CR—39探测器的α粒子径迹研究

研究了以KOH作蚀刻液、恒温60℃蚀刻时CR-39探测器的α粒子径迹情况。实验表明,α能量越低则径迹显现时间越短;能量低至70keV时,CR-39就不能显出径迹。径迹直径随蚀刻时间延长而增大。能量1—4MeV时径迹随能量变化较快;超过4MeV时,这一变化逐渐减小。当α粒子的入射角大于40°时,实际角度和根据径迹参数而求得的角度非常一致;而小于此角时,两者相差较大。     

核径迹电化学蚀刻过程中某些基本参数的研究

本文采用聚碳酸酯膜(Makrofol)和~(241)Am 标准面源,实验观测了核径迹电化学蚀刻坑的平均直径和径迹密度与聚碳酸酯膜受照后存放时间、α粒子注量等的关系,为这种核径迹探测方法的应用提供实验数据。     

黑云母中α反冲径迹蚀刻模型研究

同裂变径迹定年方法一样，α反冲径迹（Alpha-recoil tracks）定年方法也是天然放射性释放的核粒子在固体中积累产生的可蚀刻径迹。自然界中的黑云母含有微量元素铀和钍，当它们发生α衰变时，每射出一个α粒子就有一个较重的子体核素反冲，在晶体内形成30-40nm的辐射损失，经过连续反冲就会形成在干涉相差显微镜下可观测的蚀刻径迹，如果自样品形成以来的全部径迹被保存，测得这些径迹数（即α反冲径迹的体密度）就可以得到样品的年龄。对蚀刻模型的研究就是要准确得到α反冲径迹的体密度。应用该蚀刻模型可以在一个样品上多层面、多点位地测定体密度，进而减小误差、提高准确性。     

辐射径迹测量中的荧光激发影像板技术

文章利用理论模拟计算手段研究荧光激发影像板（IP）对辐射径迹的响应。计算显示,IP对各种辐射径迹的灵敏度关系为：α径迹＞β径迹＞γ径迹。实验验证了理论模拟计算结果的可靠性,探讨了在α、β、γ射线混合场中IP测量单一射线的可行性、干扰及其消除方法,并介绍了IP技术在放射性污染植物修复研究中的应用状况。     

测定固体径迹探测器体蚀刻速度的不同方法的比较

测体蚀刻速度V_g通常有三种方法,即重量法(失重法),厚度法和α径迹直径法。三种方法中,重量法简便;当V_g大时,厚度法是较适合的;α粒子径迹直径法比较准确,而且可以分别测各单面的V_g,实验上经常采用它。用三种方法测得硝酸纤维素富士片和Eastman醋酸纤维素片的V_g值的比较见表1、2。     

外测探器中裂变径迹的各种分布

潜伏径迹是进入固体径迹探测器的重带电粒子在其中产生的辐射损伤痕迹;可蚀刻径迹是入射倾角大于临界角θ_C的那部分潜伏径迹;蚀刻后径迹是经过蚀刻剂蚀刻一定时间后在固体经迹探测器中形成的蚀刻坑;可观测径迹是蚀刻后径迹中水平投影大于某最小可观测长度l_(min)的部分。我们用计算模型——分层径迹球法计算外探测器中裂变径迹的各种分布,结果     

固体核径迹探测器的最新进展

本文介绍固体核径迹探测器近几年来的主要进展,如发现α反应径迹、合成CR-39-SO_2、气泡损伤探测法,以及在各领域中应用的新进展。     

一种高灵敏显示指纹的方法

本文介绍一种利用~(10)B(n,α)~7Li反应显示指纹痕迹的灵敏方法。由于从显示指纹的原理上就与传统的光学鉴别不同,因此,不仅灵敏度高,而且突破了光学显示指纹的一些局限。初步实验结果表明,它可望在越来越复杂的指纹侦破中发挥作用。 1.α径迹指纹显象的原理 使用固体径迹探测器可以记录各种重带电粒子的径迹。我们把天然硼粉当做荧光粉洒在指纹区,由于指纹汗渍的吸附作用,硼原子将以指纹形象分布在     

核乳胶中质子径迹计算机辅助识别方法研究

为克服核乳胶质子径迹人工判读的缺点,研究了一种计算机辅助识别的方法。该方法中,对由显微镜系统获取的核乳胶图像序列依次经组合式滤波器滤波、多阈值二值化、径迹点筛选、径迹点去冗余处理后识别出图像序列中的径迹点,经径迹重建从获取的径迹点中重建出反冲质子径迹。利用该方法从经14.9 MeV中子束辐照的核乳胶中提取出反冲质子径迹,并将提取的径迹与人工判读方法提取的径迹进行了比较,结果基本一致。该方法将为核乳胶质子径迹自动判读系统的开发和核乳胶应用于脉冲中子束能谱测量实验奠定重要技术基础。     

模拟土壤湿度及地表积水对α径迹测量的影响

为了进一步提高α径迹测量的效果,我们采用不同湿度及不同积水量的矿石样品模型进行α径迹测量,研究土壤湿度及地表积水对α径迹测量影响的程度及规律性。模拟湿度的实验装置,在2000ml的烧杯中装入800ml体积的矿粉,并加水搅拌矿粉。加水量分别为5、20、30、40、60、80、100、150、200、400ml。然后将探杯倒扣在矿粉面上,盖上干燥的矿粉。每种     

Combination of sensitivity-based and random sampling-based methodologies for efficient uncertainty quantification calculations with control variates method

A combined method of the sensitivity-based and random sampling-based methodologies is proposed for efficient uncertainty quantification calculations. The proposed method is based on the control variates (CV) method, in which a mean value of a target parameter can be estimated efficiently with a help of a mockup parameter whose mean value is well known. Standard deviations can be also efficiently estimated from two mean values of stochastic parameters; a target parameter itself and its square. In the present work, the CV method is applied to a toy problem, in which a linear approximation to a target parameter is regarded as a mockup parameter. This case corresponds to our proposed method to combine the sensitivity-based and random sampling-based methodologies. Numerical results reveal that the proposed method efficiently works. As a preliminary test of application of our proposed method to realistic problems, nuclear fuel burnup calculations are considered, and uncertainties of nuclides number densities after burnup are calculated. Uncertainties of number densities of cesium-134 and europium-151 are calculated by the proposed method, and it is demonstrated that we can carry out uncertainty quantification calculations more efficiently with our proposed method than with the normal random sampling method.     

Inverse method for temperature and stress monitoring in complex-shaped bodies

The purpose of this work is to formulate a space marching method, which can be used to solve inverse multidimensional heat conduction problems. The method is designed to reconstruct the transient temperature distribution in a whole construction element based on measured temperatures taken at selected points on the outer surface of the construction element. Next, the Finite Element Method is used to calculate thermal stresses and stresses caused by other loads such as, for instance, internal pressure. The developed method for solving temperature and total stress distribution is tested using the measured temperatures generated from a direct solution. Transient temperature and total stress distributions obtained from the method presented below are compared with the values obtained from the direct solution. Finally, the presented method is experimentally verified during the cooling of a thick-walled cylindrical element. The model of a pressure vessel was preheated at 300 °C and then cooled by cold water injection. The comparison of results obtained from the inverse method with experimental data shows the high accuracy of the developed method. The presented method allows to optimize the power block’s start-up and shut-down operations, contributes to the reduction of heat loss during these operations and to the extension of power block’s life. The fatigue and creep usage factor can be computed in an on-line mode. The presented method herein can be applied to monitoring systems that work in conventional as well as in nuclear power plants.     

Computation accuracy and efficiency of a polynomial nodal method for diffusion and spatial burnup problems

The aim of this paper is to demonstrate the accuracy and computational efficiency of a polynomial nodal method (PNM) in solving multigroup neutron diffusion problems in three space dimensions, particularly the long-term burnup problems in PWRs, with their inevitable power-dependent effects. With this in mind, PNM is accurately assessed against other well-grounded nodal methods such as the analytic nodal method (ANM) and the nodal expansion method (NEM), in the case of a well-known PWR benchmark problem, and appears to be as accurate and efficient, as regards the determination of both node-average values and detailed flux distributions inside homogenized nodes. Moreover, the practical applicability of the method to the analysis of fuel cycles in actual PWRs is documented positively.     

Least-squares derivation of extremum and weighted-residual methods for equations of reactor physics—I. The first-order Boltzmann equation and a first-order initial-value equation

A least-squares method of solving the first-order Boltzmann equation is given, and it is used to derive directly a maximum principle which is shown to be equivalent to the well-known maximum principles for the second-order even- and odd-parity Boltzmann equations. This surprising result is also derived explicitly from the Euler-Lagrange equation for the functional of the maximum principle, by using the properties of even and odd functions of directions to reduce this second-order equation to a first-order equation.The maximum principle for the first-order equation is illustrated geometrically using a suitable function space to obtain a weighted-residual method having weights differing from the classical Galerkin weights. This weighted-residual method is well-behaved for solutions obtained using spatial finite elements in conjunction with spherical harmonic expansion for directional dependence of the solution, whereas the Galerkin method for the first-order equation can give rise to oscillatory solutions when phase-space finite elements are used. A scheme is proposed for isolating the causes of the oscillatory behaviour with the aid of the maximum principle for the first-order equation.The method employed to obtain a maximum principle for the first-order Boltzmann equation is illustrated further by the derivation of a maximum principle for a first-order initial-value problem. A finite element representation for an approximate solution is used to develop a first-order finite difference method which is compared with some classical difference methods. Finally complementary principles are given for the first-order initial-value problem, which can be used to provide upper and lower bounds for local characteristics of a finite difference solution.     

Three-Dimensional Analysis Method for Sloshing Behavior of Fast Breeder Reactor and Its Application to Uni- and Multi-Vessel Type FBRs

A three-dimensional analysis method for sloshing behavior of fast breeder reactor (FBRs) is developed. The method treats the coolant in a reactor vessel as a potential flow with moving liquid surfaces. The Laplace equation of a velocity potential is solved by a boundary element method with its boundary condition described by a Bernoulli equation.

The vibration test results of a rectangular water pool are calculated by the method. Then, the method is applied to analysis of sloshing behavior of uni- and multi-vessel type FBRs. The latter consists of vessels for the core, heat exchangers and pumps. These vessels are connected by piping. In the case of the uni-vessel type FBR, heat exchangers and pumps are placed in the reactor vessel. The characteristics of sloshing behavior of both the reactors are presented.     

基于FPGA与GPS的时间测量电路设计与实现

为宇宙射线缪子（μ子）测量实验设计了基于FPGA的高精度时间-数字转换器（TDC）,结合TDC测量值与GPS提供的标准时间(UTC)精确记录了粒子事件的时间信息。TDC采用粗计数+细时间测量相结合的方式,用计数器实现动态范围大于1 s的粗时间测量;使用FPGA加法进位延时链构建时间内插完成了细时间测量,并借助Wave-Union与bin-by-bin方法提高时间分辨并改善非线性。实验室测试双边沿TDC的时间分辨为16.68 ps,时间测量精度（RMS）好于45 ps。测量结果表明,该TDC满足脉冲前沿时间甄别要求。     

微观燃耗方程的求解算法比较与性能分析

燃耗方程的求解是燃耗计算的核心。常见的算法包括泰勒方法、Pade方法、子空间方法、切比雪夫有理近似方法和龙格库塔法等。通过数值实验,对每种算法在精度、效率、稳定性方面进行分析比较。结果表明：子空间方法、泰勒方法在计算效率方面具有优势;计算精度及稳定性方面,泰勒方法和Pade方法均占优势。综合考虑,泰勒方法在3个方面均表现突出,可作为燃耗计算的优选算法。     

一种全堆芯精确到每个通道的子通道并行模拟方法

为实现全堆芯精确到每个通道的并行子通道模拟,本文提出一种基于子通道的并行任务划分和进程映射方法,可对全堆芯或单个组件进行计算任务划分,计算任务和进程的映射可灵活进行。该方法可根据计算机（群）的核数确定恰当的全堆芯子通道的任务划分方式,从而使全堆芯热工水力模拟可在单机、小型集群到超级计算机等不同环境运行。在天河二号超级计算机上进行全堆芯157组件、精确到每个真实流道、轴向划分为125层的稳态模拟,可使用4～6 280核实现。使用4核时需约22 h,使用6 280核时需470 s。引入混合编程实现方式后,使用6 280核完成模拟需397 s。     

铅铋堆零功率实验装置控制棒价值测量及方法优化

零功率实验装置的控制棒价值测量一般采用周期法、置换法或落棒法对刻棒实验进行简单处理。为提高刻棒效率,本文提出了无补偿的多步降棒刻棒方法,采用该方法对我国首个铅铋堆零功率实验装置控制棒价值进行了测量,与补偿刻棒方式及落棒法测量结果进行了对比,并通过理论计算验证了该方法的准确性。结果表明：本文方法有效降低了空间效应对测量值的影响,控制棒价值测量结果准确可靠,可在较短时间内完成较高精度的刻棒实验,适用于需经常更换装料方案的临界实验装置。