Physics for Future Presidents --the Science Behind the Headlines
By Richard A. Muller
The following is excerpted, with permission of the author, from Physics for Future Presidents --the Science Behind the Headlines
The furor against nuclear power has been so intense that I felt compelled to reproduce the anti-nuke viewpoint in the opening of this chapter, including at least part of their passion. These are the arguments that you will hear when you are president. Yet it hardly matters whether you are pro-nuke or anti-nuke. The waste is there, and you will have to do something with it. You can't ignore this issue, to do the right thing (and to convince the public that you're doing the right thing) you must understand the physics.
When I work out the numbers, I find the dangers of storing our waste at Yucca Mountain to be small compared to the dangers of not doing so, and significantly smaller than many other dangers we ignore. Yet the contentious debate continues. More research is demanded, but every bit of additional research seems to raise new questions that" exacerbate the public's fear and distrust. I have titled this section "My Confession" because I find it hard to stand aside and present the physics without giving my own personal evaluation. Through most of this book I've tried to present the facts, and just the facts, and let you draw the conclusions. In this section, I confess that I'll depart from that approach. I can't be evenhanded, because the facts seem to point strongly toward a particular conclusion.
I've discussed Yucca Mountain with scientists, politicians, and many concerned citizens. Most of the politicians believe the matter to be a scientific issue, and most of the scientists think it is political. Both are in favor of more research—scientists because that is while they do, and politicians because they think the research will answer the key questions. I don't think it will.
Here are some pertinent facts. The underground tunnels at Yucca Mountain are designed to hold 77,000 tons of high-level nuclear waste. Initially, the most dangerous part of this waste is not plutonium, but fission fragments such as strontium-90, an unstable nucleus created when the uranium nucleus splits. Because these fission fragments have shorter half-lives than uranium, the waste is about 1000 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. Largely on the basis of 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 probably good enough, not the 100,000 years that I mentioned in the chapter introduction.
Ten thousand years still seems impossibly long. What will the world be like 10,000 years from now? Think backward to appreciate the amount of time involved: Ten thousand years ago humans had just discovered agriculture. Writing wouldn't be invented for another 5000 years. Can we really plan 10,000 years into the future? Of course we can't. We have no idea what the world will be like then. There is no way we can claim that we will be able to store nuclear waste for 10,000 years. Any plan to do that is clearly unacceptable.
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%—that is, to one chance in a thousand. Because the radioactivity is only 1000 times worse than that of the uranium we removed from the ground, the net risk (probability multiplied by danger) is 1000 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 linear hypothesis—that total cancer risk is independent of individual doses or dose rate—but my argument won't
depend strongly on its validity.)
Moreover, we don't need this 0.1% 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 be only 100 times as great as the mined uranium. So by then, we no longer need the risk to be at the 0.1% level, but could allow a 1% chance that all of the waste leaks out. That's a lot easier than guaranteeing absolute containment for 10,000 years. Moreover, this calculation assumes that 100% of the waste escapes. For leakage of 1% of the waste, we can accept a 100% probability after 300 years. When you think about it this way, the storage problem begins to seem tractable.
However, the public discussion doesn't take into account these numbers, or the fact that the initial mining actually removed radioactivity from the ground. Instead, the public insists on absolute security. 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. They believe that the discovery of a new fault will rule Yucca Mountain out. The issue, though, should not be whether there will be any earthquakes in the next 10,000 years, but whether after 100 years there will be a 1 % chance of a sufficiently large earthquake that 100% of the waste will escape its glass capsules and reach groundwater. Or, we could accept a 100% chance that 1% of the waste will leak, or a 10% chance that 10% will leak. Any of these options leads to a lower risk than if the original uranium had been left in the ground, mixing its natural radioactivity with groundwater. Absolute security is an unnecessarily extreme goal, since even the original uranium in the ground didn't provide it.
The problem is even easier to solve when we ask why we are comparing the danger of waste storage only to the danger of the uranium originally mined. Why not compare it to the larger danger of the natural uranium left in the soil? Colorado, where much of the uranium is obtained, is a geologically active region, full of faults and fissures and mountains rising out of the prairie, and its surface rock contains about a billion tons of uranium.37 The radioactivity in this uranium is 20 times greater than the legal limit for Yucca Mountain, and it will take more than 13 billion years—not just a few hundred—for the radioactivity to drop by a factor of 10. Yet water that runs through, around, and over this radioactive rock is the source of the Colorado River, which is used for drinking water in much of the West, including Los Angeles and San Diego. And unlike the glass pellets that store the waste in Yucca Mountain, most of the uranium in the Colorado ground is water-soluble. Here is the absurd-sounding conclusion: if the Yucca Mountain facility were at full capacity and all the waste leaked out of its glass containment immediately and managed to reach groundwater, the danger would still be 20 times less than that currently posed by natural uranium leaching into the Colorado River. The situation brings to mind the resident near Three Mile Island who feared the tiny leakage from the reactor but not the much greater radioactivity of natural radon gas seeping up from the ground.
I don't mean to imply that waste from Yucca Mountain is not dangerous. Nor am I suggesting that we should panic about radioactivity in the Los Angeles water supply. The Colorado River example illustrates only that when we worry about mysterious and unfamiliar dangers, we sometimes lose perspective. Every way I do the calculation, I reach the same conclusion: waste leakage from Yucca Mountain is not a great danger. Put the waste in glass pellets in a reasonably stable geologic formation, and start worrying about real threats—such as the dangers of the continued burning of fossil fuels. I'll discuss that in the final part of this book.
A related issue is the risk of mishaps and attacks during the transportation of nuclear waste to the Yucca Mountain site. The present plans call for the waste to be carried in thick, reinforced concrete cylinders that can survive high-speed crashes without leaking. In fact, it would be very hard for a terrorist to open the containers, or to use the waste in radiological weapons. The smart terrorist is more likely to hijack a tanker truck full of gasoline, chlorine, or another common toxic material and then blow it up in a city. Recall from the chapter on terrorist nukes that al-Qaeda told Jose Padilla to abandon his effort to make a dirty bomb and instead focus his efforts on natural-gas explosions in apartment buildings.
Why are we worrying about transporting nuclear waste? Ironically, we have gone to such lengths to ensure the safety of the transport that the public thinks the danger is greater than it really is. Images on evening newscasts of concrete containers being dropped from five-story buildings, smashing into the ground and bouncing undamaged, do not reassure the public. This is a consequence of the "where there's smoke there's fire" paradox of public safety. Raise the standards, increase the safety, do more research, study the problem in greater depth, and in the process you will improve safety and frighten the public. After all, would scientists work so hard if the threat weren't real? Scientists who propose rocketing the waste to the sun, or burying it in a subduction zone in the ocean, also seem to be suggesting that the problem is truly intractable, and that premise exacerbates the public fear.
Richard A. Muller is professor of physics at the University of California, Berkeley. He is a past winner of the MacArthur Fellowship. Physics for Future Presidents is based on his renowned course for non-science students.
Richard Muller’s website:http://muller.lbl.gov/
Website for the book: http://nortonbooks.typepad.com/physics_for_future_presid/