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
Green keeper Gareth Pugh died after he fell into a lake while collecting golf balls.
The Newsweek Quiz - where we will be testing your knowledge from the last seven days of news here in Wales.
Swansea must learn the Italian art of defending to continue their climb up the league table, says head coach Francesco Guidolin.