If extracting gold is only 300 times harder, that puts the lower bound cost at $108,000 per kilogram of gold. That's significantly more expensive than the market price of gold.
Indeed, extracting uranium itself from seawater is not cost competitive with conventional terrestrial mining at present. But the process has been demonstrated on a technical level. Either terrestrial uranium deposits will have to get closer to exhaustion or seawater extraction will have to be much more cost optimized (or both) before seawater extraction of uranium is economically competitive. I was only addressing your technical claims about the exhaustion of seawater uranium, not making economic claims.
You included my sentence: "Efficiency really matters when we have >1000 GW of installed nuclear capacity." I wanted to address that: efficiency matters.
Inefficient technologies will hit some constraints if not others.
We may run out of time: A pressure vessel production cycle is over one year[1]. By the time we reach >1000GW someone may make fusion practical or China's competent nuclear industry may start selling MSRs to everyone.
We may run out of highly skilled people required to build and operate these complex machines. The safety is highly dependent on operations and management throughout the life cycle of complex machines. From manufacturing to operations there is tiny margins for error. (Not a physical constraint.)
LWR technology is associated with military ships and submarines, no one shares it. Few countries control the technology and there are only a few places in the world to make pressure vessels. (Not a physical constraint.)
We may run out of waste disposal sites. A geological repository needs special rock formations away from earthquake zones.
The article is written by a nuclear industry professional who tells that routine things done by the nuclear industry today when applied to MSR is a "disadvantage". They open the lid of an LWR every 18 months and replace/shuffle highly radioactive fuel assemblies and say that it is a disadvantage for them to replace graphite. That is totally unfair.
TL;DR
Even small pressure vessels (used by nuscale) have lead times of about a year. A megafactory can build like 1 or 2 vessel per month. At 1.5GW/year/factory, we need like 22 factories to keep up with the production schedule if we need to reach 1000 GW of small-LWR capacity within, say 2050.
https://inis.iaea.org/collection/NCLCollectionStore/_Public/...
If extracting gold is only 300 times harder, that puts the lower bound cost at $108,000 per kilogram of gold. That's significantly more expensive than the market price of gold.
Indeed, extracting uranium itself from seawater is not cost competitive with conventional terrestrial mining at present. But the process has been demonstrated on a technical level. Either terrestrial uranium deposits will have to get closer to exhaustion or seawater extraction will have to be much more cost optimized (or both) before seawater extraction of uranium is economically competitive. I was only addressing your technical claims about the exhaustion of seawater uranium, not making economic claims.