The 12 Greenpeace activists arrested at the weekend after six of them scaled a wall of the Koeberg nuclear power plant are to be charged in court on Monday.
The activists were released on Saturday on a warning to appear in the Atlantis magistrate's court this morning, said Greenpeace anti-nuclear campaigner Michael Townsley.
Police spokesperson Bala Naidoo said that they would be charged in terms of the Maritime Act and the National Key Point Act, drawn up to protect "sensitive" installations.
Said Townsley on Sunday: "It is frightening how easy it was to get to Koeberg. We went straight from the inflatable dinghies, up the walls. People in Cape Town would be right to be shocked.
"After September 11, there has been a lot of talk about tightening security around nuclear plants, but around Koeberg this doesn't seem to have happened."
Two inflatable Greenpeace dinghies were confiscated by police because they were used "in the commission of a crime", Naidoo said. The magistrate would decide whether they should be released.
Townsley said the dinghies were worth about £45 000 (R720 000) each.
Community Safety MEC Leonard Ramatlakane said at the weekend that security was "under control" at the Koeberg power station.
His spokesperson, Bukeka Dekeda, said this meant that the security system at Koeberg was on "high alert". She could not give further details.
Ramatlakane said that the Greenpeace protest was "unacceptable" as the security of workers, of people in Cape Town and of the power station was "important to the life of our city. There will be no compromise on safety and security thereof."
Townsley said Ramatlakane's assurances of security at Koeberg were "ludicrous".
"If it was that easy, why didn't they make the plant secure before?" he asked.
Greenpeace is campaigning for an end to nuclear power in favour of renewable, sustainable power sources such as wind and solar energy, for reasons including that the generation, by nuclear power stations, of "vast amounts" of deadly radioactive waste which will be active for about 250 000 years.
The activists arrested are from the Netherlands, the United Kingdom, Argentina, New Zealand, Canada, spain, Mexico, Lebanon and Australia.