Thorium vehicle will run 100 years on 8 grams of fuel

[OnlinePoker]

There are now over one billion cars traveling roads around the world directly and indirectly costing trillions of dollars in material resources, time and noxious emissions. Imagine all these cars running cleanly for 100 years on just 8 grams of fuel each.

Laser Power Systems (LPS) from Connecticut, USA, is developing a new method of automotive propulsion with one of the most dense materials known in nature: thorium. Because thorium is so dense it has the potential to produce tremendous amounts of heat. The company has been experimenting with small bits of thorium, creating a laser that heats water, produces steam and powers a mini turbine.

http://www.industrytap.com/thorium-fueled-automobile-engine-needs-refueling-once-a-century/15649

[CFLDem]

1. Won't take long for

the oil consortium to buy this up and shut it down if it even hints at working.

[johnd83]

2. Sorry, but bunk

I am a huge supporter of Thorium fueled reactors, but they make a LOT of radiation when in operation. The advantage over Uranium based systems is that the fuel becomes safe in one or two hundred years (vs 10,000 for U235) and Thorium is plentiful. It also doesn't require processing as the most abundant isotope is used. Uranium reactors require enrichment of U235 which is expensive and polluting. The amount of shielding and danger of release in an accident make vehicles powered directly by Thorium completely impractical.

Also, Thorium reactors don't "melt down". They require an outside neutron to transmute Th232 to U233. There is no "chain reaction", meaning that if the outside excitation is removed the system will stop. The reactors are designed in such a way that they are walk away safe and don't require active cooling to prevent reactor failure.

[PamW]

5. 100% WRONG!!

johnd83 states
Also, Thorium reactors don't "melt down". They require an outside neutron to transmute Th232 to U233. There is no "chain reaction", meaning that if the outside excitation is removed the system will stop.

The reaction that transmutes Th-232 to U-233 doesn't give you any energy.

The energy comes from a neutron impact on the U-233 thus created to yield a fission. The fission reaction gives you the energy, but also gives you fission products.

Fission products are radioactive and produce what is called "decay heat". Meltdowns are NOT caused by fission energy. In Three Mile Island and Fukushima, the fission process had stopped LONG before the meltdown. So what caused those meltdowns? The heat energy from the radioactive fission products. If you produce energy, you are causing fissions, and if you are causing fissions, you get fission products, and if you have fission products, and lose your cooling and don't cool them, you get a meltdown.

It's a bit of non-scientific hype that thorium cycle reactors are immune from meltdowns. Online removal of fission products with a liquid fuel reactor, thorium or uranium, can mitigate meltdowns by removing fission products. But just because a reactor runs on a thorium-cycle doesn't make it immune from meltdowns.

Courtesy of my alma mater, the Massachusetts Institute of Technology:

Explanation of Nuclear Reactor Decay Heat

http://mitnse.com/2011/03/16/what-is-decay-heat/

When there is a SCRAM, where all the control rods are inserted and the reactor is shutdown, the fission reactions essentially stop and the power drops drastically to about 7% of full power in 1 second. The power does not drop to zero because of the radioactive isotopes that remain from the prior fissioning of the fuel. These radioactive isotopes, also called fission products, continue to produce various types of radiation as they decay, such as gamma rays, beta particles, and alpha particles. The decay radiation then deposits most of its energy in the fuel, and this is what is referred to as decay heat.

It's all right there. When you SCRAM or shutdown the reactor, the fissions STOP; the reactor is NOT critical.

If you produced nuclear energy from PRIOR fissions, then you have fission products.

If you have fission products; you have decay heat and susceptibility to meltdowns.

PamW

[johnd83]

7. I think you misunderstand my point

In a Uranium reactor there is the risk that if the control rods are damaged or the fuel melts an uncontrolled chain reaction can occur. With Thorium this is not possible because an outside excitation is needed to create the U233. Decay heat still exists, but newer Thorium reactors either use passive cooling or are based on a liquid fluoride core that is not as susceptible to overheating. Newer reactors are actually walk-away safe, the problem with Fukishima was that it was a very old (and poorly done) design that should have been shut down decades ago.

[PamW]

16. 100% WRONG

I just had to explain this to someone else.

It DOES NOT MATTER if the control rods melt or are damaged; the fact that they are in the core is enough.

The action of the control rods does NOT depend on the rods being solid or undamaged.

In fact, because of an effect known as "self-shielding" the rods will have MORE of a negative effect if they are melted and dispersed rather than being solid.

Consider the control poison that is in the center of the rod. What opportunity does that material have to absorb neutrons when it is surrounded by a bunch of other absorber material. Suppose we were to "unroll" the cylindrical control rod like one would a cinnamon roll. Then that center section wouldn't be surrounded and "shielded" from neutrons by the rest of the rod. It could then do a better job of absorbing neutrons.

If the control rod is melted or damaged. the controlling effect does NOT go away; and, if anything; will INCREASE and there will NOT be an uncontrolled chain reaction.

You are also in ERROR about an outside excitation being necessary for a U233 thorium-cycle. You aren't going to get much energy if you have a system that requires a source. For example, a 1 Megawatt reactor like at a University will require about 3.3e+16 fissions / sec. You would need a neutron source that put out 3.3e+16 neutrons / sec or be 3.3e+16 Becquerels. There are NO radioactive sources of that magnitude. Are you considering using an accelerator for your source?

The reactor at Fukushima wasn't poorly done; the support equipment including back-up generators was poorly done.

You don't have to tell me about walk-away safe reactors. I worked with Dr. Till of Argonne National Lab on one of the first "inherently safe" or "walk-away" safe reactors; the IFR. I helped design it.

PamW

[johnd83]

17. The thorium reactors use a particle accelerator

or a uranium core for the neutron source. The accelerator is preferable because it is safer.

http://www.world-nuclear.org/info/Current-and-Future-Generation/Accelerator-driven-Nuclear-Energy/

Also "melt down" to me usually mean the FUEL melts out of its containment into a puddle on the floor. In that state it can potentially continue uncontrolled fission. I guess "melt down" means different things to different people.

[PamW]

20. WRONG AGAIN!!

johnd83,

If the fuel melts into a puddle it CAN NOT go critical. With the low enrichments of fuel in power reactors, the reactor core is RELYING on the heterogeneous lattice of fuel and water to aid criticality. The lattice dimensions are chosen to optimize the following neutron "life". The neutron is born in the fuel, and "leaks" out of the fuel into the water moderator. It slows down in the water moderator, particularly through the resolved resonance region. Only when the neutron is below the resonance region in energy does it re-enter the fuel to cause a fission.

In the region of a few keV to a few hundred keV, Uranium-238 has massive absorption resonances in the absorption cross-section. Log onto Brookhaven's Nuclear Data Center site and plot the absorption cross-section of U-238. If the neutrons slow down in the water, then there's no U-238 atoms around to absorb them parasitically. If the fuel melts, so that you have a fuel / water slurry then the neutrons will slow down in the presence of U-238 and its absorption resonances and will be parasitically absorbed, and it is therefore IMPOSSIBLE for the melted core to go critical. All this crap about melted cores going critical is just that; CRAP. The material mixture in a power reactor REQUIRES a heterogeneous core geometry in order to achieve criticality. ( Remember I used to DESIGN reactors when I worked for Argonne ).

Even in your accelerated-driven throrium reactor, the FUEL region will be where Thorium is transmuted into Uranium-233, and the U-233 is fissioned; so your FUEL will have fission products in it if there is no mechanism to instantly remove them. So even in an accelerator-driven thorium reactor, you will still have fission products in your fuel. When you shutdown the accelerator; you stop the fission energy generation. That's done in a power reactor by dropping the control rods; the fission energy production STOPS. But the reactor is still susceptible to meltdown due to the energy produced by the radioactive decay of the fission products; and the thorium reactor will have the SAME PROBLEM.

In both the Three Mile Island Unit 2 reactor meltdown, and the Fukushima meltdowns, the production of energy via fission STOPPED over an hour before the meltdown started. In TMI, the reactor was sub-critical for 90 minutes and remained unmelted as the coolant pumps cooled the core. The reduction in pressure due to the stuck safety valve caused boiling in the TMI core so that the fluid that was being pumped by the pumps was a two-phase steam / water mixture. The pumps don't like that, and make strange noises. At 90 minutes, the operators turned off the pumps because of those noises; and that is when the meltdown ensued. TMI was totally reversible until the operators shutdown the coolant pumps. In Fukushima, the reactors were shutdown at the time of the quake, and were being cooled by emergency power provided by the diesel-electric generators. When the tsunami broke over the plant an hour later, it flooded out the diesel-electric generators, and swept away their fuel tank which was above ground; and without electric power, the coolant pumps stopped, and hence commenced the Fukushima meltdowns. But in both TMI and Fukushima, the fission power had LONG been STOPPED. It was the power of the decay heat that melted those reactors; and your thorium reactor will have the SAME PROBLEM. If it produces energy, it is producing fissions, and that produces fission products, and those produce decay heat.

PamW

[johnd83]

25. There is plenty of water to moderate neutrons in a damaged reactor

I understand decay heat, and I understand that we don't think there was any additional chain reaction in the most recent accidents. I wish I could share my own (very impressive) credentials but it would instantly give away my identity. I don't see how you can claim that a damaged reactor could never go critical. Is it likely? Not really, but it is certainly very dangerous to assume that. Why else would they have added boron to the water?

Liquid fluoride reactors work on a completely different principle than current generation reactors. The nuclear material is in a liquid state, not rods. This design is much less likely to overheat from decay products.

http://en.wikipedia.org/wiki/Liquid_fluoride_thorium_reactor

[PamW]

29. Reactor Physics 101

johnd83,

Boron is added to the water in a PWR as a chemical "shim". It is used to adjust for the reactivity swing between a freshly fueled cored, and a core that has been burned for some time.

Water isn't the problem; there's plenty of water to moderate neutrons. However, if the core is melted then that water is "contaminated" with U-238 which is the resonance absorber. It's elementary Reactor Physics 101 to show that for a homogenous mixture of reactor fuel, water, and control material that it is IMPOSSIBLE to have a sustained criticality.

For the fuel enrichments used in reactors; you HAVE to have the water moderator to be FREE of U-238 in order to get a criticality. A melted core will have the water contaminated with melted U-238 containing material.

I understand the design of a liquid fuel reactor, and as I mentioned several posts ago; if you have liquid fuel, one can have continuous online removal of fission products to mitigate decay heat. However, that works for BOTH thorium and uranium fuel.

I don't believe you have any impressive credentials until you realize that it's NOT the thorium fuel that results in mitigated decay heat; it is the use of liquid fuel along with continuous online removal of fission products that mitigates decay heat, and that scheme can be used for uranium fuel just as well as thorium.

PamW

[johnd83]

30. The other advantage of thorium is the decay products become inert much faster

You are correct that I am not a nuclear engineer. I work in a different field. However I still find the things you are saying is largely correct but simplified. To say it is impossible is a huge assumption.

[PamW]

35. Actually it is NOT a huge assumption...

johnd83,

Actually it is NOT a huge assumption. It's one of the very first things taught in a "reactor physics" course for nuclear engineers.

Here is an excerpt from a text. From page 2 of:

http://www.eolss.net/Sample-Chapters/C08/E3-06-01-04.pdf

The reactor design also separates the fuel from the neutron moderator so that during the moderating or slowing process the neutrons are away from the fuel and less likely to be absorbed by the strong resonance absorption peaks of the non-fissile fuel (U-238).

When you do this calculation, you can calculate what is called the "k-infinity" of the material. The "k-infinity" would be the neutron multiplication constant for a reactor which was infinitely big. If the "k-infinity" of a material is less than 1; then even if you had an infinitely large reactor; it would not go critical.

This is what happens if you mix low-enriched uranium fuel, such as used in LWR reactors, with the appropriate fractions of water, structural steel, control poison.... That would be the composition of your melted reactor core. One can calculate the "k-infinity" of this mixture and it will be less than unity (1). That means that even if you had an infinitely large mass of this material it can't go critical.

If an infinitely large mass of material can't go critical; then neither can a finite-sized mass because the finite sized mass has an addition neutron loss mechanism which is neutrons escaping from the surface of the mass.

The reason the "k-infinity" is less than 1 for the above mixture is due to the parasitic absorption of neutrons by U-238 as they are slowing down in the resonance region of energy.

If you have a heterogeneous lattice with fuel rods immersed in water, when the neutrons slow down passed the resonance region of energy, they are in the water, and there's NO U-238 in the water to absorb them.

PamW

[johnd83]

36. I still don't understand your point

There is a whole section on criticality incidents in non-operating reactors and quite a bit of worry by the IAEA that it might happen in Fukushima. Will it explode like a bomb? Of course not but it is still dangerous.

http://en.wikipedia.org/wiki/Criticality_accident

Yes, it is wikipedia, if you don't like wikipedia look at the works cited.

http://en.wikipedia.org/wiki/Criticality_accident#Notes

[PamW]

39. Criticality in non-operating - but NOT in melted.

johnd83,

In order to know what a reactor is going to do, and whether it is going to be critical or not; you need to know the neutron density function which tells you where the neutrons are and what they are doing, where they are going...

What is the dimensionality of this function; how many variables do you have to tell me before I can tell you how many neutrons there are doing whatever...

The dimensionality is 7. First you have to tell me the position and in 3-D that takes 3 variables, x, y, z. Then you need to tell me the direction which takes 2 vatriables, angles theta and phi ( just like a telescope; to define a direction you need right ascension and declination ). Then you need to tell me the energy of the neutrons you are interested in, and then the time you are interested in. That's a total of 7 variables. So it's a complicated function.

We can simplify this. First, we can say that we are interested in solutions where the reactions are self-sustaining and at constant power, i.e "critical". That leaves out the time variable; one solution for all time.

We were at this place in 1942, when an extremely clever physicist Enrico Fermi took the next step. He said consider an infinitely large mass of material. If the mass is infinite; then all points are the same, and all directions are the same. There can't be a dependency on x, y, z, theta, or phi. In this case, the equation that tells us the neutron distribution, the neutron transport equation is a function of a single variable E, the energy.

http://en.wikipedia.org/wiki/Neutron_transport

Note that if the mass is infinite there can be no loss due to neutrons leaking out of the core - the core is infinite. So a finite core has an additional neutron loss mechanism, namely leakage out of the core. Therefore, if a mixture of materials can not sustain crititicality in an infinite core, then it can't go critical in a finite geometry because that finite geometry has an additional loss mechanism.

So we come down to a neutrons transport equation in a single variable, the neutron energy, E. We solve that to determine if the mixture of materials can go critical.

If you go to the website of the nuclear data group at Brookhaven National Lab, you can plot the capture cross-section ( the propensity of a material to absorb neutrons parasitically ) for U-238 as a function of neutron energy. This is also the (n,gamma) cross-section because the impacted U-238 de-excites by emitting a gamma ray:

http://www.nndc.bnl.gov/sigma/index.jsp?as=238&lib=endfb7.1&nsub=10

Choose (n,gamma) plot from the list at right.

See all those "spikes" in the neutron cross section? They indicate that U-238 at energies from about 10 eV to 10,000 eV has a large propensity to capture a neutron parasitically, so it can't slow down to low energy and cause a fission. Neutrons are born in fissions at energies around 1 MeV to 2 MeV ( million electron volts ). The fission cross section of U-235 ( or U-233 ) is highest at low energies, so you need to slow neutrons down. The problem is how is the neutron going to slow down in the presence of U-238 which will be present in a homogeneous melted mixture like corium, and escape getting absorbed parasitically by the U-238 resonances as those peaks are called. The answer is: they CAN'T. You can show with mathematical certainty, not "assumptions" by solving the infinite medium transport equation that the mixture can NOT go critical. MATHEMATICAL CERTAINTY!!.

Since an infinite medium of corium can't go critical; then a finite mass of corium can't go critical.

But if that is the case; how does the reactor work to begin with.

When the reactor is intact, we don't have a mixture all melted together. We have a lattice - an array of rods surrounded by water.

Neutrons are born in fissions, which is in the fuel; so neutrons are born in the fuel rods. However, the fast newborn neutrons travel out of the rods and enter the water surrounding the rods. That's where they encounter the hydrogen atoms of the water. Neutrons slow down quite quickly in collisions with hydrogen atoms since the hydrogen nucleus, the proton, has about the same mass as the neutron.

Here's the important part. When the neutrons are slowing down through that energy range from 10 eV to 10,000 eV; they are in the water region. There's no U-238 in the water. That's the important part. There's no U-238 in the water So when the neutron has an energy in the resonance range of 10 eV to 10,000 eV and it would be susceptible to parasitic capture by U-238; there's no U-238 around. So the neutrons are not captured. They live on to slow to even lower energies that are in thermal equilibrium with the water at about 0.025 eV. Then the low energy or thermal neutron finds its way back into the fuel rod with the U-235 and U-238. However, now, it's energy is 0.025 eV and NOT in the "deadly" range of 10 eV to 10,000 eV. So U-238 "leaves the neutron alone"; and it can cause a fission on U-235. That's what keeps the reactor going.

That heterogeous lattice where there is separation between water moderator and parasitic resonance capture by U-238 is ALL IMPORTANT

If the rods are intact and unmelted; you have separation between water and U-238. If the U-238 is melted; then you have a mixture of U-238 and water.

Without that separation of water and U-238, the mathematics of the neutron transport equation MATHEMATICALLY PROVES there can't be a criticality.

That doesn't happen by accident; the reactor is DESIGNED that way. That is why power reactors use enrichments of 3% or 4%.

University research reactors use enrichments of 20%, and some used to go as high as >90% enrichment. We aren't worried about these low power reactors melting down. However, the big power reactors, we are worried about that. So the design decision is made to have low enrichments so that should there be a meltdown; the resulting corium can NOT sustain criticality.

As far as criticality accidents; yes there have been those accidents; but the core was NOT MELTED at the time of the accident. The core may have melted as a result of the accident; but was NOT melted during the criticality. Additionally, lots of those accidents were in nuclear weapons cores, and research reactors which don't have the low enrichment that power reactors do.

In terms of criticality accidents in US-style low enrichment power reactors; there have been NONE.

PamW

[johnd83]

38. You are 100% WRONG

About Fukushima not being poorly designed:

The warnings were stark and issued repeatedly as far back as 1972: If the cooling systems ever failed at a “Mark 1” nuclear reactor, the primary containment vessel surrounding the reactor would probably burst as the fuel rods inside overheated. Dangerous radiation would spew into the environment.

http://www.nytimes.com/2011/03/16/world/asia/16contain.html?_r=0

Everything you have said in this thread has not been quite correct either. I have no idea what your angle is.

[PamW]

40. 100% WRONG!!!

johnd83,

I have NO ANGLE, and EVERYTHING I have said is 100% CORRECT

You have to separate the claims of anti-nuke "experts" and true scientist experts like myself. It's not easy to know the difference. GE had some disgruntled employees that made wildly INACCURATE claims about the GE reactors that real scientist know about and discredit. However, that doesn't stop the media from presenting those people as "experts". ( I find Lochbaum not credible in the slightest. ) Additionally, it is a judgement call. There are some issues with Boeing 737 airliners that I don't like; but are they bad enough to ground all 737s? Also there have been modifications to the Mark I in the USA to CORRECT some of the issues raised. US Mark I reactor were REQUIRED to implement those changes; like a hardened vent to vent off hydrogen gas to prevent explosions like at Fukushima. The Japanese plants didn't make those modifications, and weren't required to.

I said the GE reactor itself and its containment is well designed for what it is supposed to do.

In regards to Fukushima, I said the support equipment was badly designed. The reactor and containment can only work as well as the support equipment that they rely on. An example is the diesel generator backup power. The Fukushima reactors had the diesels in a non-watertight basement; and the fuel tank was open and above ground. NEITHER would be legal in the USA. The diesels have to be protected from flooding, as must the fuel tanks.

I first heard about this back in 1978 when I attended the conference of the American Nuclear Society in Washington DC. I was still a doctoral student at the time. I was speaking to a young GE engineer at the conference. As I was looking to begin my own career, I asked this young engineer what the most difficult part of his job was. He stated that it was "...getting the customer to listen to me." He was on assignment in Japan as GE was building a new reactor unit for TEPCO. I asked for an example. He told me he recommended burying the fuel tank so that it would not be washed away by a tsunami. I said that sounded reasonable, and inquired why TEPCO would balk at that. He said, "Probably because that would mean they would have to bury the tanks for the other 5 reactors at the site".

It turned out he was assigned to the building of Fukushima Diachi Unit 6.

So I've known since 1978 that if a tsunami were to hit Fukushima; that the diesel fuel tanks were unprotected. The owner TEPCO was warned; but REFUSED to follow the advice of the reactor vendor GE.

In the USA, the NRC would NEVER have allowed such a plant to operate; it would be in VIOLATION of NRC rules.

The real villain here is NOT nuclear power technology, and it's NOT GE ( although some like to disparage GE for what reason I don't know ); but TEPCO and their penny-pinching on a nuclear installation, and the LAX oversight of the Japanese regulators is certainly has my highest opprobrium.

I'm unapologetically pro-nuke; and TEPCO and their regulators SOILED a very respectable safety record for GE reactors. So I'm not going to "cover-up" anything for the likes of TEPCO and their regulators. I'm MAD at them.

But at the same time; there's a LOT of dishonest and loose MISINFORMATION about this; like criticality in pools of corium; and I won't allow bad science to go unchallenged.

PamW

[Warpy]

27. Yes, I was going to remark about the five ton engine it would take

4.9 tons of it lead shielding. Thorium would be superior as a stopgap nuclear fuel but it still creates radiation and a tremendous amount of radioactive garbage once the plant has reached shutdown time.

I just can't see it parceled out to a billion cars, some of which will eventually be junkers leaking radiation.

[longship]

3. I want a nuclear vacuum cleaner!

Just kidding.

They ought to develop this technology for deep space probes. We already use Pu238, but the half-life limits the number of years it generates electricity. Still, Voyager is still going, although they've had to power down many of the scientific instruments. Nevertheless, it's like a Timex watch. It keeps on ticking.

The Mars Curiosity rover uses Pu238, too, which is why it can work at night and through Mars winter. Solar panels cannot do that.

New nuclear technologies are great for planetary science, and hopefully for interstellar science. Science is the real deal.

[johnd83]

4. Those are different technologies

Those technologies are called "radioisotope thermal generators". They work off the natural decay of the material. Atoms like plutonium and uranium naturally decay over time and release heat and radiation. This decay is normally slow and doesn't generate much energy. These RTG devices probably wouldn't power a coffee pot because they are so low power. The more recent missions including the Curiosity rover use a standardized RTG:

http://en.wikipedia.org/wiki/Multi-Mission_Radioisotope_Thermoelectric_Generator

A spaced-based plutonium nuclear reactor was supposed to be developed in the mid-2000s for use on the Jupiter Icy Moons Orbiter but was killed by the Bush administration.

http://en.wikipedia.org/wiki/Jupiter_Icy_Moons_Orbiter

The Russians however launched a plutonium based space reactor in the 80s (I think it was the 80s, don't quote me on that). Thorium has many more moving parts compared to a plutonium reactor so isn't really well suited for space where nuclear waste management isn't really as big an issue. There is so much natural radiation outside the magnetic shield of the Earth the extra radiation from a small reactor is negligible.

[longship]

6. Yup! They are talking about a Sterling engine now.

But moving parts in space are a bad idea. Consider the Kepler telescope. They say that the Pu238 will last longer with the Sterling heat engine. But the thermocouple power of the current RTG's has no moving parts and space is a very tough environment for moving parts.

And Voyager is still going, and will likely go for about another decade, albeit at lower capability. That's better than no capability when the Sterling piston siezes.

[johnd83]

8. The Voyager spacecraft only hase a few hundred watts of power

The new space based reactors will have kilowatts of power. Spacecraft already have lots of spinning parts in the reaction control wheels/gyro so it isn't exactly unheard of.

"And Voyager is still going, and will likely go for about another decade, albeit at lower capability. That's better than no capability when the Sterling piston siezes."

If all you want is a camera, some basic sensors, and a very low bandwidth comm system that is fine, but if you want mapping radar and an ion propulsion system an RTG isn't going to be anywhere near enough power.

[longship]

9. Voyager has shut down its cameras. Long ago.

And the reaction wheels on the Kepler space telescope failed in four years. (Two of the four, enough to terminate the project.)

Moving parts are not good in space.

And you're right, ion drive takes a bit of energy. It's a cool way to do things. But it still has to obey the rocket equations and when you're out of fuel, you're out of fuel.

That's why people are looking at solar sails and interstellar hydrogen ramjets. I like the latter one. Cool stuff. But that's for another century, probably.

Alas, no warp drives, probably ever. I am sorry Commander Scott.

But captain! The Sterling engine canno take it much longer!

[johnd83]

10. I think for the next 100 years or so it is going to be mostly manned/unmanned craft

within the solar system. The VASIMR style ion drive powered by a nuclear reactor is the most likely option for those projects. If the fusion systems being developed by Lockheed pan out we may wind up going interstellar sooner than I thought possible. They said today that the closest earth-like planet is 12 light years away so that is surprisingly within reach.

[longship]

11. Fusion, unfortunately, is probably a long way off.

The trouble is that you have to put so much energy in to get anything out, that it's fucking difficult. Of course, once you have crossed the barrier, you get a lot of energy out. They don't call it the Strong Nuclear Force for nothing.

The issue is complexity. One wants simple things in space, especially when one doesn't have a Montgomery Scott on board (who can perform miracles because he always multiplies his time estimates by four).

That's why solar sails and ramjets are attractive. BTW, the Planetary Society has a solar sail about ready to test.

[johnd83]

12. Fusion power is not really that far off

current technology is nearly at break-even levels. Computer modeling technologies have allowed a different magnetic containment geometry and more efficient microwave plasma generators have allowed for a design they claim can be ready in 5 years.

http://www.popsci.com/technology/article/2013-02/fusion-power-could-happen-sooner-you-think

[longship]

13. But the technology is not yet practical.

The national ignition facility at Lawrence-Livermore is very far, far away from practicality. It's only the most powerful LASER on the planet. I do not call that practical. Plus, they are no where close to being able to generating enough energy to be useful for practical power generation. It's not enough to gain energy by imploding a single pellet of fuel. One has to do it how many times a second before it pays back? And that ignores the cost of making the fuel pellets.

Fusion is still a long way off. We are making headway. But I wouldn't hold my breath. It's going to be a long road.

Sorry.

[johnd83]

14. The technology I linked to is a magnetic containment plasma system

not a laser system. It uses the same concepts as a Tokamak reactor but has a very different geometry that allows it to fit on an oversize trailer for transport from the factory to the power plant. This means they can be built in bulk.

[longship]

15. Yes! And I've heard of another in Europe.

Can't remember the name, but they're doing the magnetic pinch there as well. It's got a catchy name, though (always a good sign... Well, maybe).

I have zero hope for the national ignition facility any time soon, though.

Thanks for reminding me of that. These old brain cells need exercising. Sometimes I get such a thing here at DU.

[PamW]

22. Correct.

Although NIF is getting closer and closer to ignition; the NIF is not a power production facility even when it achieves ignition.

The NIF lasers are glass lasers; the lasing medium is a flash-lamped pumped slab of glass doped with neodynium:

https://lasers.llnl.gov/about/nif/how_nif_works/amplifiers.php

NIF's amplifiers use 3,072 42-kilogram neodymium-doped phosphate glass slabs, measuring 3.4 by 46 by 81 centimeters and set on edge at a specific angle, known as Brewster's angle, so that the laser beams have very low reflective losses while propagating through the glass.

After the laser fires, it takes many hours to cool the whole thing down before one can reset for another shot. So any power producing plant will NOT use glass-laser technology. However, LLNL has developed a number of high-power solid state lasers that look promising:

https://www.llnl.gov/str/Payne.html

https://lasers.llnl.gov/programs/psa/directed_energy/sshcl.php

LLNL has a number of potential concepts for fusion power plants designed under a program called "LIFE":

https://life.llnl.gov/

The good thing about science is that it is true, whether or not you believe in it.
--Neil deGrasse Tyson

PamW

[bananas]

18. Fusion propulsion is a lot easier than electricity generation

VASIMR is basically a fusion engine that doesn't get hot enough for fusion - it still provides lots of thrust.

A fusion engine doesn't have to generate more energy than you put in, it just has to generate more energy than a non-fusion ion engine.

http://www.space.com/23084-mars-exploration-nuclear-fusion-rocket.html

Quick Fusion-Powered Trips to Mars No Fantasy, Scientists Say
By Mike Wall, Senior Writer | October 07, 2013 06:50am ET

<snip>

The team's fusion-driven rocket would rely on a plasma created using deuterium and tritium, "heavy" isotopes of hydrogen. ("Normal" hydrogen contains no neutrons, while deuterium has one and tritium contains two.)

Bubbles of this plasma would be injected into a chamber, where a magnetic field would collapse metal rings around them, briefly compressing the bubbles into a fusion state. The energy released by the fusion reactions would vaporize and ionize the metal, which would be accelerated out the back of the spacecraft through a nozzle, creating thrust.

Solar panels would generate the energy necessary onboard the spacecraft to put all of this in motion.

<snip>

Slough and his team are building hardware and conducting experiments to help bring the technology closer to implementation. They hope to check off a big milestone sometime in 2014.

"We're in the lab, we're building the coils, we're showing the scaling and we'll be producing the neutrons within the next year to show that fusion is occurring, and it's occurring at the scales required to build a fusion-driven rocket," Pancotti said.

[longship]

19. If you're going to use it for propulsion, yes.

The rocket equation is a bitch. That's why ion drive is so cool, and why this fusion alternative may also be. The velocity of the ejecta can make for a big kick. LASER propulsion would be cool, too, as it would be the speed of light.

Of course, these would all be low thrust technologies (i.e., low mass particles instead of huge masses of burning fuel).

But they are nonetheless great because they trade off thrust for very high efficiency.

I believe the ISS has an ion drive, or it has been talked about.

Cool stuff!

[PamW]

21. Not quite...

longship states
LASER propulsion would be cool, too, as it would be the speed of light.

The laser travels at the speed of light; but not the vehicle.

What is important is not the SPEED of the rocket "exhaust" but its MOMENTUM

The momentum equations are different for photons and matter. So you don't get light velocities

PamW

[longship]

23. I never said that one would get to light speeds.

But, no matter. The applicable Newton law is all about momentum. True. Light has no rest mass, but light speed is as large a velocity one can have.

Again, it's all about the rocket equation and how to most efficiently move a rocket through space. That's why ion drives work so well in spite of their low thrust. The ions are booking when they exit the nozzle. I thought that LASERs might provide a similar mechanism.

[PamW]

41. Look at momentum per unit energy

longship,

For a material; momentum p = mv ( product of mass and velocity ), while energy is 1/2 mv^2 ( one-half mass times velocity squared ).

For photons; the relation is E = pc ( Energy = momentum time c ).

So compute the amount of momentum ( which is what you want ) per unit energy ( which is what you pay for ).

For a material; p/E = (mv) / (1/2 mv^2 ) = 2/v

For photons; p/E = p / (pc) = 1 / c

Since 2/v is always greater than 1/c for v < c; you get more momentum per unit energy with material than you get with photons.

PamW

[longship]

42. Thanks.

I was shooting from the hip. It's been decades since I studied physics. (BS)

I stand corrected.

[muriel_volestrangler]

43. That's if your concern is momentum per unit energy; but often it's not, in rockets

and that's why ion drives, which have a high exhaust velocity (and thus low 2/v ) are useful in some situations. They're inefficient in terms of energy use; but very efficient in terms of propellant mass. And a drive using photon momentum would mean no propellant has to be carried at all.

[PamW]

44. Let's examine TOTAL mass..

muriel,

So let's examine the Total mass needed for a given amount of momentum.

Let m = reaction mass. Since p = mv; the reaction mass needed for momentum p is m = p/v

Let M = fuel mass. Let "e" = energy delivered to reaction mass per unit mass of fuel.

So for momentum p; the energy needed is p / ( 2/v ) = pv / 2

So the amount of fuel mass is pv / (2e); where "e" is the specific energy of the fuel ( including efficiency )

So the total amount of mass is the sum of reaction mass and fuel mass = p/v + pv/(2e)

So total mass per unit momentum is 1/v + v/(2e)

Put some realistic numbers in for "e" to see which of the two terms dominates; and unless you use something like nuclear power with high specific energy as your energy source; the fuel mass will dominate.

Let's also see how much momentum we can get from firing a large laser. The world's most powerful laser is the one at the National Ignition Facility in Livermore. The "footprint" of the laser is the size of about 3 football fields. A shot on NIF can produce up to 1.8 megajoules.

So with E = pc or p = E/c we have 1.8 MJ / c = 1.8e+06 km-m^2/s^2 / 3.0e+08 m/s = 6.0e-03 km-m/s

So there really isn't much danger that NIF is going to break loose from its footings with a puny reaction like that.

PamW

[muriel_volestrangler]

45. Well, yes, that's the point - you use nuclear power, or solar (ie external)

The point is that chemical reactions aren't that energetic.

There are proposals to use photon momentum:

https://en.wikipedia.org/wiki/Laser_propulsion#Photonic_Laser_Thruster_.28PLT.29
https://en.wikipedia.org/wiki/Solar_sail

[FogerRox]

46. IF Polywell Fusion works VASIMIR is DOA

Proton Boron 11 fuel, Mars in 35 days, Titan in 76. And a P-B11 Polywell would be nothing but a generator of electricity anyway.....

[muriel_volestrangler]

24. Does anyone have the faintest idea what process is being claimed here?

I have no idea why firing a laser at thorium would release huge amounts of energy, allowing you to power the laser to continue to fire it, and push the car too. Neither does this guy, who tried some calculations just to justify the '8 grams' claim:

Uranium in a reactor produces about 20 terajoules of energy per kilogram. For comparison, gasoline gives you about 48 megajoules per kilogram. That means uranium gives us about 425,000 more power per kilogram than gas. Let’s assume thorium will give us roughly the same ratio. That means one gram of thorium would be like 425 kg of gas. Gas has a density of about 2.7 kg per US gallon, so that 425 kg of gas is equivalent to 156 gallons.

That’s way short of Stevens’s claim of 1 gm of thorium being equivalent to 7,500 gallons of gas. For that to be true, his laser-induced power output has to be fifty times more energy efficient than nuclear fission. That is an extraordinary claim, to put it mildly, and he’s offered no proof and precious few details.

Looking through his other claims, it sounds as if he glued together actual science together as if making a collage for kindergarten, regardless of whether the results made sense or not. You could in theory make an actual thorium laser, though that’s not what he’s doing. You can use a particle accelerator to drive a nuclear reaction by knocking neutrons out of other particles, though again that’s not what Stevens is doing despite him adding “accelerator-driven” to the description of his process. You can even induce nuclear reactions using super-powerful lasers, but Stevens says he’s not inducing fission.

So to sum up: Stevens isn’t claiming to have made a nuclear-powered car. He’s claiming to have made a steam-powered car where the steam is heated up when he shines a laser on thorium. I don’t know of any physical process that would let you get more heat energy out of the thorium than you’d spend on making the laser go. For his process to be so awesome that it would power a car for some 200,000 miles on a single gram of thorium, he’d have had to come up with something that’s fifty times more powerful than a nuclear reactor. And he hasn’t released any papers, only press releases. That’s 3 out of 3 red flags for the research not being real.

http://granades.com/2011/09/16/in-which-i-use-scientific-reasoning-to-doubt-the-thorium-powered-car/

[johnd83]

26. I didn't get that either

but it is so far down the list of bad claims I didn't really worry about it.

[arcane1]

28. "And he hasn’t released any papers, only press releases."

To me, that's all I need to know, to know that it's bullshit.

Reminds me of that kook in the 90's who claimed he invented a car that runs for some absurdly large number of miles on a single flashlight battery.

[bananas]

33. I'll try to post on it later - basically, you can increase decay rate by jiggling it with a laser

It's not fission, it's accelerated decay, a laser at a resonant frequency makes the nucleus vibrate more and decay faster.
I forgot the technical terms, if I'm not too busy I'll try to post some stuff later.

I could swear I posted something about it some time ago, but can't find it on DU, and when I search off DU, all I see is weird creationist crap.

[bananas]

34. Finally found a somewhat relevant hit

http://arxiv.org/abs/1112.6276

Accelerated alpha-decay of 232U isotope achieved by exposure of its aqueous solution with gold nanoparticles to laser radiation

A.V. Simakin, G.A. Shafeev
(Submitted on 29 Dec 2011)

Experimental results are presented on laser-induced accelerated alpha-decay of Uranium-232 nuclei under laser exposure of Au nanoparticles in aqueous solutions of its salt. It is demonstrated that the decrease of alpha-activity strongly depends on the peak intensity of the laser radiation in the liquid and is highest at several terawatt per square centimeter. The decrease of alpha-activity of the exposed solutions is accompanied by the deviation of gamma-activities of daughter nuclides of Uranium-232 from their equilibrium values. Possible mechanisms of the laser influence on the alpha-activity are discussed on the basis of the amplification of the electric field of laser wave on metallic nanoparticles.

[muriel_volestrangler]

37. Thanks - that gives us a theory that the laser is relevant

So it presumably speeds up the decay from Th-232 - https://en.wikipedia.org/wiki/Decay_chain#Thorium_series .

However, even if you could use a laser to get that to happen as fast as you want (Th-232's half life is 14 billion years, so it's got to speed up a lot ...), that says the total energy released from the series is 42.6 MeV.

42.6 MeV = 6.83 e-12 J
a Th232 atom weighs 232 * 1.66e-27 kg/AMU = 3.85 e-25 kg
So that's an energy density of 1.77 e13 J/kg = 17.7 terajoules/kg - about the same as the 20 TJ/kg in the post above for uranium. And he thought the claim was for something 50 times more energetic. Though 400g of thorium for a 100 years wouldn't be too bad, I suppose. More calculation seems to show he's claiming about a tenth of the mass of the thorium would be converted to energy.

I still don't think for a moment the LPS guy has even attempted to do what the scientists who wrote the paper you quote have done. His website - http://www.laserpowersystems.com/ - appears to steal almost random web content from other sites and put it in a frame. I can't imagine why anyone has bothered to repeat what he claims, if they've seen that.

[bananas]

48. Oh, I agree, it's as credible as his "USEING HELYXZION TECHNOLOGY WE CAN CURE “ALL” DISEASE"

from post #3 in http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=115x310925

That's probably one of the funniest threads ever, complete with skits from Rowan and Martin's Laugh-In.

[kristopher]

49. I forgot that one.

Thanks for hearty chuckle.

[FogerRox]

47. Not the faintest.

[NNadir]

31. It won't work, period.

Nuclear energy is the best form of energy ever developed, but this particular scheme has nothing to do with serious nuclear technology.

[CRH]

32. Why, Are we still thinking in individual cars, individual propulsion systems, ...

when the problem is global, and collective? Sorry, but your scale is less than relevant.