While I agree with the sentiment, comparing to a navy ship reactor isn't useful, they don't have to turn a profit, nuclear is used to make the ships less dependent on refuelling.

> Many advanced large US Navy vessels have reactors.

They are not built to be cost-efficient. The Navy doesn't really care about cost per MWh, they're after other metrics.

The civilian energy sector is the opposite: we can afford to cut a few clients once in a while, but we can't afford to overspend.

It’s the economics - larger reactors produce relatively expensive power (per megawatt-hour), and that’s while still benefiting from economies of scale from their large size (as all thermal power tends to).

SMRs are technically fairly straightforward, but they need to be able to built and operated cheaply enough to produce power cheaper than existing large nuclear plants to be economically viable, given the price of competing power sources in most grids. And that’s not on the horizon at this point. Everything points to them producing more expensive power.

"viable" probably means some else then just "technically possible".

I would also see as requirements: It must be cost effective, it must be scalable in several dimensions: fast to plan and approve, fast to build, able to be build in massive numbers, able to be financed in large numbers, able to be operated in large numbers, able to cool in large numbers, able to operate in a secure environment, ...

A key feature of naval reactors is that they operate in an extremely large heatsink by design - you have unlimited cooling media at your disposal.

Discussed yesterday https://news.ycombinator.com/item?id=40762298

If it isn't cheaper than batteries and solar in Australia, it is dead on arrival, someone has to pay for it. As of this comment, Australia has 18.4GW of coal fired generation capacity and 20GW of solar [1] (very roughly, lots of behind the meter solar that is hard to suss out, ends up being reduced demand as seen by the grid operator). Even if you assume worst case capacity factor, the last of their fossil generation will be gone before any nuclear sees first kwh to grid (global solar deployment is on track for ~660GW this year, and rapidly approaching 1TW/pa [2]). Germany is routinely pumping out 40GW of solar [3] (with ~81GW of total capacity), and Australia has far more solar potential [4] (along with appetite to lean into batteries [5]).

[1] https://app.electricitymaps.com/zone/AU?wind=false&solar=fal... ("ElectricityMaps: Australia")

[2] https://news.ycombinator.com/item?id=40727619 ("HN: Global PV installations may hit 660 GW in 2024")

[3] https://app.electricitymaps.com/zone/DE?wind=false&solar=fal... ("ElectricityMaps: Germany")

[4] https://www.ga.gov.au/scientific-topics/energy/resources/oth... ("Australia receives an average of 58 million PJ of solar radiation per year, approximately 10,000 times larger than its total energy consumption. However, Australia's current use of solar energy is low with solar energy accounting for only about 0.1 per cent of Australia's total primary energy consumption.")

[5] https://www.bloomberg.com/news/articles/2023-03-07/end-of-co... | https://archive.today/2owbd ("Australia’s rapid shift from coal-fired power to cleaner alternatives is underwriting a boom in battery projects able to store solar and wind energy. The country has at least 250 planned battery developments with a potential capacity of almost 130,000 megawatt-hours, a pipeline that’s second only to China, data compiled by BloombergNEF show. While Australia still relies on coal for more than half of its electricity generation, many major plants are set to close in the next decade.")

It can be done, the economics of it are questionable.