I asked for a second opinion to the video presentation by Arnie
Gundersen linked by NIRS:

"A new video from nuclear engineer Arnie Gunderson of Fairewinds
Associates postulates that the Unit 3 explosion was sparked by a
criticality in its fuel pool. The video includes excellent footage
and a clear explanation.

Gunderson makes an interesting case for the explosion in the
Fukushima-1 Unit 3 spent fuel pool being more than a hydrogen explosion."

Here's the reply from David Lochbaum of the Union of Concerned Scientists:

"I do not believe that there was a criticality blast at Fukushima.
Uncovered fuel is known to create copious amounts of hydrogen.
Copious amounts of hydrogen are known to explode."

In summary, I continue to agree with Gunderson that the concrete structure of the spent fuel pool in Unit 3 channeled the blast upwards with tremendous force and that the inventory of spent fuel rods laced with Plutonium was fragmented in the hydrogen explosion and dispersed around the nuclear complex site area.

Charley Noble