Piping and support structures at the No. 5 reactor of the crippled Fukushima No. 1 nuclear power plant did not have sufficient anti-quake strength under new government standards revised in 2006.
Some of the equipment could have been hit with a force as much as 4.3 times above safety standards if an earthquake of a scale forecast for the plant had struck.
Officials of the Nuclear and Industrial Safety Agency included those results in a draft report that was presented to a meeting of experts on Jan. 30.
On-site investigations conducted by Tokyo Electric Power Co. and NISA after the Great East Japan Earthquake last March did not uncover clear visible damage, but NISA officials will conduct a more thorough investigation.
After the new anti-quake standards were revised in 2006, TEPCO officials raised the scale of the expected earthquake to hit the Fukushima plant. However, confirmation of anti-quake capabilities and reinforcement work have not yet been completed.
To determine what quake damage hit the No. 1 to No. 3 reactors, in which the cores were damaged, officials decided to examine the No. 5 reactor because it was easily accessible.
The latest information concerns the results of anti-quake calculations for important equipment at the reactor. The calculations cover some equipment sections that have not been reinforced.
The calculations showed that a strength of between 1.2 to 4.3 times the anti-quake standards would be applied to the main water supply piping as well as support for seven piping systems if the expected quake under the new standards had struck the reactor.
Ordinarily, electric power companies will analyze in detail the strength of any equipment in which safety standards have been exceeded and submit a report to the central government and publicize the results only after reinforcement work has been completed and the safety of the equipment confirmed.
It is unusual for information to be released that shows the possibility of insufficient safety strength in equipment before reinforcement work has been completed.
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