Nuclear Fission
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.
Nuclear power is very cheap compared to other powers. Nuclear fission one of the least expensive.
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.
Safety Issues
In light of the September 11, 2001, ist attacks in New York City and Washington,
D.C., many have raised concerns about the safety of nuclear facilities in the event of an attack by crashing a commercial
jet liner. The Nuclear Regulatory Commission has been asked what would happen if a fully fueled airliner crashed into a nuclear
power plant. NRC officials said, "Although nuclear power plants are not explicitly designed for the crash of a commercial
aircraft, plants have inherent capability to provide for the protection of public health and safety. Pre-stressed concrete
containment buildings are robust, and it is unlikely a large commercial plane could penetrate the containment structure. Furthermore,
plant designs and redundant safety equipment along with highly trained operators are in place to limit the potential consequences."
Pacific Gas and Electric Company was asked the same question, and they reportedly said that their Diablo Canyon Nuclear
Plant is designed to withstand the impact of a fully loaded "747" aircraft.
Regarding other safety issues, please visit the NRC's website at: www.nrc.gov. the NRC has primary jurisdiction over nuclear facilities in the United States though it works closely with local and state
emergency agencies.
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 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:
- Nuclear plants may not be economically feasible in the United States. No American utility has proposed to construct a
new nuclear power plant since the late 1970s.
- 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
