The protesters gathered at Siouville-Hague, between a nuclear waste treatement centre at La Hague and the site of a third nuclear reactor at Flamanville, which is currently under construction.
The first protest against the plan took place 10 years ago at Cherbourg on the Channel coast.
French power company EDF, which is also building the Hinkley Point reactor, says it should be ready to operate in the third quarter of 2018, six years late.
Its cost has trebled to 10.5 billion euros after a number of problems.
France's nuclear watchdog has ordered construction company Areva, which is 86.5 percent state owned, to prove that the site's reservoir is safe by the end of the year, having founda "serious anomaly".
Like the Hinkley Point reactor, Flamanville is one of four European pressurised reactors (EPR) being built.
French Green MP and possible presidential candidate Cécile Duflot joined the demonstration, as did a number of British anti-nuclear activists.
Opponents claim that nuclear power is dangerous and expensive.
The sector employs about 10,000 people in Normandy.