Lead-Bismuth fast breeder reactor will generate the poison that killed Livenenko.

[NNadir]

A type of fast breeder reactor that is being developed as part of the Gen IV nuclear program will generate, as a side product, Polonium-210, the radioisotope that was used to kill the Russian spy Livenenko.

I'm very surprised our anti-nuke squad at DU hasn't been all over this saying how this nuclear reactor, if built, will wipe out all life on earth. Of course, if you're anti-nuclear, you probably don't know very much about nuclear reactors, but that's another point.

Here are the detail about how will generate Po-210 in the reactor core:

The reactor contains a eutectic coolant, which is a mixture of elements that melts at a lower temperature than either component. (A mixture of water and salt is an example.) The eutectic in this case consists of the element lead and the element bismuth. Lead is the heaviest stable element, although Bismuth, which has only recently been detected to be very slightly radioactive, was long thought to be the heaviest stable element. Lead, of course is toxic. Bismuth is an ingredient in Pepto-Bismol.

Bismuth consists of a single isotope, Bismuth-209. When subjected to a neutron flux, this isotope captures a neutron and is changed into bismuth-210. The probability of this reaction (which is measured in a unit called "barns") is fairly low for thermal neutrons, but has a few peak resonances for fast neutrons, meaning that it almost certainly will take place to some extent. Bismuth-210 is unstable and is highly radioactive. It decays with a half-life of 5.1 days to give Po-210.

The situation is subject to an equilibrium determined by what is known as the Bateman equations. For those who have a mathematical bent, the Bateman equations for this situation is given in this link:

https://engineering.purdue.edu/PARCS/Code/NewFunctionality/XSection/xsec.ppt#5

In this equation, the greek letter "phi" refers to the neutron flux, the greek letter "sigma" refers to the neutron capture cross section of the isotope of interest (the probability of which I spoke above) and greek letter lambda refers to the decay constant, which the natural logarithm of 2 divided by the half-lives of the isotopes of interest.

Because the (differential) equation contains positive and negative terms, there is a point at which the Po-210 is being destroyed as fast as it is created. Whenever the reactor is operating, however, there will always be some Po-210 present. When the reactor is shut down, the concentration of Po-210 will actually rise for a period of time and then fall off to zero.

The half-life of Po-210 is 138.376 days. For this reason it is safe to assume that the fast bismuth-lead reactor will contain some Po-210 for several years after shut-down. The reactor thus transmutes some bismuth, which is relatively non-toxic, into lead which is toxic. As it happens though, because of the presence of the lead isotope, Pb-208, the opposite effect also occurs: Some lead is transmuted into bismuth. Which effect dominates depends on the concentration of each isotope. The lowest melting eutectic mixture contains 55% bismuth. Moreover, lead contains only 52.4% lead-208. Thus, depending on the probability of the capture of neutrons by lead-208, it is likely that more bismuth will be made into lead than the other way around.

The former Soviet Union operated naval reactors cooled by lead-bismuth eutectic alloys. They have a lot of experience with this isotope.

For the record, I think the bismuth-lead eutectic reactors are a good idea, even though they obviously involve some risk. The existence of any risk is not sufficient to invalidate a technology. On the contrary, one needs to compare risks. I personally believe that the risk of lead-bismuth fast neutron reactors is considerably lower than the risk of using fossil fuels. Given that lead-bismuth reactors always contain some of the extremely potent poison that killed Livenenko, that says something about how dangerous I think fossil fuels are.

[Kutjara]

1. If I remember my old college chemistry class right...

...Po 210 emits mostly alpha particles. Alpha particles are generally safer than gamma and don't usually penetrate the skin, so Po 210 is not all that dangerous to have around. Of course, if you ingest Po 210, the alpha particles can wreak havoc with your internal organs (a la Mr. Livenenko), so it's best to keep the stuff out of the water supply. With that caveat, however, I'm much more comfortable with a reactor that churns out Polonium as waste than one that produces Plutonium.

[NNadir]

3. This is close, but not strictly true. Many alpha emitters simultaneously emit gammas.

This is certainly true of Po-210. It emits an 0.803 MeV gamma ray 0.12% of the time it decays.

But you are right. What killed Mr. Livenenko is probably the alpha rays. They were deadly only because he ingested them.

To be clear, I like the lead-bismuth reactor because it also can be used to make plutonium. It can be used to destroy plutonium as well, but I believe that if we are to survive global climate change, we will need an inventory of plutonium. We can choose the isotopic composition of this plutonium so that the risk of nuclear weapons proliferation is minimized, but we cannot prevent nuclear weapons proliferation since we cannot uninvent nuclear weapons.

All choices about technology have to be weighed on the basis of probability and the impact of outcome. From where I sit, massively fatal climate change is very likely and is of high impact. Certainly the impact is likely to be much greater than the risk that someone makes a nuclear weapon with "difficult" plutonium.

[Dead_Parrot]

2. Minor niggle...

"Bismuth-210 is unstable and is highly radioactive. It decays to give Po-210 with a half-life of 5.1 days." Sounds like Po-210 has a half life of 5 days, rather than the Bi-210... Hopefully you can beat the edit. :)

[NNadir]

4. OK, this is a misplaced modifier. I will try to fix it.

[NNadir]

5. Thanks. I fixed it.

[Dead_Parrot]

6. :-) nt

[ChairmanAgnostic]

7. thank you for this.

I am still trying to understand why the universe is 6,016 yrs old.

However, from my limited knowledge, a fast neutron reactor has so many neutrons bouncing around that the really nasty isotopes don't get created, AND you can use these neutrons to create more fuel. Kinda like free fuel.

One thing that always confused me was the need for a high temp coolant, like lead or combo you mention. Does a fast breeder need a dense material like lead to trap the neutrons by design?

[NNadir]

8. A fast reactor needs to prevent the neutrons from slowing down.

When a neutron strikes an atom it can do several things. It can be absorbed. It can cause nuclear fission. It can bounce off the atom.

If it bounces off an atom, it generally transfers some its energy to the atom it strikes. How much energy it transfers is a function of how heavy the atom it strikes is. If it strikes a heavy atom, it will keep most of its energy. If it strikes a light atom, it will transfer most of the energy to the light atom. The transferred energy ultimately shows up as heat.

If a reactor has only heavy atoms in it, like lead or bismuth, the neutrons will keep most of their own energy. Since energy is related to speed, the neutrons are said to be "fast."

On a macroscopic level, the energy of particles like atoms and neutrons is expressed as heat. Because neutrons, having no charge, interact only weakly with other types of particles they can actually be "hotter" than the substance through which they travel. If neutrons are traveling at the same speed as most of the atoms in the substance, they are said to be "thermal." If they are not traveling at the same speed as the atoms of the material through which they move, they are said to be "fast."

Referring back to the first sentence in this post, the probability that a neutron will either be absorbed, cause nuclear fission or bounce off is a function of the speed of the neutron - its temperature. It happens that faster neutrons have a lower probability, for most of the normal nuclear fuels - uranium-233, uranium-235, plutonium-239 or plutonium-241, of causing fission than slower neutrons. For this reason, a reactor that is fast must have a higher concentration of fissionable isotopes than one that is thermal. This is why nuclear engineers deliberately slow neutrons down. They can use fuel that is less concentrated in "fissionable" isotopes. A thermal reactor can operate with 3 or 4% of "enrichment." A fast reactor requires enrichments that are 30% or more.

However, it happens that for most nuclei, if they are fissioned by fast neutrons, they release more neutrons when they break apart than they do if they are fissioned by thermal neutrons. This is important because the neutrons that are released not only can sustain the chain reaction, but they can also be absorbed by atoms that are not generally thought of as fissionable. In this process they will often be transmuted. If one is speaking of uranium, this case applies to uranium-238, the most common isotope. When absorbs a neutron, it is ultimately transmuted into plutonium-239 which is useful as a nuclear fuel. A fast reactor will actually, depending on how it is arranged, produce more atoms that are fissionable than it consumes. This is called a "breeder" reactor. Strictly though, all nuclear reactors do some breeding. Fast reactors simply produce new fuel at a faster rate than they consume it. However plutonium is also formed in thermal reactors.

There are a few circumstances under which thermal reactors can be breeders, especially if they are fueled with thorium instead of uranium. Two types of reactors that can accomplish this feat are the CANDU reactor - a type of reactor used in Canada, Argentina, Romania, South Korea, India and Pakistan - and a reactor known as the molten salt reactor, which has only operated in research settings. As it happens, I think it is very regrettable that the molten salt reactor was not commercialized, since it is a superior type of reactor for many reasons. It has been selected as a reactor for the international Gen IV reactor program that will produce the next generation of nuclear reactors.

Actually fast neutrons can split atoms that are generally not thought of as fissionable. For instance, slow neutrons when they strike U-238 cause fissions less than 5% of the time. Fast neutrons on the other hand cause fission about 30% of the time. All nuclear reactors contain some fast neutrons and some slow neutrons. In a thermal reactor the latter dominate. In a fast reactor the former dominate.

The fissioning of atoms that are not generally supposed to be fissionable applies for many nuclei that are not thought of as being nuclear fuel. It is true for, for instance, neptunium-237, plutonium-240, plutonium-242, americium-241, americium-243, curium-246 and so on. Fast neutrons split these isotopes more easily than slow neutrons. All of these nuclei are called the "minor actinides" and they are the most important constituents of so called "nuclear waste." Since these atoms can be destroyed in a fast reactor, releasing energy in the process, many fast reactors are envisioned as "actinide burners," reactors that will reduce the volume and radiotoxicity of spent nuclear fuel. This is probably the application for which many fast reactors will be developed. This is not because spent nuclear fuel represents a huge risk, but because the public perceives that it is a huge risk.

I hope this wasn't too involved for your purposes and that it also answers your questions.

[Porcupine]

9. Lets see if I've got this right.......

I did some background reading......

The Polonium used in the poisoning incident came from a kind of reactor used in the former Soviet Union although there may be other sources. It has a very short half life so it had to have been processed and packaged in the last several months to be useful. This is a known quantity. Reactors produce toxins that can be abused.

The reactor type, a heavy-metal fast-breeder, can be used to consume nuclear waste of the types planned for storage at Yucca mountain should it ever go online. Another type of reactor, a fluidized-salt reactor (FSR), can also consume nuclear wastes especially if used in a plutonium seeded thorium reactor.

These thorium fueled FSR's effectively can't melt down since they are already melted and have a limited fuel supply. They could eat weapons grade nuclear materials and yield relatively low-grade waste compared with the stuff already in cooling ponds across the US. They don't produce anything you could use to make a military-grade nuclear weapon. (low yield dirty bombs excepted)

Containment of materials is about as complicated as you would need in an aluminum smelting plant. No complicated reactor cores, no fuel rods, no complicated pumping systems. No need for crazy elaborate decomissioning and fuel-rod reprocessing needed. Certainly no need for hot graphite near radioactives. Technology tested and proven circa 1968.

The conclusion that I come to is that the AEC decided at some point to scrap the safer/cheaper technology in favor of a deliberately elaborate and complicated nuclear power system. This system they chose provided guaranteed profits for industry, it provided plutonium for a growing weapons stockpile, and it led to the massive piles of waste that we have in cooling ponds. It was never the cheapest or the safest way to produce nuclear power.

The wastes in these ponds could be processed and burned in a thorium FSR for a fraction of the cost of Yucca mountain storage plan. It's the practial equivalent of shooting all the high level waste into the sun. Actually due to power production a profit would be expected. There are no serious plans or proposals to do this at present.

My conclusion is that at every turn the AEC has chosen to use the most-expensive, most dangerous option rather than safer, cheaper, simpler options. They produce waste where none needed to be produced and then come up with the most expensive and unlikely methods of disposing of that waste. Nowhere is a thorium cycle reactor currently online consuming rather than creating nuclear waste.

So what am I missing?

[NNadir]

10. There are very serious plans to build MSR's, what you call FSRs.

The Molten Salt Reactor has been selected for the Gen IV nuclear reactor program that will be developed in the first third of this century, should humanity survive global climate change.

It has four missions. The first is to provide high temperature process heat for processes like thermochemical hydrogen. The second is an actinide burner to consume minor actinides that are constituents of so called "nuclear waste." The third is as a breeder. The fourth is to minimize weapons proliferation potential.

It is an excellent design. It was invented at Oak Ridge Laboratory by the great scientist Alvin Weinberg who died recently at the age of 91.

http://www.democraticunderground.com/discuss/duboard.php?az=show_topic&forum=115&topic_id=71130

I don't know why the reactor wasn't selected for development. Probably the issue was not technical, although Molten Salt Reactors, like any technology, require some development. Although the reactor is very simple, it is not quite as simple as an aluminum smelter.

I don't think Yucca mountain is as dangerous as people like to think. Nor, given what it is doing, providing the only reservoir for the wastes any form of exajoule scale energy, achievable for anything but nuclear energy. That said, I think the best option is simply to store spent fuel above ground in casks until it is needed. It will be needed. Yucca Mountain is a throw back to the 20th century waste mentality.

[eppur_se_muova]

11. "long thought to be the heaviest stable element" ... interesting.

It joins rhenium and 85% of natural indium on the list of "we thought they were stable" nuclei.

[NNadir]

12. The half-life of Bismuth-209 is

2 X 10¹⁹ years. This means that a ton of Bismuth has three radioactive decays per second on average.

I remarked on this some time ago in the science forum.

http://www.democraticunderground.com/discuss/duboard.php?az=show_topic&forum=228&topic_id=12252

I find this matter incredibly cool, in a dorky kind of way.

I always thought it a little odd that the heaviest stable isotope was of an element that had an odd atomic number.

Nuclear stability rules favor even numbered atomic numbers, and even numbers of neutrons. In the entire table of nuclides there is only one stable isotope that has both an odd number of protons and neutrons - our friend nitrogen-14. Every other stable isotope has either an even number of protons or an even number of neutrons.

Two odd numbered elements with lower atomic numbers than bismuth don't even naturally exist in visible amounts on earth, technetium (element 43) and promethium (element 61). Both of these elements are available since the invention of the nuclear reactor in visible amounts, but they do not naturally in the universe occur outside of stars - where they are made by nuclear fusion and by neutron capture - and neither have any stable isotopes.

[eppur_se_muova]

13. Wow, that's *almost* a "millimole" of years. Sun will burn out in, what, ~10^10 yr?

[Dead_Parrot]

14. About 5 billion...

or 5x10¹². 2x10¹⁹ is 20 quintillion... And yes, I had to look it up to be certain. :D

[eppur_se_muova]

15. Oops, you're using Imperial (UK) "billion". I think it's actually 5x10^9...

I was thinking 5-10 billion, the latter being 10¹⁰.

And you just showed me how to do exponents in HTML! :thumbsup:

[Dead_Parrot]

16. Ahem.

Just making sure you were paying attention. Honest