National Academies Press: OpenBook

Analysis of Cancer Risks in Populations Near Nuclear Facilities: Phase 1 (2012)

Chapter: Appendix D: Origin of Radioactivity in Nuclear Plants

« Previous: Appendix C: Presentations and Visits
Suggested Citation:"Appendix D: Origin of Radioactivity in Nuclear Plants." National Research Council. 2012. Analysis of Cancer Risks in Populations Near Nuclear Facilities: Phase 1. Washington, DC: The National Academies Press. doi: 10.17226/13388.
×

D

Origin of Radioactivity in Nuclear Plants

Nuclear power reactors1 are fueled with uranium that is slightly enriched in the isotope uranium-235.2 This isotope is capable of sustaining a controlled nuclear chain reaction that is necessary for production of electrical energy. The chain reaction results in the production of neutrons that induce radioactivity in the fuel, cooling water, and structural components of the reactor.

Radioactivity is induced primarily through processes involving the capture of neutrons by uranium atoms in the fuel. Fission occurs when the nucleus of a uranium-235 atom (and less commonly a uranium-238 atom) captures a neutron, becomes unstable, and splits into two and (infrequently) three3 lighter nuclei; these nuclei are referred to as fission products. Uranium fission produces a bimodal mass distribution of fission products shown in Figure D.1. The most common fission products have mass numbers around 90 and 137 (for example, strontium-90 and cesium-137).

The fission products produced in a nuclear power reactor span the periodic table. They include:

  • Noble gases, for example, krypton-85 and xenon-133.
  • Halogens, for example, iodide-131.

1 The terms nuclear power reactors and nuclear power plants refer to reactors that are used on a commercial basis to produce electricity. Such reactors typically generate on the order of 1000 megawatts of electrical power and 3000 megawatts of thermal power.

2 Natural uranium contains about 99.3 percent uranium-238 and 0.7 percent uranium-235. The fuel used in power reactors is typically enriched in uranium-235 to levels of 3-5 percent.

3 Referred to as ternary fission.

Suggested Citation:"Appendix D: Origin of Radioactivity in Nuclear Plants." National Research Council. 2012. Analysis of Cancer Risks in Populations Near Nuclear Facilities: Phase 1. Washington, DC: The National Academies Press. doi: 10.17226/13388.
×

image

FIGURE D.1 Mass distributions resulting from fission of uranium-235 by thermal neutrons. SOURCE: Data from Joint Evaluated Fission and Fusion File, Incident-neutron data, http://www-nds.iaea.org/exfor/endf00.htm, October 2, 2006; see http://www-nds.iaea.org/sgnucdat/c1.htm.

  • Alkali metals, for example, cesium-137.
  • Alkaline earth metals, for example, strontium-90.
  • Less commonly, hydrogen-3, more commonly referred to as tritium (T), from ternary fission of uranium atoms.

Neutron capture can also induce radioactivity through the transmutation of one chemical element into another. The transmutation process results in the emission of nuclear particles (e.g., protons) and radiation from the nucleus. Some transmutation reactions and products of significance in power reactors include the following:

  • Production of nitrogen-16 through the capture of a neutron by the nucleus of an oxygen atom: oxygen-16 + neutron —> nitrogen-16 + proton (abbreviated as 16O(n, p)16N). Nitrogen-16 has a short (7-second) half-life and is primarily a hazard to workers at nuclear plants.
  • Production of carbon-14 through the capture of neutrons by the nuclei of nitrogen, oxygen, or carbon atoms: 14N(n, p)14C; 13C(n, y)14C; 17O(n, a)14C.
Suggested Citation:"Appendix D: Origin of Radioactivity in Nuclear Plants." National Research Council. 2012. Analysis of Cancer Risks in Populations Near Nuclear Facilities: Phase 1. Washington, DC: The National Academies Press. doi: 10.17226/13388.
×
  • Production of tritium (T) by the capture of a neutron by the nu-cleus of a boron atom: 10B(n,2a)T. This is an important reaction in pressurized-water reactors, which use boron in cooling water to control reactivity.
  • Production of tritium through capture of a neutron by a deuterium atom that is naturally present in the cooling water of a reactor.

Neutron capture can also induce radioactivity through activation. The capture of a neutron excites the nucleus, which quickly decays to a less energetic state through the emission of radiation. Some activation reactions and products of significance in power reactors include the following:

  • Production of cobalt-60 from cobalt-59 through the reaction 59Co(n, y)60Co.
  • Production of iron-55 from iron-54 through the reaction 54Fe(n, y)55Fe.

Cobalt-60 and iron-55 are common activation products in the structural components of reactors.

The isotopes produced by these neutron capture processes are almost always radioactive. Their decay involves the emission of alpha, beta, and gamma radiation, to produce both radioactive and nonradioactive decay products. A decay reaction of particular importance in nuclear power reactors is the following:

image

This reaction produces plutonium-239 by uranium-238 neutron capture followed by two beta decays.

The particles and other radiation emitted during neutron capture can interact with atoms in the fuel, coolant, and reactor structures to produce additional radioactivity. For example, the interaction of energetic electrons with materials in the reactor results in the emission of photons known as bremsstrahlung. This radiation appears as a faint blue glow when electrons interact with cooling water in the reactor and spent fuel pools.

Suggested Citation:"Appendix D: Origin of Radioactivity in Nuclear Plants." National Research Council. 2012. Analysis of Cancer Risks in Populations Near Nuclear Facilities: Phase 1. Washington, DC: The National Academies Press. doi: 10.17226/13388.
×

This page is blank

Suggested Citation:"Appendix D: Origin of Radioactivity in Nuclear Plants." National Research Council. 2012. Analysis of Cancer Risks in Populations Near Nuclear Facilities: Phase 1. Washington, DC: The National Academies Press. doi: 10.17226/13388.
×
Page 347
Suggested Citation:"Appendix D: Origin of Radioactivity in Nuclear Plants." National Research Council. 2012. Analysis of Cancer Risks in Populations Near Nuclear Facilities: Phase 1. Washington, DC: The National Academies Press. doi: 10.17226/13388.
×
Page 348
Suggested Citation:"Appendix D: Origin of Radioactivity in Nuclear Plants." National Research Council. 2012. Analysis of Cancer Risks in Populations Near Nuclear Facilities: Phase 1. Washington, DC: The National Academies Press. doi: 10.17226/13388.
×
Page 349
Suggested Citation:"Appendix D: Origin of Radioactivity in Nuclear Plants." National Research Council. 2012. Analysis of Cancer Risks in Populations Near Nuclear Facilities: Phase 1. Washington, DC: The National Academies Press. doi: 10.17226/13388.
×
Page 350
Next: Appendix E: Origin of Radioactivity in Fuel-Cycle Facilities »
Analysis of Cancer Risks in Populations Near Nuclear Facilities: Phase 1 Get This Book
×
Buy Paperback | $64.00 Buy Ebook | $49.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

In the late 1980s, the National Cancer Institute initiated an investigation of cancer risks in populations near 52 commercial nuclear power plants and 10 Department of Energy nuclear facilities (including research and nuclear weapons production facilities and one reprocessing plant) in the United States. The results of the NCI investigation were used a primary resource for communicating with the public about the cancer risks near the nuclear facilities. However, this study is now over 20 years old. The U.S. Nuclear Regulatory Commission requested that the National Academy of Sciences provide an updated assessment of cancer risks in populations near USNRC-licensed nuclear facilities that utilize or process uranium for the production of electricity.

Analysis of Cancer Risks in Populations near Nuclear Facilities: Phase 1 focuses on identifying scientifically sound approaches for carrying out an assessment of cancer risks associated with living near a nuclear facility, judgments about the strengths and weaknesses of various statistical power, ability to assess potential confounding factors, possible biases, and required effort. The results from this Phase 1 study will be used to inform the design of cancer risk assessment, which will be carried out in Phase 2. This report is beneficial for the general public, communities near nuclear facilities, stakeholders, healthcare providers, policy makers, state and local officials, community leaders, and the media.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

    « Back Next »
  6. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  7. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  8. ×

    View our suggested citation for this chapter.

    « Back Next »
  9. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!