Japan Earthquake: nuclear plants Fukushima part 2

[jim hardy]

Those artifacts are hard to determine actual dose rate though. I see similar artifacts on cameras that sit in our heater bay all cycle (1-2 R/hr). The difference is this camera has only been in for a short time.

That's interesting. What kind of life do you get from them ? Are they shielded ?

Radiation tolerance of electronics is not much studied in ciivilian circles. I once spoke with a TI old timer named Frank whose expertise was with weapons. He thought at first i was inquiring about inside the reactor because he's accustomed to working with what comes through a bomb case before it melts... The ten R/hour dose rate i was inquiring about is miniscule in comparison and he could only give estimates.

So i tested two consumer devices.
My own TI-99A computer handled several hours of 200 rad/hour just fine, 1000 R total.. Its CMOS memory Frank said might start degrading at 2000 R total so i went only halfway there.
A Fisher electronic pressure controller full of DMOS showed at 10,000 R only a slight calibration shift but at 20,000 R it was no longer responsive. So we decided to not install them in a 10R/hour area for fear they'd not last through a fuel cycle.

So my observation is electronics is tougher than humans but only by a couple orders of magnitude .
Your cameras would be one more data point.old jim

 

[Sotan]

Tepco has published a more detailed report:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170130_07-j.pdf
(in Japanese)

Page numbered 1 shows the general area targeted by this preliminary inspection - lower part of the CRD rails and part of the grating in the pedestal, jjst below the control rods.
Page 2 shows the place of this so-called "Step 5" in the general investigation carried out these days in the PCV of Unit 2.
Page 3: location of the 3 photos shown at the bottom of the page, ending with the wall of the pedestal.
Page 4: 6 photos and their location. Clockwise from top left: 1) place where grating is missing 2) guiding pipe(s) for "TIP" 3) lower part of the CRDs 4) sediment 5) opening of (between?) CRD rails and platform 6) flat bar and missing platform.
Page 5: Conclusions
- they were able to perform the inspection as planned;
- in the area that could be seen, the CRD housings, the PIP cables and the CRD changing machine were still in place;
- part of the grating on the platform was found deformed / in a different shape than when installed;
- a sediment (deposit) was found on the CRD rails and on the grating;
- water drops are falling at least over an area of the pedestal;
- they will evaluate the need/possibility of removing the sediment and driving the inspection robot in the area;
- all plant parameters indicate that adequate cooling is being achieved;
- there is no leak of gases from inside the reactor, as the sealing O-rings at the entrance of the X-l penetration performed as expected;
- there was no outside effect of the radiation from inside the reactor, which was properly contained by walls and shielding.
Page 6: aspects from the work area.
Page 7: explanations regarding the photos - camera pan, tilt.
Page 8: explanations about the video: which are is being filmed at which minute/second interval.

The video is here: http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=bo88kf1n&catid=61699

 

[turi]

More detailed report in English: http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170130_02-e.pdf

 

[turi]

There's a long video of a press conference in Japanese which I didn't have the chance to watch yet (and I won't understand 1 % of it):
http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=y95m09jy&catid=69619

Edit: I wonder whether any consequences for the planned insertion of the robot have been mentioned.

 

[Sotan]

Thank you for that link turi.
I managed to watch the first half, it is really difficult to summarize, here's a long post about it.

- They played the video from inside the PCV first. Then explained the document listed above, the one with the Conclusions on page 5 (up to 28:54). Then took questions.
- Q: What could that "sediment" be? A: We can't say for sure yet. There's still the possibility that it's made of various materials such as melted insulation (lots of aluminum in insulation) or melted cable cover... We're still analyzind thes eimages and hope to get more information.
- Q: Could it be a mixture of melted fuel and components too? A: We just can't say yet. Not enough information.
- Q: Is there any information that it is NOT corium debris? A: We can't say yet, we're going to insert the "scorpion" robot it and get more information. We'll get temperature, radiation values and we'll be able to say more.
- Q: Watching those images there was a lot of noise, can you say from that that there was an extremely high radiation in there? A: We can't give a figure from that, we'll keep analyzing the results. Q: How is the noise in these images, compared to others in the past? A: We'll make such an analysis too, look at those images and noise using video software, but there are large margins of error in such an analysis. Q: In some parts it's ot clear whether that is water falling down like rain or static/artifacts/noise cause by radiation. A: There is certainly some of that noise too. But at first glance it looks relatively low. But how many Sv is that - we'll be able to say that maybe later after serious evaluation. Those things that move in groups from up down, or sometimes at an angle i the image - those are water drops.
- (33:24) Q: If the sediment seen in the images is corium debris - would that cause a much more intense radiation? A: We can't say yet, need more analysis, there are many things inside the reactor that could have melted. Q: So you can't say definitely, "the radiation is low, therefore it's not melted fuel", either? A: Indeed.
- (34:00) There was that "flat bar" with a height of 9 cm. Looking at this photo, there's this portion where the grating is gone - is there a place where a lump of sediment is visible? A: Yes it appears so. Q: A pile of sediment, a few centimeters thick? A: Yes that's what we see too. Q: About the reason why that grating portion is gone..? A: We're still analyzing that and hope to get more info by further investigation.
- (34:56) Q: In that photo with the "slot opening", the left side of the photo means down, right? A: Yes. Consider that the grating is always "down". You might have to rotate that page 90 degrees to get the right position. Q: What is seen beyond the "slot opening"? A: The black space underneath the grating, where light does not reach. Q: Beyond that it gets whiter... A: Difficult to say, maybe some reflection of light. Q: As for the next robot investigation, do you estimate that there will not be significant obstacles/difficulties? A: We'll have to analyze a lot more. Of course we must avoid that area with no grating. Q: So apart from such re-consideration, the robot investigation itself should be doable, you'll get there and see more? A: Toshiba has a mock-up of the area and we'll investigate more the sediment situation and the route that must be taken.
- (37:36) Q: This time you got these images that you've explained to us, what is your evaluation of this result? A: We're happy about being able to carry out the investigation as planned, we didn't have before any such images of the lower part of the PCV, so it's very precious data... We saw that many/most hardware components are still in place, but cooling water falling through shows there is certainly damage to the bottom of the RPV, even though this time we can't say more, haven't seen the degree of damage.

Shorter notes from the continuation of the press conference recording:
- This time's investigation is just a peek inside the pedestal, about 2m from the entrance. Can' say in % how much of the pedestal room we covered.
- The inspection robot cannot climb up the 9 cm flatbar.
- The "cleaning robot" we can't yet say if we will use it or not. This week we probably won't send in any robot, we need some time to analyze. The cleaning robot would go in only on the CRD rails, not further.
- About the yellowish/green color in the images - we probably shouldn't think too much about colors, light is not enough, image processing also affects colors, we can't get too much info from the color, not yet...
- Water drops coming down: are there fissures, cracks in the RPV or is there a big hole that let's 3 tons of water get out of the RPV each hour - or is water also going some other direction? We can't say yet, there are rainy places and not so rainy places it seems, we're still analyzing.
- About the size/amount of "debris", "sediment"... We've seen the same images as you, we cannot yet say how big, how many tons of sediment etc... or what exactly it is.

(55:00) Sotan's note: ...lack of time prevents me from continuing in this manner, but I think you get an idea about the mood/atmosphere in the press conference room. If I get more time tomorrow I will watch the second half and post more, although I think I should make it shorter and only note the important points.

 

[Sotan]

Part 2 of the press conference (excuse the formatting...)

(56:30) The speaker is correcting a previous statement, the one when he said that perhaps next week they will send in the inspection robot. He's saying this has not yet been decided, it depends on further analysis.
- Q: You made public a few minutes of footage - how much have you taken actually? A: the whole operation, including preparations and ending... lasted from 5:45 to around 10:30. Several short films have been made during this time, probably a few hours in total. Q: No image has been shown of the grating as a whole, a "long" shot... Camera didn't take such an image or...? A: There is actually, in the sequence where the camera looks at the missing triangular piece of grating, then changes angle upward, on the way in that sequence there is probably such a shot but the lighting is limited and the images unclear. Q: What's the approximate thickness of that sediment, if the flatbar is 9 cm... A: Analysis is under way but yes if we compare it with the flatbar... its about half of the flatbar's height. Also in other images, considering the gaps in the grating are 3 cm wide, that can also be compared with sediment thickness. Q: It's been asked already but any theories about what might have caused the disappearance of that piece of grating? Was it pulled down, was it melted... A: We are not yet in position to advance a hypothesis... Grating is steel, melts at 1500-something degrees, the melted fuel might have had 2000-3000 degrees. Such material could have fallen directly on that area, or carry with it some component that hit the grating... We can't say more at this moment.
- Q: You mentioned that the actuators of the control rods looked in relatively good condition. The muon imaging indicated that some portion of the fuel is probably left in the core. Would you say these images support the results previously obtained by muon imaging? A: We cannot say yet with certainty yet, we are still analyzing and we will need more info. We were only able to see a small portion of the pedestal. Water coming through shows that a breach has been made.
- (1:05:42) Q: Is the grating frame gone too, or just the grating panel. A: The panels are made in such way that they include an exterior frame, which is gone too. Q: The sediment on the CRD rails and the one on the grating platform, are they different? A: Difficult question, we are not yet able to answer that with certainty. Previous imagery too shows that sediment on the CRD rails is rather thin, might be burned/melted paint/coating; the one in the pedestal looks different, origin may be much more diverse (thermal insulation, cables etc)... Q: You said the gratings are made of iron, melting at 1500-something degrees, but then you mentioned something about 3000 degrees, what was that about, again? A: that's the melted fuel. Q: So it is possible that the hot melted fuel might have fallen on the gratings and melted them? A: We can't say with certainty, but it is one possibility among others.
- (1:08:55) - questions from the Fukushima meeting room follow. Q: in the 4th photo on this page we see some "round-ish" artifact which looks different from other sediment, is it possible that this is a piece of hardware of some kind? A: Now that you mentioned it, yes it appears to look somehow as you say, but... we can't say yet what it is, if it is something like a piece of equipment that fell... To me it doesn't really look like equipment, so I can't really say. Q: Is it a possibility that you won;t be doing the robot inspection? And if you give that up what will happen next? A: About the inspection I said earlier and then made a correction, we will analyze its feasibility properly. Q: What is the time (minutes/seconds) when the mass of sediments was identified? A: the tape kept rolling, when all the work was done it was brought in for analysis and editing... although editing sounds funny. What time it was noticed is hard to say... Q: I see. You (Mr. Okamura), at what time did you get the report about the sediment? And what were you told? A: of course I consult my colleagues before the press conference, it was at that time. A few hours before. Q: What was your honest first impression when you received that report? A: Well I felt it was a big step forward which brought in precious information, so I was very happy and I am happy to be able to inform you about it.
- Q: When do you think the evaluation will be over and you'll be able to tell us if that sediment is remains of the melted fuel or not. A: hard to say. We haven't yet taken a sample. All evaluation is done based on imagery, and that will not change even after the inspection robot goes in. But we will also have temperature and radiation readings, and we will evaluate it all. But I think we will need additional information, such as from a direct sample. At Three Miles Island and Chernobyl there was direct contact and examination of debris at some point which allowed clear conclusions, while we are still getting only indirect proof. Q: This may be a silly question but from the information obtained today are you able to deduce by analysis data such as temperature and radiation values? or do you need to make additional inspections. A: this time there was no thermometer present (we will have one on the scorpion robot). As for the radiation, the images present that artifact phenomenon due to radiation which, in first instance, can be evaluated. But we will measure that directly with the scorpion robot, too. Q: If the sediment is found out to be highly radioactive, how will that affect the inspection robot? A: This new robot is fitted with an improved, radiation-resistant camera. The sediment could affect the route of the robot too, and we will evaluate that too. Q: On the first image of this page, there is a "slot opening" mentioned, what is that? A: During the inspection of the control rods some parts must move downwards (?), this slot provides space for that. At top left on the same image you can see the "CRD changing machine", it moves/rotates together with the platform, removes the control rod and moves it downwards. There are about 4 meters of free space under the platform.

(1:27:47, for some reason the video jumps to the end here :) I'll check again at home later.)

 

[Hiddencamper]

Just to give some info.

Water can be coming from a number of places. There are dozens of "dry tubes" in the core. These are small tubes that allow nuclear instruments and probes to enter the bottom of the core. It is possible (likely) that there is some failure of drytubes allowing water to leak out. These tubes are small and a trickle of water would make sense in my opinion through a dozen of these tubes or more. These tubes extend all the way up to the fuelled region so there is a lot of length for stress and failure to occur.

There is also a bottom head drain for the reactor water cleanup system. This is a couple inches in diameter so it's failure would involve a lot of water spilling out (unless core debris is partially blocking it).

Given what we've seen, obviously we don't have all the info, but it's possible we had some limited core relocation out of the vessel (possibly during the hot debris ejection when the bottom head began to fail). We don't have enough footage to know where the core slumped out or how much. But I would speculate some came out based on melted grating. We will see.

 

[Sotan]

This is the 3rd and last part of the press conference video available at tye link given by turi a few messages above. I said I will make it shorter but in the end I decided to keep the same format, this time, till the end. In the future I'll try to watch and summarize.

<<<Let me insert a short "disclaimer" here, this is just a quick on-the-spot translation which I by no means claim to be perfect - I have been known to make plenty of mistakes even on written documents, so... if you see something weird it may well be a mistake; if you feel it is important let me know and I will double check that particular place for you.>>>

(1:28:50) Q: Is the sediment getting more frequent, is the amount increasing towards the center of the pedestal? A: No at this time we cannot say anything like that. Q: Above the pedestal, there is a similar size cilindric equipment isn't it. The RPV? A: The pedestal is slightly smaller, at 5m diameter. The RPV is 5.5m in diameter.
(1:30:30) Q: Are these video images the result of some enhancing processing, to remove fog, to improve contrast etc. - or are they raw footage. A: Previous images have been enhanced, I think there is a possibility that some enhancing/processing has been done on these two. Q: In that case some of fog, as well as some of the artifact due to radiation might have been removed. A: There can be that too, to some degree... I couldn't say. Q: Those few water droplets that wee see in those images, they couldn't possibly account for 4.5 tons per hour, what do you think? A: Well... the whole pedestal area is pretty large, it's possible that in places we couldn't see this time there is more flow... again, this too is hard to call right now. Q: I couldn't help thinking, wasn't it possible to extend that pipe a little longer, to see farther? A: This was just a preliminary step in view of the inspection using the scorpion robot. The point was just to see whether we have access enough to place that robot there at the entrance into the pedestal area. If later on such a procedure could be useful for some purpose, and could be improved - we will analyze that posibility too.
(1:38) Q: I'm seeing a bit of contradiction between the possibility that the grating might have been melted by the hot fuel and the fact that much of the equipment in the pedestal seems intact... What did the simulations say, that the RPV was pierced right in the center or is it possible that it failed somewhere on a side... A: The simulations did not follow such an angle... The RPV has a drainage pipe right in the center so perhaps it is easy to consider that that's the weakest spot, but we simply don't know yet.
(1:39:51) Q: Can you tell us something about the team, the number of workers who carried out these operations, the exposures. Also what is the atmosferic radiation level in the area where these people worked. A: There were 4 teams each made of 4 men. The teams would take turns one after another, and there were about 3 full turns. Additionally there were 2 people doing decontamination. The planned maximum exposure was 3 mSv; thanks to shielding and working in shifts, the average value was 0.37 mSv per person. However the highest exposure was 1.23 mSv. The atmospheric radiation was similar to last time, about 3~6 mSv/h in front of shielding. Q: About that maximum exposure value... I'm thinking if that was a person who also worked last Thurdsay in the other preliminary inspection..? Or should we understand the people of today didn't work last Thursday. A: People who reached a certain level of exposure will help in other ways, preparations etc - but not work in the first line. Q: So some of them did work on Thursday and again this time? A: Yes some of them do, these are teams that have had a lot of training on mockup, they are trained to work efficiently in teams and in the shortest time possible. Q: The next inspection with the scorpion robot - will there be new people working on that, or the same teams that worked this time. A: The 4 teams of 4 that worked this time will perform the basic initial operations, pipe insertion etc. Q: The exposure in this case, as a total, are there some limits that are established? A: Certainly, the management of exposure is a priority theme and a lot of consideration is given during planning to such aspects. We have a plan that calls for limiting exposure to a maximum of 3 mSv per day, but have been able to limit actual exposure values to a 10th of this value. Q: So you don;t have an overall, long-term exporure limit (say 20 mSv over a certain period), instead you're watching for a 3 mSv/day limit.
(1:44) About the sediments that we saw, will the scorpion robot be able to drive over it, avoid it, in general do a good job in spite of that sediment? A: We will do a lot of work at Toshiba (mockup) to check for those things. The data we got this time wil be very useful in that sense.
Q: ABout the watter that seems to be falling down in the PCV. What can you do to find out the leaking place and what is the significance of such a discovery for the future operations aimed at removing the debris. A: We know from the muon measurements that a lot of the fuel is probably still in the RPV. Who knows, maybe the conclusion will be that it is easiest to approach the debris from the top of the RPV. But we have much more to find until then. Q: If you are to use the flooded approach you must be able to make the RPV watertight... A: That is one possibility, flooding the whole PCV is another one, we still have much to learn before we decide that. Q: The previous finding given by the muon measurement indicated that a significant part of the fuel is still in the RPV, however we see all this debris on the platform and in the pedestal area, if that turns out to be nuclear fuel, is it an unexpected result that contradicts the muon finding? A: I wouldn't say so, the muon measurement is not a very precise one, it just says that a lot or the majority of the fuel is still in the RPV, it doesn't say no fuel leaked out... Since water is now leaking it is quite likely that the melted 2000-3000 degrees hot fuel flowed here and there over the grating, and might have melted the grating here and there, depending on the place. Q: The scorpion robot will give you information about the extent, the spreading of this sediment, but will it be able to measure some of its properties too? such as the hardness, the "feel"... A: Well maybe we'll be able to get a feel of it, a limited feel, from how the tracks of the robot will go over it. But there is no arm on this robot to extend to and grasps the debris. The camera will get really close to it too, and that might help in that sense a little. If the robot track sinks into that stuff it will mean it is soft; if it climbs over it that will suggest a harder, metal-like composition... this will give us a hint. Q: COuld you tell us again what are the objectives of the next, scorpion robot inspection. And what are you going to be analyzing in the following days. A: The scorpion has two cameras, with high resistance to radiation. Also, the fact that we have two cameras, one in the front, one in the back near the light source, will allow us to get a sense of depth and will help avoid some light artifacts/problems. We're hoping to get some very good imagery. We'll have a thermometer on it too, and a (integrative) radiation meter. We'll get an idea of the radiation level in the pedestal. We will use all that information in the analysis aimed at finding the best solutions for removing the nuclear fuel debris.

 

[krater]

It has been said multiple times above but I too wish to thank you, Sotan, for your dilligence in providing the wealth of updates you have managed to amass. Your efforts are truly exceptional. Many, many thanks.

 

[Sotan]

(Thank you krater!)

Tepco released a report with some results of the analysis and enhancement of the images taken the other day in the pedestal area of Unit 2 PCV:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170202_03-j.pdf (in Japanese)

On page numbered 4 there are 2 columns with photos stacked over. The explanatory texts, from top down, say:
(left stack)
- CRD housing support
- LPRM cable or PIP cable
- Sediment stuck to a piece of equipment that looks like a support for the guide pipe for TIP
- CRD changing machine
- support for the guide pipe for TIP (as seen in Unit 5)
(right stack)
- fallen grating
- flat bar
- end of the CRD rails

(down left explanations - I probably need to check for the correct names of these, but no time right now)
LPRM is some system used to measure the flux of neutrons in the core.
TIP is a probe that is inserted in the core in order to do those measurements.
PIP is a system that provides information regarding the position of the control rod.

Page 5: another set of enhanced photos with some measurements. Explanations at the top say "fallen gratings" and "slot opening", and "flat bar" is written at the bottom.

Page 6 shows the location of the grating panels on the platform, as well as the initial/new routes intended for the inspection robot (this is still under consideration). The expression used this tim,e is "grating panels in the process of falling" or "started falling", so I assume they are probably still clinging on in certain portions. In fact I think they are visible in the photos.
A larger version of the photos can be consulted here:
http://photo.tepco.co.jp/date/2017/201702-j/170202-01j.html

 

[Sotan]

Article in Japanese from Asahi Shinbun:
http://www.asahi.com/articles/ASK22636GK22ULBJ00V.html

A Google translation due to lack of time - but it looks pretty correct to me:

Tokyo Electric Power Company revealed that radiation dose in the reactor containment vessel of Fukushima Daiichi nuclear power plant No. 2 which meltdown (core melting) reached a maximum of 530 sievert per hour on an estimated basis. With a dose comparable to the inside of the pressure vessel during operation, if a person stays near, it will die in less than 1 minute. It was also found that a 1 meter square hole was opened in the working scaffold right under the pressure vessel. It is said that melted nuclear fuel (debris) dropped and the scaffold could be melted.

Since late January TEPCO is using a remote camera to investigate just under the pressure vessel. When the dose was evaluated from image disturbance due to radiation, it was estimated that it reached 530 sievert per hour at the maximum in a part of the containment vessel. TEPCO believes that nuclear fuel melting down scatters, although it is said that "there is an error rather than directly measuring the dose," it seems that there is a possibility that strong radiation is emitted in the containment vessel.

TEPCO plans to investigate the survey robot "scorpion" this month and will investigate the spread of nuclear fuel by measuring the dose of each part in the containment vessel. However, as a result of analyzing the camera image, it turns out that there are multiple holes in the working scaffolding where the scorpion is about to move around. TEPCO explained that "Melted fuel dropped from the pressure vessel and there was a possibility that holes could be made by melting the scaffold," as distortion as melted by heat is seen in the dislocated scaffold.

The hole is on the traveling route scheduled by the scorpion and it is seen as one meter square as a large one. TEPCO is planning to consider other entry routes, but the investigation can not be seen. (Sugimoto Takashi)Also NHK
http://www3.nhk.or.jp/lnews/fukushima/6053580791.html (in Japanese)
Gives some additional details:
530 Sv/h is the maximum value encountered. Even with an estimation error (due to the method) of around 30%, it is much larger than that measured a year after the accident which was 73 Sv/h.
At the entrance in the PCV there are about 50 Sv/h. At the entrance into the pedestal - about 20 Sv/h.
The 1m x 1m "barely hanging" grating is in addition to the small triangle of grating found missing in the Jan 20th preliminary inspection.
A member of the NSR said that if that value is confirmed, there is a high possibility that there is nuclear fuel debris present in that region. It is also likely to affect the functioning of the cameras on the robot. He added that even if some fragment of nuclear fuel/debris (presumably located on the bottom of the pedestal) is not submerged in water, it does not send dangerous radiation in the exterior, thanks to the thick concrete wall of the PCV.

 

[Hiddencamper]

Thanks Sotan!

I think this further confirms most of the core is still in the bottom head with a few bottom head spots where failure occurred.

One thing I've been told is if we had a total core melt and all of it escaped the vessel, is the pit below the vessel would overflow. So this is a good sign that we probably don't have a major core ejection.

 

[Sotan]

(Hi Hiddencamper and thank you for your precious insight every time.)

- I watched the latest press conference - the one in which the enhanced photos and radiation levels were released. (http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=s75v7m91&catid=69619) (2h23min in Japanese)

A few impressions:

- Many reporters were troubled by the numbers reported for radiation level. So (if you look in the figures for Step 4 and Step 5 in this investigaton), we insert a guide pipe through the X-6 penetration, horizontally; as soon as we get inside the PCV, there's about 50 Sv/h. We keep inserting the pipe inside, horizontally, until we reach roughly around the middle of the space between PCV wall and pedestal wall. Here, in the air, image analysis suggests 530 Sv/h (!). Then the guiding pipe bends down and goes all the way to that hole in the pedestal wall; just as we enter the pedestal space, image analysis shows 20 Sv/h. Doesn't make much sense and they can't say how that's possible - and in my view I cannot make Hiddencamper's interpretation fit these number either. If most of the fuel is still inside the RPV (which I do believe is true), why is radiation so high in the air in the middle of the space between PCV and pedestal walls. If lots of fuel melted and flowed through the pedestal and now radiates into that space - why are values near PCV wall and at the entrance of pedestal so low... Speaker (Tepco's Mr. Okamura) insisted that all these are incomplete data, obtained through a technique which is not very precise (analysis of noise/flickering in images, caused by radiation) and that more info is needed.

- Some reporters wanted to know what in the hell could emit so much radiation, considering that Mr. Okamura cited "a few Sv/h" can usually be measured on the surface of spent fuel, after it's been used for years in a reactor and sits quiet under water. One reporter then asks "okay then maybe totally new fuel, uranium pellets even, might emit that kind of radiation?" only to be told that is not the case at all (such pellets can be handled relatively safely by workers). Mr. Okamura mentioned shroud surface radiation amounting to "a few hundreds Sv/h during operation of the reactor", so maybe that's why he didn't look too bothered by figures such as 530 Sv/h, but reporters and myself too are dumbfounded about what exactly could give so much radiation. To quote a reporter's words, "when melted, nuclear fuel can turn into something that gives away such amounts of radiation?", also, if that's in the air at a few meters away of any surface, perhaps in some places it's even higher? Somebody also mentioned the possibility that this result is grossly out of order (like with that other robot that, while crawling on grating in another inspection, would show 7...8...7.. and suddenly 40 or 50 Sv/h for a split second, only to revert to lower values immediately).

- Reporters always want more definitve answers and gave a hard time to the speaker in certain places, as in, why don't you already admit that that is corium and keep saying that you don't know yet (somebody even said "that's what you said after the accident too, that you don't know if the fuel melted or not, now it looks like you do the same". But he remained strong and kept explaining that they prefer to analyze and be sure of something before making a statement.

- Some reporters pointed out that the robot route is in peril, there is no much room for sending in the robot, with so much grating fallen (and we haven't seen all the grating yet). Speaker said that it is early to say, they will do their best to send in the robot. One reporter seemed to have a hard time to believe that the robot can look down. This made me curious, I looked for some video with the robot and found this one (was glad to see that the robot can cross certain gaps with no problem and can recover from a rollover - but the size and aspect of that sediment looked to me like it could mean trouble for those tiny tracks).
http://www.belfasttelegraph.co.uk/v...apans-fukushima-nuclear-reactor-31346978.html

 

[Hiddencamper]

The dose rate makes sense for unshielded irradiated fuel.

The story I've always been told, is if a spent fuel storage casks had the bottom welds fail and all the fuel bundles fell from the top floor of the reactor building at terminal velocity, everyone in the reactor building would have a fatal or near fatal dose by the time the fuel bundles hit the ground level.

Yes it's only a few sv in water. But unshielded it can be a lot more.

We really do need some radiation measurement devices though. Stuff outside of the pedestal is odd and would be interesting to discover and understand.

 

[Sotan]

http://www.nikkei.com/article/DGXLASDG03H23_T00C17A2CR0000/　　(in Japanese)
Very short article regarding the next inspection robot, shown to the press today by IRID. This one is to be used for investigating the lower region of Unit 1 PCV. The inspection is scheduled to be done sometime before the end of March.
It is similar to the other robots, with one difference: while moving on the grating it will stop here and there and lower a small camera+radiation meter, through the small grid "cells" of the grating, into the space below, even under water (which is supposed to be 2-3 m deep at the bottom of Unit 1 PCV) to peek at the possible debris in there.
(I saw a few images regarding this new robot on NHK TV too and, if my eyes didn't deceive me, this one will be called "the rabbit robot". I don't know exactly why it resembles a rabbit, but it sure will be easy to differentiate it from the "scorpion robot" that will crawl on Unit 2 PCV grating hopefully in a few days.)

 

[turi]

English translation of the PDF with enhanced images:
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170202_01-e.pdf

 

[Greg Bernhardt]

I'm sorry if this is old news?

Extreme Radiation Levels Detected At Fukushima Reactor, Highest Since 2011
http://www.forbes.com/sites/william...hima-reactor-highest-since-2011/#270fbde33381

 

[Sotan]

Yes, a little old, and not of the well-informed sort.
It's about the value of 530 Sv/h reported on Jan 30. At that time the internet was filled instantly with articles written in that way.
"The level of nuclear radiation detected at the troubled Fukushima nuclear plant in Japan spiked on Thursday to its highest level since the triple core meltdown in 2011." Saying it like that suggests an evolution, an event, something that happened now (I remember my heart jumped too when I read it). Except, it's more like saying that my networth spiked to double its previous value because I found $10 in the pocket of my other coat, which I didn't wear for 6 years. (Although I kind of knew that stash must be there somewhere.)
Other links are even worse. "Time to reconsider that trip to the east coast of Japan", "Radiation levels in the Fukushima reactor are soaring unexpectedly" etc. And such statements are mixed with technically correct information ("radiation that would kill even after momentary exposure" even though "it is contained inside the reactor"), so it must be hard for some people out there to dismiss the incorrect parts.

 

[jim hardy]

Einstein on reporters:

http://einsteinpapers.press.princeton.edu/vol7-trans/262?ajax (2 short pages)

 

[I_P]

OK, so is there a competent, current analysis of the situation? Seems that they still don't know where the fuel is. Is #2 the only vessel that was breached in this fashion? Doesn't this knowledge imply an increased threat to the groundwater and the ice containment wall (and thus continued releases to the sea)? Or is expected that the fuel is still within, and contained by, the concrete basement structure?

 

[etudiant]

How much of a threat can the residual fuel/corium actually be at this point? Does it matter where it is now, other than as a factor determining the eventual retrieval?
The remaining site emissions are many orders of magnitude below the releases during the acute phase of the accident and the ongoing water treatment seems to have any ground water contamination reasonably well in hand. Indeed TEPCO is managing the ground water level within the plant to keep a sustained inflow to the site and thus to prevent any further spreading of the contaminant plume.

 

[Hiddencamper]

OK, so is there a competent, current analysis of the situation? Seems that they still don't know where the fuel is. Is #2 the only vessel that was breached in this fashion? Doesn't this knowledge imply an increased threat to the groundwater and the ice containment wall (and thus continued releases to the sea)? Or is expected that the fuel is still within, and contained by, the concrete basement structure?

The fuel has been cooled and solidified for years now.

There's also still no evidence of a containment melt through at any unit (although unit 1 may have some fuel between the liner and the base mat... we don't know and won't for a while).

Remember this molten fuel is in a containment system. It's not like the reactor vessel was the only line of defense.

 

[Sotan]

Hi I_P.
In addition to what etudiant and Hiddencamper said above, I will add that it is hard to find a "current analysis", short and up-to-date, because of the amount of information that is coming out almost every day, as a result of the tremendous amount of work that is carried out every day. The closest thing that can be considered a current analysis, translated in English, is a little old: "Progress Status and Future Challenges of the Mid-and Long-Term Roadmap toward Decommissioning of TEPCO Holdings’ Fukushima Daiichi Nuclear Power Station Units 1-4 (Outline)", of 22 December 2016. You can read it here and it might help answer some of your questions.

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170206_05-j.pdf (in Japanese)
New report - this time regarding Step 6 of the investigation under way, the step in which they will try to wash away / remove some of the sediment/deposit from the lower portion of the CRD rails. Worth taking a look even if Japanese only. The operation will be carried out tomorrow.

Page number 6 also gives a correction regarding the radiation dose rates reported earlier, deduced from the radiation artifact seen in the pictures taken. The 50 Sv/h value reported for point number 1 (just after entering the PCV) was reduced to 30 Sv/h after further study of the images.

On the same page there is a note about the high value of 530 Sv/h reported for point number 2: although a direct comparison is not 100% correct, if one was to measure the radiation right on the surface of a fuel bundle one day after the stopping of the nuclear reaction, the dose rate value would be of the order of several tens of thousands Sievert per hour. (This certainly helps put things in perspective.)

 

[Charles Smalls]

So much great information on this thread. Hi Sotan, thanks for all of your effort, I have been quietly reading your contributions for so long now. Decided to make an account just to thank you and everybody else for your coverage on this.

One question about this temperature thing, before I go back to lurking; I have read that it can take up to 5 years after a reactor shuts down until the decay heat levels in the fuel reduce enough to let it be air cooled. Does anyone know how accurate that is and how it would apply to fuel in a solidified mass rather than the normal 'good configuration' where it is in separated bundles?

Many thanks to all you guys again.

 

[Sotan]

Hi Charles, welcome and thank you. FYI I am no specialist, I just follow the progress in Fukushima plant with a personal interest, and post translations of some stuff from Tepco and other sites, which is released mainly in Japanese language. I am most grateful to all the knowledgeable people who contribute to these pages.

Pages 38-39 in this forum contain several posts (see #756~...) that relate to your question.

Edit:
Tepco has just released this info
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170207_04-j.pdf (in Japanese)
As they were checking the "sediment cleaning device" before inserting it and guiding it onto the CRD rails, they discovered that the pump that is supposed to provide the high pressure water to the device was not working. The pump will be replaced with a similar one and they will do that cleaning test when all works fine.

 

[turi]

While we're waiting with bated breath for progress at Unit 2 the preparations for the removal of fuel from the spent fuel pool of unit 3 are making progress:
http://photo.tepco.co.jp/date/2017/201702-j/170207-01j.html

 

[Hiddencamper]

So much great information on this thread. Hi Sotan, thanks for all of your effort, I have been quietly reading your contributions for so long now. Decided to make an account just to thank you and everybody else for your coverage on this.

One question about this temperature thing, before I go back to lurking; I have read that it can take up to 5 years after a reactor shuts down until the decay heat levels in the fuel reduce enough to let it be air cooled. Does anyone know how accurate that is and how it would apply to fuel in a solidified mass rather than the normal 'good configuration' where it is in separated bundles?

Many thanks to all you guys again.

For fuel that still has normal configuration, BWR fuel is air coolable in 4 months and PWR fuel at 11 months according to studies headed by the us nuclear regulatory commission.

Being in a non standard configuration would likely reduce surface area and reduce heat transfer.

 

[Sotan]

Anyone able to edit the Wikipedia page? The last phrase of this paragraph especially...

2017 radiation spike

On 3 February, 2017, several news agencies reported a significant spike in radiation levels from Reactor #2, peaking at 530 sieverts per hour, the highest level recorded since the March 11, 2011 incident. [37]These levels were announced by TEPCO, the utility company that oversees the Fukushima reactors.[36] The previous high was 73 sieverts per hour, in 2011. TEPCO believes the spike may be caused by melted nuclear fuel burning through the bottom of the containment.[35]

 

[jim hardy]

Anyone able to edit the Wikipedia page? The last phrase of this paragraph especially...

i tried

but it didn't take and i got a warning about blanking pages. oh well.

 

[Hiddencamper]

i tried

but it didn't take and i got a warning about blanking pages. oh well.

Tepco officially states that dose rates are not going up

http://www.tepco.co.jp/en/announcements/2017/1374451_10494.html

 

[Hiddencamper]

Anyone able to edit the Wikipedia page? The last phrase of this paragraph especially...

2017 radiation spike

On 3 February, 2017, several news agencies reported a significant spike in radiation levels from Reactor #2, peaking at 530 sieverts per hour, the highest level recorded since the March 11, 2011 incident. [37]These levels were announced by TEPCO, the utility company that oversees the Fukushima reactors.[36] The previous high was 73 sieverts per hour, in 2011. TEPCO believes the spike may be caused by melted nuclear fuel burning through the bottom of the containment.[35]

I took care of it. I'm horrible with Wikipedia though. There probably needs to be a new section about the findings from the Pcv inspection and a screen shot of the spliced images of the grating melt. I'll try to do these later if I get my computer set up again. But if someone else wants to do it that would be great.

Edit: another use keeps changing it. Not sure how to proceed

 

[Charles Smalls]

For fuel that still has normal configuration, BWR fuel is air coolable in 4 months and PWR fuel at 11 months according to studies headed by the us nuclear regulatory commission.

Being in a non standard configuration would likely reduce surface area and reduce heat transfer.

Hi Hiddencamper, thank you too for so much valuable insight.

The fuel cooling subject is an interesting one. My tutor was talking about surface area and heat transfer comparing french fries to a baked potato and it brought me to thinking about the reactor fuel melts. The mass must have different retention properties compared to the bundles. On the other hand, I really had no idea there was such a difference between BWR and PWR fuel heat decays or that either would be so short.

https://www.nrc.gov/waste/spent-fuel-storage/faqs.html

The NRC website on the above page quotes a more typical wet storage time frame of 3-5 years before transferring to dry casks. Is the additional time to allow the fuel to 'cool' radioactively as well as thermally or just good operating procedure?

 

[Hiddencamper]

Hi Hiddencamper, thank you too for so much valuable insight.

The fuel cooling subject is an interesting one. My tutor was talking about surface area and heat transfer comparing french fries to a baked potato and it brought me to thinking about the reactor fuel melts. The mass must have different retention properties compared to the bundles. On the other hand, I really had no idea there was such a difference between BWR and PWR fuel heat decays or that either would be so short.

https://www.nrc.gov/waste/spent-fuel-storage/faqs.html

The NRC website on the above page quotes a more typical wet storage time frame of 3-5 years before transferring to dry casks. Is the additional time to allow the fuel to 'cool' radioactively as well as thermally or just good operating procedure?

The difference between PWR and BWR fuel has to do with power density. Due to lower heat transfer in BWRs because of boiling, a BWR core needs 3-4 times as many fuel assemblies to have the same power output as a PWR.

As for the duration, the 3-5 years is because of cask safety analysis for storage casks. You can store fuel in shorter times, but you would have to put less fuel rods in the cask as a result, and that is wasteful. The casks have both local heat limits and total heat limits based on loading.

 

[jim hardy]

@Hiddencamper

what little i could see of reactor bottom looked in surprisingly good shape to me.

Ours(PWR) of course had only traveling incore tube penetrations , i think not even a drain . So it was much simpler.

Did i miss sight of a lower head melt-through?

With all the seawater that went through in early days sediment is no surprise. Need a few pieces of it to analyze. Surely they've done that ?

old jim