Why Is It So Hard to Stop Meltdowns?

☢️ Why do meltdowns happen and can we stop them?

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Chapters
00:00 Let’s Talk About Meltdowns
00:59 How Nuclear Energy Works
02:30 How a Meltdown Progresses
05:10 Why Meltdowns Happen
06:27 How Scary Is It?
07:57 Our Amazing Sponsor - Brilliant
09:06 How Do We Prevent Meltdowns
11:18 Meltdown-Proof Reactors

[ProlificInvention]

As Albert Einstein said: "It's a hell of a way to boil water"

[BritishBeachcomber]

At 16 years old, my physics teacher took us on a day trip to the Aldermaston nuclear research site. I stood on the reactor core and the thought of all that energy, just inches below, blew my mind.

[ThatJay]

thankfully modern reactors (generation 3 and up) have passive safefy mechanisms to prevent meltdowns from happening at all. these safety mechanisms are designed on top of the laws of physics themselves, so they can't just be disabled.

[TheSwissGabber]

decay heat after shutdown is mainly from the decay of fission fragments not from delayed fission. Not in the first 30s but after 5 minutes the decay heat is ~100x greater then delayed fission.

[dallebull]

Feels like we can do this 1000x safer nowdays, than in the 60-70's, when the plants that actually have meltdown was built.
But for some reason we expect nuclear to be just as unsafe, it's like comparing an car from 1970 with one form the 2020s, there has been huge leaps in design and meterial science since then but apparantly not when it comes to Nuclear Plants?

[Phil-D]

Depends on the type of reactor, fuel type, coolant used, etc. Gen 1 and 2 reactors were very dangerous. The new gen 3+ are usually bullet proof. Molten salt one are excellent

[sixftin]

Commercial plants can learn a lot from US Navy ship-based reactor plants. Lots of safety built in. Very few accidents even though the fuel is HIGHLY enriched.

--US Navy veteran nuclear reactor operator

[brutonstreettailor]

Quite a big omission in this presentation is that Fukushima didn’t suffer meltdowns, they suffered Melt-throughs which is different in that the cores ( which they still aren’t sure where they are), melted through the concrete.

[marckhachfe]

For me, the most mind blowing thing about this subject is the speed at which these things happen . These are not chemical reactions, these are atomic reactions that happen almost at the speed of light. Amazing.
I always found it astounding how the entire pit in an abomb is consumed so quickly

[exiaRx]

Meltdown is one of those buzz words. We like to think of it as an unintentional energy surplus - Mr Burns

[Steven_Edwards]

Funny enough, the guys at Oak Ridge that worked on PWR reactors for the Navy said: 'yeah they work great. Right up to about 60mw' after that you are ****ing insane'

[zacharytaylor]

What we learned from SL-1:
Never have a single rod control the reactor
Don't manually manipulate the control rods with fuel in the core
Never attempt to pull on a stuck control rod
Ensure no interpersonal grievances between operators during critical phases
among others.

What we learned from Three Mile Island:
Sometimes less information is safer
Layout procedures clearly
Always have a peer checker during critical operations
Ensure regular maintenance on valves and pumps
Have a dedicated Press Representative to give accurate and reassuring information to the public
among others.

What we learned from Chernobyl:
Don't design reactor control rods with graphite followers
Never place the reactor in a configuration for an extended period that allows for xenon buildup
In reactors with positive void coefficients, don't preform rapid reactivity manipulations
Don't operate near All-Rods-Out
Don't ever allow for field changes to established procedures
Don't change shift during a reactivity manipulation
Thoroughly brief the next shift
Allow questioning of authority
among many others.

What we learned from Fukushima:
Place onsite power generators above the flood plane
Design the reactor to withstand the 1000-year event
Have at least 2x redundancy for emergency power generators
Fit sparklers to the reactor to safely burn off hydrogen
Have the spent fuel pool at ground level
Have redundant systems for core cooling
Allow controlled venting to occur in the absence of power
Better coordinate with emergency management agencies
among others.

I think that covers the most glaring points.

[runedahl]

The dangerous thing with these water cooled power plants is not the nuclear material but the water that is supposed to cool it. If the circulation of water stops the temperature of the water will increase tremendously. At 700 degrees centigrade large amounts of hydrogen is created and eventually this hydrogen will explode. The result is that nuclear material is blown up in the air and spread over a large area. In Fukushima all procedures for handling the reactor worked but since the tsunami had knock out all the backup diesel generators the circulating pumps had no power and did not work. What you see on the footage from the accident is not a nuclear explosion but one that is caused by the hydrogen. Similar things happen at Chernobyl and Three Mile Island. If you have one reactor that is not cooled by water under high pressure this would not happen. That is one of the benefits with molten salt reactors.

[evanflessner]

It’s hard to stop a meltdown, but it’s even harder to start one

[MegaSunspark]

Thank you for this explanation of why reactor cooling is so important even after the reactor is shutdown. That the nuclear fuel continues to generate large amount of heat months and years after the "shutdown".

[Alpacaluffy]

2:14 the diagram is of a PWR reactor, but you are describing a BWR reactor. In a Boiling Water Reactor, water directly passing through the core spins a turbine, but in a Pressurized Water Reactor, the water is kept under high pressure and does not boil, instead heating a separate loop that boils water and spins the generators.

[carlosenriquez]

You'd have to ask my wife why it's impossible to stop her meltdowns. Usually I grab the kids and hide two counties over till she offers up cash or expensive electronics in exchange for our return. I'm pretty sure at least one of her therapists has attempted suicide, I blame my wife but yeah once a meltdown starts you just gotta let it burn out.

[robertschemonia]

At 11:08. That is a BIG generator engine over that guys right shoulder. It looks like an EMD 2 stroke diesel, much like what EMD used in diesel electric locomotives for a LOOOONG time. They are still very common, super reliable, and very easy to repair and get parts for. That was an excellent choice for the power unit for a standby generator. Those engines are known for dependability and ruggedness. Fun fact! Just above the red writing on the side of tge engine is a valve. There is one of every cylinder. Those are blow down valves. They go directly into the combustion chamber, and are used to vent any possible moisture or oil buildup on the top of each piston from them not having been run for periods of time. If there was water or oil on the top of the piston, at best it could hydrolock the engine, at worst, it would bend or break that cylinders connecting rod and or piston. Fun fact 2: the older Detroit Diesel engines that were also used as generators, truck engines, and various other industrial applications worked almost identically to this monster EMD engine. From the individual self contained injectors with individual fuel racks to meter the fuel amd therefore engine speed, to having to have forced induction to even run, they are the same. Locomotives generally had a superturbocharger that acted as a supercharger at idle being driven by the crankshaft via an overrunning clutch, and at higher loads and RPMs they acted as a turbocharger, being driven bu the exhaust gasses.

[codaalive]

Thanks for another video. I would add Chernobyl was dual use reactor (military/civilian) from very different time and culture... After Fukushima they made stress tests at our local reactor, it was found a few ordinary fire engines can be used as a back up for existing 2 or 3 backups.

[chrisdiehl]

You forgot one thing.
During the reaction, the elements are actually changing in to different elements, and those might react with other chemicals.