临界实验装置水位外推达临界方法优化研究

带乏燃料的临界实验装置可用于开展乏燃料贮存相关的临界实验研究，考虑到其具有较高放射性，因此开展实验时最佳方法是水位外推达临界方法。目前该带乏燃料的临界实验装置尚未建成，遂使用与其堆芯结构、物理特性相似的铀棒栅轻水慢化临界实验装置开展水位外推达临界方法的模拟实验。在该实验中，由于水的屏蔽作用随水位上升不断加深导致无法得到正常的外推曲线。本文通过蒙特卡罗程序模拟外推过程，研究了中子源与探测器在不同的相对位置处中子计数率随水位变化的规律，给出了探测器与中子源的优化布置方案。此外，还提出一种以水位价值作为外推参数的外推方法，消除了水位高度外推时水位系数不均匀的影响，使得外推结果更准确。

Study on Optimization of Method of Extrapolating Water Level to Criticality in Critical Experimental Device

The critical experimental device with spent fuel can be used to carry out critical experimental research on spent fuel storage. Considering its high radioactivity，the best way to carry out the experiment is to take the method of extrapolating water level to criticality. At present, the critical experimental device with spent fuel has not been built yet, thus the simulation experiment of water level extrapolation is carried out in a critical experimental device with similar core structure and physical characteristics, which is a uranium rod grid device with light water as moderator. In this experiment, the normal extrapolation curve cannot be obtained because of the shielding effect of water deepens with the rise of water level. In this paper, the extrapolation process was simulated by Monte Carlo program, and the characteristics of neutron count rate changing with water level were studied when the neutron source and detector were arranged in different relative positions, thus the optimal arrangement scheme of detector and neutron source was given. In addition, an extrapolation method with water level worth as extrapolation parameter was proposed, which eliminates the influence of uneven water level coefficient when extrapolating to criticality with water level, and makes the extrapolation result more accurate.