Today's scenario is an incident involving the transportation of radioactive materials.
"It's extremely unlikely that an event like this could happen for real" said a spokesman for Magnox.
"However we can't allow ourselves to be complacent and need to be prepare for such eventualities".
More top news
A mild day with showers in the west, drier and brighter in the east
A team of experts are calling for people in Wales to take more responsibility over their health. We have a few tips here.
The Football Association of Wales says match fixing is 'quite possibly' the biggest threat to football in Wales.