Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Astronuc]

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111122_03-e.pdf English version.

Thanks for the link, Astronuc.

"The bulk"? For the bulk to disappear from the vessel, there have to be much larger leaks than previously thought of. At least I don't believe that dozens of tons of fuel- and control rods would be able to leak through a couple of holes only a few square centimeters wide. So there has to be a much larger hole.
Previous discussions regarding leaks discarded the theory of holes on that scale because of some temperature sensors at the bottom of the RPV, some of which still were "alive". Which's highly unlikely if the core came marching through. So how does this new analysis fit with those sensors still reporting?

See the links posted by tsutsuji.

Related article in Nuclear Engineering International (Nov 28, based on Nov 22 handouts from Tepco, those cited by tsutsuji) - http://www.neimagazine.com/story.asp?storyCode=2061233


Bear in mind, it is an analysis, not the result of observing the RPV and core. The analysis would imply essentially complete loss of cooling of the core, i.e., nearly adiabatic conditions, and effectively no water in the bottom plenum, or rather no make up. The article reports this for unit 1. It appears that Units 2 and 3 had some loss of the core, possibly through vessel penetrations, e.g., control rod drive mechanisms.

Even without melting, if a lot of fuel reacted with the coolant, there could have been dissolution of the fuel which could have washed out. The effect would have been more or less the same, namely the loss of gaseous and volatile fission products to the containment and vent systems.


I'd like to read the report.

 

[tonio]

A question for the experienced nuclear engineers.

As far as I understood, during the meltdown most or all the fuel elements in the RPV's lost their zirconium cladding. Thus a mixture of UO2 and reaction products, both in the RPV’s and at the bottom of the secondary containment, was exposed to cooling water that probably dissolved most or all of the more soluble/volatile reaction products (a.o. Cesium?) and part of the less soluble reaction products. As a result, a significant part (most?) of the radioactivity entered the cooling water and spread with it though the reactor buildings, trough the cooling systems and into the soil and the sea.

Wouldn’t it be much better that, in case of a meltdown, the fuel would be allowed to exit the RPV and the leak onto a thick layer of some kind of metal with a moderate boiling point (lower than that of concrete and steel) which it then would melt and mix with? The surface of such a pool of metal/fuel mixture could subsequently be cooled and solidified with cooling water, minimizing the dissolution of radioactive reaction products in the passing cooling water.

 

[clancy688]

It's called Core Catcher.

 

[Rive]

...According to a study made by the Institute of Applied Energy (Ministry of Economy and Industry) released on 30 November, between 85% and 90% of unit 1's fuel fell down into the primary containment vessel.

I have a gut feeling that (this time) they are overestimated it. According to the temperature and water feed graphs of U1-U3 there is not so much difference between the units.

Don't shoot, it's just a gut feeling

 

[tsutsuji]

http://www3.nhk.or.jp/news/html/20111201/t10014325321000.html In the Tepco study the worse case for unit 2 is 57% of the fuel falling down into PCV, creating a 12 cm deep concrete erosion. For unit 3 the worse case is 63% of the fuel falling down into PCV, creating a 20 cm deep concrete erosion. Tepco explained that those results have no consequence on the achievement of the below 100°C "cold shutdown". But as in unit 1 there is only about 40 cm of water at the bottom of PCV, it is questionable if cooling is stable enough and if it can be juged that "cold shutdown" is achieved.

http://news.tbs.co.jp/20111130/newseye/tbs_newseye4890525.html The study results that were shown today are nothing more than estimates. Recently, reactor temperature did not rise as expected although the water injection rate had been reduced. The recovery work is expected to go on, as if groping one's way in the dark.

 

[LabratSR]

New Video Released By TEPCO - Radiation Measurement at Fukushima Daiichi

http://youtu.be/TAPsmgrGw30

 

[zapperzero]

This

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_06-j.pdf

shows a diagram of corium flow. It is oddly specific.

EDIT: part of a big release of documents by TEPCO. I am surprised no-one except tsutsuji (thanks, again) is discussing it here, but it appears they now believe that they have core on the floor in all three reactors.

I wonder, how long they have been working under this assumption? Maybe as long as us?

 

[Rive]

Speaking only for myself: I'm waiting for English translation.

I wonder, how long they have been working under this assumption? Maybe as long as us?

It's interesting that (AFAIK) they did not tried to start the Core Spray (assuming there is a CSS) in U1. Maybe because they were already sure that there is nothing left there what can be cooled only by the Core Spray?

Ps.: I wonder if the state of the molten core on/in the containment bottom concrete was considered as a criteria regarding the recommended water level in the reactor building basements?

 

[tsutsuji]

I translated the diagrams about unit 1 on pages 21, 22, and 27 of http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_06-j.pdf

 

[Cire]

I'd still like to know how you get measurements from the bottom of the RPV if the core melted the bottom of the RPV out. All the wiring, the thermocouple junctions, everything would be vaporized. All those signals would report being "open circuit"

The thermal radiation alone would burn up all the wiring within 20+ feet just from being in proximity of the fuel. Not to mention the magnetically attached thermocouples would have all dropped off and be hanging by their wiring.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20111202/0440_goninshiki.html Plant manager etc. were mistakenly believing that the isolation condenser was running. Tepco's internal investigation panel has completed its interim report. Concerning the fact that unit 1's isolation condenser was manually shutdown shortly after 6 PM on 11 March, the report says that the managers in the seismic-isolated building and in Tokyo were mistakenly believing that the isolation condenser was still running because a data saying that the water level was above fuel had been obtained from a water level gauge. As it is thought that the water level gauge, at that time, was not measuring the true value, it is possible that based on mistaken information, they held a mistaken awareness. Fuel started being uncovered 4 hours after the earthquake at around 7 PM at the earliest. According to the interim report, it is 8 hours after the earthquake, at around 11 PM that the managers began being aware of the possibility of fuel damage, after they grasped that radiation was rising.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20111202/index.html Tepco's internal investigation panel's interim report has been publicly released. It leaves many questions unanswered such as why huge quantities of radiation were released, and via which route they were released. The report does not depart much from what was previously said. The response to the accident is judged a number of times to have been "valid" or that "its direction was good". The cause of the accident is said to be "an unpredictable tsunami which entirely robbed safety functions". The report does not address the question of why Tepco did not immediately report to the government its own prediction, made 3 years earlier, of tsunamis higher than 10 m. Eight months after the accident, there is still an enigma concerning the operation of unit 1's cooling equipment, and concerning the route via which the radiation from unit 2, which is said to be the largest amount, was released.

http://www.tepco.co.jp/cc/press/11120203-j.html Tepco's internal investigation - interim report (Japanese)

 

[m82]

Are there any photos of the pressure vesel inside Fukushima reactor buildings (before accident)?
Also, how thick is the pressure vesel?

 

[Rive]

I translated the diagrams about unit 1 on pages 21, 22, and 27 of http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_06-j.pdf

Thanks.

I could translate some parts of the documents by copying the text to the googletrans: really interesting, thanks for them.
One question. AFAIK as the fuel melts, some parts of it forms some solid crust around the liquid corium. Do anybody knows anything about the heat produced by the liquid corium and the crust, relative to the decay heat produced by the whole fuel assembly?

The analysis assumes that the whole fuel amount slumped down to the bottom of the containment: but the liquid part will escape on the first leak of the RPV, and only the crust will be left behind to erode the RPV further...

 

[zapperzero]

Thanks.
The analysis assumes that the whole fuel amount slumped down to the bottom of the containment: but the liquid part will escape on the first leak of the RPV, and only the crust will be left behind to erode the RPV further...

If there is a crust, it would be metallic in composition, something like a steel foam with decay products mixed in. It would probably not be hot enough to do further damage, even if left uncooled

 

[Astronuc]

One question. AFAIK as the fuel melts, some parts of it forms some solid crust around the liquid corium. Do anybody knows anything about the heat produced by the liquid corium and the crust, relative to the decay heat produced by the whole fuel assembly?

Melting solids absorb heat (heat of fusion). The chemical reactions, e.g., oxidation of the Zircaloy would cause heat - probably on the order of decay heat.

The issue with corium, melted core, is that is increases the risk of breach of the pressure vessel, with an additional concern that if liquid metal falls into water, there will be a steam explosion.

 

[Rive]

Sorry, I wasn't clear enough. I have to think it again.

So, as the core debris melting through the lower plenum and falling to the bottom of the RPV, the temperature there will ramp up: the slowly decreasing decay heat (and possibly other chemical heat sources) against the cooling effect of the RPV wall and the melting.

When the RPV wall breached, the liquid (and most hot) part of the core debris will immediately leave the RPV. This would create only a/some smaller leaks instead of cutting down the whole RPV bottom.

When this happens, the heat generated within the RPV will be reduced to the heat generated by the remaining crust, while the cooling will be ~ the same as before.

As the average temperature of the containment rises, the cooling of the RPV will decrease, so maybe all this will be iterated some times.

But at the end there must be an equation between the cooling by the RPV (around the melting point of iron) and he heat generation of the stuff still inside. After this equilibrium reached, there will be no more liquid corium leaving the RPV.

If the decay heat of the corium, and the RPV 'natural' cooling can be estimated then maybe we can give a number for the amount of hot stuff still inside U1 RPV.

?

 

[Idaho_246]

Melting solids absorb heat (heat of fusion). The chemical reactions, e.g., oxidation of the Zircaloy would cause heat - probably on the order of decay heat.

The issue with corium, melted core, is that is increases the risk of breach of the pressure vessel, with an additional concern that if liquid metal falls into water, there will be a steam explosion.

Can we therefore assume that there was no water in the PCV when the corium dropped. When water was later introduced, the corium would be cooled from the top and sides but not from the bottom. Why then did it not penetrate down further into the PCV?

 

[I_P]

Can we therefore assume that there was no water in the PCV when the corium dropped. When water was later introduced, the corium would be cooled from the top and sides but not from the bottom. Why then did it not penetrate down further into the PCV?

This information from TEPCO is based on modeling/simulation, not observations. Until they can physically check all such determinations will be educated guesses using the external observations (like radiation levels, composition of the emitted particles, sensor readings, etc) as inputs. The answer to your question "Why did it not penetrate down further..." is that no one really knows at this point where the corium is, except that there have not been steam explosions so far...

Still, many months after the accident, we don't know many many things and the accident scenarios put forth are best guesses based on the available (and incomplete) evidence.

 

[etudiant]

It would be helpful to have some idea of the scale of a possible corium steam explosion.
The current decay heat is less than 5 megawatts per reactor, afaik and there is water being injected at a steady pace, so at least the top of the corium is in water. That should limit any explosion.
A steam explosion would require the underside of the corium to reach new moisture and flash it into steam in a confined space, which seems to be a recipe for a corium burble rather than a massive explosion, unless I missing something important.
Has this eventuality been modeled in any public documents?

 

[zapperzero]

Can we therefore assume that there was no water in the PCV when the corium dropped. When water was later introduced, the corium would be cooled from the top and sides but not from the bottom. Why then did it not penetrate down further into the PCV?

It's the other way around. This is a scenario we are discussing. The scenario, being something of a worst-case, ASSUMES that there was no water. We don't know that to be the case (although it may be, at least for Unit 1, where the IC was off).

 

[tsutsuji]

I have translated the abstract at the top of http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_09-j.pdf

Abstract

An estimate of Fukushima Daiichi units 1, 2 and 3's core status was publicly released on 23 May, and although cores in all three units were largely damaged and melted fuel had moved or fallen into the lower plenum, while not refuting the possibility that melted fuel had fallen ouside of the reactor pressure vessel, we estimated that most of it was being cooled in the vicinity of the lower plenum. The present public release consists of core status obtained by MAAP analysis and core status estimates based on core status evaluation that can be inferred from the behaviour of measured temperatures in every part of the plant.

Material for core status estimates were obtained by various operations, investigations, studies, and analysis performed since May. The estimates that were obtained are the following ones:

1) From the temperature behaviour of every part when injection rate is changed or when injection route is changed, it can be inferred regarding unit 1, as the RPV temperature decrease is large, that there are few fuel debris inside RPV, and regarding units 2 and 3, that fuel debris exist inside RPV.

2) As a result of calibration and of filling unit 1 and unit 2's water level gauges' reference tools with water, we can infer that a water level is not formed at the original fuel location inside the reactor, and that there is no fuel at the original location.

3) Conducting nuclear substance analysis of the gasses inside unit 1 and unit 2's primary containment vessels, we infer from cesium concentrations that fuel melted more at unit 1 than at unit 2.

4) Evaluating the heat balance of decay heat production and cooling, we estimate that the part of unit 1's decay heat that could not be cooled by the isolation condenser and by the high pressure core injection is about 3 times higher than that of units 2 and 3, and that this lead to early fuel and RPV damage.

5) From an estimate based on a RPV heat balance model, we infer that as of 10 October, at both units 2 and 3, the proportion of uncovered fuel is 3% or less, and that the fuel is largely submerged.

6) From an analysis concerning core-concrete reaction, we infer that even at unit 1, which is thought to contain the highest proportion of fallen fuel, the pedestal floor's erosion depth does not reach the PCV's inner wall.

Based on the above information and general analysis, it was possible to take further the estimations of core status we had performed in May. As a result, concerning unit 1, it can be thought that nearly all of the fuel that melted after the accident fell down into the lower plenum, and that there is almost no fuel left in its original reactor location. It can be thought that a great part of the debris that fell down into the lower plenum, fell down onto the primary containment vessel's pedestal. However, although the fuel debris create a core-concrete reaction, they were stopped due to the cooling performed by water injection and due to the decrease of decay heat, and we estimate that in the present situation, it remains inside the PCV where it is receives stable cooling. Concerning units 2 and 3, it can be thought that the fuel debris are for one part in the core's original territory, and for another part they have fallen into the lower plenum or onto the pedestal, and we estimate that in whichever place they might be, they are receiving stable cooling.

Nevertheless, far from observing directly into the reactor and into the primary containment vessel, this is a core status estimate based on various indirect informations and analysis, and in the future, using some methods, we want to grasp the situation through direct observation.

 

[Astronuc]

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

The tsunami of 11 March was the 'direct cause' of the accident at the Fukushima Daiichi nuclear power plant, concluded an official investigation report. It dismissed the idea that earthquake damage was a major factor in the accident.

A safe emergency shutdown was achieved within seconds of the magnitude 9.0 earthquake, said the Fukushima Nuclear Accident Investigation Commission composed of experts independent of plant owner Tokyo Electric Power Company. Control rods were fully inserted within seconds and all 13 diesel generators started as per design when tremors disconnected the grid connection. Instrumentation was working correctly, as were cooling systems.

Shaking recorded at the site was around the maximum that the plant was designed to cope with and still maintain nuclear safety but walk-down checks by plant staff showed no indication of significant damage to coolant systems.

. . . .

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, . . . .

IF the core melted, then what the instruments tell us about water levels, temperatures and pressures may not be accurate, or maybe some are, but others aren't. See the plots by Jorge Stolfi. One question then is - at what point during the event did the instrument readings become unreliable?

IF the core melted then there was essentially no cooling of the core, which essentially means no coolant in the core. The core may have melted - but at what temperature. Stainless steel melts at about 1450°C, Zircaloy-2 melts at 1800°C and the UO₂ (+TU+fission products) melts at 2800°C. On the other hand, rapid oxidation of Zircaloy occurs at lower temperatures, so that could have reacted with whatever coolant was present and produced H₂ + ZrO₂, which is the source of the hydrogen. The cladding for these units is barrier cladding, which means it has Zr-Fe liner which can oxidize pretty rapidly at high temperature. 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.

It's not yet clear at what temperature the melting occurred (IF any melting occurred) - anywhere between 1400°C and 2800°C, or perhaps slighly higher (that all depends on whether or not there was some level of heat transfer to the RPV and other structure via whatever fluid (aqueous solution, steam or gas) was present in the core).

One critical question: Was there coolant in the bottom of the RPV? That is where the control rod drive mechanisms/tubes reside. If the core melted, how did it manage to melt through the core support plate? If it did, then it had to displace any coolant present, while it melted the control rod drive mechanisms, as the then corium collected on the bottom of the RPV. Then it would have to had continue melting through the RPV (~ 5 inches or 127 mm), while melting the stainless steel guide tubes and the control rod drive mechanism (CRDMs).

Now the density of the corium is complex because it depends on the forms and proportions of melted material. Zircaloy-2 has a density of ~6500 kg/m³, stainless steel about ~8000 kg/m³, and UO2 about 10400 kg/m³ (water = 1000 kg/m³), so a molten mass can displace water.

Could the housing for the CRDMs have rupture during the earthquake? That's not clear, and TEPCO reported that the reactors scrammed. Could some other components or piping rupture during the earthquake, or during after shocks? Certainly any failure of the piping connected to the primary system would have made it difficult to get water to the core.

As for water under the RPV but in the PCV, that's not clear. If there was water present, but the rate at which a melted core dropped through the RPV was slow enough, there would not necessarily be a steam explosion.


Some useful data here (I know both authors) - http://www.ornl.gov/info/reports/1989/3445606042920.pdf

Assessment and management of ageing of major nuclear power plant components important to safety: Metal components of BWR containment systems
http://www-pub.iaea.org/MTCD/publications/PDF/te_1181_prn.pdf

Assessment and management of ageing of major nuclear power plant components important to safety: BWR pressure vessels.
http://www-pub.iaea.org/MTCD/publications/PDF/TE_1470_web.pdf

Integrity of Reactor Pressure Vessels in Nuclear Power Plants: Assessment of Irradiation
Embrittlement Effects in Reactor Pressure Vessel Steels
http://www-pub.iaea.org/MTCD/publications/PDF/Pub1382_web.pdf

http://nuclearsafety.info/ageing-management-and-long-term-operation/

The reactor pressure vessel (RPV) wall thicknesses for the BWR fleet were obtained from Reference 9, shown in Table 2-3. The maximum wall thickness is 7.125 inches (181 mm) and the minimum wall thickness is 4.47 inches (113.5 mm). The maximum vessel inner diameter is 254 inches (6.45 m) and the minimum vessel inner diameter is 185 inches (4.7 m).

The average wall thickness of the BWR fleet is 5.897 inches (150 mm). There is one vessel each at 4.47 inches (113.5 mm), 5.063 inches (128.6 mm) and 5.29 inches (134.4 mm). All other vessels are at 5.375 inches (137 mm) or thicker.

http://pbadupws.nrc.gov/docs/ML0906/ML090630402.pdf

9. BWR Vessel and Internal Project, BWRVIP-60-A, "Evaluation of Stress Corrosion Crack
Growth in Low Alloy Steel Vessel Materials in the BWR Environment," Technical Report
1008871, Electric Power Research Institute, Palo Alto, CA, June 2003.

BWRVIP-203NP: BWR Vessel and Internals Project
RPV Axial Weld Inspection Coverage Evaluation
EPRI 1016572 NP
Final Report, January 2009

 

[tsutsuji]

I attach a translation of the figures on pages 12 and 15 of http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_09-j.pdf

 

[clancy688]

(IF any melting occurred)

Excuse me for being unpolite, but what the hell is that supposed to mean? Granted, we don't have any clue what the situation inside the RPV really looks like.
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. At the same time, temperature readings indicated that the fuel was sufficiently cooled, therefore well below its former position.
I'd like to read an explanation which describes how nearly all of the fuel could have relocated to the lower RPV plenum without melting.

There were times when we couldn't say for sure if there has "only" massive cladding damage or also melting occured. But those are long gone.
There is molten fuel in Fukushima. That's what I consider a fact.

 

[etudiant]

Not sure if melting is inherent in the core destruction process.
Presumably the fuel rod cladding could get oxidized and flake off before anything melts, with the fuel pellets falling down to collect on top of the core support plate.
That heap of fuel might then melt from the inside out and the melt would move as the TEPCO simulation suggests. Certainly it is hard to envision the fuel breaching the RPV without melting, although
I am fascinated by Astronucs comment that:

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.

That is a novel idea, that the fuel might in fact have leached out to some extent. However, that should be detected by the water treatment process and nothing has even hinted at that afaik.

 

[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.