The council has blocked publication of reports detailing emergency arrangements for coping with radiation leaks from the Dounreay and Vulcan nuclear facilities in Caithness and from nuclear submarines berthed in Loch Ewe, near Ullapool. It says it needs to "retain control" of the reports.
This is despite the fact that other authorities with nuclear sites publish their plans. The operators of Dounreay and other nuclear sites make their plans publicly available.
Councils are required to draw up plans for dealing with accidents at nuclear sites under government Radiation (Emergency Preparedness and Public Information) Regulations (REPPIR). The plans set out how people will be evacuated, anti-radiation pills distributed and contaminated food banned around the sites.
Highland Council used to put its REPPIR reports in public libraries and publish them online. But last year it removed the reports covering Dounreay, Vulcan and Loch Ewe from its website, and now refuses to release them.
The council told the Sunday Herald that the reports are for the "sole use" of the emergency services and other Government agencies "and are not written for public consumption".
Its decision to withdraw the reports was taken on police advice, disclosed a council spokesman. "The council wishes to retain control of who has access to the information they contain," he said.
"You will understand that once something is published on a website, control of that information is immediately lost. That other local authorities publish their plans on their respective websites is a choice they have made, so is a matter for them."
East Lothian Council publishes the emergency plan for the Torness nuclear power station, while North Ayrshire Council said it was about to publish the plan for the Hunterston nuclear site. Argyll and Bute Council said it would provide copies of the plan for the Faslane and Coulport nuclear weapons bases on the Clyde "on request".
The 24-page Dounreay Emergency Plan can be downloaded from the website of Dounreay Site Restoration Limited.
Highland Council's secrecy was condemned by experts.
"The council's sudden about-turn speaks volumes about its utter contempt for the people it supposedly represents and whose personal safety is meant to be protected by these documents," said Alan Turnbull, a researcher at www.secret-bases.co.uk, which posted the concealed reports online. "Why did they go to the trouble to provide all this material on the website in the first place, only to decide in late 2013 that the people shouldn't be told."
Tor Justad, a resident of Strathpeffer involved in the campaign group Highlands Against Nuclear Transport, was angered by the council's move. "I am astounded that the council is not prepared to publish these plans," he said.
Justad, a representative on the Dounreay stakeholder group, called on the council to reverse its decision. "It seems to have an inability to communicate effectively with local communities," he said.
John Ainslie, co-ordinator of the Scottish Campaign for Nuclear Disarmament, said: "We should not return to the dark and dangerous days when every aspect of nuclear programmes was kept secret."
Highland Council stressed that it was compliant with REPPIR, and distributed an "information booklet" outlining emergency arrangements.
"These plans are not secret and they are regularly trained on and exercised under the scrutiny of the relevant regulatory body," said the council spokesman. He pointed out that the emergency plan published by Dounreay was not the same as the council's, which went into detail. The Sunday Herald's request for a copy of the report was refused.
"It is both common sense and prudent that control is maintained of sensitive information which may be of use to those who wish us harm," the spokesman said.