Abstract
In this paper, a numerical procedure for thermal–hydraulic subchannel analysis of the annular fuel assembly in a PWR using the drift-flux model (DFM) is presented. The system of nonlinear equations was solved with a fully-implicit solution scheme using the Jacobian-free Newton-Krylov (JFNK) method. To improve the computational efficiency and numerical stability of the JFNK method, a semi-implicit physics-based preconditioner was implemented. To validate the present method, various annular fuel arrays with different operating conditions were modeled, and the results were compared with the results of other codes. The key thermal–hydraulic parameters were in good agreement and the difference in total pressure drop values obtained by different methods was less than 2%. Also, it was found that the departure from nucleate boiling ratio (DNBR) of the outer channel was significantly larger than the inner channel, and the heat split ratio of the inner surface to the outer surface was approximately 1.4.
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