It is possible it did go up in smoke and it happened during the first week of the disaster. Evidently when fuel pool 4 went up the fire burnt for nearly 2 weeks [enformable.com]
What we saw on the tv news [www.fukuleaks.org]
Pic of unit 4 fuel pool. [beavercountyblue.files.wordpress.com]
Consequences of fire and other unforeseen events..