In Part I, I described how the unstable uranium-235 nucleus could be induced to split by hitting it with a neutron. In order to review the risks and issues surrounding the handling of nuclear waste, I now need to introduce natural radioactive decay. Natural radioactive decay occurs when the nucleus of an atom is sufficiently unstable that it will spontaneously break apart without any external inducement. Natural radioactive decay proceeds at a much slower rate than induced nuclear fission in a power plant. While natural radioactive decay does not release sufficient energy to generate electricity, it still packs enough punch to be hazardous to your health. Examples of naturally radioactive elements include uranium-235, thorium-232, and radium-226.
Natural radioactive decay proceeds via two mechanisms, alpha particle and beta particle emission. In alpha particle decay, a small piece of the nucleus containing two protons and two neutrons is ejected. The alpha particle, since it is positively charged as a result of having two protons, rapidly acquires two electrons to even out the charge balance. Once the alpha particle captures the two electrons, it has become a helium atom. Approximately 99% of the helium on earth was produced via alpha particle decay from naturally occurring radioactive elements. In beta particle decay, one of the neutrons in the nucleus is ejected at very high speed.
Complicating the discussion of natural radioactive decay is the fact that it usually includes a complex series of alpha and beta particle emissions. You start with a large radioactive atom. As it ejects a series of alpha and beta particles, you create smaller and smaller radioactive atoms until, eventually, a non-radioactive element is created and the process stops. In the case of uranium-235, it undergoes a lengthy series of decays, creating a number of other radioactive elements, until finally lead, which is not radioactive, is formed. The most well known of the radioactive elements in the uranium-235 decay chain is radon, which lurks in the basements of many homes in the U.S.
Just like in the induced nuclear fission process I addressed in Part I, when natural radioactive decay occurs, the sum of the masses of the pieces left over after the decay is less than what you started with. The missing mass gets converted to energy, the amount of which can be calculated with Mr. Einstein’s famous equation, E = mc2. The energy released is primarily in the form of gamma rays. The term radiation, when used in the context of nuclear fission, refers to both the gamma rays and the ejected alpha and beta particles.
Gamma rays, beta particles, and to a lesser extent, alpha particles, are extremely hazardous to your health. The explanation for this could fill an entire book, so let me give you the short version. The high energies of gamma rays and beta particles allow them to penetrate into your body where they can cause molecular damage. Some of the damaged molecules are DNA. DNA damage from nuclear radiation can result in a number of different cancers, particularly thyroid cancers and leukemia.
While nuclear power plants generate a variety of radioactive wastes, by far the most difficult to manage are the spent fuel rods. Spent fuel rods contain unutilized uranium as well as a mixture of different radioactive elements which are members of the uranium-235 decay chain. The fuel rods will continue to pose serious danger to human health for millions of years.
The world has already generated a staggering amount of nuclear waste to which we are adding approximately 12,000 tons per year. All of this has occurred without a clear plan to manage the waste. While we continue to evaluate the potential long-term storage options, most of the world’s nuclear wasted is staged in temporary above-ground storage facilities where it has been incorporated into glass and ceramic composites, sealed in metal containers, and encased in concrete. This storage approach is sufficient to protect us from radiation in the short term, but is not sufficient to isolate the waste for the millions of years that will be necessary.
A comprehensive review of all of the long-term storage options being considered would be too much to cover in a single column. Any acceptable solution needs to completely and reliably isolate the waste from the biosphere for five to ten million years. There are two out-of-the-box type solutions that I find interesting. The first is ejection into space. This certainty removes the waste from the biosphere. The Achilles Heel of this approach is the possibility of an upper atmosphere explosion of the rocket transporting the waste to space, the results of which would be catastrophic. Personally, I am intrigued with a second creative proposal which suggests that we consider transporting the waste to a subduction zone at the intersection of two tectonic plates at the bottom of the ocean. Material placed into the subduction zone would be transported into the earth’s magma miles below the surface. Concerns regarding potential contamination of the oceans during the operation have stalled these efforts as well. While both of these esoteric options would meet the criteria for removing the wastes from the biosphere, their attendant risks suggest that they will never be implemented.
This leaves us with the less elegant and long debated issue of burying the waste. For the last four decades the U.S. has been evaluating the option of interring our nuclear waste beneath Yucca Mountain in Nevada. Political pressures and scientific uncertainty have thus far, kept this project from moving forward. My sense is that eventually we will have a serious incident at one of our above-ground, temporary waste storage facilities which will finally force the Yucca Mountain project to move forward.
With the serious and long-term risks associated with nuclear waste, one must consider whether the benefits of nuclear power are worth it. I’ll give you my view on that subject at the end of next week’s column after first covering operational safety.
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Nuclear Power Part II: Waste, No Solution So Far
When I started writing about nuclear power last week, I was planning on a two-part series. As I started Part II, it quickly became apparent that a three-part series would be needed to keep the segments at manageable lengths. So this week I’ll cover nuclear waste and next week I’ll move on to operational safety and some concluding thoughts on this controversial technology.