Wednesday, March 16, 2011

Fukushima : containing and preventing air pollution

It seems we have meltdown in at least one of the Fukushima reactors. With a great deal of luck, courage and skill, meltdown might be avoided in the others.
But we must prepare for the worst case scenario - four reactors in meltdown.

Meltdown means that the nuclear fuel melts, and gathers at the bottom of its container.

High temperatures mean that either the gas in the containment is vented, or pressure builds up inside containment.

At the same time the molten fuel is lying on the floor of the containment vessel, which is enormously strong, but steel loses 90% of its strength at 800*Centigrade.  It is likely therefore to melt or crack its way out of the bottom of the containment vessel.

It should then drop into a core catcher, where it will stay in a very hot condition, emitting radioactive material until if cools.

If the core catcher fails, it could go further down, onto the ground.

If it contacts ground water, steam will be formed, which will have to vent up through the reactor building, violently at first, and then in a steady flow. This steam will be carrying radioactive particles, and if allowed to do so will spread through wind to the Japanese countryside and beyond

Throughout, the aim should be to prevent as far as possible the spread of radiation in air, water and soil.

The only way of doing this as far as I can see is to fashion a set of super-sized tents.

It is not complicated.

[Click on the images to enlarge]

The reactor is covered with a dome, from which air is drawn from the duct, which is placed at the top of the structure in order to make use of convection currents and draw radiation as far as possible away from the workers. Fresh air will be drawn in from outside, passing in under the skirting of the tent. If the outside air is already significantly contaminated, pumped in from a clean source, thus reducing the workers to unnecessary exposure.

The contaminated air is then passes through a set of filters, compressors, and into storage pending more filtering.

The floor of the tent will be covered, to minimise penetration of radioactive particles with soil.

For the sake of lightness, simplicity and lessened damage in the event of losing control in a high wind, a pneumatic structure would be preferred.If the fuel has escapes containment into the ground, the dome may be destroyed or displaced depending how much steam is created. However, it will be possible to replace it once the initial geyser like reaction (if it occurs) has subsided, and backup tents should be standing by.

The tent will be fastened down as securely as possible, but it has to be accepted that in the event of a typhoon, it will be lost.

Advantage of a pneumatic structure are not only that it is easier to erect, but also that it can be rapidly deflated in the event of strong winds.

In this event, the extractor system will continue, but the structural member inflator pumps will be run in reverse, causing the dome to collapse. the continuation of the extractor pump means that the tent fabric will be "shrink wrapped" onto the reactor structure and the ground. Sharp projections on the reactor will need to be removed or covered with soft buffering in order to avoid tears in the tent fabric.

The effect of this emergency containment structure is to capture at least some of the radiation that would otherwise spread widely over Japan, the sea, and neighbouring countries, with adverse health effects, destruction of pasture and even area denial for many decades, as happened in Chernobyl.

In the event of large volumes of hot emissions that would overcome plastic, a metal cone of the same general design would have to be used.

By creating this structure, the Japanese people can help themselves, help their neighbours, and regain a sense of control of their situation.
If you think this is worth trying, you can recommend this page to TEPCO, the company that runs Fukushima.

[Update 21 March
To my surprise, this has had a response from a copy I sent to a Nuclear agency. Correspondence in progress, and I have sent an updated design to take in some problems he raised.
25 March: my contact has indicated that the situation is now under control, so no further action. I have responded by proposing that emergency containment along the lines here should be installed near every reactor]

[Update 30 March: Govt considering draping tarps over 3 reactors.]
[Update: one of the reactors has undamaged containment. We can see steam emerging from a window, and diffusing into the air. Why have they not applied a duct to this window? It shows a mentality that is overlooking the need to contain the polluted air.]

[Update 4th April:
Dr. Michio Kaku says three raging meltdowns under way at Fukushima.
Tellurium 129 Presence Is Proof Of Inadvertent Recriticality At Fukushima]

Officials at the stricken plant are also planning to cover three badly damaged outer reactor buildings with special fabric caps and fit air filters to limit the release of radiation.]


john said...

My first instinct once the cooling failed and seawater proved problematic was to bury the fuel under lead shot and both high lead and high boron content crushed glass aggregate.
By all possible means.

DocRichard said...

The long term solution will be to bury as you suggest. My design is to limit the emissions between now and when the entombment begins.

As you say, by all possible means.

DocRichard said...

The design has been refined to ease construction and give way to explosions.

Todd Boyle said...

I thought of this idea this morning and googled to find, you already thought of it. Absolutely, the fabric dome is possible.

DocRichard said...

Thanks for the encouragement, Todd. I like your blog, and have added a comment to your piece about corporate personhood.
This might be of interest