Is Solar Energy = Nuclear Energy?

mirozThe RBMK was a terrible design - it used a graphite moderator to slow down neutrons to energies where they could cause fission, but water coolant. In modern reactors, water is used as both a moderator and a coolant. if the reaction rate gets too high, the core will heat up, decreasing the density of the water and decreasing its moderating capability, slowing the reaction and pushing the core back towards stability.

I haven't talked about or read about this in a while but... Don't you want to moderate more to slow the reaction? Although I suppose I'm using a more colloquial definition of the word and I was thinking about removing neutrons from the neutron flux entirely, not slowing them.

Do the high energy neutrons not contribute to the reaction nearly as much as the slower ones? I know a 'moderated' neutron will absorb more readily than one going whatever fraction the speed of light they go. I was under the impression that the high energy ones can cause a lot of fission in the right type of reactor. Anyway, the question is that does moderation to slower speeds increase the rate of reaction relative to just leaving them as high energy neutrons in whatever sort of reactor we're talking about. BWR perhaps? They push the boron rods or whatever in to remove neutrons from the flux right?

Rosa_Parkas part of the test, yes. There are a lot of things the workers did that would usually be considered poor running of the plant, because the accident happened during a drill that was meant to practice what they would do in case of an accident.

as you said yourself:


however, I do agree with you that as computers and such start being more involved, it will be safer, but that doesn't eliminate all of the accidents. we have had 2 in the ~100 years that we have had nuclear power, even if we can go 500 without another, that still sucks, and is more than would happen with other energy sources.

I think you're arguing semantics. My point is that your description of the accident was incorrect. They withdrew the control rods because they wanted to get the reactor to the low power level prescribed by the test, not as a part of the test. It was the actions leading up to the "test" that doomed the reactor. The reactor's instability at low power was a product of design, and the operator's insistence on performing the test despite numerous signals that the reactor was suffering was plain stupidity.

What other energy sources? We cannot sustain our way of life without baseload power in some form. Power storage does not have the capacity to meet that demand even if renewables adopt a significant chunk of the generation mix. If you want change now, you have to displace coal. Burning coal affects orders of magnitude more people per unit energy generated via air pollution than nuclear ever has or will.

DrZoidbergI haven't talked about or read about this in a while but... Don't you want to moderate more to slow the reaction? Although I suppose I'm using a more colloquial definition of the word and I was thinking about removing neutrons from the neutron flux entirely, not slowing them.

Do the high energy neutrons not contribute to the reaction nearly as much as the slower ones? I know a 'moderated' neutron will absorb more readily than one going whatever fraction the speed of light they go. I was under the impression that the high energy ones can cause a lot of fission in the right type of reactor. Anyway, the question is that does moderation to slower speeds increase the rate of reaction relative to just leaving them as high energy neutrons in whatever sort of reactor we're talking about. BWR perhaps? They push the boron rods or whatever in to remove neutrons from the flux right?

The type of flux you want depends on the reactor and fuel type. Almost all reactors deployed today are thermal reactors (e.g. PWR/BWR) in that they rely on slow, "thermal" neutrons to drive the reaction. Fast neutrons contribute some fissions, but the cross-section for fast fission in a thermal design isn't as large.

Moderation is the slowing down the neutrons. In thermal reactors, this occurs as they collide with lighter nuclei to lose energy. Good moderators are water, heavy water, graphite, etc. I think you're thinking of absorption/reactivity control, which in PWR/BWR happens with dissolved boron in the coolant and control rods (boron, cadmium); these nuclei have high absorption cross-sections so they remove neutrons from the flux. Technically, neutrons can be absorbed in the moderator, but this is undesirable and not a major mechanism of removal from the flux.

I never thought I'd be posting a cross-section on newschoolers. The cross-section is the likelihood of a neutron interaction; here, it's plotted against incoming neutron energy for U-235. It gets much higher as the energy gets lower. U-235 is special (aka fissile) because it can fission with low-energy neutrons. Most nuclei that can fission will only do so with high-energy neutrons (and even then, the cross-sections are still small). In a fast reactor, you have to have fuel with a relatively high fissile content to offset the decrease in likelihood of fission, but that comes with a variety of benefits.

I'm not in reactor design, so hopefully that makes sense.

applejuice.I would love to know what a Nuclear facility's HAZOP/PHA is like.

It's crazy. The industry uses unbelievably thorough probabilistic risk assessments to quantify the likelihood of serious accidents in every aspect of plant design. I don't know much about it, but I know it's a huge deal in operation and regulation.

mirozI never thought I'd be posting a cross-section on newschoolers.

Never thought I'd see one. I'm a chemist so I'm familiar with the concept. I just never got to learn as much nuclear chemistry and the like as I wanted while in school because there weren't really any classes for it. Likewise, I don't know much about the reactor types that are currently deployed to power stuff. But yeah I guess I was thinking about just straight up soaking up neutrons with boron/whichever other high cross sectional element they've picked for their neutron energy. Reactor design is interesting stuff.

What's the reason for the oscillation at 1 to 10000 electron volts?

And as far as waste goes, we know what to do with spent fuel. We still don't know what to do with CO2 and other emissions from burning fossil fuels.

mirozIt's crazy. The industry uses unbelievably thorough probabilistic risk assessments to quantify the likelihood of serious accidents in every aspect of plant design. I don't know much about it, but I know it's a huge deal in operation and regulation.

I work in the natural gas industry designing and constructing processing facilities. Those analyses are critical.

DrZoidbergNever thought I'd see one. I'm a chemist so I'm familiar with the concept. I just never got to learn as much nuclear chemistry and the like as I wanted while in school because there weren't really any classes for it. Likewise, I don't know much about the reactor types that are currently deployed to power stuff. But yeah I guess I was thinking about just straight up soaking up neutrons with boron/whichever other high cross sectional element they've picked for their neutron energy. Reactor design is interesting stuff.

Sick! What kind of chemistry do you do? I did chemical engineering undergrad.

DrZoidbergWhat's the reason for the oscillation at 1 to 10000 electron volts?

This is wayyyy out of my wheelhouse, haha! Those are resonances. The way the reaction happens is that the nucleus absorbs the neutron to form a compound nucleus. Once a compound nucleus is formed, it "forgets" how it was formed and can go on to do any number of things (described probabilistically). So, the likelihood of all compound-nucleus reactions, including fission, depends on forming the compound nucleus in the first place. A neutron is way more likely to be absorbed into nucleus if it's energy is equal to the exact energy of a discrete energy state in the target nucleus. In that case, it fits right in, hence the high cross-sections in that region. The resonances actually continue to the right of that region, but they get wider with higher energies such that they're no longer visible.

DrZoidbergAnd as far as waste goes, we know what to do with spent fuel. We still don't know what to do with CO2 and other emissions from burning fossil fuels.

Word! I think this is one of the issues that nuclear power faces - because the coal plants and their emissions are largely out of sight, it's a distant problem. The way our grid is designed, people often don't know where their energy comes from. Meanwhile, people take issue with the prospect of generating spent fuel - even tiny amounts of it - because it's not currently here.

Anyone have an opinion on power plant security? Apparently all a terrorist would need to do to cause a meltdown is "cut off primary power and backup power sources feeding the cooling pumps."
Or they could use explosives to release radioactive material.

mirozSick! What kind of chemistry do you do? I did chemical engineering undergrad.



This is wayyyy out of my wheelhouse, haha! Those are resonances. The way the reaction happens is that the nucleus absorbs the neutron to form a compound nucleus. Once a compound nucleus is formed, it "forgets" how it was formed and can go on to do any number of things (described probabilistically). So, the likelihood of all compound-nucleus reactions, including fission, depends on forming the compound nucleus in the first place. A neutron is way more likely to be absorbed into nucleus if it's energy is equal to the exact energy of a discrete energy state in the target nucleus. In that case, it fits right in, hence the high cross-sections in that region. The resonances actually continue to the right of that region, but they get wider with higher energies such that they're no longer visible.



Word! I think this is one of the issues that nuclear power faces - because the coal plants and their emissions are largely out of sight, it's a distant problem. The way our grid is designed, people often don't know where their energy comes from. Meanwhile, people take issue with the prospect of generating spent fuel - even tiny amounts of it - because it's not currently here.

I just did bs. chem. Did lots of p chem and quantum stuff as I find the mathematical side of all this quite interesting, and I basically made my own fluorescence spectrometer for PAC detection too.