4 ms·

That's a common reaction, but it doesn't stand to much scrutiny. Before radiation gets to the public, about 4 or 5 different barriers have to fail. The first is

That's a common reaction, but it doesn't stand to much scrutiny. Before radiation gets to the public, about 4 or 5 different barriers have to fail. The first is the fuel pin, then the cladding metal, then the coolant itself (which can often absorb problematic fission products), then the reactor vessel, then the containment, and then dispersal. You're focusing on containment/dispersal. But how do the first ones fail? The answer is that lack of decay heat removal allows the earlier barriers to heat up, melt, and fail. Well, if you have an intimate connection to an infinite heat sink (the sea), you don't ever lose decay heat cooling. You can't! So your fuel and clad stay intact in almost all scenarios. Earthquakes? No problem, the sea buffers you. Tsunamis? No problem, stay in moderately deep water and the wavelengths are so long that you'll barely notice them. Heavy weather? The world's largest ship (Prelude) is designed to stay operating (it's a LNG facility) during Cat 5 cyclones. Military attack? Sink and cool passively until a designed recovery operation can occur Ship collision? Stay out of shipping lanes; worse case, sink and don't leak. Also, keep people out of your exclusion zone by being a few km offshore. Honestly it's a pretty slick low-carbon rapid deployment scenario that improves construction cost and safety. Operation will likely be more expensive, but maintenance maybe not (since you can go home to the shipyard and be relieved by a spare).

bronson 8y ago
Most energy profit comes from externalizing the costs. Floating reactors would do that fantastically! Love the "sink and don't leak" requirement.
- acidburnNSA 8y ago
  Better stated: sink and don't leak because you are intimately linked to a near-infinite heat sink, and heating up/melting are a prerequisite to leaking.
  - DoctorOetker 8y ago
    that doesn't discuss corrosion though, the ocean is full of salt, how many half-lives until corrosion prevents containment?
    - acidburnNSA 8y ago
      The ocean would take a while to corrode through a couple dozen cm of steel, especially in cold water. But you're right that eventual leakage is a concern. A viable design of this kind of system would have to come with a sink-safely-and-cool design fully engineered as well as a designed recovery process. In other words, it should be expected that a recovery and disposal operation will be required (even though it's unlikely to be needed). This system should be designed so the salvage/recovery operation is easy. Nuclear accidents generally worry about something called Large Early Release Frequency. Some of the most bioactive/dangerous fission products decay away in a few days. This kind of scenario completely eliminates those FPs from concern, though we do still have to worry about the longer-lived ones.
      - DoctorOetker 8y ago
        is that assuming steel at the same temperature as the surrounding salt still water, or assuming steel that is hotter than the constantly convecting stream of fresh salty water?
        acidburnNSA 8y ago
        The way the heat transfer would work in this scenario would have small temperature gradients on the outermost layer of heat transfer because steel and water are good heat transfer mechanisms. This isn't hypothetical. This list may interest you: https://en.wikipedia.org/wiki/List_of_sunken_nuclear_submarines https://en.wikipedia.org/wiki/List_of_sunken_nuclear_submari...
        DoctorOetker 8y ago
        I wasn't asking about a list of sunken submarines?
        acidburnNSA 8y ago
        They are scuttled floating nuclear reactors at the bottom of the sea. These are real-life examples very similar to the scenario you are inquiring about. They have not corroded away and released wholesale nuclear waste after many decades. If that's not relevant to your line of inquiry then I must be totally misunderstanding you.
mturmon 8y ago
"So your fuel and clad[ding] stay intact in almost all scenarios." With that much "no problem", it seems like something may have been overlooked in your summary above.
- acidburnNSA 8y ago
  Are you referring to "almost all"? Experienced engineers never speak in absolutes.
  - mturmon 8y ago
    It's the breeziness and imprecision of "almost all" and "no problem" that gives a bad impression about how far these words can be trusted. What does such a claim actually mean?
    - acidburnNSA 8y ago
      Ah, I see. Well I'm definitely trying to whip up excitement to the public here. If I tell you that the LERF goes from 1e-3/year to 1e-8/year, a lot of people wouldn't understand the implication, which is, effectively, "no problem". Nuclear engineers tend to speak in acronyms and numbers, I try to distill it down. There is weight behind these kinds of estimates though.
      - mturmon 8y ago
        On the other hand, one would not want to oscillate between breezy "no problem" claims, and engineering jargon. Because jargon is likewise not convincing. It might be helpful to just link to the reliability assessment. The document linked from the MIT website is just a conference publication (I looked it up) which is pretty vague and is really just a concept overview. Note: I acknowledge that you have much more expertise here than I do, but it's not translating well. OTOH, I'm receptive to actual analysis - I have a PhD and work in a model-intensive engineering field.
        8y ago
dnhz 8y ago
In order for the sea to act as a heat sink, many of the initial barriers will have failed. Only then can sea water touch overheating fuel. How does being in the sea stop the fuel rods from melting (or whatever they do when they're going bad)?
- acidburnNSA 8y ago
  Natural circulation heat exchangers. The AP1000 has this huge tank of water on the roof that can cool things for 72 hours. Then it runs out of water. At sea with some displacement you use this system but never run out of water.
e3b0c 8y ago
That risk assessment assumes only the technical aspects. But there are still institutional, management and other 'people' issues that could render any engineering guarantee fruitless. Otherwise, the delivery of nuclear plants would have no way to off schedule. I have no objection to the development of nuclear technology. But as I understand, what concerns people is not entirely the 'likelihood' of the disasters but rather the 'severity' of them. After all, People make mistakes and organizations corrupt. So, I think any tech progresses on the scale-down of the worst case where all safety is off would be far more helpful in convincing the public.

bronson 8y ago

Most energy profit comes from externalizing the costs. Floating reactors would do that fantastically! Love the "sink and don't leak" requirement.

acidburnNSA 8y ago
Better stated: sink and don't leak because you are intimately linked to a near-infinite heat sink, and heating up/melting are a prerequisite to leaking.
- DoctorOetker 8y ago
  that doesn't discuss corrosion though, the ocean is full of salt, how many half-lives until corrosion prevents containment?
  - acidburnNSA 8y ago
    The ocean would take a while to corrode through a couple dozen cm of steel, especially in cold water. But you're right that eventual leakage is a concern. A viable design of this kind of system would have to come with a sink-safely-and-cool design fully engineered as well as a designed recovery process. In other words, it should be expected that a recovery and disposal operation will be required (even though it's unlikely to be needed). This system should be designed so the salvage/recovery operation is easy. Nuclear accidents generally worry about something called Large Early Release Frequency. Some of the most bioactive/dangerous fission products decay away in a few days. This kind of scenario completely eliminates those FPs from concern, though we do still have to worry about the longer-lived ones.
    - DoctorOetker 8y ago
      is that assuming steel at the same temperature as the surrounding salt still water, or assuming steel that is hotter than the constantly convecting stream of fresh salty water?
      - acidburnNSA 8y ago
        The way the heat transfer would work in this scenario would have small temperature gradients on the outermost layer of heat transfer because steel and water are good heat transfer mechanisms. This isn't hypothetical. This list may interest you: https://en.wikipedia.org/wiki/List_of_sunken_nuclear_submarines https://en.wikipedia.org/wiki/List_of_sunken_nuclear_submari...
        DoctorOetker 8y ago
        I wasn't asking about a list of sunken submarines?
        acidburnNSA 8y ago
        They are scuttled floating nuclear reactors at the bottom of the sea. These are real-life examples very similar to the scenario you are inquiring about. They have not corroded away and released wholesale nuclear waste after many decades. If that's not relevant to your line of inquiry then I must be totally misunderstanding you.

mturmon 8y ago

"So your fuel and clad[ding] stay intact in almost all scenarios." With that much "no problem", it seems like something may have been overlooked in your summary above.

acidburnNSA 8y ago
Are you referring to "almost all"? Experienced engineers never speak in absolutes.
- mturmon 8y ago
  It's the breeziness and imprecision of "almost all" and "no problem" that gives a bad impression about how far these words can be trusted. What does such a claim actually mean?
  - acidburnNSA 8y ago
    Ah, I see. Well I'm definitely trying to whip up excitement to the public here. If I tell you that the LERF goes from 1e-3/year to 1e-8/year, a lot of people wouldn't understand the implication, which is, effectively, "no problem". Nuclear engineers tend to speak in acronyms and numbers, I try to distill it down. There is weight behind these kinds of estimates though.
    - mturmon 8y ago
      On the other hand, one would not want to oscillate between breezy "no problem" claims, and engineering jargon. Because jargon is likewise not convincing. It might be helpful to just link to the reliability assessment. The document linked from the MIT website is just a conference publication (I looked it up) which is pretty vague and is really just a concept overview. Note: I acknowledge that you have much more expertise here than I do, but it's not translating well. OTOH, I'm receptive to actual analysis - I have a PhD and work in a model-intensive engineering field.
      - 8y ago

dnhz 8y ago

In order for the sea to act as a heat sink, many of the initial barriers will have failed. Only then can sea water touch overheating fuel. How does being in the sea stop the fuel rods from melting (or whatever they do when they're going bad)?

acidburnNSA 8y ago
Natural circulation heat exchangers. The AP1000 has this huge tank of water on the roof that can cool things for 72 hours. Then it runs out of water. At sea with some displacement you use this system but never run out of water.

e3b0c 8y ago

That risk assessment assumes only the technical aspects. But there are still institutional, management and other 'people' issues that could render any engineering guarantee fruitless. Otherwise, the delivery of nuclear plants would have no way to off schedule. I have no objection to the development of nuclear technology. But as I understand, what concerns people is not entirely the 'likelihood' of the disasters but rather the 'severity' of them. After all, People make mistakes and organizations corrupt. So, I think any tech progresses on the scale-down of the worst case where all safety is off would be far more helpful in convincing the public.