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
Rain clearing this evening to leave a dry night. Winds expected to be fairly strong especially along the coast.
Traders in Monmouthshire say they could lose out when many roads are closed for the first Velothon Wales event next month.
A cat rescue charity in Ebbw Vale is worried it won't be able to find homes for its 70 cats.