Nuclear Energy in California

Nuclear Energy: An Overview

In 2010, nuclear provided almost 14 percent of the entire California power mix (which includes out of state imports). As of mid-2012, California had one operating nuclear power plant: Diablo Canyon (2,160 megawatts), near San Luis Obispo.

There are two fundamental ways to release energy from nuclear reactions: fission and fusion of atomic nuclei. Electricity generating technologies based on fission are commercially available, whereas fusion is still in the early stages of research and development and is at present only a theoretical possibility for controlled power generation. Nuclear fission is the process of splitting the nuclei of atoms, which releases energy from within those atoms. Nuclear fusion is the process of joining, rather than splitting, such atomic particles with similar releases of energy.


Of the several types of fission reactors, the most common type in the United States is light water reactors (so called because normal (light) water is used to cool the reactor core; some reactors use heavy water, which contains hydrogen atoms with an additional neutron in the nucleus), based on pressurized water reactor (PWR) and boiling water reactor (BWR) technology. PWRs and BWRs use uranium-235, a naturally-occurring radioactive isotope of uranium, as the fuel. As the nucleus of a uranium-235 atom is hit by a neutron, it splits into two smaller atoms of other elements, and releases energy and extra neutrons. Those neutrons hit more atoms of the original uranium-235, creating a fission chain reaction that releases more energy and neutrons.

In a PWR, water passes through the nuclear core and is heated. The power plant's primary circulating system passes water through the reactor core, where the water is heated by the nuclear reaction. That water (under high temperature and pressure to prevent boiling) is passed through a steam generator, where it releases its heat to the secondary circulating system. Water in the secondary circulating system is allowed to boil, and the resulting steam is used to drive a steam turbine-generator.

In a BWR, there is no need for a steam generator and a secondary circulating system, as the water in the primary circulating system is allowed to boil before exiting the reactor and is then routed directly to a steam turbine-generator.

Other Types of Fission Plants

There are several advanced reactor power plant designs being developed in the U.S. and over-seas. These include both advanced light water reactor (ALWR) and advanced modular reactor designs. The ALWR program is focusing on both evolutionary and passive designs, using both BWR and PWR technologies. Each design configuration is seeking certification by the U.S. NRC as a standard design under the U.S. Department of Energy's ALWR Design Certification Program.

The evolutionary ALWRs are advancements of today's light water reactor designs and use conventional safety system concepts. There are two evolutionary ALWR designs that are expected to be ready for commercial operation by the year 2000: the 1,356 MW Advanced Boiling Water Reactor (ABWR) and the 1,350 MW Advanced Pressurized Water Reactor (System 80+). Two ABWR units are being built in Japan. As of July 1996, the first unit is ready to begin commercial operation. The second unit is scheduled to begin operation in 1997. In June 1996, Taiwan ordered two ABWR units. The System 80+ PWR received its final design approval from the NRC in July 1994.

The passive ALWR designs are greatly simplified and employ primarily passive means for accident prevention and mitigation. There are two passive ALWR designs that have been considered: 600 MW Advanced Pressurized Water Reactor (AP600) and the 600 MW Simplified Boiling Water Reactor (SBWR). The AP600 Advanced PWR is expected to receive its final design approval from the NRC in September 1996. It could be ready for commercial operation by the year 2003. The future of the SBWR is uncertain at this time.

The Advanced Modular Reactor Program is focusing on the development of small (165 MW to 217 MW) reactors that can be grouped together as modules of a larger power station. The two advanced modular reactor designs, which are also seeking design certification, are the 1,500 MW Advanced Liquid Metal Reactor (ALMR) and the 700 MW Modular High Temperature Gas Cooled Reactor (MHTGR). These designs are expected to be ready for commercial operation by the year 2010.

Issues for Fission Power Plants

Some of the issues associated with commercial nuclear power plants include:

  • Economic feasibility of new plants in the United States
  • Need for a spent fuel disposal facility and a decommissioning plan
  • Use of large amounts of water for cooling purposes (if wet cooling towers are used)
  • Biological impacts on the ocean due to thermal discharge (if seawater cooling is used)
  • Designing for seismic safety
  • Public safety concerns
  • Transportation issues associated with the development of an emergency evacuation plan
  • Changes in visual quality due to the power plant structures, including the reactor vessel containment structure, and cooling towers (if applicable)
  • Potentially significant amounts of land
  • Potentially significant public opposition


A fusion reaction occurs when nuclei of light elements, such as hydrogen and its isotopes (deuterium, or "heavy water," and tritium), are forced together at extremely high temperatures and densities until they fuse into nuclei of heavier elements and release enormous amounts of energy. If fusion is to yield net energy, the fuel must be heated in the form of plasma (a highly ionized gas) to a very high temperature and the plasma must then be held together for a sufficiently long time such that the number of fusion reactions occurring releases more energy than was required to heat the fuel.

The Princeton Plasma Physics Laboratory's Tokamak Fusion Test Reactor (TFTR) in 1996 demonstrated fusion of deuterium-tritium plasma at 510 million degrees Celsius. That experiment produced heating equal to one-third of that needed for the fusion reaction to become self-sustaining. Thus, there is still significant research that must be accomplished before fusion achieves a net energy output, and then even more development work to develop commercial power plant applications. It is estimated that commercial availability of fusion is at least 20 years away.

To generate commercial energy, the neutron energy would be converted to heat in a surrounding blanket of coolant, probably containing solid lithium compounds, with the heat converted to electricity in a conventional steam generator cycle. Although the fusion reaction does not produce radioactive fission products, the high energy neutrons do irradiate the surrounding reactor vessel and associated components. The irradiated material poses radioactive disposal problems similar to those for the irradiated reactor vessels of fission reactors. Thus, many of the high-level nuclear waste concerns that apply to fission reactors would also apply to fusion reactors.

The term "cold fusion," as reported in the popular press in recent years, refers to the process of fusing hydrogen nuclei at room temperature. It was allegedly demonstrated in a simple laboratory apparatus in 1989 by Fleischman and Pons. Several experiments have been conducted to try to replicate their work, with limited success. The phenomenon of cold fusion cannot be reproduced on demand and cannot be explained by conventional nuclear physics. Therefore, its commercial potential as an electric generating technology is uncertain.


  1. "World List of Nuclear Power Plants," Nuclear News, March 1994, Vol. 37, No. 3, pp. 43-62.
  2. Resource: An Encyclopedia of Energy Utility Terms, Pacific Gas and Electric Company, 2nd edition, 1992, pp. 318-321.
  3. Glenn County Energy Element of the General Plan, June 1993, p. 143.
  4. Evaluation of Power Facilities: A Reviewer's Handbook, prepared by the Berkshire County Regional Planning Commission, April 1974, pp. 56-57.
  5. "TFTR Set Another Record for Fusion Power," Nuclear News, December 1994, Vol. 37, No. 15.
  6. 1992 Energy Technology Status Report - Final Report, California Energy Commission, Report no. P500-92-007, December 1992. Fact Sheet (Nuclear Fission - Full Fuel Cycle), (Nuclear Fission - Waste Disposal), (Nuclear Fission - Decommissioning), 1.2.3 (Fuel Cycles - Nuclear Fusion), 4.1 (Nuclear Fission - Pressurized Water Reactor), 5.1 (Nuclear Fusion - High Temperature), and 5.2 (Cold Fusion).
  7. 1992 Energy Technology Status Report, Appendix A, Volume I: Detailed Electric Generation Technology Evaluations, California Energy Commission, Report no. P500-92-007A V1, December 1992. Sections 5.1 (High Temperature Fusion) and 5.2 (Cold Fusion).
  8. "NRC Staff OKs Rancho Seco Plant," The Sacramento Bee, March 22, 1995.
  9. TAGTM Technical Assessment Guide: Electricity Supply - 1993, Volume 1, Rev. 7, Electric Power Research Institute Report No. EPRI TR-102275-VIR7, June 1993.
  10. "A New Generation of Nuclear Reactors," Mechanical Engineering, April 1995, pp. 70-75.
  11. Ballard, Kenneth P., Margot E. Carl Everett, Willard C. Everett, "Utilities and Decommissioning Costs: The Meeting of Technology and Society," The Energy Journal, January 1991, pg. 29.