Tokamak...Hidden Dangers?

Originally posted by Edrick


In a Tokamak, this is accomplished through Thermodynamic Effect. (Hot atoms move faster than cold atoms*BANG*)

Therefore, the Reaction inside the chamber is actually closer to vacuum than it is to Atmospheric Pressure (14.7psia, or 101Kpa if you prefer.)

-Edrick

Just to clarify, you are stating that the overall pressure is less then atmospheric? Because I could hardly see how one can idealize the reaction chaimber as having a uniform pressure throughout. Would not the pressure/density of the plasma be somewhat high in magnitude towards the reletive "center" of the chaimber (cross sectional center, you know what i mean)

Oh, and would not the use of uranium as fuel just turn into something similar to our dependence upon fossil fuels. With few controling the majority of the resource. Plus, lets face it, something as heavy as uranium isnt exactly the most abundant resorce up here on the surface of the planet. I just see another pickle passed on to another generation.

Oh, and would not the use of uranium as fuel just turn into something similar to our dependence upon fossil fuels. With few controling the majority of the resource. Plus, lets face it, something as heavy as uranium isnt exactly the most abundant resorce up here on the surface of the planet. I just see another pickle passed on to another generation.

Uranium is about 99% Uranium-238 and about 0.7% Uranium-235. Our current slow neutron (thermal) reactors use mostly use Uranium-235 as a fuel, so the Uranium has to be enriched to around 5% Uranium-235, the remainder of the fuel being Uranium-238. In the core, Uranium-235 is fissioned creates heat energy (which can be converted into electrical energy) and excess neutrons, these hit the Uranium-238, forming Plutonium-239 which can also be fissioned to create energy. The problem is enriching Uranium discards a whole lot of Uranium-238, and not enough excess neutrons are created to convert enough Uranium-238 into Plutonium-239 at a rate which matches the rate at which the fuel is consumed. The fuel then is discarded when it runs out of fuel or becomes too damaged from the intense radiation.

If you change the coolant to a gas, or liquid metal like Sodium and use fast neutrons (some of these reactors use a molten salt coolant and retain thermal neutrons) then it becomes possible to have higher temperatures which increases thermodynamic efficiency from 35%, to around 45%. And Plutonium-239 can be now be created from Uranium-238 at a rate which matches or exceeds the rate at which the Plutnoim-239 and/or Uranium-235 is burned. This kind of reactor is known as a breeder. It's the closest thing to a perpetual motion machine that is probably possible - it converts materials that are not fuel, into fuel. The end result is a reactor that utilizes Uranium around 150 times more efficiently that current reactors, apart from the starting charge to get the reaction started no enrichment is required (recycled nuclear waste can provide the starting charge and the Uranium-238...), nuclear waste now becomes the fuel, and the waste from this reactor is only more radioactive than Uranium ore for a few hundred years. It also becomes viable to use Thorium instead of Uranium-238, and it becomes economical to mine lower grade ores (or seawater). Rule of thumb with minerals is doubling of price leads to ten fold increase in reserves. Uranium now makes up 2%-4% the cost of nuclear power, this is 150 times as efficient. You do the math.





Each barrel is about 60 million megawatt hours.

Uranium itself is about as common as tin, and Uranium and Thorium are about as common as Lead. Not exactly rare. 1 gigawatt-year needs about 1000kg of Uranium or Thorium. I am not worried that we will run out of either if utilized in this way, because it will happen thousands of years into the future (perhaps millions of years) by which time humanity will either be dead, or we will of mastered fusion, or ZPE or something. The fuel cycle is generally significantly more proliferation resistant than current reactors, but involves production of either Plutonium or Uranium-233 so some issues with the sale of the technology to countries such as Iran may still occur. But those cases are a tiny minority. Also, one reactor design (denatured molten salt reactor) makes it practically impossible to use any part of the fuel cycle for weapons - if we developed this technology we could offer it to Iran as an alternative (or Russia could sell them it), then Iran could fuel it themselves because enrichment is no longer required (the majority of issues with Iran regard enrichment not the Bushehr NPP itself) and only a very small amout of Uranium is required (1000kg per gigawatt-year). There's no way to control the supply of unenriched Uranium either... there's guides on the web on how to make metallic Uranium (there's a guide somewhere in there).

We have ice on several moons in the solar system.... and we could even set up Giant Magnetic Bussard Collectors in Gravitational Lagrange orbit around the earth to soak up the solar wind.

Feed it into a fusion reactor... *BAM*

Well.. that might not happen for some time now.... there's also a ton of Thorium on the moon. We know this because it's easy to detect using spectroscopy.


(3:05 onwards... i lol'd)

I think fusion is great, but see new nuclear fission as a more achievable goal in the next few decades while retaining many of the advantages fusion promises. ITER is supposed to cost $20 billion... the technology I'm talking about would cost around 600-1000 million to develop and maybe 2 billion to build a 300 megawatt demonstration plant which can then sell electricity to the grid to recoup the investment.

reply to post by C0bzz


I just want to say thankyou. That was an awesome response.

Well can I ask one question?

Given the set up if the off switch is tripped how long would it take for the entire machine to either shut down or power down to safe levels? That to me is a critical problem.

Sorry I have forgotten most of my "A" level physics.

Rgds
T

reply to post by LeeTheDestroyer

Just to clarify, you are stating that the overall pressure is less then atmospheric? Because I could hardly see how one can idealize the reaction chaimber as having a uniform pressure throughout.
Would not the pressure/density of the plasma be somewhat high in magnitude towards the reletive "center" of the chaimber (cross sectional center, you know what i mean)

Well, if you want to get SUPER TECHNICAL, then yes... the pressure in the chamber while it is firing is greater than the initial vacuum condition.


If you would like, we could calculate the overall pressure per unit area that each atom of hydrogen contains in velocity and mass and impact area.

We could extrapolate this into a near uniform 3 dimensional pressure gradient map that plots the pressure in a given area (say... per cubic centimeter) and we would see that the Plasma Itself is of slightly higher pressure than the area near the walls of the chamber.


Since the Chamber contained as close to NOTHING as our understanding of vacuum pump systems would allow before the hydrogen plasma was injected into the chamber.

The Hydrogen is in a Plasma State, which means (among other things) that it flows along magnetic field lines, as OPPOSED to becoming Uniformly distributed inside its container, as one would expect of a GAS operating under normal conditions.


Plasma is not a "Gas" It conducts electricity freakishly well, and flows PRECISELY along magnetic lines of force.


[atsimg]http://files.abovetopsecret.com/images/member/242cf3449fd4.gif[/atsimg]

The Chamber is constructed in such a way, that the magnetic field forms a "Surface layer" on the inside of the Chamber.

The Lines of force never intersect the chamber walls.

Since the Plasma does not actually TOUCH the walls of the reaction chamber, there is no path through which heat can be CONDUCTED.

Heat energy can only be Radiated Away....

[atsimg]http://files.abovetopsecret.com/images/member/4b892a299992.jpg[/atsimg]

a Steady supply of EM radiation (Probably near Microwave) is pumped into the Plasma.


Since it cannot shed heat as fast as the heat energy is fed into it.... it increases in temperature.


What this means, from a Logistical standpoint... is that each individual Hydrogen atom is moving Faster.

Thus, the overall chance that a hydrogen atom will contain enough energy to smash into another hydrogen atom with enough force to cause them to FUSE is greater than if it were just a gas at room temperature.

This is the mechanism that the Fusion reaction chamber employs to "Combust" the Fuel...


However, the amount of air contained in a spheroid of that size is much greater than the total mass of hydrogen fuel within the reaction chamber.

-Edrick

reply to post by tiger5

Well can I ask one question?

Given the set up if the off switch is tripped how long would it take for the entire machine to either shut down or power down to safe levels? That to me is a critical problem.

Sorry I have forgotten most of my "A" level physics.

Er, while it is Firing.... if you just Cut the Power Feed to the main magnetic coils, the whole assembly would heat up.

It would probably destroy most of the reactor.

Although, it would probably be designed with an emergency pressure release manifold that would vents directly to the atmosphere.

You would get a pretty loud flame shooting up into the sky for a few seconds... then some little pops....

And then you would have to rebuild the reactor chamber.

It's Just a little bit of Hydrogen.

Although it is VERY HOT.

-Edrick

reply to post by Edrick


So, What happens if the plasma form of the hydrogen contacts the surface of it containment vessel? Other than the extreme high temperature (and associated damage), would the plasma (on a molecular level) form "ionic" bonds with the continment material, and effectively vaporize its container?

What I really want to know is How does plama interact with other states of matter

(speculation)

reply to post by LeeTheDestroyer

So, What happens if the plasma form of the hydrogen contacts the surface of it containment vessel?

Well, on the One Hand, you got Melty....

So, lets say that the interior of the reaction chamber itself (we are measuring the total mass of the surface layer of the interior of the assembly...) has a mass of approximately "Steel" (7.85 grams per cm^3)

So, if the chamber is a 3 meters sphere, and the interior mass we are measuring is 1/2 of a centimeter thick... (.005 meters)

That would be:

((4/3)*Pi*((r+.001)^2)) - ((4/3)*Pi*(r^2))

Or: 0.125768426 cubic meters of material.

(125,768.426 cubic centimeters)

With a Density of 7.85 grams per cm^3, we are talking about a total of 987,282.144 grams (987 kilograms)



Now, How is this relevant, you ask?

I'm getting to that....


Now, if we remember from my equations on page 1:
www.abovetopsecret.com...

So, 10 grams of Hydrogen at 100,000,000 degrees Celsius contains:

100,000,000 * 10 * 14.30 =

14,300,000,000 joules.

Ok, now the Specific Heat Capacity of Steel is around .5j/g(K)

en.wikipedia.org...

It takes about .5 joules per gram to raise its temperature 1 degree Kelvin (Celsius for all practical purposes)

So, the inner 0.5 centimeters of the Reaction chamber, in the event of a Full Powerdown, is absorbing 14.3 gigajoules of energy from the Hot Hydrogen.

Now, at 987,282.144 grams, and .5j/g(K) heat capacity, the inner lining of the reaction chamber would need to absorb 493,641.072 joules of energy to raise a single Degree.

14,300,000,000 / 493,641.072 = 28,968

So, it would heat the first half a centimeter by around 28 thousand degrees.

Of course, the more material, the lower the overall temperature.

So at 1 cm of interior surface, we have only half that temperature, or 14,500 degrees.

And at 2cm, we have half that, or 7,250 degrees.

And, at 4 cm of interior structure, we would get something like 3,600 degrees.

So, it would Melt the interior of the reaction chamber.

Basically, in the event of a catastrophic failure of a Fusion Reactor, You would get a LOUD bang, and the inside of your reactor would be melted and cracked and basically useless.

No Nuclear Explosion. No Fallout.

would the plasma (on a molecular level) form "ionic" bonds with the continment material, and effectively vaporize its container?

Well, yes... Hydrogen does have a tendency to form covalent and ionic bonds with lots of different materials, like the carbon in steel, for example.

But the amount of chemical energy contained within the hydrogen is really a drop in the bucket next to its Sheer Temperature at that level.

At that temperature, it could melt the chamber... but the entire assembly weighs the better part of several dozen tons... I don't think they skimped on the thickness of the reaction chamber walls.

What I really want to know is How does plama interact with other states of matter

Yes, it's a very interesting subject... I am also curious about the field of study.
en.wikipedia.org...

-Edrick