[Where from?]1.4 billion Bq/Kg of Co-60 measured from debris attached to the new fuel in SFP4, “feels like grit”

According to Tepco, significantly high level of Co-60 was measured from the piece of debris taken from SFP4.


They measured 1,400,000,000 Bq/Kg of Co-60 (half-life 5.3 years). The surface dose was 1 mSv/h.

The sample was 4g. It was taken when they washed the new fuel assembly removed from the spent fuel pool in reactor4. (8/29/2012)

Tepco states it felt like grit. Some parts were broken into sand, which couldn’t be collected.

They also collected debris from between the fuel assemblies when they removed the channel box of the new fuel from SFP4.

They measured 830 million Bq/Kg of Co-60 from the piece of sample as well.


↓ Extremely high level of Co-60

1.4 billion Bq/Kg of Co-60 measured from debris attached to the new fuel in SFP4, "feels like grit"



↓ The samples taken from the new fuel

2 1.4 billion Bq/Kg of Co-60 measured from debris attached to the new fuel in SFP4, "feels like grit"






Thank you for considering donation !


Français :

[D’où ?] 1,4 milliards de Bq/kg de cobalt 60 dans des débris collés sur les assemblages neufs dans la SFP4, “on dirait du sable”


Selon Tepco, des niveaux particulièrement élevés de Co 60 ont été relevés sur un débris pris dans la SFP4 (piscines à combustibles du réacteur 4).

Ils y ont relevé 1 400 000 000 Bq/kg de Co 60 (demie-vie 5,3 ans). La dose en surface était à 1 mSv/h.
L’échantillon pesait 4 g. Il avait été pris lorsqu’ils ont nettoyé l’assemblage neuf qu’ils avaient retiré du réacteur 4 (le 29 août 2012).
Tepco affirme que ça ressemble à du sable. Certaines parties ont été pulvérisées en sable, ce qui ne peut être récupéré.
Ils ont aussi récupéré des débris d’entre les assemblages lorsqu’ils ont retiré le râtelier de l’assemblage neuf de la SFP4.
Ils ont relevé 830 million Bq/kg de Co 60 sur cet élément aussi.

↓ des niveaux particulièrement élevés de Co 60
1,4 milliards de Bq/kg de cobalt 60 dans des débris collés sur les assemblages neufs dans la SFP4

↓ Les échantillons pris dans le combustible neuf
2 1,4 milliards de Bq/kg de cobalt 60 dans des débris collés sur les assemblages neufs dans la SFP4


Merci de penser à un don !

  1. Yes, the high radioactivity for a 4 gram sample makes sense. The shorter the half life, the more radiactive decay per unit of time, and thus, more radiactivity per Kilo/gm It is the stuff with the short half life that is the most radiactive per weight. So it makes even more sense that nukes with short half lifes are the most dangerous from a radioactive perspective, ignoring chemical toxicity in this case.
    So it also makes sense that it is the Cs134, that is the most radioactive compared to the Cs137. Approximately 15 times more radioactive than Cs137. Cs134 has a half life of approx 2 years, and Cs137 is around 30 years. 30 divides by 2, 15 times so it is 15 times more radioactive. You would think officials could at least provide general information like that on a regular basis. I am quite certain this correct. Verify everything.

  2. Fortunaetly, the boiling point of Cobalt is very high, so there is not much chance that it can boil away like Cesium unless it is a very hot meltdown i suppose. Thus it should stay in one place.
    “2,870 °C
    Cobalt, Boiling point”
    “670.8 °C
    Caesium, Boiling point”
    “1,382 °C
    Strontium, Boiling point”
    “3,232 °C
    Plutonium, Boiling point”
    Cesium is the most reactive metal of all.
    Strontium is the 4th most reactive.
    Cobalt is the 6th most reactive.
    The chart did not include the reactivity of Plutonium, but other sources say it is very chemically reactive also.

  3. (Off topic for a second.) Cesium reacts with water to form a caesium hydroxide (CsOH) and ****hydrogen gas (H2). It also reacts with Zirconium. Verify everything.

  4. The cobalt was probably not hot enough to boil into the air, and instead precipitated on, and reacted with, something nearby which imobilised it??

  5. Old reactors can have cobalt present in steel alloys. The cobalt-59 in the steel captures a neutron from the fission process and becomes cobalt-60. If the steel is rusting then the cobalt-60 flakes off or gets washed away by water or coolant.

    1. Thanks Allan. So now all i have to do is some verification on your ellucidation/explanation. Quite a learning curve.

      Some quote from Wikipedia for myself and others.
      “Cobalt-60 (Co-60 or 60Co) is useful as a gamma ray source because it can be produced—in predictable quantity, and high activity—by simply exposing natural cobalt to neutrons in a reactor for a given time.” (Natural Cobalt59)

Comments are closed.

About this site

This website updates the latest news about the Fukushima nuclear plant and also archives the past news from 2011. Because it's always updated and added live, articles, categories and the tags are not necessarily fitted in the latest format.
I am the writer of this website. About page remains in 2014. This is because my memory about 311 was clearer than now, 2023, and I think it can have a historical value. Now I'm living in Romania with 3 cats as an independent data scientist.
Actually, nothing has progressed in the plant since 2011. We still don't even know what is going on inside. They must keep cooling the crippled reactors by water, but additionally groundwater keeps flowing into the reactor buildings from the broken parts. This is why highly contaminated water is always produced more than it can circulate. Tepco is planning to officially discharge this water to the Pacific but Tritium is still remaining in it. They dilute this with seawater so that it is legally safe, but scientifically the same amount of radioactive tritium is contained. They say it is safe to discharge, but none of them have drunk it.