I do hate it when my posts end up at the top of a new page since context tends to be lost as people cannot simply scroll up and read what I am referring to. In an attempt to keep context I'll highlight a couple posts from the previous page.
Jim L. wrote:The idea behind using the plutonium in a LFTR would be the two-fold objective of destroying/fissioning the Pu while producing U233 in the thermal spectrum range. This would essentially be using the LFTR as a burner, not a breeder or iso-breeder since the CR of Pu would be under 0.65 in the thermal spectrum.
So, a place like ORNL could have multiple LFTRs burning the Pu to dispose of it, generate electricity for itself or TVA, while creating the U233 that could be used in other LFTRs by power companies like Southern. I know some will be unhappy about the efficiencies of the neutron usage, but it is superior to use in U/Pu MOX fuel in a PWR or BWR. The idea of using Pu/Th fuel in a LWR is interesting, especially if the fuel elements were annular shaped and/or metal. A metallic annular-shaped fuel element would keep the centerline Tmax low, transfer heat to water better, handle FPs, gases better, reduce swelling, achieve greater/longer burn-up, and eventually would have U233 recoverable from the fuel.
I think the politics of disposing Pu may favor using a MSR, such as LFTR, since it looks far cheaper and faster than the SRS fiasco. The politicians and regulators will not care about neutron efficiency, so LFTR will look better than using chloride salts since it is further developed. Liquid metal fast reactors have their own issues and history and are less likely to be chosen. A savvy politician could sell the idea of LFTR and make thorium a buzzword - bright, shiny, and new vs. how demonize Pu and U have become. Maybe.
Kirk Sorensen wrote:Jim L gets the picture. The fact that plutonium burns poorly in the thermal spectrum is not really that big of a deal when you're mainly trying to get rid of it. Exactly what the amount of U-233 that could be produced per unit of plutonium destroyed is not known, but the argument for going forward with the idea is pretty forgiving even if the number is bad.
After spending decades trying to make plutonium now we're trying to get rid of it. Consuming it in the presence of thorium is the ONLY way to do so without making more plutonium. That's another reason why uranium-plutonium MOX is such a dead end.
From the article referred to we have an image of what "Phase 3" looks like:
We are currently at "Phase 1" which looks like this:
Mr. Sorensen, in this article, proposes a transitional "Phase 2" which brings us to this:
My concern is that in the process of working down the "Phase 1" column in that image fissile mass is lost, that is for every atom/kilogram/whatever of U-235 put in a current reactor a smaller number of atoms/kilograms/whatever of Pu-239 comes out. This is likely to happen again while working up the "Phase 2" column of that image, the mass of Pu-239 started with becomes a smaller mass of U-233.
In order to increase the mass of fissile material we may need a "Phase 2" which has this:
This gets back to the post which started this train of thought:
Koistinen wrote:How about using molten Pu as fuel? What are the problems in getting it to selfregulate.
I figure if you use Pu to get U-233 you don't need to be careful to get as many neutrons as possible, maybe as low as getting 1 U-233 for 10 Pu would be good enough.
Would there be a need for plutonium breeding in "Phase 2" of this plan? If so, what form would that take? Would molten plutonium reactors be a good idea?
This also gets to my other concern, what would keep us (as a nation, species, whatever) from just stopping at "Phase 2" and stay in a U/Pu cycle indefinitely? Perhaps part of the answer is here:
Kirk Sorensen wrote:I doubt the economics will support the building of many more LWRs, which is the reason that I think it may be necessary to use the LWRs we have to produce the U233 needed to start LFTRs using a thorium/plutonium MOX fuel. But if the costs of that MOX fuel are even within an order-of-magnitude of the costs of the plutonium MOX fuel anticipated to be produced at the US MOX plant in South Carolina then the whole scheme will fall apart as nonsense. Thor Energy will have to show that they can manufacture Th/Pu MOX at a reasonable price.
We can possibly produce the U-233 needed for "Phase 3" using currently existing and near future LWRs. This requires someone being able to produce the right kind of fuel rods at the right price. This means people making plans for "Phase 3" by breeding the U-233 soon, and LFTRs or some other Th/U-233 cycle reactors coming online as we retire these "Phase 1" and "Phase 2" LWRs.
I seems to me that this thread has focused on two things. First, is a discussion on what "Phase 2" should look like and what technical and political challenges may prevent it from happening. Second, articles like this would seem to be a good way to address at least some of the political problems. The more people understand the technical details the less political resistance we (as Americans, thorium energy advocates, etc.) should get.
Disclaimer: I am an engineer but not a nuclear engineer, mechanical engineer, chemical engineer, or industrial engineer. My education included electrical, computer, and software engineering.