Japan Earthquake: nuclear plants Fukushima part 2

[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.)"

 

[Sotan]

Hello again and may you all have a great new year in 2026!

I thought I'd point out an interesting new post on the "Fuel Debris Portal" site:

Fukushima Daiichi Nuclear Power Station Unit 3 PCV Internal Investigation (non-submerged area) using Micro drones

A new investigation device designed to insert two small drones into the PCV of Unit 3 through the X-53 penetration stumbles because of a slight misalignment / difference in level between the internal and external side of the penetration.

 

[gmax137]

Thanks for that link, @Sotan !
Very interesting and the graphics in the report are excellent.