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).
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.
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.
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?
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.
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.
>... the ocean is full of salt, how many half-lives until corrosion prevents containment?
quoting you:
>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.
You don't misunderstand me, you purpousely misinterpret my questions so you can give easy answers...
Ah, I see what's going on here. Please review the HN guidelines.
I-131 has an 8-day half-life and is the primary threat to populations in large early releases. The direct answer to your question for I-131 is at least 2,000 half-lives. Sr-90 and Cs-137 have 30-year half lives, so for them it's at least 2. As you surely know, the longer half-life nuclides release energy more slowly and are therefore less dangerous to biological systems. At the extreme, U-238 has a few billion year half-life and can be handled safely without shielding.
In the scenario I'm painting, the reactor would be recovered from the sea within ~5 years so none of this matters. The corrosion will not fail the system within those 5 years. I do not propose to just leave any failed reactor down there indefinitely.
>Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith.
Which is exactly what I was accusing you of before you reflected the accusation. Please note there are 2 components in this rule:
1. Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize.
2. Assume good faith.
I will discuss part 1 in the context of our discussion, but first point out that 2: does not mandate to keep and maintain the a priori assumption of good faith, it only mandates to assume good faith.
Now for part 1, lets personally dissociate and review the discussion as being held by Alice and Bob:
After Bob states,
>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.
Alice asks a concise question:
>that doesn't discuss corrosion though, the ocean is full of salt, how many half-lives until corrosion prevents containment?
and later Alice adds the question:
>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?
All the while Alice is a priori assuming good faith on behalf of Bob.
Now Bob can give multiple interpretations to Alice's question, and he is required to please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize.
Bob can use interpretation 1 interpreting Alice as Alice1 implying all of the following:
* 1A) Alice is worried about shortlived isotopes
* 1B) moreover she seems to believe steel corrodes in a matter of days in the salty sea, Alice probably never heard of the Titanic recovery, Alice believes that ships can't be reused because after every trip they are decommisioned and a new ship is built for every trip.
* 1C) Also Alice seems to be unaware that Iodine is the most easily mitigated isotope since we can bulk manufacture Iodine tablets containing non-radioactive isotopes.
* 1D) Alice seems to be uninformed about all the above topics despite referencing concepts like nuclear half lives, the corrosion of metal in salty water, convection of hot water in cold water, and the concentration and saturation of metal ions in aquaous solutions...
This interpretation of Alice is easy to criticize, for obvious reasons
or Bob can use interpretation 2 interpreting Alice as Alice2:
* 2A) Alice is worried about longlived isotopes
* 2B) Alice is worried about the influence of energy release in the long tail of nuclear decay: consider a simple system of N identical unstable isotopes decaying to a stable isotope (thats ignoring the worse long decay chains), after one half life, half the number of remaining radioactive particles has halved, but half of the energy that will eventually be released as heat (not temperature!) is still contained in that long tail. Alice wonders if that energy can speed up the corrosion process on long time scales. When salty water dissolves metal, theres a thin layer of water that is saturated by dissolved metal which acts in a self-limiting way. But if the heat causes convection, that thin layer of saturated water will be constantly replenished with fresh unsaturated salty water. Similarily evaporation is much enhanced if convection or wind carries away the saturated air, which is why we like to hang our clothes to dry outside...
If Bob chooses interpretation 1 (which is easier to criticize) over interpretation 2, then it is Bob who is acting in violation of part 1 of the rule from the guidelines...
If Bob then at some point replies "They have not corroded away and released wholesale nuclear waste after many decades." Then Alice can only conclude that Bob has chosen the weaker interpretation Alice1 over Alice2. At that point she simply corrects her a priori assumption that Bob is acting in good faith, and she explicitly points it out.
Then Bob escalates by reflecting the identical accusation in a vague reference to the guidelines, simply because Alice is open about her founded conclusion on Bob's behaviour, while Bob never explicitly states he chooses interpretation Alice1 over Alice2 even though it is evident to any reader... Alice did assume good faith on behalf of Bob, but Bob's replies imply he chose the weaker interpretation Alice1. That is unless Bob genuinely believes people like Alice think ships are one-time-use items, that Iodine tablets do not exist, ...
I hope someone (dang?) who can prove their association with the platform can clear this up, perhaps in your favour perhaps in mine (don't care really, I would just like clarity / precedent, so that we maintain equality before the guidelines)
*
Also you keep changing attention to a lesser problem of containment, the short-lived nuclides, for example you state:
>Nuclear accidents generally worry about something called Large Early Release Frequency.
Why are you personifying the accident events? Surely you mean nuclear experts instead of accidents? Let me explain why they focus on the short-lived nuclides: because they can be affordibly mitigated with measures like Iodine tablets. abstaining from eating produce from the affected area for a few days, etc...
The longer lived ones are not necessarily safer, they are simply not affordibly mitigatable over longer timespans! (In case of consumption, the shortlived ones have a higher activity of course, but the longer-lived ones with a lower activity would be consumed for long timespans, such that DNA damage can integrate over time)
*
Regardless of these issues, would you consider it prudent for mankind to explicitly define an absolute reference background energy-spectrum of radio-activity? i.e. for each gamma energy bin some typical but from then on fixed reference background activity? Because the only references to background I find are currently comparing with whatever local background is found away from a target of investigation, which is good enough on short timescales, but how will future generations be able to compare their background with ours? It seems we keep assuming that the natural background can not be influenced by human activity, which seems dangerously close to the original fallacy that human activity can not influence atmospheric CO2 concentration...
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?
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.
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.
Fair. Finding the balance for a wide audience between believable and exciting is tough. I'm usually good at it but in this case, it's my favorite concept in my field of expertise so I get a little too enthusiastic.
Huh. In this entire conversation you've come across as a person way-overstating their case, and as a result being totally unbelievable and unconvincing. And in a thread which is off-topic for the posting, which is a poor choice of a place to engage at all.
I said one thing, people continued the conversation, I continued it with them. There's a collapse thread button for a reason. Yet here we are talking.
What part is least believable for you? Shipyard construction being cheap? Floating nukes being safe? Nukes being safe in the first place? Nukes being low-carbon? Many of these thing sound surprising because they go against pop culture but they're interesting in that the scientific consensus is fairly opposite of pop culture on this topic.
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.
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)?
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.
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).