CFD Analysis of Hydrogen within a Filter-Vented Canister Containing Fukushima Fuel Debris

Abstract

This paper describes experimentally verified CFD analysis that examines safety of a possible design for passive filter vented interim storage of fuel debris from the Fukushima Daiichi Nuclear Power Station. Retrieved fuel debris will be firstly placed into a small cylindrical “unit can.” Four unit cans will be stacked inside a canister whose lid contains two high efficiency filters in series. Loaded canisters will be temporarily stored in a storage facility at the power station site. Since the fuel debris contains water, hydrogen is generated in the canister due to radiolysis and it must be discharged through filter to avoid forming a flammable mixture within the canister. In this study, behavior of the hydrogen generated in the canister was estimated by CFD analysis for understanding the hydrogen discharge performance from the canister based on the conceptual design. The filter model and the canister lid model etc. were developed for the CFD analysis and the validity of these models were confirmed based on experimental results obtained by Fauske & Associates. From the CFD analysis, the hydrogen concentration distribution in the canister based on the conceptual design was not indicated locally stagnant or flammable. Furthermore, we estimated the hydrogen discharge performance from the canister when the unit-cans are stacked in an unorderly manner in the canister, and it was found that the hydrogen discharge performance was not affect by the unorderly stacked unit cans.