THE equivalent of six Olympic-size swimming pools of radioactive soil and mining equipment has been buried in Kakadu National Park.

Parks Australia said it was not nuclear waste and the level of radioactivity was low.

The soil and equipment had been stored in shipping containers.

It has now been put in containers with a structural life of 1000 years and buried four metres down.

The project to clean up abandoned uranium diggings and milling sites in the South Alligator River valley cost $7.33 million and is almost finished.

Parks Australia director Peter Cochrane said revegetation would be completed during the Dry.

The sites date back to the 1950s and 1960s when uranium mining was not subject to the strict environmental standards of today.

Mr Cochrane said the diggings were being rehabilitated to World Heritage standards, as had been requested by traditional owners.

"This is not nuclear waste - it is not the residue of uranium reprocessing in a nuclear facility, nor radioactive medical waste," he said. "It's very low-level residues of naturally-occurring uranium in soil, and materials such as drill cores and mining equipment, left from historic mining and milling in what is now the park.

"Only the 50-year-old existing soil residues from this area of the South Alligator River valley are buried here, never to be reopened. No waste from any other area, and certainly no nuclear waste, is contained here: safe, secure and for the very long-term."

Mr Cochrane said the workers recovering and transporting the soil and mining equipment were not exposed to dangerous levels of radiation.

The project took more than a decade of consultation and planning with traditional owners, governments, regulators and mine experts.