Status of nuclear power: United States
Nuclear power now provides approximately one-fifth of U.S. electricity. 1
The last nuclear power plant in the active construction pipeline, Watts Bar 1, went into operation in the spring of 1996. This has brought the total number of commercial reactors in the U.S. to 109, as of the end of 1996, with a total generating capacity of 100 gigawatts-electric (GWe). 2
Watts Bar 1 probably marked the end of the first era of U.S. nuclear power plant construction; there are no active efforts to complete the several remaining plants that are nominally still under construction.
- There has been virtually no change in total U.S. nuclear capacity since the end of 1990, with four reactors shut down (total capacity of 2.3 GWe) and two new reactors put into commercial operation (total capacity of 2.3 GWe). Nonetheless, nuclear electricity generation has risen markedly in this period, from 66 gigawatt-years (GWyr) in 1990 to 77 GWyr in 1995, due to higher average capacity factors (see Figure 1). This gain follows intensive industry efforts to achieve greater operating reliability and shorter shutdowns for reactor maintenance. There has also been a reduction in the rate of reactor "scrams," indicating more reliable operation.
Figure II.2--1. Mean capacity factor of U.S. reactors in a given year, 1973-1995. [Data from Ref. 2, Table 8.1.]
- Reactor operating licenses extend for 40 years and thus, unless the licenses are extended, the currently operating reactors will gradually go out of operation, primarily between 2010 and 2030. Of course, economic or safety considerations can lead to the shutdown of individual reactors even before the expiration of their operating licenses. Conversely, some reactor operators may apply for an extension beyond the 40-year initial term, up to an additional 20 years. As the date approaches when such applications are likely to be submitted, the Nuclear Regulatory Commission (NRC) is developing new regulations governing the procedures to be used to evaluate the safety of the plants in the face of possible degradation of some components with age.
- A historical picture of U.S. nuclear power development is given in Figure 2, in terms of utility orders for nuclear reactors. Substantial orders began in 1965, followed by a great spurt from 1970 through 1974. But all orders placed after 1973 have been canceled. Thus, virtually all operating U.S. nuclear power plants were ordered in the 1965-1973 period, giving the nuclear industry little time to learn from experience. All but a handful of these reactors were in operation by 1990.
Figure II.2--2. Reactor orders in the United States, 1953-1978, in GWe of total capacity. Annual figures are given for total orders and for those that were not subsequently canceled. [Copied from Ref. 1, p. 11]
The collapse of demand for nuclear reactors after the mid-1970s was due to a number of factors:
- The growth rate in electricity sales dropped sharply after 1973, from an average annual rate of 7.5% for 1963-1973 to an average of 2.6% for 1973-1993.
- The costs of nuclear power have risen substantially since the late 1970s, due to protracted construction times, design changes and retrofits to meet tightened safety standards, increased staffing requirements, and (until recently) low capacity factors.
- Nuclear power became a politically unattractive option for utilities, apart from economic factors, due to vigorous opposition in some localities. In a particularly stark case, from the utility standpoint, local opposition in the 1980s prevented the completed Shoreham nuclear power plant in New York from going into operation, forcing its dismantlement.
Status of nuclear power: worldwide N uclear power has provided about 17% of world electricity generation in recent years. Total capacity at the end of 1996 was 345 GWe; total electricity generation was 254 GWyr in 1995. For each, the U.S. share was about 30 percent of the total. Mirroring the U.S. situation, there has been a halt in nuclear development in Western Europe---except in France, which in 1995 obtained 76% of its electricity from nuclear power and exports substantial amounts of electricity to its neighbors. The most active nuclear power programs are now in Asia. Japan obtained 33% of its electricity from nuclear power in 1995 and South Korea 36%. Both are continuing expansion programs. China has begun a small nuclear program, but this could rapidly accelerate, particularly with the aid of collaborations with French, Canadian, and other foreign nuclear suppliers. In addition, there is some continuing construction activity in Eastern Europe and, on a lesser scale, in South America.
- The history of nuclear generation growth for a number of leading countries is shown in Figure 3 and the status of worldwide utilization of nuclear power is summarized in Table 1. Worldwide, there were 433 reactors operating at the end of 1996, and approximately 45 additional reactors under construction, with over half of the new capacity being built in South Korea, Japan, China, and Taiwan. 3
Figure II.2--3. Growth of nuclear power generation in selected countries, 1973-1995. [Data from Ref. 2, Table 10.4.]
|Table II.2.1. World nuclear status: number of reactor units and total capacity, operating and under construction |
(end 1996); nuclear generation, and nuclear share of the electricity generated by utilities (1995).
|Country ||Operating |
|Under construction |
|Net Generation |
| ||Number ||Net GWe ||Number ||Net GWe ||TWh ||GWyr ||1995 |
|United States ||109 ||100.5 || |
|673 ||76.9 ||22 |
|France ||55 ||57.4 ||4 ||5.8 ||359 ||40.9 ||76 |
|Japan ||51 ||41.0 ||5 ||5.7 ||287 ||32.8 ||33 |
|Germany ||20 ||22.2 || |
|154 ||17.6 ||29 |
|Russia ||26 ||19.8 || |
|99 ||11.3 ||12 |
|Canada ||22 ||15.4 || |
|92 ||10.5 ||17 |
|United Kingdom ||35 ||12.7 || |
|78 ||8.9 ||25 |
|Sweden ||12 ||10.1 || |
|67 ||7.6 ||47 |
|Ukraine ||14 ||12.1 ||4 ||3.8 ||66 ||7.5 ||38 |
|Korea, South ||11 ||9.1 ||9 ||7.6 ||64 ||7.3 ||36 |
|Spain ||9 ||7.2 || |
|53 ||6.1 ||34 |
|Belgium ||7 ||5.5 || |
|39 ||4.5 ||56 |
|Taiwan ||6 ||4.9 ||2 ||2.7 ||34 ||3.9 ||29 |
|Switzerland ||5 ||3.1 || |
|24 ||2.7 ||40 |
|Finland ||4 ||2.3 || |
|18 ||2.1 ||30 |
|Bulgaria ||6 ||3.4 || |
|17 ||2.0 ||46 |
|Hungary ||4 ||1.7 || |
|13 ||1.5 ||42 |
|China ||3 ||2.1 ||6 ||4.6 ||12 ||1.4 ||1 |
|Czech Republic ||4 ||1.6 ||2 ||1.8 ||12 ||1.4 ||20 |
|Slovak Republic ||4 ||1.6 ||2 ||0.8 ||11 ||1.3 ||44 |
|South Africa ||2 ||1.8 || |
|11 ||1.3 ||6 |
|Lithuania ||2 ||2.8 || |
|10.6 ||1.2 ||86 |
|Mexico ||2 ||1.3 || |
|8 ||1.0 ||6 |
|Argentina ||2 ||0.9 ||1 ||0.7 ||7 ||0.8 ||12 |
|India ||10 ||1.7 ||6 ||1.7 ||6 ||0.7 ||5 |
|Slovenia ||1 ||0.6 || |
|5 ||0.5 ||40 |
|Netherlands ||2 ||0.5 || |
|4 ||0.4 ||5 |
|Brazil ||1 ||0.6 ||2 ||2.5 ||2.5 ||0.3 ||1 |
|Pakistan ||1 ||0.1 ||1 ||0.3 ||0.5 ||0.1 ||1 |
|Kazakhstan ||1 ||0.1 || |
|0.1 ||0 ||0 |
|Romania ||1 ||0.7 ||1 ||0.6 ||0 ||0 ||0 |
|Armenia ||1 ||0.4 || |
|0 ||0 ||0 |
|WORLD TOTAL ||433 ||345.5 ||45 ||38.7 ||2228 ||254 ||17 |
- Data from Ref. 3. Units under construction include only those for which a date is specified for the start of commercial operation (see text).
- Data from Ref. 4, based on information from the International Atomic Energy Agency.
Options for future reactors A ny revival of nuclear power development in the United States would probably be based on a new generation of reactors that are expected to be safer and more economical than present reactors. The leading options under consideration have been:
- Large light-water reactors (LWRs), of "evolutionary" design---generally similar to present large reactors but designed, with the benefit of experience, for greater economy and safety. Two such reactors, the 1350-MWe General Electric Advanced Boiling Water Reactor (ABWR) and the 1300-MWe Asea Brown Boveri/Combustion Engineering System 80+ reactor are far along in the Nuclear Regulatory Commission's new licensing procedures and may be available for U.S. commercial orders in 1997, should there be demand. Two ABWRs have been built in Japan, in a collaboration with General Electric. One went into commercial operation in November 1996 and the second is expected to follow in 1997. In addition, two ABWRs were ordered from General Electric in 1996 by the Taiwanese utility, Taipower.
- Mid-sized "passively safe" light water reactors, incorporating extensive passive safety features. 4 A 600- MWe reactor, termed the Advanced Passive 600 (AP600), is being developed by the Westinghouse Corporation and may be licensed and available for orders by 1998 or 1999. Completion of the AP600 design is being aided by the Federal government and by an industry consortium known as the Advanced Reactor Corporation. In the AP600, as a major passive safety feature, emergency core cooling is provided by the gravity-driven draining of large pools of water, with the flow sustained by evaporation and subsequent condensation on the interior of a large steel containment vessel that houses the reactor, steam generators, and emergency cooling system. Thus, unlike the standard in present reactors, emergency cooling does not depend on the operation of electrically driven pumps.
- High-temperature gas-cooled reactors (HTGR). Planned HTGRs are graphite moderated and helium cooled. In a recent version, being designed by the General Atomics corporation, hot helium directly drives a gas turbine, in contrast to earlier designs where the hot gas is used to produce steam for a steam turbine. HTGRs use a rugged fuel form, capable of withstanding high enough temperatures for the reactor to be cooled by radiation if the helium flow is interrupted---an important passive safety feature. At present, HTGR development is not receiving U.S. federal support, and is thus dependent on General Atomics resources, plus foreign contracts, to bring the designs to completion.
- Liquid metal fast breeder reactors. Although breeder reactors were once considered the key to a nuclear future, by enormously reducing the demands on uranium supply, there is now relatively little breeder development activity, partly because the slow worldwide pace of nuclear growth has reduced the perceived need and partly due to fears that the potentially greater availability of plutonium would create increased proliferation dangers. At present there is only one commercially operating breeder reactor outside the former Soviet Union, the Phenix reactor in France. 5 A program at the Argonne National Laboratory, for the development of the so- called Integral Fast Reactor, was aimed at building a passively safe sodium-cooled reactor along with a fuel cycle in which extracted plutonium would never leave the plant site. The reactor could be designed either as a breeder or, in later suggestions, to transmute plutonium and other actinides into shorter lived products. However, most of this program has been suspended due to loss of federal funding.
No additional federal funding is required to bring the evolutionary LWRs to the point where they can be ordered in the United States, although an essential federal role will be to maintain licensing procedures that will assure that once Nuclear Regulatory Commission approval is given for a reactor project, additional objections will not greatly delay its completion. One mid-sized passively safe reactor, the AP600, probably has adequate support, both federal and from the utility industry, to permit design completion. However, it will be difficult to complete HTGR development and impossible to complete Integral Fast Reactor development without resumed federal support.
Reactor safety A s of the end of 1996 there had been over 2100 reactor-years of commercial reactor operation in the United States, with one accident in which core damage occurred (Three Mile Island) and no accident with a large radiation release. 6 Since Three Mile Island, design and operation modifications and retrofitting of nuclear plants have reduced the chance of another accident, as estimated by probabilistic safety assessments (5). 7 An empirical indication that safety has improved is given by the Nuclear Regulatory Commission's analyses of "inferred mean core damage frequency." This calculated index of reactor safety is determined on the basis of the observed occurrence of precursor events which might lead to core damage, were other things also to go wrong. This index dropped from an average of 3 x 10-3 per reactor year (RY) for 1969-1979 to under 5 x 10-5 per RY for 1986-1991, with much of the improvement attributed to better operator training and control room instrumentation (6).
- All of the newly designed next-generation reactors claim a very high level of safety. For example, the General Electric Company reports for the ABWR a calculated probability of less than 10-6 per reactor year of core damage and of only 2 x 10-9 of a large radiation release [an individual off-site dose of more than 0.25 Sv (25 rem)]. The other proposed new reactors, whose designs rely more heavily on passive safety than is the case for the evolutionary ABWR, also have very low calculated accident risks. It is not surprising that risk assessments indicate higher levels of safety for new reactors than for presently operating reactors. In fact, it would be remarkable if, after several decades of experience, it would not be possible to design reactors which are considerably safer than the first generation of reactors---which themselves have had a good, if not perfect, record.
Nuclear waste disposal W aste disposal presents particular difficulties because of the large gap between public and "expert" assessments of the hazards involved, along with a widespread public mistrust of the experts. Public concerns are compounded by the well-publicized problems with wastes from nuclear weapons development, although there are great differences in physical form between the spent fuel from civilian nuclear reactors and the reprocessed wastes from the weapons program. The spent fuel from U.S. commercial reactors is in solid form and the transfer of this fuel to secure protective casks has already been implemented at some reactors (see below). The wastes from the weapons program were liquefied during reprocessing and the total volume greatly increased. Facilities for converting the wastes into a stable solid form still have not been built in the U.S. and the wastes remain in large tanks, some of which have leaked.
- At present, virtually all of the spent fuel from commercial reactors is being accumulated on-site, mostly remaining in cooling pools adjacent to the reactor. It is in the same form outside the reactor as in it, namely as solid uranium oxide pellets contained within thin-walled cylindrical "fuel pins." At some plants a part of the fuel has been transferred into special steel canisters and placed in concrete casks at the reactor site. The canisters are cooled by natural air convection. Although this on-site dry storage appears to provide safe isolation of the spent fuel, it is only a temporary expedient. The final step has long been assumed to be the deposition of the spent fuel (or reprocessed wastes) in a geologic site, deep underground. An intermediate step is to establish one or more national sites for interim storage of spent fuel. As yet, there are no firm U.S. plans for the establishment of interim storage facilities.
- The search for a permanent disposal site in the United States has had many false starts, but in 1987 Congress mandated that efforts be focused on establishing the suitability of a site at Yucca Mountain, Nevada in a formation of tuff---a volcanic residue. At first, it was thought that a repository might be acceptable to the local population, but Nevada officials have made continued efforts to block its establishment. The main work at Yucca Mountain has been directed toward "site characterization," to determine whether the detailed geologic features of the site make it suitable for a waste repository.
- If at the end of this process the site is deemed to be suitable and no further delays intervene, a Yucca Mountain repository might be available to receive spent fuel shipments by the year 2010. However, there is little confidence that this schedule will be achieved. One difficulty is the stringent, changing standards that such a site must meet. In the mid-1980s the EPA put forth the criterion that the wastes must be isolated sufficiently to ensure that escaping radionuclides would not cause more than 1000 fatalities over a 10,000 year period----a rate of one per decade. This standard was promulgated at a time when the EPA was estimating 10,000 fatalities per year from indoor radon.
- As yet, no final standard has been set for Yucca Mountain, EPA authority over Yucca Mountain having been suspended in 1992 by Congressional action, pending a National Academy of Sciences (NAS) study. The NAS study (7), released in 1995, has introduced what may prove to be a major new difficulty by suggesting that the time horizon for concern be extended into the very distant future, perhaps to one million years. For long times---"perhaps 10,000 to 100,000 years"---potentially hazardous radionuclides in the wastes are deemed likely to be kept out of the accessible environment by the repository's barriers and the slow travel time of the radionuclides through the surrounding ground. Eventually, however, it may be possible for water to carry these radionuclides into the general environment and, if the water flow is small, develop local concentrations of activity that could cause relatively high radiation exposures for populations drinking the contaminated water. The greatest hazards are not expected before 10,000 years, and possibly not until after 100,000 years.
- The NAS study did not recommend a specific standard for the EPA to adopt, but suggested that it might appropriately correspond to an average risk of adverse health effects (primarily cancer) of the order of 10-6 to 10-5 per year for members of the hypothesized group at highest risk---a "critical group" that draws contaminated water from near the site and that might number "a few tens of individuals." The adopted standard should apply, in this recommendation, for 1,000,000 years. The cited risk levels correspond to annual doses in the neighborhood of 0.02 to 0.2 mSv (2 to 20 mrem), according to present risk estimates. This may be compared to the present average U.S. dose of 3 mSv/yr (300 mrem/yr) from natural radionuclides. To some observers this level of concern for a small number of our descendants, perhaps 100,000 years hence, represents an appropriate stewardship of the environment. To others, it appears quite out of proportion to the magnitude of the dangers involved and to a reasonable degree of responsibility to societies far remote from us in time, and probably in capabilities.
- The leading alternative to deep geologic disposal of nuclear wastes is sub-seabed disposal. However, whatever its technical merits, sub-seabed disposal is currently prohibited under interpretations of international agreements on ocean dumping of hazardous materials. A further alternative might be to use reactors, or even accelerators, to transmute the long-lived radionuclides in the wastes into shorter (or much longer) lived products, thereby reducing the period during which they are hazardous. This might buy some increase in future safety, but at the expense of much more extensive waste handling and processing now. An extensive study of this option was undertaken under the auspices of the National Research Council (8). The panel affirmed support of the current policy of seeking a geologic repository for spent fuel, although it also suggested that there be a "modest" program of research on separation and transmutation technologies for possible future applications.
- The most immediate needs in the U.S. waste disposal program are general acceptance of on-site dry storage and/or the establishment of interim storage facilities. There are no obvious safety problems to be solved, because suitable casks already exist for on-site storage and casks for transportation and longer term interim storage are well along in development. However, there remains the problem of gaining public acceptance for any specific waste handling action.
- Money to fund the waste disposal program in principle is provided by payments that the utilities make into the Nuclear Waste Fund, at a rate of 0.1 cent per kWh of nuclear generation---amounting to over $600 million per year. However, appropriations for waste management have been well below the amounts paid into the fund. For example, the FY 1996 appropriation for the civilian nuclear waste management program was $315 million, an amount equal to about one-half of the payments into the Nuclear Waste Fund (9). The FY 1997 appropriation was $382 million (10). Such limitations on expenditures for nuclear waste handling have helped relieve overall federal budget difficulties, but have led to additional delays in the already much delayed nuclear waste program.
- Plans for nuclear waste disposal in foreign countries also assume that deep geological disposal is the preferred option, but in no case has there been a final decision on the location of a repository. However, some countries are ahead of the United States in addressing the problems of short term or interim storage. Sweden has a centralized facility for interim storage of its spent fuel, while in France the spent fuel is reprocessed and the residue, i.e. the nuclear waste, is incorporated in solid glass 8 and stored at the reprocessing site. Swedish plans call for 40 years of interim storage to allow the fuel to cool thermally, and thus reduce the thermal load upon the ultimate repository.
Nuclear weapons proliferation N uclear weapons proliferation is perhaps the most difficult issue that must be considered in assessing nuclear energy, because the ultimate hazards are the greatest. The issue arises largely because plutonium-239 is inevitably produced in any uranium-fueled reactor. Nonetheless, the link between commercial nuclear power and nuclear weapons is tenuous. To date, the countries that have developed nuclear weapons, or have tried to, have not utilized materials from their commercial reactors and in most cases had no commercial program at the time the weapons were being developed. In many cases, the fissile material has been enriched uranium, not plutonium. However, there are potential links in that the availability of technically trained people and of some relevant facilities and materials lowers the threshold against a country implementing a decision to "go nuclear."
- The main proliferation issue may not lie with national states, because any country with a moderately advanced technological base probably could develop nuclear weapons, with or without nuclear power. For sub-national entities or terrorist groups, the path to a bomb might be eased if plutonium is readily available. This is an argument advanced against breeder reactors and the reprocessing of spent fuel, because in these fuel cycles plutonium is removed from the spent fuel where it is "protected" by the very high radioactivity levels of some of the fission products. Assuming that nuclear reactors will continue to operate in much of the world, it is important to strengthen technical and institutional safeguards against diversion of plutonium for weapons purposes.
Uranium resources U ranium resources are not now a problem, with ample uranium available at unexpectedly low prices. However, a rapid expansion in nuclear power use could hasten the possible date of uranium shortages. One possibility for vastly increased resources is the extraction of uranium from sea water. This would be expensive, but possibly not prohibitively so---perhaps 1.5 cents per kWh according to results from some Japanese pilot plant studies (11). It therefore would be valuable to pursue investigations of the potential for sea water extraction.
Hazards of low-level radiation T o the extent that nuclear reactors and nuclear waste disposal may pose hazards, these are largely hazards from low radiation doses received by many people. For example, this is the main basis for estimates that Chernobyl will lead to tens of thousands of eventual cancer fatalities. There is presently no consensus within the scientific community as to the risk posed by low radiation doses. It may be beyond the power of scientific analysis to establish these risks with any certainty, but it is important to continue and extend investigations both of epidemiology and of damage mechanisms, in order to reduce the uncertainties to the extent possible. Of course, further cancer research may lead to improved methods of diagnosis and treatment that could reduce the risks themselves, rather than merely reduce the uncertainties in estimating them.
Future prospects T he future of nuclear power in the United States is likely to depend more upon public policy attitudes than upon technological constraints or even economic competition. New reactors now becoming available could in principle permit a substantial expansion of nuclear power over the next several decades, probably at costs well below the average present costs of nuclear power. Alternatively, given sufficient opposition, there could be a continued moratorium on the ordering of new nuclear plants. If this de-facto moratorium were to last for several more decades, nuclear power might be gradually be phased out as existing plants age and the pool of nuclear engineering talent shrinks.
Even without the probable continued growth in electricity demand, it would then be necessary to replace the 100 GWe of present nuclear capacity. For example, if done with projected highly efficient gas-fired combined-cycle plants, an additional 4.5 trillion cubic feet of natural gas would be required per year---more than 20% of the total present U.S. consumption of natural gas. The environmental and resource problems created by a continually increasing consumption of fossil fuels, together with concern about limits on the potential of renewable resources, provide a motivation for, at the very least, retaining the nuclear option.
- David Bodansky, Nuclear Energy: Principles, Practices and Prospects, American Institute of Physics Press, Woodbury, NY (1996).
- U.S. Department of Energy, Monthly Energy Review, April 1996, Energy Information Division Report DOE/EIA-0035(06/04), U.S. DOE, Washington, DC (1996).
- "World List of Nuclear Power Plants," Nuclear News 40 (March 1997) [to be published].
- "Nuclear Power Contributions in 1995," Nuclear News 39, no. 7, 36 (June 1996).
- Severe Accident Risks: An Assessment for Five Nuclear Power Plants, final report NUREG-1150, U.S. Nuclear Regulatory Commission, Washington, DC (1990).
- T. E. Murley, "Developments in Nuclear Safety," Nuclear Safety 31, no. 1, 1-9 (1990).
- National Research Council, Technical Bases for Yucca Mountain Standards, Report of the Committee on Technical Bases for Yucca Mountain Standards, Robert W. Fri, Chair, National Academy Press, Washington, DC (1995).
- National Research Council, Nuclear Wastes: Technologies for Separations and Transmutation, Report of the Committee on Separations Technology and Transmutation Systems, Norman C. Rasmussen, Chair, National Academy Press, Washington DC (1996).
- "OCRWM Receives Half Its Fiscal 1996 Budget Request," OCRWM Bulletin, Winter 1996 Office of Civilian Radioactive Waste Management, U.S. DOE, Washington, DC (1996).
- "FY 1997 Appropriation Supports Revised Program Plan," The OCRWM Enterprise, December 1996, Office of Civilian Radioactive Waste Management, U.S. DOE, Washington, DC (1996).
- Ersel A. Evans, "Nuclear Fuel Cycle," in JTEC Panel Report on Nuclear Power in Japan, K.F. Hansen, Chairman, Japanese Technology Evaluation Center, Loyola College in Maryland (1990).
Footnotes * This chapter is based, to a large extent, on Reference (1).
- Nuclear power provided 22.5% of the electricity generated by utilities in 1995; it provided about 20% of all U.S. electricity, including the share generated by non-utility power producers.
- These totals exclude the 582-MWe Haddam Neck reactor, whose shutdown was announced in December, 1996.
- The number "under construction" is somewhat ambiguous, particularly in the case of partially completed reactors for which active construction has stopped but formal cancellation not announced. The total of 45 includes only those reactors for which Ref. 3 indicates anticipated dates for the start of commercial operation. It excludes, for example, 3 reactors in the United States that are nominally under construction but for which the date of completion is indefinite (perhaps never).
- Passive safety is reactor safety that does not depend on human intervention or the performance of specialized equipment; instead it is achieved by the action of unquestionable physical effects such as the force of gravity or thermal expansion.
- The French Superphenix reactor is now slated for use as an actinide burner and the start of commercial operation of the completed Monju reactor in Japan has been delayed as a result of a large sodium leak that occurred in December 1995.
- The 1986 Chernobyl accident has virtually no bearing on the likelihood of a U.S. reactor accident, because of differences in design and operating procedures, although it demonstrates the potential seriousness of an accident should one occur.
- The analyses of Ref. 5 included studies of two reactors that had also been studied in the 1975 Reactor Safety Study. Comparing the later study to the earlier one, the calculated median core damage frequencies were lower by about a factor of four for one reactor and a factor of twenty for the other.
- Storing in solid form avoids the leakage problems that in the United States have bedeviled the storage of liquid reprocessed wastes from military programs.