Heat removal characteristics of a concrete cask by a simplified test model

The present study is concerned with the characteristic cooling flow in the annular gap of a concrete cask used to store spent nuclear fuel. The concrete cask is cooled by a natural convection flow of air passing through an internal annular gap between the outside of a canister and the inside of the concrete vessel. The heat transfer coefficient and friction loss coefficient of such a flow could not be fully estimated even if we used existing handbooks, because the airflow has unique features. Simulation experiments using a simplified model for the cooling path have been conducted to estimate the heat transfer coefficient and friction loss coefficient. It was found by this study that the heat transfer coefficient well agreed with the prediction by an empirical formula applied to the free convection, and the friction loss coefficient was 2–2.5 times the value of an isothermal flow.