The operators of the Dounreay nuclear site in Caithness are to apply for permission to release "low level activity" into the environment.
UKAEA said the application covers lower levels than already permitted
The UK Atomic Energy Authority (UKAEA) may also ask environment agency Sepa for permission to take back several tonnes of nuclear waste from abroad.
It includes material loaned to France and Peru.
UKAEA said the new application covers effluent which would be discharged into the sea and as a gas.
The authority said the material it wants to release would be at lower levels than currently permitted and below the average dose of radiation from natural sources a person may be exposed to.
A spokesman said effluent from flushing out pipes and old systems could be cleaned up to the point of low level activity, before being discharged into the sea.
He said gases were filtered before being released through ventilation.
The spokesman added: "We have an authorisation from the old operational reprocessing days, but we need to make a new application which is for a reduction of what was authorised before."
Limits on what waste can be disposed of are set down by the Scottish Environment Protection Agency.
The application also covers several hundred tonnes of what UKAEA has described as "intermediate-level waste" it wants to send back to other countries under historic agreements.
Meanwhile, UKAEA said several tonnes of material may be in turn returned from abroad to be managed at Dounreay.
The authority said this included 1.5 tonnes of sodium and 7.5 tonnes of nuclear fuel loaned to the French for fast reactor research.
The option of returning this material to Dounreay was published in the Dounreay Site Restoration Plan in 2000.
UKAEA said it was in discussion with authorities in Peru about the return of 2.9 tonnes of thorium that was exported from Dounreay to Lima in 1998, but remains unused.
A lack of suitable treatment and disposal facilities in Peru means returning the material to Dounreay is being considered.
Sepa is expected to consult the public on the application, which is due to be lodged by the end of April.