR coolant conditions with low oxygen content the fast neutron flux increases the corrosion rate only slightly. On the other hand, under fast neutron irradiation at a high oxygen content in the primary coolant the corrosion is accelerated 5- to 10-fold. In addition localized oxide lenses (nodular corrosion) have been observed. However, hydrogen pick-up rates were generally low. The results are discussed in view of life-limiting aspects; under normal operating conditions of a PWR the external corrosion is not life limiting.     

Proposal of Method to Estimate Criticality Correction for Anisotropic Diffusion in Plate Lattice Fast Assembly

Measurements on the neutron and γ-ray attenuation in multi-legged air filled ducts have been carried out using a Cockroft-Walton type neutron generator. The measured spectra were obtained with an NE-213 liquid scintillator using pulse shape discrimination to resolve neutron and γ-ray pulse height data and using a spectral unfolding code to convert these data to energy spectra. Results are given for two rectangular duct geometries. A series of integral measurements have also been carried out with a long counter for fast neutrons and a radiation survey meter to measure the γ-ray dose. The biological dose arising due to the streaming of neutrons was measured with a rem counter. The results show the relative decrement of the integral counts along the axis of the duct. The spectral measurements reveal the presence of resonant windows of oxygen present in the concrete medium. Also the 14 MeV component is found to be dominant in the first leg of the duct whereas degraded neutrons dominate in the second leg. The results are compared with MORSE calculations.     

天然中子源中子测水技术的初步研究

论述了基于天然中子源的中于测水技术基本原理、仪器设备与方法技术以及在成都地区某地的试验结果。与人工中子源中子测水技术相比．虽然大气中子源方法的灵敏度较差．但避免了人工中子源的辐射防护与管理难题。这对于一些确定地层含水率要求不高．而又需长期监测的场合．如工程地质填图与地质环境动态监测等．天然中子源方法中子测水技术具有一定的应用价值。     

Novel approach to solving the inverse equation of point kinetics by the Bernoulli number generalisation method

ABSTRACT

A new approach to solve the inverse equation of point kinetics is presented. The neutron density history can be considered as a series of infinite Bernoulli numbers. In order to simplify the problem, the proposed method uses an approximation which considers only two derivatives of the neutron population density. The reactivity is calculated for different forms of neutron population density and for different time steps. Due to its high precision, the results obtained suggest that the proposed method can be used in a real-time digital reactivity meter.     

Analysis of Cavity Effect on Space- and Time-Dependent Fast and Thermal Neutron Energy Spectra

The effects of the presence of a central cavity on the space- and time-dependent neutron energy spectra in both thermal and fast neutron systems are analyzed theoretically with use made of the multi-group one-dimensional time-dependent S_n method. The thermal neutron field is also analyzed for the case of a fundamental time eigenvalue problem with the time-dependent P₁ approximation. The cavity radius is variable, and the system radius for graphite is 120 cm and for the other materials 7 cm.

From the analysis of the time-dependent S_n calculations in the non-multiplying systems of polythene, light water and graphite, cavity heating is the dominant effect for the slowing-down spectrum in the initial period following fast neutron burst, and when the slowing-down spectrum comes into the thermal energy region, cavity heating shifts to cavity cooling. In the multiplying system of ²³⁵U, cavity cooling also takes place as the spectrum approaches equilibrium after the fast neutron burst is injected.

The mechanism of cavity cooling is explained analytically for the case of thermal neutron field to illustrate its physical aspects, using the time-dependent P₁ approximation. An example is given for the case of light water.