The integrated small modular reactors (SMR) have been attracting more and more attentions in the field of nuclear energy. For PWR-type SMR with full-power natural circulation, a built-in steam generator with high heat transfer performance is required to enhance the natural circulation capability of the core. The heat exchanger with annular narrow slot tube takes the advantages of heat transfer enhancement of narrow slot and double-sides heat exchange in both internal and external sides, and results in higher heat transfer efficiency compared with the conventional heat exchanger with straight tube. Therefore, it is regarded as a promising design scheme of built-in steam generator with great potential. However, there have been relatively few researches on the design and calculation of steam generator with narrow slot tube. On the other hand, the flow boiling heat transfer in micro/mini channels (generally with hydraulic diameter less than 3 mm) is more complicated than that in a regular flow channel. Heat transfer correlations developed especially for micro/mini-channels with high accuracy are required for accurate predictions.

In the present paper, thermal-hydraulic design calculations and analysis for the once-through steam generator (OTSG) with annular narrow slot tube. The thermal-hydraulic performance was quantitatively evaluated and compared with that of the conventional OTSG with straight tube, such as the OTSG designed by B&W, based on the heat transfer coefficient, heat exchange area, area density, power density, steam generator volume power and other parameters.

Finally, the working performance of the steam generator and the coupled heat transfer characteristics with the primary loop of natural circulation under steady-state operating conditions were studied, and the feasibility and applicability of the OTSG with annular narrow slot tube used in a full-power natural circulation integrated SMR were discussed.

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