Bill Nye and nuclear reactors 101March 13, 2011 @ 9:32 am (Updated: 3:46 pm - 3/28/11 )
Japan's chief cabinet secretary announced that cooling had failed at a second reactor at the Fukushima Daiichi Nuclear Power Station, 170 miles north of Tokyo. The new problem comes one day after officials flooded the crippled No. 1 reactor at the plant with seawater too cool it. An explosion caused by hydrogen tore the outer wall and roof off the building that housed the reactor.
For awhile this weekend, a top trending topic on Twitter was "Bill Nye." CNN brought in Bill Nye the Science Guy, who began his career in Seattle at Boeing, to explain what might be going on with Japan's nuclear reactors.
In an interview from Los Angeles , Nye says it's unlikely we're getting accurate information from Japan.
"To assert that things are under control when you see an explosion like this is unsettling," says Nye.
The Washington State Department of Health does not expect health risks in our state related to what's happening in Japan.
"We understand people may be concerned about a possible health risk from the nuclear reactor in Japan, and while we are monitoring the situation, we expect no health risk," they say in a statement.
Even without a risk to our health, many of us are concerned about people in Japan. I'm realizing how little I know about nuclear power. A friend of mine at the University of Washington, Kathy Gill, has compiled an educational resource for understanding how nuclear reactors work, based on research with a nuclear scientist and other experts.
What happens when you shut down a nuclear power plant?
The self-sustaining (critical) atomic reaction that runs a reactor can be shut off in a matter of seconds; the goal is to keep the reactor sub-critical. The core material, which is radioactive, will generate heat, at a decreasing rate, for some time. Therefore, nuclear engineers need a way to keep this heat from building up in order to protect the radioactive fuel (rods) and the reactor.
In order to cool the reactor, nuclear plants must have power that runs a complex system of motors, valves and instruments that push water through the nuclear core and carry the heat elsewhere; newer plants have been engineered to simplify this system. Should there be a loss of electricity from the power grid, diesel generators provide emergency power. Should the diesel generators fail, the battery-powered systems can keep water over the core for short periods.
The initial cooling process is fairly rapid; within the first hour after shut down, decay heat may decrease to about 2 percent of the pre-shutdown level. This drops to about 1 percent of the pre-shutdown level after the first day.
In answering the question: Is this another Chernobyl? Gill writes:
In a word, no. The situation in Japan is different from Chernobyl, which had a completely different nuclear power plant design. Chernobyl had an inherently unstable graphite-moderated reactor, not an inherently stable water-cooled reactor. In addition, all western (modern) reactors must have a containment building; Chernobyl did not have one. Therefore, even if the reactor core in Japan were to melt, the primary containment, a steel liner surrounding the reactor core, should limit the release of radiation. However, we do not know if the primary containment was weakened by the earthquake. Nevertheless, the longer the time between shut-down and collapse the better the outlook because the reactor generates less and less heat with time.
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