5 ms·

I agree that average over the kilowatt-hours nuclear might be safer than coal. But the problem is that the risk is HIGHLY concentrated. I can self-insure my c

I agree that average over the kilowatt-hours nuclear might be safer than coal. But the problem is that the risk is HIGHLY concentrated. I can self-insure my computers because if one ever fails I have the cash to handle it. It's not a financial crisis. I don't self insure my car (for collision/comprehensive) because it's too big of an expense for me to absorb at any one time without severe hardship. Nuclear reactors (as they stand today) are more like cars than computers. They tend to rob a few people of their whole lives and really eff up the ones that don't die. Coal plants have the "advantage" of robbing many people of a portion of their lives in a more subtle way. LFTR reactors have physics on their side in that if containment is lost, so is criticality. Boiling water reactors, pressurized boiling water reactors, etc in my mind can't be made safe because they require power to stay safe, even if they're not generating power. You've suggested that so long as the generators and whatnot arrive eventually, things will be fine. The problem is that you've made the assumption that somehow, some way the generators will arrive and the reactor can be made safe again over the course of some weeks or months. Nuclear reactors are one of the few pieces of infrastructure that can't simply be abandoned if something bad happens, or else the problem gets worse and worse and worse. This is a positive feedback cycle rather than a negative one. Positive feedback often "blows up" (a term we use in electrical engineering) or grows without bound. Nearly everything else in modern society functions with negative feedback and that kind of intrinsic safety is what most people want. That's not to say that ALL nuclear reactors are by definition unsafe; just all the ones that are currently operating commercially because it's such a nightmare to permit new designs and the existing manufacturers have no interest in inviting competitors into their market.

dllthomas 13y ago
Frankly, I think the concentrated, visible threat is better. We're much better at dealing with those.
pdonis 13y ago
LFTR reactors have physics on their side in that if containment is lost, so is criticality. But loss of criticality isn't sufficient for the reactor to be "safe". Even with the reactor no longer critical, there are still a lot of radioactive fission products left. The way to prevent them from escaping is secondary containment, which Chernobyl did not have, as I said (Fukushima, and indeed every other reactor ever built that wasn't built by the Soviet Union, has secondary containment). Of course, as Fukushima illustrated, secondary containment is not the only necessary feature for safety. You also need decay heat cooling. The key advantage of a design like LFTR, as compared to a design like Fukushima, is passive decay heat cooling; simple thermodynamics is sufficient to keep the fission products contained and cooled after shutdown. That's why such reactors don't, in your words, "require power to stay safe, even if they're not generating power". However, LFTR is not the only possible design with passive decay heat cooling; there are ordinary pressurized water reactor designs that have passive decay heat cooling (by designing the piping circuits and placing the heat exchangers and core to take advantage of natural convection). Fukushima was not such a design, but they do exist (although AFAIK they didn't when Fukushima was built). Nuclear reactors are one of the few pieces of infrastructure that can't simply be abandoned if something bad happens, or else the problem gets worse and worse and worse. This is true, but it's just as true of passively cooled designs like LFTR. The problem here is what to do with the highly radioactive fission products. The way every nuclear-using country except the US deals with this is reprocessing: you take the spent fuel, separate out what's still fissionable (which is a pretty large fraction of it with most current designs), and put what remains through a special reactor that converts the fission products to either much longer-lived (and hence much less radioactive) or stable isotopes. Problem solved. France and Japan have been doing this at scale for several decades now. The only reason the US doesn't is politics.
- msandford 13y ago
  A loss of criticality ensures that you don't end up with a positive feedback cycle that lets the problem spiral out of control faster than you can react, and possibly faster than you can comprehend. A pressurized water reactor relies on the pressure vessel not being breached in order for the passive decay cooling to work, if that happens we're right back to Fukushima/Chernobyl style problems. I am talking about short-term "everyone evacuate the building" types of disaster scenarios. You can do precisely that with a LFTR because of the passive decay heat cooling combined with the loss of criticality that happens when the freeze plug melts. On a longer term the fission products might be a problem with an abandoned LFTR but because of the loss of criticality and the passive decay it's 100% acceptable to just wait for everything to cool down, fix the problem and restart. Or if things are so broken you can't fix them at least you don't have to keep putting people in harm's way to try and prevent a wider-scale disaster. Once things have cooled you go collect the nuclear material and send it to another plant to be used. The best way for me to explain this is with analogies using potential energy. 1. The nuclear power plants we have now are a big heavy rock precariously balanced on top of a fairly narrow peak. Small movements to one side or the other can be recovered from but at some point that rock has started to move and will move aggressively. It will eventually reach the bottom of the hill but not before crushing everything in its path. We don't really even know how bad the damage can get. 2. A LFTR is like a big heavy rock perched about 10 feet up a shallow hill. It requires some energy to keep it there or else it'll roll down hill. You can't really push it up further so it's safe from disturbances in that direction. If you push it down hill (or cease holding it up) it only rolls 10 feet before it naturally hits the bottom and comes to a stop. The majority of the things in the world act more like 2 than 1 and thus we aren't terribly scared of them. Yes there are a great many things you can do to ensure that 1 doesn't get away from you, but ultimately you're still fighting gravity. Let me reiterate, I'm not against nuclear power. I just REALLY don't like the idea of the balancing act that has to be performed in 1 and far prefer the kind of intrinsic safety that you get from 2. I'm all for building plants like 2 even if they're not LFTR based. I don't have religion about the form, I just want as much safety as I can get.
  - colin_mccabe 13y ago
pdonis 13y ago
This is a positive feedback cycle rather than a negative one. It occurred to me on re-reading that you might have been referring here to the fact that the Chernobyl reactor had a number of features that acted to increase rather than decrease reactor power as actions were taken to try to shut it down. Those features are not present in any current reactor designs that weren't made by the Soviet Union. Certainly they were not present in the Fukushima reactors.
- msandford 13y ago
  I was more referring to the idea that once you lose the ability to pump coolant, the reactor starts to heat up. Then as it heats up, it starts to melt itself. As it melts, it re-attains criticality and begins to generate more heat, which leads to more melting, which leads to more heat, ad nauseum. We don't really even know when this stops or how it stops or whatever because the only time (so far) that it really started to get away from us (Chernobyl) a bunch of brave men gave their lives and dumped boron straight on the exposed reactor core to stop it. By doing so they spared us from gaining the very painful knowledge of how a meltdown ends naturally, at what point an equilibrium is reached. EDIT: spelling
  - pdonis 13y ago
    once you lose the ability to pump coolant, the reactor starts to heat up. Then as it heats up, it starts to melt itself. As it melts, it re-attains criticality If it's the Chernobyl design, yes. Not otherwise. See my comments upthread in response to another of your posts. The Chernobyl design had particular features that are not present in any currently operating commercial reactor.

dllthomas 13y ago

Frankly, I think the concentrated, visible threat is better. We're much better at dealing with those.

pdonis 13y ago

LFTR reactors have physics on their side in that if containment is lost, so is criticality. But loss of criticality isn't sufficient for the reactor to be "safe". Even with the reactor no longer critical, there are still a lot of radioactive fission products left. The way to prevent them from escaping is secondary containment, which Chernobyl did not have, as I said (Fukushima, and indeed every other reactor ever built that wasn't built by the Soviet Union, has secondary containment). Of course, as Fukushima illustrated, secondary containment is not the only necessary feature for safety. You also need decay heat cooling. The key advantage of a design like LFTR, as compared to a design like Fukushima, is passive decay heat cooling; simple thermodynamics is sufficient to keep the fission products contained and cooled after shutdown. That's why such reactors don't, in your words, "require power to stay safe, even if they're not generating power". However, LFTR is not the only possible design with passive decay heat cooling; there are ordinary pressurized water reactor designs that have passive decay heat cooling (by designing the piping circuits and placing the heat exchangers and core to take advantage of natural convection). Fukushima was not such a design, but they do exist (although AFAIK they didn't when Fukushima was built). Nuclear reactors are one of the few pieces of infrastructure that can't simply be abandoned if something bad happens, or else the problem gets worse and worse and worse. This is true, but it's just as true of passively cooled designs like LFTR. The problem here is what to do with the highly radioactive fission products. The way every nuclear-using country except the US deals with this is reprocessing: you take the spent fuel, separate out what's still fissionable (which is a pretty large fraction of it with most current designs), and put what remains through a special reactor that converts the fission products to either much longer-lived (and hence much less radioactive) or stable isotopes. Problem solved. France and Japan have been doing this at scale for several decades now. The only reason the US doesn't is politics.

msandford 13y ago
A loss of criticality ensures that you don't end up with a positive feedback cycle that lets the problem spiral out of control faster than you can react, and possibly faster than you can comprehend. A pressurized water reactor relies on the pressure vessel not being breached in order for the passive decay cooling to work, if that happens we're right back to Fukushima/Chernobyl style problems. I am talking about short-term "everyone evacuate the building" types of disaster scenarios. You can do precisely that with a LFTR because of the passive decay heat cooling combined with the loss of criticality that happens when the freeze plug melts. On a longer term the fission products might be a problem with an abandoned LFTR but because of the loss of criticality and the passive decay it's 100% acceptable to just wait for everything to cool down, fix the problem and restart. Or if things are so broken you can't fix them at least you don't have to keep putting people in harm's way to try and prevent a wider-scale disaster. Once things have cooled you go collect the nuclear material and send it to another plant to be used. The best way for me to explain this is with analogies using potential energy. 1. The nuclear power plants we have now are a big heavy rock precariously balanced on top of a fairly narrow peak. Small movements to one side or the other can be recovered from but at some point that rock has started to move and will move aggressively. It will eventually reach the bottom of the hill but not before crushing everything in its path. We don't really even know how bad the damage can get. 2. A LFTR is like a big heavy rock perched about 10 feet up a shallow hill. It requires some energy to keep it there or else it'll roll down hill. You can't really push it up further so it's safe from disturbances in that direction. If you push it down hill (or cease holding it up) it only rolls 10 feet before it naturally hits the bottom and comes to a stop. The majority of the things in the world act more like 2 than 1 and thus we aren't terribly scared of them. Yes there are a great many things you can do to ensure that 1 doesn't get away from you, but ultimately you're still fighting gravity. Let me reiterate, I'm not against nuclear power. I just REALLY don't like the idea of the balancing act that has to be performed in 1 and far prefer the kind of intrinsic safety that you get from 2. I'm all for building plants like 2 even if they're not LFTR based. I don't have religion about the form, I just want as much safety as I can get.
- colin_mccabe 13y ago

pdonis 13y ago

This is a positive feedback cycle rather than a negative one. It occurred to me on re-reading that you might have been referring here to the fact that the Chernobyl reactor had a number of features that acted to increase rather than decrease reactor power as actions were taken to try to shut it down. Those features are not present in any current reactor designs that weren't made by the Soviet Union. Certainly they were not present in the Fukushima reactors.

msandford 13y ago
I was more referring to the idea that once you lose the ability to pump coolant, the reactor starts to heat up. Then as it heats up, it starts to melt itself. As it melts, it re-attains criticality and begins to generate more heat, which leads to more melting, which leads to more heat, ad nauseum. We don't really even know when this stops or how it stops or whatever because the only time (so far) that it really started to get away from us (Chernobyl) a bunch of brave men gave their lives and dumped boron straight on the exposed reactor core to stop it. By doing so they spared us from gaining the very painful knowledge of how a meltdown ends naturally, at what point an equilibrium is reached. EDIT: spelling
- pdonis 13y ago
  once you lose the ability to pump coolant, the reactor starts to heat up. Then as it heats up, it starts to melt itself. As it melts, it re-attains criticality If it's the Chernobyl design, yes. Not otherwise. See my comments upthread in response to another of your posts. The Chernobyl design had particular features that are not present in any currently operating commercial reactor.