General Considerations for Future Reactors The End of the First Era of Nuclear
The world is now approaching the end of the first era of nuclear power.1 Most of the reactors built in the past several decades are still operating, and many will continue to run for a number of additional decades, including the U.S. reactors that have had their licenses renewed for another 20 years see Section 2.4.4 . However, gradually the existing reactors will be shut down, and the number of commitments for further reactors is relatively small none in the United States as of the end of 2003...
Cross Sections in the Continuum Region
For neutrons with energies in excess of tens of kilovolts, the accessible states in the compound nucleus are so numerous that their spacing is small compared to their width. Thus, the levels overlap. A compound nucleus is still formed, but it involves a continuum of overlapping states. The cross section varies relatively smoothly with energy, without the rapid changes characteristic of the resonance region. The cross section for fission in 235U is displayed for this region in Figure 5.3. For...
Production of Plutonium in Reactors
The production of plutonium is accomplished most effectively if the reactor has a high conversion coefficient. This means the use of heavy water or graphite as the moderator. These are better moderators than light water for plutonium production, because their cross sections for neutron capture are low and their relatively slow moderation rates gives more time for neutron capture in 238U see Section 8.3.2 . Most weapons programs have obtained their plutonium from graphite-moderated reactors the...
Time Since Discharge Years
Fig. 10.4. Comparison of activity of alpha-particle and beta-particle emitters in spent fuel and in ground. The beta-particle activity is shown with and without actinides removed. The alpha-particle activity is only shown for the all-nuclides case, because it derives almost entirely from the actinides. Spent fuel 1 MTHM from PWR same parameters and data as for Table 10.4 . Ground 0.005 km3 of typical soil see text . to be at least several hundred meters below the surface of the Earth. The...
Design Features of the AP
The AP600 was designed to be simple in configuration and relatively inexpensive to build.8 Part of the savings comes from modular construction, in which components are built and to some extent assembled off-site, substantially reducing the construction time at the reactor site itself. When compared 8 This discussion is based primarily on information from Westinghouse, including published documents and private communications with Ronald P. Vijuk. to conventional PWRs, the design simplifications...
Design Weaknesses
Two aspects of the design have been particular targets of criticism a positive void coefficient of reactivity and an improperly configured control rod system. Both contributed positive feedbacks, which turned an initial excursion in reactor performance into the Chernobyl disaster. The void coefficient in a water-cooled reactor would be negative if the water acted only as a coolant and moderator. However, the water also acts as a poison, due to capture of neutrons in hydrogen. In an LWR, when...
References Yyr
1. H. Barnert, V. Krett, and J. Kupitz, Nuclear Energy for Heat Applications, IAEA Bulletin 33, no. 1, 1991 21-24. 2. Alvin M. Weinberg and Eugene P. Wigner, The Physical Theory of Neutron Chain Reactors Chicago University of Chicago Press, 1958 . 3. Alvin M. Weinberg, The First Nuclear Era The Life and Times of a Technological Fixer New York American Institute of Physics Press, 1994 . 4. J. Smith, Novel Reactor Concepts, in Nuclear Power Technology, Vol. 1 of Reactor Technology, W. Marshall,...
Thermalization of Neutrons Role of Moderators Kinematic Relations
As explained in Section 7.1.1, fission in natural uranium will not result in a chain reaction if the neutrons interact primarily at energies close to those at which they are emitted, in the vicinity of 1 or 2 MeV. The neutrons are reduced in energy from this region to the more favorable thermal energy region by elastic collisions with the nuclei of the 'moderator. The energy transfer in an elastic nuclear collision depends on the angle at which the incident neutron is scattered. The energy of...
Countries with Nuclear Power But No Weapons
Many countries exhibit the other side of the coin they have nuclear power but do not have nuclear weapons. Some have not shown any inclination toward weapons e.g., Canada, Germany, and Japan .28 All have strong, comprehensive nuclear power programs and could easily develop weapons with no external aid. Sweden, which also has a strong civilian nuclear power program and technological base, embarked on a sophisticated program of weapons development, but the effort was abandoned before attracting...
GasCooled Fast Reactor GFR
The GFR is a gas-cooled reactor that is designed to achieve a high burnup of fuel up to 250 GWd t and destruction of actinides. Both helium and supercritical carbon dioxide CO2 are being considered for use a coolant 53 . With helium, the operating coolant temperature would be higher, which would be an advantage for hydrogen production, while with supercritical CO2, a higher system efficiency can be reached due to less energy required to pump the coolant. Previous gas cooled reactors have a high...
The Motivation for Nuclear Energy
1.1 The Need for Energy Sources 1.2 Problems with Fossil Fuels 1.3 Nuclear Power as a Substitute for Fossil Fuels References 1.1 The Need for Energy Sources 1.1.1 The Importance of Energy The discovery and exploitation of new sources of energy has been central to human progress from the early struggle for biological survival to today's technological world. The first step was learning to control fire, with wood or other biomass as the fuel. This was followed by the harnessing of wind for ships...
References Huk
1. Bertrand Goldschmidt, Atomic Rivals, translated by Georges M. Temmer New Brunswick, NJ Rutgers University Press, 1990 . 2. Rudolf Peierls, Reflections on the Discovery of Fission, Nature 342, 1989 853-854. 3. Victoria McLane, Charles L. Dunford, and Philip F. Rose, Neutron Cross Section Curves, Vol. 2 of Neutron Cross Sections New York Academic Press, 1988 . 4. Anthony V. Nero, Jr., A Guidebook to Nuclear Reactors Berkeley University of California Press, 1979 . 5. Alvin M. Weinberg and...
US DOE NearTerm Deployment Roadmap
Lists of prospective reactor candidates have been developed in the recent initiatives by the U.S. DOE and in parallel international efforts. The reactors have been divided into those available for near-term deployment i.e., by 2010 or 2015 , and the Generation IV reactors for deployment after 2020. The U.S. thinking about the near-term was put on a formal footing in February 2002 with the announcement of the Nuclear Power 2010 program The Nuclear Power 2010 program, unveiled by the Secretary on...
Event Trees and Fault Trees
The PRA tools used in the RSS were event-tree analyses and fault-tree analyses. In an event-tree analysis, one imagines the occurrence of some initiating event and traces the possible consequences. We illustrate in Figure 14.1 the event tree for studying the consequences of a major pipe break, following which the emergency core-cooling system ECCS must operate successfully for damage to be avoided 12, Main Report, p. 55 . The worst case in this example would be the electric power failing to...
Uranium and Nuclear Weapons
It is considerably simpler to make a bomb using enriched uranium than to make one using plutonium, and uranium may be becoming the material of choice for countries or groups that want to build a bomb with minimal effort and chance of detection. The fission cross section, af, and the average number of neutrons per fission, v, are both somewhat smaller for 235U than for 239Pu, making the critical mass larger see Table 17.1 . However, premature detonation caused by neutrons from spontaneous...
Growth Until the Mids
The exploratory period ended quickly. There was a brief lull in reactor orders after 1960, with only five more orders until 1965, and then a period of rapid increase from 1965 through 1974. The dominance of LWRs in U.S. reactor orders was complete after 1960, the only exception being the gas-cooled Fort St. Vrain reactor, ordered in 1965. None of the reactors ordered before 1962 had a capacity as large as 300 MWe. After that, there was a substantial escalation in reactor size, in an effort to...
Fission Cross Sections with Fast and Thermal Neutrons
For orientation purposes, the cross sections for fission in 235U, 238U, and 239Pu are shown in Figure 6.1. The data are extracted from detailed plots given in Ref. 5 . In the thermal region, the cross sections in 235U and 239Pu are hundreds of barns. In general, they then fall with increasing energy, with very rapid fluctuations in the resonance region. In the 1-10 MeV region, the fission cross sections are in the vicinity of 1 or 2 b for these nuclei. The cross section for 238U fission is...
Formalism for Describing the Multiplication Factor Number of Neutrons per
In this section, we consider chain reactions in thermal reactors. As mentioned earlier Section 5.4.2 , the term thermal is commonly used to refer specifically to room temperature, T 293 K and kT 0.0253 eV, because cross sections are normally measured in the laboratory with the sample at this temperature. When neutrons are thermalized, they come into equilibrium with the local medium. The thermalization occurs primarily in the moderator therefore, the moderator temperature is the relevant one....
Energy Yield of Nuclear Weapons
The energy yield of nuclear weapons is commonly expressed in kilotons kt or megatons Mt of high explosive TNT equivalent, where 1 kt of TNT is assumed to release 1012 cal 4.18 x 1012 J . The complete fission of 235U in a reactor releases 8.2 x 1013 J kg see Table 9.3 . About 86 of the energy is in the kinetic energy of the fission fragments themselves and 6 in prompt neutrons and gamma rays see Section 6.4.2 . Therefore, complete fission of 1 kg of 235U would give a prompt explosive yield of...
Multiplication factor See effective multiplication factor
Natural gas. Gaseous fossil fuel found in underground deposits, composed mostly of methane CH4 . Natural radionuclide. A radionuclide produced by natural processes such as stellar nucleosynthesis or the radioactive decay of a natural radioactive precursor. Net capacity. The capacity of a generating facility measured at the input to the transmission lines carrying power away from the plant equal to the difference between the gross capacity and the power consumed within the plant. Neutrino. A...
Energy from Consumption of Fuel Energy per Unit Mass from Fission of U
The fission of a 235 U nucleus corresponds on average to the release of 200 MeV 3.20 x 10-11 J , including the associated contributions from neutron capture and the decay of fission fragments see Section 6.4.2 . The number of 235U atoms per gram of uranium is wNa M, where w is the fraction of 235U in the uranium by weight , Na is Avogadro's number, and M is the atomic mass of 235U. Thus, 1 kg of natural uranium w 0.00711 has 1.822 x 1022 nuclei Table 9.3. Energy per unit mass from fission of...
Shape of the Resonance Peak
The measured width of resonance peaks, such as those seen in Figure 5.1, depends in part on how monoenergetic the neutron beam is i.e., on how sharply defined it is in energy . However, if measurements are made of cross section versus energy with more and more closely monoenergetic beams, the peaks do not continue to get appreciably narrower. There is a certain inherent width to the resonance peak that has nothing to do with the measurement technique. It can be parameterized in terms of a level...
Conservation Rules in AlphaParticle Emission
A typical example of alpha-particle decay is the decay of uranium-238 238U to form thorium-234 234Th The initial mass number 238 equals the sum of the final mass numbers 234 4 , and the initial atomic number 92 equals the sum of the final atomic number 90 2 . These equalities are dictated by two important rules that apply in radioactive decay Charge The sum of the charges of the final products equals the charge of the original nucleus. Number of nucleons The total number of nucleons in the...
Radioactive Decay Halflife and Mean Life
The activity of a radioactive sample is equal to the number of decay events in the sample per unit time. Each radionuclide is characterized by a half-life T the time interval during which one half of the sample decays and the rate of radioactive decay is halved. For example, in 10 half-lives, the activity drops by a factor of 210 1024. Half-lives of radionuclides vary greatly, from a small fraction of a second to billions of years. As discussed in more detail in the Appendix, the activity of a...
Basic Unit for Burnup GWDT per MTHM
A useful measure of the performance in the nuclear fuel cycle is the energy obtained per unit mass of fuel, known as the fuel's burnup. The burnup is commonly specified in megawatt-days or gigawatt-days of thermal output per metric tonne of heavy metal MWDT MTHM or GWDT MTHM . This is a cumbersome notation for repeated use, and we represent GWDT MTHM in a more compact form as GWd t gigawatt-days per tonne . In standard energy units, 1 GWd 8.64 x 1013 joules J . For U.S. reactors, as well as...
Number of Neutrons per Fission Event v
A quantity of key importance in establishing the possibility of a fission chain reaction is the magnitude of v, defined as the average number of neutrons produced per fission event. Before a nuclear chain reaction could be envisaged as being achievable, it was necessary to establish that v was sufficiently large. Depending on the magnitude of v, achievement of criticality might be easy, impossible, or possible but difficult. Measurements to establish v for uranium were undertaken almost...
References Qcy
1. Alvin M. Weinberg and I. Spiewak, Inherently Safe Reactors and a Second Nuclear Era, Science 224, 1984 1398-1402. 2. A.M. Weinberg, I. Spiewak, J.N. Barkenbus, R.S. Livingston, and D.L. Phung, The Second Nuclear Era A New Start for Nuclear Power New York Praeger, 1985 . 3. J. Kupitz and J. Cleveland, Overview of Global Development of Advanced Nuclear Power Plants, and the Role of the IAEA, in Proceedings of the International Conference on Future Nuclear Systems Global '99 La Grange Park, IL...
Fissionable Materials for Nuclear Weapons
In a nuclear explosion, it is necessary to have a rapidly developing chain reaction. Therefore, the time interval between successive fission generations must be short, with the chain reaction propagated by unmoderated neutrons from fission. These neutrons typically have energies En in the neighborhood of 1 MeV. It is also necessary to have a high multiplication factor. Thus, the weapons material must have a large neutron fission cross section for En 1 MeV, and the number of neutrons emitted per...
Accident Frequency Criteria
As discussed earlier, the NRC has no official standard that specifies reactor safety requirements in terms of the probabilities for core damage or a large early release, as estimated through PRAs. However, many NRC documents have discussed the matter. Thus, a 1983 document on safety criteria stated that the Commission has selected the following design objective 36, p. 14 The likelihood of a nuclear reactor accident that results in a large-scale core melt should normally be less than one in...
The Generation Cost of Electricity Calculation of Costs Components of
The generation cost is the cost of electricity as it leaves the plant and is sometimes referred to as the busbar cost.6 The cost to the customer is higher than the generation cost because it also includes the costs of transmission, distribution, other utility costs such as billing, and any special pricing provisions established by the utility.7 The generation cost is generally described in terms of cost per kilowatt-hour kWh . It is the sum of two components 1. Production cost. This includes...
Responsibilities to Future Generations The General Recognition of the Problem
As we have seen, there is virtually universal agreement that the long lifetimes of radionuclides in the nuclear wastes impose a responsibility upon us to handle the wastes in a manner that will protect the interests of future generations. This view is reflected in the quotation from Kneese cited in Section 13.1.1 and in many statements by other individuals and groups. The responsibility is a moral one, and the evolving recommendations and regulations seek to give concrete substance to the moral...
Populations Living in Regions of High Natural Radioactivity
There are substantial variations in natural radiation background levels, but comparisons between regions of low and high radiation may be misleading in the face of other possible differences between the regions. For example, the cancer death rate in Colorado is substantially below the United States average, whereas the natural radiation level is substantially above. However, unless one can exclude the effects of differences in other aspects of the environment and in individual lifestyles, it is...
Void Coefficients
In an LWR, water is essential for moderating the reaction. If the water is removed e.g., if there is a pipe break and insufficient replacement water is provided , the moderation will be inadequate and the reactivity will drop, because with less thermalization, there will be more loss of neutrons through absorption in 238U. More voids also mean a greater escape of neutrons from the reactor. Loss of water in the reactor vessel is the limiting case of a void. The term void coefficient is usually...
Abundance See isotopic abundance and elemental abundance
Accelerator. A facility for increasing the kinetic energy of charged particles, typically to enable them to initiate nuclear reactions. Actinides. Elements with atomic numbers from Z 89 actinium through Z 103 lawrencium this group includes the fertile and fissile nuclei used in nuclear reactors and their main neutron capture products. Activity. The rate of decay of a radioactive sample. Adaptive staging. In nuclear waste repository planning, an approach in which the project proceeds in stages,...
Trends in Burnup of LWR Fuel
Average burnup values for past years are shown in Table 9.1 along with the average projected for the fuel to be deposited at the Yucca Mountain waste repository. Overall, there has been a trend with time toward higher burnup, on average roughly doubling in the 25 years from 1973 to 1998 and projected to continue to rise. Thus, in a 1993 DOE projection, it was expected that the median PWR fuel burnup for standard assemblies would be about 43 GWd t in the year 2000 a value actually achieved in...
Potential Effects of Future Bombs
The destruction that would be caused by a major nuclear attack by a nation with a substantial arsenal greatly exceeds that caused by the Hiroshima and 5 Richard Rhodes, in the Introduction to Ref. 4 . 6 The yields of the two bombs dropped during World War II were about 15 kt for the Hiroshima bomb and about 21 kt for the Nagasaki bomb 5, p. 15 . The Nagasaki bomb reportedly used 6.2 kg of plutonium, again corresponding to an efficiency of about 20 6, p. 266 . 7 Schull indicates that a precise...
Fuel Temperature Feedback Doppler Broadening
Although we have been tacitly treating the nuclei of the fuel as motionless targets undergoing bombardment by neutrons, this is not a precise description. The uranium nuclei are in thermal motion, with an average speed that increases as the temperature increases. The result is to increase the effective cross section for neutron absorption in 238U if the temperature of the fuel rises, through the Doppler broadening of the absorption resonances see Section 5.2.3 . The number of neutrons available...
A GammaRay Emission
Ordinarily, gamma-ray emission is not a primary process in radioactive decay but follows alpha-particle or beta-particle emission. It occurs in those decays where the transition is to an excited state of the product nucleus rather than to the ground state. The excited state then gives off its excitation energy by gamma-ray emission, either to the ground state or to a lower-lying excited state. When the transition is to another excited state, the de-excitation sequence continues with further...
Exposure of Population in the Affected Region
The largest exposures of people near Chernobyl initially came from 1311 and other short-lived radionuclides, in part through inhalation. After several weeks, the iodine had decayed sufficiently to be a lesser contributor, and over the longer term most of the dose came from 134Cs and 137Cs and, later, just 137 Cs. After passage of the radioactive cloud, the most important pathways for exposures were from ingested radionuclides and from gamma rays and beta particles emitted by radionuclides...
Xenon Poisoning
Reference has already been made to the buildup of poisons as the fuel is used. A particularly interesting example is xenon-135 135Xe the cause of the xenon poisoning that for a brief time threatened operation of the first large U.S. reactors in World War II, which were designed to produce 239Pu.17 The first large reactor for this purpose went into operation in September 1944. After a few hours of smooth operation, the power level of the reactor began to decrease, eventually falling to zero. It...
Beta Decay and BetaParticle Energy
decay occurs when a nuclide has too many neutrons, i.e., when the neighboring isobar of higher atomic number has a lower atomic mass.16 In that case, it is energetically profitable for a nucleus to change a neutron into a proton, with the emission of a 3 and a v. A typical process of this sort is Here the initial and final number of nucleons is 234, the 3 and the V not contributing to the nucleon count. For thorium Th , the nuclear charge is 90, while for protactinium Pa , it is 91, so charge...
EPRI Results and Comparisons to DOE Results
In the evolution of EPRI studies, the Phase 7 TSPA, published in December 2002, reported doses that were considerably higher than those of the previous EPRI studies, in particular Phase 6. The main changes going from Phase 6 to Phase 7 were a correction in the radionuclide release from regions impacted by focused flow, the addition of a branch with seepage into a higher fraction of the repository, and a more extensive consideration of diffusive release of radionuclides from the waste containers...
Homogeneous and Heterogeneous Reactors
We have been tacitly assuming that the reactors under consideration are what are sometimes known as heterogeneous, in which the fuel, coolant, and moderator if any are distinct physical entities. All reactors used today for power generation are of this form. However, in the early days of nuclear power, there was considerable exploration of an alternative configuration, the homogeneous reactor, defined as a reactor whose small-scale composition is uniform and isotropic 2, p. 378 . Homogeneity...
The Three Mile Island Accident The Early History of the TMI Accident
The Three Mile Island TMI accident occurred in one of two similar reactors at the Three Mile Island site in Pennsylvania.7 The accident was in the second 4 The number of fatalities is in question, given the uncertainties surrounding the effects of radiation at low doses and dose rates, but in the discussion of these accidents, we quote numbers based on the adoption of the linearity hypothesis see Section 4.3 . 5 This summary is based largely on an IAEA report prepared shortly after the accident...
Worldwide Radiation Exposures from Chernobyl
One of the important set of results reported at the One Decade After Chernobyl conference was an UNSCEAR assessment of total global population doses. These results, as presented in a paper by R.G. Bennett, are summarized in Table 15.4. The total collective dose commitment in the northern hemisphere is estimated to be 600,000 person-Sv, where the dose commitment is calculated until 2056 70 years after the accident . For populations that were not near Chernobyl, the accident added relatively...
SteadyState Relation in Radioactive Decay Series
In a radioactive decay series, each decay product is itself radioactive until the end of the series is reached when a stable nuclide is formed. In each of the three natural series, the longest half-life is that of the original parent, or head of the series, and the series reaches a steady state. If the radioactive series is in an isolated volume of material, then in the steady state, each member of the series decays at a virtually constant rate. We say virtually constant because there is a very...
The IRIS Reactor
The International Reactor Innovative and Secure IRIS represents a relatively recent entry in the array of reactors that were reported on by the NTDG see Table 16.1 .10 Reflecting the novelty of some of its features, it was described as not deployable by 2010, but the international consortium led by Westinghouse anticipated that it would be deployable in the 2012-2015 time period.11 First steps in seeking NRC licensing approval began in October 2002 30 . 10 This discussion is based on the cited...
Neutron Reactions in Different Energy Regions
As discussed in more detail in Section 7.1.1, a nuclear chain reaction is sustained by the emission of neutrons from fissioning nuclei. The neutrons emitted in fission have a broad energy spectrum, with the peak lying between several hundred keV and several MeV and with a typical central energy in the neighborhood of 1 MeV. Reactions take place at all neutron energies En, from several MeV down to a small fraction of 1 eV. We are interested in the main features of the reaction cross sections...
Number of Collisions for Thermalization
The factor S can be used to calculate the number of collisions n required to reduce the mean neutron energy by any given factor. For example, the reduction of the mean neutron energy from 2 MeV to 1 eV a factor of 2 x 106 corresponds to Sn 5 x 10 7. For hydrogen S 1 2 , this gives n 21. However, the distribution of neutron energies becomes very skewed in successive collisions, with many neutrons having very small energies and a few neutrons having high energies. These relatively few high-energy...
DefenseinDepth 1
A special kind of redundancy is sometimes singled out as being at the heart of nuclear safety. This is the reliance on multiple barriers or defense-in-depth, which is described as a hierarchically ordered set of different independent levels of protection 6, p. 109 . The principle of defense-in-depth is seen in considering the barriers that prevent or minimize exposures due to the release of radioactivity from a reactor The UO2 fuel pellets retain most radionuclides, although some gaseous...