Abstract The permanent magnet sodium flowmeter (PMSF) used to measure the coolant flow in fast reactors has to be calibrated in situ due to operating conditions and measurement requirements. When the large-diameter PMSF is calibrated in situ based on the cross-correlation method, there is no bluff body in the flow tube, the sodium flow measurement relied only on the turbulent fluctuation of the sodium flow, so the relationship between the cross-correlation flow rate and the standard flow rate has nonlinearity. The reasons for the nonlinear characteristics are analyzed from a mechanism perspective. The sodium flow measurement experiments based on the cross-correlation method are performed for DN150 PMSF without bluff body at a temperatures of 250 °C, and also conducted for DN300 PMSF without bluff body at the temperatures of 250 °C, 360 °C and 400 °C, respectively. The experimental data of electrodes at different positions and distances are processed by the biased cross-correlation function estimation, the maximum nonlinearity error between the standard flow rate and the cross-correlation flow rate is found to be up to 90%, and the quadratic function model is established to describe their relationship. The flow rate distribution between adjacent electrodes and the degree of nonlinearity between different electrode pairs are investigated, proving that the larger the flow rate, the more serious the distortion of the primary magnetic field, and the distortion of the primary magnetic field at different electrode positions is different. The influence of pipe diameter on the degree of nonlinearity is analyzed, the larger the diameter, the greater the degree of nonlinearity. The effect of the temperature of liquid sodium on the degree of nonlinearity is studied, the higher the temperature, the smaller the degree of nonlinearity.

中文翻译：

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基于湍流波动原理的钠流测量非线性特性分析

摘要 由于运行条件和测量要求，用于测量快堆冷却剂流量的永磁钠流量计（PMSF）必须进行原位校准。基于互相关法对大口径 PMSF 进行原位标定时，流管内不存在钝体，钠流测量仅依靠钠流的湍流波动，因此相关流量与标准流量具有非线性关系。从机理的角度分析了产生非线性特性的原因。基于互相关法的钠流测量实验是在250°C的温度下对无钝体的DN150 PMSF进行的，也在250°C的温度下对无钝体的DN300 PMSF进行，分别为 360 °C 和 400 °C。电极在不同位置和距离的实验数据通过偏置互相关函数估计处理，发现标准流量与互相关流量之间的最大非线性误差高达90%，二次函数建立模型来描述它们的关系。考察了相邻电极间的流速分布和不同电极对之间的非线性程度，证明流速越大，主磁场畸变越严重，不同电极位置主磁场畸变越严重是不同的。分析了管径对非线性程度的影响，管径越大，非线性程度越大。