Sunday, April 17, 2011
Fears and facts
Fukushima’s lessons for America’s already safe nuclear plants
The ground hadn’t stopped shaking. Tsunami waters had not receded. And yet coverage of this awful natural disaster – a scene of almost unfathomable devastation and death – was already giving way to single-minded focus on radiation exposure and meltdowns.
Addressing justifiable concerns is essential, to allay fears and refocus attention on finding the missing, burying the dead, helping 450,000 displaced people, and rebuilding ravaged communities.
Like a third of nuclear plants in American service today, providing 20% of all US electricity, the 40-year-old Fukushima Daiichi plant is a “boiling water reactor.” Uranium in fuel rods generates heat to turn water into steam that drives turbines, which power generators.
Though not designed or built according to current standards, the Japanese plant had many upgrades and enhancements over the years. For the most part, they worked.
Originally designed to withstand a Richter scale magnitude 8 quake, Fukushima was struck by a magnitude 9 earthquake. The tremor carried ten times the power and released 32 times more energy than an 8, and rattled the plant with more “peak ground acceleration” than it was designed for.
Fukushima withstood all that. But then a 45-foot tsunami roared over the plant’s 25-foot-high seawall, took out its backup diesel generators and knocked out electricity for miles. After backup batteries died, fuel rods and spent fuel began to overheat and cause explosions and radiation leaks that crews are still battling, mostly with increasing success.
While 28,000 people are dead or missing from the earthquake and tsunami, nuclear fuel damage appears to be short of a meltdown. Radiation levels are being addressed though distribution of potassium iodide tablets, evacuations for several miles around the plant, food supply testing, and other measures.
That is reassuring. But better reactor designs are clearly needed, and are under development.
High temperature gas reactors employ helium, rather than water, as a coolant. One version, the pebble bed modular reactor, replaces fuel rods with 2-inch-diameter graphite balls containing uranium granules. The South African version has been designed, and sub-assemblies and fuel balls manufactured and tested successfully, but economics have put the project on hold. A Chinese pebble bed design is under construction.
Another reactor type could be powered by molten fluoride salt containing thorium. This fuel is more plentiful and more easily handled than uranium, and produces more energy per volume of fuel.
TerraPower’s “traveling wave” reactor uses waste uranium as a fuel; Bill Gates and other investors say commercial operations are 15 years away. A new nickel-hydrogen “cold fusion” reactor, developed by two Italian scientists, is also attracting attention.
Until these futuristic systems arrive on the scene, nuclear plants already in the concept, design or construction stage will be better and safer than those that already help power America. However, existing reactors and those under construction are safe.
Twenty US plants now undergoing licensing or site preparation are all Generation III. They feature more “inherently safe design” elements and more “passive” safety features (such as auto response and gravity cooling systems) that rely less on human interaction with complex control systems.
The 104 commercial reactors already operating in the United States are all Generation II, enhanced over the years in response to new safety concepts and equipment, newly identified threats (such as terrorism after 9/11), and problems like Three Mile Island.
Gen II power plants consist of boiling or pressure water reactors surrounded by a steel wall, steel-reinforced concrete casing, and steel-reinforced concrete building. Nuclear engineers say US-based plants are designed, engineered and built to handle expected worst-case disasters like earthquakes, tornadoes, hurricanes and floods – and analyzed for possible effects of terrorism – with multiple backup systems.
These efforts are supplemented during and after construction by exhaustive design reviews and modifications, and ongoing upgrades or replacement of equipment, instruments, controls and power lines. Further enhancements to equipment, training and procedures occur during the relicensing process and in response to natural disasters, operator errors, equipment failures, terrorist acts, and the discovery of design or manufacturing defects, in the US and around the world.
The system is designed to provide defense in depth, have appropriate equipment and procedures in place, and establish a “culture of safety.” Operators are trained continually to execute normal and emergency procedures, and emergency preparedness is drilled every two years with industry, state and local officials, under oversight by the Nuclear Regulatory Commission and Federal Emergency Management Agency.
Fukushima apparently was insufficiently prepared for a disaster of the magnitude it experienced, in this major Pacific Ring of Fire earthquake and tsunami zone. The failure of diesel generators is already driving another look at passive safety systems; the hydrogen explosions a reassessment of ways to vent pressure buildups to special containment vessels; the overheating spent fuel rods new demands for reprocessing or safe offsite waste repositories, like Yucca Mountain.
The industry, NRC, FEMA, Congress, and state agencies are all reassessing and re-verifying the ability of nuclear plants, plans, equipment and personnel to handle events of Fukushima’s magnitude. Lessons from that near-disaster will be evaluated and employed worldwide.
Meanwhile, development of Generation III and IV nuclear reactors continues globally.
There can be no guarantees, no absolute fail-safe system. But those entrusted with nuclear power plant electricity generation and safety can and must come as close as possible.
Meanwhile, the rest of us must focus on helping northeastern Honshu recover – and offering thanks and prayers for the heroic workers who exposed themselves to dangerous radiation levels, to prevent a real disaster.
Paul Driessen is senior policy adviser for the Committee For A Constructive Tomorrow and Congress of Racial Equality.