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
An NHS volunteer from Wales is flying to Sierra Leone today to help fight Ebola.
The museum is undergoing a major refurbishment project that will also see new galleries and replicas of lost historic buildings.
The dog was found by a member of the public at the side of a road