Both Britain's Astute and US Virginia boats use highly enriched weapons-grade uranium fuel in their reactor cells.
The fuel cells last as long as the submarines - about 30 years. The submarines don't need refuelling during that time. These cells also allow the submarines to remain underwater indefinitely, only restricted by the endurance of their crews, which in turn depends on the amount of food they can carry.
The international nuclear non-proliferation regime could be compromised if other nuclear threshold countries, encouraged by Australia's nuclear moves, acquire their own nuclear-propelled submarines. In fact, Brazil is already doing so. The bomb-grade uranium fuel could be clandestinely extracted from submarine cores to make nuclear weapons.
Some such countries could be encouraged to arm their nuclear-powered subs with nuclear weapons.
Australians living along our coastline (the majority) would be very uncomfortable if they had to host nuclear submarine bases in their electorates.
Given that Australia has no permanent storage for even low-level uranium waste, the government would find it extremely difficult to find even temporary locations for storing highly toxic and extremely long-lasting spent nuclear reactor cores.
While it is claimed that Virginia or Astute class attack submarines are far superior in speed and quietness to conventionally powered boats, this is untrue.
Most European navies, as well as those of Japan and South Korea, have quieter and nearly as fast conventionally powered submarines. They employ auxiliary air independent propulsion systems that extend their underwater endurance to 21 days or more.
Without the pumps needed to keep reactors cool on nuclear subs, they are much quieter; they are also much cheaper. Australia could purchase or build five or more such boats for the price of one Virginia or Astute boat.
We should not expect early delivery of our subs if the Americans or British are to build them, or even only their nuclear reactors.
We should have purchased Japanese Sohryu class submarines when we had the chance.
Australia would not retain sovereignty over American or British-acquired submarines. It does not have the technology to build its own nuclear propulsion units, and will be heavily reliant on either the British or (more likely) American technology.
This will bind the Navy even more closely to US strategic planning in the Pacific, especially in its plans to confront China.
Both countries are flat out building their own fast attack submarines. It is very doubtful either country would be prepared to make space on their assembly lines to accommodate early delivery of submarines for Australia.
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