[Pseudoscience-is-malarkey (OP)]

What kind of oversites can cause a nuclear power plant to melt down?

[Michael Sally]

What kind of oversites can cause a nuclear power plant to melt down?

https://en.wikipedia.org/wiki/Nuclear_meltdown#:~:text=A%20meltdown%20may%20be%20caused,core%2C%20leading%20to%20a%20meltdown.

''A meltdown may be caused by a loss of coolant, loss of coolant pressure, or low coolant flow rate or be the result of a criticality excursion in which the reactor is operated at a power level that exceeds its design limits. Alternatively, an external fire may endanger the core, leading to a meltdown.''

[Zer0]

Hi there @Pseudoscience-is-malarkey
🙋
Nice nickname.
👍

The first & foremost thing that comes to mind is " Human Error " !
💀

Structural & Designing Faults.
Incapability of handling Complex Operations.
🥱
Probable Sabotage & personal envy or even just getting up on the wrong side of the bed.
🤤


P.S. - Prapz B.C. would have answered sayin ' Uranium ' & ' Plutonium '...
🤭
he hee heeh!

[Bored chemist]

"What usually causes nucular power plant meltdowns?"
Nothing.
That's why they don't "usually" happen.
They are actually very rare.
Wiki records just 3 major ones and another score of minor ones.
Since 8 of those were in Russian subs, you can draw your own conclusion about "what causes meltdowns".

https://en.wikipedia.org/wiki/Nuclear_and_radiation_accidents_and_incidents#Nuclear_meltdown

[alancalverd]

Loss of coolant in a properly-working reactor. Sabotage at Chernobyl.

The human error in the case of Fukushima was siting the plant near the sea in an area subject to tsunami.

[evan_au]

The human error in the case of Fukushima...

There were a few errors that contributed to this...
- No big earthquakes had been recorded in this area for hundreds of years, so obviously, no more would occur for hundreds of years (the opposite is true; when a fault-line is "stuck" for hundreds of years, it is building up pressure for a really big one!)
- Ignoring geologists who pointed to sediments well inland, suggesting that there were very big earthquakes in this region, hundreds of years ago.
- Locating the emergency generators in the basement (where they got flooded), instead of on higher floors (where they could have provided power to keep the coolant circulating in the reactor core).

Isn't 20/20 hindsight wonderful!

In the end, around 16,000 people were killed by the Earthquake and Tsunami.
- It is estimated that less than 10 people may be killed by the reactor meltdown - and these deaths will occur over the next 40 years.
See: https://en.wikipedia.org/wiki/2011_T%C5%8Dhoku_earthquake_and_tsunami

[Petrochemicals]

A meltdown is the overheating of the fuel so it melts down from solid in the reactor, overheating is caused by the heat being generated not being lost.

As you can imagine the build up of heat is because of numerous reasons. Chernobyl was caused by the design of the  reactor being a positive coefficient design.

https://en.m.wikipedia.org/wiki/Void_coefficient

Fukushima was a loss of pumping and 3 mile Island a loss of coolant. Windscale is not considered a meltdown as the fuel was not the type of modern design, even though it did melt.

[miaturner95]

these days the chances of a nuclear powerplant melt down is close to negligible, unless there is a natural disaster, like in Fukushima Japan

[alancalverd]

Chernobyl was caused by the design of the  reactor being a positive coefficient design.

That in itself is not a problem. RBMK reactors are relatively simple and generally problem-free as long as you read the handbook. Trouble with Chernobyl 4 was that the operators decided to ignore the BIG RED WARNING in the book, and drove it into a known unstable condition. The exercise was executed as planned, so this was not a matter of "pilot error" but must be seen as deliberate sabotage. That's the problem with the laws of physics - they always win. 

[Bored chemist]

The exercise was executed as planned, so this was not a matter of "pilot error" but must be seen as deliberate sabotage.

No.
Because sabotage has some sort of point to it- financial, political whatever.
They just screwed up. But there is a reason for that.

The German military command told their troops that Enigma was uncrackable. The troops believed them and got "sloppy"- which is how Enigma was cracked.

The Designers said the Titanic was unsinkable, so the captain didn't prioritise the lookouts.
So nobody saw the iceberg until it was too late.

The managers of the space shuttle project thought that the risk of failure was "One in a million"- and they still thought that after the first failure...


The guys running Chernobyl had been told "RBMK reactors are relatively simple and generally problem-free ". or as they put it "safe as a samovar".

We know what happened next...

[alancalverd]

I disagree. They had all read the book which clearly set out the correct procedure for shutting down with part-spent fuel, and the reasons for not doing what they did. This was not sloppy execution of a routine shut-down but a planned and deliberate exploration of a forbidden part of the operating envelope. The point was to see if time could be saved by cutting a corner that had been thoroughly researched by the designers.

"Safe as a samovar" has some resonance. Way back in the 1950s  my father attended a course on nuclear reactors for the Central Electricity Generating Board. His summary was "a very complicated way to boil water."

[Petrochemicals]

Chernobyl was caused by the design of the  reactor being a positive coefficient design.

That in itself is not a problem. RBMK reactors are relatively simple and generally problem-free as long as you read the handbook. Trouble with Chernobyl 4 was that the operators decided to ignore the BIG RED WARNING in the book, and drove it into a known unstable condition. The exercise was executed as planned, so this was not a matter of "pilot error" but must be seen as deliberate sabotage. That's the problem with the laws of physics - they always win. 

I can't really argue as many ran out their life times such as chernobyl other reactors, but the fellow in the TV series thought so, he was persecuted for speaking out.

The trouble is there appears to be no failsafe, why did Fukushima fail? Chernobyl surely should have had an off button, the withdrawal of moderators under their own impetus should be designed in, with any residual heat acceptable. Perhaps an emergency gravity fed water tank/ radiator cooling system ? They could have done this at Fukushima but didn't.

[alancalverd]

The 737MAX has a failsafe which has so far killed 346 people who would have completed their journeys safely without it.

The shutdown sequence for the RBMK reactor has worked every time. Problem with Chernobyl is that the operators were experimenting with a "home-made" emergency procedure (using the residual momentum of the generators and pumps to close down the system without using the backups) that was strictly forbidden in the manual.     

Fukushima was correctly designed to withstand the "100 year" tsunami but not the 1000 year beast that killed it. To do so would have made the design uneconomic. Part of the problem is one of public perception: "reactors are dangerous so must be sited on the coast" or "humans cannot be trusted to fly airplanes".

The Chernobyl TV series was superb, and can be summed up in a single phrase: Kruger and Dunning meet Stanley Milgram.

[evan_au]

Chernobyl surely should have had an off button

All power reactors have an "off" button, which stops the nuclear chain reaction.

However, the residual heat continues to produce around 6-7% of the reactor's output power, even after the fuel rods are fully inserted. This drops below 1% after a day or so.
- This is still enough to cause a meltdown if cooling is not maintained.
- Some of the more modern reactor designs support fully passive cooling, driven by the residual heat
- Reactors of Fukushima and earlier generations require external power to maintain coolant circulation, even after the reactor is shut down.
See: https://en.wikipedia.org/wiki/Decay_heat

[charles1948]

Chernobyl surely should have had an off button

All power reactors have an "off" button, which stops the nuclear chain reaction.

However, the residual heat continues to produce around 6-7% of the reactor's output power, even after the fuel rods are fully inserted. This drops below 1% after a day or so.
- This is still enough to cause a meltdown if cooling is not maintained.
- Some of the more modern reactor designs support fully passive cooling, driven by the residual heat
- Reactors of Fukushima and earlier generations require external power to maintain coolant circulation, even after the reactor is shut down.
See: https://en.wikipedia.org/wiki/Decay_heat

Is this the fundamental problem with nuclear power stations which operate on the "fission" principle.

"Fission" involves the artificial and unnatural splitting of atoms of heavy elements such as Uranium.  Thereby releasing neutrons.  And once the neutrons get released, they fly out to split other Uranium atoms, in an ultra-fast unstoppable chain-reaction which spreads in microseconds through the whole pile of Uranium
.
Resulting in the Uranium pile either detonating instantly in a devastating explosion, or simmering and festering in a slower but lethal radiation-emitting "melt-down", the effects of which go on for years or centuries

Whereas - if you had a nuclear-fusion power station, it would need a constant input of energy from the outside, to keep fusing or squeezing the atoms together. 

The energy from the outside would come from an electric current.  So if you wanted to shut down the fusion-station, you'd cut off the current by simply pulling out the plug.

[Petrochemicals]

Fukushima was correctly designed to withstand the "100 year" tsunami but not the 1000 year beast that killed it.

With pumps situated on the floor. D'oh.

[Petrochemicals]

Chernobyl surely should have had an off button

All power reactors have an "off" button, which stops the nuclear chain reaction.

However, the residual heat continues to produce around 6-7% of the reactor's output power, even after the fuel rods are fully inserted. This drops below 1% after a day or so.

Chernobyl off button was what killed it, the quick insertion of  the control rods blew it up, because they had a moderator at the end. Steam pockets ensued and not a good outcome!

If I (being very careful of the language I use, nuclear reactors and explosions I'm sure flag up at gchq) rendered a reactor incapable of being controlled by consoles, could I cut a rope to drop the control rods? If one control rod jammed could I drop the rest? Would the reactor have passive cooling capability? A clever design in  pipework(s) to a radiator(s) radiator on the roof(s) would be good. Nuclear reactors seem not to have the aarospace standard of duplicates and triplicate.

[evan_au]

to shut down the fusion-station, you'd cut off the current by simply pulling out the plug.

It has been argued that controlled nuclear fusion (if/when we ever get it to work) would be safer than fission reactors.
- Partly because the amount of fuel in a fusion reactor at any one time might be 1 gram, rather than 700 tons for a fission reactor.
- But the fuel in a fusion reactor is incredibly hot, and with an uncontrolled shutdown could burn a hole in the wall, requiring tricky repairs before the reactor could be restarted
- most fusion reactor designs use Deuterium+Tritium fuel; this reaction does produce high-energy neutrons, and the walls would become radioactive

an ultra-fast unstoppable chain-reaction which spreads in microseconds through the whole pile of Uranium

As you correctly suggest, this is a description of a fission bomb.

simmering and festering in a slower but lethal radiation-emitting "melt-down"

Unlike your implication, in a fission power reactor:
- The chain reaction is stoppable, using control rods
- A melt-down is not inevitable, provided the fuel temperature is kept below the design limits

Fortunately, most nuclear power reactors are operated properly, most of the time.
- It's the exceptions that produce headlines and exclusion zones...

[Bored chemist]

"Fission" involves the artificial and unnatural splitting of atoms of heavy elements such as Uranium. 

Why do you think it is unnatural?
https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor

[Bored chemist]

Chernobyl surely should have had an off button

All power reactors have an "off" button, which stops the nuclear chain reaction.

However, the residual heat continues to produce around 6-7% of the reactor's output power, even after the fuel rods are fully inserted. This drops below 1% after a day or so.

Chernobyl off button was what killed it, the quick insertion of  the control rods blew it up, because they had a moderator at the end. Steam pockets ensued and not a good outcome!

If I (being very careful of the language I use, nuclear reactors and explosions I'm sure flag up at gchq) rendered a reactor incapable of being controlled by consoles, could I cut a rope to drop the control rods? If one control rod jammed could I drop the rest? Would the reactor have passive cooling capability? A clever design in  pipework(s) to a radiator(s) radiator on the roof(s) would be good. Nuclear reactors seem not to have the aarospace standard of duplicates and triplicate.

They had triplicate systems.
They failed to take account of "common mode failure".

All three cooling systems were washed out at once by a single common cause.
It would also have washed the radiators off the roof..

So a quadruplicate system may not have worked any better.