A Long and Slender Position-Sensitive Helium-3 Proportional Counter with an Anode Wire Supported by a Ladder-Shaped Solid Insulator

A long and slender position-sensitive ³He proportional counter with an outer diameter of 8 mm and an effective length of 1.2 m has been developed to measure neutron flux distributions in a critical assembly. Because it is difficult to make such a long and slender counter of conventional structure where an anode wire is stretched at the center of a cylindrical cathode tube, three prototype electrode systems of which anode wires are supported by insulator plates have been proposed. Among these three electrode systems, the electrode system of which anode wire is stuck on a ladder-shaped insulator has been adopted. The neutron flux distributions in the core of the Kyoto University Critical Assembly (KUCA) have been measured with the counter. Some non-uniformity of the detection efficiency has been observed throughout the counter. This non-uniformity has been corrected by calibrating the position-dependent detection efficiency with a gold wire activation method. A fairly satisfactory distribution, where the relative deviation from the gold wire activation method is 5.0%, has been obtained. Though the non-uniformity of the detection efficiency should be solved for precise measurements, the counter can be used for quick and rough measurements of neutron flux distributions.     

Development of Position Sensitive Helium-3 Proportional Counter for Thermal Neutrons with Novel Signal Readout

A position sensitive ³He proportional counter for thermal neutrons with a novel signal read- out method which has two pre-amplifiers at only one end of the counter body has been developed. It has an advantage for usage in a special environment, such as in a subcritical facility or in water, or for insertion into a narrow space. The characteristics of the counter were evaluated with thermal neutrons. The position resolution was 7 mm with an effective length of 1,200 mm. The integral non-linearity of position signal was less than 0.5%.     

居里级Am-Be中子源产生的热中子通量密度分布

实验室中的同位素Am-Be中子源在有关中子活化方法研究以及在核反应堆中子测量系统研制过程中的调试和刻度等方面都有着非常重要的作用.为使这些应用更有效并得到更准确的实验结果,需要知道Am-Be中子源在周围慢化介质中热中子通量密度的分布.用蒙特卡罗方法并结合中子源发射率计算得到了居里级Am-Be中子源在圆柱形水池中不同半径...     

利用测热技术测量核反应堆中子通量密度

一种新型中子探测器被研究,其原理是利用带电离子在矿物中沉积的能量退火时会以热量的方式释放出来,通过测量释放的热量而确定中子通量密度。对新型中子探测器进行刻度,在反应堆内某位置测量的热中子通量密度为5.108×10¹¹ cm^-2•s^-1,与标定的热中子通量密度(5.000×10¹¹ cm^-2•s^-1)在2%内符合,说明该探测器可测量中子通量密度。本文方法制作的探测器体积小,可制作成不同形状,便于反应堆不同环境下的中子通量密度测量。选取相应中子能量反应截面较大的元素,该探测器还可测量不同中子能量的通量密度。     

环形燃料反应堆通量密度分布测量

相对中子通量密度分布是反应堆的重要物理参数之一,测量环形燃料零功率反应堆堆芯相对中子通量密度分布对了解环形燃料堆芯反应堆物理特性及开展安全分析具有指导意义。本文在环形燃料堆芯多边形装载下,采用箔活化法对辐照后燃料元件外表面不同位置金箔的γ活度进行测量,得到不同位置燃料元件轴向、径向的相对中子通量密度分布,并将测量值与蒙特卡罗理论计算值进行比对。结果表明：实验测量值与理论计算值最大相对偏差在12%以内,相对中子通量密度分布测量结果符合实验设计预期,现有蒙特卡罗分析手段可较好地分析堆内元件轴向通量密度分布情况。本文结果可为环形燃料的工程化应用提供重要的数据支撑。     

Characteristics of Neutron Guide Tubes in Upgraded JRR-3

Abstract

The JRR-3 has been upgraded to be a new high performance research reactor JRR-3M with neutron guide tubes on a large scale and a cold neutron source. The neutron fluxes and spectra were measured at the end of the two thermal and three cold neutron guide tubes. The gain of the cold neutron source is also found from these spectra. The neutron fluxes of thermal neutron guide tubes with characteristic wavelength 2 Å are 1.2x10⁸ n/cm².s at a reactor power of 20 MW. The neutron fluxes of cold guide tubes are 2.0x 10⁸ n/cm².s with characteristic wavelength 4 Å and 1.4x10⁸ n/cm².s with 6 A when the cold neutron source is operated. The neutron spectra measured by the time-of-flight method agree well with their designed ones. The gains of the cold neutron source are 8 for 4 Å and 20 for 6 Å at a reactor power of 20 MW.     

Measurement of Reactivity Effect and Thermal Neutron Flux in Non-uniformly Distributed Fuel Assemblies

A reactivity effect due to spatial variation of nuclear fuel concentration is an important problem for nuclear criticality safety in a reprocessing plant. As a method theoretically estimating this reactivity effect, the Goertzel's necessary condition is well known. To investigate this theoretical prediction, we have performed systematically a series of measurements of reactivity effect due to nonuniformity in the fuel distribution using a solid moderated core of the Kyoto University Critical Assembly. Thermal neutron flux distributions have been also measured using the activation method with gold wire. A nonuniform assembly was found to have an excess reactivity of 0.2%Δk/k when it had the same uranium mass as the uniform assembly was exactly critical. The fuel concentration of this nonuniform assembly was 40% higher in the center region than the uniform one. Moreover, the spatial distribution of reaction rate of gold wire due to thermal neutrons was flatter in this nonuniform assembly than in the uniform one, as expected by the Goertzel's condition.     

利用BF_3多柱谱仪测量临界装置中子能谱

研发了一种中子能谱测量装置——BF_3多柱谱仪。对BF_3多柱谱仪的工作原理、结构与性能,以及该探测系统的使用方法进行研究,并分析其可满足的实验要求。应用BF_3多柱谱仪在临界装置上进行了中子能谱测量的实验,将实验测量结果与MCNP程序的理论计算结果进行了比较,两者符合较好,验证了该中子探测系统的性能。该BF_3多柱谱仪可适用于低中子通量密度能谱测量、屏蔽实验、环境监督测量、实验大厅内部及周围环境中子场测量等多种工况。     

球形^3He正比计数器物理性能研究

~3He正比计数器是理想的热中子探测器。本文给出了两种气压条件下球形~3He正比计数器的热中子探测效率、能最响应、几何响应等物理性能的计算和测量结果。为更好地设计和使用此类探测器提供了依据。     

脉冲堆辐照腔内绝对中子通量及相对分布测量

本文介绍了绝对中子通量测量方法,给出了各辐照腔典型位置上的绝对中子通量及其与全堆平均中子通量的比值。还给出了各辐照腔中相对中子通量轴向分布和旋转样品槽内相对中子通量周向分布的测量结果。     

氟盐冷却高温堆精细中子通量密度分布计算方法研究

氟盐冷却高温堆(FHR)作为第4代核能系统,对安全性和经济性更加注重。FHR全空间中子通量密度的精细分布数据对于材料构件的辐照损伤计算、放射性源项分析以及辐射屏蔽设计等均有重要意义。针对这一需求,本文采用离散纵标(SN)方法为蒙特卡罗(MC)方法偏倚计算提供所需的源偏倚和权窗参数,使蒙特卡罗粒子均匀地分布于整个计算模型空间,从而有效降低中子通量密度分布计算的统计误差。在该方法的基础上,编写了耦合程序SN2MCNP,并使用该程序对FHR全空间的中子通量密度分布进行了精细计算。经对比验证,在同样的计算时间和统计方法的要求下,单独使用MCNP计算的结果中,只有30.1%的相对误差达到要求(10%),而使用SN2MCNP的计算结果中则有99.6%的相对误差达到要求(10%)。     

Construction of Neutron Guide Tubes in Upgraded JRR-3

Five neutron guide tubes have been installed in the upgraded JRR-3 (Japan Research Reactor No. 3). Two of them are for thermal neutrons and the other three are for cold ones. The characteristic wavelength of the thermal neutron guide tubes is 2 Å, and those of the cold neutron guide tubes are 4 and 6 Å. The longest guide tube is 59.9 m long and the total length of guide tubes is 232.1 m.

The beam sizes are 2 cm × 20 cm for the thermal neutron beams and 2 cm × 12 cm for the cold neutron beams. A curved part of the neutron guide is assembled by a polygonal approximation with use of 85 cm long straight units. The neutron mirrors of these units are made of natural Ni deposited borosilicate glasses. The Ni layer is about 2,000 Å in thickness.

The mean fabrication error of guide tube units is 4 μm. The mean installation errors are 8 μm for the positional abutment error and 5 × 10^?6 rad for the angular error. The neutron losses by these errors will be about 5%, and the neutron fluxes at the exits of the neutron guides are estimated to be about 2 × 10⁸ n/cm²·s.     

不同温度下~3He 计数管热中子灵敏度测定

采用 DOT3.5(R,Z)迁移程序和 CITATION(R,Z)扩散程序,对含有~(252)Cf 中子源的石墨棱柱装置进行了通量分布计算,并用 DOT3.5(R,Z)程序计算了计数管对热通量的扰动因子。测量了~3He 和 BF_3(WL-6307)计数管的热中子灵敏度;测量结果表明,在20—150℃内,~3He 计数管热中子灵敏度几乎是不变的。     

Dependence of Position Signal on Pressure of Counting Gas in Charge Division Type Position-Sensitive Proportional Counter

In the absolute radioactivity measurement of radioisotope gaseous samples with newly developed position-sensitive proportional counter (PSPC) method, it is necessary to change the counting gas pressure for the correction of the wall effect. The position signal was found to drift depending on the pressure. Theoretical explanation was given for this drift. Rise time of output pulses varies with gas pressure, which leads to a change of ballistic deficit. Consequently, the ballistic deficit differs between pulses from both the ends of the PSPC, which causes the change of position signals. Increasing the pressure of the counting gas from 0.5×10⁵Pa to 4×10⁵Pa, the range of position signals for two position calibration sources became narrower by about 8% under 6 μs shaping time.     

穿透概率法求解二维六角形轻水堆燃料组件中子通量密度分布

研究利用穿透概率法求解二维六角形轻水堆燃料组件内中子通量密度分布。子区内中子源采用线性分布,子区表面通量密度在方向上采用简化6P1近似。提出了六角形组件周边水隙的处理方法。根据提出的模型,编制了TPHEX－C程序,并对六角形组件进行了计算,结果与蒙特卡罗方法计算的结果符合良好。     

六角形轻水堆组件中子通量密度分布的计算

介绍利用穿透概率法求解二维六角形轻水堆燃料组件中子通量密度分布。子区内中子源及通量密度在空间上采用二次分布 ,子区表面通量密度在空间上采用平通量密度分布 ,在方向上采用简化 6P1近似。根据提出的模型 ,编制了TPHEX D程序 ,并对一些轻水堆六角形组件问题作了计算 ,计算结果与MC结果进行了比较 ,符合良好。本程序可用于六角形轻水堆燃料组件计算。     

用于在线测量反应堆内热中子相对通量密度分布的闪烁体光纤探测器研究

闪烁体光纤探测器采用双探头甄别中子信号,利用252 Cf裂变源对探测器系统进行了测试,并与3 He计数管的计数进行了对比。在启明星1#上进行了热中子相对通量密度分布的测量,结合Geant4得到的不同能量段的中子转化率及MCNPX模拟得到的反应堆中子能谱,对探测器进行了相对效率刻度,测试结果与固体核径迹探测器测得的裂变率分布进行了对比。测量结果表明,闪烁体光纤探测器对于252 Cf中子源的响应基本符合点源的衰减趋势,与3 He计数管的测量结果符合较好。在启明星1#热区测得的热中子相对通量密度分布与固体核径迹探测器测量到的结果一致,快区测得的热中子相对通量密度分布与3 He计数管的测量结果及MCNPX的模拟结果符合较好。测量结果为闪烁体光纤探测器的研究提供了较好的实验依据。     

New 6Li Sandwich Counter for Measurement of Neutron Spectra in Fast Neutron Systems

A new form of ⁶Li sandwich counter has been developed for use in measurements of neutron spectra in fast critical assemblies. The counters have two large surface area diodes approached very close to each other, on one of which is evaporated the target ⁶Li. This arrangement proves to provide a ten-fold increase of detection efficiency, while the resolution is improved by approximately ½ compared with currently used counters. The new counters were first tested on mono-energetic neutrons, after which neutron spectrum measurements were performed on natural uranium blocks, in the fast source reactor “YAYOI”, in the FCA IV-l-P and in the FCA V-3 core. The resulting spectra are compared with the measurements made with other types of counter and with calculated data. Proof was obtained that the new counter can serve practically and usefully for in-core measurements of fast neutron energy spectrum between 0.8 and 5 MeV.     

数字化多通道宽量程ITER中子通量密度测量系统研制

针对国际热核聚变实验堆(ITER)对中子通量密度测量宽量程、高集成度、实时性的要求,设计了一套基于PXI架构的多通道中子通量密度测量系统。该系统包括新研制的电流灵敏前置放大器及基于高速模数转换器(ADC)和可编程逻辑器件(FPGA)的主电子学插件。通过全数字化信号处理技术衔接脉冲计数和坎贝尔两种测量模式,大幅拓展了测量量程和提高了系统集成度。该系统通过使用脉冲堆积率估算算法,实现了测量模式的精确自动切换。实验结果表明,该系统具备单一裂变室大于1.7×10~(10)cm~(-2)·s~(-1)中子通量密度实时测量能力,全量程相对误差低于7.1%。     

用于反应堆内相对中子通量密度在线测量的闪烁体光纤探测系统研制

为实现反应堆不同空间和能量的相对中子通量密度在线监测,本文研究开发了一套新型的用于狭小空间且位置灵敏的闪烁体中子探测系统。该套系统由5种探头、5路光子计数器、1台计算机及相应的软件组成。5种探头的主要构成物质分别为~6 LiF+ZnS(Ag)、~(232) ThO_2+ZnS(Ag)、~(238) UO_2+ZnS(Ag)、~9Be+ZnS(Ag)以及BGO晶体,故可测量不同能量的相对中子通量密度。其中,掺有~6 LiF的探头用于热中子的测量,BGO探头用于γ测量,其余3种探头用于快中子的测量。利用该系统进行了启明星1#装置内热中子及快中子的相对通量密度分布测量,并将测量结果与利用蒙特卡罗方法得到的理论分布结果进行了比较。考虑到理论设置参数与实际实验参数的差别,可认为测量结果是可信的。