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I don't think that the safety problem with nuclear power lies in the reactors themselves. It lies in the fragility of the human civilisations operating them. E

I don't think that the safety problem with nuclear power lies in the reactors themselves. It lies in the fragility of the human civilisations operating them. Even a flawed design is safe in the hands of responsible, sane, civilised people who get to perform their jobs without disruption from war, natural disasters, famine or whatever else. And if those conditions are removed, no known reactor design is safe. The main problem with nuclear is that nobody can guarantee - let alone pay for - civilised, sane conditions for a sufficiently long time period for the operation as a whole to be considered safe (or profitable, all things considered).

DennisP 4y ago
> And if those conditions are removed, no known reactor design is safe. The claim for MSRs is that they actually are inherently safe. - There's nothing the on-site staff can do to cause a serious accident, even if they want to. The reactor is stable because of the physics of fuel and coolant, not because of active control systems. - There's a strong negative feedback the slows the reaction rate as the fuel heats up. - If somehow you get overheating anyway, or if electric power to the pumps cuts off, passive systems automatically shut down the reactor. One common design is a freeze plug that melts when you stop cooling it, causing the fuel to dump into a tank that passively cools it. Another uses a similar approach to dissolve a strong neutron poison in the fuel, shutting down the reaction. - Since the fuel is liquid, you never need a large amount of fissile material in the fuel. You can add a little at a time. It's also possible to remove some of the fission products as you go. - The most troublesome fission products are chemically bound in the salt, so even is someone destroys your reactor with artillery, you don't get a large radioactive cloud, just hot rocks at the reactor site. - For either thorium or fast uranium MSRs, the waste products are just fission products, not the long-lived transuranics. Encase them in glass and bury them, and they'll be back to the radioactivity of the original ore in 300 years. Since the decline is exponential, most of the radioactivity goes away in the first few decades.
- Schroedingersat 4y ago
  > The claim for MSRs is that they actually are inherently safe. Safer isn't safe. Hopefully safer is safe enough to make them affordable even given the much worse conditions the materiala need to withstand, but there are other risks involved (how to make the USA or Russia let you have one without installing a puppet government given they can make superweapons grade Pu is one). > There's a strong negative feedback the slows the reaction rate as the fuel heats up. This is only true of two fluid MSRs. Many of the other advantages are only true of one fluid MSRs. > Since the fuel is liquid, you never need a large amount of fissile material in the fuel. You can add a little at a time. You still need a critical mass and you don't have water as a moderator. The quantity of fissile material is equal or higher than in a PWR. There may be significantly less fertile material in the core though (but about as much in the blanket). > It's also possible to remove some of the fission products as you go. > The most troublesome fission products are chemically bound in the salt, so even is someone destroys your reactor with artillery, you don't get a large radioactive cloud, just hot rocks at the reactor site. The purification/extraction step has never been demonstrated and many of the best candidates for salts are water soluble. > For either thorium or fast uranium MSRs, the waste products are just fission products, not the long-lived transuranics. Encase them in glass and bury them, and they'll be back to the radioactivity of the original ore in 300 years. Since the decline is exponential, most of the radioactivity goes away in the first few decades. Yes. This is a huge upside. As is the corollary that there is actually enough fuel.

DennisP 4y ago

> And if those conditions are removed, no known reactor design is safe. The claim for MSRs is that they actually are inherently safe. - There's nothing the on-site staff can do to cause a serious accident, even if they want to. The reactor is stable because of the physics of fuel and coolant, not because of active control systems. - There's a strong negative feedback the slows the reaction rate as the fuel heats up. - If somehow you get overheating anyway, or if electric power to the pumps cuts off, passive systems automatically shut down the reactor. One common design is a freeze plug that melts when you stop cooling it, causing the fuel to dump into a tank that passively cools it. Another uses a similar approach to dissolve a strong neutron poison in the fuel, shutting down the reaction. - Since the fuel is liquid, you never need a large amount of fissile material in the fuel. You can add a little at a time. It's also possible to remove some of the fission products as you go. - The most troublesome fission products are chemically bound in the salt, so even is someone destroys your reactor with artillery, you don't get a large radioactive cloud, just hot rocks at the reactor site. - For either thorium or fast uranium MSRs, the waste products are just fission products, not the long-lived transuranics. Encase them in glass and bury them, and they'll be back to the radioactivity of the original ore in 300 years. Since the decline is exponential, most of the radioactivity goes away in the first few decades.

Schroedingersat 4y ago
> The claim for MSRs is that they actually are inherently safe. Safer isn't safe. Hopefully safer is safe enough to make them affordable even given the much worse conditions the materiala need to withstand, but there are other risks involved (how to make the USA or Russia let you have one without installing a puppet government given they can make superweapons grade Pu is one). > There's a strong negative feedback the slows the reaction rate as the fuel heats up. This is only true of two fluid MSRs. Many of the other advantages are only true of one fluid MSRs. > Since the fuel is liquid, you never need a large amount of fissile material in the fuel. You can add a little at a time. You still need a critical mass and you don't have water as a moderator. The quantity of fissile material is equal or higher than in a PWR. There may be significantly less fertile material in the core though (but about as much in the blanket). > It's also possible to remove some of the fission products as you go. > The most troublesome fission products are chemically bound in the salt, so even is someone destroys your reactor with artillery, you don't get a large radioactive cloud, just hot rocks at the reactor site. The purification/extraction step has never been demonstrated and many of the best candidates for salts are water soluble. > For either thorium or fast uranium MSRs, the waste products are just fission products, not the long-lived transuranics. Encase them in glass and bury them, and they'll be back to the radioactivity of the original ore in 300 years. Since the decline is exponential, most of the radioactivity goes away in the first few decades. Yes. This is a huge upside. As is the corollary that there is actually enough fuel.