Energy From Thorium Discussion Forum

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PostPosted: Jun 09, 2014 8:03 pm 
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Thorium from the Indian Point power plant in NY was reprocessed in NY in the 60s or 70s.

http://www.osti.gov/scitech/servlets/purl/5080081


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PostPosted: Jun 14, 2014 4:01 am 
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Thorium is routine in new PHWR's in INDIA as power flattener.


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PostPosted: Nov 10, 2014 8:12 pm 
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The first powerplant in the U.S. was based on an Aircraft Carrier's reactor, and incidentally prototyped partially-Thorium fuel. It's very likely that naval nuclear reactors breed fuel internally to achieve their very long core lives. Thorium is a logical way to do that.


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PostPosted: Nov 10, 2014 8:27 pm 
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According to an Indian DAE publication, thorium can be used with fissile from RG plutonium or enriched uranium to maximize power from the mined uranium.
http://dae.nic.in/writereaddata/.pdf_38
Thorium based fuel will have a high burn up, long life in reactor and superior fissile U-233 in used fuel. There is unfortunately still a bias against using it in solid fuel reactors,


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PostPosted: Nov 11, 2014 2:08 am 
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rgvandewalker wrote:
It's very likely that naval nuclear reactors breed fuel internally to achieve their very long core lives.


I have no doubt that there is breeding of fuel in naval reactors. Even in utility reactors a not insignificant portion of the energy comes from breeding U-238 into plutonium. It's no secret that naval reactors get their long fuel cycles from enriching the uranium well above what is used in utility reactors. What is a secret is just how highly enriched. While the exact enrichment level is secret there are people more informed on the topic than I that have speculated it to be somewhere between 20% and 35%.

rgvandewalker wrote:
Thorium is a logical way to do that.


More logical than enriching the uranium-235 or breeding the uranium-238? I don't think so. But then I'm a computer engineer, not a nuclear engineer.

I will emphasize that I, me, myself, don't see the logic in using thorium in power plants on warships. The reason we like thorium as a fuel is because of cost, safety, and regulations compared to uranium fuels but militaries are not so constrained.

It is great to see that thorium has been used as fuel before. What is disappointing is that this was done somewhere around four decades ago and we've done so little with that knowledge.

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PostPosted: Nov 11, 2014 11:59 am 
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I believe that I've seen in open literature that the USN's reactors use U235 enrichment as high as 93% but somewhere in the 80% range is more typical. I have to apologize in that I do not have a reference, maybe Atomic Insights (?), but I think that enrichment, and metal fuel, was used since naval vessels can have large swings in required power, and that enrichment can help overpower neutron poisons like Xe135. But again, I'm relying on memory.


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PostPosted: Nov 12, 2014 3:40 am 
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From my recollections of my days in the US Navy that the cores were metal fuel, of about 80% enrichment clad in zirconium. Our early cores had no burnable poisons in them, so they only lasted about 8 years. Later cores for the Enterprise were to have burnable poisons, and last 25 years. These reactors could go from idle to 100% power, and back to idle as fast as the throttle man could operate the valve.

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PostPosted: Nov 12, 2014 10:48 pm 
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It appears I was misinformed or recalled incorrectly the enrichment of U235 in warship power plants. My original point on the unfeasibility of thorium fueled warships still stands, unless corrected again. There is a delay from when the neutrons are released to the thorium core until the power can be output. Too many neutrons and the core develops stable elements that can change state along with the chemistry. If there is an oxidizer in the core some of these elements can burn. Oxidation of these metals can mean a more durable core material, like ceramic. It could also mean that the fuel is crumbling into sand.

I'm confident the US Navy knows what they are doing when operating this highly enriched cores. The wide range of power demand effectively rules out thorium in the core. What may be feasible is the use of U233, the breeding of the thorium would be done on-shore in a different reactor, and then placed into the core on the warship. Since the process to separate the U235 from the U238 is difficult and expensive there must be a balance struck between the purity of the core along with the price and performance.

Separating U233 from thorium is a nearly trivial process so the decision is less about if it should be taken out and more about if there is a reason to add it back in. Perhaps there are physical, nuclear, and chemical advantages that I am not aware about.

When it comes to longevity I recall that the fuel load carried must last the life of the ship. Submarines have a life span of somewhere between 20 and 30 years. At that point the reactor would have been sufficiently worn, out dated, and irradiated that it would not be feasible to refuel and rebuild for use in another ship. Aircraft carriers used to go through a lengthy refuel and refit process after 25 years at sea so that it would be prepared for another 25 years. This means now a single fuel load is expected to last the active lifespan of the hull, 50 years for the aircraft carrier.

In utility reactors there is a desire to operate them more like the naval warships. fuel them up to run for 30 to 50 years. The difference is that a land based power plant is not constrained by the wear on a hull at sea. A modern nuclear reactor should be able to run 30 years before there is a need to remove spent fuel and replace it with fresh fuel. By lacking the wear from operating at sea this theoretical reactor should be able to be refueled several times to give a safe and efficient lifespan of 150 years.

Without the need to vary the power output like that on a warship a utility power plant can use breeders. That fuel could be reprocessed again and again by removing the wastes and poisons, leaving in the long lived products for destruction by neutron bombardment, and add in fresh thorium.

I hope I'm not alone in this dream.

Another dream I have is that the old nuclear reactors from future warships could be repurposed into civilian work. Perhaps a small utility power plant. Perhaps the power plant would get to go back to sea for another fifty years moving cargo on a civilian ship.

I realize that nuclear powered civilian ships gets all kinds of people upset but if we are going to move heavy cargo we are going to need oil or nuclear. The idea of an oil tanker may become history but people will want to move corn, wheat, bananas, coffee, soybeans, scrap metal, among many other things. Without oil or coal for this then we are left with nuclear.

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PostPosted: Nov 24, 2014 4:25 pm 
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Nuclear power for ships makes all sorts of sense. It's already the most economical option. If the USS Savannah had been operating when the 1970s oil-shock hit, it would not have been closed down, because it would have had lower operating costs even than specialized freighters and passenger ships.

Adams atomic engines and Romawa Ltd. both had extensive web sites on this topic at one time. Rod Adams wanted to use a simplified throttled-pebble-bed system. Basically, when you open the throttle on a Adams gas-cooled reactor, cooling the reactor makes it more reactive from being down in the thermal range. Power increases, etc. The Adams engine would have been closed cycle, probably using nitrogen for a coolant, because Rod was hoping to reuse the design info from combustion-driven turbines.

Romawa had a more radical design. They wanted to use a helium heat-transfer loop from the pebble-bed to an open-cycle gas turbine using air. The big advantage over the Adams engine is that the Romawa engine didn't need a low-temperature heat-exchanger. They would just dump the hot air as exhaust. (Adams counter-claimed that a water-cooled heat-exchanger is not very large and expensive, anyway. Romawa countered that their would work inland, as well...) If the helium transfer loop could transfer the heat, and an air-turbine can work well at those temperatures, it's a better design because almost all successful small pebble-bed reactors have used helium for heat transfer.

I believe that they cross-licensed at one point. Adams held (holds?) the patent on throttled gas-cooled reactors.

I think both business plans were killed by the regulatory hurdles, not by anything technical or safety-related.


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PostPosted: Nov 26, 2014 8:53 am 
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Kurt Sellner wrote:
While the exact enrichment level is secret there are people more informed on the topic than I that have speculated it to be somewhere between 20% and 35%.


I had read more like bomb-grade, 95%. Then recent designs have reduced that. As you say, it is a secret. We could ask Rod Adams (since he was in charge of one of these reactors for a period), but I doubt we would get an answer.


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PostPosted: Nov 27, 2014 12:15 pm 
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AIUI Submarine reactors will still use near bomb grade enrichments because the reactor has to be as small as it physically can be.

Nuclear surface ships are a different matter but supposedly the Charles de Gaulle uses LEU level enrichments to reduce the cost of fueling her.


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