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View Diary: Sen. Wyden Sounds The Alarm on Fukushima (291 comments)

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  •  Levels (3+ / 0-)
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    bryfry, AaronInSanDiego, Imhotepsings

    So just how high do you think the levels of fission products from Fukushima Daiichi are in seawater? Are they anywhere close to the natural levels of radiation from K-40 and Rb-87? It doesn't seem so.

     The amounts of Cs-134 and Cs-137 are actually so low it takes several days or even weeks to get decent readings in the lab from the seawater samples; the isotope types and amounts are determined by measuring the energy of the radiation and matching it to known spectra. At 0.01 Bq/litre that means the detectors are measuring one particle of radiation from a fission product like Cs-137 every hundred seconds per litre of sample and they need hundreds or even thousands of readings to determine any sort of spectrum. At the same time the detectors are being bombarded by ten or eleven particles every second from the naturally occurring radioactive isotopes in seawater which complicates things.

     Using the same techniques the US government and others can detect Cs and other fission products in seawater that might reach their shores but the actual levels found will be no threat to health so far from the originating site. However that doesn't make disaster junkies feel safe so any isotopes detected at all will cause more Chicken Little reactions no matter what the levels actually mean.

    •  I thought we were talking about the potential for (1+ / 0-)
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      atmospheric fallout? Core hitting water table steam explosions or some such.

      Romney - his fingernails have never been anything but manicured.

      by Pescadero Bill on Tue Apr 17, 2012 at 08:12:14 AM PDT

      [ Parent ]

      •  Movie scripts (3+ / 0-)
        Recommended by:
        SpeedyGonzales, netop, mdmslle

        Disaster junkies have a movie script understanding of the engineering and physics of a core meltdown in a reactor which makes for great horror stories but movie scripts don't actually happen in the real world.

         Basic facts: the fuel elements contain fission byproducts from when the Fukushima reactors were operating at full power, just before they were shut down as the earthquake hit over a year ago. Once the control rods went home and fission stopped the heat production in the core dropped from about 2600 megawatts to about 50 megawatts. As the hot short-life fission elements (half-lifes measuring in seconds or minutes) died away the heating effect of the remaining byproducts decreased quite rapidly but that drop plateaued out as only the longer-lived elements were left. As of today more than a year later the fuel pellets in each reactor are putting out about 0.5 MW of heat. This plateau of heat energy from fission byproducts is why spent fuel rods from a reactor are stored for a few years in a cooling pond before being moved to either longer-term dry storage or reprocessing.

         There was about 120 tonnes of fuel pellets in reactors 2 and 3, a bit less in reactor 1 which was smaller. There was enough heat energy left after the shutdowns to boil off the remaining water once the pumps stopped for lack of electricity and the steam under pressure and heat reacted with the zirconium metal jacketing of the fuel rods causing hydrogen and oxygen to be created by catalytic disassociation. That gas mix caused the explosions which dispersed the lighter mobile fission byproducts such as I-131, Cs-134 and Cs-137 as vapour through vents. Most of the rest of the nuclear zoo of isotopes stayed put inside the containments since they required much higher temperatures to form compounds that would be vapourised easily -- uranium oxide which constitutes the fuel elements melts at about 2800 deg C, for example.

         The residual heat was enough to melt the bottom of the reactor vessel and some of the fuel elements, melted core structures etc. ended up on the floor of the primary containment where they continued to generate heat, enough, it is thought, also melt through that layer to drop more scrap through onto the floor of the secondary containment. By this time after the accident it is nowhere nearly hot enough to melt its way through the bottom of this part of the containment system into the earth and down into an aquifer where, according to the movie script believers a steam explosion will blow the reactor apart releasing even more radioactivity.

         The engineers at Fukushima have been pumping about 8-10 tonnes of water an hour into the reactors to remove as much of this decay heat as possible since a few days after the explosions, further reducing the chances of the China Syndrome event the disaster junkies have been lovingly turning over in their minds. Mostly though the water cooling reduces the amount of radioisotopes boiling out of the fuel pellets and prevents more hydrogen being produced by keeping the temps down.

         As for atmospheric fallout, we've already been through a shitload of that from atmospheric nuclear weapons tests, over two hundred of them in the 1950s and 60s including all of the biggest tests such as the Soviet Tsarbomba (55MT) and the US's Castle Bravo test (15MT). That's put a lot of radioactive material into the sea, land and air and we're mostly still all here (some Japanese fishermen got caught in the plume from Castle Bravo, at least one died from radiation burns).

         Several organisations in Japan have been monitoring radioactive materials in air as both particles and vapour. The levels are tiny now although they were substantially higher closer to the accident. Rigorous testing of some air samples provides a reading like 0.001 Bq/cubic metre of Cs-137 in dust particles measured in Fukushima city 60km NW of the reactors a few days ago. The dispersal of particles 8000 km across the Pacific to the US is going to reduce any detectable contamination to truly microscopic levels. You'd be better worrying about the radioactive material coal-fired stations emit every day as part of their normal operations, no disaster required.

    •  The contaminated water (4+ / 0-)
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      jeanette0605, Russgirl, ozsea1, dharmasyd

      moves via currents, and is now approaching Hawaii/Midway. Will be at the west coast of the U.S. within 2 years. But it's not the greatest ocean contamination event in history (acknowledged) that presents the greatest danger, it's bioaccumulation of radioisotopes through the food chain. That will tend to concentrate the higher up the chain you go. Even baleen whales caught north of Japan have tested high in cesium, and all they're eating is plankton and krill.

      Atmospheric fallout is also considerable, blankets the entire northern hemisphere and has moved south. Plutonium from Fukushima was detected in the rain in Lithuania. It's everywhere.

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