JAPON, le 16 juillet 2007
Leçons de la sûreté nucléaire après le séisme de l'été 2007 au Japon
Nuclear safety lessons from Japan's summer earthquake
11 mars 2008
Source ADIT

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By M. V. Ramana and Ashwin Kumar

     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."

     The July earthquake also points to how actual accidents could result in unexpected modes of failure. Nuclear reactors are based on complex interactive technologies, operating at high temperatures or pressures, with tightly coupled events occurring at a rapid pace, and therefore, prone to accidents. (See Charles Perrow's 1984 book, Normal Accidents: Living with High-Risk Technologies.) By simultaneously affecting large parts of a nuclear power plant, earthquakes increase the possibility of accidents. The Japanese earthquake damaged KKNPP's switchyards and water piping for the fire-suppression systems. It also caused a fire when electrical equipment near a transformer slipped, causing separated cables to short-circuit. There are reports that leaking oil was involved in this fire.
     Some events were unexpected: For example, underground electric cables were pulled down by ground subsidence, creating a large opening in the outer wall of the reactor's basement - a so-called "radiation-controlled area" that must be completely shut off from the outside. According to a TEPCO official, "It was beyond our imagination that a space could be made in the hole on the outer wall for the electric cables."
     Finally, the earthquake showed how emergency plans that look great on paper can fail when disaster strikes, with KKNPP managers admitting that "disaster-prevention measures did not function successfully." For example, the fire-extinguishing system at one reactor couldn't be used because of pipe damage, resulting in the water hose only being able to spray water at a distance of a meter rather than the normal dozens of meters. Since the plant didn't have chemical fire extinguishers, workers had no choice but to watch the fire burn. The earthquake also knocked out a hotline to the local fire station.
     Meanwhile, Plant Director Akio Takahashi was told of the fire immediately after the earthquake, but didn't dispatch the facility's firefighters because he thought management would have already done so - an example of the human error even high-level officials are capable of during stressful moments. When they were notified, the fire brigade struggled to reach the plant because of the area's other damage. So although the transformer fire was detected at 10:15 a.m., firefighters didn't start fighting it until more than an hour later. Takahashi also admitted to problems in the facility's primary firefighting system and cooperation between related organizations.
     Throughout, TEPCO's primary aim seemed to be to quell fear rather than accurately report facts. For example, TEPCO employees knew about the leak by 12:50 p.m., but the company didn't publicly report it until 8:28 p.m. Similarly, the initial estimates of radioactivity TEPCO released were significantly smaller than the final figure. If this was the case during a relatively major accident that was displayed on television screens around the world, it's easy to imagine the paucity of information nuclear authorities would make available during a smaller accident.
     The prevention of accidents at nuclear facilities depends on both technological and organizational factors. The efficacy of these factors is contingent upon them performing according to design. Though there wasn't a large-scale release of radioactivity, events at KKNPP after the July earthquake demonstrate both technological and organizational failures. Discussions about nuclear safety should begin by acknowledging the possibility of such failures.