Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[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"

 

[Susudake]

I was very surprised a couple of weeks ago when I first saw a reference to "cold shutdown" being achieved at FDI; I wondered how can there be cold shutdown when not only has the fuel melted in three of the reactors but breached at least one layer of containment.

Then Hosono Goshi made this claim, and now PM Noda has repeated it:

http://www.asahi.com/english/TKY201109230235.html

I post this on the technical/scientific thread not the political because I'd like a technical take on whether one can apply the term "cold shutdown" under these circumstances. To me it seems to be a completely mis-applied term (i.e. propaganda) but I'd like clarification. Any takers? TIA.

 

[Morbius]

I post this on the technical/scientific thread not the political because I'd like a technical take on whether one can apply the term "cold shutdown" under these circumstances. To me it seems to be a completely mis-applied term (i.e. propaganda) but I'd like clarification. Any takers? TIA.

The term "cold shutdown" essentially means "not boiling".

It does NOT mean "ambient temperature". Normally a power plant never gets down to ambient temperatures even during a refueling outage.

The usage of the term is customary and proper and not propaganda.

Dr. Gregory Greenman
Physicist

 

[Morbius]

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

It takes a mixture of hydrogen and oxygen to be explosive. One or the other but not both doesn't give you an explosive mixture.

This reminds me of all the concern during the Three Mile Island accident concerning the "hydrogen bubble". The concern is that it was going to explode and breach the system piping.

Rationality reigned again when it was realized that there was no oxygen in the system to make an explosive mixture. The hydrogen used to be part of water molecules, but the hot zirconium "stole" the oxygen from the hydrogen to make zirconium oxide. Because the affinity of zirconium for oxygen exceeds that of hydrogen, there's no way the hydrogen was ever going to get that oxygen back. Hence, they never had an explosive mixture.

Greg

 

[zapperzero]

It takes a mixture of hydrogen and oxygen to be explosive. One or the other but not both doesn't give you an explosive mixture.

This reminds me of all the concern during the Three Mile Island accident concerning the "hydrogen bubble". The concern is that it was going to explode and breach the system piping.

Rationality reigned again when it was realized that there was no oxygen in the system to make an explosive mixture. The hydrogen used to be part of water molecules, but the hot zirconium "stole" the oxygen from the hydrogen to make zirconium oxide. Because the affinity of zirconium for oxygen exceeds that of hydrogen, there's no way the hydrogen was ever going to get that oxygen back. Hence, they never had an explosive mixture.

Greg

No measurements of the oxygen content have been made public. Also, I don't think there is still significant oxidation going on, do you?

Yes, I am aware that they are injecting nitrogen and that supposedly it displaces the atmosphere inside the reactors. But I would think there is a danger of explosion or at least blowout when they start cutting into that pipe.

From a more practical point of view, if TEPCO knows that there is no danger of explosion (too little oxygen), why then did they stop the work and started preparing to vent the line?

 

[swl]

My wife was just reading an article on Asahi Shinbun online stating that the Hydrogen gas concentration from the pipe is "at least 100%."
Seems strange the way they stated it was "at least 100%" as though it could be higher.

I'll try to get the link.

Edit: from EX-SKF:

　東電によると、２３日午後に配管の出口部分の気体を複数回測定したところ、いずれも「水素を含む可燃性ガスが１００％以上」との数字が出た。今後、水素だけを計れる測定器を用意し、正確な濃度を測定する方針。

According to TEPCO, they measured the gas at the pipe exit several times in the afternoon of September 23. Each time, the result showed "flammable gas including hydrogen gas, over 100% ". The company plans to use the instrument that only measures hydrogen, in order to accurately measure the concentration of hydrogen.

http://ex-skf.blogspot.com/2011/09/tepco-it-may-be-100-hydrogen-gas-inside.html