Power companies have abandoned or reconsidered their original plans to equip emergency response facilities for 15 reactors at seven nuclear plants with quake-absorbing devices and instead simply make them quake-resistant, it has been learned.
These seven reactors are among 26 reactors at 16 nuclear plants across the country for which their operators have applied with the Nuclear Regulation Authority (NRA) for safety screening. Although the quake-absorbing structure excels in curbing tremors and is being used in buildings and other structures, it is difficult to verify its safety because little research data on it is available. Therefore, power companies are thinking twice about equipping their emergency response facilities with quake-absorbing systems.
While the quake-resistance structure is designed to enhance the strength of a building itself, the quake-absorbing structure is equipped with a buffer placed between the ground and the building to absorb tremors. Some experts say the quake-absorbing structure prevents facilities in a building from being destroyed easily so that workers can do their jobs calmly even in the event of aftershocks.
An emergency response facility built with a quake-absorbing structure is called an "important anti-seismic building," and one such building at the Fukushima No. 1 Nuclear Power Plant played a major role as a command post in responding to the nuclear crisis there. But the base isolation structure is created using a relatively new technology and therefore there is only a small amount of accumulated data on the technology. According to a senior official of a major power company, if a major earthquake occurs, components such as a buffer containing lead change shape to absorb tremors, but it is difficult to verify that buildings with the quake-absorbing structure can return to their original shape after the earthquake and even withstand aftershocks.
A total of five reactors at three nuclear plants have so far passed the NRA's safety screening for resuming their operations. These are the No. 1 and 2 reactors at Kyushu Electric Power Co.'s Sendai Nuclear Power Plant in Kagoshima Prefecture, the No. 3 and 4 reactors at Kansai Electric Power Co.'s Takahama Nuclear Power Plant in Fukui Prefecture and the No. 3 reactor at Shikoku Electric Power Co.'s Ikata Nuclear Power Plant in Ehime Prefecture. As for emergency response facilities, Takahama and Ikata nuclear reactors passed the NRA's safety screening after switching their original plans for anti-seismic buildings to the ones for quake-resistant structures.
New regulatory standards for emergency response facilities stipulate that such facilities should "be built in such a way as to prevent their functions from being lost to the biggest assumed earthquake through quake-absorbing and other means." It is said to cost more to build ordinary quake-absorbing buildings than quake-resistant ones. In reference to the quake-resistance facility at the Sendai Nuclear Power Plant, NRA Chairman Shunichi Tanaka said, "If the move is for saving money, we will inspect it severely." But the NRA explains that both quake-absorbing and quake-resistant structures are acceptable if they do not lose their functions.
Hokkaido University professor Masaru Kikuchi said, "After the Great East Japan Earthquake, nuclear plant operators assumed bigger earthquakes would occur, and I think power companies abandoned their plans for quake-absorbing structures for a technological reason. Research should be made on a sophisticated quake-absorbing structure capable of fully responding to major earthquakes."