Sunday, April 3, 2011

Solution for containment of a failed nuclear plant

The nuclear disaster in Japan will outlast our short attention span. Headlines boldly state that the disaster could last for months. This disaster will last for thousands of years.

I wrote two brief entries on the possibility of using a modular masonry system to assemble a radial structure such as a cylinder or sphere or dome as a containment structure on this blog, here and here. I remain confident that this approach makes more sense than anything else TEPCO (Tokyo Electric Power Company) has tried, or is planning to try. I’m posting this blog entry subject again, in the hope that someone at TEPCO might notice.

Cracks in the inadequate “containment” structure at Fukushima dai-ichi are observed to be spewing radioactive water directly into the sea. Currently the effort to stop these leaks involves stuffing the cracks with sawdust and newspaper. Sawdust and newspaper? Incredibly, this approach is not working.

Engineers have tried pouring concrete directly onto the crack in an attempt to seal it. Incredibly, this approach is not working either.

Good concrete is poured under controlled conditions. A concrete mix is dependent on a low water-to-cement ratio to give it the qualities which are desirable in a high strength, consolidated, uniform mix. Poured concrete must cure under controlled conditions of high humidity, cool temperatures, and be allowed to cure unmolested. These conditions are unlikely to be satisfied if concrete is poured directly onto a hot radioactive site.

If concrete is poured under controlled conditions and allowed to properly cure, it has a much better chance of withstanding the demanding environment found at a failed nuclear reactor. Pouring a huge containment structure and then moving it to cover a nuclear reactor is entirely impractical. However, a modular system could be used to assemble a containment structure from properly made concrete unit shapes.

The modular system which has been developed and has been discussed throughout this blog appears to be an optimal solution to fixing this problem. These modular units can be made at a safe distance from the stricken nuclear reactor. Once cured, they can be transported to the site and assembled robotically, to minimize danger to humans. The interlocking aspect of these modular units greatly facilitates assembly of a containment structure by providing multiple contact and guiding surfaces. A tensile web of steel cable can also be woven into the structure as the containment dome is built.  Mortar or gaskets or seals can be readily incorporated into this design to form an integral structure without 'cracks' between modular blocks; there are a number of simple methods to achieve this.  Finally, multiple concentric layers can be placed (like layers of an onion) to increase wall thickness and safety factor.

Or we can try more sawdust and newspaper.

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