Radioactive Wolves.

[Gawdzilla Sama]

Hopefully the fission plants will make them obsolete. Fusion plants didn't. I would love to stop seeing coal trains with 140+ box cars rumble past our house. It's the majority of rail traffic around here, heading for the St. Louis power plant.

Did you accidentally exchange "fission" and "fusion"? Fission plants have been around for half a century, and coal plants are still around. I doubt that fusion plants would have any different an effect.

Yeah, my bad.

[JimC]

Did a little bit of a Wiki search, found this:

"Neutron-induced swelling is the increase of volume and decrease of density of materials subjected to intense neutron radiation. Neutrons impacting the material's lattice rearrange its atoms, causing buildup of dislocations, voids, and Wigner energy. Together with the resulting strength reduction and embrittlement, it is a major concern for materials for nuclear reactors."

http://en.wikipedia.org/wiki/Neutron-induced_swelling

[Schneibster]

Isotopes of titanium: http://en.wikipedia.org/wiki/Isotopes_of_titanium

Three quarters, more or less, of titanium is 50Ti. Add two neutrons, and it's 52Ti, which has a halflife of 1.7 minutes and decays into 52V by beta emission. Vanadium and titanium do not bond well, and the presence of vanadium in the titanium matrix weakens it by an amount that increases with temperature. Since the reason for using titanium in the first place is to withstand high temperatures, its strength is compromised in the environment most likely to cause failure.

Titanium is used to build pressure vessels for nuclear reactors.

Just sayin'.

[JimC]

Isotopes of titanium: http://en.wikipedia.org/wiki/Isotopes_of_titanium

Three quarters, more or less, of titanium is 50Ti. Add two neutrons, and it's 52Ti, which has a halflife of 1.7 minutes and decays into 52V by beta emission. Vanadium and titanium do not bond well, and the presence of vanadium in the titanium matrix weakens it by an amount that increases with temperature. Since the reason for using titanium in the first place is to withstand high temperatures, its strength is compromised in the environment most likely to cause failure.

Titanium is used to build pressure vessels for nuclear reactors.

Just sayin'.

A typical engineers work-around would be to make the vessel considerably thicker that would be required without such radiation-induced weakening, so it will still be sufficiently strong at the end of its working life.

You are right, of course, about neutron-induced transmutation. When 1 or more neutrons have been absorbed, the decay process will typically be by the emission of a beta minus particle, involving a jump upwards by one in atomic number; ie. a different element, which will often result in defects within the metallic lattice.

I make lots and lots of questions based on such changes for my physics lads; they get drilled on it extensively...

[Svartalf]

Is anybody actually paying attention to the drivel warren spouts?

[Schneibster]

Isotopes of titanium: http://en.wikipedia.org/wiki/Isotopes_of_titanium

Three quarters, more or less, of titanium is 50Ti. Add two neutrons, and it's 52Ti, which has a halflife of 1.7 minutes and decays into 52V by beta emission. Vanadium and titanium do not bond well, and the presence of vanadium in the titanium matrix weakens it by an amount that increases with temperature. Since the reason for using titanium in the first place is to withstand high temperatures, its strength is compromised in the environment most likely to cause failure.

Titanium is used to build pressure vessels for nuclear reactors.

Just sayin'.

A typical engineers work-around would be to make the vessel considerably thicker that would be required without such radiation-induced weakening, so it will still be sufficiently strong at the end of its working life.

Another would be to have test strips at various critical structural points that can be pulled off and tested to see how it's holding up. They do both of those things. OTOH, there are ones that seem OK now that might or might not have problems that can't be detected because nobody foresaw them. There is a potential problem that wouldn't show up except in case of an emergency shutdown, because it is in the auxiliary cooling pipes; they could be corroded, probably are, but nobody can get close enough to find out because of the heat and radiation. The only way to check is to shut it down and send a robot "pig" in through the pipes (a "pig" is a cleaner plug that mostly fills the pipe and can be used to scrape out obstructions or take pictures as it moves along inside the pipe). This is expensive so the money people whine really loudly, and unfortunately the powers that be listen to the money people more than to the engineers. That's a general problem that needs to change if fission power is ever to succeed.

[MiM]

Is anybody actually paying attention to the drivel warren spouts?

I think you should, as he mostly seems to have the big picture right, even though the way he puts things it easily looks like he would be completely off. I think he is good at balancing what Schneib does not seem to get.

The main problem with neutron irradiation of pressure vessels is changes in micro structure and lattice, (as Jim already pointed out) not in neutron induced transmutation of the elements. Of course elements also change from neutron radiation and subsequent radioactive decay, but that is not a main player here. As an example, a few years ago at the Loviisa NPP they reheated (gloved?, don't know the exact term in English) some welds in the pressure vessel to regain their original strength after it had been degenerated by neutron damage. If the damage had been due to significant transmutation a simple heat treatment would have been of little use.

BTW: Schneib.
- You got the Ti isotopes wrong (check your own source again).
- Having double neutron hits to the same atom is a very rare event, unless you have really high neutron flux.
- Please give example of nuclear pressure vessels made of titanium. All I have ever heard of are made of steel.

[Schneibster]

Wikipedia article on titanium. Maybe you should go fix it since you think you know so much.

Really high neutron flux, like, you know, in a fission reactor, duh.

All of the ones on submarines, duh ummm.

Is there some point in this or are you just tantrumming again?

[MiM]

Wikipedia article on titanium. Maybe you should go fix it since you think you know so much.

Nothing wrong (asfaik) with that wikipedia article.You just misread the table in a quite amazing manner. The main Ti isotope is 48, not 50,and the first radioactive in the line is 51, not 52. so there is three neutron hits needed to go all the way from the most abundant to the radioactive one, not two. Which changes this factor from a second ordered to a third ordered. More importantly. In naturally occurring Ti, there is 5% of isotope 50, which would become Ti-51 with only one neutron capture and then decay to stable V-51. In any normal circumstance this would be the the dominating process for transmutation

By the way, the Ti-52 -> V-52 that you suggested would immediately decay further to Cr-52. V-51 on the other hand is stable.

So maybe you could slow down, and think twice about who is tantrumming, if anyone. I for one prefer to keep discussions factual.

[MiM]

Is anybody actually paying attention to the drivel warren spouts?

I think you should, as he mostly seems to have the big picture right, even though the way he puts things it easily looks like he would be completely off. I think he is good at balancing what Schneib does not seem to get.

Should add "keep MiM on his edge" here too. It's all too easy to start giving sloppy explanations if nobody challenges them.

[Warren Dew]

Did a little bit of a Wiki search, found this:

"Neutron-induced swelling is the increase of volume and decrease of density of materials subjected to intense neutron radiation. Neutrons impacting the material's lattice rearrange its atoms, causing buildup of dislocations, voids, and Wigner energy. Together with the resulting strength reduction and embrittlement, it is a major concern for materials for nuclear reactors."

http://en.wikipedia.org/wiki/Neutron-induced_swelling

That article appears to conflate and misreport two different effects, not surprising since the author of it didn't bother to check any sources. Even then, neither one has to do with any chemical change; the dislocations involve atoms that are moved within the lattice, but they are still the same atoms, from the same element, as before.

Basically your article just confirms that Schniebster is blowing smoke on this subject.

If you are interested, the two real, nonchemical, effects referred to are as follows. The first effect occurs only in nuclear reactor fuel rods. These fuel rods swell, due to buildup of gaseous fission products inside them. However, fuel rods are high level waste, which is not what we were talking about in this subthread. The only thing you can do with spent fuel other than dispose of it is reprocess it, which was discussed in another subthread; melting it down won't allow for reuse since it would still be spent fuel rather than new fuel.

The other effect is atomic displacement in solid materials - the microstructure and crystal lattice changes Mim refers to - some of which does happen in structural materials and not just in fuel. Different materials are affected differently by this. In steel, which is the primary structural material in most nuclear plants, the interstitial atoms that result from it actually increase the strength of the steel, but decrease the toughness; the effect is sometimes called "neutron embrittlement" - not "swelling", as the wikipedia article would have it.

In smaller nuclear plants - which include the oldest of the commercial water reactors - neutron embrittlement can limit the lifetimes of reactor vessels. As nuclear plants got larger, this became less of a problem, because in larger plants, there's more water in the reactor vessel to absorb neutrons between the reactor core where they are produced and the reactor vessel, which meant that there was less neutron flux to embrittle the reactor vessel.

Even in the smaller plants, though, the crystalline vacancies and interstitials that cause neutron embrittlement could be ameliorated by in place annealing. That would be expensive, but it would still be a lot cheaper and more efficient than ripping out the reactor vessels and trying to resmelt the mildly radioactive metal. In larger plants, reactor vessel annealing would probably not be needed to extend the lives of the plants.

Plus, with plant life extension, you get to reuse the turbines, generators, and other equipment, as well as the containment building itself.

[MiM]

All of the ones on submarines.

Do you have a source for this? This is not that I try to claim you wrong, but as I now almost nothing about naval reactors, I tried to search, but came up with nothing. Searches are muffled by the fact that some of the submarines has titanium hulls.

BTW: Typical neutron fluxes for power reactor vessels are about 10^13 to 10^15 [n/(m²*s)], giving lifetime fluencies of 10^22 to 10^24 [n/m²).* These are big number, but still small when multiplied with typical capture cross sections (probabilities) which are usually a few barns (1 barn = 10^⁻28m²). Naval reactors probably operate with significantly higher fluxes, though.

* IAEA Nuclear Energy Series No. NP-T-3.11

[MiM]

In smaller nuclear plants - which include the oldest of the commercial water reactors - neutron embrittlement can limit the lifetimes of reactor vessels. As nuclear plants got larger, this became less of a problem, because in larger plants, there's more water in the reactor vessel to absorb neutrons between the reactor core where they are produced and the reactor vessel, which meant that there was less neutron flux to embrittle the reactor vessel.

Even in the smaller plants, though, the crystalline vacancies and interstitials that cause neutron embrittlement could be ameliorated by in place annealing. That would be expensive, but it would still be a lot cheaper and more efficient than ripping out the reactor vessels and trying to resmelt the mildly radioactive metal. In larger plants, reactor vessel annealing would probably not be needed to extend the lives of the plants.

Plus, with plant life extension, you get to reuse the turbines, generators, and other equipment, as well as the containment building itself.

Not sure if I completely agree that neutron embrittlement of the pressure vessel would be that much less of a problem with newer bigger reactors. The pressure vessel is the single part in a reactor that cannot be economically replaced, so it is largely the limiting factor on the lifespan of the plant (please let's forget bad management and politics here). The main reasons for pressure vessels ageing are corrosion (google "David Besse" for a horror story) and neutron stress. The Areva EPR being built in Olikiluoto right now will be the largest reactor in the world (if they get it finished), and it is equipped with a neutron reflector inside the vessel. Of course this reflector has a role in evening out neutron flux in the core, and thus facilitating better fuel economy, but at least according to Areva, it is also a major reason that they are able to claim a 60 year design age for this reactor.

Otherwise I am all for extended usage times for reactors, as long as the country has a good enough system for retrofitting new security characteristics to old plants, something that afaik is not the case in the USA, and definitely has not been in Japan (thus Fukushima).

[Warren Dew]

The pressure vessel is the single part in a reactor that cannot be economically replaced, so it is largely the limiting factor on the lifespan of the plant (please let's forget bad management and politics here).

It's the limiting factor in the real lifespan, but not typically in the nominal design lifetime. Turbines and other equipment often have design lives of 20 years or so. If the reactor vessels were limiting to the nominal design lifetime you'd see people cutting out the reactor vessel and replacing it, continuing to use the rest of the plant, as that would be way cheaper than building a new plant.

The Areva EPR being built in Olikiluoto right now will be the largest reactor in the world (if they get it finished), and it is equipped with a neutron reflector inside the vessel. Of course this reflector has a role in evening out neutron flux in the core, and thus facilitating better fuel economy, but at least according to Areva, it is also a major reason that they are able to claim a 60 year design age for this reactor.

Neutron reflectors have been standard technology present in many plants for decades. Most likely the reason they can claim such a long initial design lifetime is because it's the largest, not because of the neutron reflector - and of course they must have pushed on the lifetimes of the turbines and pumps and the rest of the equipment.

Otherwise I am all for extended usage times for reactors, as long as the country has a good enough system for retrofitting new security characteristics to old plants, something that afaik is not the case in the USA, and definitely has not been in Japan (thus Fukushima).

The specific problem that happened in Fukushima - loss of all plant electrical power, which is why they could no longer cool the plants - was addressed in the U.S. by the "station blackout" safety initiative in the 1990s. Most plants here did some sort of retrofit, though there may have been a few plants that already met the criteria or that just calculated their way out of it.

[MiM]

Warren, these things are relative, and hardly worth arguing too much about on a forum level. Naturally overall ageing of the plant is also important.