The Nuclear Regulation Authority decided Jan. 15 to set maximum heights of possible tsunami striking individual nuclear plants and obligate their operators to take commensurate safety measures.
The requirements will be included in a draft outline of the new standards on earthquake and tsunami preparedness, to be put together by the end of January, that will help the NRA decide whether to reactivate idled nuclear reactors or build new ones.
In the aftermath of the Fukushima nuclear disaster in March 2011, the new standards will obligate nuclear plant operators to place a maximum anticipated tsunami height for each plant and take measures to mitigate the impact of possible flooding, such as building levees of appropriate height and waterproofing buildings that house key equipment.
In addition to setting a reference for tsunami heights, at least one panel member called for defining a "minimum elevation" on which nuclear plants can be built.
However, one member said that such requirements should not be imposed on all regions across the board.
Further, the definition of active geological fault lines, for which the seismic risk on nuclear plants has to be evaluated, will be expanded to include all fault lines that have shifted during the past 400,000 years or so. Currently, faults that have moved during the past 120,000 to 130,000 years are labeled "active."
The new standards will also necessitate detailed studies of subsurface formations, which affect the flow of seismic motion.
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