The team pioneering the plan to freeze hundreds of thousands of tonnes of arsenic trioxide under the defunct Giant Mine — in perpetuity — says it could be done using a cooling system that doesn't rely on external power.

The project team gave an update on its freeze optimization study last night in Yellowknife during its annual public forum.

"We looked at passive versus energized cooling," said Natalie Plato, deputy director of the Giant Mine Remediation Project. "We concluded that passive freezing is a viable option."

The study, launched in 2011, focused on freezing one of the 10 underground, arsenic-filled chambers. In total they hold roughly 237,000 tonnes of the toxic dust — a result of decades of gold production.

The study's goal was to better understand how the freeze would take place and what's needed to do it on a larger scale. A draft report on the findings is expected later this year.

"It wasn't a question of 'Will the technology work?,'" said Plato. "It was a question of refining it."

The two systems both remove heat from the rock surrounding the chamber, allowing it to freeze.

One uses freeze pipes powered by an external source to circulate coolant — like the pipes that freeze the ice at a hockey rink. The other uses thermosyphons — large tubes that allow passive heat exchange based on natural convection.

"It can be achieved just as good as other types of freezing," said Plato.

The study also revealed that the chambers and stopes — large, irregular-shaped mined areas — will stay safely frozen when cooled to a temperature of -5 C. The team also learned it's more efficient to freeze them together in one block. Results show the ground cooled faster than expected.

That information will be incorporated into the updated remediation plan.