Merged nuclear power safe?

[Christian Klippel]

If there was no water right after they shut down the reacters, wouldn't that alone cause a dangerous problem? What was keeping the reacters from being damaged at that time? They were very hot at that time, right?

It seems that you did not follow the events, did you?

The reactor was shut down due to the quake. The diesels kicked in and provided power to keep the cooling system running. An hour later the tsunami hit and probably flooded the diesels. At that moment the batteries kicked in to keep thing running, albeit at a lower level. After 8 hours the batteries died.

In the meantime they used other methods of cooling, with varying degrees of success. No one can say how this will end, but so far they did a very good job of keeping things more or less under control, given the circumstances. It could have been much, much worse right from the start.

Greetings,

Chris

 

[jnelso99]

A not-very-accurate reference to 180 workers who were rotated in groups of 50 to work in the plant.

And no, not sent in to "basically die". Their exposure limits were raised to 250 mSv, which is much higher than ordinary limits but offers little in the way of medical danger.

That said, their work was and still is dangerous, even though it appears that (a) they are making progress getting cooling water where it needs to go, and (b) there has been no major release of radioactive materials (i.e., threatening health) outside the immediate area of the problem reactors.

So, if things go well (and I understand the situation correctly), the immediate dangers should be resolved within a few days, leaving no long-term effects on any workers, but a lengthy and expensive cleanup and decommissioning. And a lot of lessons-learned sessions.

Thanks for the info! I heard it on the radio, so naturally it was overblown...

Still sucks for those guys, tho.

 

[ceptimus]

Having the roof blown off makes it easier to spray water into the spent fuel rod pools!

The helicopters drop around 7 tons a time (most of which is blown away by the wind). Even if there was no wind and they could get low enough to get the entire load accurately in the pond, the capacity of that pond is about 2000 tons, so it would require about 300 helicopter drops to fill it.

http://www.guardian.co.uk/world/2011/mar/17/japan-nuclear-crisis-fukushima-seawater-reactors

 

[r-j]

If they kept the pumps running, then why did three reactor buildings blow up? Building that had fuel rods on top of the buildings?

Why did they run out of power after 8 hours? That doesn't make any sense at all. And if something doesn't make sense, it probably isn't true.

If you lost your power supply, and you know that if the pumps stop it is disaster, why would they not fly in power for pumps? Before they fail?

This is wrong. There is something wrong here.

 

[ceptimus]

I thought they did bring in some reserve generators, but it turned out they had the wrong sort of electrical plugs/sockets so they couldn't be connected up to the pumps.

You would think it wouldn't take too long to sort out some new connectors, so if that story is true, I can only assume that increasing danger from radiation/heat/explosions pushed the workers back from the area where the connections had to be made.

 

[r-j]

It seems that you did not follow the events, did you?

The reactor was shut down due to the quake. The diesels kicked in and provided power to keep the cooling system running. An hour later the tsunami hit and probably flooded the diesels. At that moment the batteries kicked in to keep thing running, albeit at a lower level. After 8 hours the batteries died.

In the meantime they used other methods of cooling, with varying degrees of success.

Are you kidding? Three building blew up! Huge explosions. The damage is terrible. How can you even say "with varying degrees of success"? That doesn't make sense.

None of this makes sense.

If they are running out of power, and they know what will happen if they run out, that seems like the moment to send out emergency calls for help.

 

[Toke]

If you lost your power supply, and you know that if the pumps stop it is disaster, why would they not fly in power for pumps? Before they fail?

The cooling pumps are likely pretty big, the generators to power them are unlikely to fit under a helicopter, even if readily available. The switchboards is likely wet too, as well as the pump motors.

It takes a while to draw an extension cord as thick as your arm around a plant and maybe all the way to the pump motor itself. Connecting that gauge is time consuming too.

 

[r-j]

If that is true, then the design of the back up system is terrible. if anything goes wrong with the back up power system, at any power plant, the same thing will happen. Not only will the reacter be damaged before they can get power, the cooling pools will start to heat up.

It sounds like the back up power is the only thing between a disaster. How can that be true?

 

[sts60]

The explosions were from hydrogen gas generated when the reactor cores, and apparently in at least one case, a spent fuel rod pool, were partially uncovered by falling (evaporating, maybe leaking) water levels. The steam was dissociated into its components hydrogen and oxygen. These were chemical explosions, which blew open a couple of the buildings around the containment vessels. How much damage was done to pumps, plumbing, and wiring, or to the reactor vessels themselves, or to the containment vessels around the reactors, is not clear. I read that concrete around the spent fuel rod pool at #4 was damaged, though the steel pool vessel itself is still there.

It does not seem that there are any gaping holes other than a couple of the buildings which suffered the hydrogen explosions. [ETA: I mean no big holes in the reactor vessels or containment vessels.] That's not good, of course, but most of the radioactive material released seems to be in vapor form and disperses pretty quickly. Hopefully, the coolant restoration efforts will continue to progress and there will be no more damage to the units, meaning manageable hazards and less expensive cleanup.

 

[Rolfe]

If that is true, then the design of the back up system is terrible. if anything goes wrong with the back up power system, at any power plant, the same thing will happen. Not only will the reacter be damaged before they can get power, the cooling pools will start to heat up.

It sounds like the back up power is the only thing between a disaster. How can that be true?

Same reason as they didn't have enough lifeboats on the Titanic, according to an expert on Channel 4 this evening.

Rolfe.

 

[BobTheDonkey]

I thought they did bring in some reserve generators, but it turned out they had the wrong sort of electrical plugs/sockets so they couldn't be connected up to the pumps.

You would think it wouldn't take too long to sort out some new connectors, so if that story is true, I can only assume that increasing danger from radiation/heat/explosions pushed the workers back from the area where the connections had to be made.

Well, it's not that simple. As an exercise in how unsimple this is, take any appliance from England and plug it into the wall in a house in New York. Oh, the plug doesn't fit? Well, just swap for a plug that does. *snap, crackle, pop*

But all power's the same, right?


Just because it's a generator and provides electricity does not mean it provides the proper kind of electricity. The mobile generators that were delivered were from the US Navy, unless I'm mistaken. Therefore, the likelihood that they were built to output power usable by the plant was low - worth a shot, but low - and indeed, as we have found out, that likelihood was in fact a zero.

 

[ceptimus]

It sounds like the back up power is the only thing between a disaster. How can that be true?

I think it is true for the boiling water reactors, and other reactor types too.

There are some newer designs that don't rely on back-up power to keep them safe.

So anything that disrupts the back-up power supplies, or the people in control of it for a significant time, makes these older types of reactor very dangerous.

The advocates of nuclear power will argue (correctly) that not everywhere on earth is prone to earthquake and tsunami. But of course other disasters such as flooding, war, terrorist attack or an aeroplane crashing onto the site, could be just as devastating.

I'm yet to be convinced that anyone can guarantee that a reactor site is very unlikely to be involved in a war or terrorist attack, during its lifetime. How many countries have gone for a hundred years or so without being involved in a war?

 

[bobdroege7]

The evacuation zone was precautionary. So far, nothing has happened to require a complete survey before letting people return to their homes after the crisis is over.

was precautionary, is now required, sorry you are wrong.

The hydrogen explosions were far from benign incidents involving non radioactive hydrogen.

The radiation levels around the plant we have noted would be expected to be background during all normal operation. The radiation is not coming from the core through the containment or from inside radioactive systems.

When the power to the emergency cooling systems were lost, and there was no cooling capability to cool the reactor the following events will occur.

The reactor vessel heats up until the pressure reaches the setpoint of the safety relief valves. These valves also have the capability to be remotely operated to vent the reactor and lower the pressure.

They do have one drawback though, once opened or cycled, there is a chance they won't close tightly again, and the more they are operated the higher this chance is. One of these valves at TMI opened and failed to reseat and this was one of the events that contributed teo the TMI incident. These valves are common to both PWR and BWR reactor types.

With no method to refill the reactor vessel since there is no electrical power, the action of these valves will work to prevent overpressurization of the core, will eventually drain the core of water.

Leading to the overheating of the fuel rods and their subsequent failure and combustion in the steam environment as they become uncovered.

Now the pressure is still able to lift the relief valves. only now the steam going into the supression pool/torus contains the reactor fuel, fission products of all kinds, and hydrogen.
The hydrogen coming as a byproduct of the combustion of the zircalloy fuel cladding.

We have all seen these hydrogen explosions and they are scattering fission products to the four winds.

These can be very small yet highly radioactive and notoriously difficult to detect and clean up.

Look carefully at the pictures on CNN, you can see the torus on #3, I think.

The radiation levels around the plant are coming from radioactive materials that are outside the systems designed to contain them.

 

[Aepervius]

So apart from being a danger to the workers and soldiers, this is pretty much as the pro-nuke people have been saying all along, a storm in a rather hazardous teacup?

I think this is a bit of an understatement , it is quite a worrying situation, but at the moment unless it get worst, it is much less problematic for the evironment & human inhabitation as the rest of the tsunami damage. Just let us ask the FSM it does not get worst, and if so then it will be an expansive situation to clean up only. Certainly those guy prophesysing the end of japan are a bit too quick here.

 

[Rasmus]

If that is true, then the design of the back up system is terrible.

No, the design is just not adequate for a catastrophe much bigger in scale than anything they've seen there before and had planned for.

I have seen emergency generators for a nuclear power plant - the engines were the size of a garage, roughly.

The had redundant equipment on site, but it seems the tsunami wiped out both.

if anything goes wrong with the back up power system, at any power plant, the same thing will happen. Not only will the reacter be damaged before they can get power, the cooling pools will start to heat up.

It sounds like the back up power is the only thing between a disaster. How can that be true?

Simple: The plant requires power and water to run. If the supplies and whatever backups are available for more than a certain time, things go wrong. There really is no other way - after all, they *had* stored power on site, but after enough time or after enough things go wrong, you simply run out of options.

You could of course suggest that emergency generators be set up elsewhere ready to be trucked in - but even that might be kinda difficult if your reactors are situated in an area struck by earthquakes and tsunamis.

There comes are point where all your plans, emergency plans, backups and improvisation will no longer be useful.

Maybe the lesson from this is that we cannot predict nature well enough to plan nuclear power plants that we can think of as reasonably safe. I don't know - but these plants were considered reasonably safe and it just so happened that nature dealt much larger blows than ever before.

How could it happen? Nobody had foreseen it.

 

[sts60]

It sounds like the back up power is the only thing between a disaster. How can that be true?

Because that's what backup systems do. The only thing between a safe flight and your airliner crashing is the backup systems.

In this case, the redundant generators did their job after a historic earthquake, until a historic tsunami swamped their defenses. Then the backups to the backups (battery systems) did their job. But the damage was too great. Now the intrinsic toughness of the reactors' design, and the hard work and of their crews, have prevented a disastrous industrial accident from becoming a real catastrophe. As far as I can tell.

r-j, instead of breathlessly pouncing on every news item you see, why not take a deep breath and calm down?

There are many questions to be answered, and I'm sure there are ways to improve both facilities and contingency responses. But just knee-jerking to everything accomplishes nothing but raising your blood pressure.

 

[Aepervius]

The evacuation zone was precautionary. So far, nothing has happened to require a complete survey before letting people return to their homes after the crisis is over.

Case in point if it is 300 micro Sv per hour at the plant outside perimeter, it can't be that high 1km, 5km, or even 30 km away.

 

[bobdroege7]

The explosions were from hydrogen gas generated when the reactor cores, and apparently in at least one case, a spent fuel rod pool, were partially uncovered by falling (evaporating, maybe leaking) water levels. The steam was dissociated into its components hydrogen and oxygen.

This is not true.

The hydrogen comes from the zirc-water reaction.

Zr + 2H2O -> ZrO2 + 2H2

 

[Aepervius]

If they kept the pumps running, then why did three reactor buildings blow up? Building that had fuel rods on top of the buildings?

Why did they run out of power after 8 hours? That doesn't make any sense at all. And if something doesn't make sense, it probably isn't true.

If you lost your power supply, and you know that if the pumps stop it is disaster, why would they not fly in power for pumps? Before they fail?

This is wrong. There is something wrong here.

READ.

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[Belz...]

If that is true, then the design of the back up system is terrible.

Hindsight is 20/20, especially for armchair analysts.