Energy From Thorium Discussion Forum

It is currently Dec 18, 2014 10:10 pm

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 12 posts ] 
Author Message
 Post subject: Thorium Fuel in CANDU
PostPosted: May 24, 2007 12:03 pm 
Offline

Joined: Jan 24, 2007 2:24 pm
Posts: 588
Location: Montreal, Quebec CANADA
From: THE EVOLUTION OF CANDU FUEL CYCLES


Quote:
Thorium Fuel Cycles

There has long been an attraction for fuel cycles using thorium as a thermal breeder of fissile material (U-233). Thorium is three times as abundant as uranium in the earth’s crust, and U-233 is valuable as a fissile material due to its high value of fission neutrons produced per thermal neutron absorbed (eta).

Existing CANDU reactors can operate on thorium fuel cycles, with comparable fuel-cycle costs to the natural-uranium cycle and with improved uranium utilization. While ultimate efficiency is achieved with a self-sufficient cycle that relies only on bred U-233, economical once-through thorium (OTT) cycles can greatly extend uranium resources.

Several options have been identified for the use of OTT in CANDU reactors (Milgram, 1984), and on-power refuelling is the key to successful exploitation of this material. Two general approaches have emerged: the "mixed-core" approach, and the "mixed-fuel-bundle" approach (Boczar, 1998).

In the "mixed-core" approach, a number of "driver" channels provide the flux requirements for a fewer number of "breeding" channels filled with thorium-oxide fuel. This is the conventional CANDU-OTT strategy, and has the potential to be competitive, in terms of resource utilization and economics, with both natural-uranium and SEU fuel cycles (Milgram, 1982; Dastur, 1995). Complex fuel management is required to handle the different characteristics and residence times of the two fuel types.

In the "mixed-fuel-bundle" approach, thorium oxide is contained in the central elements of a fuel bundle, and SEU is contained in the outer elements. Although uranium utilization and thorium irradiation are not as good as in the "mixed-core" approach, uranium utilization is improved over the natural-uranium cycle (but not SEU), with comparable costs. Fuel management is much simpler than in the "mixed-core" approach, and refuelling rates are about a third of that required with natural uranium (Chan, 1998).

An extension of the CANDU-OTT cycle is the "direct self-recycle" of the thorium elements bearing U-233, into new "mixed-bundles" containing fresh SEU elements. This is an excellent example of a proliferation-resistant fuel-recycle option (Boczar, 1999).

In the long term, the CANDU reactor is synergistic with fast-breeder reactors (FBRs), where a few expensive FBRs could supply the fissile requirement of cheaper, high-conversion-ratio CANDU reactors, operating on the thorium cycle.

Thorium fuel cycles have additional benefits beyond uranium resource extension. Both the thermal conductivity and melting point of thorium oxide are higher than that of uranium oxide (by 50% and 340ÂșC, respectively). Thorium oxide is chemically very stable, does not oxidize, and creates fewer minor actinides than uranium. Even with the existence of economical uranium fuel cycles, thorium can be used to simultaneously extend resources and create a "mine" of safeguarded U-233 for future exploitation.


Does anyone know if work is still being done on this fuel cycle in Canada?


Top
 Profile  
 
 Post subject:
PostPosted: Jul 18, 2007 9:21 pm 
Offline
User avatar

Joined: Nov 30, 2006 9:18 pm
Posts: 2203
Location: Montreal
The latest from Jeremy Whitlock :
Quote:
Advanced fuel cycles may be fashionable today as the world struggles with strategic questions of sustainable supply, non-proliferation, and waste management, but the notion has been fundamental to CANDU design since the outset. Under a thorium fuel cycle the CANDU system can become self-sufficient in fuel-supply. In short, CANDU can burn everything but the kitchen sink (and perhaps even that as well, if it's coated with a thorium glaze).


Top
 Profile  
 
PostPosted: Oct 18, 2007 7:17 pm 
Offline

Joined: Oct 16, 2007 4:29 pm
Posts: 30
Location: Canada
DV82XL wrote:
Does anyone know if work is still being done on this fuel cycle in Canada?


The answer is "yes". There is on-going work on thorium fuel cycles in CANDU reactors.

I know this was asked a while ago, but it's a chance for me to try out my first post.

-Gary


Top
 Profile  
 
 Post subject:
PostPosted: Oct 18, 2007 7:26 pm 
Offline
User avatar

Joined: Nov 30, 2006 3:30 pm
Posts: 2861
Location: Alabama
Welcome Gary!


Top
 Profile  
 
PostPosted: Oct 19, 2007 1:45 pm 
Offline

Joined: Mar 07, 2007 11:02 am
Posts: 1062
Location: Ottawa
Gary wrote:
DV82XL wrote:
Does anyone know if work is still being done on this fuel cycle in Canada?


The answer is "yes". There is on-going work on thorium fuel cycles in CANDU reactors.

I know this was asked a while ago, but it's a chance for me to try out my first post.

-Gary


Gary,

Would you know if straight ThO2 plus PuO2 (i.e. TRU) is ever considered for CANDU or LWR solid fuel elements or is some amount of UO2 always mixed in for proliferation reasons (to dilute or denature the produced U233).

The reason I ask, is that in such a system, you are producing fairly pure U233 (along with U232). In the Molten Salt community, we constantly hear from people that any system that uses the Th-U233 cycle will have to have U238 added as a dilutent or regulators will never even consider it. Molten Salt breeders can be made to work with the added U238 but only just barely and we end up dealing with a great deal of transuranic production and many other negative aspects in terms of fuel processing.

The IEAE has I believe a denaturant limit of U232 in U233 as 10,000 ppm or a full 1%. Without tricks such as adding Th230, a typical Molten Salt reactor will be from 850 to 1500 ppm so they fall short of the IEAE's limit. Any comments on how possible you think it might be to fashion a weapon given the high energy gamma rays coming from the U232 decay chain at 1500ppm? I.e. do you think there is any hope of the IEAE lowering the limit somewhat.


Top
 Profile  
 
 Post subject:
PostPosted: Oct 19, 2007 2:30 pm 
Offline
User avatar

Joined: Nov 30, 2006 3:30 pm
Posts: 2861
Location: Alabama
Gary, when you look at CANDUs using thorium, do you consider the essential elements of the CANDU to be the D2O moderator and the use of uranium?

Because if you do, then a fluoride-fueled, D2O-moderated CANDU such as Jaro describes could be an excellent candidate.

If however, you consider the essential feature of CANDU to be solid uranium oxide fuel, then it will be very difficult to get past some of the inherent problems of solid fuel such as the retention of fission gases.


Top
 Profile  
 
PostPosted: Oct 20, 2007 3:35 pm 
Offline

Joined: Oct 16, 2007 4:29 pm
Posts: 30
Location: Canada
David wrote:
Gary,

Would you know if straight ThO2 plus PuO2 (i.e. TRU) is ever considered for CANDU or LWR solid fuel elements or is some amount of UO2 always mixed in for proliferation reasons (to dilute or denature the produced U233).

I'm not sure exactly how to answer the question. At the research level, pretty much anything you can think of has been, or is being, considered. (LEU,Th), (Pu,Th), (U233,Th), (TRU,Th), etc. [By TRU, I'm thinking group-extracted transuranics: Np, Pu, Am & Cm at typical LWR discharge compositions]. With the exception of (TRU,Th) all of those fuels have been fabricated and irradiated.

The non-proliferation debate isn't my topic. As long as there's no commercial Th-cycle, there's no real motivation for anyone to take a very hard look at what would be a reasonable barrier to proliferation.

Ya, dumping in a lot of 238 is a quick way to reduce the efficiency of a Th-based fuel cycle.

Any help?

-Gary


Top
 Profile  
 
 Post subject:
PostPosted: Oct 20, 2007 3:42 pm 
Offline

Joined: Oct 16, 2007 4:29 pm
Posts: 30
Location: Canada
Kirk Sorensen wrote:
Gary, when you look at CANDUs using thorium, do you consider the essential elements of the CANDU to be the D2O moderator and the use of uranium?

So, what makes a chicken a chicken? Actually, your question is one of those irresistable ones that has generated more debate than you can imagine.

Personally, I think it's better to look at what we have available to us in that technology [And there's a heck of a lot of very good stuff there!] and how best to exploit what we have to meet the world's evolving energy demands.

-Gary


Top
 Profile  
 
PostPosted: Oct 20, 2007 3:57 pm 
Offline

Joined: Mar 07, 2007 11:02 am
Posts: 1062
Location: Ottawa
Gary wrote:
David wrote:
Gary,

Would you know if straight ThO2 plus PuO2 (i.e. TRU) is ever considered for CANDU or LWR solid fuel elements or is some amount of UO2 always mixed in for proliferation reasons (to dilute or denature the produced U233).

I'm not sure exactly how to answer the question. At the research level, pretty much anything you can think of has been, or is being, considered. (LEU,Th), (Pu,Th), (U233,Th), (TRU,Th), etc. [By TRU, I'm thinking group-extracted transuranics: Np, Pu, Am & Cm at typical LWR discharge compositions]. With the exception of (TRU,Th) all of those fuels have been fabricated and irradiated.

The non-proliferation debate isn't my topic. As long as there's no commercial Th-cycle, there's no real motivation for anyone to take a very hard look at what would be a reasonable barrier to proliferation.

Ya, dumping in a lot of 238 is a quick way to reduce the efficiency of a Th-based fuel cycle.

Any help?

-Gary


Yes, thanks. Sort of what I thought. That paper studies might show Th+TRU only without too much thought to proliferation concerns or regulatory issues. Getting an actually true thorium cycle off the ground without added U238 will be a different story though. Many of us hope a logical debate can sort out if U238 denaturing is really needed but some people assume complete inflexibility from the regulators.


Top
 Profile  
 
 Post subject:
PostPosted: Oct 20, 2007 4:40 pm 
Offline
User avatar

Joined: Nov 30, 2006 9:18 pm
Posts: 2203
Location: Montreal
Gary wrote:
I think it's better to look at what we have available to us

No argument there, if the focus is on the very near term (not to say myopic).

I think it would also be beneficial not to lose what we had -- or rather what ORNL had, about 50 years ago.
....and possibly adapt it to today's needs and today's regulatory & non-proliferation regime, and if necessary, to national technological preferences/biases -- D2O fuel channel reactors, in the case of Canada (the HWMSR is an attempt at such adaptation).

If in another 50 years these policies & preferences change, well then the technology can be adapted again.

But it is important in the mean time to gain some operating experience with new technology & new materials, even if its perhaps not in the ideal application form, so that when opportunities do arise at a later time, it is ready for deployment.

Let us please not forget that some pretty clever people have looked at future global energy needs, and have come to the conclusion that if nukes are to make a significant contribution, then technology different from today's will be required.
Total burn reactors & fuel cycles are such a technology, be they U or Th based....

.


Top
 Profile  
 
 Post subject:
PostPosted: Nov 06, 2007 10:48 pm 
Offline

Joined: Oct 16, 2007 4:29 pm
Posts: 30
Location: Canada
jaro wrote:
Gary wrote:
I think it's better to look at what we have available to us

No argument there, if the focus is on the very near term (not to say myopic).

Don't get me wrong. I'm suggesting we abandon progress. I'm just suggesting that, rather than deciding "what CANDU is" we would be better served by looking for "what CANDU technology has to offer".

And I think that's as true in the long term as the near term, though what the technology has to offer in the future may be something different. You can find a lot of new ideas in old reports.

-Gary


Top
 Profile  
 
 Post subject: Re:
PostPosted: Jun 22, 2008 11:33 pm 
Offline

Joined: Apr 19, 2008 1:06 am
Posts: 2148
Gary wrote:
jaro wrote:
Gary wrote:
I think it's better to look at what we have available to us

No argument there, if the focus is on the very near term (not to say myopic).

Don't get me wrong. I'm suggesting we abandon progress. I'm just suggesting that, rather than deciding "what CANDU is" we would be better served by looking for "what CANDU technology has to offer".

And I think that's as true in the long term as the near term, though what the technology has to offer in the future may be something different. You can find a lot of new ideas in old reports.

-Gary


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 12 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group