Numerical approach for estimating the conditions for natural circulation in a simple nuclear passive system

The design and deployment of integrated modular water reactors (IMRs) and evolutionary reactors whose operations are based on passive systems are on the rise. The natural circulation (NC) based passive systems being adopted rely on natural convection, buoyancy driven-flow and vapour condensation. In this work, a numerical approach that can determine the required conditions for establishing this widely applied thermal hydraulic phenomenon in simple turbulent two phase nuclear passive system is presented. Through the method, other relevant thermal-hydraulic parameters which are of interest in safety and reliability analyses of such NC-based systems can also be obtained. The case of the System-integrated Modular Advanced ReacTor (SMART) based on the method was demonstrated. Furthermore, the validity of the approach was proven using the test data and simulation results of a NC-based experimental facility. The method is simple and easy to apply to NC-based systems of similar configurations. (C) 2020 Elsevier Ltd. All rights reserved

Multivariate analysis of critical parameters influencing the reliability of thermal-hydraulic passive safety system

Thermal-hydraulic passive safety systems (PSSs) are incorporated into many advanced reactor designs on the bases of simplicity, economics and inherent safety nature. Several factors among which are the critical parameters (CPs) that influence failure and reliability of thermal-hydraulic (t-h) passive systems are now being explored. For simplicity, it is assumed in most reliability analyses that the CPs are independent whereas in practice this assumption is not always valid. There is need to critically examine the dependency influence of the CPs on reliability of the t-h passive systems at design stage and in operation to guarantee safety/better performance. In this paper, two multivariate analysis methods (covariance and conditional subjective probability density function) were presented and applied to a simple PSS. The methods followed a generalized procedure for evaluating t-h reliability based on dependency consideration. A passively water-cooled steam generator was used to demonstrate the dependency of the identified key CPs using the methods. The results obtained from the methods are in agreement and justified the need to consider the dependency of CPs in t-h reliability. For dependable t-h reliability, it is advisable to adopt all possible CPs and apply suitable multivariate method in dependency consideration of CPs among other factors. Keywords: Reliability, Thermal-hydraulic passive systems, Critical parameters, Multivariate methods, Dependency consideratio