Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[etudiant]

I haven't followed this thread for more than a year now and am curious if a clearer/consensus picture has emerged about the accident.What is the status of units 5&6?

Hi I_P,
You pose good questions without good answers.
Afaik, none of your questions has been clearly addressed, much less answered, in any of the official studies. Indeed, if it were not for the sterling work done by Tsutsuji-san on this site and by the nameless author of the EX-SKF web site, there would be no new information on Fukushima
in the English speaking world.
I believe that that is how the Japanese government, which effectively controls TEPCO since the bailout, prefers to handle matters. It is clear that lots is getting done at Fukushima and money is not really an obstacle, as the documents Tsutsuji-san has found and posted show. It is also clear that there is little interest in answers to your questions. It does not matter to Japan Inc. how these reactors failed in a once in a thousand years situation, as the export business of Japanese reactor know how has resumed. The public focus now is on cleaning up the site, an effort which appears to have all the earmarks of a perpetual project, where billions are spent doing nothing especially useful, much like Hanford in the US.

Units 5 and 6 are in long term standby. I believe they could be returned to service in very short order, as they were undamaged by the tsunami, but the Abe government has not had the will to allow their restart.

 

[nikkkom]

I haven't followed this thread for more than a year now and am curious if a clearer/consensus picture has emerged about the accident.

Is it understood how/why the explosion occurred in unit 4? Was it hydrogen migration through venting systems from unit 3?

Yes, it was hydrogen.

Is it understood how much damage occurred before the tsunami? Were safety systems still functional? or were the plants already doomed? (perhaps this still cannot be answered with available information)

There are no indications that serious damage occurred prior to tsunami. (If it did, then TEPCO so far managed to hide that evidence).

Did TEPCO succeed in performing physical/visual inspections of reactors 1,2,&3 to determine the state of the respective cores?

No. Even PCVs aren't satisfactorily inspected yet.

What is the status of units 5&6?

Technically they are fine. It will be politically difficult to allow their restart.

 

[I_P]

Thanks etudiant and nikkkom, I have had a chance to browse the last 50 pages or so and have a better sense of the state of things. Seems that the consensus is that the Unit 4 SFP was never a problem so by default the assumption is that the explosion in that unit was fueled by hydrogen from Unit 3 via the shared vent stack plumbing.

I also noted some discussion suggesting that the elevated radiation levels between March 21st and 23rd were possibly associated with reactor core melting through the pressure vessel - maybe in Unit 3?

http://http://www.ltrr.arizona.edu/~cbaisan/BBTRB/Ibaraki_rad.jpg

{tried to embed an image here - maybe over a size limit...}

 

[zapperzero]

There are no indications that serious damage occurred prior to tsunami. (If it did, then TEPCO so far managed to hide that evidence).

This is not true. There are reports of significant radioactive release(s) before the tsunami.

 

[zapperzero]

Seems that the consensus is that the Unit 4 SFP was never a problem

I'm not part of that consensus. Water is supposed to be self shielding and so only gamma radiolysis yields are taken into account; no-one has seriously addressed the possibility of localized boiling on the surface of fuel elements which would have increased H2 production as lots of beta radiolysis would also take place.

 

[I_P]

This paper discusses remelting of the core material following water injection: Analyses of core melt and re-melt in the Fukushima Daiichi nuclear reactors by Fumiya Tanabe, Journal of Nuclear Science and Technology
Volume 49, No. 1, January (2012) pp. 18–36. Has there been modeling of the radioactive releases based on this scenario?

zapperzero - understood. Did they succeed in moving more than the two unused elements from the pool? (I should go back and read Tsutsuji's latest update)

 

[I_P]

managed a double post. Many aspects will likely remain forever murky/unresolved I am sure.

 

[turi]

Did they succeed in moving more than the two unused elements from the pool? (I should go back and read Tsutsuji's latest update)

No, they didn't plan to. They've just finished building the steel frame for fuel removal:
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_130529_08-e.pdf
Now they will have to install machinery for fuel removel.

 

[zapperzero]

This paper discusses remelting of the core material following water injection: Analyses of core melt and re-melt in the Fukushima Daiichi nuclear reactors by Fumiya Tanabe, Journal of Nuclear Science and Technology
Volume 49, No. 1, January (2012) pp. 18–36. Has there been modeling of the radioactive releases based on this scenario?)

http://www.tandfonline.com/doi/full/10.1080/18811248.2011.636537#.UahvrJxaeEo

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130530/0510_kiseicho.html The NRA is starting an inspection on 30 May to investigate accident causes. They will go to unit 1 and check the circumstances of a water leak that had been reported by an employee before the tsunami struck, and whose cause remains unknown. Because of radiations, the inspection on unit 1's 4th floor, to be performed by 5 Nuclear Regulation Agency employees on 31 May will be limited to about 10 minutes. On May 1st they held their first meeting and discussed the possibility that earthquake damage took place in a unit 1 cooling system. The purpose of the inspection is to check the validity of the explanation that water from the pool flowed into the air conditioning system, by looking for equipment damage. The second meeting will be held in the beginning of June.http://www3.nhk.or.jp/nhkworld/english/news/20130530_40.html Frozen wall mooted to stop Fukushima groundwater

Panel members made the proposal at a meeting on Thursday. They have discussed new measures against groundwater since April when leaks were found in underground storage pools for contaminated water.

The panel urged plant operator Tokyo Electric Power Company to freeze the ground around the buildings of 4 reactors in order to create a shielding wall.

Panel members said TEPCO should implement the measure by the middle of fiscal 2015.

Members also urged TEPCO to pump up groundwater from surrounding wells and release it into the ocean.

The measures are aimed at gradually reducing the flow of groundwater and stopping it within 8 years.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130530/0510_kiseicho.html But the fishermen are resisting groundwater releases into the Ocean, so that there is no prospect of starting those releases.

 

[tsutsuji]

Contaminated water treatment countermeasure committee, 3rd meeting, 30 May 2013 ( http://www.meti.go.jp/earthquake/nuclear/20130531_01.html )

http://www.meti.go.jp/earthquake/nuclear/pdf/130531/130531_01a.pdf Agenda
http://www.meti.go.jp/earthquake/nuclear/pdf/130531/130531_01b.pdf Participants
http://www.meti.go.jp/earthquake/nuclear/pdf/130531/130531_01c.pdf Countermeasures to refrain groundwater inflow
http://www.meti.go.jp/earthquake/nuclear/pdf/130531/130531_01d.pdf Views on the Contaminated water treatment countermeasure committee's report (by the NRA)
http://www.meti.go.jp/earthquake/nuclear/pdf/130531/130531_01e.pdf Reference

 

[tsutsuji]

Fukushima Daiichi accident analysis study group 1st meeting, 1 May 2013 ( http://www.nsr.go.jp/committee/yuushikisya/jiko_bunseki/20130501.html )

http://www.nsr.go.jp/committee/yuushikisya/jiko_bunseki/data/0001_99.pdf Agenda
http://www.nsr.go.jp/committee/yuushikisya/jiko_bunseki/data/0001_01.pdf About the study group
http://www.nsr.go.jp/committee/yuushikisya/jiko_bunseki/data/0001_02.pdf Future progression method for Fukushima Daiichi accident analysis (draft)
http://www.nsr.go.jp/committee/yuushikisya/jiko_bunseki/data/0001_03.pdf List of problems needing to be studied as raised by each accident investigation report, etc.
http://www.nsr.go.jp/committee/yuushikisya/jiko_bunseki/data/0001_04.pdf Unit 1 reactor building water outflow
http://www.nsr.go.jp/committee/yuushikisya/jiko_bunseki/data/0001_05.pdf Hydrogen source of unit 4 hydrogen explosion

http://www.tepco.co.jp/tepconews/library/movie-01j.html?bcpid=45149870002&bclid=347241149002&bctid=445953600002 Video taken on 28 March 2013 on unit 1's 4th floor (Tepco website)

 

[tsutsuji]

Fukushima Daiichi accident analysis study group 1st meeting, 1 May 2013
http://www.nsr.go.jp/committee/yuushikisya/jiko_bunseki/data/0001_04.pdf Unit 1 reactor building water outflow

Page 4 quotes the Diet investigation report, 2-2-4 b), whose English translation is available at: http://warp.da.ndl.go.jp/info:ndljp...nt/uploads/2012/08/NAIIC_Eng_Chapter2_web.pdf page 81/97

b. The cause of the gushing water has yet to be identified

On the fifth floor, the very top of the spent fuel pool was exposed. There is a possibility that the origin of the gushing water was overflow from the spent fuel pool. It is estimated that the pool water was shaken strongly by the earthquake (causing sloshing) and overflowed onto the floor, spilling to the fourth floor.[157] It is possible that the water spilled from the fifth floor to the fourth floor through the opening in the floor, but this contradicts with B’s narrative. He stated that he was standing almost right below the opening and that the water that came gushing through was from his right.

As there are many ventilation openings at the top of the wall of the spent fuel pool, it is possible that the water overflowed into the ventilation openings to the exhaust duct and to the fourth floor.

As stated in 2.2.4 2, the issue of whether the IC piping was damaged by the earthquake movement has been raised numerous times. There is a complex IC piping system on the fourth floor of the nuclear reactor building where the gushing water was witnessed, and part of it extends close to the spot. Thus NAIIC informed TEPCO that, in spite of the risk of being exposed to a certain level of radiation, NAIIC wanted to conduct an on-site inspection of the fourth floor (TEPCO was not told the purpose of the inspection).

Entering the reactor building for inspection is incredibly dangerous, as the interior of the building is pitch dark even in daytime due to the lack of lighting, wreckage from the hydrogen explosion is everywhere, and there are large openings for moving equipment in each floor. TEPCO informed NAIIC that, because accompanying NAIIC members into the building would subject their workers to unnecessary radiation exposure, TEPCO personnel would not enter the building. After much consideration, NAIIC gave up on the idea of investigating the interior of the nuclear reactor building.

So at this point, the only conclusion that NAIIC can come to is that immediately after the earthquake, there was a gush of water near the southern wall of the fourth floor of the nuclear reactor building of Unit 1 that TEPCO and NISA need to thoroughly investigate.

TEPCO must have been aware that there were subcontracted workers working there at the time of the earthquake, and the TEPCO Fukushima Nuclear Accidents Investigation Committee should have immediately interviewed the workers.[158] But workers A and B stated that they had not been interviewed by TEPCO prior to NAIIC’s interview with them about gushing water.[159]

 

[I_P]

Thanks zapperzero, I had read through the paper but not focused on their look at the radiation releases. I tried to post a jpg above of a set of monitoring data from 3/15-3/24 but it doesn't load up - about 5mb in size. More specifically, I was interested in whether the core re-melt scenario would change the overall estimates of radioactive releases that were done following the accident.

Tsutsuji, thanks for your posts. I am interested in a rough translation of "hydrogen source of unit 4 explosion" and "List of problems needing to be studied as raised by each accident investigation report, etc." if you find the time.

 

[tsutsuji]

I am interested in a rough translation of "hydrogen source of unit 4 explosion" and "List of problems needing to be studied as raised by each accident investigation report, etc." if you find the time.

First of all, I translate the first page of "List of problems needing to be studied as raised by each accident investigation report, etc.". The table on the following pages provides relevant excerpts or summarizes the Diet investigation report (middle column) and Cabinet investigation report (right column).

http://www.nsr.go.jp/committee/yuushikisya/jiko_bunseki/data/0001_03.pdf page 1/16

A) Possibility of earthquake-caused equipment/machinery and piping damage

(1) Possibility of LOCA (except IC piping)
Possibility of small scale LOCA through minute piping cracks
Possibility that unit 1 SR valve did not function

(2) Possibility of IC piping damage
Water outflow inside unit 1 reactor building
Possibility that it was not the noise from the IC
Cause of IC manual shutdown

(3) Possibility of unit 1 DG A damage
Unit 1 system A diesel generator shutdown timing

(4) Earthquake response analysis problem caused by measurement recording
Variations of the plant premises geological characteristics along the north-south direction
The fact that onsite surveys were performed considering that unit 5 is the representative unit
Existence or absence of reinforcement works to enhance earthquake resistance

B) PCV pressure rise

(5) PCV pressure rise
Possibility of earthquake-caused pipe damage and small scale LOCA

(6) Sloshing-caused PCV pressure rise
Possibility of downcomer exposure caused by the shaking of the suppression chamber water surface

C) Hydrogen explosions

(7) Assessment of core-concrete interaction consequences
Possibility of unit 1 core-concrete interaction
Possibility of unit 3 core-concrete interaction

(8) Hydrogen source of unit 4 hydrogen explosion
Hydrogen quantity generated by unit 3 backflow
Hydrogen quantity generated at unit 4 SFP

(9) Hydrogen explosion ignition factors
Possibility of metallic friction, electric fault, etc.

D) Units 1,2,3 machinery and equipment damage

(10) Unit 1 IC loss of function
Valve open/closed status

(11) Unit 2 suppression chamber pressure gauge breakdown
Possibility of PCV damage
Possibility of electric system trouble

(12) Unit 3 RCIC shutdown
Possibility of steam stop valve mechanical component trouble

E) Other

(13) Possibility of unit 3 recriticality
Cause of the hydrogen generation that was confirmed after the hydrogen explosion

(14) PCV damage caused by hydraulic dynamic load
Possibility of damage caused by localized dynamic load generated together with suppression chamber steam releases, etc.

(15) RPV damage locations after tsunami

(16) PCV damage locations after tsunami

 

[nikkkom]

This is not true. There are reports of significant radioactive release(s) before the tsunami.

Define "significant".

 

[nikkkom]

I'm not part of that consensus. Water is supposed to be self shielding and so only gamma radiolysis yields are taken into account; no-one has seriously addressed the possibility of localized boiling on the surface of fuel elements which would have increased H2 production as lots of beta radiolysis would also take place.

Betas do not penetrate fuel cladding.

 

[zapperzero]

Betas do not penetrate fuel cladding.

So, in your considered opinion spent fuel rods do not give off beta?

 

[nikkkom]

So, in your considered opinion spent fuel rods do not give off beta?

Spent fuel rods certainly emit beta particles.
Even my desk emits beta particles.
I probably need to run away in terror?

 

[zapperzero]

Spent fuel rods certainly emit beta particles.
Even my desk emits beta particles.
I probably need to run away in terror?

You probably need to educate yourself a bit (just how many beta particles? what yields?) and maybe just maybe consider a change of tonality. This one is rather grating.

 

[I_P]

Thanks for that translation Tustsuji, I hope they make some progress with their inquiry and are able to resolve some of those outstanding questions - or at least shed some additional light.

Regarding the earthquake damage - I recall reading that there were radiation alarms set off before the tsunami arrived and as the "remaining questions" list shows the state of the cooling apparatus immediately following the earthquake remains in doubt.

Clearly also there are unresolved issues about the source of hydrogen that fueled the explosion at unit 4.

 

[I_P]

dbl post again - must remember to explicitly log in before trying to post a reply. Any help on guidelines/tips for posting images to the thread would be appreciated.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130604/0445_chikasui.html Heeding to a remark by a Nuclear Regulaton Agency officer, Tepco performed a more precise measurement of the groundwater intended for release into the sea. In the past, Tepco said that the cesium 137 concentration was lower than the detection threshold. Now Tepco is providing a measurement of 0.39 Bq/l . This is lower than Tepco's internal standard of 1 Bq/l and lower than the legal requirement of 90 Bq/l. There is no prospect of starting the releases as the local fishermen have been resisting. Tepco said "we are going to politely explain to the local inhabitants that this is lower than our internal standard".

Any help on guidelines/tips for posting images to the thread would be appreciated.

What do you want to know ? If the picture is on your computer, you may use the "manage attachments" button below the edit box. If the picture is online you may type the image URL and insert it between [ I M G] [/ I M G] tags (or click on the icon above the edit box).

 

[I_P]

This is the image I tried to post on the previous page showing the spike in emissions after march 20th:

 

[I_P]

"manage attachments" worked. I tried the url and [ I M G ] tags last time and it didn't seem to work for me. Thank you Tsutsuji

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130530/0510_kiseicho.html The NRA is starting an inspection on 30 May to investigate accident causes. They will go to unit 1 and check the circumstances of a water leak that had been reported by an employee before the tsunami struck, and whose cause remains unknown. Because of radiations, the inspection on unit 1's 4th floor, to be performed by 5 Nuclear Regulation Agency employees on 31 May will be limited to about 10 minutes. On May 1st they held their first meeting and discussed the possibility that earthquake damage took place in a unit 1 cooling system. The purpose of the inspection is to check the validity of the explanation that water from the pool flowed into the air conditioning system, by looking for equipment damage. The second meeting will be held in the beginning of June.

http://www.asahi.com/national/update/0605/TKY201306040838.html The NRA released two pictures of the inspection on unit 1's 4th floor.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130605/1010_koukai.html They took hundreds of pictures and a 40 minute long video. Maximum exposure was 4.8 mSv. Results of this inspection will be announced at the second study group meeting.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130605/1010_koukai.html A patrol found a leak from an above-ground tank at 00:15 PM today. The rate was about one drop every 3 or 4 seconds. The leak was stopped about 4 hours later as a result of tightening bolts and transferring part of the water to another tank. The total amount is about 1 l.

http://www.tepco.co.jp/nu/fukushima-np/handouts/2013/images/handouts_130605_08-j.pdf Leakage from flange of G6 area tank (cylindrical metallic tank)

 

[turi]

The NRA released two pictures of the inspection on unit 1's 4th floor. [...]They took hundreds of pictures and a 40 minute long video. Maximum exposure was 4.8 mSv. Results of this inspection will be announced at the second study group meeting.

Wooo. Yet another visit and video of unit one's 4th floor. I still don't know what they were looking for during the last two visits but I find them fascinating.

 

[a.ua.]

During the May inspection, the investigators were able to remain on the fourth floor of the building--where the condensers were installed--for only 15 minutes due to high levels of radiation, which were measured at 20-30 millisieverts per hour.
http://ajw.asahi.com/article/0311disaster/fukushima/AJ201306050085

What can you learn in 15 minutes.?

Sorry, but this is ridiculous.
No one checked the availability of water in the tanks themselves, checked only tool the water.

In addition, it is clear that the valve (outside) need to be opened by hand, very quickly.
03.11.2011. Just 1.5 hours was in stock.
then on top of the reactor accumulated non-condensable gases and end all.
the condenser air pocket, it does not work....
.

 

[I_P]

What can you learn in 15 minutes.?

Sorry, but this is ridiculous.

I think the idea was to photograph and record video of relevant areas and to analyze the pictures after the fact. They had specific questions so the photography should have been well targeted.

We will see what they come up with.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130619/1300_kenshutsu.html Tritium and strontium were found above the legal levels set for sea releases, in measurement wells on the sea side of unit 2. Tepco says the cause could be the April 2011 high radioactive water leaks. Tepco will reinforce the sea bank so that the water doesn't pour into the sea, and dig additional monitoring wells.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130619/index.html nearby seawater radiation levels are stable.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130619/1920_okure.html The disclosure of this well contamination problem has been two weeks late, as Tepco was aware of it as soon as 31 May 2013. However the Tepco headquarters in Tokyo learned about it only on 11 June. The time taken to reach the management and to wait for the strontium analysis results (strontium analysis requires time) resulted in the disclosure on 19 June.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20130619/1920_moushiire.html Fukushima prefecture sent a formal request to Tepco to analyse the cause and prevent sea release.

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_130619_03-e.pdf Results of Groundwater Quality Survey at the East Side of the Turbine Building at Fukushima Daiichi NPS