Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[joewein]

If they drain the basements, what will keep the melted fuel from catching on fire?

There is no requirement to keep the reactor buildings and turbine buildings submerged to be able to cool the fuel inside the reactor pressure vessel or primary containment.

The fuel can be cooled adequately as long as water can be sprayed onto it from either the feed water pipe or the core spray system in the RPV. If melted fuel has penetrated the bottom of the RPV and has dropped onto the base of the dry well, leaking water from those two injection sources should follow the same path that liquid fuel took and reach it.

About half the water in the basements of units 1-3 is standing inside the turbine hall basements. A quarter of the total is inside the reactor building basements (such as in the triangular corners of the octagonal space holding the suppression chamber). The remainder is in the trenches or the small radioactive waste treatment buildings adjacent to the reactor buildings. This http://www.tepco.co.jp/cc/press/betu11_j/images/110603a.pdf" by TEPCO has a breakdown. Since the water levels haven't dropped much since June, when this was published, the basic data should still be meaningful.

 

[joewein]

Not sure I understand you. If filtered, desalinated water is being pumped into the RPV, what difference does it make about basement water?? I assume salt removal from the RPV (where we assume a lot was deposited) is what is desired??

I see your point. Yes, if we're talking about the salt in the RPV, it doesn't matter one bit whether the basements are drained completely or not. My point was about the larger volume of salt in the 100,000t or so of water in the basements. I am concerned about that because of metal corrosion and because of effects it may have on the concrete of the structure.

For the RPV, if water injected into the core leaks out via either the presumably damaged recirculation pump seals or through damage to the RPV bottom from melting fuel, then the salt probably has already been flushed out. Only if the RPV bottom was completely intact and the cooling water boiled off before it reached a level high enough to leak via the pumps or other pipes should there still be significant amounts of salt in the RPV.

The minimum flow of 3.8 m³ per hour (units 1 and 2 in recent months) amounts to 90 t of water a day, which could dissolve about 30 t of salt per day (assuming none of it boiled off). It's been about 180 days of fresh water cooling so far, so even if the vast majority of the cooling water had escaped as steam rather than liquid the rest should have been enough to flush out the accumulated salt.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110920/index.html Because the contaminated water level in buildings is not decreasing as quickly as the water treatment flow rate suggests, Tepco has calculated an estimate of the amount of ground water leaking every day into the buildings: from 200 to 500 tons. Tepco's thought is to keep the water level in buildings just below the ground water level. The NISA says "It is necessary that the long term contaminated water treatment plan takes into account the ground water leak rate. The amount of ground water changes with seasons, and we want to evaluate this".

http://www.yomiuri.co.jp/science/news/20110920-OYT1T01060.htm The calculation is the following:

contaminated water at the end of may: 105,000 tons
contaminated water on 13 September: 102,000 tons
amount processed at the water treatment facility during that time: 90,000 tons
water added in the basements during that time: 90,000 + 102,000 - 105,000 = 87,000 tons
water injected into reactors (estimate) : 47,000 tons
ground water and partly rain [before the roofs were repaired ?] : 87,000-47,000 = 40,000

[PLAIN]http://www.tokyo-np.co.jp/article/feature/nucerror/list/images/PK2011092002100038_size0.jpg
light blue: the amount of contaminated water as suggested by the water treatment flow
dark blue: the actual amount present in basements
black and white arrow: possibility of ground water seeping in
source: http://www.tokyo-np.co.jp/article/feature/nucerror/list/CK2011092002100008.html?ref=rank

http://www.nikkan.co.jp/news/photograph/nkx_p20110920-2.html From October, the decontamination process will rely on SARRY as the main facility. Dedicated to the backup of SARRY and Kurion, the Areva system will be used as little as possible. Instead of diminishing the volume of water in turbine buildings' basements, it will be momentarily kept at a fixed amount. The volume injected into the reactors will be increased in order to enhance the cooling of the reactors. SARRY will be operated using both lines, which will bring the processing rate from 25 to 50 tons per hour. SARRY has a better utilization rate (92.1% during the week before 13 September) than Areva-Kurion (83.3%). SARRY was developed mainly by Toshiba, using American technology as base. With only two pumps, the number of moving parts is small. While the Kurion-Areva system is a complicated, "tricky" system, to such extent that operators misunderstood closed valves as being opened, SARRY is easy to operate. Japanese companies such as Organo and Swing (Ebara group) are involved in preparing low contaminated water treatment systems. "In any case new water treatment plans are necessary", a Tepco manager said, suggesting Tepco turns its expectations to the Japanese water treatment companies together with Toshiba and Hitachi. At present low contaminated water is stored in temporary tanks. It is possible that this water will be released into the nature after being purified. For this purpose the understanding of local communities and of the fishing industry must be obtained. "I understand very well that the water treatment companies have the technology to bring the contaminants below the detection level", the same Tepco manager said.

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110920_02-j.pdf explanations (in Japanese, not yet translated) of the 3:35 minute long video available at http://www.tepco.co.jp/en/news/110311/images/110920_1e.wmv (20 MB)

 

[SteveElbows]

I think there are a few people who have an erroneous mental image of where these so-called "basements" are under the reactor buildings (not talking about the turbine or other support buildings here, only the reactor buildings proper).

Once again, there are not excavated underground rooms or chambers directly underneath the RB structures enclosing the primary containment vessels. There is nothing directly under those except concrete and Earth (and possibly a layer of sand directly under the bottom of the steel shell).

The supression chamber encircles each PCV and sits in an annular excavation of sorts. Other than this circular cut-out that contains the SC and its supporting structures and equipment, there is no other "basement" to speak of.

With this in mind, it is impossible for corium that may have flowed (or dropped) out of the RPV to migrate downward and into the torus excavation. The drywell's vent pipe arrangement would not permit that to happen.

I apologize for the tone, but all this talk about corium eating its way through the lower extremities of the drywell and somehow ending up "in the basement" makes absolutely zero sense according to my understanding of the physical layout of the reactor buildings. It could go into the concrete substrate underneath the PCV, or into the Earth beyond the structural foundations of the buildings... but there is no basement direcly under the drywells.

On the contrary, I only mention the basement stuff because it was discussed in a proper report, rather than being completely ignorant speculation. I will now spend some time struggling to find out which report it was in, but I am sure it was mentioned in this thread at the time.

I don't blame you for your tone, considering how many times I myself have become tired with some of the wacky theories we have seen people cling to despite having few facts in their favour.

 

[SteveElbows]

Happily I was able to find the report quickly.

The Impact of BWR Mk 1 Primary Containment Failure Dynamics On Secondary Containment Integrity.

http://www.osti.gov/bridge/servlets/purl/5835351-nR29Hq/5835351.pdf

Pages 5 onwards are of interest. For example it says the following, and there are also some diagrams:

Should the liner fail near the drywell floor elevation, the most probable sites for blowdown entry into the secondary containment are the reactor building basement torus room and the second floor of the reactor building (Exhibit 2). The transport path for the blowdown is the gap between the drywell shell and the surrounding reactor building concrete, and the annular gaps surrounding the drywell vent pipes and penetra- tions. These gaps provide a 145 ft2 (13.5 m2) flow path into the torus room and a 135 ft2 (12.6 m2) flow path into the second floor of the reactor building. Since elevated drywell pressures and temperatures result in swelling of the drywell liner and a reduction in the gap between the liner and the reactor building concrete (Exhibit 3), it appears that the etfective flow path area for drywell blowdown would be limited by the actual size of the drywell shell rupture or the available space between the liner and the surrounding concrete

They admit there is considerable uncertainty, but as I understand that the 'torus room' is part of the basement, so I think you were wrong to be so dismissive of these possibilities.

 

[Astronuc]

So, I think your remark needs qualification:

If the fuel has never reached temperatures high enough to become reduced to metal form then it

would be mostly oxide, or hydrated oxides, which don't burn.

But of course, we do not have enough information to support OR definitively deny. So we speculate.

But the IF statement is incorrect.

The UO2 fuel is in the form of an oxide + fission products. Some fission product species become metallic inclusions because other more reactive elements tie up any free oxygen. The environment in a BWR is oxidizing, especially when the hydrogen gas escapes.

The Zircaloy cladding and channel, and stainless steel would oxidize rapidly at temperatures below metal. Therefore, if the fuel melted, it is in the form of oxides, higher order oxides, and probably more likely hydrated oxides - which do not burn. There is no IF about it.

The presence of seawater would enhance the corrosion of steel and the fuel to some extent.

Besides designing nuclear fuel and analyzing it under normal operating conditions, I also simulate it under accident, failed and degraded conditions.


I wasn't looking at evidence optimistically, I was just looking at the evidence. Any optimism was quashed with the first explosion, which indicated that they had failed to contain the accident, as was also indicated by the activity outside of containment.

 

[SteveElbows]

OK I'm going to go one better, with a report that explores the possibility of molten core penetrating the drywell.

http://www.osti.gov/bridge/servlets/purl/6250306-2XRtiq/6250306.pdf

What becomes clear when reading this document, is that the possibility they are exploring is not about the core traveling downwards from the pedestal area, but what happens if there is enough of it, at sufficient temperatures, to travel outwards, reach a steel wall and melt through it pretty quickly.

As they point out, there are a good number of factors which can prevent this theoretical scenario from happening, e.g. if the temp isn't high enough or there isn't enough of it to reach the wall, or if it travels downwards through concrete quite quickly then there won't be enough of it left higher up to reach the steel walls. But at the time this report was written many years ago, it sounds like this was a new scenario that hadn't been properly considered before, and they decided it was plausible enough to add it to the list of possible failure modes (some of the others are mentioned in the report).

 

[Astronuc]

OK I'm going to go one better, with a report that explores the possibility of molten core penetrating the drywell.

http://www.osti.gov/bridge/servlets/purl/6250306-2XRtiq/6250306.pdf

What becomes clear when reading this document, is that the possibility they are exploring is not about the core traveling downwards from the pedestal area, but what happens if there is enough of it, at sufficient temperatures, to travel outwards, reach a steel wall and melt through it pretty quickly.

As they point out, there are a good number of factors which can prevent this theoretical scenario from happening, e.g. if the temp isn't high enough or there isn't enough of it to reach the wall, or if it travels downwards through concrete quite quickly then there won't be enough of it left higher up to reach the steel walls. But at the time this report was written many years ago, it sounds like this was a new scenario that hadn't been properly considered before, and they decided it was plausible enough to add it to the list of possible failure modes (some of the others are mentioned in the report).

The paper mentions "a wide range of hypothetical core melt scenarios." It does not address plausibility or possibility. The group is charged with considering hypothetical, often worst-case, scenarios - no matter how implausible they might be. It would be like an automotive engineer crash testing a car at 200 or 300 mph, when the top speed would be 120 mph due to engine limitations and drag.

 

[SteveElbows]

I should point out that my use of the term 'wall' is rather sloppy, should read the report to get a proper sense of what it says as I have not likely done an excellent job of abbreviating it.

Also I don't want to make it sound like I am a huge believer of ideas that involve a great big quantity of molten core doing something very dramatic. They remain possibilities to me, but not ones which we have had a lot of excellent data pointing clearly in the direction of.

So I bring this stuff up now only because, if we are going to have any discussions about various theoretical possibilities that involve corium and basements, I don't want the fact that the torus room & other basement spaces are not directly underneath the reactor pressure vessel to be taken too far. Especially if we are not trying to suggest that the entire core is sitting in the basement in the form of a big blob, but rather the possibility that just some core material has found its way down there by one mechanism or another.

 

[Most Curious]

I see your point. Yes, if we're talking about the salt in the RPV, it doesn't matter one bit whether the basements are drained completely or not. My point was about the larger volume of salt in the 100,000t or so of water in the basements. I am concerned about that because of metal corrosion and because of effects it may have on the concrete of the structure.

For the RPV, if water injected into the core leaks out via either the presumably damaged recirculation pump seals or through damage to the RPV bottom from melting fuel, then the salt probably has already been flushed out. Only if the RPV bottom was completely intact and the cooling water boiled off before it reached a level high enough to leak via the pumps or other pipes should there still be significant amounts of salt in the RPV.

The minimum flow of 3.8 m³ per hour (units 1 and 2 in recent months) amounts to 90 t of water a day, which could dissolve about 30 t of salt per day (assuming none of it boiled off). It's been about 180 days of fresh water cooling so far, so even if the vast majority of the cooling water had escaped as steam rather than liquid the rest should have been enough to flush out the accumulated salt.

I had missed YOUR point about the salt remaining in the basement. No doubt others here understand the basement construction better than me. So far, I think of the basement as the area around the torus and the control rod drive room.

Clearly the corrosion rate is a serious concern, particularly if it causes the torus to fail/leak (assuming it isn't ALREADY leaking). Particularly, unit 2 appears to have suffered torus damage - or at least the bellows connecting it to the drywell. Somewhere I read the weakest part, pressure wise, was those bellows. I guess we will eventually learn the exact nature of that damage.


No doubt, additional leaks and problems will arise - for years. IMHO the best anyone can do is solve them as they occur.

 

[SteveElbows]

The paper mentions "a wide range of hypothetical core melt scenarios." It does not address plausibility or possibility. The group is charged with considering hypothetical, often worst-case, scenarios - no matter how implausible they might be. It would be like an automotive engineer crash testing a car at 200 or 300 mph, when the top speed would be 120 mph due to engine limitations and drag.

I didn't post the report as evidence of probability, only to demonstrate why I don't think it is fair to completely rule out certain core & basement theories just because of the location of the torus room/basement. Some crude theories can be ruled out as a result of the layout, but not others. All of this is really in response to a post by MiceAndMen, which I quoted when initially responding.

Having read the report I cannot agree that it makes no attempt to look at plausibility at all. They freely admit to a range of areas where knowledge is limited, but still try to consider a range of factors that may make this scenario more or less likely to occur.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110921/index.html According to Masanori Naito of the Institute of applied energy, it is not enough to have 100°C outside of the RPV. Simulation must be performed to estimate the temperature inside. It is also necessary to bring evidence that recriticality is not occurring.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110920/index.html Tepco estimates the radiation released during the first half of September to be 200,000,000 Bq/hour which is 4 million times less than at the beginning of the accident. The equipments to extract gasses from primary containment vessels will start being installed next week. Unit 1's cover structure will be completed in the middle decade of October.

 

[Jim Lagerfeld]

http://sankei.jp.msn.com/science/news/110921/scn11092113420003-n1.htm (Japanese)

Can anyone else spot the circular logic employed by TEPCO ?

(translated excerpt; regarding reactor 3)

"TEPCO's Deputy Site Director Junichi Matsumoto stated that "the extent of damage to the lower portion of the reactor pressure vessel remains unclear".

TEPCO initially supposed that by establishing the condition of the control rod sensors, the extent of damage to the fuel and the temperature of the bottom of the reactor pressure vessel could be estimated, however the damage to the sensors was greater than predicted, and the desired information proved impossible to deduce. TEPCO are now considering other methods for investigating the extent of the fuel damage.

The same process was earlier attempted at reactor one, however almost all of the sensors there also proved non-functional, and the the extent of the damage could not be ascertained."

 

[westfield]

http://sankei.jp.msn.com/science/news/110921/scn11092113420003-n1.htm (Japanese)

Can anyone else spot the circular logic employed by TEPCO ?

(translated excerpt; regarding reactor 3)

"TEPCO's Deputy Site Director Junichi Matsumoto stated that "the extent of damage to the lower portion of the reactor pressure vessel remains unclear".

TEPCO initially supposed that by establishing the condition of the control rod sensors, the extent of damage to the fuel and the temperature of the bottom of the reactor pressure vessel could be estimated, however the damage to the sensors was greater than predicted, and the desired information proved impossible to deduce. TEPCO are now considering other methods for investigating the extent of the fuel damage.

The same process was earlier attempted at reactor one, however almost all of the sensors there also proved non-functional, and the the extent of the damage could not be ascertained."

I'm not 100% sure what you mean so forgive me if I am off track - if the only possible failure point of the Control Rod PIP (position indicator probe) sensors was right at each CRD under the RPV then maybe it would be circular logic.

Thats not the case - looking at the graphic of the result of their tests it's evident that the four "groups" of sensors have quite distinctly different test results which tend to imply that the sensors are failing at "grouped" connectors or multicore-cables rather than individual PIP sensors. That sort of fault could be anywhere in the connectors and\or cabling.

So the test turned out to be too inconclusive to be of any use.

If TEPCO had been able to get meaninful signals from even a small number of individual PIP sensors it would have been a very useful excercise as apparently each PIP has a thermocouple integrated in it as well as the position switches. So they may have been able to see which PIPs were still working to give an indication of damage and further they may have had a chance of having a second source of temperature measurements available to them.

From a laymans perspective it seems definitely worth a try where applicable.



General information about PIP's from a GE website :

"Our PIP provides position indication of the control rod drive (CRD) to the reactor protection information system (RPIS) for the purpose of controlling reactor power. There is one PIP for each CRD, with the PIP located within an indicator tube of the CRD. Each PIP consists of a thermocouple and 53 normally-open reed switches mounted along a 13 foot, 3 inch-long switch support."

(a ring magnet in a fixed position around each PIP tube actuates the reed switches to give an indication of the CR's position. I have no idea how its position is encoded, it's appears to be only a 4-way connector on each PIP. Perhaps someone here can tell us?)

 

[etudiant]

http://sankei.jp.msn.com/science/news/110921/scn11092113420003-n1.htm (Japanese)

Can anyone else spot the circular logic employed by TEPCO ?

(translated excerpt; regarding reactor 3)

"TEPCO's Deputy Site Director Junichi Matsumoto stated that "the extent of damage to the lower portion of the reactor pressure vessel remains unclear".

TEPCO initially supposed that by establishing the condition of the control rod sensors, the extent of damage to the fuel and the temperature of the bottom of the reactor pressure vessel could be estimated, however the damage to the sensors was greater than predicted, and the desired information proved impossible to deduce. TEPCO are now considering other methods for investigating the extent of the fuel damage.

The same process was earlier attempted at reactor one, however almost all of the sensors there also proved non-functional, and the the extent of the damage could not be ascertained."

I'd not throw rocks at the guys for trying.
Clearly TEPCO has, with tremendous effort, gotten the reactors to a fairly stable state.
So it is now logical to start exploring what the reactors systems can still tell us about the conditions in the reactors. Using the control rod sensors seems a natural step. It begs the question of what other systems exist that might also provide information. Given that it will be dangerous to get close to the reactors for a long time, any insights that can be gleaned from these available sources is progress to be applauded.

 

[Jim Lagerfeld]

Thank you for that added clarification. The article indeed includes the line "TEPCO believes that due to the high temperatures created by the meltdown, wires connecting to the sensors may have melted, burnt or shorted out", but there is no rationale provided, so the way the particular story is couched makes it sounds like an effort to avoid confronting the possibility of more serious damage.

"looking at the graphic of the result of their tests it's evident that the four "groups" of sensors have quite distinctly different test results which tend to imply that the sensors are failing at "grouped" connectors or multicore-cables rather than individual PIP sensors. That sort of fault could be anywhere in the connectors and\or cabling."

I couldn't find the a PDF with the diagram of the results for reactor 3 - are they the same as for reactor 1?

"I'd not throw rocks at the guys for trying"

Nor would I - there is obvious progress, and I'm looking forward to the results of their next enquiry into the condition of the fuel. On balance however, I'm still left with impression that TEPCO leans towards a confirmation bias.

 

[zapperzero]

But the IF statement is incorrect.

The UO2 fuel is in the form of an oxide + fission products. Some fission product species become metallic inclusions because other more reactive elements tie up any free oxygen. The environment in a BWR is oxidizing, especially when the hydrogen gas escapes.

The Zircaloy cladding and channel, and stainless steel would oxidize rapidly at temperatures below metal. Therefore, if the fuel melted, it is in the form of oxides, higher order oxides, and probably more likely hydrated oxides - which do not burn. There is no IF about it.

The presence of seawater would enhance the corrosion of steel and the fuel to some extent.

Besides designing nuclear fuel and analyzing it under normal operating conditions, I also simulate it under accident, failed and degraded conditions.


I wasn't looking at evidence optimistically, I was just looking at the evidence. Any optimism was quashed with the first explosion, which indicated that they had failed to contain the accident, as was also indicated by the activity outside of containment.

I apologize. I did not intend to question your knowledge.

But but but... I don't understand. Zirconium is more reactive than uranium.
All the cores have been uncovered at some point (i.e. no water for a while, salty or otherwise). The (few) studies I have read say that the corium melt stratifies in-vessel, with the oxides on top and the metal (Zr, U, Fe, whatever else) below, just like in a furnace.

What am I missing?

http://www.jstage.jst.go.jp/article/jnst/44/9/44_1210/_article

 

[joewein]

I don't understand. Zirconium is more reactive than uranium.
All the cores have been uncovered at some point (i.e. no water for a while, salty or otherwise). The (few) studies I have read say that the corium melt stratifies in-vessel, with the oxides on top and the metal (Zr, U, Fe, whatever else) below, just like in a furnace.

What am I missing?

How would any metallic form of uranium form from uranium oxide pellets during meltdown conditions in a steam atmosphere?

Both uranium and zirconium are more electropositive than hydrogen, so as long as there is steam around their metallic forms would react with oxygen from H2O, releasing hydrogen while turning into oxide form.

It's because of this high reactivity that metallic uranium is usually produced by reducing uranium halides with alkali or alkali Earth metals (such as potassium or magnesium), unlike iron which can be reduced from oxides using carbon monoxide or hydrogen.

 

[zapperzero]

How would any metallic form of uranium form from uranium oxide pellets during meltdown conditions in a steam atmosphere?

Both uranium and zirconium are more electropositive than hydrogen, so as long as there is steam around their metallic forms would react with oxygen from H2O, releasing hydrogen while turning into oxide form.

It's because of this high reactivity that metallic uranium is usually produced by reducing uranium halides with alkali or alkali Earth metals (such as potassium or magnesium), unlike iron which can be reduced from oxides using carbon monoxide or hydrogen.

You start with zirconium metal and uranium oxide. You heat them up. What happens? There is no steam inside a fuel rod, or in a corium melt.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110922/1440_higai.html Tepco reports no important damage at Fukushima Daiichi as a consequence of typhoon No. 15. Water rose in reactor buildings basements by 44 cm at unit 1 and 10 cm at unit 2 and unit 4 and entered into unit 6 turbine building. Some surveillance cameras momentarily stopped displaying. It is suspected that water flooded a transmission cable, which Tepco will further investigate.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110922_01-e.pdf Inflow spot of rainwater in the basement of Turbine Building, Unit 6

 

[zapperzero]

The Bulletin of Atomic Scientists has published a special Fukushima issue:
http://bos.sagepub.com/content/current
Japanese version is here:
http://www.thebulletin.org/web-edition/special-topics/the-fukushima-issue-japanese

posting here because the articles cover multiple topics

 

[tsutsuji]

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.

I am not sure if I remember well enough, and perhaps it would be better to refer to the relevant pages in this thread when this problem was discussed. Is there a big difference between that water found in the Daini buildings and the kind of low-contaminated water found in the drinking water in a number of areas including in Tokyo in March? If Tepco thought its first explanation was plausible, coming up with another explanation would mean retracting the first explanation, which would be newsworthy, and I have not heard anything like that. Or I may have missed it in the news too.

 

[mscharisma]

I am not sure if I remember well enough, and perhaps it would be better to refer to the relevant pages in this thread when this problem was discussed. Is there a big difference between that water found in the Daini buildings and the kind of low-contaminated water found in the drinking water in a number of areas including in Tokyo in March? If Tepco thought its first explanation was plausible, coming up with another explanation would mean retracting the first explanation, which would be newsworthy, and I have not heard anything like that. Or I may have missed it in the news too.

Sorry, should have thought of providing references to discussions.

It first came up here with post #9277 by zapperzero and was discussed on subsequent pages:

"Another link from the excellent ex-skf blog.

Circumstantial evidence that Fukushima Dai-ichi containment broke after the earthquake but before the tsunami:

http://www.yomiuri.co.jp/science/new...3.htm?from=top

http://translate.google.com/translat...m%3Ffrom%3Dtop

Apparently there's Cesium in the water found in the basements at Fukushima Dai-ni. TEPCO says that water came in when the tsunami happened."

Bottom line as I remember: there was contaminated water found in the Daini basement buildings, which couldn't have been contaminated if it had come in with the tsunami and couldn't have been subsequently contaminated by airborne releases from Daiichi, leaving the source of contamination as well as what to do with that water unclear.

 

[tsutsuji]

Sorry, should have thought of providing references to discussions.

It first came up here with post #9277 by zapperzero and was discussed on subsequent pages:

"Another link from the excellent ex-skf blog.

Circumstantial evidence that Fukushima Dai-ichi containment broke after the earthquake but before the tsunami:

http://www.yomiuri.co.jp/science/new...3.htm?from=top

http://translate.google.com/translat...m%3Ffrom%3Dtop

Apparently there's Cesium in the water found in the basements at Fukushima Dai-ni. TEPCO says that water came in when the tsunami happened."

Bottom line as I remember: there was contaminated water found in the Daini basement buildings, which couldn't have been contaminated if it had come in with the tsunami and couldn't have been subsequently contaminated by airborne releases from Daiichi, leaving the source of contamination as well as what to do with that water unclear.

Here is the link to post #9277: https://www.physicsforums.com/showpost.php?p=3345325&postcount=9277

The Yomiuri article was partly translated by Rowmag as

So they are saying there is cobalt-60 in the water, apparently from rusted piping (at Daini itself, seems to be implied). Plus there is cesium-137 and -134 that they think might have flown in from Daiichi some time in the past 3 months.

Have they reported any previous measurements made on this water?

According to NHK quoted at https://www.physicsforums.com/showpost.php?p=3345520&postcount=9295 , "The utility says the concentration of radioactive cesium in the water is 30 times the permissible limit, but that it contains no other radioactive materials exceeding the safety limits.". This means that the Cobalt 60 is within the safety limits. Does the finding of Co 60 within safety limit require an investigation further than "it is from rust of pipes" ? How common is it in a nuclear plant to detect and release Co-60 "within safety limit" ? Also I am curious to know which kind of pipes they mean. Is there a possibility that they stored some discarded contaminated pipes somewhere in the basements, which were then washed by the seawater ?

There was a story of contaminated water being generated by water unexpectedly flowing in contaminated pipes belonging to a liquid waste system at the Hamaoka plant in July: https://www.physicsforums.com/showpost.php?p=3417217&postcount=10688 . I don't know if this sort of thing is conceivable with a tsunami wave, while being compatible with the fact that Tepco does not provide more details.

How does the "30 times the permissible limit" for Cesium compare with the levels in drinking water in Tokyo or in Iitate Mura ? Does anyone know how much the "permissible limit" level is for Fukushima Daini ?

 

[mscharisma]

Here is the link to post #9277: https://www.physicsforums.com/showpost.php?p=3345325&postcount=9277

The Yomiuri article was partly translated by Rowmag as

According to NHK quoted at https://www.physicsforums.com/showpost.php?p=3345520&postcount=9295 , "The utility says the concentration of radioactive cesium in the water is 30 times the permissible limit, but that it contains no other radioactive materials exceeding the safety limits."...

While I of course don't have answers to your questions, for what it's worth, here is a link to articles on the ex-skf site dealing with Daini, the third one on the page being the translation of a report from TBS news re. the water problem - as vague as it is. Maybe of interest also the loss of cooling at Daini, which apparently wasn't all that widely discussed.

http://ex-skf.blogspot.com/search?q=daini+water&updated-max=2011-08-29T19:59:00-07:00&max-results=20

 

[joewein]

You start with zirconium metal and uranium oxide. You heat them up. What happens? There is no steam inside a fuel rod, or in a corium melt.

But to get to a corium melt the fuel rods have to heat up. The fuel rod component with the lowest melting point is the zirconium cladding. If it melts, the uranium oxide pellets are exposed to steam. Long before metallic zirconium melts however, it will start burning in the steam atmosphere, at which point it bulges up, becomes brittle and crumbles, also exposing the pellets to steam. Either way I can't see how any uranium oxide reduced to metal by zirconium metal could remain in metallic form for long.

As Astronuc wrote here recently:

The environment in a BWR is oxidizing, especially when the hydrogen gas escapes.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110923/index.html Tepco plans to decontaminate the 16,000 tons of low-contaminated water from units 5 and 6 to the levels allowed for sea bathing resorts (50 Bq/l of cesium) and then to spread it on the plant site. According to Tepco, the timber that was obtained from the forest clearances made to provide water storage space needs to be spread with water to prevent natural combustion. The decision to launch this plan will be taken after explaining it to the local communities.

http://www.meti.go.jp/english/earthquake/nuclear/iaea/iaea_110911.html Additional Report of the Japanese Government to the IAEA (Second Report). Updated on September 16, 2011

 

[zapperzero]

But to get to a corium melt the fuel rods have to heat up. The fuel rod component with the lowest melting point is the zirconium cladding. If it melts, the uranium oxide pellets are exposed to steam. Long before metallic zirconium melts however, it will start burning in the steam atmosphere, at which point it bulges up, becomes brittle and crumbles, also exposing the pellets to steam. Either way I can't see how any uranium oxide reduced to metal by zirconium metal could remain in metallic form for long.

I may have understood some of this comically wrong, but here goes:

Not all the zirconium gets oxidized. Whatever is left eventually ends up in a sub-oxidized corium layer or region along with some U and Fe. Under some conditions (those conducive to inverse stratification of the corium), this layer is at or near the bottom of the corium mass and hence not in contact with any water that may get added from above after RPV dryout.

here are some cites:
www.iupac.org/publications/pac/67/6/1003/pdf/

Cladding oxidation by steam is important in SFD because of the heat released and the hydrogen produced. When the steam is plentiful, the cladding becomes fully oxidized to Zr02 before the melting point of the metal is reached. However, if the majority of the water has escaped the core and if the emergency core cooling system is not operating, steam blankets the fuel rods. Under these circumstances, the large mass of zirconium in the core(-25 tons for a 1000 MWe reactor) can produce so much hydrogen by reaction (1)
that the gas phase becomes severely depleted in water vapor. In this event, the cladding does not completely oxidize, and the Zr02 scale dissolves in the remaining metal before the latter melts.

http://www.oecd-nea.org/nsd/workshops/masca2004/oc/papers/JPN_FUKASAWA.DOC

Thermodynamic equilibrium analyses for U/Zr=0.8 corium shows that C-50 corium under 20 wt% Fe and C-32 under 30 wt% Fe would be stratified with the metal phase being under the oxide phase. In addition, the higher the Fe fraction and the lower the Zr oxidation rate are, the higher the decay heat fraction in the metal will be.

http://www.springerlink.com/content/b25532365uw75rg4/

Two steam explosion experiments were performed in the TROI (Test for Real cOrium Interaction with water) facility by using partially oxidized molten corium (core material), which is produced during a postulated core melt accident in a nuclear reactor. A triggered steam explosion occurred in one case, but none occurred in the other case. The dynamic pressure and the dynamic load measured in the former experiment show a stronger explosion than those performed previously with oxidic corium. Meanwhile, a steam explosion is prohibited when the melt temperature is low, because the melt is easily solidified to prevent a liquid-liquid interaction. The partially oxidized corium could enhance the strength of a steam explosion due to the thermal energy from an exothermic chemical reaction between the water and the uranium metal with a sufficient superheat extracted during melting. The melt composition effect on a steam explosion load, which was not included during the nuclear design, needs to be included in it.

TL;DR: the drier the core, the more metallic (as opposed to oxidic) the corium. The more metallic the corium, the bigger the boom when/if it drops into water.

 

[tsutsuji]

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110923_02-e.pdf Detection of Hydrogen in the Piping of Spray System of Unit 1 Primary Containment Vessel

http://mainichi.jp/select/jiken/news/20110924k0000m040078000c.html The upper detection limit of the instrument (1%) being reached, the actual hydrogen concentration is unknown. Tepco will perform an accurate measurement of the hydrogen concentration. It is also studying how to inject nitrogen in order to extract the hydrogen.

http://www.nikkei.com/news/category...3E2E2E2E2E2E2;at=DGXZZO0195579008122009000000 Tepco explains that because the oxygen concentration is low, "the probability of a hydrogen explosion is extremely low". The hydrogen concentration measurement was part of a survey preparing pipe cutting work. It is thought that some of the hydrogen produced right after the the accident remained in the PCV and flowed into this pipe.

http://www3.nhk.or.jp/news/html/20110923/t10015807331000.html The pipe cutting work is part of the installation of the PCV gas extraction system. Tepco says the schedule will not be delayed. The hydrogen concentration will also be checked in similar pipes at unit 2 and unit 3.

Concerning the "no steam observed" event at unit 1 discussed in this thread in August:

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110817/1850_teishi.html(...) It is known that from about 6:30 PM on 11 March an emergency condenser was shut down for three hours. Because they could not observe any steam, the plant operators believed that the condenser was subject to a "boil-dry" as it is called when water has run out, and they shut it down in order to preserve it from being broken.

the Second Japanese government report to IAEA says the following:

However, closing operation of return line isolation valves of System A was performed at 18:25 on March 11 because it became impossible to confirm the vapor immediately after that.

After that, opening operation of return line isolation valves of System A was performed at 21:30 on March 11 to maintain the open state after steam generation was confirmed.
http://www.meti.go.jp/english/earthquake/nuclear/iaea/pdf/20110911/chapter2.pdf page II-82

Translated again by myself, it becomes:

However, immediately after that, because it became impossible to confirm steam generation, the closing operation of the return line isolation valve of System A was performed at 18:25 on March 11.

After that, at 21:30 on March 11, the opening operation of the return line isolation valve of System A was performed, steam generation was confirmed, and without further change, the open state was maintained.

Translated from Japanese version http://www.meti.go.jp/earthquake/nuclear/backdrop/pdf/20110911/chapter2.pdf page II-76

Let's translate also the paragraph that follows:

It seems that the power plant emergency response headquarters was not able to sufficiently grasp the situation of the IC.　Based on information that steam generation was confirmed at the exhaust outlet and on the information that, at the time when the water gage was recovered, it indicated a value above top of active fuel (TAF), they believed that the IC was continuing to run.

Translated from Japanese version http://www.meti.go.jp/earthquake/nuclear/backdrop/pdf/20110911/chapter2.pdf page II-76

 

[zapperzero]

http://mainichi.jp/select/jiken/news/20110924k0000m040078000c.html The upper detection limit of the instrument (1%) being reached, the actual hydrogen concentration is unknown.
http://www.nikkei.com/news/category...3E2E2E2E2E2E2;at=DGXZZO0195579008122009000000 Tepco explains that because the oxygen concentration is low, "the probability of a hydrogen explosion is extremely low".

I hope I'm not the only one who sees a bit of an issue here. Am I?

 

[westfield]

I hope I'm not the only one who sees a bit of an issue here. Am I?

Nothing wrong with that - they asked an engineer and then they asked management ;)

Seems it's how this party got started.

 

[westfield]

Sorry if this has been linked already:

http://www.meti.go.jp/english/earthquake/nuclear/iaea/iaea_110911.html"

(English)

 

[LabratSR]

Updated Roadmap Released

http://www.tepco.co.jp/en/press/corp-com/release/11092003-e.html

 

[LabratSR]

New video released by TEPCO on the status of the measuring instruments.

http://www.youtube.com/AtomicPowerReview

 

[Jim Lagerfeld]

New video released by TEPCO on the status of the measuring instruments.

http://www.youtube.com/AtomicPowerReview

Fantastic link thank you!

Regarding the thermocouples on which 'cold shutdown' claims will be based, some are deemed to be 'overscale', some 'underscale', and some destroyed. Of the remaining:

"we think that the data collected at the moment is reliable to some extent. We are not sure if the accuracy of the detectors of each thermometer is within the limits of the calibration or not, but according to the overall trend, we think that such temperature estimates will be probable. Also, recently, we can change the water injection rate to the reactor, and it appears as the temperature shift, therefore we think that the soundness of the thermometer is secured"