Rio Tinto Ltd says its majority-controlled Energy Resources of Australia (ERA) Ltd is accelerating work to minimise the risk of water overflows at a tailings dam at its Ranger uranium mine in the Northern Territory.

ERA, which is 68.4 per cent held by Rio Tinto, was forced in late January to suspend uranium processing operations at the mine for the remainder of the wet season after heavy rains filled the tailings dam to near capacity.

ERA last week committed to invest $220 million in process water management and treatment projects at Ranger.

Of this, $80 million will be spent on a feasibility study for the installation of a brine concentrator to treat and reduce water use at Ranger.

A shareholder at Rio Tinto's annual general meeting in Perth on Thursday was concerned the brine concentrator would not be fully operational until the second half of 2013.

However, chief executive Tom Albanese said ensuring water integrity at the mine was important to the company.

"We will be certainly accelerating that with engineering work to develop it in stages, and we'll certainly be taking that very seriously," Mr Albanese told the meeting.

"It was the right thing for them (ERA) to do to have proactively curtailed those processing operations in the middle of the wet season."

Mr Albanese said the brine concentrator would produce "the cleanest possible water that can be".

Weather at Ranger had been dry over the past fortnight, avoiding the need to allow water from the tailings dam to flow into the third open pit, he said.

"We've had quite unusual rainfalls over the past five years.

"We don't know if it's a trend. We just have to accept it."

Shares in ERA have plunged in the past year as production declines at the maturing Ranger mine ahead of its expected closure in 2021.

Also, plans to extend the mine life by exploiting the resource underneath the existing open pit has progressed slower than expected.

ERA shares closed up three cents at $4.80.

The shares finished at $13.77 this time last year and hit $15 a week later.