Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[joewein]

were levels "Significant" or detectaible ? I can't make out the numbers in that link.

From http://user.ecc.u-tokyo.ac.jp/~cshozu/images/seminar.pdf

Enlarged shots from the PDF attched.

 

[zapperzero]

I'd be more inclined to believe in recriticality if iodine levels exceeded cesium levels again and sampling around the site perimeter spiked, which it hasn't really since the end of March

I apologize for the sloppiness, I meant recriticality then, in the first few days, not now.

 

[tsutsuji]

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110821_01-e.pdf SFP4 desalting facility started at 11:34 AM, August 20.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110820_02-e.pdf this is SARRY line B decontamination factors. [What happened with line A ?]

http://mainichi.jp/select/jiken/news/20110821ddm008040068000c.html With a 25 m³/hour flow, SARRY will achieve removing all the water stored in one of the waste treatment facility's buildings [which one?] in nine days' time.

http://www.asahi.com/special/10005/TKY201108210168.html Two new reverse osmosis equipments have been started at the desalination facility on 21 August. They are increasing the facility's capacity from 50 to 70 tons per hour. It was said that this increase goes together with the decontamination facility's flow increase from 45 to 70 tons per hour permitted by the start of SARRY.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110821/0700_1gouki.html All the thermometers at unit 1 are now below 100°C.

http://www.nikkei.com/news/category...E3E2E3938DE0E3E2EAE0E2E3E39797EAE2E2E2;at=ALL Tepco is planning to switch to an alternative injection method using the reactor spray line at unit 3. The switching procedure will be tested at unit 5 on 22 August. Implementation at unit 3 will ensue later this week.

 

[zapperzero]

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110821_01-e.pdf SFP4 desalting facility started at 11:34 AM, August 20.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110820_02-e.pdf this is SARRY line B decontamination factors. [What happened with line A ?]

http://mainichi.jp/select/jiken/news/20110821ddm008040068000c.html With a 25 m³/hour flow, SARRY will achieve removing all the water stored in one of the waste treatment facility's buildings [which one?] in nine days' time.

http://www.asahi.com/special/10005/TKY201108210168.html Two new reverse osmosis equipments have been started at the desalination facility on 21 August. They are increasing the facility's capacity from 50 to 70 tons per hour. It was said that this increase goes together with the decontamination facility's flow increase from 45 to 70 tons per hour permitted by the start of SARRY.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110821/0700_1gouki.html All the thermometers at unit 1 are now below 100°C.

Some good news for a change. Thank you.

 

[joewein]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110821/0700_1gouki.html All the thermometers at unit 1 are now below 100°C.

Sounds good, but it would have a lot more meaning if we knew

a) that the thermocouples at the bottom of the RPV were still magnetically (?) attached to it and working and

b) if the fuel was known to be inside the RPV and not dripped onto a concrete surface lower down without any thermometers.

I guess Tepco will still consider this "cold shutdown achieved", even if the corium (wherever it is) was still liquid inside.

 

[zapperzero]

Sounds good, but it would have a lot more meaning if we knew

a) that the thermocouples at the bottom of the RPV were still magnetically (?) attached to it and working and

b) if the fuel was known to be inside the RPV and not dripped onto a concrete surface lower down without any thermometers.

I guess Tepco will still consider this "cold shutdown achieved", even if the corium (wherever it is) was still liquid inside.

Maybe we should write a petition for them to try and get images from the RPV already :P

 

[Bodge]

Atmospheric chemists at UC San Diego have analysed anomalous findings of radioactive Sulfur-35 at Scripps California.

Seawater injection into the cores began on http://www.tepco.co.jp/en/press/corp-com/release/11031301-e.html".

Natural Cl-35 in the water gained a neutron and lost a proton to become S-35.

The calculations done by UCSD suggest a powerful neutron flux during the time of seawater cooling.

links http://www.pnas.org/content/early/2011/08/11/1109449108.abstract"

Lead Author Mark Thiemens, Dean of the Division of Physical Sciences at UC San Diego:

"We were able to say how many neutrons were leaking out of that core when it was exposed."

Using a model based on NOAA's observations of atmospheric conditions the team determined the path air took on its way to the pier over the preceding 10 days and found that it led back to Fukushima.

Then they calculated how much radiation must have been released. "You know how much seawater they used, how far neutrons will penetrate into the seawater and the size of the chloride ion. From that you can calculate how many neutrons must have reacted with chlorine to make radioactive sulfur," said Antra Priyadarshi, a post-doctoral researcher in Thiemens' lab and first author of the paper.

After accounting for losses along the way as the sulfate particles fell into the ocean, decayed, or eddied away from the stream of air heading toward California, the researchers calculated that 400 billion neutrons were released per square meter surface of the cooling pools, between March 13, when the seawater pumping operation began, and March 20, 2011.

see http://www.sciencedaily.com/releases/2011/08/110815152027.htm
and http://www.fairewinds.com/content/new-data-supports-previous-fairewinds-analysis-contamination-spreads-japan-and-worldwide Remember the discovery of huge levels of Cl-38 that were found and then later denied?
How about the "13 neutron beams"?
One thing is now CERTAIN - there were significant nuclear excursions long after reactor SCRAM.

This is the sort of detective work that wouldn't be necessary if certain informed/industry sources told us the truth from the start.

 

[NUCENG]

Maybe we should write a petition for them to try and get images from the RPV already :P

As this is a Physics Forum, let's consider that. Do you mean images of the RPV or images in the RPV? Are you talking about a boroscope -type examination through piping or a drywell entry with robots or humans? What are the risks? What are the benefits- what would we learn? Based on what we might learn, what would the Japaneses be able to do differently? Compared to cooling the reactors and containments, cleaning up the site, and building the enclosures what would make this a higher priority that the current road map steps?

I see the emoticon, so perhaps you were not serious, or were trying to point out that joewein is once again tossing out the silver lining of temperatures dropping below 100 degC looking for the dark cloud that is out there someplace?

 

[etudiant]

Atmospheric chemists at UC San Diego have analysed anomalous findings of radioactive Sulfur-35 at Scripps California.



After accounting for losses along the way as the sulfate particles fell into the ocean, decayed, or eddied away from the stream of air heading toward California, the researchers calculated that 400 billion neutrons were released per square meter surface of the cooling pools, between March 13, when the seawater pumping operation began, and March 20, 2011.



Remember the discovery of huge levels of Cl-38 that were found and then later denied?
How about the "13 neutron beams"?
One thing is now CERTAIN - there were significant nuclear excursions long after reactor SCRAM.

This is the sort of detective work that wouldn't be necessary if certain informed/industry sources told us the truth from the start.

Could someone help put these numbers into perspective?
A mole of material, (about 238gm of Uranium), has 6x10**23rd molecules. So a flux of 4x10**11 neutrons/square meter over a week roughly equates to the decay of maybe 2x10**-10 gms of uranium. This does not seem that large. Is this nevertheless inconsistent with normal decay processes in a seriously damaged scrammed reactor?

 

[jim hardy]

Bodge wrote:

"How about the "13 neutron beams"?
One thing is now CERTAIN - there were significant nuclear excursions long after reactor SCRAM."

the 13 "neutron beams" was an unfortunate translation. On another thread we had a contributor from Tokyo who translated the article, 'beam' had meaning closer to 'individual ray' or particle. Word "Beam" in English immediately makes one think of an intense searchlight beam, what they had was way more feeble.
So we took the reports to be from low level indication on the neutron monitors at plant gate, which was later corroborated by logsheets. At first i figured it was somebody walking or driving by in contaminated boots or vehicle, but the times pretty well coincided with venting so i changed my opinion to airborne 'aerosols' from water injection and venting. Of course that's all speculation on my part but it sort of fits with recent find of hotspots at bottom of stack and in vent pipe...

Let's wait and see what other indications show up. From that article,

the researchers calculated that 400 billion neutrons were released per square meter surface of the cooling pools, between March 13, when the seawater pumping operation began, and March 20, 2011

That's an unusual way to describe a neutron flux activation so i wonder if it too lost something in translation into laypeople-speak? 400 billion per square meter is 40 million per sq centimeter if my arithmetic is good,,,,
and only 4E7 n/cm^2 is a low neutron flux even if it came all in one second let alone spread over a whole week. A significant nuclear excursion should produce a million times that in less than a second - perhaps more details will appear.

In my book recriticality is niether proven or disproven yet. That it would be exciting should not colour our analysis.

I do second the motion for photo of RPV's, especially around their upper heads.

Did they ever get vessel level and pressure instruments hooked up on units 2&3 like they did on 1?
[image] http://www.tepco.co.jp/en/news/110311/images/110604_10.jpg [/image]
old jim

 

[Bodge]

...Remember the discovery of huge levels of Cl-38 that were found and then later denied?

http://www.ieer.org/comments/Cause_of_high_Cl-38_Radioactivity20110330.pdf

The author calculated neutron flux from spontanoeus fission of actinides in a core melt and found that it was not enough to explain the high levels of Cl-38.

I know that TEPCO later changed their minds on the detection itself, but it makes you wonder.

 

[Bodge]

If I understand correctly, they are speaking of the number of neutrons that escaped from the surface of the storage pools, which are above the reactor cores.

4E7 n/cm^2 was not the flux, it was what escaped the pools.

That's an unusual way to describe a neutron flux activation so i wonder if it too lost something in translation into laypeople-speak? 400 billion per square meter is 40 million per sq centimeter if my arithmetic is good,,,,
and only 4E7 n/cm^2 is a low neutron flux even if it came all in one second let alone spread over a whole week. A significant nuclear excursion should produce a million times that in less than a second - perhaps more details will appear.

From the paper's abstract: http://www.pnas.org/content/early/2011/08/11/1109449108.abstract

.."we show that nearly 4 × 10^11 neutrons per m2 leaked at the Fukushima nuclear power plant before March 20, 2011."

 

[etudiant]

If I understand correctly, they are speaking of the number of neutrons that escaped from the surface of the storage pools, which are above the reactor cores.

4E7 n/cm^2 was not the flux, it was what escaped the pools.


From the paper's abstract: http://www.pnas.org/content/early/2011/08/11/1109449108.abstract

.."we show that nearly 4 × 10^11 neutrons per m2 leaked at the Fukushima nuclear power plant before March 20, 2011."

It would help if someone versed in these kinds of measurements would interpret these results. The terminology is less than clear.
The element detected was sulfur, formed from the chlorine held in the sea water salt. That transmutation takes place in the water and involves the neutrons from the reactor cores.
That suggests the neutron flux is not measuring the number escaping the pools, as that is a pretty meaningless quantity which has no relevance to the sulfur production recorded. So are they talking about neutron flux per square meter of core area?

 

[Bodge]

Somebody with access to the full article should take a look.

 

[jim hardy]

http://www.ieer.org/comments/Cause_of_high_Cl-38_Radioactivity20110330.pdf

The author calculated neutron flux from spontanoeus fission of actinides in a core melt and found that it was not enough to explain the high levels of Cl-38.

Some of us chased that Cl38 reading on another forum in March. What i remember is this:

If you take Dr Veress's equation for flux from page 5 of that article;
=5.241510/(1−−38)

and plug in his value for (lambda 38) from page 4;
λ38=0.00031021 s-1

and plug in the completely unfounded number of 1 second for irradiation time T

you get the worrisome result of about 1.7E14
which is quite reasonable for neutron flux in the reactor core during a 1 second excursion to 200% reactor power
were there reports of a steam explosion near the date of that measurement (25 March) it'd be a strong indicator of recriticality about that time.

In chasing that one I was told by a radiochemist that because Cl38's spectrum closely resembles some other nuclides it is easy to mis-report its pesence. Myself, I have accepted the official explanation that the Cl38 reading was an error.

Once again, not quite enough info for a layman to conclude anything. Even Dr Veress is not certain.

If you find reports of Cl38 closer to 14 March please post links.
old jim

 

[joewein]

The Swedes built a facility called FILTRA at their Barsebäck two-unit BWR site in the early 1980's. Here's a really thorough and well-written progress report of the project that resulted into a 10 000 m3 gravel bed being built next to the the units. That might be one approach to improve the capacity of old containments; however, it won't remove the problems related to preventing core-concrete interactions if a molten core falls to the bottom of the containment.

EDIT: Photograph of the Barsebäck site, with the FILTRA facility on the foreground.

Tepco seems to say, by contrast, that no filtration beyond the limited scrubbing by venting into the suppression pool water was necessary (http://www.tepco.co.jp/en/news/topics/11081601-e.html"):

Corrections and Clarification of a news report program, "ETV Special" by NHK, broadcasted on August 14

August 16, 2011
Tokyo Electric Power Company
NHK TV program regarding Fukushima Daiichi Nuclear Power Station reported contents that are incorrect and could cause misunderstandings. We hereby provide facts below.
(...)
3. Claim on the PCV ventilation has no filtration
In the program, it was mentioned several times that there were no filters in the primary containment vessel ventilation line. However, boiling water reactors that we operate use "wetwell vent", which has scrubbing effect to mitigate emission of radioactive materials at the comparative level to the filters. That is to say, in principle, our venting procedure uses the water in the suppression chamber as filteration and we have prepared and added the necessary equipment and procedures for accident management measures.

In other words, they claim pool water scrubbing is good as proper filters, no need to spend money on them.

 

[zapperzero]

As this is a Physics Forum, let's consider that. Do you mean images of the RPV or images in the RPV? Are you talking about a boroscope -type examination through piping or a drywell entry with robots or humans? What are the risks? What are the benefits- what would we learn? Based on what we might learn, what would the Japaneses be able to do differently? Compared to cooling the reactors and containments, cleaning up the site, and building the enclosures what would make this a higher priority that the current road map steps?

I see the emoticon, so perhaps you were not serious, or were trying to point out that joewein is once again tossing out the silver lining of temperatures dropping below 100 degC looking for the dark cloud that is out there someplace?

I was not serious in the sense that I do not believe that a petition would do anything.
Other than that, I am quite serious wrt imaging and data collection in general being a very high priority still.

I think the questions that need to be answered are:

1. is there corium in the RPVs? How much? (borescope)
2. is there corium on the drywell floors? How much? If so, is it still attacking the concrete? (robots, and underwater robots at that)
3. is there ongoing criticality in the corium?

Now, a list of what could be done differently, based on what we may learn from an answer to question
1. injection of water to the RPVs could be stopped or massively reduced.
2. an alternative cooling strategy may be possible/desirable. Additional containment measures may be needed.
3. if there is still a reaction going on somewhere, trying to filter the water in the basement is basically a fool's errand, no? Stopping any recriticality should also ease cooling. I took a look at the TEPCO webcam earlier this morning. 1F3 is still making steam.

Now for the risks
- borescope expedition may block up piping that could be useful later
- time, money, specialist equipment, man-hours, health of workers may be expended for no gain

 

[zapperzero]

Tepco seems to say, by contrast, that no filtration beyond the limited scrubbing by venting into the suppression pool water was necessary (http://www.tepco.co.jp/en/news/topics/11081601-e.html"):

In other words, they claim pool water scrubbing is good as proper filters, no need to spend money on them.

Well TEPCO's claim is true - and disingenuous, I believe. Normally, venting is done via the suppression pool. In major emergencies, iirc, venting is performed directly to the atmosphere via something called a hardened vent.

That lost TEPCO precious hours while they were trying to decide if possibly staving off meltdown was worth certainly irradiating the countryside. Frying Naoto Kan, who was coming in via helicopter, may or may not have been an additional concern.

 

[tsutsuji]

Sounds good, but it would have a lot more meaning if we knew

a) that the thermocouples at the bottom of the RPV were still magnetically (?) attached to it and working and

b) if the fuel was known to be inside the RPV and not dripped onto a concrete surface lower down without any thermometers.

I guess Tepco will still consider this "cold shutdown achieved", even if the corium (wherever it is) was still liquid inside.

The Nikkei said some prudent words on this topic on 20 August:

http://www.nikkei.com/news/editoria...E38297EAE2E2E2;n=96948D819A938D96E38D8D8D8D8D Also, it is not exactly known where the melted nuclear fuel fell. If it has fallen down from the reactor pressure vessel, as many experts point out, even if that container's temperature is less than 100 degrees, it is a far cry from saying it is safe.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110823/index.html It was found last month that a company commissioned by Kyushu Electric had entered a wrong data in the earthquake resistance assessment of Genkai NPP unit 3. The NISA then ordered all NPP operators commissioning the same company to check their data. Then Kansai Electric found the same data problem at its Mihama unit 3 and 4 reactors, although they are commissioning a different company. Now the NISA is instructing all NPP operators in Japan to check their data, regardless which company they commissioned. The NISA confesses that it "excessively held the prejudice" that the problem was circumscribed to only one company. This problem might create delays in the "stress tests" nuclear plants in periodic inspection must undergo before restarting.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110823/0445_hoshutsuryo.html The NISA is revising its estimate of the cumulated iodine 131 and cesium 137 radiation released from Fukushima Daiichi between 12 March and 5 April from 63 E16 Bq to 57 E16 Bq. It is based on newly obtained data, such as monitoring post data and air analysis data. The peak is believed to have occurred after the units 2 and 4 explosions, from 1:00 to 5:00 PM on 15 March. As was found in the previous estimate, the peak amounts for 40% of the release. The estimate was made by the Japan Atomic Energy Agency for the NISA.

 

[NUCENG]

It would help if someone versed in these kinds of measurements would interpret these results. The terminology is less than clear.
The element detected was sulfur, formed from the chlorine held in the sea water salt. That transmutation takes place in the water and involves the neutrons from the reactor cores.
That suggests the neutron flux is not measuring the number escaping the pools, as that is a pretty meaningless quantity which has no relevance to the sulfur production recorded. So are they talking about neutron flux per square meter of core area?

O.7 % of the radioactive sulfates from Fukushima reached the pier in San Diego? So why didn't similar percentages of I131, Cs-137, and noble gases, etc. make the same trip? Why is S-35 so efficient?

1501 atoms of S-35 per cubic meter measured in 4 days. Let me assume that they mean a peak of 1501 Bq/m^2 was detected during a 4 day period. And they had never seen a peak at that pier over 950 Bq/m^2 before that. So there is a background level of Cl-35 from activation of Argon in the upper atmosphere in that measurement that needs to be considered. That means a lower Fukushima source number.

Check this out:

http://www.agu.org/pubs/crossref/2011/2011GL047469.shtml

The graph shows 1600 atoms of radioactive sulfer in sulfate per cubic meter in Antarctica in January 2010 with no help from Fukushima. Same authors.

The moving box model used is also interesting. I don't know from the description if it accounts for dispersion and dilution. If their model assumes transport via the jetstream it appears that numbers like 0.7% or a concentration at Fukushima over normal background at a factor of 365, it seems that dispersion and dilution are almost non-existent. Typical US radiological consequences have dispersion factors of 10E-4 of 10E-5 for elevated releases within hundreds of yards and we are talking about 5000 miles. Their previous work with cosmic sourced S-35 was based on a uniform production of S-35 and that is different from a point source like Fukushima.

There data shows a peak they can't ex[plain from their experience. They postulate that it is
caused by Cl-35 (n,p) reactions, but other than the time coincidence I don't see why they rule out cosmic sources. I would like to see if they answer these questions in their full article, but NAS wants to get paid $10 more than my curiosity extends.

I am not ready to say they are wrong or right. Their abstracts are more confusing than informative. Just between you and me, when I see that Arnie Gunderson thinks it supports his theories, I tend to be a little bit skeptical.

 

[alpi]

... Also, it is not exactly known where the melted nuclear fuel fell. If it has fallen down from the reactor pressure vessel, as many experts point out, even if that container's temperature is less than 100 degrees, it is a far cry from saying it is safe.

If the melted fuel (corium) has fallen down from the reactor pressure vessel I think it would be easy/easier to get it covered with water since water naturally flows downwards.

What's the importance of a temperature of less than 100 degrees? Also boiling water has good cooling capacity. Or does the steam escaping from the reactors still contain considerable amounts of volatile substances being radioactive? Has anyone seen any data on the radioactivity of the steams?

 

[joewein]

What's the importance of a temperature of less than 100 degrees? Also boiling water has good cooling capacity.

Cold shutdown is a precondition for being able to open the RPV to remove fuel, which you can't do while there's steam pressure.

This aspect loses some of its significance once the fuel has melted, especially if it has left the accessible RPV, as it becomes quite difficult to remove anyway.

Or does the steam escaping from the reactors still contain considerable amounts of volatile substances being radioactive? Has anyone seen any data on the radioactivity of the steams?

Until the discovery of the 5 Sv/h and 10 Sv/h hotspots in the hardened vent path, the most radioactive spot outside the containments had been a steamy place in unit 1 discovered by a robot, with 4 Sv/h. The steam there seemed to come up from the suppression chamber.

http://search.japantimes.co.jp/cgi-bin/nn20110604x1.html

I think this is one of the reasons behind building reactor covers.

 

[tsutsuji]

http://www.47news.jp/CN/201108/CN2011082201001124.html After 7:00 AM on 22 August, a very high radiation of 3 Sv/hour was found during maintenance work at SARRY, causing to suspend that maintenance work, consisting in replacing parts. The radiation was found during flushing. Then the radiation decreased and the facility was restarted at around 8:15 PM - a 6 hour delay from schedule - without replacing the parts.

http://mainichi.jp/select/wadai/news/20110823k0000e040061000c.html Tepco announced that there is a possibility that during vessel replacement, a valve actuated by the vessel pressure called "float" was dislodged, causing contaminated water to leak into a pipe. It is believed that a cesium concretion was sticking to the pipe. Junichi Matsumoto said that they don't understand why the concretion, believed to be several grams heavy, sticked to the pipe instead of being adsorbed. The alternative injection method using the reactor spray line will be started on 26 August at unit 3 reactor.

http://www.fnn-news.com/news/headlines/articles/CONN00206003.html Tepco said that they will take measures such as closing an exhaust gas valve, in order to prevent the SARRY problem from occurring again.

http://www.bloomberg.co.jp/apps/news?pid=90920019&sid=aJHTUKQD6I50 With 3.47 mSv, no one among the 23 workers exceeded the regulatory 5 mSv limit as a result of the exposure to the 3 Sv/hour source at SARRY. SARRY was restarted at 3:00 PM on 23 August.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110823_02-e.pdf SARRY: "Outline of the location where High Radiation Dose occurred"

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110823_03-e.pdf SARRY float valve diagram explaining the 3 Sv/hour problem and countermeasure.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110823_01-e.pdf Unit 3 alternative cooling method using core spray system.

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110823_04-j.pdf (not yet translated into English) (page 2) At around 12:30 PM 23 August, a tiny leak was found in a SFP4 cooling system primary circuit hose. The cooling system is kept running.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110823_04-e.pdf "Unit 4 Spent Fuel Pool Circulating Cooling System Oozing Water from Flexible Hose"

 

[rowmag]

That suggests the neutron flux is not measuring the number escaping the pools, as that is a pretty meaningless quantity which has no relevance to the sulfur production recorded. So are they talking about neutron flux per square meter of core area?

It would seem so. From the text of their paper:

The attenuation length of neutrons in water at room temperature is 2.8 cm and increases at higher temperatures (21). Because of the high absorption cross-section of ³⁵Cl, seawater has more attenuation. The value of the attenuation length of the neutrons in seawater at temperatures higher than 1,000 °C is not known. For simplicity, the attenuation length was taken to be 2.8 cm. The concentration of ³⁵SO4²⁻ at the source (reactor core) was assumed to be 10 times higher than the model-calculated ³⁵SO4²⁻ concentration in the marine boundary layer. Considering all the possible reactions of neutrons with seawater (3), we estimate that a total of 4 × 10¹¹ neutrons per m² were released before March 20 in which a fraction of 2 × 10⁸ neutrons per m² reacted with ³⁵Cl to make ³⁵S.

They had to make some pretty rough assumptions and approximations throughout, so I would suspect their number could be off by orders of magnitude even if their mechanism is correct.

 

[zapperzero]

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110823_01-e.pdf Unit 3 alternative cooling method using core spray system.

On page 5, this document has a schematic which shows, and I quote "Cooling from bottom of fuel by FDW" which is to be supplemented by "cooling from top of fuel by CS", with a nice pool of water in the bottom head of the RPV! I thought the fuel had melted down?

 

[rmattila]

Well TEPCO's claim is true - and disingenuous, I believe. Normally, venting is done via the suppression pool. In major emergencies, iirc, venting is performed directly to the atmosphere via something called a hardened vent.

In the Swedish/Finnish system, it is possible to hard vent either from the wet or the dry side. The automatic rupture discs are on the dry side (so that they are certainly operable even if the wet well becomes flooded), but the manual ventings are preferably done from the wet side in order to take additional advantage of the scrubbing capacity of the containment (both blowdown through wetwell and containment spraying, if it happens to be available).

The design basis for the scrubbing systems in the Finnish BWR:s was that a complete core meltdown should not lead to more than 100 TBq release of Cs -137, and the danger caused by other isotopes should not be higher than that from Cs-137, and that there would be no electricity for 24 hrs to cool the containment. This translated into requirements for being able to remove 99 % of aerosols and elemental iodine, and the required iodine filtering capacity means that the water in the system can not be pure water but needs certain amounts of NaOH and Na2S2O3. NaOH is added to the containment water as well in a severe accident situation, but it can not be done timely enough to prevent too large iodine release to exceed the requlatory 100 TBq limit for severe accidents.

Regarding the FILTRA gravel filter at Barsebäck, I am not familiar with its design basis.

 

[berkeman]

(Moderator's Note -- Discussion of the Virginia US earthquake and nuclear power plant has been broken off into its own thread.)

 

[LabratSR]

The latest by Dr. Michio Ishikawa - Passage to Core Solidification

http://www.gengikyo.jp/english/shokai/Tohoku_Jishin/article_20110808.html

 

[etudiant]

The latest by Dr. Michio Ishikawa - Passage to Core Solidification

http://www.gengikyo.jp/english/shokai/Tohoku_Jishin/article_20110808.html

The only reason mentioned for a push to get the cores solidified is that it is embarrassing to have an ongoing need to cool the cores for years to come, which serves to remind everyone that the accident is not yet over.

There is plenty of cleanup to be done at that site, enough to keep people very busy even after the cores cool enough to solidify. The cores appear to be in a relatively stable state and on a path to gradually cool down. The cost benefit of any effort to speed up that process does not seem compelling.

 

[rowmag]

The only reason mentioned for a push to get the cores solidified is that it is embarrassing to have an ongoing need to cool the cores for years to come, which serves to remind everyone that the accident is not yet over.

There is plenty of cleanup to be done at that site, enough to keep people very busy even after the cores cool enough to solidify. The cores appear to be in a relatively stable state and on a path to gradually cool down. The cost benefit of any effort to speed up that process does not seem compelling.

Not sure I see this. As long as the cores are liquid, there remains the chance of something happening to cause a new release of radioactive contaminants to the environment. Once they harden, that danger drops significantly. Then you can take your time cleaning up the site.

 

[etudiant]

Not sure I see this. As long as the cores are liquid, there remains the chance of something happening to cause a new release of radioactive contaminants to the environment. Once they harden, that danger drops significantly. Then you can take your time cleaning up the site.

That is certainly true.
However, it is difficult to envisage a method that might cool the core enough to allow it to solidify which does not pose even greater risk. One way to solidify the core is to extract it and spread it, so the heat can dissipate away from the core material. That seems nightmarish difficult at best. Certainly it has never been done before.
Alternatively, it may be possible to try to dilute the core with enough inert material to get a similar effect, but as the cores are still producing some megawatts of heat, cooling will still be needed. It may simply create a bigger lump of near molten stuff. That too has not been done before.
In this case, the best is very much the enemy of the good. If the cores have not left the RPVs yet, which is afaik the implication of the continuing temperature readings from the bottom of the RPVs, the disaster is still somewhat contained. Sustained cooling seems a safer bet than trying some pioneering fix that may make things worse.

 

[alpi]

Ishikawa says here http://www.gengikyo.jp/english/shokai/Tohoku_Jishin/article_20110413.htm that the melted cores likely have crusts of "around 20-30 centimeters" which seems believable. I think there shouldn't be much difference between a completely solid core and a core with a thick crust.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110823/index.html The investigation panel made a press conference, saying they have auditioned 126 people for 300 hours, including plant manager Yoshida who was auditioned 4 times for a total of 19 hours and that they all answered with accuracy. The panel has its third meeting on 27 September and plans to issue an interim report within this year.

 

[zapperzero]

Ishikawa says here http://www.gengikyo.jp/english/shokai/Tohoku_Jishin/article_20110413.htm that the melted cores likely have crusts of "around 20-30 centimeters" which seems believable. I think there shouldn't be much difference between a completely solid core and a core with a thick crust.

The cited article is dated April 11. In view of later announcements of possible melt-throughs, it is of limited relevance.

EDIT: Upon further reading, I found this gem:

It may be time to consider allowing evacuees, who are living a life of inconvenience and hardship, to go home.

That's about it for this person's credibility, as far as I am concerned.

 

[marsupio]

@etudiant

hi and agree with your philosophy of troubleshoot. But first point, I (we ?) thunk that tragedy as Cernobyl or Fukushima will never come again.
Second point, Cernobyl learned us to have the better as possible information to act in the best way.

All this to exprim a point of view : test pionneer issue on a very little part of meltdown. For the future.

My advice. I let the professinnal of the topic discuss about boxite properties as unmagnetic.

My best regards