[ RadSafe ] Melting a reactor??

[Olsson Mattias :MSO]

Speaking from a BWR point of view:

Regarding the first quote, of course a reactor can be shut down quickly. Reduntant systems for inserting control rods, plus the option to inject boron into the reactor are available to do that. However, the lingering effect from the radioactive decay of fission products must be cooled away. There is a whole array of systems that can do this, and if all else fails, external cooling water supply from tanker tucks or nearby water supplies can be used.

But if EVERY method of cooling fails there can be a meltdown where molten controlrods and fuel make their wat to the bottom of the tank. If water can not be added, it will finally go away, and then the melt will breach the reactor tank and end up at the bottom of the containment. Here is supposed to also be water. (If there would be no water, the containment integrity *would* soon be lost due to the reaction between the melt and the concrete - leading to releases of radioactivity.) Water inside the containment will continue to evaporate, pressure will build, and finally something will have to go. It would not be good if this was the containment walls, so there are emergency pressure release systems. At least in some more modern BWRs there is a scrubber for this type of release to prevent fission products (esp iodine isotopes) to be released to the atmosphere. Noble gases would still be released.

If "the cooling system malfunctions" but everything else works fine there would not be a problem like that. Depending of course on what they mean by "the cooling system". The biggest problem with the article would be all the implied "but if"'s that are needed for a loss of containment integrity, not considering the multiple systems involved in cooling, or diversification for that matter.

I believe the most likely scenario to get a meltdown is often regarded to be a reactor scram in combination with a total loss of off-site power. There is no scenario that I know of where it is not possible to add the needed water to the containment in the long run.

Mattias Olsson

-----Ursprungligt meddelande-----
Från: radsafe-bounces at health.phys.iit.edu [mailto:radsafe-bounces at health.phys.iit.edu] För Steven Dapra
Skickat: den 3 januari 2011 03:16
Till: radsafe at agni.phys.iit.edu
Ämne: [ RadSafe ] Melting a reactor??


Jan. 2

	This quote is from an editorial page article written by Charles 
Faddis and published in the NY Times.

"But there's no way to quickly shut off a reactor: the heat that 
builds up inside it is so intense that even if something goes wrong, 
cooling water must continue to circulate through its systems for days 
before it is safe.

"If the cooling system malfunctions, even if the rest of the plant is 
operating safely, the heat will literally melt the reactor and its 
concrete containment shell, releasing radioactive gas into the 
atmosphere  in other words, a partial nuclear meltdown like that at 
Three Mile Island in Pennsylvania in 1979."

	Is it true that reactor heat will melt the containment vessel ("shell")?

	The link to the Faddis' NYT article is:

http://www.nytimes.com/2010/05/06/opinion/06Faddis.html?_r=1

Steven Dapra

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