RE: [cdn-nucl-l] " Thorium nuclear power "

UNRESTRICTED | ILLIMITÉ

Thanks for your comments and info about sodium-cooled fast reactors, Goerge.

I'm curious : Can sodium-cooled fast reactors be licensed for operation with a Rankine cycle in the US ?

Recently, I noticed this bit of text in ASME Section III Division 1, subsection NH -- "Class 1 Components in Elevated Temperature Service" :

NH-3627 Considerations for Liquid Metal Piping

NH-3627.1 Location. Routing of liquid metal piping

in the vicinity of steam and water piping shall be avoided.

This seems to suggest that only operation with Brayton cycles (helium or other gas) is allowed, since the SG's in a Rankine system would need to somehow transfer heat from sodium to water....

Perhaps the secondary sodium circuit is not considered Class 1 ?

The risk of a sodium-water fire would still remain though....

.....which brings me back to the safety advantages of fluoride salt reactors -- the stuff is virtually inert chemically, in sharp contrast to liquid sodium.

It doesn't take much to create a financial disaster for a reactor operator : Look at Japan's Monju fast reactor -- its been down for ten years, because of a secondary-side sodium fire that didn't harm anybody.

Of course the Guardian article is a bunch of hype.

I hate hype.

But it seems to work for the poll.... :O)

Jaro
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-----Original Message-----
From: cdn-nucl-l-admin@mailman1.cis.McMaster.CA [mailto:cdn-nucl-l-admin@mailman1.cis.McMaster.CA]On Behalf Of George Stanford
Sent: July 21, 2009 8:59 PM
To: Jaro
Cc: multiple cdn
Subject: RE: [cdn-nucl-l] " Thorium nuclear power "

Jaro:

         The people who read Duncan Clark's Guardian article that your message links to are being seriously misinformed. Here are the first two paragraphs of his piece, with comments interspersed.

"The uranium that makes conventional nuclear power possible has a number of significant disadvantages. For one thing, uranium reactors generate large quantities of waste."
     He's referring to today's thermal reactors, and what he calls "waste" is really used fuel with almost all of its original energy left in it. It's a major energy resource, not a waste.

"Much of this remains dangerous for thousands of years, . . ."
     That's not the true waste (fission products), but the transuranic elements, which again are a valuable fissile resource that can be utilized in fast reactors.

". . . and a proportion of it can be used to produce weapons-grade plutonium."
     Very misleading. Extracting plutonium with weapons-grade isotopics from used commercial reactor fuel would be a very intricate operation, It's very much easier to irradiate special fuel elements for brief periods, and then reprocess them -- and that can be done with any reactor, including one that burns thorium. Also, isotopically pure U-233 (an excellent bomb material) can be extracted chemically from a thorium reactor.

"A second issue is that uranium is a comparatively scarce material, which exists in significant quantities in only a small number of countries."
     That's only true in the context of thermal reactors. With fast reactors, uranium is a cheap, effectively inexhaustible energy source.

"The theoretical risk of giant explosions caused by uranium reactors is a further concern."
     Surely everyone on this list knows that is utter nonsense.

"For all of these reasons, a growing number of scientists and energy experts believe that the world should switch from uranium to thorium as its primary nuclear fuel. Compared to uranium, thorium is far more abundant . . ."
     Thorium is indeed abundant, but that is largely irrelevant, since there's all the uranium we will ever need.

". . . as well as much more energy-dense."
     Untrue. Fissioning a thorium atom releases about as much energy as splitting a uranium atom does. Mr. Clark is apparently unaware of the capabilities of fast reactors, and is thinking of today's thermal reactors, which utilize less than a percent of the energy in the mined uranium.

"In addition, the waste products generated by thorium are virtually impossible to turn into plutonium . . ."
     Irrelevant. As mentioned above, any type of reactor can easily produce weapons-grade plutonium, by irradiating special uranium fuel elements for brief periods.

" – and they remain dangerous for hundred of years rather than thousands."
     Again, that assumes that the used thermal-reactor fuel is "waste."   With fast reactors, the only waste (except for trace amounts of transuranics) is fission products -- largely gone in 300 years. And fast reactors are fueled very nicely with the used fuel from thermal reactors, so none of it needs to go to waste.

Bottom line: Thorium might well prove to be a useful fuel, but not for the reasons cited in that Guardian piece.

     -- George

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