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robinson
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They ran because everything in the buildings was falling on top of them. They even pried open the emergency doors to get out the control rooms. Which was a good idea, as anybody who stayed would have died.
NUCENG said:Can you tell us more about that chart? Source of data, how many points were used, etc.?
rmattila said:Since there's no oxygen in the containment, there is no risk of H2 explosions as long as the stuff remains contained. <..>
<..>concerning early venting: to me it would not seem a sensible approach to backfit the containment to endure the severe accident conditions without any release, and yet vent it to the atmosphere at the early stages of the accident, when there are no signs of containment not being able to contain the radioactivity as designed.<..>
robinson said:They ran because everything in the buildings was falling on top of them. They even pried open the emergency doors to get out the control rooms. Which was a good idea, as anybody who stayed would have died.
MadderDoc said:It would seem to me as a lay man, that an early depressurization of the reactor pressure vessel into the S/C might have avoided much of the damage caused to the dry-wells by the excessive heat and pressure they must have been exposed to while the pressure and temperature were allowed to remain high in the RPV, while any cooling systems of the dry-wells became inoperable due to lack of power.
snip.
MadderDoc said:I can see how water/metal interactions should lead only to H2, but radiolysis of water would theoretically produce also O2, I have been wondering about this: Might a configuration with the RPV blowing out into the S/C be conducive to accumulation of radiolysis products there, including O2?
I think in the case of Fukushima, leaving on an RPV at 7 MPa/400oC inside an uncooled containment vessel with a design limit of about 0.5 MPa/150oC should predictably lead to failure of the containment vessel, well before radioactivity containment eventually might be needed. If there is a rationale for early release of pressure and heat from the RPV, it would in turn provide a rationale for the following need for early venting. There is of course a line between the wish to contain and the risk of doing so until something gives in.
westfield said:I don't think its that black and white - I'm also speaking as a layman so someone please correct me if I'm mistaken, early depressurization to me would mean the first line of defence on a loss of power is gone, namely HPCI and RCIC both of which require high pressure steam to work as I understand it. Obvioulsy the operators would have wanted to try and keep the ability to use those systems so initially depressurization would be the last thing they want to do. The only other systems they had to control heat in the reactors were the LP ones which all require electricity (again, as I understand it).
I guess my point is that the operators are trying to remove the heat from the core to prevent a meltdown, if the heat is under control there will be no pressure issues and therefore no need to vent AT ALL - From what I understand of the systems early depressurization and venting prematurely will not help the heat problem and will remove several critical systems from the picture.[<..>
rmattila said:<..>The RPV is constantly "vented" to the S/C in any case after the shutdown (either through pressure control blowdown valves or safety valves) if the MSIVs are closed, so radiolysis O2 will also be vented to the containment and not accumulate in the RPV.
MadderDoc said:OK, that's also what I figured. That would mean non-compressible gases, including any hydrogen from metal/water interactions and any hydrogen and oxygen produced from radiolysis from the RPV would be transferred to and accumulate in the S/C.
MadderDoc said:I suggest the basis for the data estimate for that period may be in error. If there had in fact been any striking change or elevation in emissions during March 30th-31st, it would be expected to have shown up in the measurements from the site monitoring posts, but there is nothing there to be seen:
MJRacer said:Is there a reliable estimate of what percentage of Cs-137 inventory has been released so far at Fukushima?
westfield said:I don't think its that black and white - I'm also speaking as a layman so someone please correct me if I'm mistaken, early depressurization to me would mean the first line of defence on a loss of power is gone, namely HPCI and RCIC both of which require high pressure steam to work as I understand it. Obvioulsy the operators would have wanted to try and keep the ability to use those systems so initially depressurization would be the last thing they want to do. The only other systems they had to control heat in the reactors were the LP ones which all require electricity (again, as I understand it).
Of course Unit#1 with its Isolation Condenser instead of RCIC is a different case. That should have worked fine without power, something else went wrong there, perhaps as simple as running out of water.
I guess my point is that the operators are trying to remove the heat from the core to prevent a meltdown, if the heat is under control there will be no pressure issues and therefore no need to vent AT ALL - From what I understand of the systems early depressurization and venting prematurely will not help the heat problem and will remove several critical systems from the picture.
From the sparse reports I've read the operators at Fukushima 1 could not keep the IC and RCIC systems running for some reason and this is one of the most important questions in my mind. If they had functioning IC and RCIC then we might not even be here on this forum now.
Perhaps someone here in the business could clear these aspects of ECCS up for us?
Is it a bad thing to lose those steam driven HP systems and try "fight" the fight with a depressureized reactor?
NUCENG said:Let me try. I will address the IC first as it is a very simple system. I will post a follow up on the more complicated possibilities with RCIC later.
The IC basically is a system to take reactor steam and condense it in a heat exchanger then route the condensate back to the vessel, removing heat in the process. The system runs on natural circulation. The steam rises to the condenser and is condensed. The condensate is cooler than the water being heated in the vessel so it flows back into the vessel. That is the theory. In operation all that is necessary is to open valves to allow the condensate to flow back into the vessel. The standpipe of condensate is kept filled by steam which is continuously available to the condenser. The condenser is basically a water tank that boils off and is vented to atmosphere. To keep it running all that is needed is to continue to add water to the tank. Since the tank is vented this can be done by a portable pump or fire truck.
Failure modes are azlso relatively straight forward. If the valve can't be opened the system won't work. At unit 1 the system was started, but apparently was stopped over concern about exceeding a design limit on cooldown rate. Later they tried to restart the IC, but it is not clear whether it worked. Power to the valve may have failed. The valve itself may have failed or the high temperatures in containment could have caused boiling in the condensate standpipe. This would have broken the driving force for natural circulation. Other possibilities are that the tank was damaged and leaked or boiled dry removing the coolant from the heat exchanger.
I have looked at the data dump from TEPCO from the first hour after the erathquake. It is clear that the IC was initiated and stopped after about 15 minutes. Following the tsunami there was no active instrumentation readings released so it is not clear what prevented reinitiation. The concern about cooldown rate was probably a mistake since the vessel was probably already on the way to core damage due to the extended SBO. I do think the mode of failure will be easy to identify when conditions permit examining the piping and valves.
Hope this helps. I will try to post on RCIC later tonight.
The Chernobyl released something like 40% of the Cs-137 inventory IIRC, and had IIRC comparable inventory to Fukushima reactors. ZAMG estimated first 4 days release of 50% of the Chernobyl's Cs-137, based on CTBT sensors picking up the stuff that was blown into ocean. So, >7% give or take, assuming nothing was released from spent fuel pools. Very inaccurate of course. You can look up the inventory for those reactors and compare to ZAMG source term estimate directly. The source term estimates for Fukushima based on measurements are all very inaccurate because the wind was blowing to the ocean.SteveElbows said:I don't know how reliable they are, but the accident analysis documents that are public tended to estimate very percentage releases, often in the 0.6%-1% range, but I believe one of their scenarios lead to a broader range of something like 1%-6%. Its been a while since I looked at these documents, but I imagine this was for reactor 2 since their other estimates also have more stuff released from this reactor.
MadderDoc said:Ultimately HPCI and RCIC would fail due to loss of DC power, but until then the operator would of course want to use them to be able to inject water. I am not suggesting the RPV vessel might have been depressurized to atmospheric, only down to a level that would still keep those systems operable, i.e. to a pressure of about 1 MPa. It would seem to me to have provided a much better starting point, a colder and more water-filled reactor pressure vessel, once HPCI and RCIC failed. And in the meantime it would have protected the dry-well and associated systems from heat damage.
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MadderDoc said:The only respectable heat sink would seem to be the large body of water in the suppression pool. Once that had been filled, i.e. heated up, there would be no way to contain the heat produced by the core. From then on it would be either vent voluntarily, or build up excessive pressure and wait for something to give in.
zapperzero said:Goes to show how much trust we can put in TEPCO's cutely-colored site contamination maps.
I hope that worker got out of there in time
westfield said:There must be a compelling reason to have RCIC instead of IC's because it seems a big compromise to have RCIC that relies on several other systems to remain useful versus IC's which seem so simple and "stand alone". Not that having an IC system helped Unit #1's predicament.
westfield said:<..>
I would be interested to know when the operators at Unit 1 saw the cooling rate was too fast why did they not just use one IC instead of either using both or none?
[unit 1] Water injection was arranged at approx. 3.9 ㎥/h at 9:02 am on August 5
since we observed reduction of the water injection into the reactor.
[...]
[unit 2] Water injection was arranged at approx. 3.9 ㎥/h at 5:50 pm on August 4
since we observed reduction of the water injection into the reactor.
http://www.tepco.co.jp/en/press/corp-com/release/11080501-e.html
At 5:32 am on August 4, we stopped Water Treatment Facility to improve the flow rate. After the work, we activated the facility at 3:30 pm and restarted operation of the water treatment system at 4:13 pm. When we adjusted the flow rate of the system at 6:55 pm, a pump of the decontamination instruments was stopped and the whole water treatment system was shut down. We confirmed soundness of the pump and reactivated the system at 8:30 pm, and operation of the water treatment system was restarted at 8:50 pm.
-At 2:12 am on August 5, a process alarm was activated and the water treatment system was shut down. At 4:03 am, the system was reactivated and the operation was restated at 4:21 am.
-Around 7 pm on 8:04, we discovered water leakage from a flange of transfer hose of filtered water which is used to clean up salt in a vessel of the cesium adsorption instruments in the site bunker building.
http://www.tepco.co.jp/en/press/corp-com/release/11080501-e.html
From 3:20 pm to 5:51 pm on August 5, we injected water to Unit 1 by using Fuel Pool Cooling and Filtering System.
http://www.tepco.co.jp/en/press/corp-com/release/11080602-e.html
joewein said:The vertical brown-stained pipe is probably connected to one of the two smaller pipes that run along the fat pipe from the Y-section leading to units 1 and 2. There's one at each side of the fat pipe.
Ian Goddard speculates on his site that the brownish colour is not rust but cesium. However, for that the pipe would have to be leaky, for you to see cesium condensate on the outside, not just the inside.
AtomicWombat said:Exactly where does the pipe come from. It's hard to follow in the Cryptome pictures. It is not the large emergency relief duct from the airspace in the reactor building. It appears to be an emergency steam relief pipe from the reactor circulation, perhaps from the condensers.
robinson said:So after something goes very wrong you vent the reactor directly into the atmosphere? What the .. ?
vanesch said:I have to say I don't understand how you can have a hydrogen explosion blowing apart the confinement building, and not the reactor vessel.
I also don't understand how you can let any pressure build up in the confinement building at the risk of rupture if it is slowly. One should prefer steam releases (even contaminated) in order to ensure the integrity of the confinement building if ever the reactor vessel breaks, no ? Now we are not very far from a full release of the core in the environment.
AtomicWombat said:Exactly where does the pipe come from. It's hard to follow in the Cryptome pictures. It is not the large emergency relief duct from the airspace in the reactor building. It appears to be an emergency steam relief pipe from the reactor circulation, perhaps from the condensers.
robinson said:So after something goes very wrong you vent the reactor directly into the atmosphere? What the .. ?
etudiant said:The stack, unless filtered, then ensures maximal dispersion of the vented materials.
That does seem a serious oversight, as a bad accident is thereby made worse.
Are there not any requirements for filtering the hardened stack emissions in case of accident?
Torus.robinson said:It seems impossible that the solution to a leaking reactor is to vent it directly into the atmosphere. Seriously?
AtomicWombat said:The documents on Tepco's site:
http://www.tepco.co.jp/en/news/110311/
And the location of the high radiation inside the No.1 turbine building as:
"Near the entrance of the train room for the emergency gas treatment system."
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110803_01-e.pdf
Where does this "emergency gas treatment piping arrangement" fit into the safety systems for a BWR?