Shielding study on iron and concrete assemblies of bremsstrahlung photons and photoneutrons from copper target bombarded by 18, 28 and 38 MeV electrons

Following the angular distribution measurements of bremsstrahlung photons and photoneutrons, we measured the distributions of photon and neutron dose rates in the iron and concrete assemblies using a copper target bombarded by 18, 28 and 38 MeV electrons at the electron linear accelerator (linac) of Hokkaido University. In this experiment, seven types of shielding assemblies of iron and concrete layers were used and the photon and neutron dosemeters were inserted into the assemblies to get the depth–dose distribution. The measured results were compared with the results calculated using the Monte Carlo code MCNP5 to verify the calculated results. The calculated results of the ambient dose equivalent rates were in agreement with the measured results within 30% accuracy. Since no work on the radiation behavior in the shielding wall of medical linac room has ever been reported, this work gives valuable benchmark data for the detailed shielding design with high accuracy.     

An overview of the Boltzmann transport equation solution for neutrons,photons and electrons in Cartesian geometry

Questions regarding accuracy and efficiency of deterministic transport methods are still on our mind today, even with modern supercomputers. The most versatile and widely used deterministic methods are the P_N approximation, the S_N method (discrete ordinates method) and their variants. In the discrete ordinates (S_N) formulations of the transport equation, it is assumed that the linearised Boltzmann equation only holds for a set of distinct numerical values of the direction-of-motion variables. In this paper, looking forward to confirm the capabilities of deterministic methods in obtaining accurate results, we describe the recent advances in the class of deterministic methods applied to one and two dimensional transport problems for photons and electrons in Cartesian Geometry. First, we describe the Laplace transform technique applied to S_N two dimensional transport equation in a rectangular domain considering Compton scattering. Next, we solved the Fokker–Planck (FP) equation, an alternative approach for the Boltzmann transport equation, assuming a mono-energetic electron beam in a rectangular domain. The main idea relies on applying the P_N approximation, a recent advance in the class of deterministic methods, in the angular variable, to the two dimensional Fokker–Planck equation and then applying the Laplace Transform in the spatial x variable. Numerical results are given to illustrate the accuracy of deterministic methods presented.     

An overview of the Boltzmann transport equation solution for neutrons, photons and electrons in Cartesian geometry

Questions regarding accuracy and efficiency of deterministic transport methods are still on our mind today, even with modern supercomputers. The most versatile and widely used deterministic methods are the P_N approximation, the S_N method (discrete ordinates method) and their variants. In the discrete ordinates (S_N) formulations of the transport equation, it is assumed that the linearised Boltzmann equation only holds for a set of distinct numerical values of the direction-of-motion variables. In this paper, looking forward to confirm the capabilities of deterministic methods in obtaining accurate results, we describe the recent advances in the class of deterministic methods applied to one and two dimensional transport problems for photons and electrons in Cartesian Geometry. First, we describe the Laplace transform technique applied to S_N two dimensional transport equation in a rectangular domain considering Compton scattering. Next, we solved the Fokker-Planck (FP) equation, an alternative approach for the Boltzmann transport equation, assuming a mono-energetic electron beam in a rectangular domain. The main idea relies on applying the P_N approximation, a recent advance in the class of deterministic methods, in the angular variable, to the two dimensional Fokker-Planck equation and then applying the Laplace Transform in the spatial x variable. Numerical results are given to illustrate the accuracy of deterministic methods presented.     

Neutron and photon doses in high energy radiotherapy facilities and evaluation of shielding performance by Monte Carlo method

Medical accelerators operating above 10 MV are a source of undesirable neutron radiations which contaminate the therapeutic photon beam. These photoneutrons can also generate secondary gamma rays which increases undesirable dose to the patient body and to personnel and general public. In this study, the Monte Carlo N-Particle MCNP5 code has been used to model the radiotherapy room of a medical linear accelerator operating at 18 MV and to calculate the neutron and the secondary gamma ray energy spectra and the dose equivalents at various points inside the treatment room and along the maze. To validate our Monte Carlo simulation we compared our results with those evaluated by the recommended analytical methods of IAEA Report No. 47, and with experimental and simulated values published in the literature. After validation, the Monte Carlo simulation has been used to evaluate the shielding performance of the radiotherapy room. The obtained results showed that the use of paraffin wax containing boron carbide, in the lining of the radiotherapy room walls, presents enough effectiveness to reduce both neutron and gamma ray doses inside the treatment room and at the maze entrance. Such evaluation cannot be performed by the analytical methods since room material and wall surface lining are not taken into consideration.     

Thermal analysis of NAC-LWT cask under normal and fire accident conditions

Abstract

Two- and three-dimensional thermal models of a Nuclear Assurance Corporation Legal Weight Truck (NAC-LWT) cask were constructed using the PATRAN commercial finite element package. The two-dimensional model included the effect of radial stiffeners in the package’s external neutron shield but the three-dimensional model did not. A normal conditions of transport (NCT) simulation using both models predicted the peak cladding temperature was roughly 210°C. The NCT package temperatures were used as initial conditions for transient fire/post-fire simulations. Different assumptions were used to determine when the neutron shield liquid drained from the tank and was replaced by air. When the liquid was assumed to remain within the tank during and after the fire, the peak cladding temperature was predicted to exhibit a temporal maximum of roughly 300°C, ～6 h after the end of the fire. If the liquid drained from the tank during the fire, the cladding temperature did not exhibit a temporal peak. Rather, it eventually reached a maximum temperature of roughly 280°C, which is the steady state NCT peak temperature when air is in the neutron shield tank. This undergraduate project will be used to lay down a foundation for further research on NAC-LWT casks. Two and three dimension package of the cask will be constructed using ANSYS, and simulations will be run for NCT and fire/post-fire conditions. The models will also be linked to Container Analysis Fire Environment (CAFE) to predict response of the package in fire.     

Attenuation of ambient dose equivalent from neutrons by thick concrete, cast iron and composite shields for high energy proton, He, Ca and U ions on Cu targets for shielding design

Data on neutron dose attenuation by thick concrete, cast iron, and cast iron plus concrete composite shields for heavy ions and protons having high energies (200-1000 MeV/u) are necessary for shielding designs of high-powered heavy ion accelerator facilities. Neutron production source terms, shield material attenuation lengths, and neutron dose rate reduction effectiveness of the bulk shielding in the angular range from 0° to 125° were determined by the Particle and Heavy Ion Transport Code (PHITS) for beams of 300 and 550 MeV/u ⁴⁸Ca ions, 200 and 400 MeV/u ²³⁸U ions, 800 MeV/u ³He and 1 GeV protons. Calculated results of interaction lengths of concrete and cast iron were also compared with similar work performed by Agosteo et al., and to experimental and other calculated data on interaction lengths. The agreement can be regarded as acceptable.     

蒙特卡罗模拟CFETR中子输运计算中的全局减方差方法应用及对比

在具有全局特性的蒙特卡罗输运精细计算的问题中,传统的MCNP(Monte Carlo N Particle Transport Code)局部减方差方法很难得到理想的计算结果,全局减方差方法(Global Variance Reduction,GVR)则是一种有效的解决方法。针对中国聚变工程试验反应堆(Chinese Fusion Engineering Testing Reactor,CFETR)的中子输运过程中减小全局方差的问题,将多种形式的GVR方法应用到柱状CFETR中子学模型的计算中。依据不同的中子分布信息,在算例中应用和对比了6种不同形式的GVR权窗,并对不同GVR方法的品质因子(FOMG)、标准差(σ)和有效计数率(Scoring)进行了分析。与AN(MCNPanalog method)相比,GVR方法的FOMG有很大的增长,误差在空间的分布也更加平缓,且具有更高的Scoring。在前人提出的全局减方差的基础上,在计算中应用一些新的GVR形式(能量、径迹数等),计算结果表明,基于中子通量的GVR方法的全局计算效率较AN提高了6.43倍。此外,基于中子能量的全局减方差方法也是一种可行的GVR应用形式,其与AN比较,计算效率提高了5.11倍。综上,基于中子通量的GVR方法具有最佳的全局减方差效果。     

带热套管的T型接管内流动换热的数值模拟和实验研究

为了分析核反应堆冷却剂系统中带热套管T型接管内由于注入非等横向射流导致的构件热冲击状况，本文应用计算流体力学商用软件FLUENT5．3进行了紊流流动换热的数值模拟，分析了主管及接管与热套间环腔内的流动换热特性，针对套管上开有通流小孔，并采用凸台支撑的热套管结构形式，模拟了射流与主流流速比为0．05及0．5两种典型工程，传热实验，研究了主管及接管内壁近壁区域的传热特性，并讨论了热套管尺寸变化对接管热冲击的影响，结果表明，数值模拟与实验数据吻合良好，热套管对构件的热保护程度与热套管结构形式及流速比密切相关，适当减小流速比有利于改善构件热应力状况。     

中国先进研究堆冷中子源两相虹吸氢系统的概念设计及可行性试验

提出了中国先进研究堆冷中子源氢系统的概念设计方案,并进行了可行性试验。针对概念设计中采用的两相虹吸氢回路系统,使用氟里昂113进行了1：1的模化试验研究,确定了中子慢化室含气率、热虹吸系统循环能力及各部件的初步结构形式和尺寸。还进行了气泡在不同液体中上升速度的试验研究,以决定密度、粘度及表面张力等物性对气泡上升速度、含气率、系统循环能力的影响,分析得到模化关系,以便将氟里昂模化试验的结果应用于中国先进研究堆(CARR)堆冷中子源氢系统的设计。     

前剂量中的热激活和辐照熄灭研究

前剂量技术是瓷器热释光测定年代的一个重要方法，它在瓷器中有两个重要特征——热激活效应和辐照熄灭效应。本文根据这两个效应，得到了测定瓷器古剂量的两个方法，一个是“激活法”，另一个是“熄灭法”。研究结果表明，激活法适宜于测定瓷器年代的下限(小于距今100年)，熄灭法适宜于测定瓷器年代的上限(大于距今1000年)。当两个方法同时使用时，瓷器年代测定的准确性将提高。     

Energy-resolved computed tomography measurements of iron solution and adipose as a simulation for estimating the iron concentration in the human liver

To measure the iron concentration in the human liver, which comprises soft tissue and adipose as well as iron, energy-resolved computed tomography (CT) is applied using a transXend detector. The transXend detector measures X-rays as electric current and gives an energy distribution after analysis. Energy-resolved CT clearly separates iron solution from acrylic, a substitute for soft tissue, whereas conventional current-measurement CT cannot. Using CT values obtained in two different energy ranges, a two-dimensional map of iron, adipose and soft tissue is plotted. With this map, the components in the liver can be identified.     

Development of self-powered neutron detectors for neutron flux monitoring in HCLL and HCPB ITER-TBM

Self powered neutron detectors (SPND) have a number of interesting properties (e.g. small dimensions, capability to operate in harsh environments, absence of external bias), so they are attractive neutron monitors for TBM in ITER. However, commercially available SPNDs are optimized for operation in a thermal nuclear reactor where the neutron spectrum is much softer than that expected in a TBM. This fact can limit the use of SPND in a TBM since the effective cross sections for the production of beta emitters are much lower in a fast neutron spectrum.This work represents the first attempt to study SPNDs as neutron flux monitors for TBM. Three state-of-the-art SPND available on the market were bought and tested using fast neutrons at TAPIRO fast neutron source of ENEA Casaccia and with 14 MeV neutrons at the Frascati neutron generator (FNG).The results clearly indicate that in fast neutron spectra, the response of SPNDs is much lower than in thermal neutron flux. Activation calculations were performed using the FISPACT code to find out possible material candidates for SPND suitable for operation in TBM neutron spectra.     

以太网分布式测控系统在热工实验中的应用

阐述一种基于工业以太网的分布式输入输出(I/O)测控系统在某设备综合实验装置中的实际应用,分别对其硬件配置、软件设计和系统特点进行了详细介绍。经实验验证,该系统可靠性高、抗干扰能力强、控制准确、方便扩展和升级,测量和控制效果良好。     

三维结构瞬态温度,位移和热应力计算的等效时间法

本文提出了一种计算二维结构瞬态温度，位移和热应力的近似方法－等效时间法。利用事先得出的热边界幅值的单位变化所引起的结构响应的有限元分析结构。通过简单的代数运算即可求出同样热边界模式下热边界模式下热边界幅值的任意变化过程在结构中产生的响应。这种近似方法有很高的计算效率。通过算例表明，与详细的有限元计算结果相比，在工程允许的范围内误差满足工程需要。等效时间法可肜于对计算效率要求较高的复杂结构的实时分析     

应用正电子湮没技术定量估算高纯铁形变的位错密度和空位浓度

采用慢拉伸与多普勒展宽相结合．研究了单一试样以５×１０－５／ｓ的应变速率拉伸时，高纯铁形变作品５００Ｋ回复前后Ｓ参数随形变量的变化［Ｓ（ε）曲线］。实验结果表明．回复前的Ｓ（ε）曲线包含位错和空位的贡献．回复后仅食位错的贡献。对于同一形变量的样品．５００Ｋ回复后Ｓ参数下降．形变量越大下降量越大．对应空位贡献也越大：根据两态捕获模型计算可得：高纯铁拉伸变形产生空位和位错．空位浓度和位错密度均随形变量的增加而增加．空位浓度ＣＶ的数量级为１０１７－１０１９ｃｍ－３．位错密度ρｄ的数量级为１０９－１０１１ｃｍ－２．     

轻水堆核电站奥氏体不锈钢铸件的热老化及其老化管理

在轻水堆核电站中,奥氏体不锈钢铸件(CASS)在运行温度下长期工作将面临热老化问题。本文对热老化的机理进行了描述,并针对核电站的热老化问题,给出了老化管理工作的主要步骤,即部件敏感性甄别、老化状态评估和ISI大纲更新;结合CASS热老化的老化管理实践,对我国核电站的热老化管理工作提出了建议。     

红外吸收法与热导法同时测定铀硅化合物中氧、氮含量

采用氧/氮分析仪对铀硅化合物中氧、氮含量的测定方法进行了研究,以红外吸收法和热导法测定了铀硅化合物中氧、氮的含量。考察了取样量、助熔剂、加热功率、分析时间等参数对氧、氮含量测定的影响,并优化了相关的工作参数。当取样量为0.10 g(准确至0.0001 g)时,在以镍篮为助熔剂、4200 W的加热功率条件下,氧的质量分数测定范围为0.00050%～0.365%,氮的质量分数测定范围为0.00050%～0.026%,线性相关系数均大于0.999,测定相对标准偏差均优于10%。     

理想化的实际反应堆内热中子有效增殖系数的定义及表达式的讨论

目前教科书中介绍的反应堆热中子有效增殖系数keff,是对无源中子的反应堆内的中子变化情况的准确定义及相应表达式的准确介绍,它能准确解释并描述中子在反应堆内六种物理过程中的变化情况。但用它作为一个统一的定义及表达式来描述并解释和计算有源中子存在的实际反应堆时,对于部分情况它既不能准确、清楚,又不能正确解释相应的物理过程,它的表达式也不能作为一个统一的表达式,按照它的定义计算得到相应的结果。且,目前,国内外工程研究人员还没有给出过实际反应堆内有源中子存在情况下的热中子有效增殖系数的定义及表达式。因此,特撰写此文,对考虑了源中子后的实际反应堆的热中子有效增殖系数,给出一个正确且准确的定义及相应表达式。     

辐射和热对高放废物地质处置库缓冲材料性能演化的影响

辐射和释热是高放废物的内在特性,辐射和热对膨润土性能的影响对于高放废物地质处置库安全评价至关重要。本文对国外近年来有关辐射和热对工程屏障材料性能的影响研究成果进行了初步的调研,其中有关热对工程屏障材料性能影响的调研主要集中关注了在较高温度(100 ℃以上)时工程屏障材料性能的变化。     

计算流体动力学在燃料组件热工水力性能分析和格架研制中的应用

国外使用商用计算流体动力学(CFD)软件分析燃料组件中流体的三维流场和温度场,并将验证的方法用于燃料组件格架设计,获得了成功。中国核动力研究设计院空泡物理和自然循环重点实验室用CFX程序对带格架棒束内流场进行了计算,解决了小尺寸复杂结构几何体的模拟,边界条件的选取和CFX计算能力的评价,然后完成了单相,空气一水两相流场和流动特性的计算分析及试验对比验证。已完成的研究表明,尽管CFX程序目前在计算两相流动和传热方面还存在不足,但通过比较单相流场的湍流,旋涡和棒束附近流体温度分布基本可以评价格架对流体的交混性能;格架上的弹簧和刚突对于流动有相当的作用,对其进行模拟是必要的。研究还建议在使用CFD方法进行燃料组件格架热工水力分析前要先进行基准练习以保证分析结果的正确性。