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
Farmer Gareth Wyn Jones is hoping for a festive online hit with footage of sheepdog Cap rounding up sheep.
It is expected to remain wet and windy for the rest of today, overnight and tomorrow. Conditions improving on Christmas Eve
In this clip from 1959 Father Christmas gets some very practical requests for Christmas Day.