11 Avril 2013
April 9, 2013
Dr. Gordon Edwards explains the background of Chairman Jaczko’s decision:
Gregory Jaczko, Chairman of the US Nuclear Regulatory Commission until last year, has arrived at a very basic realization: every potentially dangerous machine should have an emergency “off” switch that shuts everything down completely. And nuclear power reactors don’t have one. So, he concludes, all power reactors should be phased out.
How many action adventure movies show the hero disabling an explosive device or cutting the power to some monstrous killing machine just in the nick of time — mere seconds before total disaster erupts? In the blink of an eye the device or machine goes from malevolent to benign — from catastrophic to harmless — because someone pushed the “off” switch.
But a nuclear power reactor cannot be turned off completely, no matter what the emergency may be. Talk about a design flaw! Imagine a car that can’t be stopped, or a fire that cannot be put out.
Yes, there are “fast shutdown systems” in every nuclear reactor that can stop the nuclear chain reaction in less than two seconds, and they usually work quite well. The Three Mile Island reactor was “shut off” instantly, at the first sign of trouble; it only melted down later. The three operating Fukushima Dai-ichi reactors all “shut themselves off” automatically before the tsunami hit; but they all melted down anyway.
The problem is, shutting off the nuclear chain reaction does not stop the heat production. And it is that unstoppable process that keeps adding more heat to the core, driving the temperature spiraling upwards towards the melting point of the fuel — at a few thousand degrees on whatever scale you are using.
Why doesn’t the heat stop? It’s because we do not know how to shut off radioactivity.
There is an incredible inventory of fiercely radioactive byproducts created in the core of the reactor during normal operation. Even after the fission process is stopped, heat continues to be generated at an awesome rate simply through the radioactive decay (disintegration) of the unstable atoms that have accumulated in the core as a result of the fissioning of nuclear fuel.
This heat, called “decay heat”, is more than enough to melt the core of the reactor and everything else in the core area of the reactor. Immediately after “shutdown”, the decay heat is about 7 percent of full power heat.
For a reactor designed to produce 1000 megawatts of electricity, there is normally about 3000 megawatts of heat being generated. If such a reactor is suddenyly shut down, about 7% of those 3000 megawatts of heat is still being produced by the relentless radioactive disintegration of the waste byproducts in the irradiated nuclear fuel.
That’s more than 200 megawatts of heat — and it cannot be stopped.
Emergency cooling systems can remove the heat, but if the reactor is knocked out, who’s to say the emergency cooling systems aren’t also knocked out?
A reactor that can’t be stopped is like hell on a handcart. And they’re all like that.
Ex-Regulator Says Reactors Are Flawed
By Matthew L. Wald, New York Times, April 8, 2013
WASHINGTON — All 104 nuclear power reactors now in operation in the United States have a safety problem that cannot be fixed and they should be replaced with newer technology, the former chairman of the Nuclear Regulatory Commission said on Monday. Shutting them all down at once is not practical, he said, but he supports phasing them out rather than trying to extend their lives.
The position of the former chairman, Gregory B. Jaczko, is not unusual in that various anti-nuclear groups take the same stance. But it is highly unusual for a former head of the nuclear commission to so bluntly criticize an industry whose safety he was previously in charge of ensuring.
Asked why he did not make these points when he was chairman, Dr. Jaczko said in an interview after his remarks, “I didn’t really come to it until recently.”
“I was just thinking about the issues more, and watching as the industry and the regulators and the whole nuclear safety community continues to try to figure out how to address these very, very difficult problems,” which were made more evident by the 2011 Fukushima nuclear accident in Japan, he said. “Continuing to put Band-Aid on Band-Aid is not going to fix the problem.”
Dr. Jaczko made his remarks at the Carnegie International Nuclear Policy Conference in Washington in a session about the Fukushima accident. Dr. Jaczko said that many American reactors that had received permission from the nuclear commission to operate for 20 years beyond their initial 40-year licenses probably would not last that long. He also rejected as unfeasible changes proposed by the commission that would allow reactor owners to apply for a second 20-year extension, meaning that some reactors would run for a total of 80 years.
Dr. Jaczko cited a well-known characteristic of nuclear reactor fuel to continue to generate copious amounts of heat after a chain reaction is shut down. That “decay heat” is what led to the Fukushima meltdowns. The solution, he said, was probably smaller reactors in which the heat could not push the temperature to the fuel’s melting point.
The nuclear industry disagreed with Dr. Jaczko’s assessment. “U.S. nuclear energy facilities are operating safely,” said Marvin S. Fertel, the president and chief executive of the Nuclear Energy Institute, the industry’s trade association. “That was the case prior to Greg Jaczko’s tenure as Nuclear Regulatory Commission chairman. It was the case during his tenure as N.R.C. chairman, as acknowledged by the N.R.C.’s special Fukushima response task force and evidenced by a multitude of safety and performance indicators. It is still the case today.”
Dr. Jaczko resigned as chairman last summer after months of conflict with his four colleagues on the commission. He often voted in the minority on various safety questions, advocated more vigorous safety improvements, and was regarded with deep suspicion by the nuclear industry. A former aide to the Senate majority leader, Harry Reid of Nevada, he was appointed at Mr. Reid’s instigation and was instrumental in slowing progress on a proposed nuclear waste dump at Yucca Mountain, about 100 miles from Las Vegas.
A version of this article appeared in print on April 9, 2013, on page A16 of the New York edition with the headline: Ex-Regulator Says Reactors Are Flawed.