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Ph.D., 1950, Carnegie-Mellon University Area of Research: Applications of Nuclear Technology, Health effects of radiation, Risk analysis, Environmental impacts of Energy generation, Radon problems. Dr. Cohen has served as nationally elected Chairman of the American Physical Society Division of Nuclear Physics and of the American Nuclear Society Division of Environmental Sciences. He has authored over 250 articles in scientific journals, 50 articles in non-technical journals and written five books.
Radioactive Waste Disposal:
Perhaps the principal reservation cited against using nuclear power for generating electricity is the problem of disposing of the highly radioactive waste (radwaste) in the spent fuel after it is removed from reactors. The widely recognized solution for that problem is to bury it deep underground -- a commonly considered depth is 2000 ft. How safe would that be?
It is universally agreed that the principal danger is that this buried radwaste will be contacted and dissolved by groundwater, transported in this solution as it works its way toward the surface, and eventually ingested by people with potable water, that used for drinking and preparing food -- 40% of our potable water is derived from groundwater. Once inside the body, where it may remain for many years, the radioactive materials continually expose body organs to radiation which can cause cancer.
The details of estimating the radiation dose to various body organs from ingesting a given quantity of each radioactive species are well worked out and published by the International Commission on Radiological Protection (ICRP), and the cancer risk from these radiation doses is estimated in publications by the National Academy of Sciences Committee on Biological Effects of Ionizing Radiation (BEIR) and the United Nations Scientific Committee on Effects of Atomic Radiation (UNSCEAR). Using these we can estimate the number of fatal cancers that would be caused if all of the buried radwaste from U.S. nuclear power plants were converted into digestible form and fed to people. We define this as the number of cancer doses, CD, in that radwaste. (This assumes that there are enough people involved so that none of the toxicity is wasted by feeding more than a fraction of one CD to any one individual.)
The number of CD in the ground from buried radwaste will depend on how many nuclear power plants we continually operate and on when we convert to chemical reprocessing of radwaste. Calculations are presented in my recent papers published in Health Physics Journal*. With reasonable assumptions, it is concluded that over the next several thousand years there will be something like 2 trillion CD buried, presumably 2000 ft below various locations throughout the contiguous 48 U.S. states.
How many cancers will this cause and how acceptable is the situation from the standpoint of public health? This depends on details of how the waste is buried, and there are two approaches to that operation -- there is Nature’s way, and Government’s way.
One option is to convert the radwaste into rock-like materials and assume that nature will treat this radwaste-rock as it treats other rocks -- we call this “Nature’s way”. What do we know about how nature treats radioactive rocks?
Each ton of rock in the ground contains an average of 1.7 grams of Uranium and 5.8 grams of Thorium. Both of these elements emit radiation, and in the process are converted to other elements, most importantly Radium, which also emit radiation. The quantities of these naturally occurring materials in the top 2000 ft of U.S. rock -- that is, closer to the surface (and hence more potentially dangerous) than the buried radwaste -- comes to 30 trillion CD, 15 times the number of CD in the radwaste below it.
In the normal course of events, Nature allows some of this Uranium, Thorium, Radium, etc to be dissolved out by groundwater and eventually to be ingested by people with potable water, exposing their body organs to radiation. From measurements on human corpses, we know how much of these naturally radioactive materials is in our bodies, and the radiation dose to which they expose us. From that dose, using BEIR and UNSCEAR publications, we can estimate the number of cancer deaths per year caused by this radiation. Chemical analyses of foods and water supplies tells us what fraction of these materials is derived from potable water rather than from food -- materials in food were picked up by plant roots in the top few feet of soil that is normally watered by rain or river water irrigation soaking down from above. The conclusion is that ingestion of these naturally radioactive materials with potable water causes about 68 cancer deaths per year in the U.S.
Since only 40% of our potable water is derived from groundwater, our estimate of the number of deaths from groundwater-derived natural radioactivity is reduced to 40% of 68, or 29. As these deaths are caused by the 30 trillion CD in the ground, this is about one death per year per trillion CD. A more detailed analysis provides an estimate individually for each of the 8 naturally radioactive materials involved; the average of the 8 results is 1.3 deaths per year per trillion CD in the ground.
Applying these results to the 2 trillion CD in the buried radwaste from nuclear power plants gives us an estimate of about 2 deaths per year expected from the latter. However there are several reasons why this is an over-estimate:
--The nuclear power radwastes will be buried at 2000 ft depth whereas the natural radioactivity we are considering is at depths between there and the surface through which the average groundwater flow is 7 times larger than at 2000 ft, so the above result should be divided by 7.
-- There is a substantial time delay in travel from deep underground to near the surface for materials dissolved in ground water -- these materials are temporarily filtered out by the rock though which the water passes, causing travel times to be many thousands (or even millions) of years -- during which large fractions of the radioactivity in the radwaste decay away.
-- The holes in which the radwaste-rock would be emplaced would be backfilled with a special clay (bentonite) that swell up when wet to block further water intrusion, and if the waste is eventually contacted and dissolved, this clay efficiently filters escaping radioactive materials out of groundwater, greatly extending its travel time.
-- The medical cure rate for cancer is improving at a rate of about one percent per year so the great majority of the cancers predicted in our calculation, occurring thousands (or more) of years in the future, will probably be easily cured.
-- Our calculation is based on average conditions in the ground throughout the U.S. whereas radwaste repositories will be built at sites carefully selected by the best experts in geology and hydrology to provide maximum security.
-- It would be very easy to detect any substantial amount of escaping radioactivity from these sites if it should occur, so measures could be taken to greatly reduce human exposures.
Our final conclusion is, then, that if we took advantage of Nature’s way, converting the radwaste into rocks and burying them in the natural habitat of rocks, deep underground, this buried radwaste would cause far less than one death per year in the U.S.
There are other completely independent ways of arriving at this conclusion presented in my other scientific publications**.For example, from analysis of water carried by our rivers into the oceans, we know that, on average, 12 millionths of a foot of rock thickness under U.S. is being dissolved away each year, and from hydrology studies we know that about 1/12,000 of this is derived from one foot of depth at 2000 feet below the surface. Thus, 1/12,000 of 12 millionth, one billionth of a foot of depth is dissolved out of one foot of depth each year, so an average atom in this rock has one chance in a billion per year of being dissolved into groundwater.
We know the amount of potable water ingested by U.S citizens each year, and dividing this by the total annual U.S. groundwater flow tells us that an average atom dissolved in groundwater has one chance in 2000 of being ingested by a human. Thus an atom of buried radwaste rock has one chance in 2000-billion -- one chance in 2 trillion -- per year of entering a human stomach. Applying this to the yearly contribution from each of the radioactive components in buried radwaste as they decay away with time gives us a result agreeing with the our previous conclusion from Uranium, Thorium, etc. These studies include estimated contributions from groundwater entering rivers that are used for potable water, from people eating fish who inhabited those rivers, and from using groundwater to irrigate food crops, but these have only minor effects on the conclusion.
All of the estimates described here have been published in widely read scientific journals, and none of them has been challenged, or even criticized in the scientific literature. It thus seems clear that if we were to utilize Nature’s way of managing radwaste, converting it into rocks and burying them deep underground, we could expect something less than one cancer death per year in U.S. to result. This surely compares very favorably with the many thousands of deaths per year being caused right now by the wastes, principally air pollution, from generating the same amount of electricity by burning fossil fuels. Following Nature’s way would be a simple and very acceptable solution to the issue of radwaste disposal.
For the problem of radwaste burial, the U.S. government approaches safety issues mainly through three agencies. Nuclear Regulatory Commission (NRC) sets up licensing procedures for repositories, these must be approved by Environmental Protection Agency (EPA), and Department of Energy (DOE) designs repositories and applies to NRC for a license to build and operate them. All of this is subject to substantial interactions with the public including government financing for activities of opposition organizations and their legal appeals to Federal courts. The entire process involves roles for the President, the Secretary of Energy, the government of the host state, and final approval by Congress. Obviously, these procedures introduce extensive political activity.
The principal licensing requirement set up by this system is that DOE must demonstrate with high confidence that at no time in the next million years will any single individual member of the public be exposed to a stipulated radiation dose (15 millirem) in any one year. This dose would give him a risk (assuming there is no progress in curing cancer from now until that time) equal to 2% of the average American’s present risk of being killed in an accident in any one year. There is no stipulation on how many other people are exposed to that or lower doses, or over what time period these exposures occur, so there is no consideration given to the total number of cancers caused. Isn’t that what we should be concerned about? With the present licensing requirement, nuclear bomb testing in the atmosphere could be licensed as no one person has received even one-half of the stipulated dose, but that practice was abandoned in 1962 because it was estimated to be killing thousands of people every year.
This licensing process precludes any direct use of Nature’s way. The calculations described above for Nature’s way utilize data averaged over the entire U.S. Its result, less than one death per year, is equivalent to the consequences of siting a large number of repositories at random locations throughout the U.S. But it does not predict the effects of a single repository at a specific site. I have proposed** that it is reasonable to assume that utilizing all the expert knowledge of geologists and hydrologists would select repository sites at least as secure as random selections. But Government agencies allow no place in the licensing procedures for such an assumption.
If the radwaste were simply converted into rocks and buried deep underground, licensing would require knowledge of, and future predictions for, all aspects of groundwater behavior at that site including effects of possible earthquakes and volcanic action in the vicinity, different future climates (10,000 years ago the Arizona desert was a rain forest and the Sahara desert was well watered), unpredictable geological land uplifting which often drastically alters river and groundwater flow patterns, intrusion by humans and lower life forms, etc. These are automatically taken into account in Nature’s way because they are occurring in some U.S. locales now and hence contribute to the averages used in the calculations.
Aside from problems in predicting the future, we do not well understand the present details of Nature’s way -- the interactions between factors involved in dissolution of rock by groundwater and its subsequent transport, such as the chemical composition and granular nature of the rock, the chemical composition of the groundwater, effects of cracks in the rock, etc.
The DOE solution to this problem is not to depend on Nature’s way, but rather to install the waste in a large underground man-made storage chamber in which everything is designed so as to prevent, or at least greatly delay, contact with groundwater. It includes parts made of corrosion-resistant titanium, of other special corrosion-resistant metal alloys, of stainless steel, and of carbon steel, with devices for conducting away the heat from the radioactivity. The design includes provisions for preventing and/or mitigating effects of water dripping into this chamber, of falling rock, and of a large variety of other possible intrusions. In summary, Government’s way is to depend heavily on technology to prevent, or at least delay encounters with groundwater, in contrast to Nature’s way in which radwaste rock is ordinarily exposed to groundwater from the time of burial. There is a problem here in that if and when encounters with groundwater do occur in Government’s way, they are under rather different circumstances than contact with groundwater in Nature’s way. Can we be confident that this does not severely compromise the results?
In order to satisfy the licensing requirement utilizing Government’s way, it is necessary that everything be calculated for the specific site. Such calculations require that assumptions be made about processes that are not well understood and about the probabilities for various possible future disrupting circumstances. That introduces a very serious problem in that these assumptions involve personal judgments. Such judgments can be debated, negotiated, and agreed upon by scientific experts trying to reach a consensus. But the political debate is dominated by non-experts who have never studied the thousands of pages of scientific input leading to these judgments. Many of them are committed to opposing any such consensus, motivated by politically useful slogans such as “we don’t want our area to be the nation’s garbage dump”. Politics in Nevada, where the first repository is being planned, requires that any candidate for political office adopt that position, and that includes Senator Harry Reid who now directs the U.S. Senate and has vowed to do anything in his very considerable power to obstruct the process.
Needless to say, this licensing procedure requires a lot of time and a lot of money. More than 15 years and 5 Billion dollars has already been spent on the licensing of the proposed Nevada repository, and the end is hardly in sight. The opponents, including Senator Reid, argue that there is no urgency to making a final decision as the waste is now being safely stored at the various nuclear plants where it is generated.
However the lack of a decision is impeding the construction of new nuclear power plants. Some states, including California, legally prohibit such new construction until the radwaste problem is “solved”, and some utility executives refuse to consider undertaking such construction fearing the political impacts of that “unsolved problem”. Since nuclear power is the principal source we have for generating electricity without contributing to global warming, the current situation is a real obstacle to our future energy security. And it is all caused by irrational politics.
* Understanding the toxicity of buried radioactive waste and its impact, Health Phys 89;355-358;2005 and 91:394-396;2006
** Probabilistc risk analysis for a high level waste repository, Risk Analysis 23:909- 915;2003
Risk Analysis of Buried Waste from Electricity Generation, Am.
Jour. of Phys. 54, 38 (1986).
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