Abstract: The Integrated Pressurized Water Reactor (IPWR) has great advantages in the development of small and medium reactors because of its compact structure and high inherent safety. The casing once-through steam generator (OTSG) has been widely adopted in IPWR. The heat transfer tubes are annular tubes, which adopt double-sided heat transfer, with strong hear transfer capacity. However, the heat transfer situation is complex as there are single phase regions, steam/liquid two-phase regions and superheated regions in the casing. It is therefore easy to generate two-phase flow instability during the start-up, shutdown or low power operation of the reactor. A lumped parameter analysis model for a casing OTSG of a land reactor is established by using the RELAP5 code, in order to investigate the influence of several parameter, such as system pressure, inlet subcooling and inlet throttling, on the flow instability. The calculation results show that the increase of the system pressure, the inlet subcooling and the inlet throttling under the certain conditions have a positive effect on the system stability. The study of the flow of the OTSG of the IPWR in this paper can also provide reference for the study of the OTSG for the marine IPWR.

Key words: Integrated Pressurized Water Reactor (IPWR), once-through steam generator, flow instability

摘要： 一体化反应堆结构紧凑、安全性高,在中小型反应堆的发展中具有很大优势。一体化反应堆中通常采用套管式直流蒸汽发生器（OTSG）,传热管是套管结构,采用双面传热,换热能力强,但套管内存在单相区,汽水两相区和过热区,传热情况复杂,在反应堆启动、停止或低功率运行时容易产生两相流动不稳定现象。文章采用RELAP5程序,针对某陆用反应堆套管式直流蒸汽发生器建立了集总参数分析的模型,研究了系统压力、入口过冷度、入口节流等参数对流动不稳定性的影响。计算结果表明：增大系统压力,提高入口过冷度,在一定条件下增加入口节流均有利于系统的稳定。文章是对一体化反应堆直流蒸汽发生器流动性研究,对船用反应堆的直流蒸汽发生器流动性研究同样具有参考意义。

关键词: 一体化反应堆, 直流蒸汽发生器, 不稳定性