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    Japan's nuclear crisis: the causes and the risks How did the explosion at the Fukushima No 1 power station in Japan happen? And what are the consequences?


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    Japan's nuclear crisis: the causes and the risks How did the explosion at the Fukushima No 1 power station in Japan happen? And what are the consequences?

    Post by sicran on 14/3/2011, 8:37 am

    What caused the nuclear crisis?

    Problems began when Friday's massive earthquake knocked out electricity at the Fukushima No 1 power station.
    Back-up generators kicked in to pump coolant around the reactor cores
    to prevent the fuel rods from overheating. The generators worked for a
    short time, but were damaged by the ensuing tsunami, forcing a scramble
    by engineers to fit mobile battery power units. These were insufficient
    to cool all of the reactors properly.Why did the building explode?

    makeshift attempt to cool reactor 1 at the power station failed. Heat
    from the fuel rods in the reactor core led to a build-up of superheated
    water inside.On Saturday, engineers released water vapour – which
    contained radioactive caesium and iodine – from the pressure vessel as
    an emergency measure. Superheated water can split into hydrogen and
    oxygen, and it appears that hydrogen escaped during the venting
    procedure and exploded.What damage was caused?

    blast tore the roof off the building and damaged surrounding walls.
    Four workers were injured. Japanese authorities told the International
    Atomic Energy Authority that the explosion happened outside the reactor's primary containment vessel, which appears to be intact.What is the radiation risk?

    Nuclear and Industrial Safety Agency (Nisa) reported higher levels of
    radiation around the power station over the weekend and the presence of
    caesium-137 and iodine-131 in the air. These are radioactive isotopes
    produced in fission reactions. The isotopes were released when steam was
    vented from the reactor.Monitors around the site recorded a
    radiation level of 500 microSieverts per hour on Saturday afternoon, a
    quarter of the annual dose the general population is exposed to due to
    natural background radiation. The level of radiation at the power
    station's main gate fell on Sunday to a very low level of 3.2
    microSieverts.Have people been exposed to radiation?

    least nine people have tested positive for radiation exposure near
    Fukushima, but a Nisa official said that number could rise to between 70
    and 160. Radioactivity can cause a variety of health problems, from a
    reddening of the skin and increased cancer risk to fatal radiation
    sickness. Health officials distributed potassium iodide pills, which
    protect against thyroid cancers, to residents near the power station.
    Those unable to leave were advised to limit their exposure by staying
    indoors and switching off air conditioning or wearing a protective mask
    if outside.Are the other reactors safe?

    Sunday, engineers vented steam from reactor 3 and began pumping in sea
    water after its cooling system failed.Authorities said there was a risk
    of an explosion similar to that in reactor 1. Sea water was being
    readied to pump into reactor 2.A separate state of emergency was announced at the nearbyOnagawa nuclear power station amid increased levels of radiation, but Japanese officials said this had been carried on the wind from Fukushima.When will the power station be safe?

    strategy of pumping sea water into nuclear reactors is untested. It
    could take several days to bring the temperature and pressure of the
    reactor cores down to within safe limits.If the cooling fails,
    the reactors could overheat and cause a total meltdown of the
    radioactive fuel rods in the core. This would only lead to a major
    release of radiation if the reactor's containment vessel was breached.The
    Japanese authorities have classified the situation as a level 4
    "accident with local consequences" on the International Nuclear and
    Radiological Event Scale.The scale runs from zero for a deviation in
    normal operations to seven for a major accident. The Three Mile Island
    incident in 1979 was a five and Chernobyl in 1986 was a seven on the scale.


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