Fukushima No. 1 plant designed on 'trial-and-error' basis

2011/04/07

An aerial view of the Fukushima No. 1 nuclear power plant taken Tuesday from a helicopter flying at about 7,300 meters and about 38 kilometers to the west. (Eiji Hori)

While changes improved safety at the Fukushima No. 2 nuclear power plant, overconfidence, complacency and high costs stymied such action at the now-crippled Fukushima No. 1 plant, according to people familiar with the situation.

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.

According to their analysis and TEPCO sources, there are clear differences in safety levels between the two plants concerning power source equipment, such as emergency diesel generators and transformers at the reactor cores, and pumps used to bring in seawater to remove residual heat from the cores.

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.

After the No. 1 plant lost its power sources, the reactor cores became much more difficult to control, leading to serious problems, including hydrogen explosions that damaged the housing of the reactors.

Radioactive materials have also been emitted from the damaged reactors.

No such problems have been encountered at the No. 2 plant.

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.

Emergency generators are also located within the airtight reactor core buildings at the Kashiwazaki-Kariwa plant, which has similar design features to the Fukushima No. 2 plant.

When asked about the differences in the safety designs between the No. 1 and No. 2 plants, an official at TEPCO headquarters said: "This does not mean we have admitted that a problem exists. We will conduct further detailed studies to identify the problems."

The No. 1 plant was built in the 1960s and 1970s. Improvement work was conducted in the 1970s and 1980s to strengthen its resistance to earthquakes.

A nuclear engineer who used to work for TEPCO and was involved in those improvements said no consideration was paid to the location of the emergency diesel generators or the seawater pumps.

"First of all, there was the judgment that the reactor core buildings were in a safe location in relation to the expected height of any tsunami that might strike the plant," the engineer said. "However, 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.

"At the time, no one considered making such changes," the engineer said.

Both the No. 1 and No. 2 nuclear plants were hit by waves more than 14 meters high, well above the expected limits of 5.7 to 5.2 meters estimated in safety designs.

The tsunami rendered inoperable all of the No. 1 plant's pumps, which were also not located within a sealed structure.

Although the pumps at the No. 2 plant were inside buildings, the tsunami crippled the ones to the No. 1, No. 2 and No. 4 reactors. But the pump at the No. 3 reactor continued to cool the reactor core.

Referring to the possibility of installing the seawater pumps inside buildings, the 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.

When the Fukushima No. 1 plant was being built, Japan was importing technology from the United States and learning from a more advanced nuclear power nation.

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."

With the exception of the No. 6 reactor, the other five reactors at the Fukushima No. 1 plant are Mark I boiling-water reactors developed by GE.

According to sources, the locations of emergency generators and the seawater pump structure were also based on a GE design.

In contrast, the No. 6 reactor is a Mark II reactor. Moreover, the Fukushima No. 2 plant and Kashiwazaki-Kariwa plant, which were constructed from the mid-1970s to the 1990s, used an improved and safer version of the Mark II reactor.

After Toshiba and Hitachi gained experience in constructing nuclear plants, they located emergency generators and seawater pumps within buildings.

Yet those safety improvements were never reflected in changes at the Fukushima No. 1 plant.

Other TEPCO officials said that changing the anti-tsunami design or moving the location of the emergency generators would have been an acknowledgment that previous decisions were insufficient.

Kiyoshi Sakurai, a commentator on technology issues, said that relying on a GE design also put the Fukushima No. 1 plant at a disadvantage because U.S. designers were not as cautious about earthquakes and tsunami as those working in Japan.