China is doing the same.
"Thanks to its high flexibility and low cost, this unmanned underwater vehicle equipped with the nuclear power system can be used as a conventional force like an attack nuclear submarine, rather than as a nuclear missile," China's Institute of Atomic Energy chief Guo Jian reportedly says.
Like Australia, China finds the prospect of an almost unlimited reach appealing.
The institute wants to use tiny "disposable" nuclear reactors to power long-range submarine drones. This would drastically reduce the weapon's size by eliminating the need for bulky fuel storage and making it harder to detect through a quiet, all-electric propulsion system.
Unlike Australia, China appears to be angling toward a large fleet of torpedo-sized, low-cost nuclear-powered "killer robots" that can be carried by any military vessel. Australia's defence force aspires to a $170 billion force of 12 large, fully crewed submarines.
China's researchers say they can deliver wolf-packs of the AI-controlled weapon within 10 years.
After 15 years of dithering over a replacement for the ageing Collins-class diesel-electric submarines, Australia's earliest possible date for constructing nuclear replacements is in the 2040s.
Nuclear propulsion
Atomic power has been harnessed as a propulsion system since the 1960s. It drives enormous aircraft carriers. It allows submarines to stay underwater for as long as their air and food supplies hold out. It's still powering the Voyager II space probe as it passes beyond the solar system's edge after 45 years in space.
What's changed is a fundamental redesign of the technology to make it more stable. And the ability for it to be miniaturised.
Guo says China will build the weapon with "mature and simple technology that is easy to use and maintain, inexpensive and suitable for mass production."
"We need to think out of the box," he added.
This involves removing most of the shielding around the reactor. As a result, only sensitive electronic components will be protected from radiation. The torpedo will operate on batteries for half an hour after launch. Only then will the reactor fire up to its 315C operating temperature.
The report also explains the reactor will not use expensive rare-earth minerals in its construction. Instead, it will be built with cheaper materials like graphite — which caught fire during the Chernobyl disaster and contributed to the radioactive fallout.
The result is a power pack needing just 4kg of low-grade uranium fuel. China says this will produce 1.4 megawatts of heat, of which only 6 per cent will be converted into electricity.
The allure of such a small power pack is that it can potentially drive a torpedo or underwater drone at speeds of 30 knots (56km/h). However, the Post gave conflicting reports about how long (200 or 400 hours).
It stated the torpedo would have a 10,000km range — "about the distance from Shanghai to San Francisco". And Sydney.
Poseidon junior
Russia this month put a nuclear-powered submarine weapon into service.
Dubbed "Poseidon", the giant torpedo was unveiled by President Vladimir Putin in 2019 as one of six "super weapons" destined to return Russia's military to greatness.
The first crewed submarine capable of carrying the enormous device — the K-329 Belgorod — entered service earlier this month.
Unlike the Chinese proposal, Poseidon is huge. But it is reportedly capable of loitering at sea for long periods or travelling great distances before striking its target. A two-megaton nuclear warhead (some 100 times more potent than that dropped on Hiroshima) will then trigger a tsunami large enough to level a coastal city.
This puts the likes of Pearl Harbour in Hawaii and Norfolk Naval Station in Virginia at risk of a surprise nuclear attack.
There's no reason the standard-sized Chinese torpedo can't also carry a small nuclear warhead.
But the Post reports China intends to use lurking swarms of the smart torpedo to "strike submarines as they leave a port in home waters that is difficult to reach by manned platforms."
Its designers also reject any accusation of it being a "dirty bomb" or a nuclear weapon in disguise. Instead, the small reactor will be "ejected" to the seabed shortly before the torpedo strikes its target – with the final propulsion stage powered by the on-board battery.
This would leave the radioactive material outside any blast radius.
"Even if the hull is broken, the interior is filled with water, and the whole body falls into the wet sand on the seabed, the reactor will not have a critical accident. The safety is ensured," argues Guo.
And the nuclear-powered submarine won't only be a weapon, Guo says. Its high speed and endurance will enable it to inspect distant waters and track potential targets — such as nuclear-powered aircraft carriers and crewed submarines.
"When the manufacturing cost is low enough, even if the nuclear-powered device can only be used once, the overall cost will be low," Guo says.
