TOKYO—Japanese regulators discussed in recent months the use of new cooling technologies at nuclear plants that could have lessened or prevented the disaster that struck this month when a tsunami wiped out the electricity at the stricken Fukushima Daiichi power facility.

However, they chose to ignore the vulnerability at existing reactors and instead focused on fixing the issue in future ones, government and corporate documents show. There was no serious discussion of retrofitting older plants with the alternative technology, known as "isolation condensers," government advisers said.

Fukushima Daiichi, the plant at the heart of Japan's crisis, relied mainly on electrical systems to power the emergency cooling of its reactors—a design that failed in the March 11 earthquake and tsunami. When the main power went down and backup generators failed, cooling water couldn't get to the nuclear fuel. Overheating then led to explosions, fires and significant release of radiation in the early days after the quake. Isolation condensers, by contrast, don't require electric power.

"There has been little to no talk about the need to retrofit existing reactors" with additional safety systems, said Muneo Morokuzu, a former Toshiba Corp. reactor designer who now studies industry policy at the University of Tokyo. "Mostly people thought there was no need to go that far."

Japanese officials declined to say why retrofitting older plants wasn't discussed, while the plant's operator, Tokyo Electric Power Co.,or Tepco, said it would look into the matter. Experts said doing so was likely deemed too costly and cumbersome given what was seen as a small risk of total power outage. Even if a refit had been ordered in recent months, it wouldn't have been complete when the quake struck.

On Tuesday, Tepco took another step toward recovery by reconnecting power to all six reactors and turning on the lights in reactor No. 3, the most visibly damaged of the six after a series of explosions. Tepco still needs to turn on cooling systems. Workers resumed spraying water on storage pools where radioactive rods are stowed, an effort to prevent overheating.

Click here to read more on this story from The Wall Street Journal.