Numerical study of the cooling stability of spent nuclear fuels in storage and deactivation pools

Details

Supervisors

Papalexandris, Miltiadis

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en mathématiques appliquées, à finalité spécialisée

Abstract

The safe storage of spent nuclear fuel in deactivation pools is of utmost importance. In a disastrous case such as a loss-of-cooling event, it is important to be able to predict what might happen in such scenarios. This was further emphasised by the Fukushima Daiichi disaster in Japan in 2011, when their deactivation pools lost all access to cold water. In this work, we will study the effects of spent nuclear fuel assemblies on the flow in the pool, in a scenario where no inlet of cold water is present, and no outlet of hot water is present either. Additionally, evaporation has been modelled via a non-zero Neumann boundary condition on the temperature field at the free surface of the pool. The mathematical and physical background is laid down using a three-dimensional reference frame, but the numerical simulation will be a two-dimensional projection due to computational limitations. We numerically study two different cases: a pool with a free channel of width 16 cm or 24 cm. The numerical simulation analysis is done in four different stages: a short-term stage, a medium-term stage, a long-term stage and a very long-term stage. We find that the 16 cm case is much less favourable than the 24 cm case, and that the water completely evaporates from the pool 8% faster. In the early stages, the 16 cm case is favourable due to hot spots having a lower maximum temperature, but this advantage dissipates as time flows. More importantly, an empirical relationship between time and the total amount of water that has evaporated from the pool is established.