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
The Welsh Conservative leader and the Welsh Secretary will today address their party's UK conference in Manchester.
A five-day celebration of LGBT short films will begin this evening in Cardiff.
People who smoke or are overweight may have to go on stop-smoking or weight loss programmes before having some routine operations.