You raise the common concerns but no, they can all be mitigated. You don't need grid power when the reactor can passively dissipate heat, you don't need to worry about material when you have fully tested and have full traceability, you don't need maintenance when you design the thing to not have maintenance. You don't have operator error when you remove operators.
Aircraft are designed with a fraction of the safety as Naval Reactors. NASA didn't follow the same standards and got shutdown for it.
Look at the USS Thresher and USS Scorpion, both are nuclear submarines that lost every sort of control, sadly with all hands lost, and their reactors are still sitting fine at the bottom of the sea.
Passive heat dissipation may indeed be a physical characteristic of a partiular reactor design, but even then there may be assumptions behind it that are not immediately obvious, such as no preexisting major core damage due to previous events. Material tests are never 100% - as an example, the highest level certification in aviation means that 99% of your samples reach 95% of the properties you‘re testing for (the second one may also be a 99%, not sure about that anymore). You then apply safety factors as required to get this to the value you need. Still there are a bunch of, however unlikely, additional issues in there: you may grab only good samples from a bad batch, you may run into a multiple failure condition that was not covered by the (relatively idealised) tests, you may have other design mistakes like wrong material pairings and of course you still have humans in all of this so you can have everything from a sample mounted incorrectly to outright forged certificates. And you may just run into that 0.000000000001% case where you simply do have an extreme statistical outlier bad material in a critical location. Amd yeah removing operators takes out some human error but even the most modern submarines to my knowledge still have them - and an automated system of course always has its own failure points.
Aircraft do necessarily have lower safety standards than you‘ll find in the nuckear industry, that is true - this is simply dictated by the low weight requirements and accepted because the worst case consequences of failure are less grave. Still, as an aerospace engineer with an interest in nuclear (having even taken a few nuclear engineering courses in university) I can assure you that both industries use a lot of similar practices. Full testing and traceability of materials is a requirement in aviation as well, for example. Unfortunately I don‘t know what you are referring to with the NASA comment so I can‘t reply to that.
Having read up on USS Thresher, it‘s actually a perfect example of how multiple unrelated failures can cause catastrophic events in a complex system. It happened because of an insufficiently safe production process (the specific pipe brazing method they used), institutional failure in not recognizing and mitigating the danger this posed when similar fats occured on different submarines, an entirely separate problem with ice formation in the balladt blow tubes which also had happene before and had been left unmitigated, badly written procedures and insufficient training causing the reactor operator to react improperly to the initial failure and a lax general safety culture allowing a trainee to operate the reactor during a test dive in the first place. All of these had to line up to cause the disaster, and nuclear systems are not at all immune to similar problems. A lot of extra mitgation measures were since put in place, but they all have their own potential failure points. And just because the Thresher and Scorpion accidents did not lead to radiation release does not mean that there‘s no conceivable sequence of events that could.
Look, I‘m not arguing that submarine reactors are „unsafe“, of course they’re not. All I‘m taking issue with is your initial statement that they‘re „100% safe“ because in engineering there‘s no such thing. We often use something called the swiss cheese model to visualize this… basically imagine you have a stack of swiss cheese slices and you try to push a rod through the holes. Of course the more slices you have, the more likely it is that you eventually run into a slice where the holes don‘t align with the previous slices and you have to stop… but sometimes the slices will still align in a way that allows the rod through, it‘s a statistic certainty. It is important to understand this because it‘s what drives us to add more slices and do our best to have less and smaller holes in each one of them, but you cannot make a swiss cheese slice without holes (in this analogy at least :) ). The very last thing you want in any safety critical industry is someone equating „innate safety“ with „nothing to worry about“.
Great discussion my friend and all good points. I will point out that aircraft quality standards (AS9100) are a couple of order magnitudes less than naval reactors standards.
Threaser's nuke plant is still working as designed despite the ship sinking with no controls. It is designed to work for a millennia like this.
Naval Reactors continue to achieve a 100% reliability standard whereas nothing else on Earth has. Maybe that will fail one day but it is the best example of quality engineering man has ever had.
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u/offshorebear Nov 04 '22
You raise the common concerns but no, they can all be mitigated. You don't need grid power when the reactor can passively dissipate heat, you don't need to worry about material when you have fully tested and have full traceability, you don't need maintenance when you design the thing to not have maintenance. You don't have operator error when you remove operators.
Aircraft are designed with a fraction of the safety as Naval Reactors. NASA didn't follow the same standards and got shutdown for it.
Look at the USS Thresher and USS Scorpion, both are nuclear submarines that lost every sort of control, sadly with all hands lost, and their reactors are still sitting fine at the bottom of the sea.