The investigation had found that in February radioactive dust was disturbed during testing of a ventilation system at a uranium recovery plant at Dounreay—a nuclear research center which is in the process of being decommissioned.
The "disturbance" of contaminated dust in the ventilation system was subsequently discharged into the facility itself and the atmosphere. Scottish Environment Protection Authority (SEPA) conducted an investigation which has concluded that while the discharge was well within the site's authorized limits, the operator—Dounreay Site Restoration Ltd (DSRL)—was still in breach of regulations. Investigators said there was no breach of discharge limits and any environmental impact was "very low".
"The increased discharge of radioactivity to the environment resulting from this incident was less than one percent of the relevant authorized gaseous discharge limit and there was no breach of discharge limits," Stewart Ballantine from SEPA said in a statement.
"Although the environmental impact of the discharge is considered to be very low, SEPA's investigation into the incident concluded that DSRL contravened multiple conditions of its radioactive substances authorisation," he said.
SEPA has now issued DSRL with a regulatory notice outlining the steps the operator must take to address the breaches by October 2020.
“While we welcome SEPA's assessment that there was no breach of discharge limits and environmental impact is considered very low, we take such events seriously. Environmental compliance is a high priority for us and we are making good progress against an action plan developed in response,” a DSRL spokesperson said.
SEPA had conducted an investigation earlier this year into alleged shortcomings in the system used at Dounreay to prevent radioactive substances polluting the local environment, issued a "final warning letter" following the outcomes of the investigation.
The Dounreay site—located in the far north of Scotland—was operational between 1954 and 1994. The complex comprises some 300 facilities and structures which are expected to be decommissioned entirely by the early 2030s, yet Dounreay's operators told BBC that the land at the site will not be safe to use for other purposes for another 300 years due to the risks of potential radioactive contamination.