Nuclear Engineering and Design 293 (2015) 127–137 Contents lists available at ScienceDirect Nuclear Engineering and Design jou rn al hom ep age: www.elsevier.com/locate/nucengdes SCADOP: Phenomenological modeling of dryout in nuclear fuel rod bundles Arnab Dasgupta ∗ , D.K. Chandraker, P.K. Vijayan Reactor Engineering Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India h i g h l i g h t s • Phenomenological model for annular flow dryout is presented. • The model evaluates initial entrained fraction using a new methodology. • The history effect in annular flow is predicted and validated. • Rod bundle dryout is predicted using subchannel methodology. • Model is validated against experimental dryout data in tubes and rod bundles. a r t i c l e i n f o Article history: Received 20 February 2015 Received in revised form 5 July 2015 Accepted 16 July 2015 a b s t r a c t Analysis and prediction of dryout is of important consequence to safety of nuclear fuel clusters of boil- ing water type of reactors. Traditionally, experimental correlations are used for dryout predictions. Since these correlations are based on operating parameters and do not aim to model the underlying phenomena, there has been a proliferation of the correlations, each catering to some specific bundle geometry under a specific set of operating conditions. Moreover, such experiments are extremely costly. In general, changes in tested bundle geometry for improvement in thermal-hydraulic performance would require re-experimentation. Understanding and modeling the basic processes leading to dryout in flow boiling thus has great incentive. Such a model has the ability to predict dryout in any rod bundle geom- etry, unlike the operating parameter based correlation approach. Thus more informed experiments can be carried out. A good model can, reduce the number of experiments required during the iterations in bundle design. In this paper, a phenomenological model as indicated above is presented. The model incorporates a new methodology to estimate the Initial Entrained Fraction (IEF), i.e., entrained fraction at the onset of annular flow. The incorporation of this new methodology is important since IEF is often assumed ad-hoc and sometimes also used as a parameter to tune the model predictions to experimental data. It is highlighted that IEF may be low under certain conditions against the general perception of a high IEF due to influence of churn flow. It is shown that the same phenomenological model is applicable to tubes as well as rod bundles. For application to rod bundles, the flow field was calculated using subchannel methodology. The model developed has been validated against experimental data in tubes and rod bundles. In the process a computer code SCADOP has been developed for analysis of dryout in rod bundles. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Of all regimes of two-phase flow, annular flows are one of the most widely studied in literature (Hewitt and Hall-Taylor, 1970). ∗ Corresponding author. Tel.: +91 22 25591597. E-mail addresses: arnie@barc.gov.in (A. Dasgupta), dineshkc@barc.gov.in (D.K. Chandraker), vijayanp@barc.gov.in (P.K. Vijayan). Study of annular flows is particularly important for Boiling Water Reactors (BWRs) where this flow regime is encountered during normal operating conditions. In BWRs, the maximum power achieved is limited by the phenomenon of dryout. In this condi- tion, there is a sudden deterioration in heat transfer coefficient resulting in high surface temperatures. This phenomenon is given the general name of Critical Heat Flux (CHF). Occurrence of CHF may lead to fuel clad failure and release of radioactivity which is unacceptable. Physically, dryout is caused by progressive depletion of the liquid film adhering to the wall. http://dx.doi.org/10.1016/j.nucengdes.2015.07.042 0029-5493/© 2015 Elsevier B.V. All rights reserved.