Muon scan gives detailed, but incomplete, look at meltdown of No. 1 reactor


Confirmation this week that all the fuel inside one of the Fukushima No. 1 plant’s broken reactors has long since melted leaves its operator with the tricky task of eventually scooping it all out, experts say.

Tokyo Electric Power Co. said Thursday it had performed a sophisticated scan of the plant’s No. 1 reactor core, giving the most detailed picture so far of what is going on in the high-radiation environment.

Nuclear experts said Friday that the test showed the unit’s fuel rods had melted beyond recognition.

“The results reaffirmed our previous understanding that a considerable amount of fuel had melted inside the nuclear pressure vessels,” said Hiroshi Miyano, a visiting professor at Hosei University in Tokyo.

“But there has been no evidence that the fuel has melted through the nuclear containment buildings and reached the outer environment,” Miyano said.

However, the scan — based on tomography imaging that made use of elementary particles called muons — did not look at the bottom part of the reactor, where the molten fuel would have pooled. So some experts suggested that it was not possible to tell whether the fuel had indeed been contained.

The fuel rods are installed the reactor’s pressure vessel, which is in turn enclosed by the primary containment vessel. These rods generate the heat used to drive steam turbines and produce electricity but must be submerged at all times to avoid melting.

“Eventually, Tepco is aiming to scoop out the melted fuel little by little, rather than burying it in concrete” as was done at Chernobyl in the former Soviet Union, Miyano said.

Muons, which continually shower the earth from space, penetrate solid objects to a greater depth than x-rays. The rate at which they pass through a material indicates its density and helps scientists to identify it.

Since muons move more slowly through relatively dense plutonium and uranium fuel than through the reactor vessel itself, mapping their trajectory can reveal exactly where the fuel is — or isn’t.

The data from this test should help Tepco’s effort to decommission the plant, which lost all power in March 2011 after the Pacific coast of Tohoku was swamped by huge tsunami. The blackout triggered a triple core meltdown.

The decommissioning process at Fukushima is expected to take three or four decades.

Experts say the latest results and the operator’s assessment of them were in line with earlier expectations.

“We presume that despite the meltdown, the fuel is still in the containment vessel,” said Tomohisa Ito, a spokesman for the International Research Institute for Nuclear Decommissioning, a special research unit involved in dismantling the troubled plant.

“But we still need to directly check the situation one day using remote-controlled robots,” he said.

Last month the International Atomic Energy Agency said Japan had made “significant progress” in its cleanup efforts but warned the situation “remains very complex” due to the growing amounts of contaminated water being generated by the process.

While the quake and tsunami that triggered the man-made nuclear crisis killed almost 19,000 people, mostly by drowning, no one is officially recorded as having died as a direct result of the meltdowns at Fukushima, though indirect deaths related to the disaster continue to climb.

However, tens of thousands of people remain displaced because of radioactive contamination around the plant, and scientists warn that some settlements may have to be abandoned forever.

  • Liars N. Fools

    That model of probity is just a wonderful paragon.

    When a conniving mendacious company like TEPCO tells a truth inimitable to its interest, only then is it the real truth.

  • Geoffrey Small

    There is enough plutonium in that melted core that they “cannot find” to kill over 100 million people.

  • Frank Energy

    Effen azzhats, of course it melted out. To even pretend that any significant amount is still in the reactor is a criminal lie.

  • Den of the Chaldes

    All of the 3 reactor’s piles and #4’s SPF are either melt outs or blown to smithereens .

    It is either in the ground or long since in the atmosphere for all the fish, fowl, fauna and humans to enjoy… Many tons of radionuclide’s for all above to ingest.

    Ten years from now all life will be under its spell…and curse… And a score of yeàrs from now radioactive death will be the norm.

    Clean, green, low carbon annihilation is what just one nuclear plant failure will bring us, ànd just wait for the next two or three bring… And remember, there are more than 250 world wide.

    Stupid humans!


  • Bob Johnson

    How convenient, tepco forgot to look for leaks where gravity would take all the melted fuel. They know, if there were no leak they would report it to the world, but they are covering it up like they have the last 4 years.

  • greenthinker2012

    The article ends on an incorrect statement.

    It should read “However, tens of thousands of people remain displaced because of FEAR of radiation”

    The radiation levels in the areas around Fukushima are lower than the background radiation in some other areas of the world where people have lived healthy happy lives for countless generations.

    • Geoffrey Small

      Lol. You have got to be kidding. Let me guess, you work for Tepco’s PR bureau, right?

    • Nuke Pro

      Oh jeez, you trying to play that card/lie?

    • SykeWar

      Fear kept man alive for over 200,000 years. No reason to stop relying on it now. Especially when dealing with people who are, shall we say, less than completely and totally honest?

      In some areas around Fukushima, levels are low, in others, they’re very high. And it changes with the wind, rain and snow.

    • bo

      Those reading this thread: you can find out who the paid trolls are, by clicking on the ‘thumbs down’ button. The downvote option is locked for the trolls. Thank you.

  • SykeWar

    Lest we overlook the elephant in the room; radiation is not to escape containment in an uncontrolled manner… ever. If it can, then those reactors should not be put in service… ever. I hear the replies, “But, there was earthquakes and tsunamis”. And enough human error to insure that what happened, happened. Nuclear power is a great idea. In the hands of humans? Absolutely not.

  • I’m Not Here

    Japan can live on without having any operating nuclear power plants, all their nuke plants have been shut down now. Maybe make a deal, clean up Daiichi then restart other nuke plants.

    It is obvious with Japan passing a secrecy act to hide details of their nuclear industry’s failures or the US Navy losing or sealing sailors medical records that were aboard the USS Reagan’s flotilla or EPA raising background radiations levels along with radiation exposures limits after the Japanese melt-outs, that the nuclear industry relies on deception to pretend everything is fine and say there is nothing to see here, please move along and not worry about it.

    Worldwide, there is still no answer for safely storing spent and wasted nuclear fuel rods for hundreds to thousands of years. With the blobs of melted fuel rods at Daiichi, there is no answers for dealing with them. They don’t even know where the melts are.

  • Starviking

    Scientific references please.

  • Michael Mann

    Steve, I thought you sounded familiar, still linking to your own site?.. Is this your fourth alias? Frank Energy, SteveO,, Nuclear Professor, Nuke-Pro, did I miss any?

  • Frank Energy

    Fuku 3 blew up in a type of nuclear explosion called a Prompt Moderated Criticality.

    MOX is way too dangerous. Check the Nukepro website for real information

  • Frank Energy

    For those interested in the truth about nuclear, its lies, and radiation

    agreenroad blog does an excellent job. GE owns the news media, you are not going to get good information from the main stream.

  • Michael Mann

    Still trying to send people to your website Steve? Isn’t there some sort of rule about referencing yourself as proof of what you’re saying?

  • Tom kauser

    We halfassed everything but the muons

  • greenthinker2012

    I challenge you to…
    1) make a proper assertion (one that is provable or disprovable)
    2) back up your claim with scientifically valid proof. (not your own website)
    For example…
    Where do you get your preposterous idea that 200,000 lbs of uranium got into the air?
    Let’s start with that.
    Are you up for the challenge?

  • Michael Mann

    Still using your own website as a reference, don’t you think people have more sense than that? They know that Frank/Nuke Pro/ SteveO are the same person and it seems that the easiest way to know it’s you is that you reference your own website as proof of your statements. Just how dumb do you think people are? I think you should give people more credit. You are incorrigible

  • Michael Mann

    Most people think it’s bad form to reference your own website as proof of anything…I said this.. if you don’t believe me, just ask me, and I’ll tell you….doesn’t really cut it

  • Enkidu

    Just a few thoughts on a quick examination of your link:

    1. It should go without saying, but you can’t simply multiply length and width to calculate surface area on a sphere (e.g., the earth). This is a basic mistake.

    2. Assuming a uniform distribution through 457,000,000 cubic kilometers of air is a pretty astounding assumption (especially when the dispersion simulator on which you rely contradicts it).

    You may want to go back and give this another shot.