The standard risk analysis algorithm for making risk comparisons is to multiply the severity and magnitude of hazards with their probabilities of occurrence. This algorithm is considered by some to be callous, as it can excessively minimize a dreadful hazard which has a small probability, dooming some to experience it. As Nassim Taleb has argued in his black swan theory, scenarios with high risks and small aggregated probabilities like nuclear emergencies are still likely to occur at some point.
Yet the risk analysis algorithm still offers a place to begin in going beyond an intuitive risk perception that might be inflamed by imagination and what cognitive scientists call “heuristics”: mental shortcuts about risk based on associations rather than information and data.
The idea of a terrorist attack on a nuclear plant is a frightening one, and one easy to mentally envision. But we may subject this idea to three questions: I) What is the real hazard of a terrorist attack on a nuclear plant? II) What is the real probability of a terrorist attack on a nuclear plant? III) What are the alternative hazards and probabilities of other available options? I will ask this in a series of questions, addressing the possibilities of both ground/sea and air attacks in turn.
1. Ground/sea attack.
I) What is the hazard of a successful terrorist attack on a nuclear plant from the ground/sea?
The hazard of a successful nuclear terrorist attack could be a) sabotage to prompt a meltdown, or else b) the stealing of nuclear materials that could be used to build an improvised nuclear bomb or dirty bomb.
a) What is the hazard of a reactor meltdown and radioactive release? Fukushima and Three Mile Island are good examples as they may be considered typical meltdowns, unlike Chernobyl. After Fukushima, the typical dose in the 20 square kilometers in around the plant (the exclusion zone) in the first two weeks was one millisievert (msv). This typical dose was the same as the maximum dose to a civilian after the Three Mile Island meltdown. One msv is 100 times smaller than the lowest one-year dose clearly linked to cancer risk, conservatively observed to begin rising at a rate of 1% per annual dose of 100 msv . For civilians near Fukushima, the increased risk is thus indiscernible, as the United Nations concluded. At Fukushima 176 workers received doses of between 100 and 670 msv with the vast majority on the lower end of this scale. Thus the cumulative health effects of Fukushima may be conservatively put at an additional two fatal cancers above the 35 probable ones that will already occur among the worker population. The two worker deaths are tragic, but on the very low end for deaths related to energy production, even wind and solar power. Finally, it is notable that new reactor models such as Molten Salt Reactors are designed not to not melt down under any circumstances, thus reducing the hazard of a terrorist attack or accident dramatically.
b) What is the hazard of an improvised nuclear bomb or dirty bomb? Certainly an improvised nuclear bomb with explosive capabilities could be very hazardous, but according to Robin Frost its construction is practically elusive to terrorist groups, considering the requirements of advanced equipment, machining, vacuum pumps, et cetera (Adelphi Papers 2005). Further, the fuel that might be stolen from a reactor is so poorly enriched it could not be converted into a nuclear explosive, as we have learned in the civil nuclear power negotiations with Iran.
By contrast with an improvised nuclear bomb, a dirty bomb is simply a device designed to disperse or emit radiation. While the idea of a dirty bomb had some public currency in the post-9/11 era, it has been observed since that the dread associated with the idea was overblown. Frost, a defense analyst with the Canadian government, claims “it is generally acknowledged that, in most plausible scenarios, such weapons would pose little material threat to the public due” to the low dosage they could plausibly emit ("Dirty Bombs"). Expert concerns around dirty bombs consequently tend to address the spreading of fear and causing of disruption by such an apparatus rather than the perpetration of physical harm. Further, the materials considered most practical for making dirty bombs are used in medical applications and can not be found in usable forms in nuclear power plants. By contrast, the radioactive materials such as spent fuel rods located in nuclear power plants are effectively untransportable due to "the heat generated by large quantities of such material and the extreme exposure hazard from the intensity of the radiation.” Terrorists attempting to steal them would get burned and receive serious radiation poisoning long before they would have the chance to dissipate the materials.
II) What is the probability of a successful ground or sea intrusion of a nuclear plant?
The probability of a successful intrusion is considered to be quite low. Robert Wilson, an energy analyst, pointed out in a recent article on nuclear safety that “there has never been [a terrorist attack on a nuclear plant], and there appears to be no evidence that a plan to attack a nuclear power plant has ever moved beyond the basic planning phase in any terrorist group.” He described a recent report commissioned by the German Renewable Energy Federation into insurance costs for nuclear plant, which calculated there was a probability of terrorist attacks on nuclear plants happening 1 every 1000 operating years, as "junk science," given there have so far been 15,500 operating years without one.
Nuclear plant intrusion is not considered to be an attractive goal for terrorists, for two major reasons. The first reason is the relative difficulty of penetrating the security systems that are mandated of signatories to the IAEA Convention on Nuclear Safety, which include guards and electronic devices in communication with defense forces. The only reported successful intrusions of nuclear plants have been by Greenpeace activists who did not want to cause harm but to send an anti-nuclear message; in all cases they were observed and apprehended. As well, a Green Party representative once shot rocket-propelled grenades at a plant under construction but missed the empty core.
The second reason why nuclear plant intrusion is not considered an attractive goal for terrorists is that nuclear sabotage, short of obtaining material for a bomb, would not have immediate dramatic effects of the kind of public explosions terrorists favor. Rather, it would result in release of radiation with invisible and possibly long-term effects, at the worst. Only one group has managed to put one together--Chechen rebels in 1995--but they alerted the media before detonating the explosive intended to disperse the material (Frost, "Dirty Bombs"). Overall, it would be far easier to penetrate other facilities with home-made explosives and do far more dramatic and instantaneous damage.
2. Air attack
I) What is the hazard of a successful terrorist attack on a nuclear plant from the air?
The worst hazard is that a penetration would cause an explosion or fire that could initiate a meltdown and radioactive release. For the hazard of a meltdown and radioactive release, please see above.
II) What is the probability of a successful terrorist attack on a nuclear plant?
It has been experimentally proven that nothing short of a jumbo jet can penetrate a typical containment dome, which have 3-6 feet thick walls made of concrete reinforced with embedded steel bars and a half-inch steel liner. Opinions are mixed about whether a jumbo jet could penetrate the containment shell of a nuclear reactor. In a review by the U.S. Nuclear Regulatory Commission, it was considered very difficult for a jumbo jet to target "small, low-lying nuclear power plants" while “a sustained fire…would be impossible unless an attacking plane [including the fuel-laden wings] penetrated the containment completely” (Report to Congress 2006).
Even if a jumbo jet penetrated a nuclear reactor, the NRC concluded that “likelihood of both damaging the reactor core and releasing radioactivity that could affect public health and safety is low.” Steven Kraft, technical adviser for the Nuclear Energy Institute, pointed out that “the storage pools at Fukushima survived [with minimal damage] the fourth-largest earthquake in recorded history, hydrogen explosions that blew the roofs of three of the reactor buildings and the debris resulting from those explosions.” The New York Times accordingly observed that, “[t]errorists would have a far easier time igniting a conflagration at a toxic chemical plant or refinery than at a nuclear plant.”
III) What is the risk of not building more nuclear power plants?
More and more energy analysts and climate scientists are coming to the conclusion that nuclear power is an essential part of a decarbonized energy mix to avert global warming. In the words of climate scientists who wrote an open letter to those who influence policy-makers in the New York Times in November, 2013, “there is no credible path to climate stabilization that does not include a substantial role for nuclear power.” This is because while “[r]enewables like wind and solar and biomass will certainly play roles in a future energy economy… those energy sources cannot scale up fast enough to deliver cheap and reliable power at the scale the global economy requires.” Renewable sources apart from hydro-electric power continue to play a minor role in energy production, and experienced energy analysts anticipate they will continue to do so due to many factors, including the intermittency of wind and solar power generation and the elusiveness of techniques for storing large amounts of electricity for a substantial amount of time.
Thus we must seriously consider that an associated risk of not using nuclear power to produce carbon-free energy on a large scale is climate change itself, with the hundreds of millions of climate refugees that are projected to be engendered by it in the coming century. These hazards—we need not look at probabilities, because these patterns are already in motion—are apart from the millions of respiratory and other deaths already caused by fossil fuel burning and generation every year. Only carbon-free forms of generation like nuclear power can avert these tides of displacement and death, and only nuclear power—which does not require a switch to another kind of generation, almost always fossil fuel whenever the sun is down or the wind does not blow—can avert them on large scales, as it already does.
In short, I believe that these are the kinds of scrutiny we must undertake when we decide a technology is "too risky."