靶堆耦合零功率装置中子学实验研究

发布时间：2018-05-11 00:38

本文选题：ADS次临界系统 + 活化法　；参考：《中国科学院大学(中国科学院近代物理研究所)》2017年博士论文

【摘要】：加速器驱动的次临界系统(Accelerator Drived sub-critical System,简写为ADS)是国际公认的嬗变核废料的有效手段之一。随着ADS系统研究的深入,对于装置系统内中子学的掌握程度提出了更高的要求,为了保证设计计算的可靠性,建立了安全性相对高,容易进行实验测量的靶堆耦合实验装置对于中子学进行综合测量。由于ADS系统宏观中子学与反应堆及散裂靶内发生的各种核过程,如内部材料对中子的吸收、散射以及中子的泄露等等,都密切相关,因此开展靶堆耦合装置中子学实验是进行宏观测量检验的重要手段。本论文主要工作是采用离线和在线相结合的方法对靶堆耦合装置进行实验研究,重点就如何提高测量中子通量分布的精度及实验中所涉及的相关问题作了深入调研。首先将活化法在散裂反应实验中加以应用并优化,同时对在线测量中子通量实验方法进行了深入探讨,研制了一套针对零功率反应堆的闪烁体光纤探测器系统,并完成其在启明星1#次临界装置上的测试,最终两种实验方法都应用到启明星2#铅基零功率装置上。实验结果均与MCNPX2.7.0的模拟结果进行深入比较,从而对截面数据库及计算模型进行校验。本文的研究内容及得到的物理结果如下:(1)通过分析250Me V质子束轰击铅靶的水浴实验,获得整个水浴环境中的中子通量空间分布,并且推导出散裂反应的有效中子产额为2.23±0.19n/proton,与MCNPX模拟的中子产额2.14±0.01n/proton,误差在5%以内;通过分析靶材附近放置的Au、In、Mn三种活化片活度,得到了超热中子能区的中子能谱分布,并与MCNPX模拟结果对比,分析了能谱测量中自屏蔽效应的影响。(2)完成了反应堆用闪烁体光纤探测器系统的研制,创新采用双探头甄别中子信号,在252Cf中子场中进行了系统的测试,最终在启明星1#次临界装置上完成了热中子通量分布的测量,测量结果与固体核径迹探测器结果及MCNPX模拟结果均能较好符合,验证了探测器在反应堆上测量的准确性及可靠性。(3)采用金属线活化法在铅基零功率装置上测量了临界时堆芯内的空间中子通量分布,通过分析Au线和In线在反应堆照射后的反应率,得到径向不同燃料孔道内核反应率的轴向分布,并与MCNPX模拟结果对比,校验数据库的准确性,最终采用同一数据库模拟得到堆芯内中子通量密度的空间分布。(4)利用闪烁体光纤探测器在铅基零功率装置上开展了反应堆的时空动态特性研究。其中,动态实验包括反应堆启动、运行及停堆的动态监督;利用跳源法测量了不同次临界度下的有效增殖系数,与外推周期法测量结果的相对误差在1%以内,通过对比不同实验孔道的测量结果,分析了零功率装置测量的空间效应;利用脉冲中子源法测量了不同次临界度下的瞬发中子衰减常数,并与MCNPX模拟结果对比,分析了探测器测量与模拟之间的相对误差。同时,通过光纤驱动系统,在铅基零功率装置上在线测量了不同次临界条件下的热中子通量空间分布,并与MCNPX模拟结果对比,验证了次临界装置设计初衷,同时校验了截面数据库的准确性。实验结果有助于了解和认识次临界系统的中子学时空特性,对合理设计、安全运行次临界系统具有重要的指导意义,也为日后开发ADS反应性监督用的探测系统奠定了实验基础。
[Abstract]:The accelerator driven subcritical system (Accelerator Drived sub-critical System, short of ADS) is one of the most effective means for the transmutation of nuclear waste. With the deepening of the research on the ADS system, a higher requirement for the mastery of neutrons in the device system is put forward, and the reliability of the design calculation is ensured and the safety is established. Relatively high, the target reactor coupling experimental device, which is easy to carry out experimental measurements, carries out a comprehensive measurement of neutrons. Because of the various nuclear processes in the ADS system and the various nuclear processes in the reactor and the spallation target, such as the absorption, scattering of the neutrons and the leakage of neutrons in the internal materials, the neutrons of the target reactor coupling device are carried out. The main work of this paper is to study the target reactor coupling device with the method of combining off-line and online. The emphasis is on how to improve the accuracy of the measurement of neutron flux distribution and the related problems involved in the experiment. First, the activation method is used in the spallation reaction. The experiment is applied and optimized. At the same time, the method of measuring the neutron flux on line is discussed. A set of scintillator fiber detector system for zero power reactor is developed, and the test on the 1# sub critical device is completed. Finally, the two experimental methods are applied to the 2# lead based zero power device. The experimental results are all compared with the simulation results of MCNPX2.7.0, so that the cross section database and the calculation model are checked. The contents and physical results of this paper are as follows: (1) the spatial distribution of the neutron flux in the whole water bath environment is obtained by analyzing the water bath experiments of the 250Me V proton beam bombarding lead targets, and the dispersion of the neutron flux is derived. The effective neutron yield of the cracking reaction is 2.23 + 0.19n/proton, the neutron yield is 2.14 + 0.01n/proton with the MCNPX simulation, and the error is within 5%. The neutron energy spectrum distribution in the ultra hot neutron energy region is obtained by analyzing the activity of Au, In, Mn, which is placed near the target, and compared with the simulation results of MCNPX, and the self shielding effect in the spectrum measurement is analyzed. 2. (2) complete the development of the reactor scintillator fiber detector system, innovating the dual probe screening neutron signal, testing the system in the 252Cf neutron field, and finally completing the measurement of the thermal neutron flux distribution on the star 1# sub critical device, the result of the measurement and the result of the solid nuclear track detector and the MCNPX simulation junction. The accuracy and reliability of the detector in the reactor are verified well. (3) the distribution of the space neutron flux in the core is measured on the lead based zero power device by the metal wire activation method. The reaction rate of the Au line and the In line after the irradiation of the reactor is analyzed, and the core reaction rate of the radial different fuel channels is obtained. The axial distribution and the MCNPX simulation results are compared to verify the accuracy of the database. Finally, the spatial distribution of the neutron flux density in the core is obtained by the same database simulation. (4) the study of the space-time dynamic characteristics of the reactor is carried out on the lead based zero power device by the scintillator fiber detector. Dynamic supervision of moving, running and stopping piles; using the jump source method to measure the effective multiplication coefficient under different subcritical degrees, the relative error of the extrapolated periodic method is less than 1%. By comparing the measurement results of different experimental channels, the spatial effect of the zero power device measurement is analyzed, and the different sub criticality is measured by the pulse neutron source method. The instantaneous neutron decay constant is compared with the MCNPX simulation results, and the relative error between the detector measurement and the simulation is analyzed. At the same time, the spatial distribution of the thermal neutron flux under different subcritical conditions is measured on the lead based zero power device by the optical fiber drive system, and compared with the MCNPX simulation results, the subcritical loading is verified. At the same time, the accuracy of the cross section database is verified. The experimental results are helpful to understand and understand the space-time characteristics of the subcritical system. It is of great guiding significance for the rational design and safe operation of the subcritical system. It also lays the foundation for the development of the detection system for ADS reactivity monitoring in the future.

【学位授予单位】：中国科学院大学(中国科学院近代物理研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TL81

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