Anti-radiation tablets are due to be handed out to people living near Sizewell B in Suffolk.
The tablets are being distributed to people near the power station
On Thursday the potassium iodate tablets are being given to everyone living within one and a half miles of Sizewell by the Suffolk Coastal NHS Primary Care Trust.
It follows advice from the Department of Health.
The iodine contained in the tablets is absorbed by the thyroid gland, preventing it from taking in any radioactive iodine that would be present in a dangerous leak.
But anti-nuclear group the Shut Down Sizewell Campaign has expressed concern that any major incident at Sizewell would also release other types of radiation - not stopped by the pills.
'Small radius of Sizewell'
A spokesperson for the group said: "The truth is that it would be impossible to protect people from the radioactive fallout if a nuclear power station was seriously damaged.
"The numbers hit could run into thousands, perhaps millions."
Earlier this year, Dr Amanda Jones, of the Suffolk Coastal Primary Care Trust, said: "The people we're thinking of pre-distributing to are people within a relatively small radius of Sizewell, about two kilometres - two or three hundred people.
"Research has shown that if there was a small incident, these are the most likely people to be affected."
The pills are aimed at reducing the risk of cancer in the thyroid.
The pills are being distributed from the Sizewell Community Centre from 1700 to 2100 BST on Thursday 21 August and Thursday 4 September.