This paper contains a discussion of the work being performed in the UK
to validate the CHYMES coarse mixing model. Attention is focussed on
the MIXA experiments performed at Winfrith Technology Centre in which
3 kg of molten fuel simulant were released into water. The validation
of CHYMES against one of these experiments (MIXA06) is discussed in de
tail. It is concluded that CHYMES can reproduce some features of the e
xperiment (such as the existence of a steam chimney around the mixture
and the steam production rate within a factor of two) but it does not
predict the observed mixture development (the radial spreading and th
e deceleration of the first melt arriving at the surface) well. Additi
onal model development and experimental analysis underway to resolve t
hese differences is discussed.