Nuclear Energy: Benefits and Risks

1. Nuclear Energy: Benefits and Risks Chapter 11

2. The Nature of Nuclear Energy • Radioactive - Nuclei of certain atoms are unstable and spontaneously decompose. • Neutrons, electrons, protons, and other larger particles are released, along with energy. • Radioactive Half-Life - Time it takes for half the radioactive material to spontaneously decompose.

3. The Nature of Nuclear Energy • Only certain kinds of atoms are suitable for development of a nuclear chain reaction. • The two most common are uranium-235 and Plutonium-239. • Requires certain quantity of nuclear fuel (critical mass).

4. Radiation • Types: • Alpha - Moving particles composed of two neutrons and two protons. • Stopped by layer of skin. • Beta - Consists of electrons from nucleus. • Stopped by layer of clothing. • Gamma - Form of electromagnetic radiation. • Can pass through several centimeters of concrete.

5. Radiation • If the radiation reaches living tissue, equivalent doses of beta and gamma radiation can cause equal amounts of biological damage. • Alpha particles are more massive, thus can cause more damage to biological tissues.

6. The Nature of Nuclear Energy • Nuclear Fission - Occurs when neutrons impact and split the nuclei of certain atoms. • Nuclear Chain Reaction - Splitting nuclei release neutrons, which themselves strike more nuclei, in turn releasing even more neutrons.

7. Nuclear Fission Chain Reaction

8. History of Nuclear Energy Development • First controlled fission - Germany 1938. • 1945 - U.S. dropped atomic bombs on Hiroshima and Nagasaki. • Following WW II, people began exploring other potential uses of nuclear energy. • U.S. built world’s first nuclear power plant in 1951.

9. Dwight D. Eisenhower • “Atoms for Peace” 1953: • “Nuclear reactors will produce electricity so cheaply that it will not be necessary to meter it.” • Today’s Reality: • Accidents have caused worldwide concern. • Most new projects have been stopped. • Many experts predict rebirth.

10. Nuclear Fission Reactors • Nuclear Reactor - Device that permits a controlled fission chain reaction. • Nucleus of U-235 atom struck by slowly moving neutron from another atom. • Nucleus split into smaller particles. • More neutrons released. • Strike more atoms.

11. Boiling Water Reactor

12. Nuclear Fission Reactors • Control Rods - Made of a non-fissionable material (boron, graphite) that are lowered into reactor to absorb neutrons. • Withdrawn to increase rate of fission. • Moderator - A substance that absorbs energy, slowing neutrons, enabling them to split the nuclei of other atoms more efficiently.

13. Workings of A Nuclear Reactor • Nuclear reactor serves same function as fossil-fuel boiler: produces heat - converts water to steam - turns a turbine - generating electricity. • Boiling Water Reactors (BWR)

14. Plans for New Reactors Worldwide • Currently 439 nuclear power reactors in 31 countries. • Combined capacity of 354 gigawatts. • Provide 16% of world’s electricity. • Currently 32 reactors under construction in 10 countries. • Forecasting becomes uncertain after 2005. • Most planned reactors in Asia and parts of former Soviet Union.

15. Plant Life Extension • Most nuclear power plants originally had normal design lifetime up to 40 years. • Engineering assessments have established many plants can operate much longer. • Economic, regulatory, and political considerations have thus far led to premature closure of some plants.

16. Nuclear Power Plants in North America

17. Nuclear Power Concerns • Currently, 17% of electricity consumed worldwide comes from nuclear power. • Accidents raised questions about safety. • Contamination and disposal problems. • Plants may be terrorism targets. • Spent fuel storage facilities. • More total radioactivity than the reactor. • Still not easy, or prime target.

18. Reactor Safety • Three Mile Island - Pennsylvania • March 28, 1979 - Partial Core Melt-Down. • Pump and valve malfunction. • Operator error compounded problem. • Crippled reactor was de-fueled in 1990 at a cost of about $1 billion. • Placed in monitored storage until its companion reactor reaches the end of its useful life.

19. Reactor Safety • Chernobyl - Ukraine • April 26, 1986 • Experiments being conducted on reactor. • Multiple serious safety violations. • Reactor Explodes. • 31 deaths. • 116,000 people evacuated. • 24,000 evacuees received high doses of radiation. • Increased thyroid cancer in children.

20. Reactor Safety • A consequence of both of the accidents has been a deepened public concern over nuclear reactor safety. • Since 1980, 10 countries have cancelled nuclear plant orders or mothballed plants under construction. • Increased Public Opposition: • United Kingdom: 65% - 83% • Germany: 46% - 83% • United States: 67% - 78%

21. Exposure to Radiation • Type and degree of damage vary with radiation form, dosage and duration of exposure, and type of cells irradiated. • Because mutations are permanent, radiation effects may build up over years and only appear later in life.

22. Thermal Pollution • Addition of waste heat to the environment. • Especially dangerous in aquatic systems. • In a nuclear power plant, 1/3 of heat used to generate electricity while the other 2/3 is waste. • Fossil fuel plants are 50:50. • To reduce the effects of waste heat, utilities build cooling facilities. • Ponds • Towers

23. Decommissioning Costs • Life expectancy of most electrical generating plants is 30-40 years. • Unlike other plants, nuclear plants are decommissioned, not demolished. • Involves removing the fuel, cleaning surfaces, and permanently barring access. • Over 70 nuclear power plants in the world are awaiting decommissioning.

24. Decommissioning Costs • By 2005, 68/104 U.S. plants will be at least 20 years old. • Nuclear Regulatory Commission may extend authorization an additional 20 yrs.

25. Decommissioning Uncertainties • Utilities Have (3) Options: • Decontaminate and Dismantle plant ASAP. • Shut Down plant for 20-100 years, allowing radiation to dissipate, then dismantle. • Entomb plant within concrete barrier. • Recent experience indicates decommissioning a large plant will cost between $200 and $400 million.

26. Radioactive Waste Disposal • Today, the U.S. has 380,000 cubic meters of highly radioactive military waste temporarily stored at several sites. • Waste Isolation Pilot Plant (WIPP) Carlsbad, NM began accepting waste in March, 1999. • Transuranic wastes - High-level radioactive waste consisting primarily of various isotopes of plutonium.

27. DOE Radioactive Transuranic Waste Sites

28. Radioactive Waste Disposal • In addition to high-level waste from weapons programs, 2 million cubic meters of low-level radioactive military and commercial waste are buried at various sites. • About 30,000 metric tons of highly radioactive spent fuel rods are stored in special storage ponds at nuclear reactor sites. • Many plants are running out of storage.

29. Radioactive Waste Disposal • High Level Radioactive Waste: • At this time, no country has a permanent storage solution for the disposal of high-level radioactive waste. • Politics of disposal are as crucial as disposal method. • Most experts feel the best solution is to bury waste in a stable geologic formation.

30. High-Level Waste Storage in the United States • In 1982, Congress called for a high-level radioactive disposal site to be selected by March 1987, and to be completed by 1998. • In 2002, the Secretary of Energy indicated the choice of a site at Yucca Mountain in Nevada was based on scientifically sound and suitable science. • Current work is primarily exploratory and is seeking to characterize the likelihood of earthquake damage and water movement.

31. High-Level Waste Storage in the United States • If completed, the facility would hold about 70,000 metric tons of spent fuel rods and other highly radioactive material. • Not to be completed before 2015. • By that time, waste produced by nuclear power plants will exceed the storage capacity of the site.

32. High-Level Nuclear Waste Disposal

33. Low - Level Waste • Currently, U.S. produces about 800,000 cubic metersof low-level radioactive waste annually. • Presently buried in various scattered disposal sites. • Political limbo.

34. Low-Level Radioactive Waste Sites

35. Exposure to Radiation • Human exposure usually expressed in rems. • Measure of biological damage to tissue. • The higher the dose, the more observable the results. • No human is subject to zero exposure. • Average person exposed to 0.2 to 0.3 rems per year from natural and medical sources.

36. Politics of Nuclear Power • Nuclear power projections are subject to considerable uncertainty, both economic and political. • In large part, governmental support for nuclear power has waxed and waned with the changing of government regimes.

37. Politics of Nuclear Power • Nuclear power is projected to represent a shrinking share of the world’s electricity consumption from 2004 through 2025. • Most nuclear additions are expected to be in Asia. (China, India, Japan, S. Korea) • Life extension and higher capacity factors will play a major role in sustaining the U.S. nuclear industry throughout this period.