Earthquake in Japan....9.0...ouch!

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Ricochet J

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physichull said:
The power usage of the coolant pumps use is phenominal, it is therefore likely that the best solution was to shut the reactor down and deal with the decay heat (which is initially roughly 7% of the heat of the reactor at full power). Unlike Chernobyl, the reactor was firmly shut down, when the reactor is operational, the rods merely "dip into the bottom of the core", as boron in the primary coolant actually controls the reactor at full power. The rods can then have maximum effect when they are inserted (in this case the control rods are inserted from the bottom of the RPV as is typical of BWR's).
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Do their stations have a RUHS (reserve ultimate heat sink)?
 

Arc

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physichull said:
But at this stage, it is very likely that if any core internals do begin to melt, they would be entirely contained within the Reactor Pressure Vessel, and indeed further contained within the Containment building. The outer cladding that was blown away in the explosion seems to me to be quite typical of quite a lot of the older sites, it serves no safety purpose. As to why the explosion happened, I can't quite figure yet.
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The explosion is probably the result of steam pressure inside the secondary containment structure. That structure, as you say, probably serves no real or little safety purpose and therefore won't take anywhere near as much pressure as the primary containment. Its an older style BWR reactor so a bit different to anything that we have.

With no coolant flow in the primary circuit the pressure of the coolant will begin rise. To prevent damage to the reactor pressure vessel and primary circuit, venting will take place into the primary containment. The key here is to contain and cool the vented water to prevent it flashing off into steam and causing a steam explosion.

On the BBC news website:
Japan's Nuclear and Industrial Safety Agency says serious damage to the nuclear reactor container is unlikely despite the explosion at the Fukushima-Daiichi plant - Kyodo news.
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Assuming the reactor pressure vessel is maintained, fuel remains covered with coolant and any failed fuel is contained then the resultant offsite release should be small. Think more of a minor three mile island style incident rather than Chernobyl. As long as the fuel remains covered then the chance of a meltdown is greatly reduced.

Ricochet J said:
Do their stations have a RUHS (reserve ultimate heat sink)?
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Their decay heat removal systems will have some form of large air coolers but its probably a bit different to an RUHS.
 

Jonnycoupe

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physichull said:
But at this stage, it is very likely that if any core internals do begin to melt, they would be entirely contained within the Reactor Pressure Vessel, and indeed further contained within the Containment building. The outer cladding that was blown away in the explosion seems to me to be quite typical of quite a lot of the older sites, it serves no safety purpose. As to why the explosion happened, I can't quite figure yet.
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Whats the performance of the core catcher like when all the control rods come in through the bottom on a BWR rather than at the top which simplifies things in a PWR core melt.
 

drunkenmaster

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Andr3w said:
Hopefully they will be wearing proper suits full of charcoal etc so nothing gets through to the skin.....hopefully
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Its hard to know, protection is just that, it isn't forever, theres only so much a moveable flexible radiation suit can do before you frankly get a lethal dose.

The radiation levels, its hard to say what they are and if they are dangerous because anyone that doesn't know what they are hearing will go ZOMG, radiation levels coming out at the reactor/in the explosion/whatever are can be incredibly high, but the radiation thats in the air 10km away will be massively massively lower than that, not great, as radiation all rather adds up, your body can only deal with so much.

The problem is knowing two things, the actual danger level being churned out by the plant, AND the distance you are, direction of winds, type of radiation all factor in. It can be basically 100% lethal doses within 100metre's of the plant, and yet almost harmless at 10km and 20km barely above normal.


The question here though is, if they are detecting the byproducts of meltdown, you really can't say its just decay heat, if its gotten hot enough to start the meltdown process suddenly you've got a significant amount extra heat being produced, which can in turn continue the meltdown of the rest of the rods due to the extra heat. It doesn't look great.

AS for the explosion, I wouldn't be surprised if that was indeed a huge clowd of concrete thats simply been turned into powder in an explosion.

The problem is, if that diagram a couple pages back is the design of those containment buildings I'm not sure where the gas gets released or where the pressure goes. It seems like the reactor/turbine/water is all one sealed system but it doesn't show where the pressure is siphoned off too, you would think there should certainly be a valve/back up containment, I'm not sure if they simply release this into either or both those buildings, meaning they release the gas into the reactors building outside the chamber, that pressure rose, they didn't vent it, or vent it enough, and that building blew, meaning if the heat is rising because some of the material has started melting,then I don't see where the pressure will head off to, surely the main reactor casing eventually will buckle under the pressure, how do they stop the pressure from rising without working coolant systems?
 
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Ricochet J

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physichull said:
I don't know enough about that particular design, or BWR's really. I know Sizewell B definately does though! Not that it helps!

It is very likely they will have a multi-barrier safety system set up though with many contingency systems.
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Pretty much it tbh - the nuclear industry relies on defence in depth.
 

physichull

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Jonnycoupe said:
Whats the performance of the core catcher like when all the control rods come in through the bottom on a BWR rather than at the top which simplifies things in a PWR core melt.
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I don't think it has one. I think the term "core catcher" was coined for the new EPR station designs of which a plug in the RPV will melt and allow melting core internals to flow into a safe geometry.
 
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