Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[StrangeBeauty]

Seawater analysis from reactor 2 leak also showed high Iodine levels larger than Cesium. Draw your own conclusions.

Not having a nuc eng background makes it quite difficult for me to draw realistic conclusions from that data. Could you (and others!) enumerate the possible conclusions, and perhaps guesstimate the likelihood of each? I'm sure there is a diversity of opinion here -- I've seen where some people think that the iodine level must point to recriticality, but other knowledgeable people disagree. I do realize that people are speculating based on the available, incomplete data and fully expect one of the possibilities to be 'unknown source.' Any enlightenment is appreciated. :)

 

[daumphys]

What is important at this point? I think to obtain the more detail and accurate information about the destroyed power plant is important. It will bring more wise solutions.

 

[shogun338]

“We must move highly contaminated water at reactor number 2 and elsewhere to a radioactive waste processing facility as soon as possible without leaking it into the sea,” Banri Kaieda told reporters after his first visit to the Fukushima Daiichi Nuclear Power Station Saturday. “The plant chief said it must be given the priority right now and I agree with him.” On Sunday, Tokyo Electric Power Co (TEPCO), which runs the plant, was to complete the release into the Pacific Ocean of relatively low-level radioactive water from the disposal facility at the plant, which was crippled by the March 11 earthquake and tsunami. http://www.thehindu.com/news/international/article1684699.ece

 

[shogun338]

A massive Russian cargo plane has been used to pick one of the world's largest concrete pumps to pour water on the stricken nuclear power plant in Japan.
The 95-ton pump is mounted on a 26-wheel truck and can be operated from two miles away by remote control, allowing it to shoot water into the damaged reactors.


Read more: http://www.dailymail.co.uk/news/art...ed-Fukushima-nuclear-plant.html#ixzz1J5MDOGtL

 

[StrangeBeauty]

...Could you (and others!) enumerate the possible conclusions...

What is important at this point?

I assume that was in reply to my question, if not, please ignore ;)
An answer is important 1) to spread accurate information rather than inaccurate info. If the answer is simply "unknown" or "not enough data to say anything reasonable" that's a fine answer! A much better answer than repeating someone potentially less knowledgeable saying "it definitely means there is recriticality" which I've heard elsewhere. 2) I'd also like to know why if that's possible/easy -- for my own education ;) I think the people that find their way to this forum are a pretty curious and scientifically oriented group.

I think to obtain the more detail and accurate information about the destroyed power plant is important. It will bring more wise solutions.

I agree that is far more important to try and obtain better and more accurate data than the question I ask, which is possibly excessively speculative -- I don't know if it is or isnt' excessively speculative though! That's why I ask my question. "Too speculative at this point to be useful" is a perfectly acceptable answer and gives me more data! If I get no answers, then my assumption is precisely that, and if you do not post further, I would assume that is also your answer. :) I do not mean to offend, or waste anyone's time here -- I only wish to understand and have the best info currently available. Thanks for any info on this, and I appreciate everyone's time and effort put in.

 

[NUCENG]

I have a question regarding Iodine-131...

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110328e12.pdf

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110409e7.pdf

Those two pdfs are showing "results of nuclide analyses of radioactive materials in the air" (at Fukushima Daiichi).

But from March 26th until now, Iodine-131 concentrations basically stayed at the same level. And I don't understand why. Iodine-131 decays after 8 days, so the numbers should have halfed. Since the scale is logarithmic it's hard to see... or I could be imagining things. But it's still odd.
And it's been nearly one month since the accident (= stop of nuclear fission), so the Iodine left should be well below 10%, So why don't the numbers change? And why are there still such high Iodine concentrations in the water in the reactor buildings?

Iodine-131 and cesium-137 have an intial ratio of about 8-1 per one of my prvious posts. Cesium is a metal. Iodine can form particulates or emege as a gas. Cesium is a metal and non-volatile so it would normally stay in the coolant and probably inside containment. Depending on the transport path the inital ratio at the point it is being meaured could be drastially different.

After a month the total actity of Iodine shoud have dropped by about a factor of 16. Your two graphs are just over a week apart or about one half life. The logarithm of 0.5 is -0.3. So the levels on the later graph should be about 1/3 of a decade lower. That looks about right to me.

The large majority (APPROX 95%) of iodine released from damaged fresh fuel will form CsI cesium iodide. This is a particulate wthat tends to form larger clumps as particle sizes increase it woll settle out as surface contamination. It is also very soluble in water, but will plate out if the water evaporates. If boiled smaller particles of CsI can be carried with the steam or water vapor. Seawater is slightly basic. However if the pH drops below 7 (acidic) the iodine will be re-evoved as gaseous I2 and would rapidly drop the proportion of Iodine. As long as the pH is basic the CsI will stay in solution.

For further info look up NUREG-1465.

Hope that is clear. The short answer is the graphs appear to be consistent with iodine decaying faster than the cesium. If iodine suddenly increased in air samples it could indicate reevolution of iodine gas, not recriticality.

 

[biffvernon]

No chance of the seawater pH dropping below 7 (I hope).

 

[NUCENG]

No chance of the seawater pH dropping below 7 (I hope).

Not in the sea, but inside the plant radiological and chemical processes may be generating iodic acid, carbonic acid, hydrochloric acid, nitric acid and probably others. Considering how much seawater has been added, and how high rad levels are, this could become an issue.

 

[htf]

If the Iodine was produced in the reactor by a fission reaction resulting from re-criticality, shouldn't they also find the shorter living Iodine Isotope I-134? Or does it take hours for the Iodine to escape from the reactor?

 

[Astronuc]

Iodine-131 and cesium-137 have an intial ratio of about 8-1 per one of my prvious posts. Cesium is a metal. Iodine can form particulates or emege as a gas. Cesium is a metal and non-volatile so it would normally stay in the coolant and probably inside containment. Depending on the transport path the inital ratio at the point it is being meaured could be drastially different.

After a month the total actity of Iodine shoud have dropped by about a factor of 16. Your two graphs are just over a week apart or about one half life. The logarithm of 0.5 is -0.3. So the levels on the later graph should be about 1/3 of a decade lower. That looks about right to me.

The large majority (APPROX 95%) of iodine released from damaged fresh fuel will form CsI cesium iodide. This is a particulate wthat tends to form larger clumps as particle sizes increase it woll settle out as surface contamination. It is also very soluble in water, but will plate out if the water evaporates. If boiled smaller particles of CsI can be carried with the steam or water vapor. Seawater is slightly basic. However if the pH drops below 7 (acidic) the iodine will be re-evoved as gaseous I2 and would rapidly drop the proportion of Iodine. As long as the pH is basic the CsI will stay in solution.

For further info look up NUREG-1465.

Hope that is clear. The short answer is the graphs appear to be consistent with iodine decaying faster than the cesium. If iodine suddenly increased in air samples it could indicate reevolution of iodine gas, not recriticality.

Another good source of information is NUREG/CR-5732, Iodine Chemical Forms in LWR Severe Accidents
http://pbadupws.nrc.gov/docs/ML0037/ML003726825.pdf

However, I believe the interpretation of the activity data is made murky by the use of seawater (salt water) which complicates the chemical forms and their distribution. Use of seawater in the primary system was not forseen, and as far as I know, has not been analyzed.

Determining the quantity of failed fuel is difficult because of the use of seawater - probably higher corrosion of the fuel (which is consistent with an observation that the hydrogen generation is enhanced in the presence of seawater) and the uncertainty with respect to the water level in the cores during the period March 12 - present.

New breaches would change the ratios of nuclides present. Short half-lived radionuclides continually decay away, so the ratios of short-lived to long-lived isotopes should be decreasing.

Recriticality could be possible only if sufficient fuel was configured in some volume with water (moderated), but in the absence of competing neutron absorbers, e.g., B-10. An indication of recriticality would be a sudden increase in short-lived radioisotopes, e.g., Xe-138 and Xe-135 compared to Xe-133, or increases in I-132 and I-134 compared to I-131, 133, 135.

On the other, if the recriticality event lasts on the order of seconds or minutes, then the new inventory of short-lived fission products may not be very substantial, because the time is short and the power is low (the reactor would go critical from decay heat/power conditions).

 

[hbjon]

If molten fuel from FUK2 has bored through the plants foundation and into the bedrock, how far does it travel before it hits enough water to resolidify the mass of heavy metal? Is there an outlet for the steam produced? What sort of pressure would build in this scenario? Some information suggests there could be a steam explosion beneath the earth.

 

[Joe Neubarth]

If molten fuel from FUK2 has bored through the plants foundation and into the bedrock, how far does it travel before it hits enough water to resolidify the mass of heavy metal? Is there an outlet for the steam produced? What sort of pressure would build in this scenario? Some information suggests there could be a steam explosion beneath the earth.

As it melts its way down it picks up solid material from the pathway and becomes diluted. Dilute it enough and it slows down and just sits, not hot enough to move further.

 

[clancy688]

Hope that is clear. The short answer is the graphs appear to be consistent with iodine decaying faster than the cesium. If iodine suddenly increased in air samples it could indicate reevolution of iodine gas, not recriticality.

Recriticality could be possible only if sufficient fuel was configured in some volume with water (moderated), but in the absence of competing neutron absorbers, e.g., B-10. An indication of recriticality would be a sudden increase in short-lived radioisotopes, e.g., Xe-138 and Xe-135 compared to Xe-133, or increases in I-132 and I-134 compared to I-131, 133, 135.

Okay, that's good to hear. But apparently, TPECO isn't measuring other nuclides than I131, C134 and C137 any more... ^^;

If anyone is interested, I collected all TEPCO aerial nuclide measurements (at Daiichi):

http://www.megaupload.com/?d=Y62QY5R5

 

[AntonL]

http://english.kyodonews.jp/news/2011/04/84547.html

People in the 20 to 30km zone around Fukushima are told to prepare for evacuation although radiation levels are deemed to be "safe". Further, specific areas outside the 30km zone are being evaluated to evacuate.

 

[AntonL]

Tokyo Electric Power Co. President Masataka Shimizu visited the Fukushima prefectural government office Monday afternoon to apologize for the nuclear disaster at its Fukushima Daiichi power plant, but Gov. Yuhei Sato has declined to meet him, according to officials from the utility and the prefectural government.

Sato seemingly does not want apologies he want's to see more action.

 

[AntonL]

... But apparently, TPECO isn't measuring other nuclides than I131, C134 and C137 any more...;

They are measuring, but because of many apparent blunders and so-called false measurements NISA is now controlling the release of these.

http://www.tepco.co.jp/en/press/corp-com/release/11041007-e.html][/URL]
Three nuclides (Iodine-131, Cesium-134 and Cesium-137) are released as
fixed figures. Other nuclides figures are to be released as soon as
identified under instruction of NISA

effectively stopping all criticality discussion but opening the box for speculation.

 

[AntonL]

http://english.kyodonews.jp/photos/assets/201104/0411028.jpg
Unmanned helicopter to probe troubled nuclear plant
File photo shows an unmanned helicopter being utilized to collect information on the buildings at the troubled Fukushima Daiichi nuclear plant's No. 1 to No. 4 reactors in Fukushima Prefecture on April 10, 2011. (Photo provided by Tokyo Electric Power Co.)(Kyodo)

Apparently fitted with both visual and IR cameras.

 

[rmattila]

Also, one doesn't necessarily need O₂ as the oxidizer for a hydrogen explosion. Chlorine gas (Cl₂) mixed with H₂ makes for a pretty good explosion. If there was H₂ produced from the Zr + 2 H₂O => ZrO₂ + 2H₂ reactions, and seawater release Cl₂, then I wonder if an H₂ + Cl₂ => 2 HCl reaction in the top of the RPV would be possible.

I've been thinking about this possibility as well. Not being a chemist, I don't know if it is possible to get significant Cl₂ release at the conditions prevailing in the reactor pressure vessel, but assuming that Cl would qualitatively behave like I, low pH would increase the rate of Cl₂ gas generated by radiolysis and released from the water. Since boric acid has been added, there apparently is low pH in the brine.

Another possibility would be evaporation, if the core would melt and mix with the salt at the bottom of the RPV.

Are there chemists present, capable of commenting on the relevance of the above speculation?

 

[artax]

The most shocking video I've seen of the Tsunami!

 

[Krikkosnack]

Tsunami Warnings/Advisories

http://www.jma.go.jp/en/tsunami/


A strong earthquake with a preliminary magnitude of 7.1 shook buildings in Tokyo and a wide swathe of eastern Japan on Monday, with an advisory for a one-meter tsunami issued after the quake. reuters

 

[AntonL]

http://www.nisa.meti.go.jp/english/files/en20110406-1-1.pdf

I cannot recall noting above reference in this forum - hence I post

above is the presentation by
Nuclear and Industrial Safety Agency (NISA)
Japan Nuclear Energy Safety Organization (JNES)
dated 4th April, 2011 regarding seismic damage to the NPPs4

Nice reference for basic data, chronology of events, etc

 

[tsutsuji]

http://www.nisa.meti.go.jp/english/files/en20110406-1-1.pdf

I cannot recall noting above reference in this forum - hence I post

above is the presentation by
Nuclear and Industrial Safety Agency (NISA)
Japan Nuclear Energy Safety Organization (JNES)
dated 4th April, 2011 regarding seismic damage to the NPPs4

Nice reference for basic data, chronology of events, etc

That chronology is not as thorough as I would have expected, as it does not mention the black smoke on 23 March at unit 3.

 

[AntonL]

The most shocking video I've seen of the Tsunami!

COMPLETELY OFF TOPIC: ... and some people like 30metre waves, enjoy
http://www.youtube.com/watch?v=JdFBtHU-SmU&feature=related

 

[NUCENG]

I've been thinking about this possibility as well. Not being a chemist, I don't know if it is possible to get significant Cl₂ release at the conditions prevailing in the reactor pressure vessel, but assuming that Cl would qualitatively behave like I, low pH would increase the rate of Cl₂ gas generated by radiolysis and released from the water. Since boric acid has been added, there apparently is low pH in the brine.

Another possibility would be evaporation, if the core would melt and mix with the salt at the bottom of the RPV.

Are there chemists present, capable of commenting on the relevance of the above speculation?

I'm not a chemist, but am learning a lot from this event. Boric acid is described as a weak acid. From what I've read about it, it seems it takes a lot of it to make the [H+] ion that lowers pH. Something like HCl is a strong acid because each molecule forms a [H+} ion. How much the added boric acid lowers the pH is beyond my knowledge, but it may not be enough alone to relase iodine gas.

 

[MadderDoc]

I've been thinking about this possibility as well. Not being a chemist, I don't know if it is possible to get significant Cl₂ release at the conditions prevailing in the reactor pressure vessel <..>
Are there chemists present, capable of commenting on the relevance of the above speculation?

Well, I am a chemist, and I can't see how the chloride from the seawater could be chemically changed to Cl₂ in the reactor environment -- and even less how it could accumulate there. (Cl₂ is a strong oxidant species and -- if generated -- it would quickly react with e.g. metal and in turn revert to chloride ion.

 

[NUCENG]

http://www.nisa.meti.go.jp/english/files/en20110406-1-1.pdf

I cannot recall noting above reference in this forum - hence I post

above is the presentation by
Nuclear and Industrial Safety Agency (NISA)
Japan Nuclear Energy Safety Organization (JNES)
dated 4th April, 2011 regarding seismic damage to the NPPs4

Nice reference for basic data, chronology of events, etc

Note: This indicates that the Diesel Generators at Fukushima are in the basement of the turbine buildings. This seems to be a recurrent design flaw. Some US plants also have EDGs below ground. This may have been done to reduce probability of tornado or hurricane damage, but it increases vulnerability to flooding. US BWRs and PWRs have had design basis issues related to potential diesel generator flooding from internal sources such as circulation water to the main condensers. I remember at least one significant operating experience report on this topic and personally helped conduct reviews on the issue at several US NPPs.
If the diesels are there it is also possible that one or both divisions of essential AC power switchgear may also be in the basement.

Potential Root Cause: The design failure of the tsunami wall being topped by a larger than design basis tsunami became a single point of failure that made the accident inevitable.

 

[AntonL]

Potential Root Cause: The design failure of the tsunami wall being topped by a larger than design basis tsunami became a single point of failure that made the accident inevitable.

There is no tsunami wall around the nuclear power plant I can only see a breakwater to protect the harbour and the intakes from wave action.

I still maintain that ground floor elevation of the nuclear reactors is determined by basic sizing constraints to keep the basement above sea water level.

The tsunami study of 2007 that is cited earlier in this forum and proudly presented by Tepco that it calculated a tsunami of 5.7metres for design, was an afterthought and not a original design parameter. (If they looked at historical data they should have been extremely worried since the study which they preferred to ignore) The model for the Tsunami was developed in 2002 but the reactor was built in the sixties. If Tsunami was an consideration for design back in the sixties they would have fallen back on historic records.

 

[NUCENG]

Well, I am a chemist, and I can't see how the chloride from the seawater could be chemically changed to Cl₂ in the reactor environment -- and even less how it could accumulate there. (Cl₂ is a strong oxidant species and -- if generated -- it would quickly react with e.g. metal and in turn revert to chloride ion.

"The most important acids in containment will be
nitric acid (HNO3), produced by irradiation of water
and air, and hydrochloric acid (HCI), produced by
irradiation or heating of electrical cable insulation.
The most important bases in containment will be
cesium hydroxide, cesium borate (or cesium carbonate),
and in some plants pH additives, such as
sodium hydroxide or sodium phosphate." (NUREG/CR-5950)

Their analysis doesn't even assume any seawater.

 

[NUCENG]

There is no tsunami wall around the nuclear power plant I can only see a breakwater to protect the harbour and the intakes from wave action.

I still maintain that ground floor elevation of the nuclear reactors is determined by basic sizing constraints to keep the basement above sea water level.

The tsunami study of 2007 that is cited earlier in this forum and proudly presented by Tepco that it calculated a tsunami of 5.7metres for design, was an afterthought and not a original design parameter. (If they looked at historical data they should have been extremely worried since the study which they preferred to ignore) The model for the Tsunami was developed in 2002 but the reactor was built in the sixties. If Tsunami was an consideration for design back in the sixties they would have fallen back on historic records.

In the METI slides (see posting #3402) it shows a 10 meter elevation difference beween sea level and the foundation of the Turbine Building. That would allow a basement depth of 4.3 meters and it would still be at the design tsunami elevation. So you are right, but that is a distinction without a difference because the tsunami was 14+ meters and the basement was flooded.

Tsunamis, seiches, hurricane storm surges, and external flooding have been considered in reactor site licensing in the US since the 1960s. If the Japanese didn't consider tsunamis during initial plant siting and design I would be floored - after all tsunami is Japanese for harbor wave.

Once the plant was built, it is tough to move it to higher ground. If a later study indicated a bigger threat existed, it would be up to the regulators to insist on additional precautions, because plant owners might be reluctant to pay for the new work. That kind of thing has happened repeatedly here in the US. Japanese Industry/Government relationships are reputedly somewhat backwards by the US model.

 

[AntonL]

A strong earthquake with a preliminary magnitude of 7.1 shook buildings in Tokyo and a wide swathe of eastern Japan on Monday, with an advisory for a one-meter tsunami issued after the quake. reuters

It is now downgraded to 6.6 but most interesting it triggered a swarm of nine aftershocks within two hours, a 5.2 only ten minutes later followed four minutes later by a 4.7

Whereas, the 7.1 quake on 7 April had two 4.6 aftershocks about an hour later and the third 7.5 hours later

http://earthquake.usgs.gov/earthquakes/recenteqsww/Maps/10/140_35_eqs.php