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Comment by natcombs | Hacker News Reader

>> What happens when the ultimate heat sink is lost?

What's an example event where the ultimate heat sink might be lost?

Many inland rectors are built on waterways. A plant can shut down due to drought. That's a slow enough process that you have plenty of advance warning, though.

Some are built on man-made reservoirs held together with dams..

No expert, but if it's a pool of water then an earthquake might cause a leak?

Or an attack, of course. Or some other event (social unreset, invasion, coup, etc...) causes an evacuation of staff and it boils off during the resulting excursion.

People tend to have poor mental models for the long tail of external failures that happen in real life. It's easy to imagine that things that have never happened in the last century would Never Happen. But... they will, somewhere.

Nuclear sites are designed to withstand a strike from a commercial airliner (747). Like you, the designers imagined many of the events you mentioned and more. A good rule of thumb is that if you, a non-expert, can think of a scenario within 10 minutes, an expert has probably already thought of this scenario. Nuclear power plants and weapons sites have always been considered targets and thus considered extra scrutiny in their design.

Wow. How do they design them to withstand a strike from a 747? That seems really difficult.

A whole lot of concrete, mostly.

They shot an F4 target drone at a block of "reactor grade" concrete wall back in the 80s and they took measurements and did science on the resulting lack of damage and concluded that a reactor can shrug off one of anything. They didn't change containment buildings to be plane proof. It's just a side effect of the design required to contain a melting down reactor with a sufficient safety factor.

video of the test https://www.youtube.com/watch?v=F4CX-9lkRMQ

Yes. A NRC requirement for utility scale reactors after 9/11. One wonders why nuclear reactors are so expensive.

It's a good reason to design reactors to be as small as possible, with a small containment building. Much easier to build.

You'd hope so. Reactors yes, but not spent fuel pools. Everyone misses things. I've found 3 design flaws myself in the industry. Not too big of a deal as actions can be taken to mitigate some of the flaws. The other flaws are less probable of causing an issue due to redundant and diverse systems but there's always the off chance...

>but not spent fuel pools. Everyone misses things

Everyone who remembers the post 9/11 "but what if the terrorists attack X" pandemonium knows that spent fuel pools are outside the containment building. That was one of the scenarios that got paraded around to maximize FUD.

I was involved in closing of case, when terrorists wanted to create dirty bomb and throw it at Ukraine. S*it happens.

Wanted to is very different than doing. As far as I'm aware there has never been a dirty bomb attack. You could effectively create a dirty bomb with less radiation with more easily obtainable materials (still pretty expensive and labor intensive). The threat would be similar to a more radioactive substance because the biggest damage is the fear (that's what terrorism is about. They could do MUCH more _damage_ if they weren't as concerned about striking fear). The reason it hasn't been done is because it is impractical and difficult to do without killing yourself. There's better and far easier ways to strike fear into people's hearts. Killing a single person is more effective for them than increasing the chance of getting cancer in one's lifetime by 10% for a dozen people. The much bigger threat is a briefcase nuke but that is several more orders of magnitude difficult/expensive to obtain.

There is plenty of people which want to kill themselves for few, but common reasons, like cancer. It's not a stopper for terrorists.

NuScale claims "The reactor building is able to withstand aircraft impact". The reactors and spent fuel pool are in the same room:

https://www.researchgate.net/figure/Cut-away-view-of-reactor...

https://interestingengineering.com/crashed-jet-nuclear-react...

> the designers imagined many of the events you mentioned and more

Designers are awesome. Sadly they were also unable to find some time in 50 years to raise a wall a few m so it can stand a Tsunami. It seems that the extra scrutiny, was not so extra in the real life when the company will need to allocate real money.

The event you are referring to was also a freak event. The Tohoku earthquake was the 4th largest _ever_ recorded and the largest ever recorded in Japan (by 0.2M, it is a log scale btw). The closest earthquake to that, in the region, in the previous 100 years was 0.7M lower (and the 6th largest ever recorded, in the area). The Tohoku earthquake also resulted in one of the largest tsunamis ever recorded.

We should note that a lot of rare things happened all at once, more than just the freak earthquake and freak tsunami. There is no such thing as perfect. But consider that there were no lives lost due to the reactor accident. Yes, there is economic damage, but that is the worst. Lives were not lost and the environment was not irreparably damaged. Nature has actually started to take back the region and it more looks like a scene out of I Am Legend rather than The Road or The Book of Eli. I do not intend to dismiss the event, as it is concerning (and we've learned a lot since then), but however you measure it coal or oil or gas have had far greater environmental (or human/health) impacts than nuclear. The difference is that it is more in our mind. Despite the Fukushima cleanup estimate (2x Chernobyl's) costing about 9x Deep Water Horizon (2010) I'll let you decide what costs more[0], even if we ignore all the costs to health and atmosphere. There simply is no free lunch.

[0] https://ourworldindata.org/oil-spills

There’s no free lunch but wind and solar are a hell of a lot cheaper than this.

Economically cheaper, but that isn't the only factor that we're discussing. We're also talking health and environmental.

> consider that there were no lives lost due to the reactor accident.

Repeating this again is infuriating. No lives lost? seriously?

> "The event you are referring to was also a freak event. The Tohoku earthquake was the 4th largest _ever_ recorded and the largest ever recorded in Japan"

There is no doubt that the 2011 earthquake was an extreme event, but it's incorrect to say that it was not foreseeable or that the plant's safety systems could not have prevented the disaster.

Further up Japan's coast, the Onagawa nuclear plant was much closer to the earthquake's epicentre. It was subjected to extreme shaking, far more than any other nuclear plant in history, and like Fukushima was also flooded by the tsunami.

Yet it was able to shut down safely as designed in the hours that followed, and its structure was "remarkably undamaged" considering the extreme magnitude and duration of the shaking. 2 of its 3 reactors are expected to be restarted soon following structural repairs and seismic upgrades.

I am not trying to say that things couldn't be designed better. They could (that is never _not_ true). But it is also important to remember that this was a crazy accident as well and several uncommon things had to go wrong at once. The reactor was designed to withstand 100 year earthquake and tsunamis (that's equivalent to flipping almost 7 heads in a row) (we're also not accounting for the odds of the tsunami). But what I am suggesting is that there is a limit. Sure, we could foresee 100 heads landing in a row, it is certainly possible, but at the end of the day you have that end up with an acceptable amount of risk. I do not think 100 year events (1:99 probability) is correct as climate change is changing those odds, but it isn't like this was engineers being lazy and dumb. You are using post hoc analysis to justify actions made without that knowledge. As they say, hindsight is 2020. I do want to remind you that this was the largest earthquake to EVER hit Japan. That's much harder to predict and extremely reasonable to believe such an event is unlikely during the expected lifetime of the reactor.

You don't even need a tsunami, as a plain immaterial "cascade" can wreak havoc: https://en.wikipedia.org/wiki/Forsmark_Nuclear_Power_Plant#J...

> an evacuation of staff and it boils off during the resulting excursion.

It is trivial to design a system that powers off when unstaffed. Without power, this reactor will SCRAM and passively switch to air cooling over the course of a month.

Presumably, a skilled attacker could compromise the passive safety systems and force a meltdown, but wouldn't it be easier to steal some spent fuel and disperse it?

Once an attacker is inside the plant, with just some Wiki knowledge, any plant is as good as melted down. It's a much better plan to simply drain the spent fuel pool.

I think it takes a bit more than Wiki knowledge to drain an in-ground pool... you would need to keep a large pump running for hours, under duress.

You don't need to be an expert. Ask anyone who has owned an in-ground pool. Leaks are rare but do happen.

Nuclear power plants were designed with this in mind. It would take a substantially larger earthquake to damage a nuclear power plant and cause it to leak than a commercial pool. Such a comparison is in bad faith and disingenuous.

Cool it (pun intended) with the accusations of bad faith. Unless you have enough data to prove it, don't accuse it.

"Substantially larger" is not the same as "impossible". And, given substantially larger consequences if a reactor pool breaks (compared to a swimming pool breaking), I don't think the question is out of line.

We learned from Fukushima that natural disasters don't always follow the parameters that we expect them to.

It's a people problem.

People are fallible on the best days, assuming everyone did their very best from nuclear physicists to construction workers, mistakes are made. You take steps to reduce the risk. Research gets review. Engineering schematics get review. Construction gets inspection. Still some mistakes will get through.

And people always act their very best all the time right?

You can even have a perfect design, perfect construction, that is mismanaged years after it's built, after the original engineers and bureaucrats lose control.

The same people problems apply to basically every human endeavor, but nuclear's capability to cause accidents that have a lasting impact is pretty scary. You don't feel even a twinge of existential dread when you think about? If you don't, then I don't think I want you working on a reactor.

This. Humans are spectacularly bad at this kind of scale in time/project budget/size...

We are scary good at it actually. For example check out this and think about the architects who started vs those who finished it: https://en.m.wikipedia.org/wiki/Florence_Cathedral

I was actually going to reply with something similar, but I don't think this stacks up to the damage that can be unleashed in a nuclear accident. Building this took a few lifetimes. Nuclear accidents can have effects that are orders of magnitude larger and longer.

I am not sure something built by the catholic church, one of few institutions that lasted for the last 2k years, is the perfect example.

Unless we plan on getting the pope to build nuclear power plants, which does sound cool.

A sufficiently large pool can be built, that any plausible leak will take many days. Think about it: a million liters of water take a long time to dissapear, after all lakes stay there for a long time without rainfall. Weve built many many ponds, it's not hard.

I'm not sure it's that simple.

It's literally a big hole with water in it; what are you unsure about?

Our largest manmade lakes are created by dams, and you can find plenty of example of dams failing in ways that don't take many days.

If our smallest manmade lakes (swimming pools) can leak a lot, and our largest manmade lakes (dams) can also leak a lot the idea there's an in-between size that doesn't leak might need a bit of elaboration.

There's a big difference between a dam and a pool; the pool is supported by the ground, and even if you bash holes in it, the water still has to find somewhere to go. Also, pools are not typically built from concrete and stainless steel.

The safety requirement here is not "doesn't leak", it's "holds most of the water for 30 days (after which water is not required)". You would have to get an implausibly-large leak, during a situation where nobody can add more water for a month.

The water in a glass can take a long time to evaporate, but if you put your fist inside the glass and press you will have a sudden loss of 2/3 of the water in seconds.

There are pools and pools and there are leaks and leaks. Anybody that has built an aquarium knows that a 80cm high design is much more complicated to made leak-proof than a 40cm high design holding the same water.

A shallow pool would not be enough to contain a small nuclear plant, so you need a non standard bigger pool. Higher the pool, higher the weight of water column, the force pressure against the walls will increase, and the leak will be much faster because the water weight in the upper level of the pool will force the water in the low levels to go out. If your leak is in the upper side of the pool will be a small self contained problem but if the bottom leaks is a different thing. As the bottom needs to support much more force against it and there is a weak area when walls meet bottom, is more probable to fail first.

It’s not bad faith or disingenuous. Fukushima happened because of an earthquake, remember?

An earthquake that was one of the largest ever recorded and resulting in one of the largest tsunamis ever as well. So you know, pretty common circumstances.

That the '1000 year tsunami' happened 40 years after commissioning is more suggestive of engineering incompetence than bad luck. And unlike bad luck, incompetence is a lot more prevalent.

You just defined bad luck. They did plan for better than a 100 year earthquake. They met those standards. Problem is sometimes you flip 10 heads in a row (equivalent to 1000 year event), when they could only handle 7.

evaporation?

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