类蜂窝结构高灵敏度裂变室探测器模拟仿真研究  

Simulation Study on High Sensitivity Fission Chamber Detectors with Honeycomb-like Structures

作　　者：包超[1] 刘立兴 罗庭芳 BAO Chao;LIU Lixing;LUO Tingfang(Science and Technology on Reactor System Design Technology Laboratory,Nuclear Power Institute of China,Chengdu 610213,China;Tsinghua University,Department of Engineering Physics,Beijing 10000,China)

机构地区：[1]中国核动力研究设计院核反应堆系统设计技术重点实验室,成都610213 [2]清华大学工程物理系,北京100000

出　　处：《核电子学与探测技术》2024年第3期428-437,共10页Nuclear Electronics & Detection Technology

摘　　要：目前的反应堆功率监测系统要求使用单一裂变电离室在适应反应堆堆芯的高γ辐射场下的中子注量率测量的同时可以以高灵敏度的脉冲工作模式适应反应堆启动阶段的低中子注量率情况下的测量。然而,由于裂变碎片在易裂变物质涂层中的射程较短,具有较强的自吸收效应,因此无法通过增大裂变材料涂层厚度提升探测器的灵敏度。本文提出了一种类蜂窝结构的圆柱栅格裂变室探测器,将探测器比表面积提高为普通圆柱电离室的3倍,从而在不增加裂变物质涂层厚度的情况下,大幅度增加了裂变物质的有效质量,实现了高的中子灵敏度。基于Geant4的蒙特卡罗模拟表明21片栅格板和2.5mg/cm^(2)的^(235)U涂层的裂变电离室可以实现3cps/nv的热中子探测灵敏度。使用Garfield++对探测器内电离电子的迁移和扩散的仿真结果表明,使用Ar/CO_(2)(96/4)作为工作气体可以平衡电离电子的漂移速度和横向扩散,并实现极间电压为725V时96.5%的电子迁移效率。本文的模拟和仿真结果表明,该类蜂窝结构裂变电离室在脉冲模式下具有高的热中子灵敏度,有希望适应反应堆从启动到满功率运行的宽量程的功率监测。Current reactor power monitoring systems require the use of a single fission ionization chamber to accommodate neutron flux rate measurements in the high gamma radiation field of the reactor core,while at the same time being able to accommodate measurements at low neutron flux rate during reactor start-up in a highly sensitive pulsed mode of operation.However,the sensitivity of the detector cannot be improved directly by increasing the thickness of the fissile material coating due to the short range of the fission fragments in the fissile material coating and the strong self-absorption effect.In this paper,we propose a honeycomb-like cylindrical grid fssion chamber detector,which increases the detector specific surface area to three times that of an ordinary cylindrical ionization chamber,thus dramatically increasing the effective mass of the fissile material and achieving high neutron sensitivity without increasing the thickness of the fissile material coating.Monte Carlo simulations based on Geant4 show that a thermal neutron detection sensitivity of 3 cps/nv can be achieved for a fission ionization chamber with 21 grid plates and 2.5 mg/cm^(2)^(235)Ucoating.Simulation results of the migration and difusion of ionized electrons within the detector using Garfield++show that the use of Ar/CO_(2)(96/4)as the working gas balances the drift velocity and lateral diffusion of ionized electrons and achieves an electron migration efficiency of 96.5%at an high voltage of 725 V.The results in this paper show that this type of honeycomb-like fission ionization chamber has high thermal neutron sensitivity in the pulsed mode,which is promising to adapt to a wide range of power monitoring of the reactor from start-up to full power operation.

关 键 词：裂变室探测器 高灵敏度 类蜂窝结构 

分 类 号：TL362[核科学技术—核技术及应用]