MORE than a dozen workers were exposed to a "concerning" level of uranium during a clean-up operation at the Ranger mine near Jabiru.

The workers were not wearing their TLD monitoring devices at the time but urine tests showed they had been exposed to uranium oxide.

The incident is among 210 outstanding matters before the mine's safety committee, Australian Manufacturing Union state secretary Andrew Dettmer said.

Energy Resources of Australia business development manager David Paterson said the workers probably ingested uranium through their mouths after licking their lips while cleaning out the yellowcake.

"Absolutely it's a concern," he said. "We'll be reviewing our procedures and taking all steps necessary to make sure it doesn't happen again."

The incident took place over three days in late October when workers were cleaning yellowcake out of a "hopper" where it was clogged after a rainstorm. Mr Paterson said they were wearing only paper overalls and face masks.

AMWU NT organiser Steve Milne said eight workers who were tested "were all over the acceptable limit for uranium".

But Mr Paterson said of the 15 workers on the clean-up job only six wanted to be tested.

He said the company's "most pessimistic credible case" estimate was that they received only a slight level of exposure, a small fraction of the yearly safe levels.

Mr Patterson denied union claims the workers were not wearing their TDL monitoring devices at the time.

But the company later admitted they were in fact not wearing the monitors.

NT WorkSafe director Laurene Hull said the agency visited the mine and was reviewing the work practices and the health monitoring results.

The exposure followed an incident about a month earlier when a worker was hit in the face by a lump of yellowcake that fell from a hopper and knocked his face mask off, Mr Dettmer said.

Tests were understood to have cleared him of dangerous levels of radiation.