Japanese utility Tepco has announced two construction projects to improve safety at the Fukushima Daiichi plant: reinforcing the unit 4 spent fuel pool, and building a temporary mansard levee. It said that although a structural integrity evaluation of the heavily-damaged unit 4 reactor building has shown that it should be able to withstand an earthquake as strong as the March earthquake, 9.0 on the Richter scale, it would have a greater safety margin with the support structure. Steel columns will be installed under the spent fuel pool, and encased within a concrete wall. The void space between the new support structure and the original wall will be filled with grout. Preparatory work was scheduled tol begin in early May, the steel columns will be installed in mid-June, and the project is expected to finish in July.
Tepco has also announced plans to build a temporary levee along the coast to protect the site against potential future tsunamis. Aftershocks up to magnitude 8.0 are predicted by experts, according to Tepco. The levee would be built to protect against a swell of up to 4m on plant structures near the sea, and up to 10m around major buildings. Tepco has moved vulnerable power supply equipment and some diesel generators upland.
The levee will be built between the sea and units 3&4. It will be built of mansard blocks, wire cages filled with rocks, with an impermeable layer running vertically through the stack.
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The following sites are also posting continuing updates:
<http://www.tepco.co.jp/en/index-e.html>
<http://www.iaea.org/>
<http://www.jaif.or.jp/english/>
<http://bravenewclimate.com/2011/03/15/tepco-reactor-status/>
<http://www.world-nuclear-news.org/>
<http://www.kantei.go.jp/foreign/index-e.html>