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SECOND EDITION Nuclear Engineering Handbook MECHANICAL and AEROSPACE ENGINEERING Frank Kreith Series Editor RECENTLY PUBLISHED TITLES Air Distribution in Buildings, Essam E Khalil Alternative Fuels for Transportation, Edited by Arumugam S Ramadhas Computer Techniques in Vibration, Edited by Clarence W de Silva Design and Control of Automotive Propulsion Systems, Zongxuan Sun and Guoming (George) Zhu Distributed Generation: The Power Paradigm for the New Millennium, Edited by Anne-Marie Borbely and Jan F Kreider Elastic Waves in Composite Media and Structures: With Applications to Ultrasonic Nondestructive Evaluation, Subhendu K Datta and Arvind H Shah Elastoplasticity Theory, Vlado A Lubarda Energy Audit of Building Systems: An Engineering Approach, Moncef Krarti Energy Conversion, Second Edition, Edited by D Yogi Goswami and Frank Kreith Energy Efficiency and Renewable Energy Handbook, Second Edition, Edited by D Yogi Goswami and Frank Kreith Energy Efficiency in the Urban 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Efstathios E Michaelides, Clayton T Crowe, and John D Schwarzkopf Nanotechnology: Understanding Small Systems, Third Edition, Ben Rogers, Jesse Adams, and Sumita Pennathur Nuclear Engineering Handbook, Second Edition, Edited by Kenneth D Kok Optomechatronics: Fusion of Optical and Mechatronic Engineering, Hyungsuck Cho Practical Inverse Analysis in Engineering, David M Trujillo and Henry R Busby Pressure Vessels: Design and Practice, Somnath Chattopadhyay Principles of Solid Mechanics, Rowland Richards, Jr Principles of Sustainable Energy Systems, Second Edition, Edited by Frank Kreith with Susan Krumdieck, Co-Editor Thermodynamics for Engineers, Kau-Fui Vincent Wong Vibration and Shock Handbook, Edited by Clarence W de Silva Vibration Damping, Control, and Design, Edited by Clarence W de Silva Viscoelastic Solids, Roderic S Lakes Weatherization and Energy Efficiency Improvement for Existing Homes: An Engineering Approach, Moncef Krarti SECOND EDITION Nuclear Engineering Handbook Edited by Kenneth D Kok CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2017 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S Government works Printed on acid-free paper Version Date: 20160812 International Standard Book Number-13: 978-1-4822-1592-2 (Hardback) This book contains information obtained from authentic and highly regarded sources Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained If any copyright material has not been acknowledged please write and let us know so we may rectify in any 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infringe Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com Contents Preface xi Acknowledgments xvii Editor xix Contributors xxi Section I Introduction: Nuclear Power Reactors Historical Development of Nuclear Power Kenneth D Kok Pressurized Water Reactors 11 Richard Schreiber Boiling Water Reactors 85 Kevin Theriault Heavy Water Reactors 141 Alistair I Miller, John Luxat, Edward G. Price, and Paul J Fehrenbach High-Temperature Gas-Cooled Thermal Reactors 199 Chris Ellis and Arkal Shenoy Integrated Fast Reactor: PRISM 229 Maria Pfeffer, Scott Pfeffer, Eric Loewen, Brett Dooies, and Brian Triplett MSR Technology Basics 257 David LeBlanc Small Modular Reactors 289 Richard R Schultz and Kenneth D Kok Generation IV Technologies 299 Edwin A Harvego and Richard R Schultz Section II Introduction: Nuclear Fuel Cycle 10 Nuclear Fuel Resources 317 Stephen W Kidd 11 Uranium Enrichment 335 Nathan (Nate) Hurt and Kenneth D Kok vii viii Contents 12 Nuclear Fuel Fabrication 351 McLean T Machut 13 Spent Fuel Storage 365 Kristopher W Cummings 14 Nuclear Fuel Recycling 387 Patricia Paviet and Michael F Simpson 15 HWR Fuel Cycles 471 Paul J Fehrenbach and Alistair I Miller 16 Waste Disposal: Transuranic Waste, High-Level Waste and Spent Nuclear Fuel, and Low-Level Radioactive Waste 521 Kenneth D Kok, Joseph Heckman, and Murthy Devarakonda 17 Radioactive Materials Transportation 557 Kurt Colborn 18 Decontamination and Decommissioning 589 Cidney B Voth Section III Introduction: Related Engineering and Analytical Processes 19 Risk Assessment and Safety Analysis for Commercial Nuclear Reactors 637 Yehia F Khalil 20 Nuclear Safety of Government-Owned, Contractor-Operated Nuclear Facilities 655 Arlen R Schade 21 Neutronics 687 Ronald E Pevey 22 Heat Transfer, Thermal Hydraulic, and Safety Analysis 721 Shripad T Revankar 23 Thermodynamics and Power Cycles 815 Peter D Friedman 24 Economics of Nuclear Power 863 Jay F Kunze and Edward S Lum Contents ix 25 Radiation Protection 899 Mark R Ledoux 26 Health Effects of Low Level Radiation 931 Jay F Kunze Index 941 Preface Purpose The purpose of this handbook is to provide an introduction to nuclear power reactors, the nuclear fuel cycle, and associated analysis tools, to a broad audience including engineers, engineering and science students, their teachers and mentors, science and technology journalists, and interested members of the general public Nuclear engineering encompasses all the engineering disciplines that are applied in the design, licensing, construction, and operation of nuclear reactors, nuclear power plants, nuclear fuel cycle facilities, and finally the decontamination and decommissioning of these facilities at the end of their useful operating life This handbook examines many of these aspects in its three sections The second edition of this handbook contains some new and updated information including chapters on liquid metal cooled fast reactors, liquid fueled molten salt reactors, and small modular reactors that have been added to the first section on reactors In the second section, a new chapter on fuel cycles has been added that presents fuel cycle material generally and from specific reactor types In addition, the material in the remaining chapters has been reviewed and updated as necessary The material in the third section has also been revised and updated as required with new material in the thermodynamics chapter and economics chapters, and also includes a chapter on the health effects of low level radiation Overview The nuclear industry in the United States grew out of the Manhattan Project, which was the large science and engineering effort during World War II that led to the development and use of the atomic bomb Even today, the heritage continues to cast a shadow over the nuclear industry The goal of the Manhattan Project was the production of very highly enriched uranium and very pure plutonium-239 contaminated with a minimum of other plutonium isotopes These were the materials used in the production of atomic weapons Today, excess quantities of these materials are being diluted so that they can be used in nuclear-powered electric generating plants Many see the commercial nuclear power station as a hazard to human life and the environment Part of this is related to the atomic-weapon heritage of the nuclear reactor, and part is related to the reactor accidents that occurred at the Three Mile Island nuclear power station near Harrisburg, Pennsylvania, in 1979, and Chernobyl nuclear power station near Kiev in the Ukraine in 1986 The accident at Chernobyl involved Unit-4, a reactor that was a light water cooled, graphite moderated reactor built without a containment vessel The accident resulted in 56 deaths that have been directly attributed to it, and the potential for increased cancer deaths from those exposed to the radioactive plume that emanated from the reactor site at the time of the accident Since the accident, the remaining three reactors at the station have been shut down, the last one in 2000 The accident at Three Mile Island xi Radiation Protection 925 where: D = dose rate in rad/h Γ = radionuclide-specific gamma ray constant A = activity in curies r = distance in meters 25.4.1.2 Beta Shielding Shielding of beta rays is relatively easy Intense beta radiation is normally accompanied by substantial amounts of gamma radiation as well, which is harder to shield Shielding sufficient to lower the gamma dose rates to acceptable levels automatically lowers the beta dose rates as well In situations where beta radiation is especially intense, one modification to the shielding design that may be employed is to use a multilayered shield with an inner layer specifically designed to shield beta radiation The reason for this is that the best material to use to shield gamma rays, lead, is one of the worst to use to shield beta rays When betas pass through high-atomic-number materials such as lead, they can emit what is known as “bremsstrahlung” or “braking radiation.” This happens when a beta particle passes near a high-atomic-number nucleus and its direction of travel is bent by the electric attraction between the positively charged nucleus and the negatively charged beta particle, and it gives off an X-ray that much be shielded like a gamma ray This effect is much more prevalent in high-atomic-number materials and with higher energy beta particles Therefore, the best materials to use for shielding betas have low atomic numbers, such as plastics, water, and concrete If lead shielding is being used to shield a mixed beta–gamma radiation source, then a plexiglass or other plastic shield is placed in front of it to stop the beta particles without emitting bremsstrahlung X-rays that would increase the gamma shielding requirements A centimeter of plastic shielding is usually sufficient to totally stop the beta particles or reduce their energy to the point where bremsstrahlung is no longer a concern 25.4.1.3 Neutron Shielding Designing shielding for neutrons is much more complicated than shielding for gammas or betas The objective of a neutron-shielding material is to slow the neutrons down and eventually absorb them However, neutrons not attenuate exponentially as gammas This is due in main part to the many scattering interactions that occur for neutrons before they are absorbed In essence, the neutron “rattles” around in the shielding medium until it escapes or is slowed down and absorbed Once the neutron is absorbed, the absorption reaction often produces a gamma ray that must also be shielded Neutrons may be absorbed at any energy, but for most materials the probability of absorption is inversely proportional to the velocity of the neutron and thus is much more likely at lower neutron kinetic energies and thus lower velocities The easiest way to this is to use light-atomic-weight materials and especially hydrogen in the shielding material Neutrons scattering off of hydrogen can lose significant fractions of their kinetic energy in a single collision, up to 100%, whereas neutron scattering off of a uranium nucleus would have a maximum energy loss of less than 1% On average, a neutron scattering off of hydrogen will lose half of its energy The primary objective of a neutron shield is to deflect the neutrons from heading outward, slow the neutrons down as quickly as possible, and absorb them This is accomplished by the use of a laminate or multilayered shield The inner layer of the shield is 926 Nuclear Engineering Handbook constructed using relatively high-atomic-weight materials such as iron This layer will tend to reflect neutrons back inward toward the reactor core or deflect their trajectory from heading directly through the shield The purpose of the second layer of the shield is to slow down and absorb the neutrons Water makes the best neutron shield for this purpose followed by plastics and then concrete due to their relative hydrogen contents This is the reason spent fuel pools are deep pools and why the reactor vessel is submerged underwater during refueling The water serves an important role in cooling the fuel rods as well, but the depth of the pools is dictated by the need for shielding When a hydrogen atom absorbs a neutron, it gives off a 2.26-MeV gamma ray in an (n–γ) reaction This high-energy gamma ray requires additional shielding to control the overall external dose rate outside of the shield The additional shielding required is included in the depth of the spent fuel and refueling pools Although exponential attenuation of neutrons through a shielding material is not a physical phenomenon, in the case of laminate shield containing a high proportion of hydrogen in the outer layers, it is a close approximation For gammas, there is the linear attenuation coefficient that describes how fast gammas are attenuated For neutrons, this value is called the “macroscopic removal cross section,” Σ Table 25.4 gives a few example values of Σ The effective attenuation of the neutron fluence through the shield by the first inner shield layer is exponential In actuality, the attenuation is not exponential, but the neutron scattering reactions in the first layer either scatter the neutrons back into the core where they are of no concern or scatter them through sharp angles such that the following layer(s) of hydrogenous materials can finish slowing and absorbing the neutrons before they make it through the shield Calculation of neutron shielding is best handled by computer codes The calculations required are too involved to permit effective computation by hand except for very simple geometries and situations 25.4.1.4 Shielding Computer Codes There are many computer codes available to assist with radiation shielding design They fall into two generic categories: deterministic and probabilistic The deterministic codes replicate what a person could calculate by hand but with increased speed and the ability to handle additional complexity A common example of this sort of code is Microshield™ (Grove, 2005) Microshield calculates gamma shielding for simple geometries (slabs, cylinders, spheres) and one or more layers of shielding taking into account shielding attenuation, buildup, and geometric attenuation Although limited to simple geometries, many real-world situations can be modeled as one of these simple geometries reasonably well The codes are relatively easy to use and give quick results TABLE 25.4 Example Macroscopic Removal Cross Sections Shielding Material Water Iron Concrete Uranium Macroscopic Removal Cross Section (cm−1) 0.103 0.168 0.089 0.174 Radiation Protection 927 The second type of codes, probabilistic codes, can also be referred to as Monte Carlo codes One of the most widely used Monte Carlo codes is MCNP (LANL, 2003) Fundamentally, radiation interactions with matter are probabilistic events that are described by statistical quantities such as linear attenuation coefficients Deterministic codes use the statistical quantity, or the average behavior, to perform their calculations Monte Carlo codes replicate the underlying probability distributions and “roll the dice” using random number generators to determine how far a particle goes before interaction, what type of interaction it has, and what angle it scatters through These codes are extremely powerful and can model any geometric configuration and any combination of radiation fields The downside of these codes is that they are cumbersome to use, require laborious input, can be slow to yield answers, and require expert users to ensure valid results 25.4.2 PPE PPE has two primary purposes: to prevent internal dose and to prevent the spread of contamination It also can prevent or lower the dose to the skin Occasionally, PPE is designed to reduce external dose such as lead aprons worn in hospitals, but this is not a common practice In power reactor settings, radiation fields tend to be more isotropic, that is, coming from all around, rather than from a discrete point source, reducing the effectiveness of an apron work on only one side of the body Aprons, skirts, or jackets that provide isotropic protection are quite heavy and not practical The PPE required is specified in a graded approach consistent with the hazards in a particular area and the tasks to be performed A radiation work permit (RWP) is prepared by the facility health physics staff that specify what PPE is needed for particular areas and tasks The PPE needed to perform a walk-through inspection of an area with no handson work being performed can be dramatically different from that required for performing cutting, grinding, and welding When entering an area where PPE is required, an entrance/exit portal is set up where the PPE may be donned prior to entering the area and doffed on exit The portal also has survey instrumentation to permit the individual to check for contamination after removing the PPE and prior to exiting the area To prevent or reduce internal dose due to inhalation of radioactive material, respiratory protection is worn (Figure 25.22) The type of protection worn is dependent on the amount of potential airborne radioactive material Any type of respiratory protection places some degree of burden on the wearer from the weight of the device, reduced mobility, increased difficulty breathing, reduced field of view, and thermal stress These burdens can negatively influence the length of time it takes to complete a task, increasing the person’s external dose received during the job Therefore, the objective is to optimize the respiratory (and other PPE) provided to minimize the total dose received The types of respiratory protection that can be used, in order of increasing effectiveness and increasing burden, are half-face respirators, full-face respirators, self-contained breathing apparatuses, suppliedair respirators, and fully encapsulating supplied air suits (Figure 25.23) Respiratory protection devices are rated as to the effectiveness of the protection provided A typical protection factor for a full-face air purifying respirator, those with filter cartridges and no separate air supply is a factor of 100, implying that the contaminant concentration inside the respirator is no more than 1/100th of the concentration in the ambient air; 10 CFR 20 Appendix A contains a table of respiratory protection factors for different types of respiratory protection As the degree of inhalation risk increases, the risk of skin contamination also increases Therefore, half-face respirators, those without a covering for the eyes, are not commonly worn In addition, some form of anti-contamination 928 FIGURE 25.22 Air-purifying full-face respirator (Courtesy of FRHam.) FIGURE 25.23 Fully-encapsulating suit (Courtesy of FRHam.) Nuclear Engineering Handbook Radiation Protection 929 clothing (anti-C) is used in conjunction with the respirator to prevent skin contamination In extreme cases, a fully encapsulating suit with either supplied air or an integral air filtration unit is worn The primary purpose of anti-C clothing is to prevent skin contamination and the spread of contamination In most instances, the use of anti-C clothing precedes the use of respirators It is more common for areas to be contamination areas, indicating that there are surfaces and structures in the area with removable contamination, than it is for an area to be an airborne radioactive material area Any airborne radioactive material area is automatically a contamination area because it is not possible to have a high concentration of airborne radioactive material without having removable contamination on the surfaces and structures in that area The amount of anti-C clothing worn is specified by the RWP for a particular task and area Walk-through inspections of an area may only require the wearing of gloves and shoe covers with or without company-issue coveralls Light hands-on activities adds the wearing of anti-C coveralls over company-issue clothing and two layers of gloves, inner surgeons gloves, and outer gloves suitable for the task being performed Joints between articles of clothing, especially between the gloves and the coverall sleeve and between the shoe cover/bootie and the coverall leg, are sealed with tape A hood may or may not also be required If light dust-generating activities are being performed, a minimum of a full-face respirator is also worn and the respirator is sealed to the hood with tape as well Multiple layers of anti-C clothing are also sometimes used, although heat stress for the wearer becomes a concern at this point and must be balanced against the extra protection provided In the most extreme conditions, a fully encapsulating suit is worn with or without additional clothing for abrasion resistance or additional protection 25.4.3 Engineered Controls As a best practice, engineered controls should be used in lieu of administrative controls or PPE Engineered controls can be implemented to control both external and internal dose Obvious engineered controls are shielding barriers built into the design of a facility The spent fuel pool itself and the transfer canal between the pool and the reactor refueling pool is one such obvious engineered control Others are features such as placing filter media and ion-exchange media that accumulate moderate quantities of radioactive material in below-grade housings or within thick concrete shielding to reduce radiation dose rates Valve banks can be equipped with handle extensions that penetrate through shielding walls to permit manual operation of the valves from a safer location Such design features obviously require forethought before the facility is constructed In some areas, it is not possible to install permanent shielding and still permit access for inspection and maintenance In these cases, portable shielding can be set up to provide a work area with lower radiation dose rates during a maintenance task In this manner, only the workers who set up the temporary shielding are exposed to the unshielded radiation If the temporary shielding can be set up quicker than the following task, the overall, collective, radiation dose received by all the workers is reduced This sort of shielding can include lead blankets on frames or draped over equipment or plastic barriers filled with water that can also provide neutron shielding With regard to controlling internal dose, engineering controls can also be used An additional benefit of using engineered controls is that they not restrict the mobility of the worker, enabling tasks to be completed quicker, which also lowers the total dose received Local ventilation is one common means Providing increased ventilation or air filtration in 930 Nuclear Engineering Handbook the vicinity of a job may allow the task to be performed without wearing respirators The ventilation could be general area ventilation or filtration or task-specific ventilation such as vent hoods, or local suction to capture welding, cutting, grinding, or similar fumes References Cember, H 1996 Introduction to Health Physics 3rd ed New York, NY: McGraw-Hill Eckerman, K.F., A.B Wolbarst, and C.B Richardson 1988 Limiting Values of Radionuclide Intake and Air Concentration and Dose Conversion Factors for Inhalation, Submersion, and Ingestion Federal Guidance Report No 11 Washington, DC: U.S Environmental Protection Agency Grove Software, Inc 1992–2005 MicroShield, Version 6.01 Lynchburg, VA International Commission on Radiological Protection (ICRP) 1994 Human Respiratory Tract Model for Radiological protection Publication 66, Vol 24(1–3) Oxford, UK: Pergamon Press International Commission on Radiological Protection (ICRP) 1977 Recommendations of the ICRP International Commission on Radiological Protection Publication 26 Annals of the ICRP Oxford, UK: Pergamon Press International Commission on Radiological Protection (ICRP) 2001 ICRPDOSE2 ICRP Database of Dose Coefficients: Workers and Members of the Public, Version 2.0.1 New York: Elsevier Science Lessard, E.T., X Yihua, K.W Skrable, G.E Chabot, C.S French, T.R Labone, J.R Johnson, D.R Fisher, R Belanger, and J.L Lipsztein 1987 Interpretation of Bioassay Measurements, NUREG/CR-4884 Washington, DC: U.S Nuclear Regulatory Commission Los Alamos National Laboratory (LANL) 2003 MCNP—A General Monte Carlo N-Particle Transport Code, Version Los Alamos, NM: LANL Shleien, B., L.A Slaback Jr, and B.K Birky eds 1998 Handbook of Health Physics and Radiological Health, 3rd edn Baltimore, MD: Williams & Wilkins 26 Health Effects of Low Level Radiation Jay F Kunze CONTENTS 26.1 Summary 931 26.2 Historical Background 932 26.2.1 Quantifying Radiation and the Amounts That Would Appear to Cause Cancer or Death 932 26.2.2 The Advent of the Linear No-Threshold Hypothesis 933 26.2.3 Subsequent More Strict Regulations a Consequence of the LNT 933 26.2.4 The Appearance of Conflicting Data 933 26.2.5 The Plutonium-239 Concern 934 26.2.6 The Radon-in-Homes Saga 934 26.2.7 The Industry and Regulatory Response to the Hormesis Data 935 26.2.8 Can the Effect Be Tested Using the Methods Similar to Those Used in Certifying Beneficial Effects of a Medical Treatment or Pharmaceutical? 936 26.2.9 Cancer, Overall Health, and Longevity 937 26.2.10 Estimating Risks Using the Collective Dose Hypothesis 937 26.2.11 Conclusions .937 References 938 26.1 Summary Contrary to conventional understanding of radiation by the public, low levels of nuclear (or ionizing) radiation are not harmful to animals or humans but are actually beneficial to health This chapter cites some of the vast amount of epidemiological and demographic studies that support this characteristic of low-level radiation and its positive effects on humans Public understanding of this hitherto seldom recognized characteristic of radiation is crucial to the public having a more rational attitude toward nuclear energy utilization The following is a brief summary of some of the most significant studies that show the hormetic effect of low levels of radiation, with the optimum for good health being nominally 50 times the average background radiation on earth 931 932 Nuclear Engineering Handbook 26.2 Historical Background Nuclear radiation, emanating from interactions with the nucleus of the atom, generally represents the release of energy in the range of million electron volts (MeV) to as high as 200 MeV, as is released in fission of uranium or plutonium nuclei This compares with about eV released in the combustion of one atom of hydrogen or carbon Nuclear radiation was first discovered by Becquerel in 1896, and further investigated by Marie and Pierre Curie, who isolated and identified radium as one of these natural sources of nuclear radiation The nucleus, extremely small in apparent size (compared to the size of the atom, defined as the outer “orbit” of its electrons), was not discovered until 1913, by Rutherford In 1932, Chadwick identified the neutron as a basic particle included in the nucleus In 1938, Hahn, Straussman, and Meitner split (fissioned) the U-235 nucleus using neutrons, identifying an enormous release of energy per fission The applications were initially for fashionable uses, such as luminescent dials on watches, the results of carefully painting numbers on the dials and on the hands of the watches, using radiant paint containing radium It was tedious work, generally done with fine brushes by women, who would shape the point on the brush with their lips and tongues Most developed mouth or tongue cancer It is also believed that Marie Curie died of cancer initiated (and stimulated) by large amounts of radiation that she may have absorbed in processing many tons of uranium ore on the way to isolating radium During these early periods of novel uses of nuclear radiation, methods of measuring doses had not been developed, and regulating doses for personnel or the public had not been adopted With the initiation of the Manhattan project to develop a nuclear weapon during World War II, the involved scientists developed methods of both estimating and measuring ionizing radiation, which is any radiation capable of displacing electrons in molecules, so as to modify the chemical composition, or even to destroy the molecule completely Such modifications generally required energies greater than a few electron volts deposited per atom, which are small compared to the alpha, beta, and gamma ray energies emitted from excited nuclei Hence, any of those nuclear radiations could likely damage many DNA molecules, and hence destroy or mutate many cells in the body 26.2.1 Quantifying Radiation and the Amounts That Would Appear to Cause Cancer or Death During the latter days of the Manhattan project, two criticality accidents occurred (1945 and 1946), resulting in the deaths of one scientist in each accident at Los Alamos National Laboratory, plus exposures of other in the laboratory to large amounts of radiation These early experiences, and the radiation deaths of several other nuclear workers in U.S Atomic Energy Laboratories in the next 15 years, provided estimates of acute radiation doses that would result in probable deaths From these incidents, plus data from other countries, and experiments on animals (specifically dogs), regulations for safe amounts of radiation were developed In the early 1950s, scientists from around the world came to an agreement that rad (or REM)* was a safe annual dose for “radiation workers.” A one-time dose up to * A RAD, the unit used in the 1950 to 1980 period, is 100 erg of deposited ionization energy per gram of tissue The REM is the RAD Equivalent Man, allowing for multiplication factors to be applied to especially damaging radiation, neutrons, and alpha particles The SI accepted units now are the gray and sievert, respectively The gray is equal to J of ionizing radiation deposited per kg of tissue Gy = 100 rad, and similarly Sv = 100 REM Health Effects of Low Level Radiation 933 10 rad (0.1 Gy) was considered tolerable and not likely to affect a person’s longevity Doses to the public were generally recommended to be the order of at least ten times smaller than those to a radiation worker, which implied that radiation workers had a very small risk of dying from exposure to radiation in their working environment, and the risks to the public were considered negligible 26.2.2 The Advent of the Linear No-Threshold Hypothesis When the discipline of “health physics” developed in the 1950 decade, these rules were formalized into a statistical theory, known as the “Linear No-Threshold” (LNT) hypothesis This theory stated that the long-term health effects of radiation on the human body were primarily statistical in nature, determined by the number of radiation particles (for instance, gamma ray photons) to which a person was exposed, and that any gamma ray penetrating the body could initiate conditions that sometime in the future would become a cancer Because it was assumed that any gamma ray (or beta particle, or other ionizing radiation) could be detrimental to human life, it was concluded that there was no lower threshold of radiation that would be completely safe This LNT hypothesis has been used for the last six decades to develop regulations for exposures of workers and the public, and to estimate the overall risks of the number of the public who would be expected to die (from cancer) should there be a release of radiation (intentional or accidental) to the environment This theory (and its corollary, the Collective Dose Hypothesis—see Section 26.1.10) and the resulting method of regulating doses and calculating risks continues to be used throughout the world up to the present (several exception nations to be noted later) 26.2.3 Subsequent More Strict Regulations a Consequence of the LNT In 1978, the Nuclear Regulatory Commission (NRC) in the United States went a step further in developing regulations based on the LNT, and adopted a rule for all licensees that personnel doses should be kept as low as reasonably achievable (ALARA) Failure to implement an ALARA program effectively could result in violations and fines to a company having an NRC license Consequently, workers in the nuclear industry have developed a deeply entrenched fear of radiation, because all have been well schooled in the LNT hypothesis 26.2.4 The Appearance of Conflicting Data Shortly after the ALARA concept was mandated, demographic data began to appear indicating that the LNT may not always apply One such source of data was from UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation), which had been tracking the survivors of the two nuclear bombs dropped on the Japanese cities of Hiroshima and Nagasaki in 1945 An anomaly appeared in the data for personnel doses from the nuclear explosions in the range of 0.1 Sv (10 REM), showing that persons receiving doses in that range not only had no increased risks of developing leukemia but actually had less risks than the average Japanese citizen exposed only to typical background radiation [1] As a result of this apparent anomaly in the Japanese data, some other demographic studies were undertaken The Society for Nuclear Medicine in the United States examined the health of the many U.S military personnel who had been detailed to gather data where nuclear bombs tests had been conducted, both in Nevada and in the Pacific Islands That study showed a definite trend that those exposed to radiation were healthier and were contracting less cancer than the average soldier 934 Nuclear Engineering Handbook In the early 1990s, the National Institutes for Health and the U.S Department of Energy [2] undertook a study of nuclear navy civilian and military personnel who had received radiation in their work environment (all well below the upper limits allowed by the existing regulations) and found that those receiving radiation were healthier than their counter parts who did not receive radiation (for instance, office workers) Similar studies of radiation workers for Ontario Hydro (which operates most of the Canadian Nuclear Power plants) [3] and for the nuclear workers in the United Kingdom [4] showed similar results In all of these studies, there was a clear trend of longer and healthier lives for those workers exposed to low levels of radiation compared to the workers not exposed to radiation 26.2.5 The Plutonium-239 Concern Because most of the nuclear weapons made in the United States used Pu-239 as the fissile material, personnel protection from the inhalation of this material became a high priority for the health physics profession Plutonium tends to exhibit physiological behavior similar to calcium (though the chemical valences are not the same), and appeared to seek the bones Consequently, bone cancer could develop from the ingestion of a few milligrams of Pu-239, with its 24,000 year half-life and its emission of very damaging alpha particles Consequently, plutonium began to be known as one of “the most dangerous substances on earth.” In 1995, a follow-up study [5] was done on the 26 soldier machinists who did the machining on the plutonium bombs made at Los Alamos in the 1944–1946 period The inhalation doses of these soldiers averaged 1.25 Sv (125 REM), with the highest being 7.2 Sv, from plutonium These lifetime dose estimates included the multiplier of 20 for the damaging effects of the alpha particle radiation from the plutonium, a multiplier indicating its “relative biological effectiveness” or the “quality factor.” The follow-up study in 1995 attempted to determine how these 26 had died However, 19 were still alive and healthy (aged 69–76), and of the who had died, only had died of cancer, only of those from lung cancer 26.2.6 The Radon-in-Homes Saga Radon is the noble gas element in the decay chain of uranium down to lead Radon forms no chemical compounds, but remains a gas and seeps up through the ground, and finds its way into basements of homes through cracks in the concrete It can accumulate to presumably dangerous levels over time if ventilation is poor in the basement The discovery of levels of concern occurred in the early 1980s, in the northwestern part of the United States The LNT hypothesis was applied to the levels measured, based on death rates from lung cancer for uranium mine workers in Czechoslovakia Many of those workers developed and died of lung cancer, presumably the result of radon ingested into the lungs, which, while there, decayed into the solid Po-218 This atom would lodge itself in the lungs and decay to bismuth and eventually stable lead-206 The EPA proceeded to develop kits that could be placed in any home for a few weeks, and then be sent to a laboratory for analysis of radon in the home In 1990, Dr Bernard Cohen [6], who had urged the EPA to undertake these studies, examined the data obtained from some 1600 counties in the United States and compared that data with lung cancer death rates in those counties The data fit a reasonably reliable straight line when lung cancer death rates were plotted versus radon levels in the homes However, the slope of the line was inverted, showing that the highest radon levels had the fewest deaths, the lowest radon levels having the highest deaths 935 Health Effects of Low Level Radiation These radon concentrations in the homes were orders of magnitude less than the levels exposing workers in the uranium mines in Czechoslovakia, and hence the results imply that low doses are not only harmless but beneficial to avoiding lung cancer Nevertheless, to this day (2015) the EPA continues to ignore the results of their own data and places information spots on the broadcast media about the dangers of radon in homes, and what actions homeowners should take to reduce the radon concentrations 26.2.7 The Industry and Regulatory Response to the Hormesis Data The above examples are just a few of the many studies that have shown that radiation health effects demonstrate a hormetic effect, a characteristic of most pharmaceuticals and even to many foods Hormesis is the concept that large doses of a substance may be detrimental to health, but small doses are beneficial The evidence for this knowledge was effectively presented in a text published in 1980, titled Radiation Hormesis, by Dr T.D Luckey, and in 1991 followed by the second edition [7] This text included over 1000 references of data on radiation hormesis From about 1994 to 2008, a public interest organization known as Radiation Science and Health, headquartered at Worcester College in Massachusetts gathered and disseminated much of the vast amounts of data that then existed [8] In 2005, the International Dose Response Society was formed at the University of Massachusetts at Amherst and has since been a major organization in an effort to disseminate further data as they become available [9] Three presidents of the American Nuclear Society (Alan Waltar, Larry Foulke, and Eric Loewen) have made special efforts to promote knowledge and understanding of radiation hormesis, the most recent being a 200-page publication of a special session held at the Chicago Annual Meeting of the ANS in June 2012, and is available online [10] Figure 26.1, derived from the work of T.D Luckey, represents the nominal hormetic effect of low levels of radiation on human beings The ordinate axis indicates nominal negative Relative negative biological response 1.2 1.1 Control group response 1.0 0.9 10 20 cGy of acute radiation 10 100 1,000 Chronic radiation (mGy/yr) FIGURE 26.1 Nominal hormetic effect of low levels of radiation on human beings 10,000 936 Nuclear Engineering Handbook effects of radiation, such as the induction of leukemia or solid cancers, the death rates from cancer, or the overall negative effect on health or longevity as a function of the amounts of radiation shown on the abscissa The numerical values on the ordinate will likely vary around the 1.0 control group, depending on the type of negative biological effect being presented However, the abscissa values appear to be nominally the same for all of these effects The minimum negative effect occurs at approximately 100 mGy (10 rad) per year for chronic radiation exposure (effectively a continuous exposure), and at cGy (3 rad) for acute radiation (received instantaneously or over a short period of time) The chronic radiation minimum value is approximately 50 times the nominal annual background radiation dose The acute dose minimum (a desirable dose) is approximately 50% higher than that received from a full-body CT scan Numerous health professionals and publications continue to caution against full-body CT scans, despite the fact that these probably are beneficial to overall health of the individual, irrespective of the outcome of the diagnosis However, despite the preponderance of data clearly showing radiation hormesis, few current textbooks used in our universities for nuclear engineering or health physics even mention the hormetic effects of radiation The National Council on Radiation Protection and the International Council on Radiation Protection, and the Committee on the Biological Effects of Ionizing Radiation (BEIR) refuse to give more than casual comment about hormesis, taking the position that it is best to be “safe” in dealing with low levels of radiation, and keeping the doses as low as possible The few significant deviations from the antihormesis approaches have been with the radiation councils in France, China, and Japan 26.2.8 Can the Effect Be Tested Using the Methods Similar to Those Used in Certifying Beneficial Effects of a Medical Treatment or Pharmaceutical? In medical practice, the efficacy of a new pharmaceutical or new treatment modality is evaluated by what is usually designated as a “double-blind study.” One group of patients will receive the treatment, and another similar group will receive a placebo Neither the patients nor their physicians will know in which group a particular patient was placed There is a general lack of understanding of the hormesis of radiation by the public, the media, and even many nuclear professionals Because of this ignorance, it has always seemed most unlikely that a double-blind study of radiation hormesis would be allowed by authorities However, a nominal double-blind study that was not planned occurred spontaneously in the 1980 decade in Taipei, Taiwan Several large apartment buildings were built in 1982, using rebar contaminated with Co-60 that apparently came from a scrapped radiation therapy machine The “contamination” of the concrete in the buildings was not discovered until 1992, which was two half-lives after the initial construction and occupancy of the buildings In the 2004 and 2006 period, two studies reported on the health effects of radiation on the nearly 10,000 residents in those apartment buildings over a 9–20 year period Average doses were only about 0.5 cGy though 11% of the cohort received average doses approaching cGy By analyzing the residents by age groups, Chen et al [11] expected cancer death rates during that period would have been in the range of 200 among those 10,000 residents However, less than 10 cancer deaths could be found from death records This ratio is most significant, even if several standard deviations of uncertainty might be attributed to the accounting of actual cancer deaths In a second study, Hwang et al [12] found virtually no difference in contracted cancers between the exposed population and the average citizens in Taiwan, except for a somewhat higher rate of leukemia among the exposed children This difference between the two studies is not inconsistent with the hormetic effects observed with some Health Effects of Low Level Radiation 937 pharmaceuticals, such as those for treating the common cold, for which the OTC drugs are not recommended for children Furthermore, the latter study tracked those who developed cancer, whereas the former study tracked those who died of cancer Hormesis has the effect of curing those with an illness, and hence they not die from that illness (including cancer) 26.2.9 Cancer, Overall Health, and Longevity Because the study of health effects of ionizing radiation usually focuses on cancer, it is surprising that the data clearly show that the hormetic effects of low-level radiation doses improve the quality of life and longevity It is uncertain if these improvements produced by low-level radiation are because of the lessening of cancer incidence or the curing of cancer once it develops The work of Otto Raabe [13], especially experiments with cancer induced by high doses of radiation in dogs, may help clarify the above question Raabe has essentially shown that cancer from radiation is not a statistical effect on the human body, but that cancer itself is essentially a deterministic effect He has demonstrated that it takes repeated attacks, perhaps over years, to bring a cancer to fruition This may explain the apparent delay of the order of years for leukemia and up to 20 years for solid cancers from the time the individual was initially exposed to a cancer-causing agent (for instance, radiation, or chemical) These apparent latent periods for cancer are well documented 26.2.10 Estimating Risks Using the Collective Dose Hypothesis A corollary to the LNT is the Collective Dose Hypothesis, which, because of the presumed linearity of negative effect versus dose even to very low levels, says that the product of risk versus dose is a constant, regardless of the magnitude of either factor The BEIR V report (1990) adopted a factor of 800 deaths per million person REM (cSv) of collective dose received Thus, if 1,000,000 persons each received 1.0 REM (0.01 Sv), 800 of those would die If billion persons each received 0.001 REM (0.01 mSv, equivalent to about two days of natural background radiation), 800 of those would die as a result of the radiation exposure Extending these risk estimates to low doses of radiation is as ridiculous as the example originally introduced by Alan Waltar, which is: If 100 aspirins were all taken by one person at one sitting, that person would die Hence, 100 person-aspirins produce one death, so if 100 persons each took one aspirin (100 person-aspirins), one of those 100 would die This kind of false reasoning in making risk analyses continues to be applied to nuclear power plant safety analysis reports, despite the fact that the LNT theory has been proven to be false when applied to low doses of radiation and is in fact 180° out of phase (what was assumed to be a negative effect is actually a positive effect up to a level that is orders of magnitude above average natural background) 26.2.11 Conclusions Radiation hormesis has been demonstrated to be real phenomenon in experiments on plants, bacteria, insects, animals, and with epidemiological and demographic data from humans Not only does hormesis apply to radiation but also to low doses of physical, 938 Nuclear Engineering Handbook chemical, and biological agents This is especially true for most pharmaceuticals So why is it considered so unusual for radiation? According to T.D Luckey, there are over 3000 references which support the hormetic effect of radiation Failure for the industry and regulatory bodies to recognize the hormetic effects of radiation and to revise radiation protection standards accordingly is a travesty To quote the late Theodore Rockwell, “…radiation protection policy and procedures more harm than good, generally by focusing on reducing harmless radiation doses still further, fostering fear and uncertainty with no compensating benefit.” The harm in not applying the hormesis information to radiation exposures is considerable, not only in cost but in preventing appropriate development and utilization of nuclear power and of nuclear applications (such as CT scans) Quoting Nobel Laureate in Medicine, Rosalyn Yallow, “The unjustified excessive concern with radiation at any level, however, precludes beneficial uses of radiation and radioactivity in medicine, science, and industry” [14] Doses below 10 cSv (10 REM or 0.1 Sv) per year (“chronic” dose) or cSv (3 REM or 0.03 Sv) in a single dose are not worth avoiding, need not be a subject for regulation, and evidence shows that such doses are actually beneficial to health Not until chronic doses are greater than about 500 times natural background levels, or acute doses times that received in a full-body CT, is the physiological effect likely to be worse than it is for unexposed persons receiving only normal natural background radiation In summary, radiation doses up to these limits are not merely harmless but beneficial to health Radiation regulations need to be revised accordingly References Japanese bomb survivor data: Kondo, S., Health Effects of Low-Level Radiation, Medical Physics Publishing, Madison, WI (1993) U.S Radiation Workers: Manatoski, G M., Health Effects of Low-Level Radiation in Shipyard Workers, Department of Energy Report E 1.99, DOE-AC02-79EV10095-T1 and (1991) Canadian Workers: Abbatt, J.D., Hamilton, T.R., and Weeks, J.L., Epidemiological studies in three corporations covering the nuclear fuel cycle, Biological Effects of Low-Level Radiation, International Atomic Energy Agency, Vienna, Austria, pp 351–561 (1983) U.K Radiation Workers: Kendall, G.M., Muirhead, C.R., MacGibbon, B.H., O’Hagan, J.A., Conquest, A.J., Goodill, A.A., Butland, B.K., Fell, T.P., Jackson, D.A., and Webb, M.A., Mortality and occupational radiation exposure, British Med J., 304, 220–225 (1992) Plutonium Workers Report: Voelz, G., Lawrence, J., and Johnson, E., Fifty years of plutonium exposure to the Manhattan Project Plutonium workers: An update, Health Physics, 73(4), 611–619 (1997) Lippincott, Williams & Wilkins, Hagerstown, MD Radon: Cohen, B.L., Test of the linear-no-threshold theory of radiation carcinogenesis for inhaled radon decay products, Health Physics, 68, 157–174 (1990) Luckey, T.D., Radiation Hormesis, CRC Press, Boca Raton, FL (1991) It’s time to tell the truth about the health benefits of low-dose radiation: Muckerheide, J., 21st Century Science & Technology Magazine Available at: https//www.21stcenturysciencetech.com/ article/nuclear.html (accessed May 2016) International Dose Response Society, Focusing on the dose-response in the low-dose zone (2014) Available at: http://dose-response.org (accessed December 2015) Health Effects of Low Level Radiation 939 10 American Nuclear Society, President’s Special Session on Low Level Radiation and Its Implications for Fukushima Recovery, June 2012 Available at: www.ans.org/ /specialsession-low-level-radiation-version (accessed May 2016) 11 Effects of Cobalt-60 exposure on health of Taiwan residents suggests new approach needed in radiation protection: Chen, W.L., Luan, Y.C., Shieh, M.C., Chen, S.T., Kung, H.T., Soong, K.I., Yeh, Y.C., Chou, T.S., Mong, S.H., Wu, J.T., Sun, C.P., Deng, W.P., Wu, M.F., Shen, M.L DoseResponse, 5, 63-75 (2007) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2477708/ (accessed May 2016) 12 Taiwan Cancer Risks Report: Hwang, S.L., Guo H R., Hsieh W A., Hwang J S., Lee S D., Tang J L., Chen C C., Cheng T C., Wang J D., and Chang W P Cancer risks in a population with prolonged low dose-rate γ-radiation, 1983–2002, International Journal of Radiation Biology 82(12), (2006) CRC Press, Boca Raton, FL 13 Raabe, O.G., Ionizing Radiation Carcinogenesis in Current Topics in Ionizing Radiation Research, March 2012, Chapter 15 (2012) 14 Yalow, R., in Mayo Clinic Proceedings vol 69, pp 436–440 (1994) http://www.mayoclinicproceedings.org/issue/S0025-6196(12)62639-5/fulltext (accessed May 2016) ... Systems, Third Edition, Ben Rogers, Jesse Adams, and Sumita Pennathur Nuclear Engineering Handbook, Second Edition, Edited by Kenneth D Kok Optomechatronics: Fusion of Optical and Mechatronic Engineering, ... public Nuclear engineering encompasses all the engineering disciplines that are applied in the design, licensing, construction, and operation of nuclear reactors, nuclear power plants, nuclear. .. of the fuel core 16 Nuclear Engineering Handbook Steam generator Reactor coolant pump Pressurizer Nuclear reactor vessel FIGURE 2.2 Layout of nuclear island 2.5.1 Fuel The nuclear core comprises