Seconds From Disaster – Fukushima

Seconds From Disaster – Fukushima

The Fukushima Daiichi nuclear disaster (福島第一原子力発電所事故 Fukushima Dai-ichi (About this sound pronunciation) genshiryoku hatsudensho jiko?) was an energy accident at the Fukushima I Nuclear Power Plant, initiated primarily by the tsunami of the Tōhoku earthquake and tsunami on 11 March 2011.[6] The damage caused by the tsunami produced equipment failures, and without this equipment a loss-of-coolant accident followed with three nuclear meltdowns and releases of radioactive materials beginning on 12 March.[7] It is the largest nuclear disaster since the Chernobyl disaster of 1986 and the second disaster (after Chernobyl) to be given the Level 7 event classification of the International Nuclear Event Scale.[8]

The plant comprised six separate boiling water reactors originally designed by General Electric (GE) and maintained by the Tokyo Electric Power Company (TEPCO). At the time of the earthquake, reactors 4, 5 and 6 were shut down in preparation for re-fueling.[9] However, their spent fuel pools still required cooling.[10] Immediately after the earthquake, the electricity producing reactors 1, 2 and 3 automatically shut down their sustained fission reactions, inserting control rods in what is termed a SCRAM. Following this legally mandated “safety precaution” which ceases the reactors’ normal running conditions, the reactors were unable to generate power to run their own coolant pumps. Emergency diesel generators came online, as designed, to power electronics and coolant systems, all of which operated right up until the tsunami destroyed the generators for reactors 1 – 5 due to their location in unhardened low-lying areas. The two generators cooling reactor 6 were undamaged and were sufficient to be pressed into service to cool the neighboring reactor 5 along with their own reactor, averting the overheating issues that reactor 4 suffered.[10]

The largest wave in the tsunami arrived some 50 minutes after the initial earthquake. The 13 meter tall wave overwhelmed the plant’s seawall, which was only 10m high,[6] with the moment of impact being caught on camera.[11] Water quickly flooded the low-lying rooms in which the emergency generators were housed.[12] The flooded diesel generators failed soon afterwards, cutting power to the critical pumps that must continuously circulate coolant water through a Generation II reactor for several days to keep the fuel rods from melting down following the SCRAM event, as the ceramic fuel pellets in the fuel rods continue to generate Decay heat even after the fission process has terminated. The fuel rods will become hot enough to melt themselves down during the fuel decay time period if no adequate cold sink is available. After the secondary emergency pumps (run by back-up electrical batteries) ran out, one day after the tsunami, 12 March,[13] the water pumps stopped and the reactors began to overheat due to the high decay heat produced in the first few days after the SCRAM (diminishing amounts of this decay heat continue to be released for years, but with time, passive cooling through water convection in a pool is sufficient to prevent fuel rod melting).

As workers struggled to supply power to the reactors’ coolant systems and restore power to their control rooms, a number of hydrogen-air chemical explosions occurred, the first in Unit 1, on 12 March and the last in Unit 4, on 15 March.[13][14][15] It is estimated that the hot zirconium fuel cladding-water reaction in reactors 1-3 produced 800 to 1000 kilograms of hydrogen gas each, which was vented out of the reactor pressure vessel, and mixed with the ambient air, eventually reaching explosive concentration limits in units 1 and 3, and due to piping connections between units 3 and 4, or alternatively from the same reaction occurring in the spent fuel pool in unit 4 itself,[16] unit 4 also filled with hydrogen, with the hydrogen-air explosions occurring at the top of each unit, that is in their upper secondary containment building.[17][18] Drone overflights on 20 March and afterwards captured clear images of the effects of each explosion on the outside structures, while the view inside was largely obscured by shadows and debris.

Comments

  1. The mlg Lol
    The mlg Lol 24 June, 2016, 22:23

    How is the tremor scaled 9.0 It is weird right? …

    Reply this comment
  2. Laurence S
    Laurence S 24 June, 2016, 22:23
  3. robert cummings
    robert cummings 24 June, 2016, 22:23

    to bad they didn't have Godzilla around to absurb all the radiation like in his movies!!!

    Reply this comment
  4. Berlin or bust lillis
    Berlin or bust lillis 24 June, 2016, 22:23

    thank god they survived

    Reply this comment
  5. Sune Spelberg
    Sune Spelberg 24 June, 2016, 22:23

    Jesus christ, i know a family in japan that survived that

    Reply this comment

Write a Comment

Leave a Reply