Japan Earthquake: nuclear plants Fukushima part 2

[mheslep]

still very radioactive

I wonder what qualifies as very radioactive in the context of units 1 or 2 and Tesco analysis.

 

[Bandit127]

I don't know what quantifies as "very radioactive" but it surveyed at 10 Sv/h after the accident so it probably still qualifies.

 

[Rive]

Also, those mobile rad-shields on the photos are surely not for just show...

 

[Sotan]

Hm... I checked again and to be honest I must say I inserted the word "very" without it being needed. So easy to get carried away. My apologies, the text doesn't really say "very". A more careful translation would be "the air radiation dose in the area is still high and hinders investigations". As for the radioactivity of the water - if there is any water in the pit - they don't really know anything, but they seem to be making careful preparations for its transfer if they find it there.
Page numbered 3 in the first link gives a few readings of the atmospheric radiation dose in that area at the basis of the smoke stack, most recently in October 2015; highest is 12 mSv/h, measured at 1.2m height.
As Bandit127 mentioned, in other spots, especially in the immediate vicinity of some pipes designated as "SGTS", they measured more than 10 Sv/h in August 2011 and still 2 Sv/h in October 2015. (http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_151026_04-j.pdf - page 16)
This time, the workers operating the remote controlled machines will be using a room located at the basis of the stack, in which the radioactivity is much lower (0.04 mSv/h).

 

[Sotan]

Fukushima nuclear plant prepares for typhoon (NHK news)
http://www3.nhk.or.jp/nhkworld/en/news/20160829_22/

 

[Sotan]

Remember the X-6 penetration to which access is needed for an internal investigation of Unit 2 PCV, but proved difficult to decontaminate to an acceptable level until now?
On Aug 26 this report was published (in Japanese) as part of a new "mid- and long-term roadmap" update:
http://www.tepco.co.jp/nu/fukushima-np/roadmap/images1/images2/d160825_08-j.pdf

Just a few points I picked from it:

-Decontamination work at the entrance of X-6 started in October 2015. They washed and vacuumed and scraped the floor and walls in the area, but the measurements on the floor still indicated values as high as 8 Sv/h (in January). Even if they were to use some form of shielding, it was assumed that doses in the air in the work area would not fall below 100 mSv/h.

- They would like to attain a value of 20 mSv in the air, behind shield - a value considered low enough to allow a worker to spend 5 minutes in there.

- Page 4: initially they were thinking of installing a simple shield based mainly on a 90 mm thick, simple square lead plate. This is called Case 1. As an alternative, they now came up with a more complicated shield design, with multiple lead plates arranged as a container and aiming to provide better blocking of radiation. This is Case 2. These two designs have been analyzed to see what results they can provide.

- Page 5 shows the results of the simulation for Case 1 shielding; the conclusion is "not good enough".

- Page 6 shows that Case 2 shielding could give the desired effect; the higher remaining values (17.3 and 13.2 mSv/h) are due to the poorer shielding in areas that will be occupied by various devices to be used effectively in the later investigation, devices which have less shielding power.
So they are now trying to design and construct that complicated shielding structure, which poses a weight problem (they can only move a 2t weight at a time in the area), so most likely the "shielding container" will have to be made of two separate parts.The advantage is that it can be installed by remote controlled machinery and it can achieve the desired degree of shielding without requiring further decontamination work, which has been a big pain and unsuccessful until now.

- From this report I (think I) learned somethign about the various radioactivity measurement results that appear in Tepco reports. If you look at page 3, you see the highest value given for the floor is 278 mSv/h. On the other hand, Page 10 shows some radioactivity values, measured in June this year, which are rather in the Sv range (exceeding the device maximum scale of 10 Sv in one spot); these are actually measures in June this year. Page 13 explain the mystery: the "lower" values reported on page 3 are measured using a device equiped with a lead "colimator" which has a reduction factor of 1/500... I did then try to read a little about radiation detection and measurement, but it's such a complex subject. Two conclusions I draw, 1) numbers are not everything, their meaning & the method behind them must be well understood, and 2) as you see it is very likely that I make mistakes every so often in my posts, so... I kind of rely on you to correct them when needed.

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images2/handouts_160905_05-j.pdf
One-page follow up regarding the sump pit located at the bottom of the smoke stack of Unit 1-2.
They made an opening in the concrete walls of the pit.
This is a photo/screenshot of the inside, but it doesn't say much... to me at least.
Just the photo and two arrows, one pointing at a pump, one at some "absorbing sheet".

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images2/handouts_160909_04-j.pdf
(in Japanese)
They measured the water level in the drain sump pit at the foot of the smoke stack of Units 1/2.
Water level is at ~60 cm.
As mentioned before, the internal dimensions of the sump pit are about 1m x 1m x 1m.

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images2/handouts_160913_01-j.pdf
(in Japanese)
They removed the first piece of the side walls of the cover of Unit 1 Reactor Building. A few small photos are included.

Based on other reports in the media, the cover walls dismantling will continue until late November. Removing the debris from the operating floor will follow, and if all goes well, they will start to remove the spent fuel from Unit 1 SFP sometime in 2020.

 

[Sotan]

Update of the last post above (too late to edit, it seems):
- Nice little video of the panel removal operation available here:
http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=hz09ww85&catid=61699

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images2/handouts_161007_04-j.pdf
(in Japanese)

One page report about Tepco finishing the removal of the top panels of the walls of the cover of Unit 2 building.
It's just the announcement and 4 photos taken from a distance.
The operation ended without any dust-related problems.

The much larger versions of the photos and a 68 Mb video can be found here:
http://photo.tepco.co.jp/date/2016/201610-j/161007-01j.html

 

[etudiant]

Thank you, Sotan, for these updates.
They show that serious work is continuing in Japan, even though it no longer generates headlines in the foreign press.
Removing spent fuel from these reactors SFPs will be challenging, as these structures have experienced serious explosions and contamination. So the 2020 date probably reflects the need to fabricate some support facilities that neutralize those risks. Japan is certainly breaking new ground here and presumably after a few more years the fuel pools at reactors 2 and 3 will also be emptied. Going beyond that to recover the corium looks to be much more challenging.

 

[turi]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images2/handouts_161007_04-j.pdf
(in Japanese)

One page report about Tepco finishing the removal of the top panels of the walls of the cover of Unit 2 building.
[...]

Thank you. But is this really about Unit 2? My almost inexistent Japanese only decripts references to Unit 1.

 

[Sotan]

Of course you're right, turi.
No idea what made me type Unit "2" there
My apologies and thanks for pointing it out.

 

[Sotan]

Tepco is cautiously moving towards reducing the amount of water poured into the damaged reactors:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images2/handouts_161019_07-j.pdf
(in Japanese)

Page numbered 2: while at present they are pouring 4.5 m3/h in each reactor, calculations based on the decay heat made around August this year show that 1.4 to 1.8 m3/h should be sufficient.

Page 3: for starters they will gradually cut at most 1.5 m3/h for each reactor (interestingly, such cuts aren't that easy to make and it's not easy to go straight to 2m3/h, for example, as there are various limitations regarding to equipment such as valves and alarm signals etc; this is why they feel they still need to pour 3 m3/h, for now.).

Page 4: they will keep a close eye on the plant parameters, to see the effect of the reduced water injection. They want to keep the temperature in the lower side of RPV and in the PCV under 65 Celsius; they want to check every hour the amount of water actually going in; they will even pay attention to the dust monitors.

Page 5 shows a flowchart they will use in the transition phase. The water flow will be cut in 0.5 m3/h increments and will reverse to the previous value in case that negative changes are observed. The whole transition period, until things settle, might take about a week.

Page 6 shows the expected changes brought about by reducing the water input to 3 m3/h, in view of the time allowance they have in case water flow is stopped.
Reactor 1 RPV bottom is now at 28 degrees Celsius and would take 8.4 hours to reach the limit value of 80 degrees Celsius if water cooling stopped completely. Reactor 2: now at 33 degrees Celsius, would take 8.3h to reach 80 degrees Celsius. Reactor 3: now at 31 degrees Celsius, would take 8.9h to reach 80 degrees Celsius. These are the values at present; if the water flow was cut to 3 m3/h it is presumed that the RPV bottom temperatures would rise by 7-8 degrees Celsius (theoretically; practically it might be a bit less), and if water flow stopped they would have 7.2, 6.9 and 7.3 hours until the RPV would reach 80 degrees Celsius.

Page 8: past data showing how Reactor 1 responded to the change in water flow. A rise in temperature is observed only about 10 hours after the water flow reduction, and it took about 5 days from the manoeuver till the temperatures got stable again (new value, higher by about 8 degrees Celsius).

Page 9: in case of Reactor 2, the effect of reducing the water flow was almost immediate, and stability was reached again after about 4 days, about 10 degrees Celsius higher.

Page 10: in case of Reactor 3, it took about 12 hours to notice a rise in temperature after reducing the water flow, and new temperature stability (about 4 degrees Celsius higher) was reached after about 7 days.

 

[Sotan]

One-page report on Units 1-2 smoke stack inspection using drones
http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images2/handouts_161020_03-j.pdf
(in Japanese)
Today they used a drone to inspect the inside of the stack, only to find a beam or some other kind of construction material stuck inside at 10-20m from the top of the stack. So they gave up the inspection of the interior and will use data - images and radiation measurements - obtained during the exterior inspection (finished earlier) to assess the state of the stack.

 

[Sotan]

Tepco finished removing the wall panels of the cover building of Unit 1.
Several photos and a movie can be seen here:
http://photo.tepco.co.jp/date/2016/201611-j/161110-01j.html

 

[SteveElbows]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images2/handouts_160909_04-j.pdf
(in Japanese)
They measured the water level in the drain sump pit at the foot of the smoke stack of Units 1/2.
Water level is at ~60 cm.
As mentioned before, the internal dimensions of the sump pit are about 1m x 1m x 1m.

The following english pdf has radiation measurements of the water. Since years have gone by since I learned something about how to interpret the scale of such readings, and I've gone really rusty on this front in the meantime, would anybody be so kind as to say something about these numbers and their implication? Many thanks.

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2016/images/handouts_160913_02-e.pdf

Gross beta: 6.0x10⁷Bq/L
Cs-134: 8.3x10⁶Bq/L
Cs-137: 5.2x10⁷Bq/L

 

[Rive]

The following english pdf has radiation measurements of the water. Since years have gone by since I learned something about how to interpret the scale of such readings, and I've gone really rusty on this front in the meantime, would anybody be so kind as to say something about these numbers and their implication? Many thanks.

Way higher than it was for the water in the turbine building basements right after the accident.
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110327e15.pdf
Quite serious stuff, even if there is just a small amount of it.
However, I think this concentration implies that there was no leak.

 

[nikkkom]

What are they waiting for with this water? Why not pump it into a metal box, add some cement powder and make it a solid?

 

[etudiant]

Surprised there is so much Cs-134.
I'd thought that given its 2 year half life, it would be a fraction of 1% of the Cs-137 concentration. So what is generating the extra Cs-134?

 

[Rive]

The report linked above states, there was ~ equal amount of Cs-134 and 137 around in the water at the time of the accident.
68 months: 2.8 times the half time of CS-134 passed, so ~ 1/7 part of the original amount remained.
That ~ fits with the numbers I think.
I hope I did the math correctly...

 

[etudiant]

The report linked above states, there was ~ equal amount of Cs-134 and 137 around in the water at the time of the accident.
68 months: 2.8 times the half time of CS-134 passed, so ~ 1/7 part of the original amount remained.
That ~ fits with the numbers I think.
I hope I did the math correctly...

Thank you, that explains things nicely.

 

[Sotan]

The most recent "monthly progress report" translated in English has been posted on the METI site on October 27.
I am a little late but maybe some of you haven't seen it.
http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20161027_e.pdf

Also, the IRID site has several relatively new reports on topics such as "laser gouging technology for fuel debris", "concrete injection technology for repairing water leaks in the PCV", "full scale mock-up facility to simulate the lower part of the PCV".
http://irid.or.jp/en/topics/

 

[LabratSR]

Earthquake reported off Fukushima

http://geofon.gfz-potsdam.de/eqinfo/event.php?from=rss&id=gfz2016wxkb

Tsunami Warning Issued

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

 

[elektrownik]

Cooling stopped in Fukushima Daini reactor 3 after earthquake.

 

[LabratSR]

Tsunami warning issued after quake off Fukushima in Japan

http://hosted.ap.org/dynamic/stories/J/JAPAN_EARTHQUAKE?SITE=AP&SECTION=HOME&TEMPLATE=DEFAULT&CTIME=2016-11-21-16-20-38

 

[elektrownik]

SFP in unit 3 also lost cooling but they say that there is enough water to cool SFP.
(This is from NHK English Live stream)

 

[etudiant]

Surely the fuel in SFP 3 is decayed enough by now that the water does not need much cooling.
If power is restored before year end, I'd think there would not be a serious problem, but it would be better to hear from someone expert.

 

[Sotan]

From what I just heard from FNN (Japanese TV station), the cooling stopped at Unit 3 SFP in Fukushima Daini plant (not in the damaged Daiichi).
A safety device signalled that the water level is too low, therefore the cooling system stopped. But they presume it was only the sloshing caused by the earthquake. The temperature of the water rose by about 0.8 degrees Celsius (to a maximum of almost 30 degrees) before cooling resumed, so no danger there.

A tsunami of about 1m height has reached the shores in the area of the Fukushima nuclear plants, but didn't cause any additional issues.

Edit: more detailed report here:
http://kyodonews.net/news/2016/11/22/89417

 

[etudiant]

From what I just heard from FNN (Japanese TV station), the cooling stopped at Unit 3 SFP in Fukushima Daini plant (not in the damaged Daiichi).
A safety device signalled that the water level is too low, therefore the cooling system stopped. But they presume it was only the sloshing caused by the earthquake. The temperature of the water rose by about 0.8 degrees Celsius (to a maximum of almost 30 degrees) before cooling resumed, so no danger there.

A tsunami of about 1m height has reached the shores in the area of the Fukushima nuclear plants, but didn't cause any additional issues.

Edit: more detailed report here:
http://kyodonews.net/news/2016/11/22/89417

Thank you, Sotan, for an informative update. No US news service realized that it was Daini that was involved, so this is material new information for us here.

 

[Hiddencamper]

If it is the spent fuel pool cooling system, there is a low NPSH (Net positive suction head) trip on the spent fuel pool surge tanks. This also doubles as a low water level trip.

Due to vortexing and flow effects, any kind of sloshing can cause this instrument to have a false trip. Several US BWRs have removed this trip or added a time delay relay because it is problematic during refuelling activities.

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images2/handouts_161121_04-j.pdf
(in Japanese)

Short report on how Tepco actually dug a 1.2m deep hole in the ground, in one point right next to the "ice wall", to confirm that the soil is frozen.
There's a photo of a thermometer measuring minus 13 degrees Celsius.

As usually, larger images and a video (which I haven't been able to see) are available at:
http://photo.tepco.co.jp/date/2016/201611-j/161121-01j.html

 

[Sotan]

https://www.nsr.go.jp/data/000170874.pdf
Document (in Japanese) submitted by Tepco to NRA, dated November 18, containing a variety of topics.
What I found most interesting is the section from page 37 to 45 (page numbers as shown by Adobe Reader), with results of the video investigation of the Operating Floor of Unit 1.
Page 38: Until now they were able to confirm the position of several of the concrete blocks that make up the upper 2 layers of the 3-layered well plug. Namely, they can see a little of the upper layer's North and South block (center block not visible), as well as Center and West blocks of the middle layer. The other blocks can't be seen yet, they hope to see more as they remove debris from the surroundings. Middle layer's Center block has moved up and in the process has raised up the west tips of the upper layer's North and South blocks.
Page 39 gives a description of the well plug. A total of 9 huge concrete blocks, placed in 3 layers.
Page 40 shows the general location on the operating floor of the DSP slot plug, well plug and ceiling crane, as well as photos of the debris that allow a peek at the well plug blocks as described above. (I confess I don't understand very well what these photos are saying.)
Reactor well plug concrete blocks appear displaced in various directions... DSP slot plug (?), same... Unfortunately I lack the knowledge to interpret those photos.
Page 42 gives radiation measurements on the Operating Floor. Values over 50 mSv/h in the area of the reactor well plug. (Together with the well plug info, they seem very suggestive. Did the massive well plug concrete get jolted up during the accident? The hydrogen explosion wasn't likely to cause the movement of the concrete plug, I think...?)
Page 43-45 - damage sustained by the ceiling crane's wheel... runway girder... trolley.

 

[Rive]

...

Thanks for this document.

I might be wrong but for me the relative low radiation around the plug (and ~ the same levels for the whole floor) suggests that for this unit the containment cap did not failed.
I don't know how much void space might be under those concrete blocks, but the displacement might be due vacuum after the explosion and not due steam release.