Govt N-plant tsunami data perplexing

Govt N-plant tsunami data perplexing
This aerial picture taken on May 31, 2010 shows Hokkaido Electric Power Co.'s Tomari nuclear power plant in Hokkaido prefecture.

Tsunami up to 5.8 meters high could hit Hokkaido Electric Power Co.'s Tomari nuclear power plant if a powerful quake occurs around the Sea of Japan, while a 3.8-meter-high tsunami could strike the coast off Hokuriku Electric Power Co.'s Shika nuclear power plant in Ishikawa Prefecture, according to a report released by a government panel.

Heights of tsunami anticipated by the panel for each of the 11 nuclear power plants located along the Sea of Japan-including one under construction-were lower than previous estimates by the power firms, indicating that the operators' calculations gave severer figures of maximum tsunami heights to meet the government's new safety screenings for nuclear power plants. Even operators of plants that have yet to submit applications for safety checks have reviewed their previous estimates.

The power companies' estimates were made under worst-case scenarios of a massive earthquake that could be generated as a result of multiple phenomena such as the movement of underwater faults, seafloor landslides, seafront slope failures and volcanic eruptions.

As the power firms' calculations also were made in consideration of details of geological formations, figures of anticipated tsunami heights are larger than those released Tuesday by the government panel.

Explaining the differences from the plant operators' estimates, a member of the panel in charge of the report said: "Simply based on fault movements, our estimates cover areas in a grid of 50 meters square. We didn't consider how tall tsunami could be at specific locations [of each plant]."

However, differences about anticipated tsunami heights have confused some local governments of cities, towns and villages that host the nuclear power plants.

According to previously compiled estimates by the Fukui prefectural government, the No. 1 reactor at Japan Atomic Power Co.'s Tsuruga nuclear power plant and Kansai Electric Power Co.'s Takahama nuclear power plant could suffer a tsunami taller than the sites' elevation above sea level. In the government panel's estimates, however, none of anticipated tsunami heights exceeded the 11 plants' elevation above sea level.

"The lower [the figures], the safer we feel," said a Fukui government official. "But we want clear explanations on how the panel's calculations were made as they are different from ours and the power companies'."

The official added: "The highest level of safety must be ensured at nuclear power plants. Given that, I understand that estimates under the new safety standards became severer."

Regarding Tokyo Electric Power Co.'s Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture, a tsunami up to 3.4 meters high could hit the nearby coast, according to the government report.

Commenting on this figure, a Niigata prefectural government official who heads the section in charge of nuclear safety, said: "It was within the range of previous calculations by the Niigata government and TEPCO. We're not thnking of taking new safety measures for the plant as that [the latest figure] doesn't have a big impact [on existing measures]."

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