Steam generator is the heat transfer component of sodium-cooled fast reactor (SFR). It is possible to happen flow instability in the tubes of sodium heated once-through steam generator (OTSG). In order to investigate the flow instability of parallel channels in sodium heated OTSG, a numerical analysis code called COSFIAS has been developed in Fortran language based on time-domain method. The experimental data of parallel channels flow instability with uniform heating power condition and sodium heated condition have been applied to validate the code. The relative errors between calculation results and experimental data of uniform heating power condition are within 10%. The relative errors between calculation results and experimental data of sodium heated conditions are within 7%. The comparison results indicate that the COSFIAS program is reasonable and accurate for practical engineering application. In addition, the effects of important parameters on flow instability of parallel channels have been analyzed. From the calculation results some conclusions could be drawn: the decrease of water pressure would cause the increase of heat transfer power and destabilize the parallel channels system; in high subcooling region, the increase of inlet subcooling would stabilize the system; in low subcooling region, with the decrease of inlet subcooling, the parallel channels system would turn to be unstable and then return to be stable again; the increase of water mass flow rate could stabilize the parallel channels system.; the sodium heated condition is more stable than uniform heat flux condition in the same heat transfer power; the increase of sodium inlet temperature could destabilize the parallel channels system; the increase of sodium mass flow rate could destabilize the parallel channels system. In addition, the code could be applied to support the design work of sodium heated OTSG.

中文翻译：

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钠冷快堆蒸汽发生器并联通道流动不稳定性数值分析

蒸汽发生器是钠冷快堆（SFR）的传热部件。在钠加热直流蒸汽发生器 (OTSG) 的管道中可能发生流动不稳定。为了研究钠加热OTSG中平行通道的流动不稳定性，基于时域方法用Fortran语言开发了一种名为COSFIAS的数值分析代码。应用均匀加热功率条件和钠加热条件下平行通道流动不稳定性的实验数据对代码进行了验证。均匀加热功率条件下计算结果与实验数据的相对误差在10%以内。钠加热条件下计算结果与实验数据的相对误差在7%以内。比较结果表明，COSFIAS 程序对于实际工程应用是合理且准确的。此外，还分析了重要参数对平行通道流动不稳定性的影响。从计算结果可以得出一些结论：水压的降低会引起传热功率的增加，并使平行通道系统不稳定；在高过冷度区域，增加入口过冷度会使系统稳定；在低过冷度区域，随着入口过冷度的降低，平行通道系统会变得不稳定，然后又恢复稳定；水质量流量的增加可以稳定平行通道系统。在相同的传热功率下，钠加热条件比均匀热流条件更稳定；钠入口温度的升高会破坏平行通道系统的稳定性；钠质量流量的增加可能会破坏平行通道系统的稳定性。此外，该代码可用于支持钠加热 OTSG 的设计工作。