Aukus: Biden urged to fast-track research into submarines using non-weapons grade uranium

The Biden administration is being urged to fast-track research into submarines that do not use weapons-grade uranium, as four Democratic politicians warn the Aukus deal with Australia makes the task “even more pressing”.

Australia’s deputy prime minister, Richard Marles, arrived in the United States for crucial talks with the defense secretary, Lloyd Austin, on Friday (US time), amid renewed congressional concerns about aspects of the flagship Aukus project.

With March looming as the deadline for key decisions on how Australia acquires at least eight nuclear-powered submarines with help from the US and the UK, all three countries maintain the work remains on track.

But in the latest sign of congressional jitters, four politicians from Joe Biden’s party have sounded the alarm about broader risks to the global nuclear non-proliferation system.

Related: Malcolm Turnbull says Labor has failed to answer if Aukus deal compromises Australian sovereignty

A newly published letter coordinated by Bill Foster, a physicist serving as US representative for an Illinois congressional district, asks the Biden administration to ramp up research into alternatives to using weapons-grade uranium to power submarines.

It adds to concerns already raised by experts that if the Australian submarines are powered by highly enriched uranium (HEU), other countries may seek to follow the precedent – even though they will not be armed with nuclear weapons.

“It is more important than ever to promote the safe, secure, and peaceful use of nuclear technologies,” wrote Foster and fellow US representatives Rick Larsen and Donald Beyer, and US senator Jeffrey Merkley.

They noted Biden had authorised funding of $20m to the National Nuclear Security Administration (NNSA) for nuclear fuels development.

But in a letter to the administrator of the NNSA and the navy secretary, the politicians formally requested a detailed report on “the feasibility and performance impact of a Virginia-Class replacement SSN(X) nuclear-powered attack submarine” that is fuelled by a low-enriched uranium (LEU) reactor with a life-of-the-ship core.

They said previous reports indicated it “may be feasible for the navy to use LEU fuel for naval nuclear propulsion, as France and China already do”.

“A leading technical challenge is that a greater volume of LEU fuel is required to produce the same amount of energy as HEU fuel,” the letter said.

“The Naval Reactors office has suggested this would not pose a problem for existing aircraft carriers, which have sufficient space for a larger LEU reactor core. However, submarines face more severe space constraints, raising a question that we request you address in a report to Congress.”

Related: Aukus won’t undermine Australia’s stance against nuclear weapons | Penny Wong

The politicians said this research was “even more pressing with the September 2021 Aukus agreement under which the US and UK will provide nuclear submarine technology to Australia”.

“Minimizing the global presence of HEU by reducing its use in military applications would reduce the risks associated with making and transporting HEU and demonstrate significant leadership on nonproliferation,” the letter said.

The Australian government has said it will comply with the highest non-proliferation standards and pledged to work with the International Atomic Energy Agency.

With concerns that the first Australian-built nuclear-powered submarines may not be ready until about 2040, there has been speculation that Australia could seek to buy the first couple of boats from offshore.

Austin promised in December that the US would not allow Australia to have a capability gap between the retirement of its existing Collins class conventional fleet and the entry into service of new nuclear-powered submarines.

Related: Anthony Albanese says he would likely have signed up to Aukus if he had been PM at the time

That has prompted a vigorous debate within US politics about how to help Australia in the short to medium term without undermining its own submarine needs.

Democratic senator Jack Reed, the chairman of the Senate Armed Services Committee, and then-Republican senator James Inhofe wrote to Biden in December to implore him not to stress “the US submarine industrial base to the breaking point”.

A subsequent bipartisan letter coordinated by the Democratic representative Joe Courtney said the US would gain from providing “our closest ally with an undersea capability to better posture itself in the region”.

Courtney’s grouping said while it was essential for the US to stick to its own plan to build a minimum of two submarines a year to meet its requirements, “we are supportive of expanding the industrial base to meet Aukus expectations”.

There is renewed speculation the three countries might work on a shared future submarine model, after the UK defence secretary, Ben Wallace, said the options included “the sharing of technology and the understanding of how to do it, the sharing of the build, or the sharing of the design”.

Marles and the Australian foreign affairs minister, Penny Wong, joined their British counterparts Wallace and James Cleverly for annual high-level talks in the UK on Thursday, with Aukus one of the key topics on the agenda.

Related: Malcolm Turnbull says Labor has failed to answer if Aukus deal compromises Australian sovereignty

At their joint press conference in Portsmouth on Thursday, Marles said: “This is a huge moment in our country’s history. This will change Australia’s international personality. It will dramatically build our capability and with that it will build our sovereignty.”

In the National Defense Authorization Act for Fiscal Year 2023, which was signed by Biden in late December, the US Congress requested Austin to order an independent assessment of the “challenges” to implementing Aukus.

The assessment would examine “alternatives that would significantly accelerate Australia’s national security”. Interim options could include “leasing or conveyance of legacy United States submarines for Australia’s use” or the supply of B-21 bombers.