Fukushima Japan Earthquake: nuclear plants Fukushima part 2

[Sotan]

A new NRA meeting was held on Jan 13, 2023 to discuss the materials listed here (in Japanese).
I opened this document, which is a general review of what is known about the nuclear accident until now. I will post below the translation of a portion of this document, starting with the page numbered 26 in the PDF file. It's google translation with just a few small edits by me where the result seemed odd. The fragment presents the findings on debris at the bottom of the PCV of Unit 1, based on the investigations made up to date, and suggests/discusses 3 scenarios that are taken into consideration. The text on the 3 scenarios is presented in the post following this one, in case there is a limit in size (apologies for the length of these posts.)

Chapter 2
Behavior of the Falling Core and its Impact on the Primary Containment Vessel
Section 1 Inside the Unit 1 Primary Containment Vessel, Examination Status
2-1-1 TEPCO Report and Features

Since February, we have been taking pictures of the inside of the Unit 1 reactor containment vessel. The specific equipment, details of implementation, and photographing results are described in Attachment 4-1. Prior to this, TEPCO and IRID have taken pictures of the inside of the reactor containment vessels of Units 2 and 3. Although it is not yet sufficient due to the severity of the environment, the information obtained in the process is summarized in Attachment 4-2. The results of the photography inside the PCV of Unit 1 differed greatly from the results of photography inside the PCV of Units 2 and 3, which had already been carried out, and this attracted attention. In addition, photography of the inside of the reactor containment vessels of each unit has not progressed sufficiently, and the above understanding may change in the future.

The photographing results that attracted attention are as follows (see FIGS. 8 to 10). (See Attachment 4-3)

(1) TEPCO determined that there was a mound-like object with a height of about 1.0m, which was likely derived from the fallen molten core, near the Unit 1 pedestal opening.

(2) Concrete near the Unit 1 pedestal opening has been lost over a considerable area. On the other hand, the reinforcing bars and inner skirt that were inside the concrete have remained almost unchanged. Such a phenomenon has not been confirmed in Units 2 and 3 so far.

(3) A terraced structure was observed around the pedestal, with a height of 1.0 to 1.1m from the bottom of the primary containment vessel near the opening, and a height of 0.2 to 0.4m on the opposite side of the opening. Moreover, it seems that the concrete failure occurs only in the part below the terrace structure.

(4) Although it is a small part, a cross-sectional image of a terrace-like structure has been obtained, and a structure with bubbles can be seen, but nothing more is known about these. The thickness of the section is estimated to be approximately 3 cm. Note that the lower surface of the terraced structure appears smooth.

(5) Deposits thought to have arrived from the pedestal can be seen on the back side of the jet deflector located at the outermost periphery of the reactor containment vessel, but no major damage is seen on the jet deflector itself. As far as it can be seen, there is no major damage to the inner surface of the reactor containment vessel.

(6) It has been confirmed that the lower part of the terrace structure is hollow near the pedestal opening, but it is unknown at this stage what happens in places away from the opening. In addition, in places where there are few structures in front of the pedestal opening, the terraced structure has fallen onto the floor of the containment vessel.

(7) Metal structures such as pipes located at the bottom of the terrace structure appear to be mostly maintained. However, the RCW (Reactor Cooling System) piping near the opening is not in its original position, and its whereabouts have not been confirmed.

(8) The lead shield mats (lead wool mats) appears to have melted and fallen at the position of the terrace structure. At the top of the terrace structure, the covering material (glass fiber) of the lead shield mat (lead wool mat) seems to be maintained, and the effect of the significant high temperature seems to be limited to the vicinity of the terrace structure. In addition, TEPCO confirmed that the lead shielding was lost below the same height as the opening of the pedestal even on the opposite side of the pedestal opening.

(9) A bubble-shaped object can be seen at the pedestal opening at a height of 1.4m, but it is clear that there is a space below it. However, no information has been obtained as to what the back surface of the bubble-shaped portion looks like.

(10) Debris deposits on the floor surface of the reactor containment vessel around the pedestal are unclear, but some hemispherical objects have been photographed. (It is not clear at this stage what exactly it is.)

 

[Sotan]

(Following up from the previous post)

2-1-2 Draft Scenarios, etc. proposed by the Accident Analysis Committee (Attachment 4-3 and Attachment 5)

The investigation team is proceeding with consideration of the following three basic questions.

(1) Why does the molten core not seem to spread thinly? Conventionally, it has been thought that the molten core spreads thinly and widely. The height of the terraced structure near the pedestal opening is 1.0 to 1.1m from the bottom of the containment vessel, and although it is unconfirmed at this time, it is possible that about 1.0m has accumulated at the pedestal opening or behind it. There is a possibility that it is inconsistent with this conventional knowledge.

(2) Why was the concrete of the pedestal wall lost? Conventionally, in MCCI (Molten Core Concrete Interaction), which has been considered for safety evaluation, it is thought that molten debris of about 2000°C comes into contact with reinforced concrete and melts/damages the reinforcing bars as well. However, this time, metal structures such as rebar remain mostly intact, and the temperature seems to stay below 1000°C (not only the rebar but also the relatively thin piping around it remains in its original shape. In addition, considering the way the lead shield mats (lead wool mats) are affected, it is possible that the melted-down area is the result of 'cold' interactions, including the very close proximity of the terraces.

(3) How was the terraced structure formed? The formation process of the terraced structure is not known at this stage. Assuming that the molten debris layer exists up to the present position of the terrace structure, if the fallen molten core simply takes with it all the metal structure directly below the reactor pressure vessel (RPV), it is thought that the resulting debris it will not accumulate to such a height. The 33rd Meeting of the Accident Analysis and Investigation Committee Document 1-1 P8 states, “Even assuming that all the fuel and internal structures inside the reactor have melted, the deposition height should be about 1.1 m inside the pedestal.

The following three models were proposed to the Accident Analysis Study Group as potentially able to answer the three basic questions above. These models were presented from the perspective of promoting future discussions and experiments, and we are not at the stage where we can discuss the superiority or inferiority of the proposals at this stage.

The scenarios proposed by the accident analysis study group can be roughly divided into the following three types:
A: Concrete melting model at high temperature
B: Concrete dissolution model in water
C: Molten core expansion model due to gas

A: Concrete melting model at high temperature (Attachment 5)
- The molten core falls into the pedestal and spreads outside of it through the pedestal opening.
- The melted material raises the temperature of the concrete, and the concrete melts.
- A crust is formed, causing concrete damage and cavities when the melt contents inside move on.

Through the above process, it is believed that the falling core melted material raised the temperature of the concrete near the pedestal opening, resulting in concrete failure and the formation of table-like deposits. In this scenario only the concrete failed because the temperature of the concrete did not reach the melting temperature of the rebar.

B: Concrete dissolution model in water (Attachment 5)
- Water temperature and pressure rise locally due to core meltdown falling in an environment where water or steam exists in the pedestal.
- Concrete is damaged by dissolution of concrete components in high-pressure water. A highly viscous liquid phase is formed consisting of concrete components and a large amount of water. As the water temperature rises and the local pressure is released, the water evaporates and the dissolved concrete components solidify while foaming.
- More water evaporates, creating cavities at the bottom of the condensate. Through the above process, the fallen core melt generates high-temperature water or steam, which reacts with the concrete components to break the concrete and create a highly viscous liquid phase that is the source of table- (terrace-)like deposits. Water at high temperature and pressure is known to dissolve rocks, especially SiO2 in rocks. Concrete is composed of aggregate and cement, and if the aggregate contains a lot of SiO2, the aggregate in concrete may dissolve in high-temperature, high-pressure water. It is also known that glass containing a large amount of water, which is produced by the reaction of high-temperature, high-pressure water and SiO2, expands and becomes porous when the water evaporates. A similar phenomenon may have occurred in the reactor, resulting in the formation of terrace- or table-like deposits.

C: Molten core expansion model due to gas

The fallen molten core appears to form a 1m-high bulge at the back of the pedestal opening, and it is highly likely that it also spreads to the outer periphery of the pedestal. On the other hand, the bulge within the pedestal does not currently appear to fill the pedestal. If it is confirmed that a bulge is formed, there are two possibilities considered at the present, one being that the viscosity of the fallen core was high [and somehow led to such formations], and another is that gas ejection left such structures after the fallen core accumulated to some extent at the bottom.

After that, it is thought that the dropped molten core passed through the pedestal opening and gradually flowed out to the outer periphery of the pedestal. The degree of spreading cannot be determined without additional information from internal vessel investigations that will follow.

The energy / heat (including the effects of gamma rays) from the radiant core from the molten core increased the temperature of the pedestal wall, causing the concrete to decompose, lose its strength, and become powdery. Mechanisms for loss of strength include desorption of calcium and generation of stress due to phase changes in crystal components in the concrete. A radiation-induced warming failure mechanism does not require direct contact between the molten core and concrete and may explain why so little solidification of the molten core is found in the remaining rebars of the pedestal walls. In addition, it is known that the compressive stress of concrete is greatly reduced in the above reaction at around 700 to 1000℃. It may be reasonable to think that the concrete with reduced cohesive strength was washed out after the alternative water injection got into full swing.

When the pedestal floor or pedestal wall reacts with the molten core, carbon dioxide and water vapor are generated. Cooling water that leaked from the core (thought to be limited in quantity) may also have been involved. These gas-rich layers (hereafter referred to as “swollen layers”) are sometimes referred to as “swelled melt” in MCCI-related literature, but since the experimental conditions vary greatly it is not clear whether it refers to exactly the same phenomenon.) It is unclear whether such layers were integrated with the molten core body or present as a separated layer, but here we are thinking of it as a separated state (like in an image of beer foam) . At present, the temporal relationship between the outflow of the molten core from the pedestal opening and the formation of the "expansion layer" is unknown.

Components containing silicon separated from the concrete located at the top of the "expansion layer" to form a sort of film or layer. It is conceivable that this film solidifies due to factors such as a temperature drop and adheres to the surrounding pipes and equipment. The phenomenon of sticking to pipes, etc. is a phenomenon called "anchoring" in previous MCCI experiments, but it has not been confirmed whether it would have occurred reliably under the conditions of this time. It is also possible that some of the powdered concrete deposited on top of this film and facilitated its formation. It should be noted that the adhered membranes/layers seen in past MCCI experiments are relatively fragile, and in open spaces such as the front of the pedestal opening, where there are no pipes for "anchoring", it is quite possible that such a layer will collapse. Also, the "thin membrane" contains many air bubbles and can be quite insulating. If so, it may explain that the concrete failure is confined to the bottom of this 'thin film'.

After that, due to the decrease in decay heat and the progress of alternative water injection, the temperature of the "expansion layer" dropped and contraction occurred, leaving only the "thin membrane" in its original position. It should be noted that if a crack occurs in the "thin film" during the growth process of the "expansion layer", it is quite possible that the "expansion layer" and the "thin film" will be formed on top of it. It may be possible to explain this way that there are places where the terraced structure is multi-layered.

It may be unlikely that a “thin film” (terrace-like structure) remains in the pedestal at a height of about 1 m. While the diameter of the pedestal is about 6m, it seems that there are not many pipes that can serve as anchoring at a height of about 1m. Furthermore, it is believed that a considerable amount of water flowed down from the damaged part of the pressure vessel to the pedestal when the alternative water injection got into full swing.

 

[Sotan]

New article (from 5 days ago) on the IAEA site about recent developments at Fukushima Daiichi.
It contains a link to a new report from the Government of Japan which "summarizes the events and highlights the progress related to recovery operations at the Fukushima Daiichi Nuclear Power Station." The report covers the developments up to September 2022 so it's not very up to date but it's a good lecture and... it's in English.

 

[Sotan]

- A report published on April 4 by Tepco includes many photos taken inside the pedestal of Unit 1 showing the inner walls of the pedestal with exposed rebar but also debris presumed to be CRD housings, CRD housing supports and CRD's, together with more rubble-like and lumpy deposits.

 

[Sotan]

An even better report published on Apr 24 on the NRA meetings page.
(Using the page numbers printed at bottom right in the PDF file)

- Most impressive, on page 11 you can see a panorama stitched from photos taken inside the pedestal of Unit1.

- Page 3: Steel bars exposed, "about 1 m above the floor" - not clear if the mean the whole 1m from floor up or just a smaller region in the area of the 1m height level. (A full 1m of concrete missing somehow seems a lot to me, but I suppose it's possible.) Still, they seem happy that the bars do not seem melted or deformed, they even preserve the striations from factory (Photo 2). Suggesting they still support the RPV weight well. A fallen CRD housing in Photo 3. Photo 3 also shows a remaining portion of "terrace-" or "shelf-shaped" debris, which I imagine is part of the crust formed after the solidification of the molten innards of the reactor. Above that shelf-shaped debris the concrete of the pedestal walls is still in place.

- Page 5: At the bottom of the pedestal the largest fallen structural components identified appear to be CRD housings. In particular, the "CRD replacement machine" (can't remember the correct term. CRD exchanger?) main assembly was not visible, only part of its rails and (a) wheel. All around there is debris, as high as ~1m, and fallen structural components such as CRD housings can be identified.

- Page 6: Looking up in the pedestal. CRD assemblies can be seen. Some of them seem displaced, being lower than originally (also shown on Page 23 Photo 3). Some of them have fallen. Around the point indicated by number 7 a "black spot" appears (Photo 2) where normally should have been some CRD unit; it is possible that this is a hole in the RPV bottom.

- Page 7 gives a photo of the area before the accident.

- Page 8: again, looking up in the pedestal. A stream of water drops are falling up from above, in an area roughly in the center of the pedestal (Photo 1), creating a foamy patch on the surface of the water. Probably flowing through the breach of the RPV bottom. In the area of the opening used by the CRD exchanger there appears to be a fallen CRD housing, it will need to be taken in consideration (as an obstacle, I guess?) for the planning of next investigations or debris removal operations.

- Page 11 - the "panorama". (After that there are a number of pages with photos already reported before.)

- Page 24-25 - a comparison with other units. Unit 1 was without cooling for the longest time so it is assumed to be the worst affected. The photos on these pages seem to support that assumption.

 

[Rive]

Thank you for still following the topic and providing updates on the situation.

 

[Sotan]

* Article in Asahi (google translated) reporting the request from Nuclear Regulation Authority to TEPCO "to evaluate the impact of radioactive material scattering outside the site, including the possibility of a hole (that might occur) in the containment vessel due to subsidence of the pressure vessel (for example in case of an earthquake), and to consider countermeasures". NRA is not convinced of TEPCO's optimist conclusion that the pedestal of Unit 1 is still able to support the reactor vessel in case of a large earthquake.

* There are many articles (like here or here or here) about the upcoming release of tritiated water from Fukushima into the ocean. All the work needed (including an underground tunnel) for this purpose has been done and efforts are being made to convince the public that the release is safe. IAEA representatives are visiting the site these days and IAEA is planning to issue a final report next month.

 

[etudiant]

* Article in Asahi (google translated) reporting the request from Nuclear Regulation Authority to TEPCO "to evaluate the impact of radioactive material scattering outside the site, including the possibility of a hole (that might occur) in the containment vessel due to subsidence of the pressure vessel (for example in case of an earthquake), and to consider countermeasures". NRA is not convinced of TEPCO's optimist conclusion that the pedestal of Unit 1 is still able to support the reactor vessel in case of a large earthquake.

* There are many articles (like here or here or here) about the upcoming release of tritiated water from Fukushima into the ocean. All the work needed (including an underground tunnel) for this purpose has been done and efforts are being made to convince the public that the release is safe. IAEA representatives are visiting the site these days and IAEA is planning to issue a final report next month.

I'm really surprised that the Japanese government is so determined to dump the Fukushima water immediately.
It is less than 2 million tons, so a dozen tankers would easily hold all of it in safe storage, at a construction cost of a few billion dollars at most, a trifle compared to the overall cost of the. cleanup.

Japan is clearly interested in reopening its nuclear power segment. That will be made easier if there is no new nuclear pollution event such as the dumping of this contaminated water. Instead, move the tankers to some non typhoon susceptible location for a few decades to allow further tritium decay, thereby defusing the issue entirely
Afaik, The area around Christmas Island is one such location and I'm sure a long term anchorage could be arranged reasonably cheaply, with due provisions for ongoing maintenance and supervision.

 

[Astronuc]

13 years after meltdown, the head of Japan’s nuclear cleanup is probing mysteries inside reactors​

https://apnews.com/article/japan-fu...tdown-debris-ae9cea4db2a839b7fe4a8c53f22f3fd7

Yes - we need samples of what is left of the damaged fuel, otherwise, we are simply speculating based on indirect evidence. At TMI, cameras were lowered into the core and it was clear that some chemical interaction and possible melting has occurred in the fuel. Fuel samples were collected and analyzed. TMI-2 is still sitting there with contamination. When I was at the site in the 1990s, it was still too radiologically 'hot' to enter.

https://en.wikipedia.org/wiki/Three_Mile_Island_Nuclear_Generating_Station#Decommissioning

Soluble fission products may permeated the concrete, which make decommissioning challenging.

 

[Vanadium 50]

Soluble fission products may permeated the concrete, which make decommissioning challenging.

I assume you're worried about cesium and strontium? Presumably dissolved in the water and exchanged with water in the concrete?

If so, isn't that a good thing? It's already partially sequestered. Spray some plastic sealant on it and dispose of it.

 

[gmax137]

Many years ago a co-worker summarized our rad safety training as, "don't lick the walls."

 

[Astronuc]

cesium and strontium?

Yes, primarily, and their decay products, e.g., Ba and Y, and a little Rb, precursor to Sr. They will be distributed at the surface and into the concrete. It's what accumulates at the surface, and it's not so much beta and decay gammas.

They could spray a binder on the concrete, but then disassembly, which would cause dust is an issue. One would have to do a wet grind and collect the fragments and particulate matter, and filter what dissolves in the water.

 

[Rive]

If so, isn't that a good thing?

If you can just leave it alone then could be fine, but they are still supposed to work there for some time. And to keep the radiation levels of such working environment low enough to keep limits is troublesome. It's no longer an emergency, so limits are strict...

As I recall even in the very first years they already had some attempts and tests on this, and indeed, removing surface (possibly contaminated) layers was an option they tested.

Grinding, pressure washing, shot-blasting, acidic etching and so on...

 

[Astronuc]

Fuel debris removal attempt halted at Fukushima Daiichi
https://world-nuclear-news.org/Articles/Fuel-debris-removal-attempt-halted-at-Fukushima-Da

On 19 August, Tepco announced that it planned to remove a few grams of melted fuel debris from unit 2 on August 22. The operation was expected to last about two weeks using a telescopic device equipped with a gripper tool. The device can extend up to 22 metres and access the debris through a penetration point in the primary containment vessel (PCV). The removal technique, which is being used for the first time in unit 2, will then be gradually extended to unit 3, where a large-scale recovery is expected in the early 2030s.

"Unit 2 was selected as the first block for the recovery of the fuel debris because we take into account the situation in terms of safety, reliability, speed and progress in the removal of the used fuel elements," Tepco said.

Workers at the plant today began inserting the guide pipe of the telescopic debris retrieval device into the PCV penetration point. The guide pipe was inserted to the front of the isolation valve and the first of five 1.5-metre-long push pipes to be used was prepared to be connected. The pipes are used to push the device inside the PCV and pull it back out when the operation is completed.

However, it was then noticed during the final checking process that the order of the first push pipe was different from the planned order. The workers had in fact prepared the second push pipe for insertion instead of the first one. It was confirmed the push pipe that should have been in the first position was in the fourth position. The incorrect order of the pipes meant they could not be connected correctly.
. . .

 

[berkeman]

Yikes. I wonder how many times they did dry-run practices. Apparently not many times...

 

[Astronuc]

AP News - A robot has begun a 2-week mission to retrieve melted fuel from the damaged Fukushima nuclear plant
https://apnews.com/article/japan-nu...debris-robot-f36c5ead0bdb0facf77688dde644b7dc

TOKYO (AP) — An extendable robot began on Tuesday a two-week mission to retrieve the first sample of melted fuel debris from inside one of three damaged reactors at the Fukushima Daiichi nuclear power plant.

Highly radioactive fuel and other materials in the reactors melted when a massive earthquake and tsunami in 2011 damaged the plant’s cooling systems.

The plant’s operator, Tokyo Electric Power Company Holdings, has previously used small robots to examine the inside of the reactors, but this is the first time for it to collect a sample of the melted debris in what will mark the start of the most challenging part of the plant’s decadeslong decommissioning.

The mission was initially scheduled to begin on Aug. 22 but was suspended when workers noticed that five 1.5-meter (5-foot) pipes to be used to push the robot into the reactor had been arranged in the wrong order, TEPCO said.

It looks like they reconstructed the system properly this time.

The tongs will be used "to collect a fragment measuring less than 3 grams (0.1 ounce)." There are 28.35 grams per ounce (oz), to 3 grams is about 0.106 oz.

 

[Vanadium 50]

These robots are very impressive, if you've ever seen one.

It seems like an easier solution would be to full the containment vessel floor to ceiling with borated high density concrete. ("blue blocks") Any idea why they don't?

 

[Rive]

Any idea why they don't?

Nuclear people these days already has a tendency for OCD, and they are ...
So likely it'll be clean when done.
Not buried: clean.

 

[gmax137]

retrieve melted fuel ... a fragment measuring less than 3 grams

I'm curious about what information the analysis results from such a sample will provide, and how that info can be used going forward. In other words, what does TEPCO hope to find out?

 

[Astronuc]

I'm curious about what information the analysis results from such a sample will provide, and how that info can be used going forward. In other words, what does TEPCO hope to find out?

I think they will need to collect multiple samples to characterize the nature of the fuel and core support structure. In a severe accident case in which the 'core' (assemblies, control elements, and core support structures) melts, then one often refers to 'corium'.

It may be difficult to tell what happened with any certainty, since they flooded the containment eventually with seawater, so there will have been many chemical reactions beyond just melting fuel - if the fuel did indeed melt.

 

[Astronuc]

These robots are very impressive, if you've ever seen one.

It seems like an easier solution would be to full the containment vessel floor to ceiling with borated high density concrete. ("blue blocks") Any idea why they don't?

I suspect they want to deconstruct and remove the structure and return the site as close to natural as possible. If they basically entomb the structure in concrete, they will likely be required to do some kind of monitoring indefinitely.

 

[Sotan]

Looks like they ran into trouble again.

"On Sept. 17, TEPCO could not confirm camera images of equipment being used to remove the debris from the No. 2 reactor of the plant, bringing a stop to the project, the utility said."

 

[Sotan]

A new (at least for me it's new) site by TEPCO with information about the fuel debris and news for Units 1, 2 and 3. It has an English version too. I'm thinking maybe not everyone has found it.
FUEL DEBRIS PORTAL SITE
Japanese version
English version
If you check Unit 2, for example, you get nice explanations, photos & videos about the ongoing process of debris sample retrieval operations.

 

[Sotan]

On the "Fuel Debris Portal Site" linked in the previous post there are new reports added, most recent ones from Oct 31.
One of them is a video showing the tip/fingers of the robotic arm pinching and grasping a little piece of fuel debris. A short explanation of this operation is here.
Then there's this report on the "Unit 2 PCV Internal Investigation/ Status of Fuel Debris Trial Retrieval", and this one about "Analysis of fuel debris sampled from Unit 2 on a trial basis".

 

[Astronuc]

TEPCO ex-chair at time of Fukushima nuclear disaster dies at 84 while on trial over responsibility​

https://apnews.com/article/japan-te...iminal-trial-38bb91ef7862eac5b874791637e4c833

TOKYO (AP) — Tokyo Electric Power Company Holdings’ former chairperson, who led the emergency response after a meltdown at its Fukushima Daiichi nuclear plant and was accused of being responsible for failing to prevent the disaster as top management, has died, with his trials still pending. He was 84.

Tsunehisa Katsumata died on Oct. 21, TEPCO said Thursday, without providing further details including the cause of his death.

Katsumata was TEPCO chair when Fukushima Daiichi was hit by a magnitude 9.0 earthquake and tsunami in March 2011 and suffered triple meltdowns. He led the emergency response after the company’s then-president stepped down due to health problems and served until mid-2012.

He later became one of the defendants in high-profile criminal and civil lawsuits seeking TEPCO management’s responsibility over their alleged failure to anticipate the massive quake and tsunami and to take preventive measures.

Firstly, I express my condolences to Tsunehisa Katsumata's family, friends and associates, who lost a significant person in their lives.

TEPCO had been warned for years that the tsunami defenses were inadequate, and in fact, it appears the government ignored historical evidence that such tsunamis had affected Japan's Pacific coastline over the past several centuries. Fukushima Daiichi should have been properly protected. An site evaluation should have captured the significance of the history of tsunamis and the consequences, especially with respect to necessary protective measures.

http://historyofgeology.fieldofscience.com/2011/03/historic-tsunamis-in-japan.html

https://en.wikipedia.org/wiki/1923_Great_Kantō_earthquake

A tsunami with waves up to 10 m (33 ft) high struck the coast of Sagami Bay, Bōsō Peninsula, Izu Islands, and the east coast of Izu Peninsula within minutes. The tsunami caused many deaths, including about 100 people along Yui-ga-hama Beach in Kamakura and an estimated 50 people on the Enoshima causeway. Over 570,000 homes were destroyed, leaving an estimated 1.9 million homeless.

https://en.wikipedia.org/wiki/1896_Sanriku_earthquake

The 1896 Sanriku earthquake (明治三陸地震, Meiji Sanriku Jishin) was one of the most destructive seismic events in Japanese history. The 8.5 magnitude earthquake occurred at 19:32 (local time) on June 15, 1896, approximately 166 kilometres (103 mi) off the coast of Iwate Prefecture, Honshu. It resulted in two tsunami waves which destroyed about 9,000 homes and caused at least 22,000 deaths. The waves reached a then-record height of 38.2 metres (125 ft); this would remain the highest on record until waves from the 2011 Tōhoku earthquake exceeded that height by more than 2 metres (6 ft 7 in).

 

[Sotan]

Fukushima Daiichi Nuclear Power Station Completion of fuel debris trial retrieval from Unit 2
1-page report of November 7

 

[Astronuc]

It's really difficult to determine if the fuel is 'melted' as opposed to 'chemically reacted', since the focus is rather poor.

A tiny grain of nuclear fuel is pulled from ruined Japanese nuclear plant, in a step toward cleanup​

https://apnews.com/article/japan-nu...ommissioning-b7dd956a86401b39f04ae839f768d29f

The extendable robot, nicknamed Telesco, first began its mission August with a plan for a two-week round trip, after previous missions had been delayed since 2021. But progress was suspended twice due to mishaps — the first involving an assembly error that took nearly three weeks to fix, and the second a camera failure.

On Oct. 30, it clipped a sample weighting less than 3 grams (.01 0.1 ounces) from the surface of a mound of melted fuel debris sitting on the bottom of the primary containment vessel of the Unit 2 reactor, TEPCO said.

Three days later, the robot returned to an enclosed container, as workers in full hazmat gear slowly pulled it out.

On Thursday, the gravel, whose radioactivity earlier this week recorded far below the upper limit set for its environmental and health safety, was placed into a safe container for removal out of the compartment.

It will be interesting to know the chemistry of the material and how much Zr (from cladding), U,Pu,FP (from fuel) and (Fe, Cr, Ni, Mn, . . . ) from the stainless steel, ostensibly in the form of oxides. FP = fission products.

I know from informed sources that they expected the fuel did melt (based on simulations and what little evidence was available at the time). I'm waiting for the physical evidence.

 

[gmax137]

3 grams (.01 ounces)

Something isn't right here.

 

[Astronuc]

Something isn't right here.

Fixed. It should be 0.1 oz.

 

[Sotan]

Regarding the results of analyses, quoting from this report mentioned in a previous post,
"The results from overall analysis performed at the JAEA Oarai Research and Development Institute (fuel debris surface element distribution, etc.) should be compiled in several months, and the results of analyses performed at other facilities should be compiled in approximately one year. The time required for analysis may vary depending on work conditions and analysis results."

So it will take a while.

- I hope that little piece of debris is not being considered representative for the whole deposit at the bottom of the PCV - what was it, 200 tons plus? I mean, spending months to analyse that chip, okay but how valuable will those conclusions be. Or maybe they will keep getting samples during these months? Didn't seem so, from the wording ("completion of fuel debris retrieval").