Despite the conflict over nuclear plant discharges, the risks are actually quite small, but could be further reduced
Ernest C . Tsivoglou Georgia Institute of Technology Atlanta, Georgia
Nuclear power: the social conflict
D
uring the past year or two there has been a crescendo of conflict between proponents of nuclear power on the one hand and environmentalists on the other. The nuclear industry has been under increasingly strong attack by environmentalists-some extreme, but many more of moderate temper-all deeply concerned about the radioactive and thermal wastes produced by nuclear plants. There is no real need for either radioactive pollution of the environment or for blackouts, so far as nuclear power is concerned. Nor is there any practical need for moratoria on new nuclear power plants. By known technology and for very reasonable
404 Environmental Science & Technology
costs, radioactive pollution from nuclear power plants can be virtually eliminated without impeding the develpment of the industry. The federal government, in the form of the Atomic Energy Commission (AEC) has played a peculiar and conflicting role, in claiming exclusive responsibility both for sponsoring nuclear industry development and for regulating the same industry for health protection and environmental safety. This apparent conflict of function seems to deny our fundamental concept of checks and balances in government. Although it appeared earlier that this problem would be solved by a transfer of the regulatory function to
the new Environmental Protection Agency, recent congressional activities of the Joint Committee on Atomic Energy have left this matter in doubt. There can be no real question that new power sources are needed soon to supply the sharply increasing demands for power, and nuclear power plants will play an important part in meeting those demands in the near future. There is no question, either, regarding the serious intent of society to demand a much greater degree of environmental protection than has been evident in the past, since the environment’s capacity to dilute and disperse wastes without serious harm is not unlimited.
feature Public concer power plants, this BWR elect generating st& feared for the potential polli
The fundamental issue at stake involves the question of whether this industry or any other possesses the right to contaminate the environment beyond the limits of real necessity. The nuclear power controversy can he resolved t o the satisfaction of the vast majority by a reasoned, responsible, and moderate approach that will allow the full development of the essential power industry and at the same time provide full protection, and even enhancement, of the other three great fundamentals-arth, air, and water. Sources of nuclear wastes
A nuclear power plant is different from a conventional power plant only in terms of the energy source. The commercial nuclear power generating plants being built today use uranium metal pellets as fuel. Typically, the pellets are enclosed in vertical thinwalled tubes of a corrosion-resistant metal such as stainless steel or an alloy of zirconium. These tubes, or “cladding’’ may he ten or more feet long and perhaps l/,-inch or less in diameter. A typical 500-MW electric reactor contains over 20,000 such tubes, or fuel rods. Nuclear fission of the uranium in the fuel rods produces heat, and ordinary water is circulated rapidly
through the reactor fuel rods t o remove the heat. In the boiling water reactor (BWR) this primary cooling water is allowed t o boil within the reactor vessel, and steam is produced in the top of the reactor vessel. This primary system steam is then delivered directly to the steam turbines. In the pressurized water reactor ( P W R ) the primary cooling water is maintained at sufficiently high pressure and temperature to prevent boiling within the reactor vessel. The bighpressure, high-temperature water is delivered from the reaator vessel t o a heat exchanger, where pressure and temperature changes produce steam in a secondary water system. This uncontaminated secondary steam is then delivered to the turbines. The “fission products” formed when an atom of uranium is split by a neutron are radioactive and are the main source of radioactive wastes from a nuclear power plant. The fission products include such materials as strontium-90, cesium-137, radioactive iron isotopes, and many others. Some of the fission products are gases and include radioactive isotopes of iodine, krypton, and xenon. However, the fuel cladding (the metal tube that contains the uranium pellets) forms a first containment harrier. Fission occurs inside the tube, and if these tubes did not sometimes develop tiny pinhole leaks or fractures, the radioactive fission products could not escape. If there were no fuel rod leaks, very little radioactivity would leave the primary system, because the primary cooling water is of very high
quality through demineralization, and the fuel cladding material, a zirconium alloy, is very resistant to corrosion. Unfortunately, the fuel rods d o develop some leaks, even though the manufacturing process attempts to prevent this. Such fuel leaks, allowing fission product leakage into the primary cooling water, represent the main potential for serious environmental contamination with radioactivity. Liquid wastes from a nuclear pow plant may contain radioactivity fro laboratory drains, laundry facilitii and floor drain systems that recei small amounts of leakage from pun seals and other sources. In both tl PWR and BWR systems, the liqu wastes typically are collected in war storage tanks and are released t o i environment only on a hatoh b a (after the batch has been sampled and monitored to assure low radioactivity). Typically, the waste hatch can. he treated by filtration and demineralization before release to the condenser cooling water and a nearby stream. Gaseous wastes, including isotopes of iodine and other halogens and noble gases such as krypton and xenon, must be continuously removed from the primary cooling water, t o prevent accumulation to undesirable levels. In the PWR system, such waste gas quantities are very small, and the gases are delivered t o storage tanks and held for relatively long periods (30 days or more), During that time, radioactive decay reduces the radioactivity to very low levels before the gaseous wastes are released to the plant stack. In the BWR system, because of water dissociation and air inleakage, gaseous waste volumes are greater. As a re sult, in currently designed BWR systems holdup for decay before release is Volume 5, Number 5, May 1971 405
much shorter-30 minutes or sohence, much larger radioactive quantities are released via the plant stack. Other wastes include the more usual, nonradioactive, domestic-type wastes produced only in small quantity and presenting no special treatment and disposal difficulties. Also, thermal wastes, produced in large amounts, are the subject of considerable concern. In some cases, cooling towers are used to transfer most of the heat load to the atmosphere instead of releasing it directly to nearby streams. Environmental fate
The best way to describe the effects of nuclear power plant wastes is to review briefly their fate in the environment. Radioactive wastes make excellent tracers-extremely sensitive detection and measurement methods are available for radioactivity-and much is known about the environmental fate of nuclear wastes as the result of many field studies around nuclear facilities and from earlier nuclear weapons tests. Radioactive waste released in liquid effluents (below) may contain radioactivity in both the dissolved and undissolved state and is diluted and dispersed in the stream flow. Both the suspended and dissolved radioactivity may be transmitted directly to humans
through treated or untreated water supplies and indirectly via crop irrigation, stock watering, and recreation. The suspended radioactivity may settle in areas of low stream velocity, accumulate on the stream bed, and subsequently add to the dissolved radioactivity already in the water. The dissolved radioactivity is further accumulated and concentrated by aquatic biota (plankton, insects, mollusks, fish) and may be subsequently transmitted to humans through consumption of fish and shellfish. Any dissolved radioactive gases in the water will be desorbed, in part, and thus transferred to the atmosphere. Although released as liquid effluents, the radioactive constituents eventually become distributed throughout the air, water, and terrestrial environments. Nuclear power plant stack effluents (upper right), both gases and particulate matter, are first diluted and dispersed in the atmosphere. Persons in a plant’s vicinity may be directly exposed to the radioactivity by immersion and inhalation and indirectly exposed by using contaminated cistern water supplies. Topsoil and vegetation may become contaminated through settling out of radioactive particulates, by direct washout in precipitation, and by direct absorption of gases. Soil wa-
Human exposure routes of radioactive gaseous effluents
ter is also subject to contamination by precipitation and absorption, as well as by leaching of the topsoil radioactivity. Hence, human radiation exposure also occurs through well waters, food crops from contaminated vegetation, and domestic and game animals. Some of the radioisotopes released in nuclear power plant effluents have very short lives (decaying to harmless materials in minutes or hours) ; others last for days, and a few remain radioactive for years. Some radioisotopes, such as cesium-1 37 and iodine- 13 1, tend to accumulate and become highly concentrated in certain plant and animal forms, whereas others, such as tritium and krypton, d o not. Also, some radioisotopes, such as strontium-90, are produced in larger quantities than others. As a result, many pathways to human radiation exposure are of small concern, while certain others are more important. For example, iodine-13 1 can become highly concentrated in milk and dairy products due to stock feeding on contaminated graze, and subsequently, the radioiodine can accumulate and concentrate in the thyroid glands of persons consuming the milk and dairy products-ne of the most widely recognized “critical” pathways to human exposure. Krypton85, one of the gases released, has a long life, measured in decades, but it is not reactive in a chemical or biological sense, and does not become concentrated in the environment. However, because of its long life, there is legitimate concern that worldwide atmospheric concentrations could eventually reach serious levels, with unrestrained widespread nuclear industry development. Tritium is another radioactive waste that deserves mention. This heavy hydrogen isotope occurs in reactor wastes as heavy water molecules. Although it is not a highly hazardous material compared to other radioisotopes, it has a long lifetime and may be produced in relatively large quantities in pressurized water reactors. As it is present in the form of water, no practical methods for its removal by waste treatment exist, and so there is legitimate concern regarding eventual tritium buildup and contamination of the world hydrosphere. Risks
Risks associated with radioactive releases from nuclear plants depend primarily upon the quantities of radioactivity released and the resulting 406 Environmental Science & Technology
Human exposure routes of radioactive liquid effluents
seems only rational to expect a small percentage of leakers. Nevertheless, the best solution to the radioactive waste problem from nuclear power plants is to continue perfecting and refining fuel rod manufacturing procedures-ultimately eliminating leakers. A second solution, also designed to ’control the problem at its source, would be the routine removal of fuel leakers from the reactor core. As uranium is used up in a reactor, the spent fuel must be replaced with fresh uranium, otherwise the process would become too inefficient. Normal practice is to shut the plant down about once a year and replace perhaps 25 or 30% of the fuel rods with fresh ones. If the fuel leakers could be identified and selectively removed at such times, the radioactive waste problem could be greatly minimized. These two solutions involve some technological difficulty. Nevertheless, control at the source is invariably the least costly and the most effective means of industrial waste control. T h e BWR and waste gases
real levels of radiation exposure. Generally, all human radiation exposure must be taken to be harmful, and all responsible authorities recommend that any such exposure should be minimized to the fullest extent practicable. However, all persons are exposed to some radiation in the normal course of their lives-in the form of natural radioactivity and medical X-rays-and, as long as any additional exposure is restricted to small fractions of this usual amount, there is no sound reason to fear nuclear industry development. This becomes, then, a matter of carefully limiting the radioactive waste quantities released from nuclear plants, so that the added level of risk will be insigni-
ficant. There is no real or practical reason why that goal cannot be achieved by a vigorous and healthy nuclear power industry. Leaking fuel
Clearly, if it were possible to prevent completely fuel rods from developing leaks, there would be no significant radioactivity problem directly associated with nuclear power plants. Great effort is made during fuel rod manufacture to prevent leaks and to eliminate any cladding ruptures under the temperature and pressure stresses that occur in the reactor core. Since there may be more than 20,000 fuel rods in the reactor core, it
The standard gaseous waste release system for currently built BWR’S is shown below. The highly radioactive rejected gases are monitored, and then passed through a 30-minute holdup pipe to allow decay of very short-lived radioactivity. They then pass through high-efficiency filters to remove particulate matter, through an “isolation valve,” and finally to the plant stack. If the radioactivity is too high, the isolation valve is supposed to close automatically and shut down the entire power plant. There is no capacity to capture, store, or treat the gaseous waste except by plant shutdown. Because of the potential for high rqleases of radioactivity, this offgas design is regarded as deficient.
Volume 5, Number 5, May 1971 407
x
Offgas flow f r o m high efficiency particle filtei and isolation valve
Future storage capacity as needed
The additional offgas control system that has been designed for the BWR at the Monticello, Minn., plant is illustrated schematically above. Following the isolation valve, and before release to the plant stack, the gases pass through storage tanks having a 48-hour retention period. This accomplishes two important purposes : The gross radioactivity release will be reduced, by decay, to about 5% of the amount otherwise expected at the stack. An unusually high release can be sent to any one tank, sealed off, and held there for longer decay periods. In addition, activated carbon filters after the storage tanks provide for highly efficient removal of radioiodine if present in any substantial quantity. This system, then, provides full control of the gaseous wastes, and effectively changes the release to a batch process instead of a continuous-flow process. By utilization of only obvious and proved equipment, its estimated cost is quite reasonable, in the range of $1 million or so. Quite recently, the U.S. Public Health Service has advised that the Dresden 2 and 3 BWR’S should be modified to include substantial offgas storage capacity, as is being done at Monticello, Minn. Within the past few months, the General Electric Co. has announced 408 Environmental Science & Technology
a new ”augmented” offgas control system designed to reduce sharply the radioactivity of the gaseous effluents from its BWR nuclear power plants. This system’s principal feature is routine filtration of the offgas through activated carbon beds before release to the plant stack. The activated charcoal will remove other radiogases as well as radioiodine and will substantially reduce the total radioactivity release. However, this “augmented” system would still be a continuous-flow process, and it does not have provision to capture and segregate a particularly high release. A new freon absorption process for noble gas absorption has been announced by Union Carbide, costing about $175,000 for a 1000-Mwe BWR. The best control system for minimizing gaseous radioactivity from BWR’S should combine adequate gas storage capacity and activated carbon filtration for positive protection against radioiodine releases. If it would significantly reduce operating costs, and adequate gas storage is used routinely, the activated carbon filtration might be used on an “as needed” basis. PWR and tritium
The Pwn may produce relatively large tritium waste quantities. As the
tritium occurs as water molecules, there are no practical treatment or removal methods after it escapes the plant’s primary system. Last May the Westinghouse Electric Co. announced a new “zero release” system, again reasonable in cost, that will prevent the escape of virtually any radioactivity, including tritium, to the environment. Unfortunately, that announcement was apparently premature, as the “zero release” system is now said to be still in the design stage. Hopefully, it will be available soon, to solve the Pwn tritium problem. H e a t load
The current nuclear power plant generation is quite inefficient in converting heat generated in the reactor to electricity. The overall conversion efficiency is about 30%, as compared to perhaps 40% in conventional plants. This means that large quantities of waste heat (seven Btu for every 10 generated) will be discharged either to rivers or to the atmosphere. A short-term solution protects receiving waters by the use of cooling towers which deliver the waste heat to the local atmosphere. But ecologists and climatologists are concerned with the long-term effects of regional and even wider temperature changes as power sources multiply.
The long-term solutions to the waste heat problem are either to develop other more efficient power sources, thereby reducing both the quantities of waste heat and, hopefully, the cost of electric power, or to develop economical, profitable ways to use the waste heat. A bill recently introduced in the U.S. Senate would result in reviewing the national energy economy, and thus work toward solving the waste heat problem. Fuel reprocessing
No discussion of nuclear wastes would be complete without considering environmental contamination associated with reprocessing spent fuel elements from nuclear power plants. After use, the spent fuel rods are sent to a plant where the remaining uranium is reclaimed and repurified. Most of the radioactive fission products are contained in the fuel rods, and the quantities of radioactivity are very large. In reprocessing, the fuel is dissolved in acids, and the uranium is then reclaimed by chemical processing. All of the fission products are wastes, and the very large quantities indicate that preventing radioactive contamination of the surrounding environment can be a serious problem. Previously, all fuel reprocessing was performed for the federal government by contractors, but a privately owned and operated fuel reprocessing industry is now developing. Presently, the high activity radioactive liquid wastes are delivered to underground storage tanks for longterm containment and decay. Heat generated by their radioactivity causes these wastes to boil for periods up to two years, and confinement of longlived nuclides such as strontium-90 and cesium-137 is necessary for much longer periods. The gaseous wastes are still released to the atmosphere for disposal by dilution and dispersion. The radioactivity quantities released to the atmosphere are quite large, and there is little question that this disposal procedure is unsatisfactory and unacceptable over any long period of time. For example, it is estimated that a single fuel reprocessing facility planned in South Carolina may release as much as 12 million curies per year of krypton-85 and 500,000 curies per year of tritium from its stack. Practical procedures for the control of such gaseous wastes d o exist, and they must be put to use in the near future.
Radlatlon hazard
The hazard due to chronic longterm, low-level radiation exposure is not all that well understood or defined. A general standard for radiation protection does exist-the standard recommended by the International Commission on Radiological Protection (ICRP) and by the Federal Radiation Council (FRc)-and this standard has been adopted and enforced by the AEC. However, there is no conclusive scientific proof that this currently applied radiation standard is either adequate or inadequate for long-term protection of the public and environment. Over the past two or three decades, as research and studies have provided additional information, the trend has been to limit the allowable radiation dose to lower and lower amounts. Both the ICRP and the FRC have recognized the lack of hard evidence as to the complete safety of the currently applied radiation standard. T o quote the ICRP : “[Tlhe maximum permissible doses recommended . . . are maximum values; the commission recommends that all doses be kept as low as practicable, and that any unnecessary exposure be avoided.” The FRC has stated the case as follows: “There can be no single permissible or acceptable level of exposure without regard to the reason for permitting the exposure. It is basic that exposure to radiation should result from a real determination of its necessity.” From such admonitions, a policy of actively minimizing all human radiation exposure is clearly required of any responsible regulatory agency. In this respect, the social issue involved in controlling radioactive wastes from nuclear power plants becomes clear. On the one hand, the AEC and the industry insist that nuclear plants must have the right to release radioactive wastes to the full extent allowed, according to the current radiation protection standard. This is the same as insisting on a right to expose persons up to the maximum radiation dose currently regarded as acceptable. On the other hand, there is an increasingly strong movement among conservationoriented groups and pollution control agencies to heed the admonitions of the ICRP and FRC and to insist that no radioactive wastes should be released to the environment without showing real need. The current standard is not a justification for “dumping” radioactive wastes into the environment.
In all fairness, neither the AEC nor the nuclear industry wishes actually to practice a policy of maximum radiation exposure, and both make what they regard as reasonable efforts to keep exposure well below the maximum allowed. However, both still insist that the nuclear industry possesses a right to use the environment to its maximum capacity t o dilute and disperse radioactive wastes, and both resist any effort to regulate in any more restrictive manner. The record shows clearly that radioactive waste releases from nuclear power plants can be held far below the quantities allowed under the current standards. With few exceptions, the nuclear power industry has thus far been quite successful in preventing excessive or unsafe levels of radioactivity in the environment. However, such releases could be further reduced, sharply in some cases, by the application of proved economical waste control measures. The social issue involved seems quite clear-it is whether this industry, or any other, should possess the right to pollute the environment or to expose members of the public to hazardous materials to a needless extent. If the nuclear industry does, in fact, have such a right, then all other industries will insist on a similar right with respect to other contaminants. The only acceptable solution is to require all industries, including nuclear power plants, to reduce and minimize all releases of contaminants to the full extent that is both technologically feasible and economically reasonable. costs
The only real issue between the nuclear power industry and the AEC on the one hand and the conservationists and pollution control agencies on the other is the costs of pollution control, and with very few exceptions the costs issue is the main obstacle to pollution control in any industry. The business of cleaning up environmental pollution after it has occurred is not only expensive but in some cases virtually impossible. As a result, the public now is insisting on a policy of minimizing pollution of all kinds-a policy of prevention rather than cure. If this policy is accepted, then the problem is reduced to determining the reasonable level of costs. Regarding the nuclear power industry, it is generally agreed that all “reaVolume 5, Number 5, May 1971 409
“There is universal agreement that human radiation exposur minimized to the full extent practicable. If responsible engineer industry and the public protection agencies can be free to perfo pe L . ” ! ,
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...
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arguments a s t o how much radiation exposure is “safe,” and how mahy neonle . . mav be harmed. will become trulv academic. as there will not be enough additional radiation exposure to measure.”
Ernest C. Tsivoglou, professor of civil (sanitary) engineering, has been with Georgia Institute of Technology since 1966. Dr. Tsivoglou received his B.C.E. from Manhattan College, M.S. in civil engineering from the University of Minnesota, and Ph.D. from Ohio State University. Besides teaching graduate courses in stream sanitation, environmental radiation surveillance, and radiological health, Dr. Tsivoglou is presently conducting research on the characterization of stream reaeration capacity.
sonable” measures for radioactive pol. lution control should be practiced However, there is the question of who will decide what cost is “reasonable.’: The AEC apparently feels that it should be tbe sole arbiter. But it is the public who will pay, not the industry or the AEC, and the decision on “reasonable” costs cannot be unilaterally made by the industry or its federal representatives. It is, then, a social decision, requiring the responsible participation of health and environmental protection agencies. Looking at the real costs of radioactive pollution control, there is some impression that the cost of preventing environmental radioactive pollution is high and unreasonable. However, both the new Westinghouse “zero release’’ system and the new GE “mini-release” system have been estimated to cost less than 1% of the capital cost of a new nuclear power plant. Also, the annual operating costs are estimated to be very small. For instance, a 500Mwe power plant, costing perhaps $100 million or more, can reduce its radioactive waste releases to the environment nearly t o zero for an additional $1 million or less. Qualified power company representatives say that the additional cost would be so small that it could never be found as an increase in monthly bills to power consumers. The additional radioactive waste control measures would suhstantially reduce radioactive releases t o the environment and would provide more positive control and containment of any abnormal releases.
confrontations between the industry and the public and to threats of power blackouts on the one hand and new plant moratoria on the other. Hopefully, this experience will lead to a more cooperative analysis of the factors affecting the siting of nuclear power plants, and to basinwide and regional priority lists of preferred new plant sites that adequately consider public health and water resource protection as well as the economics of electric power production and transmission. If this can be done, there should be no need for blackouts, moratoria, or confrontations.
Siting of nuclear plants
Slansky, C. M., “Separation Processes for Noble Gas Fission Products from the Off-Gas of Fuel Reprocessing Plants,” International Atomic Energy Agency, Vienna, Austria (1969). U. S. Atomic Energy Commission. “Standards for Protection Against Radiation.” Title 10, Part 20, AEC. Washington, D. C., (April 1966, rev.). “Westinghouse Offers Systems for Essentially Zero Release’ of Radwaste,” Nud. Ind. 17 (5) 40 (1970).
The siting of nuclear plants is also clearly a matter for public as well as private decision. The failure thus far of the industry and the AEC t o seek the participation of other responsible public agencies in the decision on new plant siting has led to a continuing series of unfortunate and unproductive 410 Envimnmentsl Science & Technology
Additional Reading Federal Radiation Council, “Radiation Protection Guidance for Federal Agencies.” Fed. Regist. 25 (97). 4402 (May 18, 1960); also, Fed. Regist. 26 (185) 9057 (Sept. 26, 1961). Int. Comm. Rad. Prot. ”Report of Committee II on Permissible Dose for Internal Radiation,” ICRP Publ. no. 2 (1959); Pergamon Press, London, ,England (1964); also, ICRP Publ. no. 6.
Kent, C. E., Levy, S.,. Smith, J. M. “Effluent Control for Boiling Water Reactors,” General Electric Co., San Jose. Calif. (Aueust 1970).
