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".
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Ghosts and ghouls a plenty will be out on the streets of Wales this evening, but it's not the first time they've been spotted this year.
It will be very mild, with early cloud lifting and breaking to allow some warm sunny spells by the afternoon.