Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110917/1330_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]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110917/1330_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]

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]

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]

Thanks rmattila. Another question. Salt being a crystal, could it be storing energy via the Wigner effect (which I don't really understand other than atoms are pushed out of place and store energy in the process, yes?).

 

[Rive]

Tsk-tsk-tsk. Salt.

Could the molten core debris be cooled by the molten salt? Preventing it from breaking the RPV?

 

[swl]

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]

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]

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]

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 that's 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 don't 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]

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]

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]

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]

I have begun to read the big Fukushima Daini report that was published on 12 August : http://www.tepco.co.jp/cc/press/betu11_j/images/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]

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]

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]

Atomic Power Review update on some testing done by TEPCO.

http://atomicpowerreview.blogspot.com/2011/09/fukushima-daiichi-reactor-update.html

 

[CaptD]

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-ways-p*revent-new*-nuclear-r*eactions-c*ould-happe*n-fuel-ade*quately-co*oled-conta*inment-ves*sels-large*ly-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.

 

[SteveElbows]

Any thoughts on why the temperatures measured at reactor 2 suppression chamber have been creeping slowly upwards?

http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/11091912_temp_data_2u-e.pdf

 

[Shinjukusam]

Any thoughts on why the temperatures measured at reactor 2 suppression chamber have been creeping slowly upwards?

http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/11091912_temp_data_2u-e.pdf

Just a thought, but they did change the delivery method of water in that reactor late last week. Possibly the suppression chamber is getting less water than before.

 

[Rive]

Possibly the suppression chamber is getting less water than before.

The suppression chamber has no heat generation of its own: so if its temperature is rising then it gets more heat (from the core).

 

[Shinjukusam]

The suppression chamber has no heat generation of its own: so if its temperature is rising then it gets more heat (from the core).

Well, what I meant was that if the injection vector has changed than that area may be getting a different flow, hence being affected differently.

 

[Azby]

If this was already posted and I missed it, my apologies.
An interesting report on the accident co authored by one of the designers of RPV of Unit 3.

TECHNICAL REPORT: FUKUSHIMA ACCIDENT SUMMARY (AUG. 19, 2011)
Association for the Study of Failure

http://www.shippai.org/images/html/news559/FukuAccSummary110819Final.pdf

 

[SteveElbows]

Well, what I meant was that if the injection vector has changed than that area may be getting a different flow, hence being affected differently.

Well I've been looking at the data. Suppression Chamber temperatures stopped declining, and started to slowly rise, around August 31st. This was just a few days after the sudden leap in recorded RPV Bellows temperature, which was mentioned on this thread, with an official explanation that it was probably an instrument malfunction.

The pace of the suppression chamber temperature rise appears to have increased as September has gone on, with quicker climbs in recent days. Reactor Suppression Chamber Gas temperatures have also gone up a few degrees in recent days.

And then I looked at the CAMS data for the first time in months. Drywell CAMS A has been falling more quickly in recent days, and both S/C CAMS A and CAMS B have risen. In the case of the B readings, its risen by almost 1 Sv/h in the last 6 days.

I need to look at slightly older data and do some graphs in order to firm up my impression of the data, but I find this stuff interesting.

 

[LabratSR]

If this was already posted and I missed it, my apologies.
An interesting report on the accident co authored by one of the designers of RPV of Unit 3.

TECHNICAL REPORT: FUKUSHIMA ACCIDENT SUMMARY (AUG. 19, 2011)
Association for the Study of Failure

http://www.shippai.org/images/html/news559/FukuAccSummary110819Final.pdf

Interesting. Thanks!

 

[Caniche]

If this was already posted and I missed it, my apologies.
An interesting report on the accident co authored by one of the designers of RPV of Unit 3.

TECHNICAL REPORT: FUKUSHIMA ACCIDENT SUMMARY (AUG. 19, 2011)
Association for the Study of Failure

http://www.shippai.org/images/html/news559/FukuAccSummary110819Final.pdf

"the situätion with the spent fuel is not clear". Oh Oh

 

[clancy688]

http://www.shippai.org/images/html/news559/FukuAccSummary110819Final.pdf

Interesting statements about Unit 1 on March 12th:

02:45: RPV pressure decreased from 7.0MPa to 0.95MPa, on the other hand, PCV pressure increased to 0.95Mpa. This means that RPV broke, and its pressure dropped to the same with PCV.
Where did the RPV Break?
Very high radiation was observed in the TIP (Traversing In-core Prove) room of F1 (Figure 7). Oak Ridge National Laboratory (ORNL) reported that the instrument guide tube is the weakest point at the bottom of RPV [6]. So, we estimate that several instrument guide tubes were broken, and some portions of fuel pellets fell down to the bottom of PCV through these holes. Small portions of fuel pellets reached the 1st floor of the reactor building. That is, PCV was also broken.

08:30: 3 months later, Government released a very important piece of information. At 08:30 of March 12th, Te(Tellurium)-132 and its daughter Iodine-132 were observed 7km away from Fukushima reactors. Vaporizing temperature of Te is about 988deg.-C, and this was an evidence that the temperature of fuel pellets reached over 1,000deg.-C. The reason why the Government did not immediately open this information is not clear. If this news was open on March 12th, the following remedies might have been better, or at least we could have recognized the status of the reactors correctly.

Haha. Anyone remembers the government spokesperson who told the press at March 12th that the government was suspecting a meltdown? The government didn't use him again for statements and denied any meltdowns.

 

[joewein]

The suppression chamber has no heat generation of its own: so if its temperature is rising then it gets more heat (from the core).

That is not quite true: Since the RPV was vented into the S/C, the nuclear soup in there should have received a fair amount of fission products that give off decay heat. Nuclear decay, wherever it takes place in the buildings, is the only heat source around there. It's hard to say how much of the radioactive inventory is still in the core, how much is in the S/C and how much is in the flooded basements. The 4 Sv/h spot in unit 1 near where steam rises up from the S/C suggests to me that the S/C does still put out a lot of decay heat.

If the S/C temp goes up, it would suggest one of two things to me:

1) More radio-nuclides were washed out from the RPV by the added core spray water flow and that water somehow drained into the S/C at the bottom, increasing decay heat output there.

2) The added core spray resulted in more steam production (instead of conduction via the hot RPV metal), more steam condensation in the dry well and a larger flow of still hot condensate from there down into the S/C.

Well I've been looking at the data. Suppression Chamber temperatures stopped declining, and started to slowly rise, around August 31st. This was just a few days after the sudden leap in recorded RPV Bellows temperature, which was mentioned on this thread, with an official explanation that it was probably an instrument malfunction.

The pace of the suppression chamber temperature rise appears to have increased as September has gone on, with quicker climbs in recent days. Reactor Suppression Chamber Gas temperatures have also gone up a few degrees in recent days.

And then I looked at the CAMS data for the first time in months. Drywell CAMS A has been falling more quickly in recent days, and both S/C CAMS A and CAMS B have risen. In the case of the B readings, its risen by almost 1 Sv/h in the last 6 days.

I need to look at slightly older data and do some graphs in order to firm up my impression of the data, but I find this stuff interesting.

If that data is reliable and D/W radioactivity decreases while S/C radioactivity goes up, perhaps it means that fission products are getting flushed into the S/C, as per the first of my 2 theories.

In unit 2 the S/C is supposed to have ruptured. If radioactivity gets washed into the S/C from the RPV or D/W there's a good chance it will leak from there into the basements. In the best case it will eventually end up in the cesium sludge filters of the Areva/Kurion and SARRY plants. In the worst case it will end up in the soil or ocean.

 

[westfield]

If this was already posted and I missed it, my apologies.
An interesting report on the accident co authored by one of the designers of RPV of Unit 3.

TECHNICAL REPORT: FUKUSHIMA ACCIDENT SUMMARY (AUG. 19, 2011)
Association for the Study of Failure

http://www.shippai.org/images/html/news559/FukuAccSummary110819Final.pdf

It's unfortunate that the authors contradict themselves regarding the EDG locations and then still get it wrong. Also unfortunate that some of the claims don't have sources listed - like "Very high radiation was observed in the TIP (Traversing In-core Prove) room of F1 ". I'm not saying it's not true but with no source it makes the document hard work.

Ditto for the authors stating that TEPCO backpeddaled from the May 15th press release regarding Unit #4 Hydrogen coming from Unit 3 via SGTS. The authors state that the next day TEPCO retracted the theory because because it found closed valves would preclude that possibility. Again, I'm not implying its not true, just where is the source. (Regarding that subject, can anyone say why hydrogen from the supplies in the turbine building has not been brought up as a possibility as the source for the Unit 4 RB hydrogen? Not enough stored there? It would seem a slightly more plausible path as opposed to a path from Unit #3)

Also the authors apparently not understanding the major construction difference between the upper part of the RB of Unit 1 and all the other RB's is not indicating a good general knowledge of the Fukushima daichi plant. They state Unit 1's walls as concrete. They also seem to not understand the function of blowout panels, instead implying that ALL the walls are designed to blow out. Yes, they certainly should have talked to a GE engineer as they state.

There are other problems with statements in the document but to be fair there are problems with the grammar in the document so some information seems to have not come across very well. If it was rewritten with all sources listed and theories clearly demarked then it would read a lot more credibly.

Thanks for the link.

EDIT: Another Quote from the document "Another cause is the small size of hydrogen gas molecules. They can easily penetrate PCV walls. "
Is that true? On that basis how can we keep hydrogen in ANY container?

Can someone clarify that? Perhaps they meant via seals, penetrations etc, not directly through the PCV wall?

 

[westfield]

Interesting statements about Unit 1 on March 12th:





Haha. Anyone remembers the government spokesperson who told the press at March 12th that the government was suspecting a meltdown? The government didn't use him again for statements and denied any meltdowns.

Did the government actually deny there may be meltdown\s at that period of time?, I can't remember any denials but it was a while back.

Also, I don't see the quoted authors point, so what if the government\tepco had released that information on the 12th March, why would issuing a press release have changed TEPCO's immediate strategy in dealing with the disaster?