脉冲堆瞬态特性参数的裂变偶诊断技术研究

The transient temperature on reactor fuels is an important diagnostic parameter for critical safety,and is also one of the major factors for a burst reactor restricting.The understanding of transient temperatures is of fundamental importance in determining the physical behavior of materials, reactor safety, scram mechanism, reactor periods, and theoretics calculate. during reactor excursions.The accurate record of the energy release in order to understand the transient response characteristics and detailed fuel studies on reactor.However,most methods for measuring transient temperature have their disadvantages because of their slower response. The fission-couples have advantages over other temperature measuring methods in directly measuring at fast temperature transients on fuels during reactor tests,withstanding strong gamma radiation environment, responding rapidly to changes in neutron flux, offering minimum perturbation to the measured parameter, and having great accuracy which has been successfully carried out in US,while it is under developing in China. In this work,the theory to intepret the neutron dynamic in fission-couples to determine the physical behavior of materials will be studied,and a Monte Carlo code and ANSYS tool which will directly simulates the measurements and the response of fission-couples to pulse intensity will be used in conjunction with measured values. By analyzing the relationship of fission-couples parameters and spectra,and solving a series of key techniques, a dynamic diagnistic mathod which will be used to monitor fast temperature transients on reactor fuels could be established.

活性区燃料温度和瞬态中子通量是脉冲堆技术研究中的重要诊断参数，在核能释放、瞬态核反应以及反应堆临界安全中占有独特地位。裂变偶技术是基于裂变物质的中子致热原理而在中子诊断中得到应用的，能快速响应燃料元件的瞬态物理行为，具有较高的测量精度。本研究拟从裂变偶对中子的响应特性研究入手，利用CFBR-II堆脉冲辐射场，通过理论和实验相结合的方式研究裂变偶对燃料温度和瞬态中子通量的响应特性，分析其输出特征量与中子脉冲特性的关系，探索裂变偶性能参数对瞬态中子诊断的影响，解决裂变偶非线性输出的关键技术，建立一种可直接用于脉冲辐射场瞬态特性参数诊断的技术。项目拟采用激光焊接和四引线独特结构，解决微米量级焊点的可靠连接与稳定封装；将非裂变材料用于裂变偶的γ补偿，以扣除γ射线引起的致热效应，提高裂变偶测量瞬态中子通量的准确性。该技术可望用于脉冲中子的动态诊断，从而为核安全与控制提供一条新的途径。

利用裂变偶进行反应堆瞬发临界下燃料温度的精确测量直接反映了反应堆的瞬态行为。通过研究裂变偶对脉冲中子的响应特性，揭示了影响裂变偶测试精确性的物理因素，提出了裂变偶优化设计方法，为开辟其在中子诊断及反应堆控制方面的应用打下基础。理论研究方面，基于蒙特卡罗方法建立了中子伽马联合输运模型，得到了CFBR-II堆超瞬发临界下裂变珠内的裂变沉积能量响应曲线，并以该结果作为输入量，建立了裂变珠及热偶丝的温升模型，给出了裂变偶的理论设计参数，通过工艺优化成功制作了基于理论参数的裂变偶探测器；同时，以CFBR-II堆为应用场合，建立了伽马补偿裂变偶结构模型，并基于ANSYS工具得到了不同材料的伽马补偿结果，提出了伽马补偿裂变偶探测器的设计方法。实验研究方面，建立了裂变偶瞬态测量系统及实验模拟系统，获得了CFBR-II堆超瞬发临界下裂变偶输出的瞬态温升波形，输出线性度达92%以上；通过光电管对测量结果的标定，验证了研制的裂变偶探测器可以实现瞬发中子通量水平达1E15n/cm2·s以上的中子脉冲的响应特性，脉冲初始周期为606.09μs。通过对试验结果分析，揭示了因传导端面氧化及偶丝尺寸带来的热传导损失是造成测量中响应滞后的主要因素，为优化裂变偶设计提出了方向。