Part 1 of 2 Parts
I have made reference to “generations” of nuclear power reactors in previous posts. Currently, most of the reactors generating electricity are considered to be Generation II. The old Generation I reactors have been retired. There are about a dozen Generation III reactors in commercial operation out of about four hundred reactors across the globe.
Generation IV refers to a set of nuclear reactor designs that are being researched for possible commercial application in power generation. The Generation IV International Forum is leading this research. The designs are in different stages of technological readiness from needing a demonstration of basic principle to demonstrating economical competitiveness. The new designs are dedicated to such goals as improving safety, sustainability, efficiency and cost. Most of these new designs are not expected to be available for construction until 2020 at the earliest and 2030 at the latest. There are theoretical designs for Generation V reactors but they have received little funding to date.
Broadly speaking, the Generation IV designs fall into two main categories. The first category is called thermal reactors. This term refers to the use of what are called slow or thermal neutrons. A moderator is used to slow down the neutrons that are emitted by the fusion reaction. This makes them more likely to be captured by atoms in the fuel.
The Very-High-Temperature Reactor (VHTR) uses a core moderated by graphite with a once-through uranium fuel cycle. Helium or a molten salt are used for coolant. This reactor can produce heat in the range of a thousand degrees Centigrade. Physically, the reactor can be a prismatic-block or pebble bed reactor design. The high temperature heat that a VHTR can produce is being considered for use as an industrial heat source for production of hydrogen as well as for generating electricity. The Chinese are working on a series of experimental VHTR reactors. The U.S. hopes to complete a prototype VHTR by 2021 at the Idaho National Laboratory.
The Molten-salt Reactor (MSR) utilizes a molten salt mixture as the coolant and may mix the fuel into the molten salt. There have been many designs and a few test versions of such reactors built. The most popular approach dissolved uranium tetrafluoride in molten fluoride salt. Graphite is used as a moderator in the core. Using molten salt for cooling is a low pressure, high temperature method of cooling. A number of different cooling schemes and fuel types are being explored. One possible use of an MSR would be to burn nuclear waste from other reactors to reduce the volume of waste.
The Supercritical-water-cooled Reactor (SCWR) is a light water reactor operating at higher temperature and pressures than current light water reactors (LWR). The neutrons in an SCWR are faster than thermal neutrons and are referred to as epithermal neutrons. Supercritical water is the working coolant with a once-through heat exchange cycle. This type of reactor can operate at higher temperatures and pressures than pressurized water reactors and boiling water reactors. SCWR have a high thermal efficiency which is about fifty percent better than current LWRs. Because of the supercritical water, the design of the plant is much simpler than LWR plant designs. SCWRs have benefits but they also have technical difficulties in that all the piping and other machinery must be designed to handle much higher temperatures and pressures than current power reactors.
Please Read Part 2
