反应堆物理实验中的源倍增法研究

给出了反应堆物理实验中临界测量和次临界度测量通常所采用的源倍增方法研究。首先从有源的扩散理论出发,导出了与以前不同的源倍增方法的公式。源倍增方法测量的参数实际是次临界系统在外源作用下的有源次临界中子倍增因子ks,而不是在这之前的中子有效倍增因子keff,然后研究了实验装置的临界质量,研究了ks与外源位置和能谱的关系,证明了导出的源倍增方法的理论是正确的。该方法可像过去那样用于反应堆物理实验中的临界外推测量,但不能用于次临界度测量。解决了长期困扰人们有关源倍增方法测量的参数问题。最后讨论了ks和keff的差别和关系以及对临界外推测量和核临界安全的影响。     

核临界安全中的监督现场测量技术--源倍增方法的某些问题

给出了核临界安全中监督现场的测量技术——源倍增法的实验理论和实验方法。源倍增法实际测量的是有源次临界中子有效增殖系数k2而不是中子有效增殖系数Keff。在铀溶液核临界装置上进行了实验研究用源倍增法测量了次临界系统在外中子源作用下铀溶液不同液位的有源次临界中子有效增殖系数k2;用周期法测量了单位铀溶液位的反应性系数,然后用临界液位与次临界液位之差乘以单位铀溶液位的反应性系数,给出系统次临界液位时的反应性．由反应性给出传统观念上的中子有效增殖系数keff 。讨论了它们的差别及对核临界安全的影响。     

外推-周期法测量ADS模拟装置的次临界度

在ADS次临界中子学研究中，将次临界外堆法和超临界周期法相结合，实验测量了模拟ADS次临界装置中心布置不同缓冲区材料时的有效增殖因子keff和缓冲材料所相当的反应性。实验结果与其它实验方法的结果进行了比较，相互符合较好。     

跳源法在启明星1#次临界装置中的应用

简要介绍了跳源法在启明星1#次临界装置上测量次临界度的原理、外源驱动的次临界中子学实验装置、堆芯布置及中子源驱动系统。主要研究了中子源在堆芯轴向中心位置、不同装载情况下的反应性变化,并给出不同的有效倍增系数keff。实验测量结果与理论计算结果进行了比较,结果符合较好。     

高次谐波滤除方法在ADS次临界堆瞬发中子衰减常数计算中的应用

欧盟开展的外源倍增(MUSE)系列实验表明:脉冲中子源(PNS)方法是一种适用于深次临界堆中子增殖系数(keff)测量的方法,在PNS方法中,瞬发中子衰减常数α的准确与否是精确测量keff的关键.本文针对“快热”耦合次临界装置——“启明星1#”上的α测量进行分析,采用高次谐波滤除方法,得到拟合α值的时间区间,在该时间区间内得到的α与探测器位置无关.同时将由α计算出的次临界系统的瞬发中子倍增系数kp与蒙特卡罗程序(MCNP)计算结果进行对比分析,两者符合较好.研究表明:高次谐波滤除方法可有效避免α值测量依赖于探测器位置的问题,由该方法得到的α值可用于加速器驱动洁净核能系统(ADS)次临界反应堆keff离线监督.     

浓缩铀柱形临界装置徒手装配临界安全检验

为完成徒手装配浓缩铀柱形临界装置临界安全检验实验,设计了基于薄膜装配的验证系统,以替代浓缩铀柱形临界装置上半部分结构。用MCNP程序计算了浓缩铀柱形临界装置上半部分及验证系统密合时的有效增殖因子keff。实验测得验证系统中心增殖不会超过12.50,满足徒手装配装置中心增殖限定值15的要求。实验结果表明,验证系统设计合理,徒手装配浓缩铀柱形临界装置是安全的。     

单次脉冲中子源方法测量瞬发中子衰减常数

瞬发中子衰减常数α是核系统的重要标志性特征参数,该值的准确测量对于核临界安全具有重要意义。本工作采用单次脉冲中子源的方法测量了某次临界核系统的瞬发中子衰减常数,获得了几种不同次临界状态下的瞬发中子衰减常数,测量结果与²⁵²Cf随机脉冲源法测量结果一致。     

ADS启明星1#次临界反应堆缓发中子有效份额的测量

本文提出了利用改进的源倍增法测量次临界系统的绝对反应性与跳源法测量的相对反应性相比获得缓发中子有效份额β_eff的方法。用改进的源倍增法测量了ADS启明星1#次临界反应堆某次临界状态下的绝对反应性为-2.235×10^-3。在相同的次临界状态下,用跳源法测量了以β_eff为单位的反应性ρ/β_eff为-0.291 5 $,二者相比得到ADS启明星1#次临界反应堆的缓发中子有效份额为0.007667。利用MCNP建模计算的结果为0.007 783,两者在2%内符合。     

近临界核系统中弱源中子的涨落行为

在近临界核系统中，弱源中子的涨落行为是一个典型的Markov分支过程。文章介绍用Markov理论与母函数方法建立相关微分方程，并导出近似解析解，着重对常数源在系统中的涨落作了数学描述，给出了数值例子。     

柱形金属铀次临界系统瞬发中子衰减常数测量

次临界核系统的瞬发中子衰减常数α与反应性有着重要联系。采用²⁵²Cf随机脉冲源法测量了一柱形金属次临界系统的瞬发中子衰减常数。为对源中子的影响进行分析,借助蒙特卡罗模拟方法建立模型进行了模拟,对源直穿中子和核系统瞬发中子时间分布特性进行了比较,分析了源中子对瞬发中子衰减曲线的影响。模拟结果表明,对该柱形金属铀系统,源中子注入100 ns后源直穿中子对核系统瞬发中子的影响可忽略。根据分析结果选取了合理起始道,对实验数据进行单指数最小二乘拟合,得到该次临界系统的α为15.5μs^-1。     

快热耦合系统的中子学计算工具——采用确定论方法

对于既具有高能量外中子源又包含热中子区域的快热耦合系统，本文将离散坐标法Sn与栅格计算程序相结合，给出可用于快热耦合系统的中子学确定论计算工具。用该方法计算了启明星1号次临界装置的k_eff，并给出了计算结果。     

跳源法测量ADS启明星Ⅱ号的次临界度及动态特性

本文主要利用²⁵²Cf外中子源驱动的ADS启明星Ⅱ号次临界装置来验证理论计算的次临界度及不同次临界度下的断束动态特性。简要介绍了利用跳源法在ADS启明星Ⅱ号上测量次临界度的原理、实验装置、测量系统、堆芯布置及实验结果等。实验通过变化堆芯燃料棒的装载来模拟3个次临界状态,即k_eff分别为0.99、0.98和0.97。实验结果与理论计算结果符合较好,验证了理论计算的正确性。经过实验验证的理论计算程序和核数据,为将来的中国科学院战略性先导科技专项--未来先进核裂变能ADS嬗变系统的次临界反应堆设计提供参考价值。     

Study of the neutron multiplication effect in an active neutron method

The neutron multiplication effect appears when an item contains large amounts of nuclear material. The neutron multiplication effect in this paper means the effect of subsequent fission reactions which are caused by fission neutrons produced by interrogation neutrons from a neutron generator. The previous active neutron method could not distinguish between first-fission and subsequent-fission neutrons and might overestimate the amount of nuclear material. However, the neutron multiplication effect in the active neutron method has not been adequately investigated. We discuss the evaluation method of the multiplication effect in the fast neutron direct interrogation method, one of the active neutron methods, using simulations with the Monte Carlo code MVP and experiments involving uranium waste drums. The first-generation neutrons from an external neutron source generate fission neutrons called second-generation neutrons, the second-generation neutrons generate third-generation neutrons, and so on. This study supposes that the neutron multiplication effect is mainly caused by the third-generation neutrons under the condition that the fourth-generation neutrons are much fewer. This paper proposes a correction method for the neutron multiplication effect in the measured data.     

Subcriticality Measurement by Neutron Source Multiplication Method with a Fundamental Mode Extraction

A new neutron multiplication method has been proposed for an accurate measurement of subcriticality. The proposed method consists of two correction processes for (1) extraction of the fundamental mode from measuring data of a neutron detector that contains higher modes as well as the fundamental mode feeding from an external neutron source and (2) spatial corrections for perturbations induced by a reactivity addition in the distributions of the fundamental mode and a neutron importance field. Feasibility of the proposed method has been verified from a numerical study, although under some limitations such that the neutron multiplying system to be analyzed is small-sized and a reactivity change takes place homogeneously in a fuel loaded region. With extraction of the fundamental mode and the spatial corrections, the subcriticality can be estimated accurately even with measuring data highly contaminated with higher modes due to a detector position near to an external point neutron source. For a future application to measurement of control rod bank worth of a nuclear power plant from measuring data during a reactor physical testing, some useful guidelines have been obtained.     

MOX燃料贮存水池核临界安全分析

利用MONK程序对MOX热室项目燃料贮存水池进行了核临界安全分析。针对给定的水池尺寸和燃料棒数量,确定燃料以分区方式贮存。选取国际公布的临界基准实验数据,验证并确定MONK程序计算分析类似物料形态时的偏倚和次临界限值,其次进行保守假设,确定贮存水池在正常及事故工况下其中子有效增殖因数,评价贮存水池的安全性。计算结果表明,贮存水池在最危险事故工况下,其最大中子增殖因数小于次临界限值,系统处于临界安全状态。     

Effects of neutron spectrum and external neutron source on neutron multiplication parameters in accelerator-driven system

The neutron multiplication parameters: neutron multiplication M, subcritical multiplication factor k_s, external source efficiency φ^*, play an important role for numerical assessment and reactor power evaluation of an accelerator-driven system (ADS). Those parameters can be evaluated by using the measured reaction rate distribution in the subcritical system. In this study, the experimental verification of this methodology is performed in various ADS cores; with high-energy (100 MeV) proton–tungsten source in hard and soft neutron spectra cores and 14 MeV D–T neutron source in soft spectrum core. The comparison between measured and calculated multiplication parameters reveals a maximum relative difference in the range of 6.6–13.7% that is attributed to the calculation nuclear libraries uncertainty and accuracy for energies higher than 20 MeV and also dependent on the reaction rate distribution position and count rates. The effects of different core neutron spectra and external neutron sources on the neutron multiplication parameters are discussed.