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
In the second of our special series Welsh education: Making the grade? we visited Bishop Hedley High in Merthyr Tydfil.
More wintry showers will continue overnight and a yellow warning of ice has been issued for central and eastern parts.
Swansea Dry Dock says it's missed out on a number of contracts to dismantle warships because they've gone elsewhere.