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
Most places will become dry overnight, although it will remain generally cloudy with patches of hill fog.
Police have told people in Pontypridd that the cordon around the rugby club could be in place until next week.
Two soldiers have avoided jail despite being caught on camera brutally beating two men close to their barracks in North Yorkshire.