Saturday, December 12, 2015

The ThorCon fuel Plan

ThorCon Plans to Use 19.75% enriched Uranium in its initial start charge.  Burning Mixed U-235 and U-238 Uranium fuel in a reactor core usually produces a useful amount of Pu-239, that can be burned as nuclear fuel in the reactor.  Both Transatomic Power, and terrestrial energy plan to burn 3% to 5% enriched uranium fuel, and produce a substantual amount of Pu-239, as well as a lesser amount of fissionable Pu-241.  These Plutonium isotopes can add significantly to the Fuel of uranium cycle reactors.  Transatomic Power plans to use a core design "trick" to increase Plutonium production, while I would not be shocked to discover that Terrestrial Energy's David LeBlank also has a similar trick with the same goal in mind.

Mark Massie and Leslie Dewan, as well as David LeBlanc anticipate relatively high conversion ratios in their MSRs, without the use of Thorium.  Jorgenson anticipate Thorium cycle conversion, and pays no attention to Plutonium burning.

Here is the Thorcon comment on its fuel:
On a once through basis, ThorCon is not that uranium efficient. Over 8 years, we feed 2,185 kg of U-235 to a 250 MWe module. This equates to 208 tons of natural uranium per full power GW-y. For comparison a standard 1 GW Light Water Reactor (LWR) requires about 250 tons of natural uranium per year. However, at the end of 8 years, the module’s “spent” fuel will contain 1289 kgs of U-233 and U235. ThorCon’s net consumption of fissile is less than half that of a LWR, due to higher thermal efficiency, removal of Xe-135, and U-233 production from thorium. ThorCon “spent” fuel is about 9% U-235 and 4% U-233. This is highly enriched by normal standards. Re-enriching this back to 20% will take about 48 SWU per kg U-235. Currently, an SWU costs $90 and this is likely to drop in the future as the last of the diffusion plants are pushed out of the market. $4000 per kg of U-235 is extremely cheap. Such re-enrichment would cut ThorCon’s uranium requirements in half.
Notice that no mention of Plutonium is made, even though Plutonium will be produced and burned in the ThorCon Reactor, and Pu-238, Pu-239, Pu-241, and so on will be present in the fuel salts.  I am sure that this is understood by ThorCon, and that they have appropriate plans regareding the role of Plutonium, but Plutonium does not have a role in the ThorCon story.

It is gaps like this that bother me, but perhaps I  expect to much.  ThorCon Includs at lrsst three people who influenced my thinking about MSRs and Thorium.  These are Lars Jorgensen, Ralph Moir and Robert Hargraves.  ThorCon, caught on to the idea that the workd needed MSR now, and in large numbers.  They hit on a formula that in many of my original readers would be familiar with.  I never suggested shipyard production, but if I recall correctly David Walters did. I should note that I did not originate most of the ideas I talked about in Nuclear Green.  Although my championing MSRs for providing load ballancing, peak demand electricity, and back up power was based on Ideas, that I found in no other source, so I tenatively clame them as my contribution.

At any rate in the first decade of the 21st Century a group of visionary champions of the idea that nuclear power in the form of Molten Salt Reactors, could save humanity from the scourge of Anthropogenic Global Warming.  Among these champions of the cause of humanity, were a number of older men who had extensive careers in science, in various educational vinues, and in business, step forward to create the embodiment of a radical approach to solving the problem of Anthropogenic Global Warming.
I recently talked with Robert Hargraves who is one of the retired Argonots who is working with the ThorCon progect, primarily by being a public face of the project.  What Rober said suggested to me, that the ThorCon project drew heavily on an ORNL report, ORNL-4528.  ORNL 4528 describes a two fluid reactor, but the ThorCon reactor is a one fluid reactor.  (Also see Part 3, of ORNL 4119.) The ORNL design team which came up with the 4528 reactor design intended to build a near breeder with a slightly less than 1 to 1 conversion ratio.  ThorCon, recognized that this was a too lofty goal, and decided to stick with the less neutron efficient consepts of the MSRE design concepts.  This is in accord with arguments which emerged during a debate that spilled over from the discussion pages of Energy from Thorium on to Nuclear Green,

The advantages of the MSRE design concept was that almost no research  would be needed, and design would be simple and streight forward.  This in turn could lead to Rapid development.  What was attractive about the ORNL 4119, ORNL 4528 approach is that it offered a practical solution to the MSR graphite problem.  The Gaphite problem was a consequence of prolonged and intense bombardment by neutrons of core graphite in Molten Salt Reactors.  As graphite undergoes prolongued bombardment, it at first shrinks, and then swells. These graphite transformations gradually introduce safety problems into the MSR core.  Before those problems get serious, the core graphite needs to be replaced.  Ed Bettis appears to have come up with the very creative idea of using 4 small (250 Mwe) MSRs in a nuclear power fcility, so if one reactor is taken off line for graphite replacement, the other 3 will be avaliable to produce electricity.  ThorCon appears to have based their concept on this approach.  For ThorCon the flaw of the Bettis two fluid approach was that it would have required considerable research.  But building 4 small cores instead of 1 big one solved more problems than it created, and nothing really required that those cores use more than one fluif.  Hense Thorcon chose the quickest path to a practical MSR, namely basing their design on MSRE and other proven reactor technologies.  There were some costs for doing so, of course.  Replacing the core every 4 or 8 years is certainly one, but hardly the only.  But the costs must be weighed against the benefits, rapid production of a completed prototype is one.  The 2021 goal for the beginning of prototype operation is one of the benefits.  The time target is doable, if enough money is made avaliable, and if the anointed shipyard proves competent to perform the task.  There are other risks, but despite the risks, the goal should not be removed from the table.


Lars Jorgensen said...

Charles, Plutonium generated inside the reactor supplies about 25% of the fuel in the baseline design. In the thermal spectrum thorium/uranium cycle is more neutron efficient than the uranium/plutonium cycle. If you have technology to separate plutonium from fission products we can consume all our own generated plutonium. But such technology has proliferation concerns that will slow deployment so we don't depend on it for now. IN fifty years the plutonium will still be there waiting for us to make productive use of it. Once we start recycling the plutonium and re-enriching the uranium and use FLiBe our fuel efficiency will be like others who make similar assumptions.
But the main point is that there is good reason to get started now before those things are available and even without assuming the long lead items we still have a very interesting proposal.

Charles Barton said...

Lars, I agree with you. It is a good plan to get to market quickly. It is a good idea to not solve every possible problem if a decent product can be produced sooner, while leaving minor projects for later solutions. You have very respectable neutron economy, even if it might be possible to improve it if you take several more years. That is what David LeBlanc and Mark Massie seem to be doing.

TerjeP said...

Sorry to come in at a tangent here but I've looked at the ThorCon design for a prototype plant and I have a few questions around safety. The plant is below ground level and ground level is at sea level. As such I worry about the risk of flooding. How does the design deal with the plant being flooded? Cleaning up after a flood would be expensive. Also the approach made by the ship for swapping cans appears to be face on to the plant. Why risk a collision? To me the entire plant is somewhat like a dry dock with a ship approaching the closed gate and a collision invites a flooding event. Why not have the ship approach along side rather than head on? I know these are rather basic questions but they have been bugging me for a week now.


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