Nuclear Safety Discussion - Split Thread

[mfb]

Nuclear energy is one of those fields were people should learn to listen to professionals instead of forming their own opinion from the cable news.

What is not one of those fields?
As long as a significant fraction of the population would agree to a law that bans atoms, ...

[split from this thread: https://www.physicsforums.com/threads/stunning-reversal-in-sweden-re-nuclear.875103/ ]

 

[Salvador]

Well, @mfb , a local club for country music singers is up to the peoples to say their opinion , or they can form a fine opinion on Trump's haircut from the cable news , that was my original thought.
It's somewhat illogical that most of the population would not be allowed inside a nuclear facility simply because they know nothing about it and could cause danger to themselves or others.Yet when a fine working plant has to go into premature shutdown all the local pub drunks and football fan's otherwise rioting in the stadium while being drunk now have a opinion about stuff like which is then amplified if not entirely made in the first place by groups like Greenpeace , which otherwise do good things but sometimes I think they themselves can't understand what they are fighting for. And all of this garbage is then taken seriously by politicians because they are worried to loose public support for reelection or money from donors.
A bit stupid ,Christ was spot on when comparing people to sheep.

Sorry for the off topic bits.:)

 

[russ_watters]

What is not one of those fields?

True in general, but on specific issues nuclear power may well have it the worst. Contrast it with, say, anti-GMO or anti-vax crackpottery which get a lot of press, but don't kill very many people. For either to have been as successful as the anti-nuclear movement, they would have had to succeed in getting vaccines and GMOs protested to oblivion. Off the top of my head, I can't think of another piece of useful technology that has been so successfully marginalized by fearmongering.

 

[mheslep]

Agreed. I think the difference with nuclear is that other technologies like GMO and vaccines did not threaten to abolish trillion dollar industries by replacing them as nuclear did, and does. Ads for solar power and the like can be found going back to the 70s paid for by fossil fuel interests. More recently, see the natural gas money taken by the rabidly anti nuclear Sierra Club

 

[nikkkom]

True in general, but on specific issues nuclear power may well have it the worst.

Maybe nuclear power should, you know, try to NOT melt their reactors from time to time?

 

[russ_watters]

Maybe nuclear power should, you know, try to NOT melt their reactors from time to time?

They of course do put quite a bit of effort into that. Doesn't change the point.

 

[anorlunda]

True in general, but on specific issues nuclear power may well have it the worst. Contrast it with, say, anti-GMO or anti-vax crackpottery which get a lot of press, but don't kill very many people. For either to have been as successful as the anti-nuclear movement, they would have had to succeed in getting vaccines and GMOs protested to oblivion. Off the top of my head, I can't think of another piece of useful technology that has been so successfully marginalized by fearmongering.

I think you are right, but we shouldn't be surprised because nuclear power has always been associated with nuclear bombs in the public mind.

 

[mfb]

Maybe nuclear power should, you know, try to NOT melt their reactors from time to time?

Several hundred nuclear power plants never released relevant amounts of radioactivity. Just a single one released so much that it had measurable health effects. Meanwhile, coal power plants released more radioactive material than all nuclear power plants combined - including the Chernobyl accident (and Fukushima and TMI and whatever you want to add, doesn't change the conclusion). And radioactive materialis by far not the worst thing that is released by coal power plants.

 

[russ_watters]

I think you are right, but we shouldn't be surprised because nuclear power has always been associated with nuclear bombs in the public mind.

Yes, the tactic has been very successful. Fortunately, vaccines=autism less so.

 

[nikkkom]

Several hundred nuclear power plants never released relevant amounts of radioactivity. Just a single one released so much that it had measurable health effects.

The point is, nuclear power industry's promises about safety were such that over last 50 years, statistically, there should have been not even one major meltdown of the power reactor. But in reality, there were FIVE meltdowns.

I'm not counting "small" accidents, such as partial meltdowns damaging just a few assemblies, and accidents on small reactors such as SL-1 accident. Just the major meltdowns.

 

[mheslep]

Maybe nuclear power should, you know, try to NOT melt their reactors from time to time?

In the context of a technology being under much severe scrutiny, the two major light water reactor accidents don't explain the pressure on nuclear. The extraction and use of fossil fuels has a much worse record. But there's no Helen Caldicot out there protesting fire.

 

[russ_watters]

The point is, nuclear power industry's promises about safety were such that over last 50 years, statistically, there should have been not even one major meltdown of the power reactor. But in reality, there were FIVE meltdowns.

Who made such a promise? I've never seen such a thing. Regardless, promises are not realities. The actual safety record is the reality that matters.

 

[Salvador]

Civilization is the triumph of the masses , or we could say proletariat, after all most of the things we argue over like fossil fuels and energy needs and manufacturing are there because we have come to the point were we ask for them and can't live without them , also refuse to. A friend once told me , he said , "We need to change the system" , i thought about it , yes his right but he sees the system in the wrong way , I said you know what, you are the system , you are part of it and the blind majority actually are the ones that dictate most things without them even realizing that.

As for nuclear I think the scare is 50/50 half of it is because nuclear came into the world first in the shape of a deadly weapon whose power was showcased in WW2, since then literally every action movie with a bad guy trying to take over the world has shown us the images of US atomic tests to make the point of the movie more illuminating.
The second reason could very well be pure lack of knowledge.Few posts earlier Nuke showed a good example of this by the story he told of the protester.

It would be hard to tell people because the basic opinion has already set in the last decades but they should look and compare fossil vs nuclear for example.
Yes a nuclear accident might involve higher risk and worse aftermath yet we have had countless accident involving fossil fuels , in fact so much that it would be impossible to even produce a precise estimate of all the deaths caused by the industry itself (workers, people affected by accidents etc) not to mention the ones indirectly affected by global warming etc.
Let me give you just one simple example of a seemingly harmless thing going bad.A natural gas pipeline developed a leak near the city of Ufa , back in 1989 in the USSR. near the pipeline were train tracks and two passenger trains were driving opposite directions , the wheels made some sparks and ignited the cloud of gas which due to atmospheric conditions was lying low, the trains were literally blown to pieces , 575 people died.
This is just one "tiny" accident involving fossil fuel industry , there have been countless over the 100+ years of us intensively using it.

You might ask what is my point here ? Simple , every major industry man has ever known involves some sort of danger and trial and error as we learn and progress.
Out lining one as good and the other as bad is simply one of two cases , either the person doing so is paid to do so, or he or she is simply ignorant and uninformed, mostly both.I also want to point out that actually most of the nuclear accidents, we have had , were due to deliberate and ignorant actions from authorities and the ones in charge , they were not a technical malfunction, or some sort of unpredictable scientific problem.
For example , the Russian military weapons research etc Mayak plant, of which the majority knew nothing about until recently used to have some very bad practices of waste disposal , the few people living in that region as well as wildlife has been affected yet no one knows how much because , well you know , nobody is told anything.
Also Chernobyl , used as the most frightening phrase in recent human history , was most of all an accident partly because of human error and partly because of ignorance at many levels.Cheap easy to build and very powerful reactors that produce plutonium without the need to go offline , yet with some dangerous features like the positive void coefficient etc, but you folks already know that , you also know that after the accident they upgraded the remaining reactors to make them safer.
It just goes to prove we can do many great things if we want to.sadly many times money and interests or simply laziness kicks in and problems arise , yet nuclear power asks for both the authorities and scientists and operators to do their best and be on the edge.
We shouldn't be scared of technology but rather of our own ignorance or that of our fellow citizens.The accidents that were technical failures happen to be the less dramatic ones , like Three Mile Island , United Kingdom's Windscale fire etc.

P.S. nikkkom I doubt anyone in their right mind has ever made a promise that there won't be any accidents.Much like no one can promise there won't be any wars.
Progress comes with some accidents and dangers, but I'd rather risk an accident for something better and developing and promising than for something we have used for decades , which starts to run out and causes so many well documented and proved problems along the way.I apologize if you find this too long , just my morning coffee gave me some impulse to write down some thoughts while reading this discussion.

 

[nikkkom]

Who made such a promise? I've never seen such a thing.

The technical promise is the design core damage frequency. Example:

http://www.edf.com/fichiers/fckeditor/Commun/Innovation/conference/BWRsbasics_va.pdf page 21:

BWR4: 10^-5 per year
BWR6: 10^-6 per year
ABWR: 10^-7 per year
...

Even the "high" 10^-5 per year core damage frequency would mean that 1000 reactors need to run for 100 years to statistically have about one core damage event. We now have only ~450 operating power reactors.

Regardless, promises are not realities. The actual safety record is the reality that matters.

The reality is: nuclear power industry repeatedly failed to deliver on its promises of safety and cost.
Why would anyone be surprised that general public has a not too favorable opinion about it now?

 

[russ_watters]

The technical promise is the design core damage frequency. Example:

http://www.edf.com/fichiers/fckeditor/Commun/Innovation/conference/BWRsbasics_va.pdf page 21:

BWR4: 10^-5 per year
BWR6: 10^-6 per year
ABWR: 10^-7 per year
...

Even the "high" 10^-5 per year core damage frequency would mean that 1000 reactors need to run for 100 years to statistically have about one core damage event. We now have only ~450 operating power reactors.

A few things:
1. That data is for specific makes/models of reactor an certainly doesn't apply to the industry as a whole.
2. You are improperly separating the Fukushima meltdowns in your count: they were 1 accident.
3. The basis of the predicted reliability is not provided. I suspect it is based in part on other additional assumptions about support system reliability.

That link is way too focused to support your broad/sweeping claim.

The reality is: nuclear power industry repeatedly failed to deliver on its promises of safety...

Why would anyone be surprised that general public has a not too favorable opinion about it now?

You connected the statements as if they are related: they aren't. The successful anti-nuclear campaigns happened prior to any of the accidents except TMI (not sure if you included that) and we're based in large part on lies; in particular the inappropriate link between nuclear power and nuclear weapons.

If anything, nuclear power is seeing a resurgence today as the old lies gradually get forgotten. It has a long way to go though.

This "promise of safety" claim remains a powerful red herring though. The wording implies "not safe" when in reality, at worst (pending you proving your claim about the promise even existing as you claim) "not as safe", which is still really, really safe. So a proper understanding of the claimed "failure to deliver on its promise of safety" should still result in one supporting nuclear power.

 

[mheslep]

The point is, nuclear power industry's promises about safety were such that over last 50 years, statistically, there should have been not even one major meltdown of the power reactor. But in reality, there were FIVE meltdowns.

I'm not counting "small" accidents, such as partial meltdowns damaging just a few assemblies, and accidents on small reactors such as SL-1 accident. Just the major meltdowns.

No that's not the point, but a (non unique) facet of the industry on which you choose to concentrate.

 

[mheslep]

I was working the Barsebaek plant and was witness to an anti-nuke demonstration in the city of Malmo, Sweden. I asked a protester "Where will you get your electricity?" She answered "Oh, those are NUCLEAR PLANTS not ELECTRIC PLANTS!" So it goes...

Protester was also probably a polio and measles carrier, as vaccines [strike] are radioactive[/strike] whatever.

 

[nikkkom]

A few things:
1. That data is for specific makes/models of reactor an certainly doesn't apply to the industry as a whole.

Yes, they do apply to industry as a whole.
To prove me wrong, please give me an example of a post-1970 power reactor design which did not promise at least 10^-5 core damage frequency.

2. You are improperly separating the Fukushima meltdowns in your count: they were 1 accident.

What's improper about it? Did nuclear plant designers ever say "BTW, no guarantees about co-sited reactors: if one goes up in smake, all others will too"? Not at all. All we ever heard that NPPs are incredibly safe and won't melt down.

3. The basis of the predicted reliability is not provided. I suspect it is based in part on other additional assumptions about support system reliability.

You are trying to make an argument, but I don't understand which. Are you trying to say that nuclear power plant designers did NOT promise core damage frequency of 10^-5 and lower?

You connected the statements as if they are related: they aren't. The successful anti-nuclear campaigns happened prior to any of the accidents except TMI (not sure if you included that) and we're based in large part on lies; in particular the inappropriate link between nuclear power and nuclear weapons.

If NPPs would, since 1970, work WITHOUT meltdowns for decades on end, these anti-nuclear campaigns would gradually abate and people get much more supportive of nuclear power.

This "promise of safety" claim remains a powerful red herring though.

Are you disputing that nuclear power industry did promise the stations to be safe, specifically promise core damage frequency of 10^-5 and lower?

 

[nikkkom]

(pending you proving your claim about the promise even existing as you claim)

http://www.nrc.gov/docs/ML0230/ML023010606.pdf
"GE BWR/4 Advanced Course R-504B. - NRC"
Figure 6.4 - 16 Simplified Event Tree For Large LOCA
Total: 2.5E-5

https://nuclear.gepower.com/build-a-plant/products/nuclear-power-plants-overview/abwr.html
"ABWR Nuclear Power Plant"
Lowest-in-class core damage frequency at power (1.6 x 10-7/year)

 

[Salvador]

Did they calculate this core damage frequency including all the support systems a NPP has or simply the very active zone parts durability along their lifetime ?

Another factor one must take into consideration is that not all nuclear accidents are to due with the frequency or their safety record , that's like saying the Airbus or Boeing or Mig have a bad safety record because they have crashed but we must look at exactly why they crashed and most of the time it was either human error or as in late times a deliberate terrorist attack whether smashing them into the WTC or simply setting the autopilot to crash the plane into the Alps etc etc.
Please correct me if I leave out some or have forgotten but to my mind the only real core meltdowns that were technical failures were TMI and Fukushima, all the others were either small scale ,navy or military objects.
Chernobyl was more of a core blast than meltdown but we can't actually count Chernobyl fully into the reactor safety table simply because it was mostly a human error on many levels, both the oversight and the actual staff that night which made dangerous and fatal errors.Like running the reactor with too low of a power allowing core poisoning then running at almost no moderation to compensate the poison burn up and shutting off all automatic safety features ,(oh i hear Nikkkom yelling that RBMK is at fault for being super dangerous :D) Well I sort of admit , even the operators agreed to this in the other RBMK facility were I was, that RBMK is a very sneaky and rather dangerous machine especially prior to 1986 security updates, so it required the crew to be both very wise and skillful and experienced in nuclear physics of which atleast two of the three named were missing somehow at that night shift.
Also they saw 3 years before Chernobyl at Ignalina that the control rod tips increased the reactivity when first inserted , they told this to the higher authorities but they were dismissed as it was not seen as a big enough potential threat.Again is the reactor to blame or the authorities for being ignorant and not fixing things earlier.Although I must say as I read from time to time there have been some other mostly unknown incidents in nuclear reactors that could have escalated to the highest INES 7.
And most of them if not all have been the operator error, so the industry should really put up it's awareness and oversight.I'm especially concerned (I'm not a racist) with the developing countries like India and various Asian countries etc of developing nuclear reactors because they don't have the experience most of the former USSR and US , Europe has also their oversight might lack the needed attention to detail and such seemingly tiny errors can lead to a major accident.

 

[russ_watters]

Yes, they do apply to industry as a whole.
To prove me wrong, please give me an example of a post-1970 power reactor design which did not promise at least 10^-5 core damage frequency.

Chernobyl was constructed starting in 1972. Which of those reactors did it use? This is still your claim, not mine. You have not substantiated it adequately.

What's improper about it? Did nuclear plant designers ever say "BTW, no guarantees about co-sited reactors: if one goes up in smake, all others will too"?

Dear god, I hope so! I would not assume any designer would be so much of an idiot that they would assume an earthquake/tsunami would hit one reactor on a site and not affect the others. So yeah, without substantiation, I'm not willing to accept your assumption.

Not at all. All we ever heard that NPPs are incredibly safe and won't melt down.

"won't melt down"? That's an even more extreme (absolute) claim than the previous unsubstantiated claim.

You are trying to make an argument, but I don't understand which. Are you trying to say that nuclear power plant designers did NOT promise core damage frequency of 10^-5 and lower?

Several:
1. You haven't proven that those numbers are typical of claims 50 years ago.
2. The "core damage frequency" stat is not adequately enough defined to say what it means. If you want to use it, you need to find a definition/description of its breadth/constraints.

If NPPs would, since 1970, work WITHOUT meltdowns for decades on end...

Again:
1. The nuclear industry's grind to a halt in the US in particular was completed in 1980, prior to Chernobyl.
2. They have worked for decades on end without meltdowns. Not sure if you are including TMI, but that was in 1979, Chernobyl was 1986 and Fukushima was 2011. So, prior to 1970, zero. In the 2.5 decades between Chernobyl and Fukushima, zero.
3. That's still an unreasonable standard, but I get that:

...these anti-nuclear campaigns would gradually abate and people get much more supportive of nuclear power.

That's trivially true, but at PF our intellectual quality standards require you to be better than that. Your assessment needs to be based on facts and logic, not the illogical scaremongering of the anti-nuclear crowd. You need to weigh the risks against each other and weigh the logical conclusion, not imply that the fear a lot of people have of flying the day after a plane crash is something reasonable to act on. Speaking as a moderator, you need to do better than you are doing. Similarly:

Are you disputing that nuclear power industry did promise the stations to be safe, specifically promise core damage frequency of 10^-5 and lower?

I am saying you have not adequately supported your claim that they did. I'm also saying that you are applying misleading logic to the implications of it (bait and switch of "not as safe" for implied "unsafe and reasonable to oppose"), even if it is true.

 

[russ_watters]

Here's how the nuclear safety promise vs actual logic works, using the rough numbers we are dealing with:

Let's say I give you a choice between two options:
1. Option 1 will kill 1 person a year*.
2. Option 2 will kill 100,000 people a year***.

You'd pick option 1 in a no-brainer, wouldn't you? Fast forward 50 years, to find out I was wrong in my promise in #1 by a factor of 100**. You'd have a right to be upset about that, but if you knew that going in, you'd still have picked option #1, wouldn't you? So the implication that nuclear power failing in a safety promise is a legitimate reason not to use it is wrong either way. And that's what happened:

Enough people chose Option 2 in the 1970s to stunt nuclear power's growth and many people still choose Option 2, 40+ years later. I'll say it more directly: The choice you've (and others like you have) made and continue to make results in tens of thousands of additional/unnecessary deaths a year. It boggles my mind that people who appear to know the reality of the options continue to make and argue in favor of that choice.

*This number is a placeholder in lieu of zero in order to avoid a divide by zero error later.

**This is based on the estimated total number of pre-mature deaths to be casued by Chernobyl of about 4,000 -- divided by 50 years, yielding an average of 80 per year.

***100,000 is an obsolete global number, but I think is reasonable. The US in particular has markedly improved its health/safety record with coal power to the point where it only kills on the order of 5,000 people per year vs something like 20,000 per year a decade or two ago. Moving in the other direction, 100,000 globally was a commonly cited number a decade ago, but has been swamped recently by the economic rises of China and India, with a quick google supporting numbers of about 500,000 per year, most of them in those two countries alone.

Additional assumptions:
1. Option 2 does not count future impacts of global warming.
2. Option 1's analysis does not include differing reliability factors between countries or improvements in safety with time. Since Chernobyl was the only power plant accident that killed anyone so far, that's a big problem with the analysis. In other words, just to do the analysis at all, I have to vastly over-state the risk in order to make it calculable. Unfortunately, nuclear power is too safe to do accurate/reliable accounting of its safety record (twisted irony intended).

 

[Salvador]

I think russ , that in our modern world , especially in countries like China the policy to build more coal and less nuclear was not a public decision rather a government one , also there are countries for whom coal is cheaper in the short term so they simply go with what's cheaper.

As for radiation , in small to medium exposure I think it's a really big gamble to say precisely how much it will affect , even after Chernobyl some of the liquidators live as if nothing had happened while others have developed cancer and died , yet both received similar dosages.Also the fact that this happened in one of the most secretive countries in the world - the former USSR , much of the data and true scale of things has been hidden and left unknown.
Not all of the medical reports were true so we can only estimate the true numbers.
Surely Chernobyl affected many , some simply psychologically and Nikkom comes from Ukraine so i understand his sentiment about nuclear energy , the liquidation was one of the most complicated emergency operations in human history.

I think the problem with accidents like Chernobyl is twofold , firstly people don't know the whole workings behind as to why it happened and why similar things can't repeat themselves elsewhere and also such an accident gives a big focus on itself yet on the other hand coal power plants and fossils in general are like smoking , nobody is scared from it directly not even the smokers as in the short term it seems almost harmless it doesn't affect you in any certain way , it develops it's effects slowly and gradually over the years and because the society has a very short memory for long term evils its easy to focus on the short term blasts , much like the whole modern media takes something blows it out of proportion to gain views and then leaves it behind to grab the next hot story.Add heavy lobbying and biased opinions to that and don't wonder we live in a mixed up world.

 

[Salvador]

Also I wanted to add another thing i just thought of , surely the general public would not understand but there is a big difference in meltdowns , if I'm correct all the other meltdowns including Fukushima happened when the reactor is shut down and all control rods are inserted and emergency cooling provided and then lost.

Chernobyl on the other hand experienced a progressing and total meltdown along with atleast two powerful explosions and all this happened seconds after the reactor was driven first by operators then picked up on itself into supercriticality.
In other words no other meltdown has happened in a state when the reactor is operating at it's absolute maximum and by maximum I don't mean the design maximum specification but the close maximum a pile of stacked uranium can reach if all control is removed.
The reactor control room meters stopped at some 30 000 MW, and that's simply because the detectors were blown apart the actual power probably hit even higher.
that's enough power so that if harvested could cover multiple smaller countries I think , because the one in which I live is fully covered by a Hydro station which has an output capacity of 950MW.

I read experts say that the blasts both first and second were equal to many tons of TNT , I have to say it makes me wonder how the reactor building's foundations and largest support structures remained standing and how the third unit, whose reactor hall had not that much between the unit 4 reactor hall , were unaffected and continued operation until morning.

All in all we must understand that modern reactors are built such that upon any trigger of danger they will automatically shut down.So even if all coolant and cooling is lost the meltdown will not be anywhere close as tragic and out of all proportion as in Chernobyl.
To bring some fun in this discussion I want to say I have heard upon discussion that some really fanatic religious people have said that they think Chernobyl was partly an act of God which made all the right criteria for such an awful and never before seen tragedy so that this event could be one of the few large factors contributing to the collapse of the USSR (evil empire). About the second part they were right , the cleanup did cost some serious money and resources both material and human.and it still continues to cost a fortune.
But from the bright side , even religious nuts understand that such events are very very unlikely to happen , they are like the births of genius composers , once in a few centuries.
So I go with one of my favorite musicians of which I have many , by the name of Bob Marley who sang a verse in his "Redemption song"
quote "

Have no fear for atomic energy,
'Cause none of them can stop the time.

"

I think a very intuitively bright conclusion from a man otherwise very far standing from nuclear physics.
P.S. While thinking about this I want to ask the more experienced folks here , assume a thought experiment, the same thing somehow happens in a reactor with up to date containment structure like most modern BWR and PWR.Somehow all control and moderation is lost and it happens when the reactor is at it's or near it's maximum output thermal power.Also assume that no further moderation or operator control is given and the reactor is allowed to "ride free" as it pleases , what would happen could it jump to RBMK energy levels at the accident and develop pressure strong enough to blow the containment vessel into pieces?
I know that atleast in the PWR the water itself largely acts as the moderator and upon it's loss the ratio of thermal neutrons vs fast ones would be in favor of fast so that is like a self limiting safety feature.

I guess that the answer goes like this, if such pressures in the vessel would be achieved the vessel would collapse but the thing is such conditions cannot be achieved normally or even abnormally in most functioning modern reactors so that won't happen.But still any opinions are appreciated.

 

[mfb]

Chernobyl is also a good example in terms of risk estimates: A series of really blatant violations of safety measurements (of the type "never do this, no matter what happens") was necessary to make the accident happen. How to include that in a risk estimate? You can use basically everything in a way that is dangerous to humans. Do we need assessments how likely a pen is used to be as murder weapon? Does that make pens inherently dangerous?

 

[mheslep]

With respect, the pen can't even theoretically kill hundreds and force population evactuations.

 

[nikkkom]

Here's how the nuclear safety promise vs actual logic works, using the rough numbers we are dealing with:

Let's say I give you a choice between two options:
1. Option 1 will kill 1 person a year*.
2. Option 2 will kill 100,000 people a year***.

The problem with your argument, it's very far from what actually happened.

People who think that nuclear reactors are not a good way to generate electricity do not necessarily *advocate building coal power plants*. You are inventing it because it's convenient for your argument.

Nuclear power industry did not give us the choice as you depicted it, either.

Nuclear power industry promised nuclear plants whose energy would be "too cheap to meter", and which have multiple layers of protections, good enough to make meltdowns and large releases of radioactivity statistically improbable. THAT was the promise.

Retroactively going backwards on it and saying that the real promise was "there will be fewer people dying from nuclear power than from coal power" only erodes the remnants of credibility nuclear power industry still has.

 

[jim hardy]

I want to ask the more experienced folks here , assume a thought experiment, the same thing somehow happens in a reactor with up to date containment structure like most modern BWR and PWR.Somehow all control and moderation is lost and it happens when the reactor is at it's or near it's maximum output thermal power.Also assume that no further moderation or operator control is given and the reactor is allowed to "ride free" as it pleases , what would happen could it jump to RBMK energy levels at the accident and develop pressure strong enough to blow the containment vessel into pieces?
I know that atleast in the PWR the water itself largely acts as the moderator and upon it's loss the ratio of thermal neutrons vs fast ones would be in favor of fast so that is like a self limiting safety feature.

You have the answer, inherent LWR moderator feedback stabilizes the reactor at low power albeit at elevated temperature. So no RMBK runaway.
That's why Rickover and the other old timer geniuses of the day settled on light water reactors. They did their best to make one run away, look up Borax experiments.


Your containment building is designed to contain X amount of energy .
That's why there's such an elaborate system to detect a steam line break inside containment - in that scenario reactor's energy quits going outside as steam to the turbine, instead it stays inside containment raising pressure there. You mustn't let that one go on for long.

What you describe was one of the "What If duJour" 's from 1970's that ate up a lot of analysis time and money .
Look up "Anticipated Transient Without Scram". It postulates failure to trip the reactor when you need to. The acronym for it is ATWS.
Should ATWS happen you need to do something to shut down the reactor. So all US plants added some feature to respond to ATWS.
We added a micocomputer backup to reactor protection system . It disconnects the two little generators that make power for control rods.

I don't know what other plants did. And I'm not familiar with BWR ATWS scenario .

old jim

 

[anorlunda]

P.S. While thinking about this I want to ask the more experienced folks here , assume a thought experiment, the same thing somehow happens in a reactor with up to date containment structure like most modern BWR and PWR.Somehow all control and moderation is lost and it happens when the reactor is at it's or near it's maximum output thermal power.Also assume that no further moderation or operator control is given and the reactor is allowed to "ride free" as it pleases , what would happen could it jump to RBMK energy levels at the accident and develop pressure strong enough to blow the containment vessel into pieces?

Moderated reactors, which includes both water (LWR) and graphite (RBMK) reactors, can't sustain a nuclear reaction if the moderator is removed. Neither can they slip into prompt neutron fast reactor criticality. There isn't enough reactivity in the core to do that.

What could cause overpressure in the containment? The only candidate is steam. Hydrogen can be produced, but there is no Oxygen in the containment so we can't get a Hydrogen explosion. A melting core can melt a hole in the bottom of the containment, but I don't see how it could produce overpressure.

But I think what you are trying to ask about are so-called intrinsically-safe or walk-away reactors Where if everything stops working, no further action is needed, you just walk away. Several such designs have been proposed. To my knowledge, none of the worlds power reactors are intrinsically safe.

One of the ironies of the history of this industry happened in 1986. ASEA ATOM (who I worked for at the time) designed an intrinsically-secure walk-away district heating reactor called SECURE. It was brilliant, because the reactors are much better at making hot water (100% efficient) than making electricity (35% efficient). ASEA ATOM reached agreement to build one in downtown Helsinki. It was to heat the whole city in winter. A press conference was scheduled to announce contract signing. The day before the press conference the Chernobyl Accident happened, and all plans were cancelled. It is a nice pipe dream to imagine all the major cities in Europe heated by SECURE. How might public attitudes on nuclear power differ today?

SECURE had a sister design called PIUS for power production. Neither saw the light of day. Grenoble France also had (still has?) a small district heating reactor.

But I am uninterested in technical debates about nuclear power plant safety. It's not about technology. It is about public trust and about costs. When it comes to trust, all the worlds foremost nuclear scientists and engineers are no match for a Hollywood film studio making a film like The China Syndrome. Scary stuff sells films, TV shows, books, and speaking engagements. The side saying "Trust us, there is nothing to fear," draws only snores and the sound of TVs changing the channel.

 

[mheslep]

... no RMBK runaway.
That's why Rickover and the other old timer geniuses of the day settled on light water reactors. They did their best to make one run away, look up Borax experiments.

Yes an LWR won't run away, but that in itself does not explain Rickover's choice, as other designs also have negative reactivity and also without water in the core. No steam, no steam explosions.

 

[anorlunda]

es an LWR won't run away, but that in itself does not explain Rickover's choice

The actual reasons are of course classified. My suspicion about PWR versus BWR in subs, had to do with the subs heeling over at an angle. Since BWRs depend on voids, tilting is bad for them. Sloshing of the void/water mixture would be worse.

The most remarkable part of the US Nuclear Navy is the training site at West Milton, NY. There, they use actual duplicates of the submarine reactors to train novice operators. All their training, including critical accidents is done on those reactors. No simulators were allowed under Rickover's command. I figure that those training reactors have been subjected to more mishandling than any real sub reactor, yet in my memory, the alarms warning the nearby residents to flee have never sounded. (I used to be a volunteer fireman 6 miles away from West Milton) The evidence suggests that those reactors must be very robust indeed.

A question I always had about submarine reactors (PWR or BWR), had to do with the fact that a sub can roll over 360 degrees. What happens when the reactors are upside down? Unfortunately, all my navy nuke friends give me the same answer to that question, "Classified."

 

[jim hardy]

Yes an LWR won't run away, but that in itself does not explain Rickover's choice, as other designs also have negative reactivity and also without water in the core. No steam, no steam explosions.

i think another point was he didn't want sodium in a submarine.

 

[nikkkom]

P.S. While thinking about this I want to ask the more experienced folks here , assume a thought experiment, the same thing somehow happens in a reactor with up to date containment structure like most modern BWR and PWR.Somehow all control and moderation is lost and it happens when the reactor is at it's or near it's maximum output thermal power.Also assume that no further moderation or operator control is given and the reactor is allowed to "ride free" as it pleases , what would happen could it jump to RBMK energy levels at the accident and develop pressure strong enough to blow the containment vessel into pieces?
I know that atleast in the PWR the water itself largely acts as the moderator and upon it's loss the ratio of thermal neutrons vs fast ones would be in favor of fast so that is like a self limiting safety feature.

I guess that the answer goes like this, if such pressures in the vessel would be achieved the vessel would collapse but the thing is such conditions cannot be achieved normally or even abnormally in most functioning modern reactors so that won't happen.But still any opinions are appreciated.

IOW, "can a Chernobl-like thing be achieved with a BWR or PWR?"

In Chernobyl, personnel was disabling safety mechanisms. Let's say we are allowed to do so too.

In BWR, control rods are inserted from below. If their mechanisms are disabled, BWR power can't be controlled and reactor can overheat and rupture. This does stop the reaction because moderator is lost, but the already happened overheating can be quite bad to the reactor structure. And decay heat will continue to be generated. If containment cooling and/or venting mechanisms are also disabled or impaired, containment can overheat and be breached too (Fukushima).

If you manage to override various systems and can command all control rods to be removed and stay removed, of course reactor will overheat.

In PWR, control rods are on top and losing power makes them drop down, so disabling that should be harder than in BWR. If doable, then it also can prevent reactor from being scrammed when requested, overheating and RPV damage. In PWR, reactivity is usually controlled by boric acid levels in the coolant. Thus the sabotage method of removing all control rods is usually not available (the rods are already removed), but you probably can try replacing boric acid tanks with a soluble salt of U235, and command the reactor coolant to be "borated" to the max. Getting U235 salts is not trivial at all...

Sabotage will be most successful on a freshly loaded reactor, since its reactivity is highest and modern fuel is also poisoned. If power spike is bad enough, poison burnoff may somewhat enhance the kaboom you seek.

I believe with some thought to it BWR and PWR reactors can have bad accidents. Well, for one, they _did_.

 

[russ_watters]

The problem with your argument, it's very far from what actually happened.

People who think that nuclear reactors are not a good way to generate electricity do not necessarily *advocate building coal power plants*. You are inventing it because it's convenient for your argument.

No.

Opponents of nuclear power may not think they support coal (and other fossil fuels), but they do. The fact of the matter is that protests are far more successful in getting something stopped than getting something started, so when you stop something, the alternative fills itself in on its own and the protestors bear some of the responsibility for that. Not a lot of protest banners list a viable alternative to what they are protesting! The primary alternative to nuclear power always had been coal until recently displaced (in the USA anyway) by natural gas.

This was particularly true in the 1960s and 1970s when nuclear power's expansion was halted in the USA, when the currently favored alternatives of solar and wind did not, for all practical purpose, even exist.

Nuclear power industry did not give us the choice as you depicted it, either.

You're inventing an "industry" that does/did not exist. Power plants are owned by power companies, not "nuclear power" companies. They build the power plants that make the most economic sense to them. If you force one type to be abandoned, the power company fills-in the next best option: which was coal.

Nuclear power industry promised nuclear plants whose energy would be "too cheap to meter", and which have multiple layers of protections, good enough to make meltdowns and large releases of radioactivity statistically improbable. THAT was the promise.

Retroactively going backwards on it and saying that the real promise was "there will be fewer people dying from nuclear power than from coal power" only erodes the remnants of credibility nuclear power industry still has.

We're discussing one specific aspect of that promise: the promise that it would be clean/safe (two sides of the same coin). Your argument was about it not being as clean/safe as promised. So I pointed out why that argument fails: Right or wrong (you keep moving the goalposts, so I can't really pin it down), it is a red herring because what really matters with safety isn't comparing something to itself, but comparing something to its alternatives.

 

[Salvador]

Well it seems that the most easy to blow apart and with a huge bang reactor is/was the RBMK pre 1986 version.

All in all I think Chernobyl gave a very unfair shadow to the whole nuclear physics not just atomic energy for electricity.
Also it proved that even designs that are very sensitive to well educated and experienced and probably most of importantly -talented workers can run safe for years on end and fail when they are literally driven to and over the margin.
It just doesn't stop to amaze me after all these years of knowing about it , how so many fatal errors at so many different levels were made that day and night and nobody of all the probably 100 and more folks involved saw this coming.Delaying the test , then allowing it to be done on night shift all the senior most experienced folks already home and only the younger ones left to carry out a very dangerous test.Well this is a topic that can go on and on it's all history now anyway , maybe so much so that the newer generation is slowly forgetting the tragic events of that day and their attitude towards nuclear will change.
Sometimes the short memory of people is a good thing as it allows fresh air to come in , otherwise the Germans should still hate the French simply because they had war 70+ years ago, but we have moved past that and we will probably move past Chernobyl one day.

It's already 30 years and counting and what is even more weird is that folks are going there on tours now and paying money to see the thing that scares the living sh**&^ out of them and their relatives.Maybe that's a good thing, people need to confront their fear.

My friend was there too , well his a bit crazy ofcourse but even though he isn't generally interested nor educated about nuclear physics he now knows more and that also gave him an impulse to come with me and visit another nuke plant , one that never blew up.
As for what anorlunda said and he navy reactors , well yes they may say it's classified etc but I wonder haven't you figured it out or someone , probably someone has , simply because it's the navy doesn't mean their running on different physics laws than the rest of us , much like the Brits were visiting the US back in the day and they were frustrated that they aren't as successful with nuclear energy as the Americans and the response was that last time we checked the UK had the same laws of physics that we do , so it comes down to a matter of "think this one through."

As for the reactor being more effective at heating water than turning steam into electricity well actually a couple of RBMK had the idea that is now popular with biomass and is called cogeneration were you use the steam to generate electricity and the leftover hot water which condenses and cannot be directly used for electricity to heat a nearby city in winter.
The RBMK in my neighboring Lithuania did this , it had an additional loop and used the leftover heat after the turbine to heat the near cities.
the thing is the city needs to be rather close as we all know heated water cannot go through long pipes or it's effectiveness will be so low that it will become useless.
so that means a big reactor located at your eyesight, which was the case in almost all soviet nuclear reactors that they were at or very near populated areas.

Just to throw a little rock in your garden folks , your talking about safety and saying that we shouldn't fear nuclear energy yet in the west most of the nuke plants are located much further away from cities and populated areas and I bet that is a deliberate step made.
As for the soviets , placing the plant in a remote location was not their primary concern.Ofcourse the military research ones were placed far away from eyes.

That being said I have spoken mostly as a man who fears not nuclear energy but I must say I fear peoples disregard for safety a bit , and I must admit knowing the Russians and their mentality they sort of lack the fear from risk and possible death the western people have developed over the years , in some cases it plays in their favor but in some other it's a rather dangerous mixture , one of such places is nuclear power.The military weapons systems are kept under closer inspections and tougher control but the civil facillities are the ones I am bit worried about I must say as they are the ones less controlled and kept after.

I by no means count myself on the green peace fear proponents who claim that all Russian nuclear engineers are nothing but monkeys with a grenade , no their rather smart and talented people but it's the lower class staff at the power stations that are sometimes not up to their task and simple mistakes can then lead to dangerous results , for example the Leningrad nuclear power plant which still operates 4 RBMK 1000 reactors which were among the first RBMK units to be built and also one of the first high power reactors in the world , and I must say the LNPP has had a pretty alarming track record with accidents like
loss of coolant for a fuel assembly , primary and secondary coolant circuit pipe bursts, and the maintenance workers leaving behind a rubber clad which block the coolant flow in certain fuel channels and if not spotted could have caused overheating and rupture.

if you want to read the wiki page has a short list of accidents that have happened in LNPP over the years.I can assure you there have been more just not all have been written down.

https://en.wikipedia.org/wiki/Leningrad_Nuclear_Power_Plant
[PLAIN]https://en.wikipedia.org/wiki/Leningrad_Nuclear_Power_Plant[/PLAIN]
It's partly the fault of authorities that some people are against nuclear power because as you can see virtually none of the accidents were ever reported and when one tries to hide even s a small accident it forms a sort of aura of mysticism and lies around the whole thing which then goes on to affect peoples uneducated opinion for the worse.

there's one quote I particularly like

The plant has agreed to report on all incidents that threaten the safety of the environment to neighbouring Finnish authorities. When asked to report on other incidents as well, the plant answered negatively, stating that they have so many daily incidents that their whole time would be wasted in filling out incident reports

 

[nikkkom]

As for the soviets , placing the plant in a remote location was not their primary concern.

Russian _do_ care about location. Specifically, they deliberately located all big reactors farther than 200 km from Moscow. Here is the map of Russian NPPs, with blue dot added where Moscow is. The only plant closer than 200 km to is the closed Obninsk plant, with small experimental 5MW power reactor. The nearest operating plant is Kalinin, it is 200 km from Moscow. The next is in Smolensk, it is 320 km from Moscow. Other are much farther still.

 

[nikkkom]

We're discussing one specific aspect of that promise: the promise that it would be clean/safe (two sides of the same coin). Your argument was about it not being as clean/safe as promised. So I pointed out why that argument fails: Right or wrong (you keep moving the goalposts, so I can't really pin it down), it is a red herring because what really matters with safety isn't comparing something to itself, but comparing something to its alternatives.

For you maybe. For me it does matter when someone failed to deliver on their promises. Specifically because this makes me suspect that they will *continue* to not deliver on their promises. This suspicion only grows stronger when nuclear power crowd, for example, successfully groupthinked themselves into believing that emergency vents on US NPPs do not need filtering. Because, apparently, Fukushima can't happen.

Today, we do have alternatives which are less polluting than coal, *far* less potentially dangerous than nuclear, and also getting cheaper.

 

[Salvador]

Nikkkom I must say sometimes your way of thinking goes parallel to the conspiracy theorists reasoning, actually there is a fine line between conspiracy, unknown facts , and various probabilities and to master a valuable and more importantly educated opinion takes quite some time and effort and also some intellectual capacity.Please don't be offended I'm just expressing the formula for such things according to my understanding.

For example the same people who think that 9/11 was an "inside job" and that small nuclear bombs were detonated inside the WTC towers and that there were "no planes" instead rockets flown into the buildings , the very same people also think that the Russian government has hidden the truth about nuclear accidents in their facilities and downplayed the level of danger caused by Chernobyl.
Now in the 9/11 case hey are ridicilously wrong and their opinion is so wrong and totally sci-fi that even doctors are afraid of them and such thinking usually shows some other deeper problems with how they see the world and themselves , yet on the Russian government thing they are correct.

You see there is a fine line between being a crackpot and simply knowing some stuff that someone doesn't want you to know.
Also I doubt the idea about the 200km zone around Moscow , then tell me why did they build the first RBMK units near Leningrad, now called St Petersburg , one of the most beautiful cities not only in Russia but the whole world with all its monuments and medieval and newer age castles and relics and also a large population?
the plant is just 70km from the center.The argument about failing to deliver on the promises is also a bit single-ended.Name me one industry or major corporation that hasn't failed to deliver on all of it's promises??
Name the chemical plant Dupont for example , for all the cool stuff they made including teflon, cellophane and various lubricants and oils they also caused some environmental pollution and exposed their workers to chemical substances and all of this happened in the so called "best country on earth" the US were control from authorities is large and the law is implemented better than in Russia.

http://highline.huffingtonpost.com/articles/en/welcome-to-beautiful-parkersburg/

for those who want to read.In the end of the day it all comes down to the lesser evil and least dangerous prospect not to an ideal perfectionist utopia were all babies grow up happy , nothing ever brakes down and no man takes more for himself than needed and all share everything equally without crime and greed.
By the way doesn't this idea sound familiar ? Let me give you a hint - communism, also the "promised land" from the bible.
The reason communism had to be pushed by force and terror is because it doesn't happen naturally , humans are selfish and not thinking in long term.So are accidents , they happen naturally all we can do is make sure we do our best to keep them at minimum.
I think if Chernobyl wouldn't have happened we would never have this discussion here , all the other meltdowns were so small and insignificant that even the hungry media let them go after a few short stories.Chernobyl truly was and still is the only event in nuclear history that is of biblical proportion.
So it comes down to one big tragedy out of very bad attitude and errors by operators and undoubtedly nuclear weapons testing especially in the cold war and that was simply due to our inability to share the same planet without the egocentric need to control one another and prove how big we are.

I remember once standing next to a steam locomotive ,an old museum one that was working just for the fun of the visitors and I too had the chance to drive in it.Well the smell was next to unbearable I thought , hell if I would have to travel like this everyday I would rather push myself to become a marathoner and just run the necessary distance.And after all these years i still visit a larger city and the distinct smell of diesels from large buses and cars is quite annoying.
So why attack nuclear so much ? apart from giving cancer and radiation sickness to those who get large doses it doesn't do anything else to the general population.

I too have thought why is it so that everything slightly technical and advanced in this world is also bad for the environment at some level and to our own health , but that's a topic for a different thread and a rather philosophical one.It's almost like nature doesn't want us to live a fancy life with all the comforts that we now take for granted in the modern world.I like technology and I think it's good if used properly but I think civilization has gone down the wrong road because of our greed and inability to use what we have differently.
P.S. I would love to hear if someone has a different or more in depth perspective of the other RBMK accidents that have been pushed under the carpet.

 

[anorlunda]

How sad to see any PF topic degrade to name calling. I'm out of here on this thread.

 

[Salvador]

No I don't want to name call anyone that's why I said that it's not meant to be an attack, rather just an expression of the dangers of thinking a certain way , I know this personally because I myself once believed a few conspiracy theories and various half truths about things , as time passes and you learn more you start to see that not everything is what it looks like or what one thinks it is.
There is much misinformation out there about everything , all kinds of opinions etc etc , after all not all people have the chance to be in the academic level and around well educated and experienced people to be able to sort between what's correct and what's not.

 

[russ_watters]

For you maybe. For me it does matter when someone failed to deliver on their promises. Specifically because this makes me suspect that they will *continue* to not deliver on their promises.

Matters how? What does this get you? You're talking about this failed promise, but as pointed out, a lot of things fail to live up to the promises. So what do we do with that? It seems like you are implying, but not explicitly stating that the failed promise is a good reason not to support nuclear power. Is that what you are saying? But that's not automatically true: in order to judge whether that failed promise makes nuclear power the wrong choice, it still has to be compared to other real choices.

Today, we do have alternatives which are less polluting than coal, *far* less potentially dangerous than nuclear, and also getting cheaper.

"Today..." Should I take that as an acknowlegement that you agree that 30-40 years ago, when nuclear power's expansion was successfully halted in the US, there were no such alternatives? Causing fossil fuels to fill-in the gap?

And continuing into the next part of the discussion, which you appear to have dropped: shouldn't opponents of nuclear power in the 1960s-70s have taken into account - and be held accountable for - that outcome (the lack of viable clean/safe alternatives)?

 

[Hiddencamper]

You have the answer, inherent LWR moderator feedback stabilizes the reactor at low power albeit at elevated temperature. So no RMBK runaway.
That's why Rickover and the other old timer geniuses of the day settled on light water reactors. They did their best to make one run away, look up Borax experiments.Your containment building is designed to contain X amount of energy .
That's why there's such an elaborate system to detect a steam line break inside containment - in that scenario reactor's energy quits going outside as steam to the turbine, instead it stays inside containment raising pressure there. You mustn't let that one go on for long.

What you describe was one of the "What If duJour" 's from 1970's that ate up a lot of analysis time and money .
Look up "Anticipated Transient Without Scram". It postulates failure to trip the reactor when you need to. The acronym for it is ATWS.
Should ATWS happen you need to do something to shut down the reactor. So all US plants added some feature to respond to ATWS.
We added a micocomputer backup to reactor protection system . It disconnects the two little generators that make power for control rods.

I don't know what other plants did. And I'm not familiar with BWR ATWS scenario .

old jim

BWR ATWS has a redundant alternate Rod insertion system which, on high high pressure (just above the highest relief valve psig) or low level 2 water level, will trip the Recirculation pumps to void the core and lower power, and will also operate separate scram pilot air header vent valves to cause a redundant scram. In newer models, if power is not downscale within 2 minutes after that, the boron injection system will auto start. Meanwhile, operators will manually scram, manually try to insert rods, disable any in-shroud ECCS injection systems, disable automatic depressurization, and lower water level to at least 2 feet below the Feedwater injection spargers to allow Feedwater to mix with steam to preheat and minimize core power. It's a very complicated and rapid moving transient, especially in high power ATWS scenarios with boron injection failure and the turbine or steam lines isolated. But once level is stabilized, even with all rods out, power is low enough to be similar to decay heat levels.

 

[Hiddencamper]

IOW, "can a Chernobl-like thing be achieved with a BWR or PWR?"

In Chernobyl, personnel was disabling safety mechanisms. Let's say we are allowed to do so too.

In BWR, control rods are inserted from below. If their mechanisms are disabled, BWR power can't be controlled and reactor can overheat and rupture. This does stop the reaction because moderator is lost, but the already happened overheating can be quite bad to the reactor structure. And decay heat will continue to be generated. If containment cooling and/or venting mechanisms are also disabled or impaired, containment can overheat and be breached too (Fukushima).

If you manage to override various systems and can command all control rods to be removed and stay removed, of course reactor will overheat.

In PWR, control rods are on top and losing power makes them drop down, so disabling that should be harder than in BWR. If doable, then it also can prevent reactor from being scrammed when requested, overheating and RPV damage. In PWR, reactivity is usually controlled by boric acid levels in the coolant. Thus the sabotage method of removing all control rods is usually not available (the rods are already removed), but you probably can try replacing boric acid tanks with a soluble salt of U235, and command the reactor coolant to be "borated" to the max. Getting U235 salts is not trivial at all...

Sabotage will be most successful on a freshly loaded reactor, since its reactivity is highest and modern fuel is also poisoned. If power spike is bad enough, poison burnoff may somewhat enhance the kaboom you seek.

I believe with some thought to it BWR and PWR reactors can have bad accidents. Well, for one, they _did_.

BWR control rods are deenergize to insert. They use accumulators to insert the rods on loss of air to the scram valves, and there is a ball check valve to allow the reactor's primary water pressure to insert the rods.

 

[nikkkom]

Matters how? What does this get you? You're talking about this failed promise, but as pointed out, a lot of things fail to live up to the promises. So what do we do with that? It seems like you are implying, but not explicitly stating that the failed promise is a good reason not to support nuclear power.

I'm not implying, I'm quite open about it. These guys are not trustworthy enough to let them run machinery which can lead to Chernobyl-scale accidents. Or worse - for example, we were one step away from fuel pool fire in Fukushima, which had 400 tons of spent fuel, more heavily enriched than in Chernobyl.

 

[nikkkom]

BWR control rods are deenergize to insert. They use accumulators to insert the rods on loss of air to the scram valves, and there is a ball check valve to allow the reactor's primary water pressure to insert the rods.

How reactor's water pressure can insert a rod into the reactor which has the same pressure? You need *higher* pressure to do that, no?

 

[Hiddencamper]

How reactor's water pressure can insert a rod into the reactor which has the same pressure? You need *higher* pressure to do that, no?

It's a hydraulic system, you need a pressure difference. The bottom part of the control rod piston has 1000 psig reactor pressure applied to it, and the top part goes to the scram discharge volume which is at 0 psig. This pressure difference drives the piston upwards and causes the rod to go in.

Normal rod moves use a 250 psid across the piston, and take up to a minute for a full rod stroke. At over 1000 psid across the piston you get 3 second scram times. My plant has 1600 psid using our scram accumulators and we get 1.8 second scram times on our rods.

 

[nikkkom]

I doubt the idea about the 200km zone around Moscow

You can doubt all you want, but there is no operating or planned power reactor closer than 200 km from Moscow. It's a fact.

Here is the map of Chernobyl fallout.

Note the peculiar arc-shaped deposits on Russian territory. None of other fallout blobs have this shape. Above those arcs, you see a dot. That's Moscow.

Russian seeded clouds with rain inducing agents (https://en.wikipedia.org/wiki/Cloud_seeding) to not let that fallout reach Moscow.

http://www.telegraph.co.uk/news/worldnews/1549366/How-we-made-the-Chernobyl-rain.html

"Russian military pilots have described how they created rain clouds to protect Moscow from radioactive fallout after the Chernobyl nuclear disaster in 1986.
Major Aleksei Grushin repeatedly took to the skies above Chernobyl and Belarus and used artillery shells filled with silver iodide to make rain clouds that would "wash out" radioactive particles drifting towards densely populated cities.
More than 4,000 square miles of Belarus were sacrificed to save the Russian capital from the toxic radioactive material."

Draw whatever conclusions you want.

 

[Salvador]

Hmm interesting , I didn't know that the Russian top authorities started cloud seeding as fast as two days after the accident, i guess they understood better than most and even some scientists that the cloud coming from Chernobyl is no ordinary one and needs to be stopped.

thanks for pointing this out I didn't knew this or have missed before.

But still Nikkkom the idea stands that you have to be extremely unlucky , win a lottery or simply sabotage a reactor on purpose to achieve such tremendous consequences.