Neutron & radioactive waste production in p11B polywells

Discuss how polywell fusion works; share theoretical questions and answers.

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cuddihy
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Re: Neutron & radioactive waste production in p11B polyw

Post by cuddihy »

MSimon wrote:
ANTIcarrot wrote:
MSimon wrote:No long term contamination with fusion. Only neutron activation.
Contamination can mean more than just 'can't clean away the last of the uranium'.

Mr Bussard assumes the use of super conductors in his machines. Two of the better ones which is beginning to be used in mains systems (albeit experimentally in limited quantities) are BSCCO and YBCO. It may not be possible to shield these coils, so these materials may also have to withstand neutron activation. If any of them decay into other materials afterwards, then that is also an issue of contamination; one that coudl inhibit the super conducting effect.

Of bismuth, calcium, copper, strontium, oxygen, ytterium and barium, there are a few potential activation problems:

40Ca to 41Ca HL 1e5 years and decays to potassium
88Sr to 89Sr HL 50 days and decays into rubidium
89Y to 90Y - HL 2 days and decays to zirconium
41Ca is not going to be very radioactive.
90Y will be gone in 10 days - 20 max
89Sr if it is significantly activated is going to be a little problem. 500 days to 1/1,000th activity. 1,000 days to get to 1E-6 of initial activity.

Activation rates will not be really high because the neutrons coming out of the reactor are going to be at 2 Mev or greater where the capture cross sections are low.
Msimon, agree, anything activation concern that falls out of the 90 day-50 yr half life is not a big deal, long term: shorter because it will decay rapidly away, longer because it will result in low radiation flux and exposure.

Stay away from Co!
Tom.Cuddihy

~~~~~~~~~~~~~~~~~~~~~
Faith is the foundation of reason.

drmike
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Post by drmike »

MSimon wrote: Because I'm a nuclear engineer. How about you?
Raises hand - ME TOO!!

"50 thou a year will buy a lot of beer..."

8)

MSimon
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Post by MSimon »

drmike wrote:
MSimon wrote: Because I'm a nuclear engineer. How about you?
Raises hand - ME TOO!!

"50 thou a year will buy a lot of beer..."

8)
Mike I haven't been an RO since my Navy days - '66.

I do have a reactor design book from '53 that I go to bed with every night. It covers the basics pretty well.

tonybarry
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Post by tonybarry »

Thanks to all correspondents on this thread. I am learning a lot. Still many things that are cloudy ... but it's great to be learning this stuff.

drmike
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Post by drmike »

MSimon wrote:
Mike I haven't been an RO since my Navy days - '66.

I do have a reactor design book from '53 that I go to bed with every night. It covers the basics pretty well.
I wasn't born until '54 :) I met a lot of Navy guys, and one roommate went into geology so he could stay on dry land for the rest of his life! 6 months under water at a time is a bit much.

Right now I'm working on some math to figure out the spacing of N coils around a sphere so I can compute the B field from the arangement. I hope to have something in pdf form in a few weeks. With luck a few people here can double check my math. Documentation is really one of my weak points, but I think to get polywell going some good solid mathematical descriptions will help a lot.

Fission reactors were built with slide rules. So were H-bombs. The computational ability of a bottom of the line desktop computer is way beyond "supercomputer" ability of the 1960's. Seems to me we can design a polywell and prove the math with an experiment pretty easily. I think it'll be fun to find out!

ANTIcarrot
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Post by ANTIcarrot »

MSimon wrote:Because I'm a nuclear engineer.
Yes, and? I'm an engineer too! An aerospace engineer. Whenever I raise an issue that fall under my education and outside of yours (like SSTO, ground-side aircraft operations, or rocket science) you treat me and my views like filth. So tell me, Mr Fellow Engineer, why should I not copy your example?

Though I must regret that I did misphrase the question. The intent was not about neutron energy or activation cross sections, but rather 'how do you know the neutron flux (using whatever mechanism you chose) will not degrade critical materials inside the reactor shielding'? Specifically referring to the super conductors (which may have minimal or zero shielding) what degradation rate would you calculate? And since you are a nuclear engineer, I’ll ask you to show your working.

Activation is merely one way that can happen. What happens when the 2MeV (not to mention the occasional 16MeV) neutron hits an atomic nuclei? There are also Frenkel defects, Wigner effects, neutron-induced swelling, and the creation of dislocations and voids; all of which can alter material properties; which is usually a bad thing. You knew that didn’t you?

Many people (who are also nuclear engineers) seem to share the view that neutron damage (of all types) will be severe enough to be measurable in the ITER reactor. So much so that shielding in ITER is not only useful to model a full scale reactor, but also necessary. If that is run at it's maximum capacity and power once a day, it will produce 200GJ of neutrons. Run continuously at equivalent fusion output, a p11B polywell will produce 43GJ over the same day; and may spread that neutron flux over a smaller area. Now 1/5th of the flux (before area effects) will produce (presumably) 1/5th the effect. Are you saying this will have effectively zero effect on all new materials in the ploywell reactor; again, specifically materials which you likely may not have worked with?

It is notable that while Mr Bussard has said he can make a working reactor for only $150M, not a working reactor free from operational issues.

Your point of view seems contrary to logic to me; though I am aware that would not be the first time such a contradiction has existed in atomic physics. Though if you can prove it, please do so to help fill in some of the gaps in information surrounding the polywell proposal.
Do you know the difference in absorption cross sections between 2 Mev neutrons and thermal neutrons? Is it typically a 10% difference or more like 2X to 10X difference?
In layman's terms it's like a large fast moving asteroid moving through earth's gravity well; it's going too fast to be captured. To be captured it would have to fly much closer to the earth where the potential well is stronger, or hit it directly, which is less likely. I lack easy access to the precise mathematics, but yes I do understand the basic concepts.
Any superconductors used in a Polywell will have to be cooled in the 20K range (or lower depending on the material) because of the magnetic field requirements. There are no 77K high mag field superconductors. You knew that didn't you?
I hadn't read that before no. And having spent a few days looking about the internet, I've been unable to find confirmation of it either. I’ll continue to look. I like learning new things. Though as I’m sure you’re aware there is a deplorable lack of easily accessible information on this subject available online. Can you make any useful suggestions for further information?

I have found a few papers discussing the exciting possibilities of YBCO and >100T fields. From what I can gather there are no commercially available HSC materials, but that's not the same as saying they're fundamentally impossible.
http://www.iop.org/EJ/article/1367-2630 ... j226629bib
http://www.iop.org/EJ/ref/-prog=article ... /9/3/047/6
And just to be clear, this is not a matter of believing you or not believing you, it's a matter of you providing no evidence for your statements.
(how much hydrogen do you contain?)
Based upon water composition of the human body, roughly 5kg; give or take. It not that difficult to work ou for the average human bodyt. You're sure you're a fully qualified engineer? As an engineer you might be aware of the legion of problems NASA has experienced with the stuff.
B10/B11 has a low high energy neutron cross section. You knew that didn't you?
You're proposing using boron for shielding in a nuclear reactor which uses boron as a fuel? That sounds like building a fire-wall out of gunpowder. You know this would sound a little strange didn't you?
You seem very ignorant on the subject.
You seem more concerned with using your knowledge as a high horse to belittle people, rather than as a tool to educate people curious about the details. I'd be rather be ignorant than think like that.
You ask why I believe capture cross sections are lower for 2 Mev neutrons than thermal neutrons.
Actually no I didn't.

It is simple really. I looked it up.
Translation: Misread the question, losing your rag, and posted something not particularly relevant while failing to give any evidence.
Some light reading material: Half Way To Anywhere, The Rocket Company, Space Technology, The High Fronter, Of Wolves And Men, Light On Shattered Water, The Ultimate Weapon, any Janes Guide, GURPS Bio-Tech, ALIENS Technical Manual, The God Delusion.

ANTIcarrot
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Post by ANTIcarrot »

Edit: Not a clue what that was. Possibly too many windows open.
Last edited by ANTIcarrot on Wed Aug 29, 2007 10:10 pm, edited 1 time in total.
Some light reading material: Half Way To Anywhere, The Rocket Company, Space Technology, The High Fronter, Of Wolves And Men, Light On Shattered Water, The Ultimate Weapon, any Janes Guide, GURPS Bio-Tech, ALIENS Technical Manual, The God Delusion.

Zixinus
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Post by Zixinus »

Why did you just quote yourself?

MSimon
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Post by MSimon »

Activation is merely one way that can happen. What happens when the 2MeV (not to mention the occasional 16MeV) neutron hits an atomic nuclei? There are also Frenkel defects, Wigner effects, neutron-induced swelling, and the creation of dislocations and voids; all of which can alter material properties; which is usually a bad thing. You knew that didn’t you?
Yes and it is fascinating really.

ITER running at 500 MW will produce around 250 MW or more of neutrons. My recollection may be off but it is the right order of magnitude.

A Polywell running at the same power production rate will produce 5 kW of neutrons.

Overall neutron damage will be in proportion to total neutron power.

Now consider a fission plant. A 1 GWe plant will produce 3 GWth of neutrons. Those plants are designed to last structurally 40 years under those bombardment intensities. Given that fact I think you might be on solid grounds to say the pB11 Polywell reactor vessel would last at least 400 years with proper design.

Damage to the superconductors is another question. That will take operational experience. It may also be mitigated by proper design. We shall see. It may just be a matter of adjusting current densities to allow for damage. i.e. take a coil capable of 10T and run it at 1 or 2T.

BTW anti in what country do you practice nuclear engineering?

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Post by MSimon »

You're proposing using boron for shielding in a nuclear reactor which uses boron as a fuel? That sounds like building a fire-wall out of gunpowder. You know this would sound a little strange didn't you?
Please explain why this is a problem.

Will the B10 explode if bombarded by neutrons?

Let me start at the beginning. If you don't understand Polywell to at least a first order you will be making statements that appear to folks who have studied the reactors involved to be nonsense based on ignorance and misunderstanding.

The above bit I quoted is a case in point.

It would be like saying you were a nuke engineer and had no idea that the capture cross section for 2 Mev neutrons is much smaller than for thermal neutrons. Any one trained in fission knows that in their bones. It is drilled in from the first day. It is inherent in the difference between fast neutron reactors and thermal neutron reactors.

Your ignorance indicates to me that you are either multiple people posting under one name or a poseur.

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Post by MSimon »

anti

Your postings are similar to trying to tell an electronics engineer how to handle the design details of a bipolar junction transistor circuit based on vacuum tube theory.

You are so close. And yet so far.

Really. Fix you ignorance problem. Then come back. You might have some useful ideas if you actually understood the technology.

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Post by MSimon »

Quote:
Any superconductors used in a Polywell will have to be cooled in the 20K range (or lower depending on the material) because of the magnetic field requirements. There are no 77K high mag field superconductors. You knew that didn't you?

I hadn't read that before no. And having spent a few days looking about the internet, I've been unable to find confirmation of it either. I’ll continue to look. I like learning new things. Though as I’m sure you’re aware there is a deplorable lack of easily accessible information on this subject available online. Can you make any useful suggestions for further information?
The above is a joke right? Do you live in a country where the 'net is filtered? The info is widely available.

OK yes I do have a suggestion:

Go to:

http://iecfusiontech.blogspot.com/

read all the technical articles. Including the superconductor articles. Follow all the links.

Once you are up to speed come back. You have an interesting mind. Once it is educated it may be of some use.

drmike
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Post by drmike »

You all must be brothers, you sound just like my kids.

But let's take one thing at a time and just stick to facts. As engineers we build stuff that works, and it works well for a long time. And we're all proud of it and we all have big egos. You can't accomplish anything without a big ego. But name calling and goading doesn't really accomplish a lot. It is fun though, so as long as nobody is serious, ego bashing on high armour ego can't be too bad.

As for Boron as both fuel and shield, it does make sense. It is fuel with protons - the proton cross section is what is important. It is a shield for neutrons - the neutron cross section is very high and the reaction is B11 + n -> B12 -> C12 + beta- in 0.02 seconds.

But it does raise a question - why not slam a proton beam into a boron slab? You get energy and can trap the neutrons a lot more easily so energy extraction would be simpler.

MSimon
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Post by MSimon »

drmike wrote:You all must be brothers, you sound just like my kids.

But let's take one thing at a time and just stick to facts. As engineers we build stuff that works, and it works well for a long time. And we're all proud of it and we all have big egos. You can't accomplish anything without a big ego. But name calling and goading doesn't really accomplish a lot. It is fun though, so as long as nobody is serious, ego bashing on high armour ego can't be too bad.

As for Boron as both fuel and shield, it does make sense. It is fuel with protons - the proton cross section is what is important. It is a shield for neutrons - the neutron cross section is very high and the reaction is B11 + n -> B12 -> C12 + beta- in 0.02 seconds.

But it does raise a question - why not slam a proton beam into a boron slab? You get energy and can trap the neutrons a lot more easily so energy extraction would be simpler.
The reason slamming protons into a boron slab is not a winner is all the collisions that do not produce fusion and all the alphas that lose energy heating up the Boron.

BTW an engineer who can't stand up to criticism of a most descriptive nature would never have made it in the aerospace companies I have worked for. The culture is merciless.

And please tell me why a competent Nuclear Engineer wouldn't know the difference between proton capture and neutron capture? It seems absurd on the face. Or not knowing that 2 Mev neutrons have lower capture cross sections than thermal neutrons. A nuke engineer in America who didn't know that would be asked to hand in his license.

So maybe anti is not an American engineer.

The other possibility is that anti is more than one person. Which would explain the range of replies - from smart and knowledgeable to stupid and ignorant.

esecallum
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Post by esecallum »

chazmataz wrote:
Stefan wrote:High temperature superconductors can't be used for strong electromagnets.
ITER uses niobium-tin and niobium-titanium alloy.

Even if YBCO or BSCCO could be used, it is likely that cooling further down would increase the critical current density enough to warrant the effort.

I see no reason to use hydrogen for cooling. Unless I am very mistaken usually liquid helium is used (boiling point ~4K, critical temperature for NbTi ~10K).
The major disadvantage of using liquid He for cooling is obviously COST. Liquid He costs dozens of times as much as liquid hydrogen. When you use liquid helium, you also need to be very effective in your recycling. Yes, the lower temperature of helium will let you get a higher magnetic field, even with the MgB2 superconductors, but overall the hassles and expenses of working with liquid helium are big enough that basically everyone who uses it would happily switch to LH2 if they could.

Traditional low-temperature superconductors generally don't work at the 20K boiling point of hydrogen. MgB2 doped with carbon is superconducting up to about 40K, so it is capable of generating high magnetic fields at 20K, and even at the 33K critical temperature of LH2.

The only rationale to go with traditional NbTi superconductors and liquid helium would be if your research project was extremely well funded and/or if you could get off-the-shelf coils that fit your design perfectly.

I suggest that magnetic fields are not used at all.

Use electrostatic fields instead.

no coils,no losses from i squared*r heating,lighter,cheaper,much more compact.

always puzzled why is everyone obsessed with magnetic fields to confine charged particles.

why not electric fields instead.

in some tv sets instead of using helmholtz magnetic coils to steer/paint the picture on the screen by the electon beam electrostatic fields are used instead...it's not exactly an unproven or untested idea.

electric fields are extensively used in industry...for example painting/spraying new cars,etc,etc.

so could you people please explain why it is impossible to use electric filds to confine charged particles?

any answers?

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