Editor's note: Stephanie Cooke is author of "In Mortal Hands -- A Cautionary History of the Nuclear Age" and editor of Nuclear Intelligence Weekly. The views here do not reflect those of the newsletter. For a different view, read "Don't be too hasty to reject nuclear power"
(CNN) -- As frightening as Japan's unfolding nuclear crisis is, worrying about the possibility of an earthquake-related nuclear disaster in the United States should not be our only concern.
The next nuclear disaster is more likely to be the result of something far more common -- human error, a technical malfunction, a large-scale power outage -- or some combination of all three.
The possible event sequences leading to a large-scale nuclear accident are so numerous they are almost unquantifiable. It is impossible to design against every eventuality.
Who would have thought that putting diesel generators in the basement of the Daiichi-Fukushima power plant would lead to the disaster in Japan -- and yet it did. When the tsunami rolled in on Friday, the plant's emergency back-up power systems ultimately failed. Within a matter of hours, the plant operators had to resort to seawater to keep the units from overheating. The outcome of that battle is still not known.
The nuclear industry has staggered under the weight of near-misses and catastrophes since its beginning more than a half-century ago. In October 1957, fire swept through the first of Britain's reactors at Windscale in northwest England, sending a radioactive plume into the air that showered radionuclides across the country and into northern Europe.
As men battled the blaze, working in relays because of the high concentration of radioactivity, health physicists drove on narrow twisting roads to take radiation readings on the Lake District's windswept hills and lush meadows where cows and sheep grazed. Then they started distributing potassium iodide pills. But they were a day or two too late.
The fire started during an attempt to release a build-up of excess energy. In the process, they realized the plant's designers had failed to provide the instruments needed to measure power levels and temperatures inside the core during the operation.
As a result, the fire was not discovered until three days after it started. It took another three to put it out. A recent study confirmed radioactive iodine and cesium were released, as well as polonium and a very small amount of plutonium -- and roughly twice the amount than was initially assessed. This led to an increase in the estimated numbers of excess cancers the accident may have caused, from 200 to about 240.
In October 1966, the Fermi Unit 1 reactor in Michigan suffered a partial meltdown only two months after it started operating. The reactor was eventually restarted -- although the process was marred by a fire and explosion -- and ran for a little over two years before it was refused an extension of its operating license.
A few years later, in 1973, consumer activist Ralph Nader said, "If the country knew what the facts were and if they had to choose between nuclear reactors and candles, they would choose candles."
What even Nader apparently didn't realize at the time was that at the Tennessee Valley Authority's Browns Ferry nuclear station in northern Alabama, technicians routinely used candles to check for air leaks. There were occasional small fires, but they were usually extinguished without a problem.
On March 22, 1975, the workers weren't so lucky. While workers using candles checked for leaks, fire broke out at Unit 1 and spread too quickly, burning for seven hours and leaving the plant without an emergency core cooling system. Luckily the operators were able to shut down the reactor when there was still enough water in the core to prevent damage or radioactive release.
Three decades later, in 2002, the country had what former Nuclear Regulatory Commissioner Victor Gilinsky called "its closest brush with disaster" since Three Mile Island's 50% meltdown in 1979. A workman at the Davis-Besse reactor near Toledo, Ohio discovered a rust hole the size of a pineapple in the top of the reactor pressure vessel. Once again, fortune was on the side of the operator: The plant was down for maintenance, which is partly why the hole was discovered.
But reactors are also vulnerable to unpredictable human behavior and malfeasance.
In February 1993, a man drove his mother's car past a guard booth the Three Mile Island plant, then smashed through an entry gate. He kept going until he crashed through a metal door and entered the turbine building of the Unit 1 reactor. The intruder, who had recently released from the mental ward of a local hospital, hid in a building and was not apprehended until four hours after he entered the site.
What if he'd been a terrorist armed with a ticking bomb?
The Tokyo Electric Power Co., operator of the crippled Fukushima plant, was forced to shut down its massive seven-unit nuclear plant at Kashiwazaki-Kariwa after a major earthquake in 2007. Afterward, the International Atomic Energy Agency revealed the plant had not been designed to withstand the 6.8-magnitude of the quake. Last week's quake measured 9.0.
The industry knew it was on trial then. "We cannot afford another accident," the IAEA's then director-general Mohamed ElBaradei said after the event.
Now it's on trial again.
In most countries, the global community has few ways of knowing what really goes on inside nuclear reactors because the industry is shrouded in secrecy. Corporations and governments control what information is made public. When information is made available, it is often couched in jargon and incomprehensible prose. Countless incidents worldwide have been insufficiently documented or not documented at all, according to a detailed 2007 study on nuclear safety conducted for the Green Party in the European Parliament.
In the United States, the Nuclear Regulatory Commission recently released its 2010 report card for the country's 104 operating reactors.
Six of them scored C. In two of those, H.B. Robinson in South Carolina and Wolf Creek in Kansas, the agency said there were too many unplanned shutdowns. Fires and turbine problems were listed as the cause in the case of the Robinson plant and a number of other technical malfunctions in the case of Wolf Creek.
While that may seem encouraging given there were only six with the lowest rating, the NRC's own effectiveness is under the spotlight in the wake of events in Japan.
The agency gets mixed reviews in a report released this week by the Union of Concerned Scientists. The report examines 14 "near-misses" at U.S. nuclear plants during 2010 that exposed "a variety of shortcomings, such as inadequate training, faulty maintenance, poor design, and failure to investigate problems thoroughly." The UCS said that "since NRC inspections cannot reveal more than a fraction of the problems that exist, it is crucial for the agency to respond effectively to the problems it does find."
The report offers examples of both effective and ineffective responses.
Most people think the industry has been under the microscope -- and held to strict safety standards -- since Three Mile Island. While there have been some improvements, human error and technical malfunctions have been its scourge since the 1950s. When the human cost of nuclear accidents -- particularly at Chernobyl and now in Japan -- are weighed, the cost of generating nuclear electricity looks like a different order of magnitude from all other forms of electricity generation, including coal mining.
If you don't buy that argument, imagine being told to evacuate your home or to stay inside and keep the windows closed. How long should those windows remain closed? How long must important but impractical precautions be taken? Then imagine realizing -- in a worst-case scenario -- you can never return.
In Japan, people of all ages living in the vicinity of the Fukushima Daiichi plant could now spend the rest of the lives wondering whether they've inhaled invisible radioactive products that might cause cancer in themselves of their loved ones or genetic damage to the unborn.
For an energy source once touted as too cheap to meter, the true costs may be too great to fathom.
The opinions expressed in this commentary are solely those of Stephanie Cooke.