There is an almost primal fear of radioactivity. It may be a new manifestation of an old Jungian archetype: the fear of unseen danger, perhaps originally a predator or enemy lurking in ambush. Other incarnations include the fear of witches, germs, communists, and monsters under our beds. But radioactivity is worse. Not only is the threat hidden, but so is the attack. Your genes are invisibly mutated, showing no sign of the assault until a decade or two later when the damage manifests itself in a growing cancer.I put radioactivity on this witch list in an effort to make sense of the furor over nuclear waste storage at the Yucca Mountain facility in Nevada. When I work out the numbers, I find the dangers of storing our waste there to be small compared to the dangers of not doing so, and significantly smaller than many other dangers we ignore. And yet a contentious debate continues. More research is demanded, and yet every bit of additional research seems to raise new questions that exacerbate the public’s fear and distrust.
I’ve discussed Yucca Mountain with scientists, politicians, and many concerned citizens. The politicians believe it to be a scientific issue, and the scientists think it is a political one. Both are in favor of more research-scientists because that is what they do, and politicians because they think the research will answer the key questions. But I don’t think it will.
Let me review some pertinent facts. The underground tunnels at Yucca Mountain are designed to hold 77,000 tons of high-level nuclear waste. The most dangerous part of this consists of “fission fragments” such as strontium-90 and iodine-131, the unstable nuclei created when the uranium nucleus splits. Because these isotopes have a shorter half-life than uranium, the waste is about a thousand times more radioactive than the original ore. It takes 10,000 years for the waste (not including plutonium, which is also produced in the reactor, and which I’ll discuss later) to decay back to the radioactive level of the mined uranium. Based largely on this number, people have searched for a site that will remain secure for 10,000 years. After that, we are better off than if we left the uranium in the ground, so 10,000 years of safety is clearly good enough.
How can we plan to keep Yucca Mountain secure for this long? What will the world be like 10,000 years from now? Think backwards in order to appreciate the time involved: ten thousand years ago humans had just discovered agriculture, and writing wouldn’t be invented for another 5,000 years. Can we possibly see 10,000 years into the future? No. It is ridiculous to think we could. So nuclear waste storage is obviously unacceptable. Right?
Of course, calling storage unacceptable is itself an unacceptable answer. We have the waste and we have to do something with it. But the problem isn’t really as hard as I just portrayed it. We don’t need absolute security for 10,000 years. A more reasonable goal is to reduce the risk of leakage to 0.1 percent, i.e. to one chance in a thousand. Since the radioactivity is only 1,000 times worse than that of the uranium we removed from the ground, that means that the net risk (probability times danger) is 1,000 x 0.001 = 1-that is, basically the same as the risk if we hadn’t mined the uranium in the first place. (I am assuming the unproven “linear hypothesis” that total cancer risk is independent of individual doses or dose ratebut my argument won’t depend strongly on its validity.)
Moreover, we don’t need this 0.1 percent level of security for the full 10,000 years. After 300 years, the fission fragment radioactivity will have decreased by a factor of 10; it will only be 100 times as great as the mined uranium. So by then, we should rationally require only a 1 percent risk that all of the waste leaks out. That’s a lot easier than guaranteeing absolute containment for 10,000 years. Moreover, this calculation assumes 100 percent of the waste escapes. For leakage of 1 percent of the waste, we can accept a 100 percent probability. The storage problem is beginning to seem tractable.
But the unobtainable-and unnecessary-criterion of absolute security dominates the public discussion. The Department of Energy continues to search Yucca Mountain for unknown earthquake faults, and many people assume that the acceptability of the facility depends on the absence of any such faults. Find a new fault-rule Yucca Mountain out. But the issue should not be whether there will be an earthquake in the next 10,000 years, but whether there will be a sufficiently large earthquake in the next 300 years to cause 10 percent of the waste to escape its glass capsules and reach ground water with greater than 1 percent probability. Absolute security is too extreme a goal, since even the original uranium in the ground didn’t provide it.