The difference in the safety designs was the main reason why the crisis continues to unfold at the Fukushima No. 1 plant--one of the oldest in Japan--while the No. 2 plant a few kilometers south remains relatively unscathed by the March 11 Great East Japan Earthquake and tsunami.

Officials at another Tokyo Electric Power Co. nuclear plant in Kashiwazaki-Kariwa, Niigata Prefecture, analyzed the differences in safety designs at the two Fukushima plants.

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TEPCO documents show that the emergency diesel generators located in the turbine buildings at the Fukushima No. 1 plant were flooded by the tsunami and rendered inoperable, except for the one at the No. 6 reactor. This effectively disabled the cooling mechanisms.

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The emergency generators at the No. 2 plant were in buildings housing the reactor cores. Because the reactor buildings are much more airtight, the generators at the No. 2 plant continued to function after the tsunami struck.

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"...even if they wanted to move the generators, there was no space within the reactor building, so that would have meant a major revision in design" [ - ... a] former TEPCO engineer said. "It would have been a major project because various pipes are laid out under the pumps, and so all of that would also have had to be moved."

A midlevel TEPCO official also said money was a big reason why repairs and changes to the No. 1 plant were not made.

"The blueprints for the reactor cores at the No. 1 plant were bought 'as is' by Toshiba Corp. from General Electric Co., so the priority at that time was on constructing the reactors according to those blueprints," the official said.

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The No. 1 plant was considered a "learning experience."

A former TEPCO executive said, "The Fukushima No. 1 plant was a practice course for Toshiba and Hitachi Ltd. to learn about GE's design on a trial-and-error basis."