Summary of nuclear accident -2/2

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But it makes life more difficult for the operators and mechanics when they have to deal with activated (i..e. slightly radioactive) water.

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But Plan A had failed – cooling systems down or additional clean waterunavailable – so Plan B came into effect. This is what it looks like happened:In order to prevent a core meltdown, the operators started to use sea waterto cool the core. I am not quite sure if they flooded our pressure cooker with it (the second containment), or if they flooded the third containment, immersing the pressure cooker. But that is not relevant for us.

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The point is that the nuclear fuel has now been cooled down. Because the chain reaction has been stopped a long time ago, there is only very little residual heat being produced now. The large amount of cooling water that has been used is sufficient to take up that heat. Because it is a lot of water, the core does not produce sufficient heat any more to produce any significant pressure. Also, boric acid has been added to the seawater. Boric acid is “liquid control rod”. Whatever decay is still going on, the Boron will capture the neutrons and further speed up the cooling down of the core.

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The plant came close to a core meltdown. Here is the worst-case scenario that was avoided: If the seawater could not have been used for treatment, the operators would have continued to vent the water steam to avoid pressure buildup. The third containment would then have been completely sealed to allow the core meltdown to happen without releasing radioactive material.After the meltdown, there would have been a waiting period for the intermediate radioactive materials to decay inside the reactor, and all radioactive particles to settle on a surface inside the containment. The cooling system would have been restored eventually, and the molten core cooled to a manageable temperature. The containment would have been cleaned up on the inside. Then a messy job of removing the molten core from the containment would have begun, packing the (now solid again) fuel bit by bit into transportation containers to be shipped to processing plants. Depending on the damage, the block of the plant would then either be repaired or dismantled.

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Now, where does that leave us? My assessment:

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§ The plant is safe now and will stay safe..

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§ Japan is looking at an INES Level 4 Accident: Nuclear accident with local

    consequences. That is bad for the company that owns the plant, but not for

    anyone else. 

                                                                                                           § Some radiation was released when the pressure vessel was vented. All

     radioactive isotopes from the activated steam have gone (decayed).

     A very small amount of Cesium was released, as well as Iodine.

     If you were sitting on top of the plants’ chimney when they were venting,

     you should probably give up smoking to return to your former life

     expectancy. The Cesium and Iodine isotopes were carried out to the sea

     and will never be seen again.

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§ There was some limited damage to the first containment. That means that

     some amounts of radioactive Cesium and Iodine will also be released into

     the cooling water, but no Uranium or other nasty stuff (the Uranium oxide

     does not “dissolve” in the water). There are facilities for treating the

     cooling water inside the third containment. The radioactive Cesium and

     Iodine will be removed there and eventually stored as radioactive waste in

     terminal storage. 

                                                                                                            § The seawater used as cooling water will be activated to some degree.

    Because the control rods are fully inserted, the Uranium chain reaction is

    not happening. That means the “main” nuclear reaction is not happening,

    thus not contributing to the activation. The intermediate radioactive

    materials (Cesium and Iodine) are also almost gone at this stage, because

    the Uranium decay was stopped a long time ago. This further reduces the

    activation. The bottom line is that there will be some low level of activation

    of the seawater, which will also be removed by the treatment facilities.

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§ The seawater will then be replaced over time with the “normal” cooling

    water

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§ The reactor core will then be dismantled and transported to a processing

     facility, just like during a regular fuel change.

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§ Fuel rods and the entire plant will be checked for potential damage. This will

    take about 4-5 years. 

                                                                                                            § The safety systems on all Japanese plants will be upgraded to withstand a

     9.0 earthquake and tsunami (or worse)

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§ (Updated) I believe the most significant problem will be a prolonged power

     shortage. 11 of Japan’s 55 nuclear reactors in different plants were shut

     down and will have to be inspected, directly reducing the nation’s nuclear

     power generating capacity by 20%, with nuclear power accounting for about

     30% of the national total power generation capacity.. I have not looked into

    possible consequences for other nuclear plants not directly affected.

    This will probably be covered by running gas power plants that are usually

    only used for peak loads to cover some of the base load as well. I am not

    familiar with Japan’s energy supply chain for oil, gas and coal, and what

    damage the harbors, refinery, storage and transportation networks have

    suffered, as well as damage to the national distribution grid. All of that will

    increase your electricity bill, as well as lead to power shortages during peak

    demand and reconstruction efforts, in Japan.

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§ This all is only part of a much bigger picture. Emergency response has to

     deal with shelter, drinking water, food and medical care, transportation and

     communication infrastructure, as well as electricity supply. In a world of

     lean supply chains, we are looking at some major challenges in all of these

     areas.

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If you want to stay informed, please forget the usual media outlets and consult

the following websites:

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§ http://www.world-nuclear-news.org/RS_Battle_to_stabilise_earthquake_reactors_1203111.html

§ http://www.world-nuclear-news.org/RS_Venting_at_Fukushima_Daiichi_3_1303111.html

§ http://bravenewclimate.com/2011/03/12/japan-nuclear-earthquake/

§  http://ansnuclearcafe.org/2011/03/11/media-updates-on-nuclear-power-stations-in-japan/ .

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Michael Molenda