Very interesting project by Thor Energy, they are executing formal tests with a Plutonium-Thorium fuel on a heavy water cooled reactor.
Why is this important:
1 - They use just enough Plutonium (combined with the absense of U-238) that its guaranteed to fission most of the plutonium (80 to 90% of the Pu gets fissioned depending on the mix of Plutonium and Thorium).
2 - Thorium is the only fertile nuclear fuel that can be breed efficiently in the thermal spectrum (98% of the world's operational reactors operate in the thermal spectrum, opposite of fast spectrum reactors). Thorium 232 makes Uranium 233 which then gets fissioned. U-233 is the least desirable fissionable material for nuclear weapons. Nuclear reactions are a game of probabilities, when a fissile material is hit with a neutron it has a probability of fissioning. Pu-239 has just a 2/3 probability of fission in the thermal spectrum, while U-233 has an 85% probability of fission. When Pu-239 doesn't fission, it becomes Pu-240 which leads to the formation of minor actinides (very undesirable nuclear material), while when U-233 doesn't fission it becomes U-234 which then captures another neutron leading to U-235 which is the most desirable nuclear fuel in a conventional uranium fueled reactor. In the end the probability of U-233 fissioning (85% as U-233, 80% as U-235, 80% as Np-237, 67% as Pu-239) is around 99.8%, the odds of U-233 forming a minor actinide is around 0.2%, compared to 33% for U-238 / Pu-239 !
http://indico.cern.ch/event/222140/session/6/contribution/24/material/slides/1.pdf
While I'm a big fan of molten salt reactors (able to use Thorium fuel much better than water cooled reactors), water cooled/solid fueled reactors could go from being a generator of plutonium and minor actinides using enriched uranium to being a disposal mechanism for plutonium using Thorium-Plutonium fuel, while making U-233. In the long run, U-233 reprocessed from Th-Pu fuel could be used to make U-233/Thorium fuel which could lead to a solution for migrating all water cooled reactors from enriched U-235 + U-238 fuel to U-233 + Thorium fuels.
How does this change the economics of nuclear reactors ?
1 - Thorium is essentially free. It is a byproduct of rare earth mining, meaning rare earth miners might even pay for someone to take the Thorium away from their hands, worst case Thorium will be 90% cheaper than Uranium.
2 - Thorium is 3x more plentiful than Uranium in the earths crust. But it gets even better, since Thorium has a unique radioactive signature that allows its detection by satellites, essentially we know exactly where there is Thorium in the earth.
3 - Countries that don't mandate nuclear reprocessing but that allow reprocessing need an economical interest to reprocess spent nuclear fuel (extracting unfissioned Uranium and Plutonium, throwing the Uranium back into the enrichment cycle to extract as much U-235 as possible from it and use the Plutonium to make Th-Pu or conventional Pu+U fuel). Plus there are tens of thousands of tons worth of reactor grade plutonium worldwide that countries want to dispose of (reactor grade plutonium is useless for making bombs, but much more radioactive than spent nuclear fuel, so it has much higher storage costs per ton). If all of this reactor grade plutonium were used to make Th-Pu fuel we could migrate the worldwide water cooled reactor fleet from uranium fuel to thorium fuel. This test in halden will provide the blueprints for this migration.
2 - U-233 is a far more desirable fissile material for nuclear reactors than Plutonium, because of much higher burnup, running any thermal spectrum reactor with Thorium based fuel will result in spent nuclear fuel with lots of U-233, which needs reprocessing to avoid creating a stockpile of spent fuel consisting Thorium+U-233 (plus fission products plus U-234,U-235 and further neutron capture). But this spent nuclear fuel is far more valuable than plutonium rich spent nuclear fuel, since U-233 is a better nuclear fuel than both U-235 and Plutonium. In the end higher burnup means less reprocessing is needed for more electricity produced (3-5x more electricity per reprocessing cycle than conventional uranium / plutonium+uranium fuel).
This could help satisfy some of the anti nuclear crowd that is mentions spent nuclear fuel as the main problem with nuclear. In an economical fashion, which is fundamental since the biggest real problem with nuclear is cost rather than safety.
Thorium+Plutonium and Thorium+U-233 fuels work better with CANDU and other heavy water reactors since they offer better neutron economy.
Spent nuclear fuel from Thorium+Plutonium fuel will contain higher levels of fission products and will generate more electricity per ton (higher burnup), so less spent nuclear fuel per GWh of electricity produced.
For those that understand we need nuclear to get rid of fossil fuels, it is very positive news. The current stage of testing started in 2013 and ends in 2015, when the fuel will be removed and undergo chemical/isotopical analysis. Notice this isn't a research test. All fuel characteristics have been precisely simulated and the test is just to prove that the simulations are correct. This could lead to the first batches of Thorium+Plutonium fuel being loaded into operational (full sized) reactors circa 2018, which is much sooner than even the most optimistic molten salt reactor schedule (DMSR by Terrestrial Energy in Canada).
