Shetland and other councils are alarmed at proposals to discharge quantities of radioactive gases and liquids that are hundreds or even millions times greater than in recent years. They are worried about the long-term risks for human health and the environment.
Dounreay's reactors and reprocessing plants were shut down in the 1990s when the UK Government abandoned the development of an experimental nuclear technology. It has since embarked on a £2.5 billion decommissioning programme currently aimed at closing the site within the next 13 years.
But the work is expected to produce lots of additional radioactive waste. Dounreay has told the Scottish Environment Protection Agency (Sepa) that it intends to hugely increase its emissions.
Annual discharges of liquid tritium into the Pentland Firth are scheduled to be more than 500 times greater than in the last five years. Aerial emissions of the radioactive gas krypton-85 are due to leap by more than 250 million times.
There are also planned increases in discharges of alpha radioactivity, which includes plutonium, as well as iodine-129 and strontium-90 (see table ).
Such huge increases flout Dounreay's legal duty to use "best practical means" to minimise the creation and disposal of radioactive waste, the councils argue.
According to Pete Roche, policy adviser to the 50-strong group of anti-nuclear local authorities, some of the projected increases were founded on the "old fallacy" that they were harmless. "This is just plain wrong," he said.
"Sepa should force Dounreay's operators to take a more precautionary approach and as a matter of principle make absolutely certain that decommissioning is not being used as an excuse to increase discharges of radioactivity into the Pentland Firth and the atmosphere."
The Nuclear-Free Local Authorities group has objected to the proposed discharges as part of a consultation carried out by Sepa. The group's members include Glasgow and Renfrewshire councils.
Another member, Shetland Islands Council, has made its own submission to Sepa. It pointed out that tritium and krypton-85 emissions have been linked by some scientists to increased cancer rates around nuclear reactors.
The council suggested the plans for increased discharges may be response to pressure from the UK Government to decommission the site as quickly and cheaply as possible. It also suggested the consortium of private companies that operate Dounreay may be trying to maximise their profit at the expense of the environment.
"The council is very concerned about the tremendous increases in discharges of nuclear waste into the atmosphere and Pentland Firth," Councillor Michael Stout, Shetland's representative on the Dounreay Stakeholder Group, told the Sunday Herald.
"Very little information has been provided to justify the increases. There is a worry that waste management options are being chosen because of cost considerations, and environmental concerns or policies have been too easily dismissed."
Sepa promised it would consult the Scottish Government before it decided on new radioactive discharge authorisations for Dounreay and pointed out that the Government had recognised that some decommissioning operations could increase emissions.
The public consultation on the discharges has been completed, said Sepa's radioactive specialist, Linda Buchan. She added: "Sepa will be considering all of the responses received as a result of the consultation as part of the determination process."
Dounreay declined to comment on its planned discharges. "Dounreay will await Sepa's decision in due course," said a spokeswoman.