ABSTRACT
Critical heat flux (CHF) is an important parameter in the design and operation of nuclear reactors as it limits the power that can be produced. CHF in steady flow condition has been extensively investigated and fairly well understood. Many modern reactor designs are now proposed with passive primary heat transport systems which are susceptible to flow oscillations due to the onset of hydrodynamic instabilities. Hence it is important to study CHF in such abnormal conditions.
The fundamental objective of the present work was to investigate whether the CHF prediction methodology using the existing steady state predictive approaches, such as the Look- Up-Table (LUT-2006), are also applicable for transients. For this purpose, both transient and quasi-steady methodologies were employed. While the quasi-steady approach assumed that the fluid states can be constructed out of a sequence of steady states, the transient method used a numerical solution procedure for solving the mass, momentum and energy equations for the fluid, together with the energy equation for the wall.
The analysis has thrown up several interesting results: (a) the values of CHF obtained by previous researchers at steady conditions agree well with LUT-2006. (b) The value of CHF obtained using a quasi-steady approach in conjunction with LUT-2006 for the data available in the literature is fairly close. (c) The transient methodology is also able to mimic the wall temperature fluctuations and is therefore in a position to predict the available experimental results with reasonable accuracy. However, the model needs further refinement for it to predict the data accurately.
