The project's 27 kilometres of tunnels may reach 12.5 metres wide - bigger than the Sydney Harbour crossing, the Euro Tunnel or the planned Melbourne Metro project.

Officials from Snowy Hydro Limited fronted a Senate inquiry in Canberra on Tuesday. They revealed the intense difficulties faced by engineers seeking to bring to life what the government describes as a "supercharged" proposal for affordable, reliable power. It could add 2000 megawatts of hydro-electric energy to the grid, and carries a tentative $2 billion price tag.

A feasibility study due in December involved up to 250 people at its peak, including a host of international experts.

Snowy Hydro chief executive Paul Broad said the project involves digging a 200 metre-long cavern - the length of two football fields. It will be fed by 27 kilometres of tunnels, which may be between 9.5 metres and 12.5 metres wide.

Depending on the width of the tunnels, rock in "the order of 10 million cubic metres" would be excavated, Mr Broad said.

"Where are you going to put that?" asked Labor senator Kim Carr.

"Presumably you are not going to leave it in the [Kosciuszko National] park?"

The rock's resting place would be determined after "an enormous amount of community consultation" and would be outlined in an environmental impact statement, Mr Broad said.

Constantly varying rock types - volcanic, sedimentary and metamorphic - could wreck tunnel boring machines. Once stuck, tunnel borers cannot be reversed. In some cases, tunnels will have to be blasted open.

"The other issue is quite a number of fault locations, which also prove challenging," chief operating officer Roger Whitby told the inquiry.

Senator Carr's ears were pricked.

"You have used the word 'challenging' several times now, perhaps you could explain to the committee what you mean?" he asked.

"Well, simply not easy," Mr Whitby replied.

About 6000 people are expected to be employed by the project, which may take six years to build.

The scale and challenges of the proposal meant it was generating excitement "on a global scale", Mr Broad said.

"We are going to give a lot of Australian, young engineers fabulous experience in building this project," he said.

Even if Snowy 2.0 itself proves feasible, the cost of upgrading power transmission lines to transport the energy to Sydney and Melbourne is yet to be determined.

Snowy Hydro executives have estimated the upgrade may cost $2 billion, effectively doubling the total project cost.

It has been expected the upgrade would involve lines into Sydney and Melbourne, however Mr Broad told the inquiry it was "feasible" that Snowy Hydro power could be transmitted to South Australia, which suffered a statewide blackout in September last year.