Tuesday, March 15, 2011

Severe but not catastrophic

Formerly an “opponent” of nuclear power, Ben Heard gives a more up-beat view than commonly reported of the nuclear crisis in Japan following last Friday’s horrifying earthquake and tsunami catastrophe:

  • When the earthquakes struck, Japan’s nuclear power stations did as they were designed to do and shut down with the insertion of control rods. This halted the nuclear chain reaction that generates the power. In response the plants rapidly dropped in power to around 5% of normal.
  • Other (non-uranium) constituents of the fuel remained “hot” i.e. reacting, which is normal.
  • Back up power systems (diesel generators) were applied to continue to provide cooling to the reactor core. This worked as expected.
  • Approximately 1 hour later, two power plants housing seven nuclear reactors were struck by a 7 metre tsunami. These plants were Fukushima Daiichi and Fukushima Daini. This disabled the diesel generators that were in use, and all other back-up generators that were available. It is this second disaster that triggered the problems at these power plants, as the plants began to experience a loss of cooling on the fuel.
  • Back-up cooling from batteries was applied, and provided cooling for approximately a further 8 hours
  • Other measures have then needed to be implemented as this power source ran out. This has included pumping sea-water into the reactor core. This is not a preferred action as it causes some damage.
  • Some portions of the fuel rods remained exposed from the coolant for long enough to heat up and melt. This is the meaning of “partial meltdown”
  • Some build up of radioactivity has occurred within the reactor buildings. This has been periodically vented in a controlled way to maintain pressure within the reactor at a safe level. The radiation being vented is of a type that is short lived, decaying rapidly to harmless substances
  • The venting gas has contained hydrogen. Unfortunately, perhaps due to not venting quickly enough, the hydrogen concentrations have become elevated and resulted in explosions occurring outside of the reactor building when the venting occurred
  • Presently the reactor cores are being successfully cooled and progressively moved to a state of cold shutdown, meaning fully under control.
  • Critically, throughout the disaster the integrity of the very strong Containment Structures, which separate the nuclear reactor from the outside world, has been maintained. The reactor building itself then contains the core of nuclear fuel, and these reactor buildings have also remained intact. This means there has never been a risk of a “Chernobyl-type” incident, with serious releases of radioactivity to the surrounding environment that would pose a threat to human health. The Chernobyl power stations had no such structure, which greatly increased the consequences of that accident.
  • The incident has received a severity rating of INES 6. It is clearly very serious. The Three Mile Island Accident was a 5. Chernobyl, however, was a 7 (the highest), and is a very different league.


The bottom line of the events at Fukushima and the nuclear power sector more broadly would appear to be as follows:

  • Zero deaths from radiation
  • Zero release of radiation levels of a danger to human health, except for brief periods for those working within the plant compound (not Public exposure). These workers would be well protected and monitored to avoid excessive accumulated doses
  • Minimal injuries (about a dozen) as a result of the hydrogen explosions
  • No significant or lasting environmental impact whatsoever
  • A major evacuation, which has no doubt been distressing for all involved
  • 8 - 10 of Japan’s 55 nuclear reactors known to have varying levels of damage that will impact their ability to provide electricity. The remainder will no doubt require inspection, but would appear to be relatively undamaged.


If Japan’s nuclear power sector can withstand the worst natural calamity I hope to ever see in my life and contribute no deaths, minimal injuries and minimal environmental impact, then nuclear power must be just about the sturdiest, best designed, best managed and least dangerous infrastructure in the world. And in a world that is quickly cooking itself through climate change, nuclear power must not be allowed to suffer from the hype, headlines and hyperbole that have stemmed from this tragic event.

We sincerely and fervently hope Mr Heard’s assessment won’t be requiring any major rewrites.

Disclaimer: I have no interests whatever in the nuclear industry.

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