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Old 2008-06-06, 18:29   #56
xilman
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Quote:
Originally Posted by cheesehead View Post
Yes, but the problem is really the lithium moderator in which they're swimming. It (lithium) would burn upon contact with air, so it's not a matter of just having a simple escape valve. :-)
The T and He production is very nearly trivial. For a start, calculate the production rate assuming a power generation of, say, 100kW from the known emission of neutrons by fission of a U-235 nucleus and its energy yield, together with the neutron capture cross-section by Li6 and/or Li-7. (Incidentally, I'd be surprised if the reactor uses isotopically pure lithium.)

Even if the tritium is vented (and I'm not suggesting it should be), it's not much of a problem. The half-life is short and the electrons come off at very low energy. In fact, they have lower energies than those in a good many TV sets. They're stopped by a few microns of solid or liquid shielding. The major problem is that HTO and T_2O is chemically very similar to water and so will get well within a few microns of cell nuclei.


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Old 2008-06-07, 09:39   #57
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Yes, so I'd be more concerned about inadvertently venting Li than about venting H, D, T, or He.

Quote:
For a start, calculate the production rate assuming a power generation of, say, 100kW from the known emission of neutrons by fission of a U-235 nucleus and its energy yield, together with the neutron capture cross-section by Li6 and/or Li-7.
I'll let that be my nephew's homework.

Last fiddled with by cheesehead on 2008-06-07 at 09:41
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Old 2008-06-08, 18:15   #58
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Ok, I know this is off topic, but I just have to know because I don't understand. What's the difference between this kind of lithium and the kind they give people in pill form for mental problems? I mean, I realize that there's radioactivity involved, but what else? I mean, if they are the same thing, you'd think they could just build it in such a way as to safely remove the lithium after it was no good for the process any longer and then remove the radioactivity and then use it for more lithium pills. I realize this may be idiotic because I don't know much about this.
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Old 2008-06-08, 19:16   #59
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Quote:
Originally Posted by Jwb52z View Post
Ok, I know this is off topic, but I just have to know because I don't understand. What's the difference between this kind of lithium and the kind they give people in pill form for mental problems? I mean, I realize that there's radioactivity involved, but what else? I mean, if they are the same thing, you'd think they could just build it in such a way as to safely remove the lithium after it was no good for the process any longer and then remove the radioactivity and then use it for more lithium pills. I realize this may be idiotic because I don't know much about this.
While not professing to a knowledge that I don't possess, when the body incorporates a radioactive substance it can put it in vulnerable places. Early concerns about above nuclear testing brought up this concern and I haven't seen much to placate it since. With DNA or RNA, I would think the concerns are the incorporation of radioactive Carbon, Phosphorus, Oxygen. When they decay, they would not only damage things nearby, but by decaying they would change/break the structure that they are incorporated within.
As for Lithium, Wikipedia tells me that:
Quote:
Naturally occurring lithium is composed of two stable isotopes 6Li and 7Li, the latter being the more abundant (92.5% natural abundance).[8] Seven radioisotopes have been characterized, the most stable being 8Li with a half-life of 838 ms and 9Li with a half-life of 178.3 ms. All of the remaining radioactive isotopes have half-lives that are shorter than 8.6 ms. The shortest-lived isotope of lithium is 4Li which decays through proton emission and has a half-life of 7.58043x10-23 s
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The active principle in these salts is the lithium ion Li+, which having a smaller diameter, can easily displace K+ and Na+ and even Ca2+, in spite of its greater charge, occupying their sites in several critical neuronal enzymes and neurotransmitter receptors.
Salts are ionic compounds that break into two charged portions when dissolved. In the above examples the positively charged ion (cation) and one type (potassium, sodium, calcium) them can displace another to some extent depending on size and charge. The differences in size/mass affect the rate that things that happen because the more massive ones do things more slowly and they do not fit everywhere the smaller ones do (also calcium ions have twice the charge of potassium or sodium). So these charged ions are wandering around going in and out of cells and following charged pathways that use them to accumulate and dissipate electrical charge or to control timing. This is pretty much in the thick of things. As for types of radioactive decay alpha, beta, gamma -- alpha particles are like helium atoms but stripped of electrons. People like to quote that they are stopped by a piece of paper, but I am told that if they are actually inside a body they can wander around a short range for weeks causing damage (until I assume, but don't know, it it some way acquires electrons from something else and becomes inert helium). Beta particles are very high energy electrons. Gamma particles are very high energy photons, more energetic than X-rays (also photons), and so are very penetrating. The fact that they are photons does not mean that they can be low-harm like visible light; they are high energy and are a form of ionization radiation. Most of the discussion of the harm of electromagnetic radiation focuses on ionization radiation.

Biologically active metal compounds are not the simple forms of the elements themselves. As for how people would be exposed to this Lithium, I don't know. I expect someone will pitch in along with corrections to my partial understanding of things.

Last fiddled with by only_human on 2008-06-08 at 19:46 Reason: twiddled with phrasing
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Old 2008-06-08, 20:00   #60
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Quote:
Originally Posted by Jwb52z View Post
Ok, I know this is off topic, but I just have to know because I don't understand. What's the difference between this kind of lithium and the kind they give people in pill form for mental problems? I mean, I realize that there's radioactivity involved, but what else? I mean, if they are the same thing, you'd think they could just build it in such a way as to safely remove the lithium after it was no good for the process any longer and then remove the radioactivity and then use it for more lithium pills. I realize this may be idiotic because I don't know much about this.
There's no difference in the lithium whatsoever. The only difference is that the reactor moderator is pure liquid metallic lithium whereas the stuff in the pills is a lithium salt.

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Old 2008-06-08, 20:50   #61
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The European Physical Society (EPS) Position Paper on the Nuclear Option

The European Physical Society (EPS) has just published a position paper on โ€œENERGY FOR THE FUTURE - The Nuclear Optionโ€. The Position Paper aims at a balanced presentation of the pros and cons of nuclear power and at informing both decision makers and the general public by communicating verifiable facts.

For the position paper, please click here.

Source
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Old 2008-06-09, 12:49   #62
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Quote:
Originally Posted by Jwb52z View Post
I realize this may be idiotic because I don't know much about this.
No, no, it's not at all idiotic. (What would be idiotic would be not to ask! Well, not idiotic, but less efficient at least.) And I think I see why you're confused.

Quote:
Ok, I know this is off topic,
It's directly relevant to the preceding postings about lithium.

Quote:
but I just have to know because I don't understand.
... and you're smart enough to ask!!

Quote:
What's the difference between this kind of lithium and the kind they give people in pill form for mental problems? I mean, I realize that there's radioactivity involved, but what else?
Ah ... there's merely a slight misunderstanding about the "radioactivity involved".

What only_human, xilman, and I previously posted is correct -- as far as it goes. It's just that I confused you by posting nuclear reactions in which Li-6 and Li-7 undergo fission, whereas everyone agrees that Li-6 and Li-7 are stable and thus not radioactive!

In the reactions I posted (I'm depending on my source being correct -- I don't know independently that these reactions are correct):
Quote:
Originally Posted by cheesehead
Li-6 + slow neutron -> He-4 + H-3 + 4.8 MeV

Li-7 + fast neutron -> He-4 + H-3 + slow neutron
the Li-6 and Li-7 are not just sitting there minding their own businesses (which would be to remain stable in each case), but are being molested by neutrons hitting them. Those incoming neutrons bring extra energy with them, which causes the molested nucleus to be "excited".

(BTW, in my explanation here, the term "excited" is indeed proper nuclear physics terminology, but the term "molested" is my own usage, _not_ (AFAIK) standard nuclear physics terminology )

The following description is according to my understanding, but I could easily be mistaken about one or more details.

When an Li-6 nucleus absorbs the incoming neutron, it becomes an excited Li-7 -- which would be stable if it were not "excited". Only because it is excited does it split into He-4 and H-3, radioactively emitting extra energy, as shown above.

When Li-7 absorbs a neutron, it becomes an excited Li-8, which could immediately fission as shown above, or settle down a bit and radioactively decay later.

So, the Li-6 and Li-7 are normally (such as when used in medicine) nonradioactive -- but when they're in the split-second midst of absorbing neutrons as they do when acting as a moderator surrounding the core of a nuclear reactor, the Li-6 can be transmuted into a temporarily-radioactive excited Li-7, and a previously-stable Li-7 can be transmuted into a radioactive Li-8.

Last fiddled with by cheesehead on 2008-06-09 at 13:17
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Old 2008-06-27, 01:09   #63
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It might be rational (in a rational-self-interest sense) to accept a small risk of a bad nuclear accident for someone who:

* has a democratic say in choosing the government that regulates (or fails to regulate) the nuclear industry

* can take legal action against a company that builds or operates a nuclear power plant in an unlawful way

* receives a share of the economic benefits from the products of the nuclear power plant in proportion to their share of the risk

But what reason is there for someone to accept even a tiny risk when they receive zero benefits and have no political or legal rights in the country where the nuclear plant is located?
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Old 2008-06-30, 04:34   #64
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Quote:
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But what reason is there for someone to accept even a tiny risk when they receive zero benefits and have no political or legal rights in the country where the nuclear plant is located?
Can you give a more specific example of the situation you have in mind?

Going on only what you've posted above:

Re: "accept even a tiny risk" -- We're surrounded by risks of various probability and magnitude. Studies have shown that people generally do a bad job of informally calculating the probabilities of various risks (not to mention ignorance of some risks). We're all influenced by the familiarity or scariness of the risk, for instance -- estimating that familiar/unfamiliar or nonscary/scary risks have significantly different probabilities than they actually have.

Re: "have no political or legal rights in the country where the nuclear plant is located" -- including/excluding the case of living in, or being citizen of, a country other than the one having the plant (regardless of whether you'd have rights in your own country, or they'd have in theirs), as well as the case in which the plant is in your own country but you don't have the rights you listed?

Last fiddled with by cheesehead on 2008-06-30 at 04:36
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Old 2008-07-04, 01:40   #65
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Quote:
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Can you give a more specific example of the situation you have in mind?
I think one of the biggest risks of using nuclear power to replace fossil fuels is that the current unjust global political-economic situation, where a minority of the world's population is able to appropriate a majority of the world's energy resources by force or by corrupt dealing with the dictators of countries who control the resources, will continue.

Wind, solar, hydro resources are much more difficult to carry off with the spoils of war.
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Old 2008-07-10, 20:52   #66
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It was sobering to listen to this talk at Xerox PARC about the challenge of meeting the world's energy needs in the coming decades. Based on back-of-the-envelope calculations, we'll have no problem using things like coal and oil products to meet 2050's anticipated energy needs, but will have a huge problem meeting the energy budget using alternative means. The only possibility is nuclear power, and even 50x the reactors we have now will barely be enough.

PS: The PARC forum archive is a wonderful collection of talks on a wide variety of interesting subjects, highly recommended.

Last fiddled with by jasonp on 2008-07-10 at 20:54
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