Japan Earthquake: nuclear plants Fukushima part 2

[jim hardy]

Thanks for the kind words, Sotan

No shortage of pipes in there

Does anybody know if Nuclear News did a cutaway of Fukushima ?

PS
Hiddencamper's SRV line is what i was thinking, too.

Do I remember correctly "Neutrons at the Gate" were during attempts to depressurize and reflood? Been almost six years now...

 

[turi]

Do I remember correctly "Neutrons at the Gate" were during attempts to depressurize and reflood? Been almost six years now...

"[...]over three days from March 13 and is equivalent to 0.01 to 0.02 microsieverts per hour[...]" from http://www.japantimes.co.jp/news/2011/03/24/news/neutron-beam-observed-13-times/ is all I could find between tons of pseudo-science-noise. The Wikipedia-Timeline for March 14 says for Unit 2:

• 13:15: The reactor core isolation cooling system for reactor 2 stops and, shortly afterwards, the water level within the reactor starts falling.[20]
• 18:00 (approximate): The water level in reactor 2 reaches the top of the fuel.[20]
• 20:00: Core damage starts occurring in reactor 2.[20]

 

[Sotan]

I'll add just a bit to finish the reporting on the press conference after the latest inspection of Unit 2 PCV.
- At one point a reporter asks what would happen to the whole work process at Fukushima Daiichi if Toshiba (at least its nuclear section) would go bankrupt. The speaker didn't really have an answer, they haven't really considered such a possibility.
- Much doubt remains about the nature of the sediment, which puzzles reporters and everybody else. Lower radiation values this time... the fact that temperature in the area is low (same as in the whole PCV), isn't that an indication that it is not corium/fuel debris? The speaker said they can't yet give an answer. They will continue to examine images, compare them to corium samples known from Cernobil and Three Miles Island, do all sorts of analyses.
- The lower value reported this time for the radiation dose in approximately the same spot as before was the source of many questions. In the end - which value is the correct one? The speaker tried to explain that it's not that simple; different methods, even small differences in location and shielding may cause very different results. They consider them "similar enough", of the order of hundreds of Sv/h. Another reporter wondered if such variations may signify that something radioactive is physically moving around in the PCV, or maybe it has somethign to do with the cooling water going in different directions at different times - but the speaker dismissed this as a very low probability hypothesis, things are pretty much stable at this time in the PCV.
- One reporter was intrigued why this time the camera lasted for 6 hours without problems, considering it was similar to the one that went dark after only 2 hours in the case of the sediment-cleaning robot. Again, no concrete answer, so many factors could have affected the cameras in the two instances.

 

[jim hardy]

"[...]over three days from March 13 and is equivalent to 0.01 to 0.02 microsieverts per hour[...]" from http://www.japantimes.co.jp/news/2011/03/24/news/neutron-beam-observed-13-times/ is all I could find between tons of pseudo-science-noise. The Wikipedia-Timeline for March 14 says for Unit 2:

• 13:15: The reactor core isolation cooling system for reactor 2 stops and, shortly afterwards, the water level within the reactor starts falling.[20]
• 18:00 (approximate): The water level in reactor 2 reaches the top of the fuel.[20]
• 20:00: Core damage starts occurring in reactor 2.[20]

Thanks Turi
that Japan Times article jogged my memory
what the reporters called "beams" were hardly what we'd call "beams", they were instead miniscule upscale readings on neutron monitors out at the entrance gate . I remember checking wind direction it was in direction from plants to gate, and concluding to my satisfaction some fission fragments had gone up the stack during some venting during reflood.

Tepco said the neutron beam measured about 1.5 km southwest of the plant’s Nos. 1 and 2 reactors over three days from March 13 and is equivalent to 0.01 to 0.02 microsieverts per hour. This is not a dangerous level of radiation, it added.

That's not a lot of neutrons.

 

[Sotan]

• 20:00: Core damage starts occurring in reactor 2.[20]

There were a lot more neutrons a little later, though, if this wikipedia page is correct?

"At 21:37 JST, the measured dose rates at the gate of the plant reached a maximum of 3.13 mSv/h, which was enough to reach the annual limit for non-nuclear workers in twenty minutes,[50] but had fallen back to 0.326 mSv/h by 22:35.[52]"

 

[Hiddencamper]

Didn't an explosion occur around then on unit 3 or 4?

There was an info graphic with all the spikes and what they correlated with

 

[Sotan]

I have saved the official IAEA report of the Fukushima accident.
Checking the event timeline for Unit 2: Unit 1 explosion was on March 12 at 15:36; Unit 3 explosion happened on 14 Mar at 11:01. So both these had already happened by the time discussed above (evening of March 14). The explosion on Unit 4 occurred next day at around 06:14.

Quoting from the vol. 1 of the technical report, about Unit 2:

A revised estimation at 15:57 [March 14] indicated that the reactor water level would reach TAF (uncovering the
core) at around 17:30, based on the presumed time of the loss of the RCIC system. By 16:00, a
containment vent path had not yet been re-established, and it was clear that achieving a successful
venting was going to take some time. With uncovering the core predicted to be imminent, it was
decided at 16:28 to depressurize the RPV by release through the SRV to the SC, to enable water
injection, whilst recognizing the potential adverse impact on the confinement as a result of the release
of steam from the reactor into the containment as there was no venting path to ensure PCV integrity in
case of further over pressurization.

The first attempt to open the SRV from the switch in the MCR at 16:34 failed.114 After several further
unsuccessful attempts with five different SRVs, operators opened an SRV at 18:02. Additional SRVs
had to be opened, before the RPV pressure dropped to about 0.65 MPa (6.5 bar) at 19:03 (from about
7 MPa (70 bar) at 16:34), which was below the fire engine pump discharge pressure. During this
pressure relief, there was no apparent increase in the PCV pressure. On the other hand, the rapid
pressure drop caused the water inside the RPV to flash to steam and, without make-up water injection,
the water level continued to drop.115

[...]

At 20:30, the RPV pressure started to rise again, exceeding 1.0 MPa (10 bar) at 21:00. Two more
SRVs were opened, so that the RPV pressure started to drop at 21:20. The RPV pressure rose
repeatedly afterwards, and water injection was considered to have been interrupted.
At 21:55, the containment atmospheric monitoring system (CAMS) — radiation monitoring
equipment inside the PCV — was restored and its readings showed significantly elevated radiation
levels in the DW and SC compared with the earlier readings at 15:15, prior to the CAMS going offline.
The radiation level increase was 5000-fold (from 1.08 mSv/h to 5360 mSv/h) in the containment
atmosphere (the DW) and 40-fold (from 10.3 mSv/h to 383 mSv/h) in the SC section of the
containment. Additionally, neutrons had been detected between 21:00 on 14 March and 01:40 on
15 March, by a mobile radiation monitor near the main gate (approximately 1 km away from the RBs
of Units 1, 2 and 3). The measured neutron dose rates were 0.01–0.02 μSv/h.118

Note 118*:
It was thought by TEPCO that the neutrons came from the spontaneous fission of actinides that were released following
core damage in one of the three reactors, probably from Unit 2 [5].

[...]

At 06:14 [March 15], the sound of an explosion was heard on site, and tremors were felt in the MCR. This was
followed by a drop in the Unit 2 SC pressure indication, which went off scale. The MCR initially
reported to the ERC that the indicated SC pressure was at nearly atmospheric pressure, as zero bar
was displayed in the MCR indicator at 06:30, inferring potential loss of the confinement function.
After re-checking the readings, however, it appeared that the DW pressure was still at 0.73 MPa
(7.3 bar) and the SC pressure went off scale.

This information indicated a possible containment vessel failure and the possibility of uncontrolled
releases from Unit 2. On this basis, the on-site ERC ordered all personnel in all the units to
temporarily evacuate to the seismically isolated building where the on-site ERC was located. At about
the same time as the event associated with the Unit 2 SC, an explosion in the upper part of the Unit 4
RB was observed by the evacuating personnel.119

 

[turi]

New detailed info on Unit 1 hydrogen explosion (long pdf and animations):
http://photo.tepco.co.jp/date/2017/201702-j/170217-01j.html

 

[Astronuc]

I have saved the official IAEA report of the Fukushima accident.

There are numerous reports from the IAEA and AESJ, and other institutions.

https://www.iaea.org/newscenter/focus/fukushima/status-update - plenty of update reports

2015 Report - http://www-pub.iaea.org/books/iaeabooks/10962/the-fukushima-daiichi-accident

I'm not sure what 'highest' radiation level means in the context of recent specific events, but there are likely locations of high activity associated with pieces of fuel or activated materials from the core. It's difficult to know what exactly happened with core; some believe the fuel melted, which is possible, but the fuel could have chemically reacted (and oxidized) with whatever water was able to get into the core. The hydrogen has to be produced by reaction of the water with metals and fuel. One likely reaction is Zr + H₂O => ZrO₂ + 2H₂, which is expected. The UO₂ fuel goes through several oxidation states, but ultimately to UO₃, which is readily soluble.

Another presentation from 2015.
https://ceiden.com/wp-content/uploads/2015/01/3-SekimuraPresentation20150115all.pdf

There was a presentation - APS Division Nuclear Physics Hawaii Meeting, 2014.
http://adsabs.harvard.edu/abs/2014APS..DNPAA2002S

The Atomic Energy Society of Japan (AESJ) published the Final Report of the AESJ Investigation Committee on Fukushima Daiichi NPS Accident in March 2014. The AESJ is responsible to identify the underlying root causes of the accident through technical surveys and analyses, and to offer solutions for nuclear safety. At the Fukushima Daiichi, Units 1 to 3, which were under operation, were automatically shut down at 14:46 on March 11, 2011 by the Tohoku District-off the Pacific Ocean Earthquake. About 50 minutes later, the tsunami flooded and destroyed the emergency diesel generators, the seawater cooling pumps, the electric wiring system and the DC power for Units 1, 2 and 4, resulting in loss of all power except for an air-cooled emergency diesel generator at Unit 6. Unit 3 lost all AC power, and later lost DC before dawn of March 13. Cooling the reactors and monitoring the results were heavily dependent on electricity for high-pressure water injection, depressurizing the reactor, low pressure water injection, and following continuous cooling. In Unit 3, for example, recent re-evaluation in August 2014 by TEPCO shows that no cooling water was injected into the reactor core region after 8 PM on March 12, leading to the fuel melting from 5:30 AM on March 13. Even though seawater was injected from fire engines afterwards, the rupture of pressure vessel was caused and the majority of melted fuel dropped into the containment vessel of Unit 3. The estimation of amount of radioactive materials such as Xe-133, I-131, Cs-137 and Cs-134, emitted to the environment from Units 1 to 3 is discussed in the presentation. Direct causes of the accident identified in the AESJ Report were, 1) inadequate tsunami measures, 2) inadequate severe accident management measures and 3) inadequate emergency response, post-accident management/mitigation, and recovery measures. These were caused by the following underlying factors, i.e., a) lack of awareness on the roles and responsibilities by experts, b) shortfalls in establishing safety measures and fostering safety awareness by utilities, c) lack of safety awareness by the regulatory body, d) inadequacies in attitude of learning from efforts and collaborations in the international community, and e) shortage of qualified personnel to ensure safety and inadequacies in organization and management framework.

 

[jim hardy]

Photos in those reports are better resolution than i remember from 2011.

Thanks !

 

[turi]

A lot of handouts today on various topics (some of them the usual daily ones, others with more in depth information):
http://www.tepco.co.jp/nu/fukushima-np/handouts/index-j.html

Among them a lot of information about the work at Unit 3, including radiation measurements:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170220_02-j.pdf

 

[Sotan]

Indeed lots of documents - a more recent one presenting the plans to test, in the following days, a British-made "multicopter", a remote-controlled drone that can fly over the buildings and record high resolution images and radiation dose values and plot them as three dimensional maps.

The second link posted by turi above speaks about progress in the preparations for installing the building cover and crane that will serve to remove the spent fuel from Unit 3.
I just wanted to point out pages number 8-9: impressive reduction of the radiation dose values after the installation of shielding on the operation floor.
Same conclusion can be drawn from the comparative images taken with a "gamma camera" in March 2014, March 2016 and December 2016.

 

[I_P]

etudiant, Hiddencamper, and Sotan, thanks for the feedback. Sotan, the report was helpful. The complete story of what happened during the accident won't be known for some time as it has not been possible yet to enter critical areas within the damaged units - correct? 5k+ workers/day average... What was the staffing level when they were operational?

Edit: should have quoted the post I was responding to on p56

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/roadmap/2017/images1/d170223_08-j.pdf (in Japanese)
A report on two subjects: first part covers the recent investigation of PCV of Unit 2, while the second half is about the planned investigation of PCV of Unit 1.

- Regarding the first part there is not much new in this report. Just a couple of new facts that I noticed:
- The cables found inside X6 penetration had their "chloropren gum" covers gone, which means that the temperature in that area exceeded 300 ^o Celsius at some point.
- The "deposit" or "sediment" is roughly of three types: a black paste, thin pieces of material, and peble/rock sized stuff.

- The second part begins on page numbered 17 as given by Adobe Reader, which is also page 0 of this second part.
- The water level is higher in this unit. They will send a robot in using the X-100B penetration, which is located higher than the X6 that was used in Unit 2. The robot will go in through a pipe, fall down on the "1st floor grating", go around the pedestal about 180 degrees and drop a camera/radiation sensor, through the grating, through air and later on through water, to examine an area right below the pedestal opening (Page 1). That is because they assume much more fuel (most of it?) melted in this unit, so it might have spilled over through the pedestal opening.
- Page 4 gives the first step of this investigation: the replacement of the guiding pipe which is inserted at this moment in that penetration. Must be replaced because the end of it has some bellow which might impede the advancement of the robot.
- Page 5 shows something new, a graph that plots the radiation dose measured in air vs the distance from the pedestal floor; based on how those values will plot, compared to the so-called "background values" corresponding to measurements made on the pedestal floor, they will be able to indirectly assess the presence (or absence) of melted fuel debris/corium in that area.
- Page 6 shows the intended route as seen from above, and the main points of interest: D0, check for signs of debris spilled from the "drain sump"; D1-D2, check for debris spilled from the pedestal opening; D3, check whether the debris has made contact with the PCV wall (shell).
- Page 7 shows the robot.
- Page 8 shows Step 2, the insertion of the self-propelled robot. Page 9 lists the main improvements made on the robot since the last investigation (April 2015), when it got stuck in a ditch and the cameras performed unsatisfactorily.
- Page 10-11 show another new aspect: Step 3, the prelevation of a sample from the sediment that was observed disturbed and floating through water during the last investigation, when the camera approached the bottom of the vessel. A suction hose will be lowered through the same route and used to take a sample of the water and sediment. (Rather small particles of the later, considering that there's a sieve at the tip.)
- Finally page 12 gives the schedule: step 1 to begin in the first days of March, the robot will go in around the middle of the month, and the sample will be taken sometime at the end of March.
- Page 13 shows a few aspects regarding training on mockups.

 

[Astronuc]

On Sunday, February 19, Asahi Shimbun reports "Radiation levels at Fukushima reactor puzzle nuclear experts"
http://www.asahi.com/ajw/articles/AJ201702190042.html

Based on the images, TEPCO estimated 530 sieverts per hour at a point almost halfway between the metal grating directly beneath the pressure vessel and the wall of the containment vessel. Black lumps on the grating are believed to be melted fuel.

A different robot sent in on Feb. 9 to take pictures and prepare for Sasori’s mission estimated 650 sieverts per hour near the same spot.

It would help to have an idea of what elements (radioisotopes) are responsible for the activity. If it is compounds of U/Pu it would mean fuel somehow got there, or if it is Cs/Sr, it could mean the water level was that high and soluble fission products were deposited there. It would help if they did gamma spectroscopy.

Speculation about molten fuel outside of containment are not helpful, especially when analogies to lava pouring into the sea are not consistent with observation.

 

[Rive]

... it could mean the water level was that high and soluble fission products were deposited there.

That is a really good idea. It could also explain why is the radiation level seems to be so different at so close places.

 

[Jeremy Thomson]

I'm looking to refute a YouTube video that states "uncontrollable fission is continuing under the site"
I'm sure if this were the case there would be reports from the CTBTO (Comprehensive Test Ban treaty Organistion) of elevated readings of noble fission products (Xenon 135). Does anyone know if the CTBTO publishes the station data anywhere on the web?

Thank you,
Jeremy Thomson

 

[Rive]

I'm looking to refute a YouTube video that states "uncontrollable fission is continuing under the site"
I'm sure if this were the case there would be reports from the CTBTO (Comprehensive Test Ban treaty Organistion) of elevated readings of noble fission products (Xenon 135). Does anyone know if the CTBTO publishes the station data anywhere on the web?

Thank you,
Jeremy Thomson

Hi,

First: if you think that you can clear the thing then don't be disappointed if no success. Debunking some Fukushima clickbait theories is just as impossible as winning against some fake-moon-landing conspiracy stuff. That video is just awful stupid. No connection between the video and the voice, no background for the claims, no scientific base for anything - just a pile of rubbish.

Second: natural fission is always happening and cannot be controlled. It happens at the nature too. Maybe it'll be about some 'criticality' event? If so, the nature of the thing is not limited to Xe135. The most noticeable effect is the increase in heat production and in the direct radiation. So what you have to look for is a peak in CAMS radiation monitors, followed by a sudden temperature increase, and the increase in noble gas output is just a confirmation.

Third: here you can find some data, both actual and historical.

 

[Sotan]

http://photo.tepco.co.jp/date/2017/201702-j/170227-01j.html
5 short films presenting the pedestal area in Unit 5 PCV - to serve as reference for the incoming robot investigation of the correspondent area in the PCV of Unit 1.

 

[turi]

Work at unit 3 SFP continues:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170302_08-j.pdf
Reduction of water injection in Units 1, 2 and 3:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170302_05-j.pdf

 

[etudiant]

The 'Simply Info' site reports that consideration is being given to tunneling under the reactors and then drilling up through their base to extract the fuel remains.
http://www.fukuleaks.org/web/?p=16176

It is not obvious whether this is the preferred concept, but it does indicate that a very wide range of options is being considered.
Clearly some planning is under way for what would be a decades long retrieval effort.
Given the obvious difficulties, one wonders whether these studies are simply preparing the public for
the less costly and less fraught 'seal and abandon in place' alternative.

 

[LabratSR]

Tepco will send an investigative robot inside unit #1 PCV next Tuesday.

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170309_01-e.pdf

 

[Sotan]

They ran into some trouble right from the start, with a cable drum that didn't work properly and (probably) cut a cable which caused loss of image from a camera. They will replace the cable drum assembly "starting on 16th" and then resume the preparations for inserting the robot. They said in Monday's press conference that first results (some still photos most likely) will probably be released the day after inserting the robot, so I say we might expect something on 17th or - more likely - on 18th.

http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170315_05-j.pdf

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170318_03-j.pdf
(in Japanese)

Just one page, presenting the starting of the robotic investigation of Unit 1 PCV.
Thick blue line on the top-left diagram shows the (short) path traveled today by the robot.
At top right there are two small photos - one taken as the robot is being lowered from the access pipe onto the grating platform, the other as the robot has taken the U shape and started rolling onto the grating.
Photo at lower right shows workers in action.
Lower left gives the main objectives of the first part of the inspection:
at D0 - try to assess whether there is fuel debris spilling over from the sump pit;
at D1, D2 - try to assess whethere there is fuel debris flown through the opening of the pedestal;
at D3 - try to see if the fuel debris has got in contact with the PVC wall;
at BG - take radiation measurements to serve as "background" or control, to be compared with measurements taken at D0~D3.

Slightly larger photos here:
http://photo.tepco.co.jp/date/2017/201703-j/170318-01j.html

 

[Sotan]

On March 19 a new 4-page quick report has been added by IRID/Tepco, regarding the inspection of Unit 1 PCV.
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170319_02-j.pdf (in Japanese)

Page 1 shows little new content compared to the previous report. The two photos at top-right are new; one was taken with the right-hand camera on the robot and shows the gratings; the other one was taken with the camera/radiation meter unit lowered through the grating, just before getting submerged in water.

Page 2, right side:
- one photo taken under water;
- tentative results regarding radiation dose: 7.8 Sv/h on the grating; 1.5 Sv/h when the measurement unit was lowered at the lowest point (more than 1m above the bottom of the PCV, still working out the precise depth). They are now analyzing imagery and radiation measurements in order to evaluate the state of the bottom of the PCV.

Pages 3 and 4 are there just to show that there were no changes in plant parameters and no effects on the surroundings, during the investigation. Trying to avoid mistaken interpretations that happened in the past, the red text at top of Page 4 states "a value of 7.8 Sv/h has been measured during this investigation. That only means that a radiation measurement has now been taken in a place inside the PCV, which could not be accessed since the accident, but became accessible now. It does not mean that a new phenomenon/event has occurred".

 

[Sotan]

New report from IRID/Tepco, dated 21 Mar - on the ongoing investigation of Unit 1 PCV
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170321_03-j.pdf (in Japanese)

Page numbered 0
- The robot continued to move from D0 to BG and then to D1 point (Mar 19)
- Top-right: View of the grating and view of the surface of water, just before submerging of the camera/radiation meter

Page 1
- Top-right: Underwater view taken in point BG. Radiation dose on the grating: 3.8 Sv/h. Radiation at the lowest point reached with the underwater camera/radiation meter (about 30 cm above PCV floor): 11 Sv/h. Radiation dose values and height above floor are tentative values.

Page 2
- The robot continued to move from D1 to D2 point (Mar 20)
- Top-right: View of the grating and view of the surface of water, just before submerging of the camera/radiation meter

Page 3
- Top-right: Image taken underwater at D2. Also, radiation measurement in D2 was 12 Sv/h on the grating and 6.3 Sv/h underwater at the lowest point reached (about 1m above PCV floor). Values are tentative.

Page 4
- Access route from D2 to D3 was narrow/risky so for the time being they returned the robot to D1. On Mar 21 they will re-try D3 (which is close to the opening in the pedestal wall), then go back to D1 and continue the measurements there.

Page 5-7
- Emphasizing the existing shielding by steel and concrete, the fact that there are no changes in plant parameters and the fact that this investigation and its findings do not mean additional threats for the surroundings.

Slightly larger photos here:
http://photo.tepco.co.jp/date/2017/201703-j/170321-01.html

Edit: After checking other sites in the last couple of hours, it appears that they decided to extend the investigation another day - that is on 22 March too, to gather more data. What they got until now is still inconclusive, they still don't have a direct confirmation of the location and state of fuel debris, and they couldn't get really close to the floor in places of interest, fearing the sensor will get stuck. So - one more day.

 

[nikkkom]

If you step back a bit (stop thinking about everyday details of the investigation, look at a bigger picture), what could be the plan for dealing with the station?

The fuel can and should be unloaded from the pools.
Everything exterior to PCVs can be cleaned up and where beneficial, partially dismantled.

But what next with the PCVs and everything inside? What with basements?

BTW, is Japanese public opinion softening up to an idea of eventual restart of Units 5 and 6? IIUC, they are essentially undamaged and in working shape?

 

[etudiant]

I don't think there can be any clarity for the long term as yet.
The cleanup will run as outlined for the next few years, so hopefully early in the 2020s the SFPs will be emptied and the location of the corium will be known.
By that time, the political and social picture will also have evolved, but who knows in which direction.
Fukushima looks to become the Hanford of Japan, a perpetual clean up project, because the recognition that the site be best encapsulated and left to itself is politically unacceptable.

 

[turi]

BTW, is Japanese public opinion softening up to an idea of eventual restart of Units 5 and 6? IIUC, they are essentially undamaged and in working shape?

I can't imagine TEPCO restarting units 5 & 6. They are using them (or at least unit 5) for testing equipment to be used in units 1-3. They have drilled various holes etc. TEPCO has other nuclear power stations waiting for reactivation, getting the safety updates and paper work for them done is more than enough work and has a higher potential for a positive return on investment.

 

[Rive]

BTW, is Japanese public opinion softening up to an idea of eventual restart of Units 5 and 6? IIUC, they are essentially undamaged and in working shape?

That's not practical. To operate a NPP you need a lot of auxiliary stuff/area around the reactor and the turbine building: like you can see the pre-disaster pictures about Fukushima.
After the tsunami all these areas were sacrificed in order the restoration work.
To restart U5 and U6 a lot of work would be needed, and the conflict with the restoration work would be unavoidable.
I think the best is to write them off.

 

[nikkkom]

That's not practical. To operate a NPP you need a lot of auxiliary stuff/area around the reactor and the turbine building: like you can see the pre-disaster pictures about Fukushima.
After the tsunami all these areas were sacrificed in order the restoration work.

I looked at the Google map and area around Units 5/6 does not look significantly altered.
Fields of water tanks, debris storage areas and such are located mostly inland from Units 1-4. not up north along the coast where Units 5/6 are.

 

[Sotan]

- From what I have seen there is no talk whatsoever about a possible restart of Units 5-6 at Fukushima plant.
- I agree with etudiant's post above, for now they have a plan and are sticking with it and trying to give it their best; nobody says the plan itself cannot be changed, but they will probably consider that later (maybe after removing all the spent fuel).

- Today there's a new post of IRID/Tepco, about the investigation of Unit 1 PCV. (The investigation is over and the robot has been retrieved.)
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170323_05-j.pdf (in Japanese)
- Photo on page 1 shows intensive image blurring when the camera/radiation sensor gets very close to the bottom of the PCV.
- Photo on page 2 has been shown before, looks a little enhanced now, but seems (at least to me) to show a rather clean area on the bottom.
- Photo on page 3 shows... I don't know what it shows :/
It is a bit frustrating, I think we need to wait for more materials and results to be released.

Edit: (quoting a Mainichi article)
Tepco announced on February 23 that it was impossible to confirm the nuclear fuel melted in the core melt accident from the images obtained as a result of the internal investigation of Fukushima Daiichi No. 1 Reactor containment vessel from March 18th to 22nd. They will analyze the animation and radiation data obtained in the survey and announce final findings on March 27th.

 

[Sotan]

Correction: Above, obviously, I should have written "Tepco announced on March 23...", not February.

 

[Charles Smalls]

Hi guys

I was curious about the large amount of sediment or 'sand' that the recent robot observations of Unit 1 found inside the containment vessel. It is well known that concrete exposed to high temperatures can undergo a process of spalling, where the heat causes individual constituents in the concrete to expand at different rates causing small explosions in the material and debris goes popping off.
You can see the process here:



and a much more dramatic example here:



Is it possible that the sand/sediment we see in the latest footage is from this process where the fuel has met the CV concrete floor and caused this large amount of spalled material? I have read the sediment may be from seawater injection/flooding but I'm not sure how probable that is. Is there any special material or liner in the CV concrete mix that would prevent the spalling process?

Many thanks for your insights and expertise as always.

 

[turi]

New info on unit 1 examination: http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170327_14-j.pdf

[...]
Is it possible that the sand/sediment we see in the latest footage is from this process where the fuel has met the CV concrete floor and caused this large amount of spalled material?[...]

I am no expert on concrete, so no opinion on this from me. But I could imagine that the sand/sediment we can see could be metal oxides from farther up, oxidized zirconium and the like.