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HOME > PAST ISSUE > March-April 2014 > Article Detail

TECHNOLOGUE

A Path for Nuclear Power

A novel but tested technology, the pebble-bed reactor, can make fission energy safe.

Lee S. Langston

Avoiding Another Fukushima

Overall, the safety record of the hundreds of nuclear power plants around the world has been outstanding. But as asserted by industry critic Arnold Gundersen, “Nuclear power is a technology that can have 40 good years and one bad day.”

The industry had a very bad day on March 11, 2011, when magnitude 9.0 earthquake struck at 2:46 PM local time in the Pacific Ocean seabed, 80 miles east of the Japanese coastal city of Sendai. Nuclear power plants in the northeast part of Japan automatically shut down, with control rods inserted into the reactor cores. The 4,700-megawatt Fukushima Daiichi nuclear power plant complex was one of these. The complex, located on the coast some 150 miles north of Tokyo, is made up of six separate boiling water reactor units. These units were designed to withstand a magnitude 8.2 scale earthquake, comparable to the 1906 San Francisco event. The March 11 earthquake was seven to eight times more powerful than that.

Of the six Fukushima Daiichi reactors, Units 5 and 6 were offline for planned inspection and Unit 4 had been completely defueled. Unit 1, with a nominal output of 498 megawatts, and Units 2 and 3, both of which put out 796 megawatts, were in operation before their earthquake induced automatic shutdown. Even with control rods fully inserted, these three units still needed cooling from an electric-powered circulating water pump, due to the residual heat generated by intermediate radioactive elements created in uranium fission.

At 3:44 PM, a 15-meter-high tsunami reached the Fukushima Daiichi complex, overtopping facilities designed to withstand a 5.7-meter tsunami. Both the offsite and onsite emergency diesel generators were knocked out by floodwaters, depriving the reactor cores of cooling water. Once the backup battery power ran out, the reactor coolant water overheated, increasing pressures and temperatures in the reactor pressure vessel. Pressure was automatically relieved to a suppression pool designed to condense steam, but this reduced the amount of water in the reactor.

The fuel rods continued to heat up, and a reaction between the zirconium fuel rod cladding and the remaining coolant generated hydrogen. The hydrogen eventually escaped from the reactor pressure vessel, causing explosions and further damage. The inability to provide reactor coolant, despite multiple-layered backup systems that all depended on AC power, led to the meltdown of the reactor cores in Units 1, 2, and 3. The root of the problem was that the backup systems were overwhelmed by disasters worse than the worst-case scenario they were designed to protect against.

Similar damage occurred in 1979 at one of the two nuclear units at Three Mile Island in Pennsylvania, due to operator error when an emergency cooling system was turned off. In a New York Times interview, Lake H. Barrett, the senior U.S. Nuclear Regulatory Commission engineer for Three Mile Island, noted that cleanup of the site—which took 14 years and the removal of about 150 tons of radioactive rubble—“was a walk in the park compared to what they’ve got” in Japan.

Barrett is now an adviser for Fukushima’s cleanup. Writing in the September 9, 2013, issue of the Bulletin of Atomic Scientists, he outlines the herculean measures the Japanese company is taking to cool the melted-down reactor cores in Units 1, 2, and 3, and the spent fuel pools in Unit 4. It involves the circulation and recycling of radioactive water—some 90 million gallons and growing—into more than 1,000 temporary water storage tanks, through tens of miles of piping throughout the four earthquake-damaged plants, each of which is also being affected by ground water leakage. Barrett notes that such a program of containment cannot continue indefinitely, bringing up questions about a long-term solution to the problems at Fukushima.

Although the measureable health impact of the Fukushima accident has been thankfully small, the social, political, and economic effects have been vast. Experts estimate that a 40-year decommissioning of Fukushima could cost $100 billion. That figure doesn’t even account for the destruction of land values and productivity in the region and other less tangible economic factors.




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