r/NuclearEngineering • u/SideAgitated4661 • 6d ago
Need Advice What makes nuclear safe?
/r/NuclearPower/comments/1vyl7ai/what_makes_nuclear_safe/Is it because it doesn’t produce greenhouse gas emissions, it’s clean energy, and after the Three Mile Island, Chernobyl, and Fukushima disasters?
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u/Mantergeistmann 6d ago
and after the Three Mile Island, Chernobyl, and Fukushima disasters?
You mean various reforms/improvements made? Not really.
It's safe because a lot of people have put a lot of effort and thought into making it safe, and the culture around it is focused on keeping it safe. You might as well ask "what makes cooking safe?" "What makes cars safe?" "What makes airplanes safe?" Although, actually, all of those are far more dangerous to the average individual than nuclear power is.
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u/zolikk 6d ago
I think it's a bit of column A and B. Yes, the design, planning and safety culture improvements do make a difference, but it is also a rather safe enough technology by its nature too. Even with misuse it still ends up being statistically better than most other forms of energy generation.
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u/Definitely_CSP_guru 6d ago
This is true but the average person doesn’t really believe in the scale of the disasters in this mindset. The Ford Pinto or Chevy Corsair, although extremely unsafe by flawed design, didn’t leave a large portion of land unusable for thousands of years. So, most people outside of the community just can’t rationalize that logic I feel like
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u/SideAgitated4661 6d ago
Why were they testing Chernobyl? And did other reactors did the test Chernobyl did?
And Chernobyl caused the USSR to collapse. If it didn’t happen, then it would have stayed a country.
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u/Fun-Butterscotch9942 6d ago
What makes it safe? Defense in depth in the design. Operator training. Procedures. A negative (most of the time…) moderator temperature coefficient. Technical Specifications that provide operating requirements/ restrictions. Staffed by smart people who care. The most dangerous thing - high level management too far detached from the reactor who have allowed themselves to forget what is most important, and allow cost and schedule considerations to creep up and overtake reactor safety as the most important thing. Operator - “there’s a leak and we need to shutdown the reactor to fix it.” Executive - “but it’s the middle it July and it’s really hot and if we shutdown the company would have to buy electricity on the spot market and will lose money. Can’t you just monitor the leak more frequently until we can shutdown later?”
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u/zolikk 6d ago
By the metric of physical harm done versus amount of energy generated it is inherently safe, by nature. It produces a lot of energy in a compact manner using little in terms of material resources. Of course the lack of harmful emissions plays a big role overall, and GHG emissions are just one so far neglected side of that. There's stuff coming out of a coal plant's stack that is more immediately harmful to humans, than GHG emissions.
Accident scenarios don't move the needle much because they harm very few people. Even worst case it tends to only be a danger to those in immediate vicinity of the power plant. Usually more harm is done by unnecessary preventive measures in case of such accidents, than the accident itself could cause. That is something to be reviewed for better future policy. But again, by the statistical number of harm vs. energy produced, simply because of the large amount of energy the ratio is low, with accidents and all.
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u/SideAgitated4661 6d ago
Its the same with nuclear accidents and deaths by pollution.
Everybody knows about Chernobyl and Fukushima. Yet it’s enviromental impact and human casualties is Nothing compared to deaths by fossil fuel power generation. Major climate change and around 5 million premature deaths every year.
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u/Dumb_Cow5408 6d ago
That’s a great question. This is going to be a long answer, but let me see if I can give an adequate one.
The truth of the matter is that nuclear fission power is not safe. I know that sounds like a terrifying prospect, but let me explain. It isn’t safe, but the way our systems our engineered and operated, through the care and attention to quality assurance of materials, conservative design, defense in depth, and design considerations (like the hot channel concept, redundancy requirements, interlocks, control rod design considerations, etc…), in conjunction with high qualification and operational standards, strict adherence to approved operating and maintenance procedures, and intrusive supervisory control (including and especially in the form of intensive oversight from entities like the NRC for civilian side or NR for the U.S. Navy) make it safe. There needs to be a HEALTHY fear and respect when operating and supervising the operation of these systems. That’s not an option.
We’ll start with design, and there’s a lot to cover. Firstly, hot channel concept. What is it? Well, the hot channel concept is essentially an analysis of THE worst case scenario. It takes into account the fact that there are certain uncertainties in fuel and poison loading, uncertainties in material properties in the core, uncertainties in core dimensional tolerances, uncertainties in fuel loading tolerances, swelling of the fuel plates due to buildup of fission product gasses over core life, etc…. If we can ensure that THE hottest and most stressed part of our core remains well under our thermal/hydraulic limits, we can ensure that the entire core is safe at all times.
Secondly, control rod design considerations. We need to ensure that our reactor can remain shutdown even with the most reactive rod withdrawn to the top of the core (a lesson learned from the SL-1 reactor accident). We need to ensure that our rod speed can overcome the worst case xenon transient. Xenon is a fission product poison, the burnout of which will increase reactivity in the core (a lesson learned from Chernobyl). We need to ensure that our rods are able to SCRAM from both operator action and automatically in the event of an abnormal condition/loss of power.
Thirdly, redundancy. Whether it’s from multiple components powered from different power sources (like reactor coolant pumps, feed and condensate pumps), single integral component powered from separate auctioneered/parallel power sources, primary and backup decay heat removal methods, redundant indications, coincidence circuitry, redundant control signal paths, etc…, redundancy in design ensures that in the event of a casualty, we keep the reactor safe. If we lose a reactor coolant pump, we can still maintain adequate core cooling by reducing power. If we lose an indication, other indications ensure we can monitor our systems adequately. If we lose electrical power, an emergency means of core cooling via natural circulation due to thermal driving head is vital (lesson learned from Fukushima).
Other things of note for design considerations. The vast majority of reactors now have what is known as a negative temperature coefficient of reactivity (another lesson learned from Chernobyl), meaning that as temperature increases, reactivity decreases, and vice versa. This keeps the reactor inherently safe in the sense that if we increase reactor power, thermal output increases, and therefore temperature increases. As temperature increases, this adds negative reactivity, preventing reactor power from “running away”. So, while critical, control rods control average coolant temperature, not reactor power. Reactor power ultimately follows the cooling force for the coolant. And we have interlocks as a backup to operators to ensure no situation in which reactor protection cannot be shown. Things like cold water interlocks for PWRs (which is what I’m most used to). This doesn’t cover all design considerations, and certainly not in as much detail as they are analyzed, but it should give a pretty good idea of how seriously we take into account these design considerations.
Now, onto the operational portion. Operators are the first line of defense for overpressure/underpressure conditions, cold water casualties, control rod casualties, etc…. Automatic actions should serve only as a backup to the operator and should never be relied on as the primary means of demonstrating protection. In the event of something like a reactor coolant rupture, operator action in a timely manner is REQUIRED to demonstrate protection. As such, the operators MUST strictly adhere to operating procedures and must have thorough understanding of those procedures and of their indications (lessons learned from Chernobyl and Three Mile Island). Therefore, it is imperative that the qualification process be rigorous and that constant training for operators be performed.
Supervision is also critical. Yes, it often feels like it sucks for the operators, but it’s necessary. Believe me, I’ve been there. And it sucks WAY worse in the navy because the khaki also care way more about bullshit militaristic standards that I frankly didn’t give a shit about. And it’s way worse when NR is onboard. And you can have your liberty secured. I’m out now, working as a senior reactor operator and almost done with my master’s in Aerospace Engineering. In the navy, I was an ETN (reactor operator and watch supervisor qualed on first sea tour). Now that I’m out, I know I get to go home every day. When I was in, especially while in shipyard, it was a lot of, “Well, work isn’t getting done as fast as we’d like, so everybody loses this weekend.” Or, “Some dumbass fucked up, so as a corrective action, all E6 and below lose liberty until further notice.” And almost always, the issue was caused by the chiefs, but chief’s mess being chief’s mess, they always found a way to blame the most junior guy and fuck on everyone below them while they faced little to no consequences. But I digress.
Yes, supervision is important. Having senior people who have operated for years and have thorough understanding of the procedure to back people up and supervise their operations is essential. And supervision and regulations from larger entities like the NRC is also vital. Where it gets dangerous, as I’m sure you’ll hear others mention, is when people who have no real clue about plant operations try to impose regulations based on their deadlines that directly impact reactor safety, which should be the absolute, unequivocal priority. Scheduling requirements and whatever else be damned.
Once again, this doesn’t cover everything, but the highlights are that nuclear power should be treated as inherently unsafe and worthy of fear and respect. It is our engineering and operating standards that make nuclear power safe. Ultimately, it is well-worth the risk, provided we properly mitigate that risk and maintain radical accountability and integrity in operations. It is clean energy. And in addition to that, if we can standardize breeder reactors using elements like Thorium, then we can extend our energy supply, based on current energy demands, to almost 4 million years for the entire globe. We can meet, and even exceed, energy demands without adding carbon.
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u/WeAreSolarAF 4d ago
SMRs are supposedly far safer because if anything goes sideways, the whole thing drops into a concrete material below the reaction sequence.
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u/Ok_Voice_1295 3d ago
The only reason its seen as dangerous is big oil propaganda. It is inherently the second safest power source (deaths / twh), much safer than any fossil fuels and hydro. The few incidents are both cases of poor management by government, chernobyl being the kgb hiding the reactors flaws from the plant operators, and fukushima being the higher ups not giving approval to raise the floodwall. These both were preventable, and are blown out of proportion.
Coming back to my opening point, anti nuclear propaganda is pushed because nuclear is antithetical to fossil fuels; it could be cheap, its compact, its reliable, and, for all intents and purposes its wasteless (compared to renewables and fossil fuels). You look at the success it has in countries like France, you can see how dangerous it is for fossil fuel companies and nonrenewables.
So yeah, in reality it was never dangerous :3
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u/singing-kettle 6d ago
I think a better question would be: How safe is nuclear power?
Nuclear power is inherently dangerous but has been engineered to be adequately safe.
Maybe an engineer from a regulator or OEM can explain the results of a risk analysis and compare to the accident rate of gas and chemical plants.
I don’t envy those who work in Risk analysis. As a physicist words like “High risk, low risk” contain a lot of assumptions. Predicting the likelihood of particular failure modes and the statistics associated with many contingent and independent failure modes, while keeping a safe and accurate margin for error seems like a nightmarish job that would keep one awake.
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u/Godiva_33 6d ago
The fact that the industry doesn't hide from the power it seeks to use.
Every other industry falls well short of this type of acknowledgement with the possible exception of hydro.