基于D-D中子源的中子毒物材料检测技术研究

Research on the Detection Technology of Neutron Poison Materials Based on the D-D Neutron Source

摘要:

随着核能技术的不断发展，燃料元件的运行寿命和安全性面临着更高的要求。通过在燃料元件芯体中添加中子毒物可以有效提升反应堆系统的安全性与稳定性，而准确检测中子毒物的含量则成为关键环节。利用中子毒物的高中子吸收截面特性，采用模拟与实验相结合的方法，开展了基于D-D中子源的中子毒物含量无损检测方法研究，并对其可靠性进行了评估。采用Geant4蒙特卡罗模拟软件，建立燃料元件中子毒物含量与透射热中子强度的响应模型，获得毒物元素含量与中子透射率的演化规律。基于紧凑型D-D中子源建立硼材料中子毒物的检测方法，设计专用的中子慢化体将2.45 MeV的快中子慢化到He-3探测器探测灵敏的热中子，通过模拟计算获得He-3探测器的效率曲线，并利用高效He-3探测器对透射热中子进行探测。通过与EJ-309液体闪烁体探测器监测的中子产额进行归一化计算得到中子透射率，进而确定实验中子透射率与中子毒物含量之间的关系。研究结果表明，不同B₄C质量分数的Geant4模拟计算结果与实验结果偏差不超过3%。采用破坏性化学分析方法对检测精度进行验证，基于D-D中子源的检测方法对中子毒物含量的检测精度优于5%，验证了本技术方法的可靠性与准确性。作为一种新型的核燃料芯块中子毒物含量非破坏性分析技术，该方法可应用于燃料芯块中子毒物含量及空间均匀性在线检测，助力我国核能的安全高效发展。(专精特新·特殊环境材料服役行为专辑十五之十五)

Abstract:

With the continuous development of nuclear energy technology， the operating lifepan and safety of fuel elements are facing increasing demands. By adding neutron poisons to the core of fuel elements， the safety and stability of the reactor system can be effectively improved. Consequently， accurate detection of neutron poison content has become a key part of this process. In this study， a non-destructive detection method for neutron poison content based on a D-D neutron source by combining simulation and experiment was developed， leveraging the high neutron absorption cross-section characteristics of neutron poisons. And its reliability was evaluated. The response model of the neutron poison content of fuel elements and the intensity of transmitted thermal neutrons was established using the Geant4 Monte Carlo simulation software. The evolution law of the poison element content and neutron transmittance was obtained. Based on the compact D-D neutron source， a detection method for neutron poisoning boron materials was established. By designing a special neutron moderator， the fast neutrons of 2.45 MeV were slowed down to the sensitive thermal neutrons detected by He-3 detector. The efficiency curve of He-3 detector was obtained by simulation calculation， and the transmitted thermal neutrons were detected using a high-efficiency He-3 detector. The neutron transmittance was obtained by normalizing the transmitted thermal neutrons detected by the He-3 detector with the neutron yield monitored by the EJ-309 liquid scintillation detector. The relationship between the experimental neutron transmittance and the neutron poison content was determined. The research results demonstrated that the deviation between the Geant4 simulation calculation results and the experimental results did not exceed 3% for different B4C mass fractions. The detection accuracy was verified by using a destructive chemical analysis method. The detection accuracy of the neutron poison content based on the D-D neutron source was better than 5%， which verified the reliability and accuracy of this technical method. As a new type of non-destructive analysis technology for the neutron poison content of nuclear fuel pellets， this method can be applied to the online detection of the neutron poison content and spatial uniformity of fuel pellets， supporting the secure and efficient development of nuclear energy in China.