Introduction
Worldwide, more than 15% of electricity is generated from nuclear power, with the United States, France, and Japan being leaders in this technology. According to the International Energy Agency, as of 2007 there were 439 nuclear power reactors operating in 31 countries. As nuclear power generation has become established since the 1950s, the size of reactor units has grown from 60 MW to more than 1300 MW, with corresponding economies of scale in operation. At the same time many hundreds of smaller reactors have been built, both for naval use (primarily in submarines) and as neutron sources, yielding enormous expertise in the engineering of small nuclear units.
Figure 1:Nuclear Reactor
Image: greenoptimistic.com
How Does Small-Scale Nuclear Energy Work?
Conventional nuclear technology is considered a mature technology. Significant progress is also being made in the development of small-scale, sealed, self-contained nuclear reactors, which can essentially operate as a ‘battery’ to supply energy in the form of electricity and/or heat. These modern, small reactors for power generation are expected to have greater simplicity of design, the economy of mass production, and reduced siting costs. They are also designed for a high level of safety in the event of malfunction and may be built independently or as modules in a larger complex, with capacity added incrementally as required. The International Atomic Energy Agency (IAEA) defines ‘small’ as reactors under 300 MW. To put this in perspective, ‘small’ is over 25% higher than the current peak power demand in the greater Fairbanks area (on the GVEA grid).
Already operating in a remote corner of Siberia are four small units at the Bilibino co-generation plant. These four 62 MWt (thermal) units are an unusual graphite-moderated boiling water design with water/steam channels through the moderator. They produce steam for district heating and 11 MWe (net) electricity each. They have performed well since 1976, much more cheaply than fossil fuel alternatives in the Arctic region.1
Nuclear Fission
Figure 2: Nuclear Fission
Image: chm.bris.ac.uk
Within a nuclear reactor, a controlled nuclear chain reaction takes place. These chain reactions take place in the nuclear reactor core, which contains fuel rods, filled with Uranium-235, and control rods, filled with substances that readily absorb neutrons, such as boron, hafnium, or cadmium. In nuclear fission, a slow-moving neutron is absorbed by U-235 to create U-236. U-236 is struck by a stray neutron, releasing U-235, lighter elements, stray neutrons, and energy, initiating the continued chain reaction. Control rods absorb excess neutrons to prevent the reaction from escalating out of control (See Figure 2).
Water, the moderator contained in the reactor core, absorbs the heat released by the continual nuclear fission reaction and is converted into steam, which drives turbines that generate power. Some nuclear reactors also use graphite as a moderator.
Nuclear Energy in Alaska
Small nuclear reactors are an intriguing emerging technology option for Alaska. Unlike conventional reactors, these nuclear ‘batteries’ are designed to be delivered to the site, installed with the generator system, and operated for the prescribed life (typically 5-30 years). After this time period, the fuel assemblies are removed and returned to the manufacturer, and the reactor assembly is refueled or shipped to disposal intact.
This type of fueling protocol allows plants to be simpler and less expensive to design and build. For designs that have no on-site spent nuclear fuel, the security requirements are reduced. The safety systems are passive and highly reliable without maintenance. The plants emit no greenhouse gases and can be small enough to be buried to minimize security issues. The power plant could be transported by barge in modules and installed in a building, with an excavation for the reactor vessel and containment system as deep as 100 ft deep.
There are a number of potential applications for these nuclear ‘batteries’ in Alaska. One of the most obvious would be to supply power for remote mines where diesel power would otherwise need be imported at high cost. Six of this type of reactor have been proposed for the Alberta oil sands region to provide heat to facilitate separation of oil from the sands. Power generation for remote communities is another potentially attractive application. The community of Galena has been working with Toshiba on obtaining a reactor for a number of years, and several other Alaskan communities have expressed interest in this technology. Galena is interested in a 10 MW reactor system, the 4S; designed by Toshiba to provide power and heat to the community. The city has passed a resolution supporting the installation of this reactor.
Links and Resources
- Nuclear in Galena
- Galena Power Plant Wikipedia Article
- World Nuclear Association. "Small Nuclear Power Reactors." Helpful information on small nuclear reactors.
- U.S. Nuclear Regulatory Commission
