By now everyone has seen the videos of explosions at Japan’s crippled Fukushima Daiichi nuclear plant and the aerial photos of what looks like the result of a World War II bombing. The Fukushima accident has revived the long-dormant issue of nuclear safety, and these indelible images will no doubt accompany all future debates over nuclear energy. Lately, policy discussions have focused on expanding the role of nuclear power; they must now shift to making sure the existing nuclear plants, and especially the older ones, meet strict contemporary standards.
Of the 13 nuclear reactors along Japan’s coast that were directly impacted by the earthquake and tsunami, it was the four oldest ones that failed completely. The more modern units sustained damage but rode out nature’s onslaught, even if just barely, despite facing forces far greater than what they were designed to withstand. Postmortems will likely disclose that the older plants were designed to lower standards than more recent ones and were not adequately upgraded. Such findings will raise questions about older reactors elsewhere, including in the United States.
The operating Fukushima reactors shut down immediately upon sensing the March 11 earthquake, but radioactive fission products in the reactors’ uranium fuel continued to generate heat after the shutdown and therefore required continuous cooling. But cooling was unavailable as the reactors lost all electric power, including from backup emergency diesel generators. Without adequate cooling, fuel temperatures rose to dangerous levels. The zirconium tubing surrounding the fuel reacted with hot steam to produce hydrogen, which mixed with air and exploded, destroying the surrounding structures.
As the heating continued, at least part of the fuel in the reactors likely melted and released radioactive material, some of which then escaped through the breached protective structures and spread into the surrounding air. The multiple failures of safety systems in the four reactors at Fukushima went beyond any emergency scenario the Tokyo Electric Power Company had ever envisioned, forcing it to improvise solutions, including using fire pumps
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