The operators of the Dounreay nuclear plant face prosecution for releasing radioactive particles into the open.
Radioactive particles were released from Dounreay in the 1960s
The procurator fiscal is currently examining a report prepared by the Scottish Environment Protection Agency (SEPA) into the issue.
The pollution watchdog began its study to chart the spread of the metallic fragments of reactor fuel in 2003.
The fiscal confirmed he had received the SEPA document but had still to decide whether or not to act upon it.
The potentially dangerous particles were inadvertently released from the nuclear reprocessing plant into the Pentland Firth in the 1960s.
Divers have discovered hundreds of the so-called hotspots on the seabed near the Caithness facility and more than 50 have been found on the public beach at Sandside to the west of the site.
A group of independent experts is currently reviewing what risks the particles pose to public health.