PICKERING, Ont. - Greenpeace activists blocked a main gate at the Pickering nuclear station Thursday to demand that nuclear energy be replaced with green energy.

Three activists tied themselves to a flatbed truck carrying a large caricature of Energy Minister George Smitherman with a caption reading, "Don't nuke green energy."

Smitherman should explain why he won't replace the Pickering nuclear station with green energy when the reactors reach the end of their lives in 2013, said Greenpeace spokesman Shawn-Patrick Stensil.

The minister talks a lot about green power but needs to take concrete action, he said.

Smitherman said he wasn't bothered by the nature of the protest.

"It's not offensive to me in any way that Greenpeace would seek to use those tactics," he said.

"Greenpeace is going to use tactics that it wants to use to highlight an issue. That's very fair in the context of the public discussion. It's a very important matter."

Smitherman said the government is taking advice this year on the future of the Pickering plant, which has been running since the early 1970s, but he wouldn't speculate further.

Bill McInlay of Ontario Power Generation said while people have a right to protest, "they don't have a right to break the law by blocking the road."

He said police monitored the situation, and the protest had no impact on plant operations.

Stensil, one of 14 activists who took part in the protest, said if Smitherman is really interested in expanding green power, he can prove it by replacing the nuclear reactors.

Spending money on nuclear plants robs renewable energy of the financing it needs to grow in the province, he said.

"You can't plan to spend tens of billions on nuclear reactors and call yourself green. That's green-washing."