Henry Spencer wrote:

For example, I see no mention of the problem of keeping the collection
system free of barnacles and other sea life, a problem that's never been
fully solved even for ships.

Bear in mind that we're talking about doing chemical processing on an
enormous scale. To get 30 TW-yr worth of U-235 per year, assuming
complete recovery of U-235 from natural uranium, would require complete
extraction of the uranium content of about a cubic kilometer of seawater
per *minute*. I'm not aware of any chemical process -- not even
purification of drinking water -- which has ever been done on anything
like that scale.

Henry,

The chemical processing proper is done on the saturated adsorber. This
has already been tested, in the ocean, and fouling was not a problem.
Understand that this chemical processing is only a small part of the cost of
the extraction, since the adsorber is something like 1% uranium when
it's pulled out for processing. It would be nice to reuse the adsorber
several times, but you don't need to reuse it hundreds of times in
order for the economics to work out.

Yes, lots of water would need to be processed. To fuel a single large
nuclear reactor, with absorbers in a 2 m/s ocean curremt, you'd need
to absorb the uranium in an area ~700 m^2 perpendicular to the current.
That's not excessive (although it would be spread out, and adsorption
wouldn't be 100%). Of course 30 TW requires a much larger
system, but then ANY energy system capable of supplying that much
energy will be extremely large and extremely expensive. The global
economy is really big, and it will be able to (and have to!) spend
many trillions of dollars on energy over the coming century.

If you want to be concerned about fouling, worry about growth
of organisms on the support structure, not the adsorber itself
or its cages (if this was what you *were* worrying about, then
I agree it would need to be addressed.)

Paul