Nuclear Power… Continued
Generation IV Nuclear Power
Gen IV reactors will definitely deviate from current LWR technology. Many will not use water, but elements such as helium, fluoride salt, or liquid sodium as a coolant, with sizes ranging from 150 to 1500 MWe. At least four of the systems already have significant operating experience. In addition, expanded uses for the Gen IV might include sea water desalination and process heat production. Based upon safety, environmental concerns, resistance to diversion of weapons grade materials, waste production and cost-effective solutions, the GIF has initially selected six supported designs. A very brief discussion follows for each:
Gas-cooled fast reactor (GFR): This reactor is high efficiency, and helium is used as the coolant instead of water, with an outlet temperature of 850 degrees Celsius, much higher then the Gen III.
LWR design: The core material of this reactor holds the potential of excellent retention of fission products and minimizes the production of long lived radioactive waste.
Lead-cooled fast reactor (LFR): This rector has inherent safety due to the use of un-reactive molten metal as the coolant, and natural primary coolant circulation. This reactor design, for the core, can use depleted uranium or thorium fuel matrices and burn actinides from LWR spent fuel.
Molten salt reactor (MSR): This reactor embodies liquid fuel. The uranium is dissolved in a sodium fluoride salt coolant which circulates through a graphite core. The positive side of the MSR technology is no spent fuel, continuous fission products removal, no fuel fabrication, and minimization of radiotoxic nuclear waste.
Sodium-cooled fast reactor (SFR): With 390 reactor-years of experience in sodium-cooled reactors over five decades, the SFR uses liquid sodium as the coolant. Core options for the SFR include depleted uranium.
Supercritical water-cooled reactor (SCWR): A high temperature, high pressure water-cooled reactor with a single phase coolant, supercritical water directly drives the turbines, and translates into improved economics. This reactor’s core is enriched uranium oxide.
Very high-temperature gas reactor (VHTR): These are graphite-moderated, helium-cooled reactors with substantial experience. Heat removal is passive. The core can be blocks or pebble bed. This reactor design has potential of low operation and maintenance costs, modular construction, and passive safety.
The closest to commercial use is a small pebble bed reactor under development in China. Its uranium fuel is encased in tennis-sized balls called pebbles, where the fuel doesn’t get hot enough to melt.
Nuclear Future: Even More is Happening Now
New power plants are designed with passive safety systems that do not depend on action such as operator action or a pump turning on to circulate coolant through the core to prevent melting. Nuclear power plant vendors such as Westinghouse have designed their Advanced Passive 1000 (AP1000), for example, and are halfway through construction of several of these reactors. GE is developing modular passive reactors with their own safer designs.
When it comes to nuclear reactors, some think smaller is better; by reducing the output and size in-half, all cooling can be handled by simple gravity flow through natural convection. Smaller reactors cost less, are built faster and produce less spent fuel. And finally, there is fusion. The technology for this panacea for nuclear energy, however, is still around fifty years out.
Gen IV International Forum. Evolution of Nuclear Power, Generation IV Sytems. (2011). Accessed January 2, 2012.
World Nuclear Association. Generation IV Nuclear Reactors. (2010). Accessed January 2, 2012.
U.S. Department of Energy. Gen IV Nuclear Energy Systems, Program Overview. Accessed January 2, 2012.
Coy, Peter. New nuclear plants designed to be safest ever. Bloomberg Businessweek. (2011). Accessed January 2, 2012.
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