裂变电离室系统时间性能的改进

一、引言在用时间关联法测量裂变截面以及研究裂变瞬发中子和γ时,用于定时的裂变信号上升时间应尽可能小,同时要求裂变-α幅度比大,讯噪比好。为此,我们对原有裂变电离室进行了改进,并与快电子学插件组成系统,其时间分辩和裂变电离室效率均有提高。     

基于GEM工艺的裂变时间投影室性能模拟研究

基于GEM工艺的裂变时间投影室具有探测效率高和空间分辨率高的特点,可实现裂变产物的多参量测量。本文主要研究基于GEM工艺的裂变时间投影室在不同条件下的测量精度,使用Garfield++软件计算得到裂变时间投影室中不同的裂变产物质量数测量误差约为4～6 u,并通过时间信息的径迹重建研究了裂变碎片在不同工作气体中的角度分辨。研究发现,电子漂移时间长的工作气体中,裂变产物具有更好的角度分辨,并可依此在实验中选择合适的工作气体、气压和漂移电场强度来进行裂变碎片的测量。     

裂变伽马射线探测器的时间响应特性研究

根据国内首次研制出的载铀材料裂变伽马射线探测器的工作原理及其输入-输出等效电路,利用M.C建模计算的方法研究获得了探测器的灵敏体在δ辐射脉冲作用下产生并输出的脉冲电流波形g0(t),同时通过实验方法研究获得了其灵敏单元在脉冲射线作用下产生的电信号在输出电路中的时间过程gRLC(t),并最终得到了探测器的时间响应特性:响应波形前沿时间为0.72 ns,后沿时间为3.9ns,半宽为2.08 ns,探测器响应时间很快;最后通过数值计算的方法考察了探测器时间响应对不同宽度源波形的影响。结果表明:源波形时间越慢,探测器对其测量的影响就越小,其中探测器的时间响应对于半宽为100 ns的高斯型源波形的峰值、半宽、前沿以及后沿时间的影响基本上都小于0.2%,所以探测器时间响应特性完全满足这样宽度下的脉冲中子源的测量要求,对测量结果不需要进行逆卷积处理。     

钚及其裂变产物钯 、银 、镉 、锡 、锑 、锆的系统分离方法

描述了钚及其6种裂变产物钯、银、镉、锡、锑、锆的系统分离方法：在强碱性阴离子交换树脂柱上将盐酸介质的辐照靶溶解液中的这些元素分为5组,然后再针对各组目标元素进行分离和纯化,可简便快速地从同一份靶溶解液中分离以上7种元素。采用辐照铀靶对分离方法进行了验证,结果表明,分离流程对6种裂变产物的化学回收率均大于70%,对γ谱仪测量干扰的主要核素去污因子均大于1.0×10³,可满足²³⁹Pu裂变谷区核素裂变产额测量对化学分离的要求。     

钚及其裂变产物钯、银、镉、锡、锑、锆的系统分离方法

描述了钚及其6种裂变产物钯、银、镉、锡、锑、锆的系统分离方法：在强碱性阴离子交换树脂柱上将盐酸介质的辐照靶溶解液中的这些元素分为5组，然后再针对各组目标元素进行分离和纯化，可简便快速地从同一份靶溶解液中分离以上7种元素。采用辐照铀靶对分离方法进行了验证，结果表明，分离流程对6种裂变产物的化学回收率均大于70%，对γ谱仪测量干扰的主要核素去污因子均大于1.0×10³，可满足²³⁹Pu裂变谷区核素裂变产额测量对化学分离的要求。     

物理-热工耦合对超临界水堆系统特性的影响分析

物理-热工耦合是超临界水堆系统分析的关键问题之一。以日本超临界水冷热堆Super LWR的堆芯设计为例,借助Dragon编制中子截面数据库,建立双群中子扩散方程计算模块,联系同时建立的热工计算模块,得到超临界水堆的物理-热工耦合计算模型。通过对比稳态与瞬态工况下耦合前、后的热工工况,分析物理-热工耦合条件下的超临界水堆系统热工特性。结果表明：在稳态工况下,物理-热工耦合将导致内、外组件堆芯功率峰值沿轴向发生明显偏移,使得部分节点的包壳温度升高,但包壳最高温度降低;在瞬态工况下,物理-热工耦合将导致堆芯包壳最高温度的发生位置有所改变。发生给水加热丧失瞬态后,在某一时刻,外部组件的包壳最高温度将转而超过内部组件的包壳最高温度。可见,物理-热工耦合对包壳最高温度的大小和发生位置均可能产生明显影响。计算分析可为超临界水堆瞬态及安全分析提供相应理论参考。     

超临界水热力系统的稳定性的简化模型分析

针对超临界水热力系统建立了简化模型,采用微扰动线性化及Laplace变换,对热力系统的非线性守恒方程进行线性化处理,建立了传递函数;用无量纲的次拟临界数和过拟临界数建立了稳定边界图;考察了一些重要参数对系统稳定性的影响.研究结果表明,系统在拟临界点附近存在不稳定区域;增大系统入口阻力或流体入口速度均有利于系统稳定,而增加加热段长度和重力加速度均不利于系统稳定.     

Physical investigation for neutron consumption and multiplication in fusion–fission hybrid test blanket module

Inelastic scattering of high energy fusion neutrons does affect the performance of fusion blanket based on the choice of different materials. It will also affect the behavior of source neutrons in a subcritical fusion fission hybrid blanket and consequently the transmutation and tritium breeding performance. A fusion fission hybrid test blanket module (HTBM) is designed which is presumed to be tested in a large sized tokamak and plasma neutron source is similar to ITER. In this preliminary design of HTBM the neutron source and loss factors are computed for the detailed neutronic performance analysis. The neutronic analysis of hybrid blanket module is performed for five different TRU fuel types: TRU-Zr, TRU-Mo, TRU-Oxide, TRU-Carbide and TRU-Nitride. In this module design, it is aimed to burn and transmute the TRU nuclides from high-level radioactive waste of PWR spent fuel. The effect of TiC reflector on transmutation and tritium breeding performance of HTBM is also quantified. MCNPX is used for neutronic computations. Neutron spectrum, capture to fission ratio and waste transmutation ratio of each fuel type are compared to evaluate their waste transmutation performance. Tritium breeding ratio is also compared for two coolant options: Li and LiPb eutectic.     

MC simulation of a PGNAA system for on-line cement analysis

A prompt gamma neutron activation analysis system with a 252Cf neutron source for on-line cement analysis has been simulated with the MCNP code.The results indicate that the optimum arrangement is a Bi shield of 20-mm thickness,a polyethylene moderator of 50-mm thickness,a source-to-sample distance of 70 mm,and cement samples of 1200 mm×600 mm×170 mm.To absorb thermal neutrons and suppress low-energy γ-rays,the optimum-sized sheets are 150 mm×7 mm Cd,and 150 mm×15 mm Pb.     

长寿命裂变产物在聚变驱动次临界堆包层中嬗变的中子学优化分析

商用裂变堆乏燃料中高放长寿命裂变产物(LLFP)由于其具有很强的放射毒性,所以对于它们的嬗变处理非常重要。在对世界上关于LLFP嬗变处理的广泛调研的基础上,考虑到LLFP的同位素分离技术的发展水平,选择了LLFP中99Tc、129I和135Cs的嬗变处理(?)料的化学形式,分析了不同慢化剂材料对嬗变能力的影响,同时针对聚变驱动次临界堆的多功能双冷核废料嬗变包层(DWTB)进行了LLFP嬗变的中子学设计和优化分析。     

Numerical simulation of heat transfer deterioration phenomenon in supercritical water through vertical tube

In this study, a numerical investigation of heat transfer deterioration (HTD) in supercritical water flowing through vertical tube is performed by using six low-Reynolds number turbulence models. All low-Reynolds models can be extended to reproduce the effect of buoyancy force on heat transfer and show the occurrence of localized HTD. However, most k–ε models seriously over-predict the deterioration and do not reproduce the subsequent recovery of heat transfer. The V2F and SST models perform better than other models in predicting the onset of deterioration due to strong buoyancy force. The SST model is able to quantitatively reproduce the two heat transfer deterioration phenomena with low mass flux which have been found in the present study.     

Numerical analysis of thermal-hydraulic behavior of supercritical water in vertical upward/downward flow channels

Investigations on the thermal-hydraulic behavior in the SCWR fuel assembly have obtained a significant attention in the international SCWR community. However, there is still a lack of understanding of the heat transfer behavior of supercritical fluids. In this paper, the numerical analysis is carried out to study the thermal-hydraulic behaviour in vertical sub-channels cooled by supercritical water. Remarkable differences in characteristics of secondary flow are found, especially in square lattice, between the upward flow and downward flow. The turbulence mixing across sub-channel gap for downward flow is much stronger than that for upward flow in wide lattice when the bulk temperature is lower than pseudo-critical point temperature. For downward flow, heat transfer deterioration phenomenon is suppressed with respect to the case of upward flow at the same conditions.     

Chemical reaction kinetics dataset of Cs-I-B-Mo-O-H system for evaluation of fission product chemistry under LWR severe accident conditions

In order to improve LWR source term under severe accident conditions, the first version of a fission product chemistry database named ‘ECUME’ was developed. The ECUME is intended to include several datasets of major chemical reactions and their effective kinetic constants for representative severe accident sequences. It is expected that the ECUME can serve as a fundamental basis from which fission product chemical models can be elaborated for use in the severe accident analysis codes. The implemented chemical reactions in the first version were those for representative gas species in Cs-I-B-Mo-O-H system from 300 to 3000 K. The chemical reaction kinetic constants were evaluated from either literature data or calculated values using ab-initio calculations. The sample chemical reaction calculation using the presently constructed dataset showed meaningful kinetics effects at 1000 K. Comparison of the chemical equilibrium compositions by using the dataset with those by chemical equilibrium calculations has shown rather good consistency for the representative Cs-I-B-Mo-O-H species. From these results, it was concluded that the present dataset should be useful to evaluate fission product chemistry in Cs-I-B-Mo-O-H system under LWR severe accident conditions, where kinetics effects should be considered.     

Subcritical multiplication factor and source efficiency in accelerator-driven system

The subcritical multiplication factor k_s   and the external neutron source efficiency φ^∗${\phi }^{\ast }$ are important parameters in the accelerator-driven system (ADS) performance assessment. The theoretical relation between k_s and the effective multiplication factor k_eff in a subcritical system is discussed in different cases of subcritical system. On the basis of the theoretical background, the dependence of k_s   and φ^∗${\phi }^{\ast }$ on subcriticality, source position, and energy is numerically investigated using a simple thermal subcritical model. For the sake of experimental evaluation of k_s   and φ^∗${\phi }^{\ast }$, the ADS experiments have been carried out in the subcritical systems combined with 14 MeV pulsed neutrons of the Kyoto University Critical Assembly (KUCA). The k_s   and φ^∗${\phi }^{\ast }$ parameters are successfully measured by utilizing the reaction rate distribution obtained by the optical fiber detectors in the subcritical system, within a relative difference of less than 7% and 12% for k_s   and φ^∗${\phi }^{\ast }$, respectively, between measured and calculated values for most studied cases.     

裂变气体分离器气泡分离轨迹的数值模拟

钍基熔盐堆是我国重点开发的第四代核反应堆之一,其裂变反应产生的中子俘获截面大的Kr、Xe等裂变气体以微气泡的形式存在于熔盐冷却剂中,对裂变气体的分离是提高熔盐堆中子经济性、实现燃料深燃耗的重要环节。为定量地获得分离器内气泡的分离行为,采用数值模拟和理论建模相结合的方法,得到旋流场的流场分布特征;通过建立旋流场中气泡运动控制方程,分析并计算不同旋流度和气泡直径下的分离长度。与实验数据对比发现,数值模拟结果和实验数据吻合良好,表明数值模拟方法可以用于气液分离器的优化设计。