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
A son who stole thousands of pounds from his elderly mum to fund a gambling addiction was caught after boasting on Facebook.
Around 150 people turned out in Crickhowell High Street to oppose plans to convert a pub in the High Street into a convenience store.
Cloud will become more widespread this afternoon but expected to stay dry. Overnight, winds likely to strengthen with rain at times