The operators of the Dounreay nuclear plant in Caithness are facing the possibility of legal action over the release of radioactive particles.
The Dounreay nuclear plant is in Caithness
The Scottish Environment Protection Agency (Sepa) said it had submitted reports to the procurator fiscal.
Sepa is now waiting to see whether proceedings are taken against the site's operators, the UK Atomic Energy Authority (UKAEA).
UKAEA declined to comment on the threat of legal proceedings.
The move has led to a two-month delay in the release of a report by an independent body on the monitoring of particles.
Statements were issued on Wednesday by Sepa and the Dounreay Particle Advisory Group (DPAG), which has postponed the publication of its third report.
Sepa said it considered that DPAG's report contained information which, if published now, may jeopardise any future court case.
DPAG said it had agreed to delaying the report's publication.
The group was convened by Sepa in 2000, but is an independent body of experts who advise on improving monitoring and research into particles in the local environment.