Sustainable nuclear reactors
Dutch researchers at the Delft University of Technology are working on 'Generation IV' nuclear reactor designs. These future 'Gas Cooled Fast Reactors' (GFR) should produce more new fissile materials than the ones consumed by the reactors. They will use helium as coolant at high temperature and should bring us sustainable nuclear energy. In fact, the goal of the GFR is to obtain a 'closed nuclear fuel cycle,' where natural uranium is used as raw material and fission products would be transformed into harmless waste material. But don't expect to see these reactors working before at least 2050.
This research work about GFRs -- or GCFRs as they're also called -- has been done by a team of TU Delft researchers including Wilfred van Rooijen working in the Physics of Nuclear Reactors (PNR) group. Here is a link to his research at PNR which is one of the members of the European GCFR-STREP (Specific Targeted REsearch Program).
His research about Generation IV nuclear systems has taken place at the Reactor Institute Delft. And her are some details about how these nuclear reactors will work.
The fourth generation GFR uses helium as a coolant at high temperatures. GFR's ultimate objective is to create a closed nuclear fuel cycle, in which only natural uranium is used as a raw material and in which the resulting waste consists of only nuclear fission products. Uranium and heavier isotopes, such as plutonium and americum, are recycled in the reactor and ultimately burned up (fissioned).
In the reactors in use today, these heavy isotopes determine the long-term radioactivity of the nuclear waste. A closed nuclear fuel cycle therefore allows for maximum use of the raw materials, while at the same time substantially reducing the life-span of the waste.
Such reactors will use what is called a Fast Breeder mechanism. "The Breeding Gain (BG) of a nuclear reactor [will take] into account compositional changes of the fuel during irradiation, cool down and reprocessing. [And these reactors] should have a closed fuel cycle, with a BG equal to zero, breeding just enough new fuel during irradiation to allow refueling by only adding fertile material.
Below is an image showing the fuel assembly of such a GFR (Credit: Wilfred van Rooijen et al., TU Delft). "The light coloured wrapper and central mechanical restraint are made of SiC. The darker fuel slabs contain the fuel mixture clad with SiC. Each assembly contains 21 fuel plates. The fueled length is 1.95 m, the overall length of the assembly about 4 m."
For more information about these future reactors, here are two links to scientific papers co-authored by Wilfred van Rooijen, "Fuel design and core layout for a Gas Cooled Fast Reactor" (PDF format, 15 pages, 462 KB, September 2005) and "Definition of breeding gain for the closed fuel cycle and application to a Gas Cooled Fast Reactor" (PDF format, 10 pages, 262 KB, May 2006). The picture above has been extracted from this second paper.
Wilfred van Rooijen has presented his thesis called "Improving Fuel Cycle Design and Safety Characteristics of a Gas Cooled Fast Reactor" on December 11, 2006. The full text of his thesis should be available in a few weeks at the TU Delft Repository.
Finally, don't expect to use electricity produced by such reactors before a long time. These concepts are projected to become operational in 2050 -- at least.
Sources: Delft University of Technology news release, via EurekAlert!, December 11, 2006; and various websites
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