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Japan Earthquake: nuclear plants

by gmax137
Tags: earthquake, japan, nuclear
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tsutsuji
#11233
Sep17-11, 10:41 AM
PF Gold
P: 1,220
http://www3.nhk.or.jp/news/genpatsu-...30_kaisui.html An internal document reveals that on 16 March, the NISA had given Tepco a calculation estimating that the reactors would be filled with salt up to 5 metres above reactor bottom, preventing any further cooling, between 2 April early in the morning and 3 April in the morning. Tepco actually stopped using seawater and started using freshwater between 25 March and 26 March.
rmattila
#11234
Sep17-11, 11:42 AM
P: 242
Quote Quote by tsutsuji View Post
http://www3.nhk.or.jp/news/genpatsu-...30_kaisui.html An internal document reveals that on 16 March, the NISA had given Tepco a calculation estimating that the reactors would be filled with salt up to 5 metres above reactor bottom, preventing any further cooling, between 2 April early in the morning and 3 April in the morning. Tepco actually stopped using seawater and started using freshwater between 25 March and 26 March.
That is a relatively straightforward calculation to make, and I suppose it was done by many people following the event at that time: estimate the decay heat, assume that the coolant reaches the core in such a way that the decay heat will be transmitted by evaporation, and you get the evaporation rate of the order of about 100-200 tons per day. This translates into 3 - 7 tons of salt per day.

The only problem is that nobody knew then (and does still not know) how much of the cooling water will actually reach the core and how much will leak past it e.g. through the recirculation pump seals, and how intact the pressure vessel bottom is. That estimate given by NISA seems to be the conservative maximum estimate obtained by assuming no leaks at the RPV. (Conservative in the sense of estimating the amount of accumulated salt - hopeful in the sense of estimating the core damages.)

A similar calculation could also be made concerning the amount of oxygen brought into the containment in the cooling water and released into the containment when the water was being heated. IIRC, the number was several kilograms per day (don't have the relevant papers at hand now to double-check).
dezzert
#11235
Sep17-11, 12:26 PM
P: 23
First post after lurking since March. A quick question.

They estimated at the time that after 20 days of seawater injection there would be 15+ feet of salt in the bottom of the reactor. They used seawater for 14 days, so the estimate of salt levels inside the reactors would be approximately 10+ feet of salt on March 26. I know that this is purely hypothetical, and the true amount unknown, but the alternatives if I read this right are a) salt accumulation of that amount or b) a less amount if the bottom has been breached. Assuming no large breach in the RPV, and assuming that a fair amount of salt did make it into the reactor where it still resides, how can there be accurate measurements of temp at the bottom of the reactors if they are buried in salt.
rmattila
#11236
Sep17-11, 12:49 PM
P: 242
Quote Quote by dezzert View Post
First post after lurking since March. A quick question.

They estimated at the time that after 20 days of seawater injection there would be 15+ feet of salt in the bottom of the reactor. They used seawater for 14 days, so the estimate of salt levels inside the reactors would be approximately 10+ feet of salt on March 26. I know that this is purely hypothetical, and the true amount unknown, but the alternatives if I read this right are a) salt accumulation of that amount or b) a less amount if the bottom has been breached. Assuming no large breach in the RPV, and assuming that a fair amount of salt did make it into the reactor where it still resides, how can there be accurate measurements of temp at the bottom of the reactors if they are buried in salt.
The RPV temperature measurements usually measure the temperature from the outside surface of the pressure vessel metal, so if the RPV is intact, its contents should have no effect on the measurement thermocouples. However, based on the current data it's very difficult to say anything about the contents of the RPV, as all depends on the condition of the RPV and the route the coolant water has been flowing during the past several months. In any case, there seems to be quite a lot of salt in the water they pump from the basements, and at least this salt has not accumulated in the RPV. It doesn't take a big leak to wash away the stuff, if there is a constant flow of water during several months.
dezzert
#11237
Sep17-11, 01:24 PM
P: 23
Thanks rmattila. Another question. Salt being a crystal, could it be storing energy via the Wigner effect (which I dont really understand other than atoms are pushed out of place and store energy in the process, yes?).
Rive
#11238
Sep17-11, 03:03 PM
P: 355
Tsk-tsk-tsk. Salt.

Could the molten core debris be cooled by the molten salt? Preventing it from breaking the RPV?
swl
#11239
Sep17-11, 06:25 PM
P: 108
Quote Quote by Cire View Post
For those that want to argue corium melted through the bottom you need to answer this for me.

How do you get temperature readings from a sensor on the bottom of the RPV that would have melted off (wires) and destroyed the thermocouple before the RPV failed?
If the thermocouples were held in place by magnetic recepticles, the steel of the RPV would have lost it's magnetic properties at about 770C, and the thermocouple(s) would have fallen to some position either hanging by their leads or at the bottom of the dry well.

With the information released by TEPCO, I am only certain that I don't know where the fuel is.

BTW, if the fuel is in a configuration of unmelted pellets, is recriticality possible, or is it impossible in such a configuration. If it did occur, it seems as though it would stop quickly as the water boiled away, but such a condition could make cooling difficult. As all 3 reactors are near or below 100C it's probably not an issue.
dezzert
#11240
Sep17-11, 06:48 PM
P: 23
Quote Quote by Rive View Post
Tsk-tsk-tsk. Salt.

Could the molten core debris be cooled by the molten salt? Preventing it from breaking the RPV?
Since they started seawater on the 12th, and supposing the contents of the RPV have melted into a corium mass, wherever it might be, wouldn't the salt just be a part of that mass. And a fairly big part. At least in R2 and R3.

And supposing if this is the case, would that hinder or help re-criticality.
LabratSR
#11241
Sep17-11, 10:50 PM
P: 176
Quote Quote by MiceAndMen View Post
Discredited. Fantastical rumor mongering and unsubstantiated speculation. If the site had paid advertisemets it would be the Fox News of Fukushima. But there are no ads there so it's more like Tinfoil Central.

Hey, Nancy, is building 4 still leaning? What do your inside on-site sources say?
100 percent, Spot on.
Cire
#11242
Sep18-11, 03:22 AM
P: 64
Quote Quote by swl View Post
If the thermocouples were held in place by magnetic recepticles, the steel of the RPV would have lost it's magnetic properties at about 770C, and the thermocouple(s) would have fallen to some position either hanging by their leads or at the bottom of the dry well.
The type of thermocouple used on the RPV would have been completely damaged before reaching 770C. The wiring, cold junction connections, would also be damaged. They would be reading open or shorts on those sensors. Instead we see something that looks like a valid temperature. A reading that changes appropriately with water injection rates.

I don't see how thats possible with a dry well full of slag and corium glowing at >> 2700F. The radiant heat alone would have melted all the cables and wiring leading into and out of the RPV near the bottom.

I dont see how you get corium under the reactor and a few feet away a functioning temperature sensor. Think of what a steel induction furnace looks like.. That the environment people are suggesting these low temperature sensors are operating correctly in.
tsutsuji
#11243
Sep18-11, 06:59 AM
PF Gold
P: 1,220
Quote Quote by rmattila View Post
A similar calculation could also be made concerning the amount of oxygen brought into the containment in the cooling water and released into the containment when the water was being heated. IIRC, the number was several kilograms per day (don't have the relevant papers at hand now to double-check).
Is there more oxygen in seawater than in freshwater ?
Is oxygen a cause for other troubles apart from hydrogen explosions ?
How is oxygen controlled during normal operation of a nuclear power plant ? You say "when the water was being heated". Does it mean that as long as water is not heated beyond the temperatures allowed in normal operation, there is no need for other control tools apart from controlling the temperature ?

The other day I read the following (a 2005 JNES course on nuclear safety)
Flammable gas control system:
The system is designed to prevent combustion of hydrogen and oxygen being generated in the containment vessel at the time of loss of coolant accident. After recombination of hydrogen and oxygen, remaining air goes back to the dry well through the vacuum breaker, so that gas concentration can be controlled in this manner throughout the containment vessel. In many cases, this system is composed of the portable recombiners of full 100 percent capacity and some others. At Unit No.6 and No.7 respectively of Kashiwazaki Kariwa Power Station, the system is arranged for common use at each reactor building.

Summary of Safety Design of Nuclear Power Station (Case of BWR) http://www.ansn-jp.org/item_file/2005-09.pdf
They didn't have those at Fukushima, did they?
rmattila
#11244
Sep18-11, 07:49 AM
P: 242
Quote Quote by tsutsuji View Post
Is there more oxygen in seawater than in freshwater ?
Is oxygen a cause for other troubles apart from hydrogen explosions ?
How is oxygen controlled during normal operation of a nuclear power plant ? You say "when the water was being heated". Does it mean that as long as water is not heated beyond the temperatures allowed in normal operation, there is no need for other control tools apart from controlling the temperature ?
By "fresh" I meant pumping "new", cold, possibly oxygen-rich water (whether it is seawater or freshwater has no significant effect on the solubility) into the containment as opposed to circulating the same water, as is done during normal reactor operation. Solubility of oxygen is larger at lower temperatures, and when the water is heated, excess oxygen is released as gas. After reaching boiling point, all dissolved oxygen has been released from the water.

During outages, oxygen (as well as nitrogen) from the air is dissolved in the primary water, and removal of oxygen is one stage during the heating of the reactor when starting it up after a cold shutdown. During operation, oxygen enters the primary circuit both by radiolysis of the cooling water and by leaking into the condenser vacuum, and the vacuum must by continuously maintained with ejectors or vacuum pumps, which suck the non-condensible gases from the condenser through recombiners to the exhaust stack.

In addition to being released from the water used to cool the (damaged) fuel, oxygen may also enter the containment if the cooling rate is not constant, and at some points of time the condensing rate of the steam within the containment is larger than the rate of evaporation, and the contaiment consequently falls below the ambient pressure. The possibility of oxygen entering the containment is the reason they've continued the injection of nitrogen in order to keep the gases from accumulating to such concentrations that the hydrogen (possibly still present as a lighter gas within the containment dome) might ignite.
Rive
#11245
Sep18-11, 10:23 AM
P: 355
Quote Quote by dezzert View Post
Since they started seawater on the 12th, and supposing the contents of the RPV have melted into a corium mass, wherever it might be, wouldn't the salt just be a part of that mass. And a fairly big part. At least in R2 and R3.
IMHO NaCl cannot be part of the corium. The melting point of salt is 801 Celsius, what means that the core debris had a kind of liquid coolant before it could melt: and NaCl has 1465 Celsius boiling point, what means salt must boil away before core debris could melt to corium. What also means some phase-changing cooling.

Am I right?
mscharisma
#11246
Sep18-11, 11:01 AM
P: 82
Quote Quote by tsutsuji View Post
I have begun to read the big Fukushima Daini report that was published on 12 August : http://www.tepco.co.jp/cc/press/betu...es/110812b.pdf ......
Forgive me if I simply missed it in the news, etc., but have they meanwhile come up with a plausible explanation and solution for the contaminated water found in the building basement(s) of the Daini site (the "from airborne emissions from Daiichi" not being plausible imho)?

Thanks.
etudiant
#11247
Sep18-11, 05:07 PM
PF Gold
P: 858
Has there been anything published on the effects of salt water cooling for a disintegrating core?
Specifically, it would be useful to have some idea of the likely reactions between the fuel oxides and the nuclear reaction products with the chlorine ions in the salt, both dissolved as well as molten.
As I remember my chemistry, the chlorine should have no trouble displacing the oxygen under high temperature conditions.
Would the resultant chlorides be materially more soluble than the fairly inert oxides?
What are the implications for the nature of the airborne emissions from the site and could that help explain the finding of plutonium and neptunium depositions quite a distance from the plant?
dezzert
#11248
Sep18-11, 05:33 PM
P: 23
Quote Quote by etudiant View Post
Has there been anything published on the effects of salt water cooling for a disintegrating core?
Thanks Rive and etudiant. To add to the above, another question, what is the effect of salt in the R3 and R4 SFPs. The photos don't show much, but there would have to be some if Tepco's analysis of no leaks in the pools is correct, and steaming is the sole lose of water during the period they were using seawater. And this salt wouldn't have reached it's melting point.
LabratSR
#11249
Sep18-11, 07:39 PM
P: 176
Atomic Power Review update on some testing done by TEPCO.

http://atomicpowerreview.blogspot.co...or-update.html
CaptD
#11250
Sep18-11, 08:13 PM
P: 20
WSJ: Tepco needs to find ways to prevent new nuclear reactions — May happen if fuel not adequately cooled — “Containme*nt vessels are largely empty of water” after leakage -Sept.14,2*011
http://ene*news.com/w*sj-tepco-f*ind...y-empty-w*ater
snip
[...] The most difficult challenge facing Tepco is how to plug leakages in the primary containmen*t structures [...]

The primary containmen*t vessels, the main shield against radiation leaks, and the reactor buildings that house them, have been damaged [...]

The leakage means that the containmen*t vessels are largely empty of water [...]

Tepco also needs to find ways to prevent any new nuclear reaction, which could happen if the fuel is not adequately cooled during the entire process.


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