heat output of SCRAMed nuclear reactor

[Chuck]

Does anyone have any reference to the heat output of the nuclear fuel in a Diichi unit 1 type reactor after the control rods are inserted? I am trying to estimate how much water flow is required to cool it, how much salt must be building up in the reactor vessel, and whether there is any chance that seawater pumped into the reactor vessel to keep it cool would eventually deposite so much salt in the reactor that cooling fails do to clogging.

[Welsh cake]

(16th March 2011 19:13)Chuck Wrote:  Does anyone have any reference to the heat output of the nuclear fuel in a Diichi unit 1 type reactor after the control rods are inserted?

Where would one find this type of reactor? Which power stations is it, or are they currently operational/non-operational in?

[Chuck]

(16th March 2011 23:11)Welsh cake Wrote:  

(16th March 2011 19:13)Chuck Wrote:  Does anyone have any reference to the heat output of the nuclear fuel in a Diichi unit 1 type reactor after the control rods are inserted?

Where would one find this type of reactor? Which power stations is it, or are they currently operational/non-operational in?

That's the first reactor to blow up in Japan this last week. It was a GE MK 1 boiling water reactor. If they are cooling it by directly pumping seawater into the reactor vessel, then that could only go on for so long. Water does not take with it any of the stuff dissolved in it when it evaporates. Each release of radioactive steam from the reactor vessel is leaving behind more salt. Eventually the reactor vessel will clog and fill with salt. If they must still pump more water into it to cool it at that point I am not sure what will happen because the water will not be able to reach all parts of the fuel rod due to the salt. Perhaps the salt will melt and you have to somehow cool the liquid salt.

[theVOID]

What have they done? Changed the definition of 'safe' so they can send people in to fix it...

http://www3.nhk.or.jp/daily/english/16_19.html

Apparently the land is worth more than the people.

[Chuck]

One might suggest they weighed the likely fatality figure over the long run of a large radiation release against the number of people in the party they are sending back. I understand soldiers are making up an increasing proportion of the work party.

Given some culturally inspired behavior one saw from the Japanese in, say WWII, one might not be surprised if the party took a vote and decided to go back.

[Welsh cake]

(16th March 2011 23:21)Chuck Wrote:  That's the first reactor to blow up in Japan this last week. It was a GE MK 1 boiling water reactor.

You mean Daiichi. ^^ Hang on though, I thought it was a BWR-4/3 reactor? Are we both wrong?

Quote:If they are cooling it by directly pumping seawater into the reactor vessel, then that could only go on for so long.

Correct. It shows how quickly the situation is getting increasingly desperate. From what I've heard nuclear scientists are most concerned about the spent fuel getting too hot, not the reactors, if they can’t keep them cool that could result in uncontrolled highly radioactive emissions making the Chernobyl accident look like an anomaly by comparison, in the worse case scenario, there is always that chance that the stored Plutonium could go critical.

[lilphil1989]

(16th March 2011 19:13)Chuck Wrote:  Does anyone have any reference to the heat output of the nuclear fuel in a Diichi unit 1 type reactor after the control rods are inserted? I am trying to estimate how much water flow is required to cool it, how much salt must be building up in the reactor vessel, and whether there is any chance that seawater pumped into the reactor vessel to keep it cool would eventually deposite so much salt in the reactor that cooling fails do to clogging.

An order of magnitude estimate to start with would be about a MW/kg

This isn't reactor specific, but order of magnitude is probably all you'll get from a calculation of this type anyway, unless you know specifics of fuel rod size/shape, moderator geometry etc.

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(20th March 2011 14:38)lilphil1989 Wrote:  An order of magnitude estimate to start with would be about a MW/kg

Ignore that, I was thinking of newly spent fuel.

Something around 10MW total would be more reasonable.

[Chuck]

Ignore that, I was thinking of newly spent fuel.

Something around 10MW total would be more reasonable.
[/quote]

10 MW is about 35 TJ per hour, so an unpressurized reactor will boil approximately 15 tons of water each hour under 1 atmosphere pressure. So if the reactor is completely being cool by salt water injection and steam release, then salt will accummulate inside the vessel at a rate of approximately 500 KG / hour as water is evaporated at rate of approximately 15000 L/hour. This tells me the inner vessel of the reactor can not be cooled by direct seawater injection alone. If it were, it would be completely filled with salt in under 4-5 days.

Also, the rate of heat output is actually not as high as I expected. At 10MW, an emergency water resevoir of the size of an oylmpic pool placed over the reactor vessel and feeding water by gravity into the reactor vessel could keep the reactor core cool for a week. Pity no such backup measure appears to have been designed into the structure.

[Chuck]

Uhem, this thread is about power output of nuclear reactors, and is located in the physical sciences forum.

[leo-rcc]

(21st March 2011 09:21)Chuck Wrote:  Uhem, this thread is about power output of nuclear reactors, and is located in the physical sciences forum.

Indeed, so I've split the offtopic messages off.