On July 16, 2007, an earthquake with a magnitude of somewhere between 6.6 and 6.8 struck Japan. Its epicenter was about 16 kilometers north of the Kashiwazaki-Kariwa Nuclear Power Plant (KKNPP), the biggest such plant in the world. The known results of the earthquake include a fire and leaks of radioactivity. However, news of damage to the reactors continues to emerge, the most recent being the discovery of a jammed control rod in Unit-7. Though there was no major release of radioactivity, the many failures and unanticipated events that occurred at the reactor after the earthquake have important implications for nuclear safety worldwide.
     To start, the Japanese nuclear establishment never anticipated the magnitude of the earthquake. Under Japan's old guidelines, which formed the basis of the KKNPP design, the seismic hazard for each nuclear site is defined in terms of two intensities, termed S1 and S2. (See Status Report on Seismic Re-Evaluation) The S1 earthquake, referred to as the "maximum design earthquake," is less intense and determined by historical events and current and past fault activity. The S2 earthquake, called the "extreme design earthquake" and supposedly an impossibility, is derived from seismo-tectonic structures and active faults. These requirements were believed to provide a "sufficient range of earthquakes to assure reactor safety for any potential earthquake shaking." (See A Developing Risk-Informed Design Basis Earthquake Ground Motion Methodology) But clearly the S2 design earthquake wasn't extreme enough: The peak ground acceleration of the July 16 earthquake was two-and-a-half times greater than what was assumed for the S2 earthquake.
     After the recent earthquake, Takashi Nakata at the Hiroshima Institute of Technology and Yasuhiro Suzuki at Nagoya University analyzed the data in the Tokyo Electric Power Co.'s (TEPCO) license application and concluded that it indicated a fault five times longer than the one TEPCO identified. Between 1979 and 1985, TEPCO found four small faults off the coast of Kashiwazaki-Kariwa, but it concluded that they were either inactive or unimportant. However, Nakata and Suzuki believe that three of these small faults constitute one 36-kilometer long fault, which is probably active, too.
     Such differences in conclusions suggest that there were organizational pressures to ignore inconvenient data or interpret it to ensure it supported vested interests - in this case, building the reactor at a specific site. A similar example (albeit from a different technological arena) is the 1986 Challenger space shuttle explosion. In her 1996 book, The Challenger Launch Decision: Risky Technology, Culture, and Deviance at NASA, sociologist Diane Vaughan observed that the ultimate origins of the accident "were in routine and taken-for-granted aspects of organizational life that created a way of seeing that was simultaneously a way of not seeing."