Fukushima Japan Earthquake: nuclear plants Fukushima part 2

[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").

 

[Astronuc]

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?

Fukushima Daiichi Unit 2 was a BWR/4 type with a gross electrical power generation of 784 MWe gross, 760 MWe net (so about 24 MWe used by the plant). Units 2, 3, 4 and 5 were much the same design, and apparently not uprated.
https://en.wikipedia.org/wiki/Fukushima_Daiichi_Nuclear_Power_Plant

The Fukushima BWR/4s would have 560 assemblies in the core, and I believe each assembly has about 180 kg of fuel (which could be in terms of U metal), about about 200 kg of fuel (UO2) + structural materials like Zircaloy-2 (~46 kg Zr-2, not including channels/shrouds), stainless steel (~6.7 kg), and Inconel (incidental).

Estimating about 270 kg/assy x 560 assy/core, one has 151,200 kg (or 151 tonne) in the core, excluding core support structures.

The limited sampling can only give a clue as to what might have happened. It there is little or no U (and Np, Pu), then one is left with mostly stainless steel and/or Zr. If there is little or no Zr, then one is left with stainless steel. All metals are probably oxidized. I think they will look for metals that are characteristic of fuel, cladding and stainless steel structures, in order to determine where the sample originated, or what it represents. If they find some fission products, e.g., Ru, Rh, . . . . , then that would be from the fuel.

More samples are needed, but at least, TEPCO was successful in retrieving a sample, however small.



FYI - Comprehensive Analysis and Evaluation of Fukushima Daiichi Nuclear Power Station Unit 2
https://www.tandfonline.com/doi/full/10.1080/00295450.2019.1704581#abstract

 

[Sotan]

Two new posts on the "Fuel Debris Portal" site, dated March 19:

- Status of preparations for the second fuel debris trial retrieval from Unit 2 (pdf)
- Training at the Kobe Factory for the second fuel debris trial retrieval from Unit 2 (video)

 

[Sotan]

They completed the second "fuel debris sampling" operation.
Link to report

I don't want to sound disappointed but... This time it seems they retrieved 0.2g.

 

[Sotan]

New report on Tepco's Fuel Debris Portal site, about the first results of the analysis of the second sample (May 29).
>> Link

 

[Sotan]

New post on the "Fuel Debris Portal" site.
"2025.7.29 Fukushima Daiichi Nuclear Power Station Unit 3 Design Deliberation for Fuel Debris Retrieval Method"
There are two links at the bottom of that article, one is the report of a sub-committee regarding fuel debris retrieval (published in March, unfortunately only in Japanese) and the second is TEPCO's own report on this matter, submitted to the sub-committee on July 23 (in English).

"At present, it is estimated that approximately 12 to 15 years will be necessary to prepare the top and side access points regardless of which option (North-South work platform or the East-West framework) is employed. (However, the results of this deliberation are based on the assumption that progress will proceed as expected, even though there remain issues that require additional review.)"