[2I06-11] Phase Change

[2I08] Experimental analysis of clad rewetting in downward water/air flow

*Marco Pellegrini¹, Tomio Okawa², Masanori Naitoh¹ (1. The Institute of Applied Energy, 2. University of Electrocommunications)

Keywords:rewetting front velocity, precursory cooling, water/air flow

In operation of BWRs, AOO can result in clad film dry-out. The current regulations in Japan imposes such limits so that film dry-out should never occur. However, it has been shown that this condition, might not lead to high fuel temperature harming the plant safety. In order to control the temperature nevertheless the time and method of clad rewetting need to be modelled correctly. The correct evaluation of clad rewetting is complicated because the heat transfer across the rewetting front is difficult to be measured. The heat transfer is influenced by sputtering of the front crating a precursory cooling effect which affects the heat transfer shape. Even though recently investigated by several authors the dynamics of the precursory cooling are still not clear. In this experiment water is introduced from the top of the facility creating a film on the cladding moving downwards. Air is injected also from the top in a concurrent way. Such facility allows to perform experiments with and without air with the objective to evaluate the effect of the airflow on the sputtering and cooling effect. This set-up presents remarkable advantages compared to a more typical upward flow design.