Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[elektrownik]

But a few months ago TEPCO recalibrated the water level gauges of Unit 1 and discovered that, at that time, the water level was actually BELOW the bottom of the fuel.

I must add that they did the same thing for reactor 2 and there also water level is below bottom of the fuel rods.

 

[nikkkom]

Once the Zircaloy cladding fails, the fuel (UO2+fission products) is exposed, and at high temperature, the (M=U,Np,Pu,Am,Cm)O2 oxidize to higher order oxides M4O9, M3O8, and MO3, the latter of which is more soluble in water. The use of seawater, and the tsunamic flooding, complicated the scenarios regarding what happened with whatever contaminated coolant escaped. So some, or a lot, of fuel material and core could have simply chemically reacted and become an aqueous solution.

Zr fails at more than 700 C. Zr/H20 reaction is exotermic, so temperature quickly rose much higher after 700 C was reached. This also increases pressure, making it rather hard to pump cooling water into reactor in those conditions.

I don't see how anything "aqueous" could form under those conditions until corium melted through the bottom and thus pressure was released.

 

[thebluestligh]

These photos were captured Dec 1st here in the US. Interested to find out what was going on here

 

[SteveElbows]

Earthquake not a factor in Fukushima accident
http://www.world-nuclear-news.org/RS_Earthquake_not_a_factor_in_Fukushima_accident_0212111.html
02 December 2011
I think this is premature.

Industry folks like myself are waiting to get a look inside before concluding what actually happened. Before that, we can only make some engineering/educated guesses/speculations based on external or indirect evidence. That means trying to piece together or make sense of the activity releases, the explosions, the visible damage, sounds reported by those onsite or by instrumentation, . . . .

Yes, any conclusions at this stage should be considered very tentative. Especially as the latest core melt analysis features graphs which highlight a number of different instances where they cannot get the recorded data to match the results of their model analysis. For example the measured pressures quite early on at reactor 2 do not quite fit their models, which is why in past analysis they had to make assumptions about certain breaches/leaks in reactor and containment in order to make the model analysis results more closely match the recorded data. In the latest analysis documents its the one with filename ending in 6 that features such graphs for all 3 reactors and draws attention to periods of time where there are differences between the measured data and model results. Although we should note that back in May when NISA cross-checked TEPCOs analysis, they got some different results in places, but I think TEPCO still use their own analysis for the latest corium analysis, rather than using NISAs even though the NISA stuff does seem to make more sense in places. An example of this is that TEPCO don't have reactor 2's RPV failing until sometime on March 16th, but available data and other analysis tends to point to this happening earlier than TEPCO think. Due to the rather poor machine-translation of the corium melt stuff, I can't say how much this may have affected TEPCOs theories about status of core at reactor 2.

Certainly I do not have very many fixed and certain conclusions in my brain at this point. There are a few that we can be pretty certain about, such as certain extreme scenarios not having happened because there are not the very high radiation doses necessary at the site of the power station to support some of the more extreme 'reactor blew up and shot fuel everywhere' doom scenarios that a few people were very keen on in the first months. And am I correct to say that we can be reasonably sure that the reactors did SCRAM immediately after the earthquake, otherwise we would have seen much worse stuff unfolding as it would not only have been decay-heat that they had to deal with?

 

[SteveElbows]

The desalination 'evaporative condensation' equipment has leaked, allowing some water with 2.9Bq/cm³ Cs137 to head for a gutter.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111204_02-e.pdf

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111204_01-e.pdf

And a description of the problem from the latest plant status (http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111204_03-e.pdf)

11:33 Workersfoundthattherewaspuddlewaterinsidethebarrieraroundtheevaporativecondensation
・12/4
apparatus (the estimated volume of water was approx.45 m3). At 11:52, stopped the apparatus.
12:14 Workers made visual inspection of the apparatus and thought that the leakage stopped. After that, conducted investigation. At 14:30, we found crack in the barrier made of concrete and water was leaking to the gutter (surface dose rate of leaked water: beta ray 110mSv/h, gamma ray 1.8mSv/h). We are considering emergency response to stop leakage of water to the outside of the barrier. In the meantime, water desalination apparatus is continuing operation. As we have sufficient volume of desalinated water, there is no impact on the Reactor water injection.

 

[SteveElbows]

These photos were captured Dec 1st here in the US. Interested to find out what was going on here

I don't see anything interesting. What do you possibly think is interesting in these photos? They are out of focus or affected by weather conditions. The colours above reactor 2 building are from a crane, which can presently be seen very clearly on the live video. The orange colour to the right of reactor 3 building is probably a light. There is a light of a different colour in about the same place currently showing on the live video.

http://www.youtube.com/user/tbsnewsi#p/l/24eGVuK4G4M

I would have hoped people would have learned not to let their imaginations run wild over poor quality images by now.

 

[tsutsuji]

http://www3.nhk.or.jp/news/html/20111205/t10014402061000.html 45 tons of water have leaked from the desalinating facility. The leak was found at around 11 AM on 4 December. Cesium levels are brought to 45 Bq/cm³ but strontium levels are still high with 130,000 Bq/cm³. Tepco is checking if the water flew into the sea while putting sandbags in the downstream part of a 600 m long side ditch in which the water might flow before reaching the sea.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111204_02-e.pdf "Leakage from evaporative condensation apparatus"

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111204_01-e.pdf "Fukushima Daiichi Nuclear Power Station Sampling result of leaked water from the evaporative condensation apparatus"

12/4 11:33 Workers found that there was puddle water inside the barrier around the evaporative condensation apparatus (the estimated volume of water was approx.45 m3). At 11:52, stopped the apparatus.

12:14 Workers made visual inspection of the apparatus and thought that the leakage stopped. After that, conducted investigation. At 14:30, we found crack in the barrier made of concrete and water was leaking to the gutter (surface dose rate of leaked water: beta ray 110mSv/h, gamma ray 1.8mSv/h).

We are considering emergency response to stop leakage of water to the outside of the barrier. In the meantime, water desalination apparatus is continuing operation. As we have sufficient volume of desalinated water, there is no impact on the Reactor water injection.
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111204_03-e.pdf

http://mainichi.jp/select/jiken/news/20111205ddm002040092000c.html Beta radiations due to strontium and other substances are between 100,000 Bq/cm³ and 1,000,000 Bq/cm³. The strontium concentration in the leaked water is about one million times as high as the standard set by the nuclear power regulating law for sea releases.The building's area is 30 m x 30 m. As the leaked water's height was about 5 cm, the leak's volume is 30 x 30 x 0.05 = 45 m³.

In all, as much as 220 tons of water may now have leaked from the facility, according to a report in the Asahi Shimbun newspaper that cited Tepco officials.
http://www.nytimes.com/2011/12/05/world/asia/more-leaks-from-fukushima-daiichi-nuclear-plant.html

 

[SteveElbows]

Thanks for the info, as TEPCO didn't mention the strontium in the documents about the leak I posted earlier.

In other news from the last week I see they found quite a lot more tritium in unit 1 sub-drain compared to unit 2, from samples taken mid-November.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111203e15.pdf

Also I see that the last line of an Asahi story about the recent core melt analysis sounds very much like what someone on this forum suggested a long time ago:

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201112010004

TEPCO is considering the use of a special camera, resembling an endoscope, to monitor the interior of the reactors in the future.

 

[etudiant]

Is the source of the water specified, whether from the SFPs or the reactor building basements?
It would seem unlikely for the spent fuel pool water have such an elevated strontium content unless there has been significant damage to the stored fuel.

 

[Joffan]

tsutsuji
It wasn't clear to me from the earlier information http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111204_03-e.pdf how much water leaked. Was it 45 tons (seems a lot) or was it 0.45 tons (seems more likely)? The ambiguous phrase was "(the estimated volume of water was approx.45 m³)" where I don't know if the period belongs to the number or to the "approx".

The other thing I'm confused about is that I thought desalination was upstream of cesium removal in the Fuku-ichi water treatment sequence, so I don't see why cesium levels should be low.

 

[etudiant]

Seems clear enough from Tsutsuji-san's postings:

http://mainichi.jp/select/jiken/news...40092000c.html Beta radiations due to strontium and other substances are between 100,000 Bq/cm³ and 1,000,000 Bq/cm³. The strontium concentration in the leaked water is about one million times as high as the standard set by the nuclear power regulating law for sea releases.The building's area is 30 m x 30 m. As the leaked water's height was about 5 cm, the leak's volume is 30 x 30 x 0.05 = 45 m³.

In all, as much as 220 tons of water may now have leaked from the facility, according to a report in the Asahi Shimbun newspaper that cited Tepco officials.
http://www.nytimes.com/2011/12/05/wo...ear-plant.html

The thing that throws a US reader is the reference to a 'puddle' of contaminated water, which does not convey the same impression as learning of a 45 ton or even 200 ton leakage.
In fairness to TEPCO, they have thus far treated some 180,000 tons of water, so perhaps by that standard, the term 'puddle' is quite appropriate.

 

[Joffan]

etudiant; absolutely clear on the volume now. I don't know how I missed it.

 

[Caniche]

5.8 trillion becquerels ! As far as leaks go ,how would this score on the INES scale ?

Is there much point in TEPCO just reducing cesium contamination and leaving other isotopes undiminished? Did that official really drink all that strontium?

 

[rmattila]

As far as I understand, the leak is in the last stage of the process, where the salty waste liquid produced in the reverse osmosis is further concentrated by evaporation. And apparently it is from the more concentrated side of that process as well. Certainly not from the water that's being recycled into the reactors.

As to why they are leaving it as liquid, I'm no chemist but assume that it might have something to do with the high salt content messing up the possibilities to extract strontium from the liquid, and it is therefore for time being stored as it is.

The amount of leak appears to be somewhat unclear: I got the impression that the 45 tons would be the amount found inside the building - I don't now how that relates to the amount that has actually leaked outside or found its way to the sea.

 

[tsutsuji]

http://www3.nhk.or.jp/news/html/20111205/t10014421611000.html Concerning strontium, the analysis takes about two weeks. The NISA requests Tepco to write a report on the cause of the leak and on countermeasures. The water leaked for 21 hours or less before Tepco found it. A concrete barrier recently installed to contain leaks, had cracks.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111205_01-e.pdf Status of the water leakage

http://mainichi.jp/select/biz/news/20111206k0000m040083000c.html According to Tepco, 300 l flowed outside the building.

 

[joewein]

Did that official really drink all that strontium?

You are probably thinking about Yasuhiro Sonoda, parliamentary secretary at the cabinet office who drank water in front of journalists about 5 weeks ago.

That water was not from the basements of the wrecked units 1-3, where the water in this current leak originates from. It was from units 5 and 6, whose fuel rods are still intact, as one air-cooled diesel in unit 6 survived the tsunami to provide power for the cooling.

 

[SteveElbows]

I just noticed that the recent core melt analysis stuff is available in english:http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_04-e.pdf
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_05-e.pdf
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_06-e.pdf
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_07-e.pdf
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_08-e.pdf

Not had time to read it all yet but as per my earlier post based on the Japanese version, we see a repeat of stuff first mentioned a long time ago but not dwelled upon that much, such as a presumption that there was a drywell leak 22 hours after the earthquake at reactor 2. And somewhere they also mention one of the subjects that interests me, why the reactor 2 suppression chamber water temperature readings went up in the latter part of October - they say its because after water injection rate was increased, steam decreased so there was more hot water ending up in the suppression chamber. Speaking of which, I see that s/c temperatures at 2 have started creeping up again in recent days after falling for quite some time.

 

[elektrownik]

I don't understand one thing, from those analysis we can see that tepco think that part of unit 2 core is still undamaged, but I see problem here, they also recalibrated water level sensor and from data we can see that it is -5m from top of 4m fuel rods. So it is possible that fuel will not melt without cooling ?

 

[Shinjukusam]

I don't understand one thing, from those analysis we can see that tepco think that part of unit 2 core is still undamaged, but I see problem here, they also recalibrated water level sensor and from data we can see that it is -5m from top of 4m fuel rods. So it is possible that fuel will not melt without cooling ?

Good point, it's possible that if that level is accurate and there is still standing material then the rising steam is sufficient to provide a modicum of cooling.
That is dependent on their hypothesis being correct, of course.

 

[tsutsuji]

I just noticed that the recent core melt analysis stuff is available in english:http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_04-e.pdf
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_05-e.pdf
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_06-e.pdf
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_07-e.pdf
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_08-e.pdf

These are the press conference / workshop slides. The the main report ( http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_09-j.pdf ) (207 pages) is still not available in English.

"All fuel melted through PCV from　original position" on page 20 of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_04-e.pdf is presumably a translation mistake. The Japanese text at http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_07-j.pdf says "all fuel moved downwards from original position". Then, "Further, as there is a high probability that RPV damage occurred, we estimate that a considerable amount dripped down to PCV bottom".

 

[zapperzero]

I don't understand one thing, from those analysis we can see that tepco think that part of unit 2 core is still undamaged, but I see problem here, they also recalibrated water level sensor and from data we can see that it is -5m from top of 4m fuel rods. So it is possible that fuel will not melt without cooling ?

I don't see where they say that?

Given current water levels and the fact that they estimate that less than 3% of fuel is uncovered, it would seem that all the fuel has relocated to the bottoms of the RPVs in units 2&3 and even further to the bottom of the PCV in the case of Unit 1.

 

[Rive]

I don't see where they say that?

Given current water levels and the fact that they estimate that less than 3% of fuel is uncovered, it would seem that all the fuel has relocated to the bottoms of the RPVs in units 2&3 and even further to the bottom of the PCV in the case of Unit 1.

Well, in http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_04-e.pdf they state that

Even though the fuel was damaged and melted , a part of the fuel remains inside the core of RPV and the others dropped to the bottom of RPV plenum or the PCV pedestal.

.

I think the 'uncovered' is just a translation error and they mean 'uncooled'.

 

[tsutsuji]

I don't see where they say that?

See the green colour squares labelled "Damaged fuel piled (Maintain of fuel rod figure)" on page 8 (9/29) of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_08-e.pdf

Given current water levels and the fact that they estimate that less than 3% of fuel is uncovered, it would seem that all the fuel has relocated to the bottoms of the RPVs in units 2&3 and even further to the bottom of the PCV in the case of Unit 1.

I agree. The "3% (or less) uncovered" result and the "Unit 2 result of estimation with analysis code" ( page 8 (9/29) of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_08-e.pdf ) seem to contradict each other.

"Therefore, it is evaluated that all the moved fuel is expected to be cooled directly by water injection." written on page 23 (24/28) of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_04-e.pdf could alternatively be translated as "Therefore, it is evaluated that all the moved fuel is being cooled in a condition where it is largely in contact with water". It sounds like that the question of how the unmoved fuel is being cooled is left unanswered.

I think the 'uncovered' is just a translation error and they mean 'uncooled'.

Well, after reading http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_06-e.pdf it seems that they mean just the opposite, because they say :

Considering the results that water injection from the core spray system exerted a great effect (...) In the new model, a part of the injected water directly removes the heat from the uncovered core.
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_06-e.pdf page 2 (3/10)

It sounds like that what they mean by "uncovered" means "uncovered and cooled by core spray system or cooled by heat conduction/convection/radiation".

 

[zapperzero]

See the green colour squares labelled "Damaged fuel piled (Maintain of fuel rod figure)" on page 8 (9/29) of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_08-e.pdf

Yeah, they're saying it should look a bit like TMI on the inside, which does not seem to be consistent with their other estimates.

 

[tsutsuji]

Yeah, they're saying it should look a bit like TMI on the inside, which does not seem to be consistent with their other estimates.

Even their "Conservative scenario Approx.109 hours after the earthquake" on page 8 (9/29) of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_08-e.pdf has 12 little orange squares above original bottom of fuel. That makes 12% and this is still higher than the 3% result from the "improved JAEA heat model" explained on http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_06-e.pdf

The other scenario translated as "Based on the indicator" on the English version can alternatively be translated as "relying on indicated values".

 

[Rive]

It sounds like that what they mean by "uncovered" means "uncovered and cooled by core spray system or cooled by heat conduction/convection/radiation".

Yeah, thanks. You are right.

3%... I thought it'll be more than that: the change when they switched on the CSS was really impressive.

Of course the cooling of the covered fuel was also improved by the water amount pushed in through the CSS, so it's logical... But a bit sad.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20111206/index.html According to Tepco, about 150 litres of water contaminated with beta-radiating substances such as strontium flowed to the sea. A maximum of 300 litres flowed through the cracks in the building's foundation. The 150 litre figure is the result of an estimate based on data such as leaking time.

The density of radioactive materials contained in the water leaked is 2.6 x 10^10 Becquerel (provisional) in total, calculating from
the density of strontium 89, 90, cesium 134, and 137.

Strontium 89: 7.4 x 10^4 Bq/cm3 (1.1 x 10^10 Bq)
Strontium 90: 1.0 x 10^5 Bq/cm3 (1.5 x 10^10 Bq)
Cesium 134: 1.6 x 10^1 Bq/cm3 (2.4 x 10^6 Bq)
Cesium 137: 2.9 x 10^1 Bq/cm3 (4.4 x 10^6 Bq)
(Water collected on Dec 4, 2011. Amount of strontium estimated from the density of all-beta radioactive materials.)

This value accounts for 12 % of 2.22 x 10^11 Bq, which is the annual discharge control target of radioactive liquid waste at
Fukushima Daiichi Nuclear Power Station.
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111206e16.pdf

http://www3.nhk.or.jp/news/genpatsu-fukushima/20111206/1910_reikyaku.html Suspecting that it caused a delay in the response to the accident, the NISA investigated and heard witnesses in August on the question whether plant managers had mistakenly believed unit 1's isolation condenser was running while it was not. The results of the NISA's investigation were publicly released on 6 December : the managers were not aware that a plant operator had closed the IC's valve, and it is 8 hours after the earthquake, after 11 PM, after knowing that the radiation inside reactor building was rising, that they first grasped the IC status. It is possible that this caused a delay in the response to the accident.

The documents released by the NISA:

http://www.meti.go.jp/press/2011/12/20111206002/20111206002-2.pdf List of questions (asked by the NISA to the witnesses)

http://www.meti.go.jp/press/2011/12/20111206002/20111206002-3.pdf The NISA's conclusions

(they cover a wide range of topics, not only unit 1, not only unit 1's IC)

 

[Pakman]

I just noticed that the recent core melt analysis stuff is available in english:

It seems they don't take into account the additional heat from the steam-zirconium exothermic reaction.There suppose to be hydrogen at unit 3 at least, so some part of zirconium reacted. How much?

 

[Caniche]

You are probably thinking about Yasuhiro Sonoda, parliamentary secretary at the cabinet office who drank water in front of journalists about 5 weeks ago.

That water was not from the basements of the wrecked units 1-3, where the water in this current leak originates from. It was from units 5 and 6, whose fuel rods are still intact, as one air-cooled diesel in unit 6 survived the tsunami to provide power for the cooling.

Cheers Joe , I'm convinced you are spot on dead accurate.
Question is ,what impression "TEPCO" are trying to convey to the general public.;)

 

[SteveElbows]

And somewhere they also mention one of the subjects that interests me, why the reactor 2 suppression chamber water temperature readings went up in the latter part of October - they say its because after water injection rate was increased, steam decreased so there was more hot water ending up in the suppression chamber. Speaking of which, I see that s/c temperatures at 2 have started creeping up again in recent days after falling for quite some time.

Oops I made a mistake. The documents were talking about the temperature rise of reactor 1 suppression chamber in the past, not reactor 2. I think they mentioned reactor 3 s/c temp as well.

The interesting temperatures mentioned for reactor 2 are the ones for the CRD housing, and SRV, some of which are much higher than the other temperatures we are used to seeing regular data about. (page 6 of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111130_05-e.pdf )