Australia's ageing Collins Class submarines could be kept in the water for another 30 years as Defence works to acquire a new fleet of nuclear-powered boats.

A senate committee has examined last month's shock decision to dump a $90 billion contract with France in favour of building submarines using British and American technology.

Chief of the Navy, Vice Admiral Mike Noonan, said it was possible Australia's existing conventionally powered submarines could receive another round of upgrades.

Asked by Labor senator Kimberley Kitching whether this meant the Collins Class boats would still be in the water in 2040 or 2050, Vice Admiral Noonan said: "Yes Senator, potentially."

The federal government has previously confirmed all six Collins Class boats will undergo a life-of-type extension, giving the fleet an extra 10 years of service.

Plans for a possible second rebuild of the submarine fleet has not been previously disclosed by Defence.

The Chief of the Navy has also confirmed US and British nuclear-propelled submarines might be based in Australia in the coming decades while Defence develops an understanding of the technology.

Australia's nuclear regulator has confirmed changes to legislation and other concerns will need to be addressed before nuclear-powered submarines can be operated by the Australian Defence Force (ADF).

The CEO of the Australian Radiation Protection and Nuclear Safety Agency, Carl-Magnus Larsson, told the committee it was too early to know what precise action would need to be taken.

"I think that there are clarifications that are needed with regard, for instance, definitions, for instance nuclear powered propulsion, and there are a number of other matters that need to be looked at."

Defence urged to examine ethical problems in staffing 

The parliamentary committee has also been told of concerns about the movement of senior Defence bureaucrats and uniformed officers into highly paid jobs with military companies.

On Friday the ABC revealed an official appointed to oversee Australian industry capability in Defence had taken up a position with a British firm specialising in nuclear submarines, just weeks before the AUKUS partnership was unveiled.

Martin Hamilton-Smith, the director of the Australian Sovereign Capability Alliance, told the inquiry into Australia's sovereign naval shipbuilding capability that Defence staff should face similar restraints to those imposed on government ministers.

"Leaving those posts and turning up in a very short time frame later with the purchases and the customers, that may point to some problems," he told the committee.

The former Liberal MP turned independent, who served as defence industries minister in a South Australian Labor government, believes Defence and the government need to study the issue.

"There'd some cultural problems, there'd be some ethical problems, there'd be some matters of concern," he said.