Claims the nuclear reactor of the new Hinkley Point C power plant will be of an unsafe design have been dismissed.
Nuclear inspectors raised safety queries in their initial assessment of the European Pressured Water Reactor (EPR) planned for the site.
The Stop Hinkley campaign says this is proof the facility should not be built but the Health and Safety Executive says it has no major concerns.
It comes as EDF, which will build the plant, begins public consultations.
The Nuclear Installations Inspectorate raised safety issues over the EPR reactor.
Jim Duffy, of the Stop Hinkley campaign group, said the reactor had proved problematic at another power station in Finland, leading to a four-year delay in building the plant.
"We could avoid a great waste of time and money by a change of direction and fully backing renewables before that's too late to help stop climate change," he said.
However, the Health and Safety Executive - which oversees nuclear safety - told the BBC it was "completely and utterly wrong to say that these designs are unsafe".
A spokesman said inspections had found no "show stoppers" and that it was working to ensure the designs were "right at the drawing board rather than on the construction site".
The Stop Hinkley campaign sponsors include Lord Ashdown, actor and academic Terry Jones, cartoonist Raymond Briggs and actress Julie Christie.
EDF began their consultation process at Cannington Village Hall on Saturday.