An enforcement notice has been issued on Devonport Dockyard after a radioactive water leak.
An investigation into the leaks is under way at the dockyard
About 20 litres of water containing Cobalt 60 was spilled last Friday during the refit of the Trident nuclear submarine HMS Victorious.
It was the second incident within a week, but the Environment Agency said there was no hazard to the public.
Dockyard owner DML said the spillages were contained within the dock and an investigation was currently under way.
The enforcement notice means all arrangements for handling radioactive waste in the dock must be reviewed.
Cobalt 60 is a radioactive isotope. It is used in radiotherapy in hospitals; and also for industrial radiography, a process similar to taking X-rays which are used to detect structural flaws in metal parts.