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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Winter sunshine with cloud creeping in during the afternoon and a frosty night ahead.
The Revd Canon Joanna Penberthy will be consecrated as Bishop of St Davids at Llandaff Cathedral.
Temperatures will tumble under clear skies tonight with a widespread frost developing.