What Makes New Nuclear Reactors Safer : Discovery News
Nuclear reactors planned for the U.S. are safer and more efficient than the 40-year-old Japan facility that has suffered explosions and leaks, experts say.
Nuclear reactors in development have passive cooling systems that could continue functioning if power is lost.
A new reactor design by Westinghouse could be shut down for three days without power.
Industry predicts that production of these plants will now slow down as new scrutiny is placed on safety.
Nuclear reactors planned for the United States are safer, stronger and more energy-efficient than the 40-year-old Fukushima Daiichi facility that has suffered explosions and radiation leaks, according to experts.
At the same time, the nuclear crisis in Japan will probably further delay their approval by federal regulators.
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U.S. and international firms are banking on these new reactor designs that use so-called "passive cooling" to remove heat from a reactor, rather than the kind of active cooling system that failed at Daiichi when the system's cooling water intake pumps and diesel generators were knocked out by a 30-foot tsunami.
"The biggest takeaway is the preparation for the tsunami was inadequate," said Robert Corradini, a distinguished professor at the University of Wisconsin College of Engineering and a member of the Nuclear Regulatory Commission's advisory committee on reactor safeguards.
"You're going to see refortification of plants for the tsunami. I expect that the NRC is going to slow down the process and do a re-analysis to make sure that nothing has been unturned in terms of lessons learned."
Corradini says the "Generation III-plus" plants proposed by Westinghouse, General Electric, Mitsubishi and the French firm Areva incorporate new designs that take in the lessons of past nuclear accidents at Three Mile Island and Chernobyl.
The AP1000 reactor, designed by Westinghouse, can be shut down for three days without power. Instead of pumps, valves and human operators, the plant uses airflow, pressure changes and gravity to gradually cool the reactor.
"Going forward you will see more reliance on passive safety systems that will automatically shut down the plant instead of generators and pumps," said Scott Shaw, a Westinghouse spokesman in Pittsburgh.
The firm is currently building four AP1000 reactors in China, with the first one scheduled to go online in 2013. Utilities in Georgia and South Carolina each want to build two of the new reactors, but are still waiting for NRC approval.
The NRC approved the initial AP1000 design back in January 2006, but federal officials put out new rules in the wake of the 9/11 attacks to make the reactors able to withstand a direct hit from a jet airplane. Now some industrial officials worry privately that they'll have to do another redesign to make their plants safe from giant waves.
Shaw said it's too early to tell the fallout from the situation in Japan. "Things are still unfolding," he said.
Paris-based Areva is working on its own version of a generation III-plus plant called the EPR or evolutionary power reactor, which is considered the world's largest.
Areva is building 1,650 megawatt EPRs in Finland, France and two in China, according to company officials. The firm is also planning a new reactor at an existing plant at Calvert Cliffs, Md., with a prospective U.S. partner.
The EPR has a double containment dome and four levels of safety systems, said Jarret Adams, a company spokesman in Bethesda, Md. It also has something called a "core catcher" that spreads out nuclear material in a underground circular concrete basin should a complete meltdown occur and the reactor melt through the containment vessel.
In contrast, some critics have pointed out that the type of containment vessel and pressure suppression system used in the failing reactors Daiichi plant -- and in 23 American reactors at 16 plants -- is physically less robust, and it has long been thought to be more susceptible to failure in an emergency than competing designs, the New York Times reported Tuesday.
G.E. officials said the reactor design that failed in Japan, called the Mark 1, hasn't had a problem in 40 years of operation.
The plant in Japan also needed a great deal of cooling water from the nearby ocean to keep it cool, whereas newer plants recirculate more water, said Michael Podowski, visiting professor at the Massachusetts Institute of Technology's department of nuclear engineering.
Podowski believes that another new technology may that uses smaller, less radioactive plants could avoid some of the problems at Daiichi. These "small modular reactors" produce 100 to 200 megawatts of power, about one fifth to one-tenth the size of many current U.S. nuclear reactors.
The advantage is that these smaller plants can be located off the main electric grid to supply rural customers. Since they are smaller, utilities can conduct maintenance work without the entire power production going offline. They produce both less heat (reducing the need for cooling systems) and less radioactivity.
Podowski and others said most of the existing U.S. nuclear reactors are reaching the end of their lifespans. They need to be replaced, or the American public has to find another source for 20 percent of its power.
"Reactors get old and they will have to be decommissioned," Podowski said. "They will be shut down and we will hear more about this issue. The outcome is to build new safer power plants."
While safety concerns are at the forefront this week, many observers point out an equally urgent problem is what to do with the radioactive waste produced by nuclear plants.
Attempts to build a single repository in the Nevada desert have failed over the past 30 years, so spent fuel rods are stored in liquid pools at each of the 104 reactors across the country.