Fusion Power Plants

[Judas Iscariot]

It has been a while since I have read theh material on Fusion plants. I just read the T4 FFS about Power Plants, and it did nothing to answer my questions...

So, here goes:

What is used to shield the fusion power plant so that it does not kill the crew of any vehicle that is near it?

Anyone who knows anything about fusion (D-D reactions, or D-T reations, which are the only ones possible with Deuterium or Hvy Water) will understand this question...

 

[atpollard]

It has been a while since I have read theh material on Fusion plants. I just read the T4 FFS about Power Plants, and it did nothing to answer my questions...

So, here goes:

What is used to shield the fusion power plant so that it does not kill the crew of any vehicle that is near it?

Anyone who knows anything about fusion (D-D reactions, or D-T reations, which are the only ones possible with Deuterium or Hvy Water) will understand this question...

Gravitics? It propels craft, focuses lasers ... and absorbs radiation?

 

[Judas Iscariot]

OK.. If gravitics can absorb radiation... Why is there a need for Nuclear Dampers?

Why are not gravtics used as Screens on vehicles/ships to protect against other forms of kenetic/particle energy?

 

[Judas Iscariot]

I guess that I should also have asked:

What do you know about th eeffects of D-D and D-T Fusion Reactions?

They are DIRTY (Essentially, think Neutron Bomb Constantly detonating).

I have seen the materials used at Lawrence-Berkeley and Lawrence-LiverMoore's NIT, and the shielding needs to be replaced OFTEN, and looks like someone tried to make Styrofoam out of an alloy is capable of shielding against both Neutron and Alpha Radiation... I have been trying to find out exactly what the material is, but it seems to be one of their proprietary secrets...

I would tend to think "Garv" too, were it not for the fact that you would still need to do something with the neutrons, or their eventual build-up could cause almost any element to become fissile (then you have the problem of your relatively harmless alloy reaction vessel becoming a multi-megaton fission/fusion bomb)

 

[Anthony]

What is used to shield the fusion power plant so that it does not kill the crew of any vehicle that is near it?

The same unobtainium which is used to shield a starship's hull so ship crew don't get cancer after a couple of terms, or die of radiation poisoning from flying through radiation belts to do gas-giant refueling.

 

[Judas Iscariot]

Not quite the same thing...

The radiation around a Gas giant is Alpha and beta particles... Both of which carry a pretty heavy charge.

They can be deflected by a simple magnetic field. Same with cosmic rays.

Neutrons, on the other hand, have NO charge, and are deadly-deadly. Not only to people, but to anything short of a Bose-Einstein Condensate (coherent matter). a Bose-Einstein Condensate is effectively a grouping of molecules/atoms who have lost their individual differentiations between leptons and bayrons (ie Fermions) lose their individuality, an coallesce into one giant super molecule where all particles are one giant particle...

Theoretically, there is no limit to the size of a Bose-Einstein Condensate.

What makes them effective Neutron shields is that they can absorb neutrons into their condensate and the condesate just becomes more massive rather than suffering from the Wigner Effect (The decomposition of materials that occurs due to neutron bombardment)...The Neutrons are just incorporated into the coherent mass.

This is about the only method of safely shielding a reactor. Magnetics won't work as the neutron (as I have already said) carries no charge... Just passes through a magnetic field.

Gravitics CAN shield from Neutrons, but if you have a grav shield for a fusion vessel, why hasn't the same shield been used as a weapon's shield, as the power in a fusion reaction vessel is (by common sense) going to be more powerful than any weapon it provides power to.

There is another problem with gravitic confinement... You need some sort of vessel to confine said neutrons in... If you leave them in the fusion reactor, eventually you get such a build-up of neutrons, that they will cause any material in the fusion chamber to become so neutron heavy that they will beging to become fissile, and eventually you get a runaway fission-fusion reaction (ie, a thermonuclear bomb of pretty great size) going off inside your reactor... I am not sure of any shield in the TU that can defeat that without halting the fusion reaction itself)

You could eventually vent said neutrons, using a gravitic confinement beam, but this would quickly be adopted by militaries as one of the most deadly weapons in space... So, since it is not in Traveller canon... I do not think that this is th emethod used.

Any other material that could shield the vessel would eventually succumb to the Wigner effect, adn need to be replaced (I have seen th estuff that comes out of the NIF's (National Ignition Facility) reactor, and it looks like someone made styrofoam out of some incredily dense material (that is no longer incredibly dense... You can pick it up and crumble it with your bare hands... Before this stuff goes into the reactor (when it is new), it takes a machine to handle the peices (They are too heavy to pick up).

So, if such a stuff lines the fusion reactors in the Traveller universe... Why is it not being used as a shielding against weapons (most of which are child's play when compared to a hard-neutron bombardment)?

 

[pendragonman]

I have two different guesses for you:

1) Our ever present handwavium. Clearly it has the property of venting excess neutrons into deep space. Perhaps a honeycomb of handwavium leads directly from the reaction chamber to the outside of the ship, with internal sensors and controls to vent only the excess. And when combined with unobtainium, can contain the reaction, at least up to annual maintenance. As the ship passes annual maintenance, without a flushing of the system, the excess neutrons are what react with the J drive to cause misjumps or power plant failures or...

2) Perhaps the reactions are contained in a magnetic bottle ala Star Trek. Since it takes an external structure to the bottle (the warp nacels) to create the bottle, this would be why it cannot be used as a screen.

Or perhaps it is a combination of the two?

 

[far-trader]

I tell you, if you all keep trying to look behind the curtain you'll go blind

It could be "explained" a lot of ways but we all know the truth is it simply wasn't considered an important detail for a game

Maybe it's not the same fusion reactor you're thinking of. Maybe it's a variant cold fusion reaction of some type. (No no, don't bother with the details, I know that won't work either )

The idea of a condensate shielding seems the best. Part of annual maintenance is to replace the contaminated(?) shielding with fresh. Skip that and it starts to cause safety shutdowns at inconvenient moments.

Why isn't it used as armor? Maybe it would interfere with jump? Maybe it is too brittle to survive the hard pounding of exposure? Maybe it melts upon reentry? Maybe it interferes with the magical radiators that keep all Traveller ships from turning into molten handwavium as soon as the powerplant is turned on? Doesn't really matter why it's not, it just isn't

 

[Anthony]

Not quite the same thing...

The radiation around a Gas giant is Alpha and beta particles... Both of which carry a pretty heavy charge.

Much of it is high energy protons.

They can be deflected by a simple magnetic field. Same with cosmic rays.

The magnetic field required to block high energy primaries is strong enough to cause direct health problems on any ship much smaller than a Tigress (field strength required is inversely proportional to size, so at 1/30,000 the size of the earth, it needs a 30,000x stronger magnetic field, or 1-2 tesla).

I'm befuddled by why you think a BEC is useful as a neutron shield. The primary issue with neutron shielding is that neutrons are only stopped by collisions with nuclei (this is also mostly true for protons above ~500 MeV), so for neutron shielding you need enough mass that a neutron is going to hit a nucleus on its way through.

It's possible that Traveller fusion reactors use some aneutronic cycle, however.

 

[flykiller]

What is used to shield the fusion power plant so that it does not kill the crew of any vehicle that is near it?

any material that contains lots of hydrogen works well as shielding against neutrons. water is good, as are certain plastics. one may figure that annual maintenance covers this shielding.

 

[Spinward Scout]

I thought this was something that was covered with Fusion Plus in T4?

 

[robject]

Hey Judas,

As far as I know, I've not heard satisfactory how's for a lot of Traveller stuff. Like heat and radiation. And reactionless thrusters. And jumpspace. And traders. Asteroids accelerated to Near-C speeds. Piracy. Feudal Technocracies. And what kind of footwear Aslan females own.

The game goes on. And continues to drive many physicists, astronomers, economists, futurists, tacticians, strategists, doctors, and mechanical engineers to strong distraction and concern.

I'll make a stronger point. Every single piece of Traveller rule ever published is unrealistic, or wrong, or both, and this will be plain to people in each area of expertise.

This will happen.

However, if you find a good shielding for fusion reactors, please share it.

So consider this an opportunity, not a problem.

 

[atpollard]

Whatever the shielding is, at TL 9 reactor has 28 inches (0.7 meters) more of it than a TL 15 reactor for a 1 EP fusion reactor.

At TL 13 armor is made from collapsed matter (like a neutron star) and at TL 15 the collapsed matter has it's bonds artificially strengthened. I would say that the Imperium has a materials technology advantage over modern Earth.

 

[Judas Iscariot]

A couple of points about established canon:

Aneutronic reactions: Established TU canon has fusion plants powered by Deuterium or Tritium (The two products obtained from the atmosphers of gas giants or from Heavy Water).. It is not possible to produce an aneutronic reaction with these.

So, it is probably not that kind of reaction considering described canon.

Neither is it possible to support a protium reaction (which can be obtained from the same sources, gas giants and hevay water, or reglar water for that matter). Protium reactions are probably teh least effiecient reactions there are, and they require stellar pressures and gravity fields to sustain ignition... Any reactor that could produce a protium reaction would require a power source for ignition that would make the reactor redundant

So, no protium reactions....

Cold-Fusion: This produces the same neutron radiation as "hot" fusion. The only difference being that "hot" fusion uses a high-temperature plasma for ignition, and "cold" fusion does not... They are the SAME reactions though.

Magnetic confinement: I thought I explained that one (and I would figure that people were smart enough here to realize). Neutrons have no charge.. They are not affected by magnetic fields.

Gravitic confinement: this is great, but it mean that you have a gravitic control that cold also be used on the external areas of vehicles as a sheilding against energy weapons (It doesn't have to be starships... I am talking ground/grav military vehicles here)... Unfortunately, I have not seen any such technology in TU canon

BECs: The reason that these would make decent neutron shielding is that they are effectively a giant nucleous (and electron cloud in one big pool of "stuff"). They are usually liquids, but can be made "solid" by the appropriate energies to maintain their shape (Theoretically). Any particles that enter a BEC simply become part of its matrix until the BEC coherence collapses, when the energies are released.

Also, water, hydrogen, etc do NOT make good neutron shielding.. If that were the case, Lawrence-Livermoore and Lawrence-Berkeley labs would not need to spend a fortune on shielding replacement every year.

My point is basically this...

The whole fusion reaction pricinple needs to be looked at, as the required technology to sheild the crew from neutrons would be usable in other applications.

Think of it this way:

How many of you would have considered that the development of stealth technology would allo you to cook a better pizza in the microwave?

 

[atpollard]

Gravitic confinement: this is great, but it mean that you have a gravitic control that cold also be used on the external areas of vehicles as a sheilding against energy weapons (It doesn't have to be starships... I am talking ground/grav military vehicles here)... Unfortunately, I have not seen any such technology in TU canon.

I think that you are dismissing this point too quickly.

I hear two common complaints about Traveller Fusion:
1) Where is the heat going? (your Neutron arguments, like heat, are a variation on "this does not agree with real science".)
2) Why is it so inefficient?

I propose that they are related.
Let us assume that it requires huge amounts of energy to create a gravity containment field able to stop a neutron – not an unreasonable assumption. Let us further assume that the confinement field for a 1 EP reactor is about the size of a golf ball. If the energy required to sustain a field of this strength increased with the square of it’s volume, then a “shield” around a ship would require an impossibly large amount of energy – hence the limited application of this technology. Let us assume that the D-D or D-T reaction generates the correct amount of energy (thousands of times the cannon output) but 99.999 percent of the output is used to generate the gravity shell that stops the neutrons.



Another comment:
Could a protium reaction be comprised of as a series of pulses (like the supercolliders) so the star like conditions were maintained for only an instant and the missing 99.999 percent of the fusion energy powers the next pulse?

 

[Judas Iscariot]

To take the last point first.

NO... A protium reaction, aside from requiring a HUGE amount of power to sustain fusion, produces so little energy in relation to that required to sustain it that it essentially produces a steady-state system.

Protium reactions only produce about 5MeV per fusing quatrain of protium while requiring roughly the same amount of energy to sustain ignition. (The acutal numbers are around 6.5 MeV producesd and 6.49 MeV required to sustain the reaction... I have ignored these reactions for so long because they are considered so completely useless to fusion power research. They have PLENTY of applications in stellar simulations, where they are the driving reaction of the stellar fusion engine).

Compared this to the 5 to 17 MeV for the different variations of D-D, D-T, and D-T-H3 reactions. This lower number of 5MeV is for a D-D reaction, which is really a two-stage fusion reaction.. The Deuterium first fusing into Tritium, which then must have a Helium3 atom to fuse with... It is a woefully wasteful reaction, much like the protium reaction, which only produces around 5MeV. But, unlike the p-p-p-p (Proton-Chain) reaction, the D-D reaction only requires 3 to 4 MeV to sustain ignition (This could be the source of the "woefully inefficient" fusion reactions in Traveller). Unfortunately, D-D reactions tend to conflict with canon as they require a source of Helium3, which Traveller never mentions.

I also agree on the two points of "where is the heat going?" (Although this is MUCH more easily dealt with if you deal with the Neutron problem, as between .66 and .8 of the energy released in the fusion reactions stated as being used in TU canon is released as Neutron energy.

Neutronicity, which tells how much of a fusion reaction energy is released as Neutrons, the higher this number, the more power the reaction is capable of producing (although this is not the only indicator of the power produced in a Fusion reaction). Unfortunately, it also relates to the degree of neutron radiation that must be dealt with by the reactor. The higher the number, the more neutrons produces in each reaction*

As for the size of the reaction vessel... It would have to be pretty large, as the pressures created by the reaction would begin to produce even more complex and difficult to assimilate technical issues.

But, to get back to my point... It isn't how much or how little power the reaction produces, but the application that the technology is being used for.

Any such gravitic field could be used in other applications. It doesn't matter how much power is required to create it... It is the fact that the field can be created and controlled.. That degree of control and precision can be used in other applications with smaller fields.

Much like the example above where I asked how many people considered the development of the Stealth technologies when they cooked a pizza in the microwave (The "Browning foil" that is on microwave pizza containers is the same stuff that lines the skin of the F-117 and B-2). Fusion power has similar related technologies that would have spun off to other applications.

Try not to think about finding a way to fix the canon fusion reaction (or explaining it), but rather "What else can I use this technology for if it is capable of producing a fusion reaction with no neutron radiation (or capable of shielding said reaction safely and efficiently only requiring the changing of the shielding in the yearly maintenance of the ship)?"


* As an example.. A .5g reaction of D-T (.2g of Deuterium and .3g of Tritium - or .1 mol of each) will produce a reaction with 88.5x10^22 MeV (or 141.6 GJ, if I have done my math right... 1.6x10^-19 x 88.5x10^22 MeV should equal the number of Joules produced by .1 mol of reactant)

 

[Anthony]

Aneutronic reactions: Established TU canon has fusion plants powered by Deuterium or Tritium (The two products obtained from the atmosphers of gas giants or from Heavy Water).. It is not possible to produce an aneutronic reaction with these.

Established TU canon has fusion plants powered by liquid hydrogen. We know it's not actually liquid deuterium -- the density is wrong. Thus, somehow, TU fusion plants do protium fusion. We don't know how, and it may be a peculiar reaction cycle. It's also possible that damper tech is involved.

Magnetic confinement: I thought I explained that one (and I would figure that people were smart enough here to realize). Neutrons have no charge.. They are not affected by magnetic fields.

You did, but totally missed the point, which is that magnetic shielding isn't effective against GCRs either.

BECs: The reason that these would make decent neutron shielding is that they are effectively a giant nucleous (and electron cloud in one big pool of "stuff").

No they aren't. They're effectively a giant molecule. They aren't any better shielding than any other similar mass of another material. The Vast Quantities of Liquid Hydrogen on board a Traveller starship are excellent neutron shielding.

Also, water, hydrogen, etc do NOT make good neutron shielding.. If that were the case, Lawrence-Livermoore and Lawrence-Berkeley labs would not need to spend a fortune on shielding replacement every year.

Water, hydrogen, etc, make perfectly fine neutron shielding -- bulky but lightweight. However, they don't make good structural materials, and since a reactor needs structural materials, you're going to have materials that need to be replaced every so often.

My point is basically this...

The whole fusion reaction pricinple needs to be looked at, as the required technology to sheild the crew from neutrons would be usable in other applications.

On the scale of problem technologies, fusion is way down below reactionless drives, nuclear dampers, meson guns, black globes, jump drives, and gravitics, all of which break fundamental laws of physics. It's probably on a par with plasma/fusion guns (which have inexplicable focusing abilities), superdense armor (which corresponds to no known or theoretical material), X-ray lasers, and the like.

 

[Judas Iscariot]

I have since discovered that while Bose-Einstein condensates would make GREAT neutron shields (as has been pointed out... They are essentially huge molecules, and will absorb any particle that encounters them), they also have a VERY dangerous feature that would make them impractical:

When they have absorbed a specific amount of energy, they implode and then explode. They do so pretty destructively, equivalent to or greater than a nuclear reaction of an equivalent amount of fissile material...

So, it was not something that would work out in that manner.

Also, if water and hydrogen are such good shields for fusion reactors, why are they not used in any of the following reactors:

NIF (National Ignition Facility/ Lawrence-Livermoore)

http://www.llnl.gov/nif/

and

http://www.llnl.gov/nif/project/index.html

The NIF reactor uses aluminun Titanium and 16 inches of concrete... The concrete and titanium require replacement at 6 and 12 month intervals.. The aluminum reaction vessel requires replacement every few years depending upon use

JET (The Joint European Torus - currently the largest operating reactor in the world)

http://www.jet.efda.org/

http://www.jet.efda.org/pages/content/rh/index.htm

(JET has six feet of Iron shielding, which is removed by robots due to its irradiation from reactor operation, whic is why I included this link)

DIII-D (General Atomics Fusion)

http://fusion.gat.com/global/Home
(I have been in contact with Keith Burrel, who is the Transportation and Turbulence Research head for GAT and The ITER facility. He is supposed to provide me with information on both facilities, but I have already found out that their shielding is extensive and expensive)

I could keep going with this, but I will include another link to a basic explanation of fusion from one of the project scientists on the Princton Fusion project (Robert Heeter, I believe now Dr. Heeter):

http://fusedweb.pppl.gov/FAQ/section1-physics.txt

It has a few things to say about Protium reactions and neutronicity:

"Fortunately for life on earth, the sun is an aneutronic fusion
reactor, and we are not continually bombarded by fusion neutrons.
Unfortunately, the aneutronic process which the sun uses is
extremely slow and harder to do on earth than any of the reactions
mentioned above. The sun long ago burned up the "easy" deuterium
fuel, and is now mostly ordinary hydrogen. Now hydrogen has a
mass of one (it's a single proton) and helium has a mass of four
(two protons and two neutrons), so it's not hard to imagine sticking
four hydrogens together to make a helium. There are two major
problems here: the first is getting four hydrogens to collide
simultaneously, and the second is converting two of the four protons
into neutrons. "

So much for Protonic fusion...

Now, anyone else have anything to support their views..

Like... Show me a reactor that uses water, hydrogen or some other light element to shield against neutrons.

I am going to point out a little problem with this.

Water, when struck by a neutron, can decay into Deuterium or Tritium, which when struck by another neutron can cause it to eventually become heavy water, which becomes radioactive pretty quickly... The Neutrons "stick" to the molecules, rather than becoming stuck in the intersitial spaces (a thing called the "Fenkel defect").

Hydrogen has its own problems.. Notably that it is a REALLY small atom... As a matter of fact, it is the SMALLEST atom. Neutrons are stopped only when they hit a neucleus and stick, or become trapped in intesitial spaces in a crystalline lattice (only possible with crystalline materials). So, hydrogen doesn't stop all of the neutrons passing through it... roughly 1/20th of them as a matter of fact.

Now, if you create metallic hydrogen... That WILL stop neutrons pretty well.

But, then you are right back to my original position, that this shielding would be a technology that would be occuring in other areas as well.

I have been holding onto one small secret in this discussion... Annealing.

It IS possibe to relieve or release the neutron energies built up in a material that is used as a neutron shielding... Heat it. The exact temperature needed to relieve the stresses of the wigner effect depends upon the material and the amount of neutrons built up. I have been trying to avoid doing any math (I am on vacation dammit!) so I will not start now.

This still leaves me back where I began... There needs to be a material that is capable of absorbing these neutrons that can last a year before being dealt with during yearly maintenance... I will find out specifics when I hear back from the ITER facility. My guess is that the material is still going to need to be pretty impressive.

 

[flykiller]

The concrete and titanium require replacement at 6 and 12 month intervals.

could you give a more direct cite link for that? I spent about half an hour looking through the website and didn't find anything about replacing any concrete at any interval.

Like... Show me a reactor that uses water, hydrogen or some other light element to shield against neutrons.

(shrug) any u.s. navy surface ship reactor. the way it was explained to us is that a fast neutron that impacts a large nucleus bounces off without transfering much energy to it, and thus wouldn't slow down, while an impact with a single proton (i.e. hydrogen) would allow the most energy transfer and thus the best ability to slow the neutron - thus, we used water and a plastic with a high hydrogen content. yeah it's a fission reactor but I figure a neutron is a neutron.

can't recall what they said about where the slowed neutrons would wind up.

 

[Anthony]

Also, if water and hydrogen are such good shields for fusion reactors, why are they not used in any of the following reactors:

Per unit mass, hydrogen is excellent shielding and water is good shielding. However, mass isn't really the biggest problem for a terrestrial reactor, and it's a lot easier to build a slab of concrete than to build a wall containing a water tank. Also, per unit thickness water and hydrogen aren't particularly good shielding.

It has a few things to say about Protium reactions and neutronicity

Bog. That seems to be somewhere between confused and wrong. The solar reaction is:
p+p->D + positron + antineutrino
D+D->T + proton or 3He+neutron
D+T->4He + neutron
D+3He->4He + proton
Either way, the reaction is 6*p -> 4He + p + n + positron + antineutrino. That neutron in turn usually gets absorbed by a proton, but the reaction is not actually neutron-free.

Like... Show me a reactor that uses water, hydrogen or some other light element to shield against neutrons.

Any conventional fission reactor?