discovered_01_2015

discovered 01 .15 RESEARCH WWW.HZDR.DE In order to control such a chain reaction, all nuclear reactors use neutron absorbers. In light water reactors, water as the cooling agent also decelerates the neutrons. In a fast reactor, the heat-removing agent is liquid sodium. In contrast to water, neutrons bounce off of a metallic atomic nucleus almost without any loss of energy, much like a pool ball that hits the rail. Fast neutrons also facilitate the efficient breeding of plutonium. For opponents, this only adds more fuel to the fire, as this could also be weapon-grade plutonium. Supporters, on the other hand, consider this one of the great benefits of the technology. The idea is to always produce about as much plutonium as is burned in the operation of the facility. The substance is needed as a sort of catalyst for uranium-238, the almost sole natural form of uranium, which could otherwise not be used as fissile material. This kind of uranium does not require complicated enrichment or processing in order to be used in the fast breeder. What is more: sodium-cooled reactors can also burn many of the extremely long-lived, heavy nuclei that are generated in the operation of a reactor, thus transforming them into shorter-lived substances; this greatly relieves the problem of radioactive waste management. Even plutonium waste could be used as a fuel. By comparison: Generation II versus Generation IV HZDR-researcher Bruno Merk has studied the operation and shut-down times of fast reactors and compared them to particularly stable German light water reactors. His premise was that facilities with few unplanned down-times and maintenance intervals are technologically mature and safe. Together with colleagues from the US and India, and on behalf of the International Atomic Energy Agency IAEA, he analyzed data from the now shut-down demonstrator power plant Phénix in France and the Russian reactor type BN-600 in Beloyarsk, which has been in operation for over 30 years. ‘The technology is past its growing pains, as evidenced by few unplanned down-times, especially for the BN-600, which has operated safely for more than 30 years,’ says Merk. ‘We adjusted the data by subtracting scheduled revision times. In the past ten years, operation has been excellent with an adjusted availability of almost 97 percent. Only few light water reactors achieve such figures.’ In their study, researchers found that the German nuclear power plants Grafenrheinfeld (launched in 1981) and Emsland (launched in 1988) have similar availability rates of 96.2 and 99.8 percent. Merk emphasizes: ‘BN-600 has not undergone any major repairs either in this time period. The safety level of the fast breeder matches that of the best 2nd generation light water reactors. During scheduled revisions in this period, they even prepared the reactor for an extension of its operational life-span.’ Of course, Merk knows about the problems with sodium technology: ‘As nuclear scientists, we are aware of the issues that have come up. The steam generator and the pumps are the trouble spots.’ Leaks caused by poorly sealed welding seams can cause water or steam to come into contact with ‘The French ASTRID reactor will be built, for sure. We need nuclear power ex- perts in Germany whose voice will be heard when it comes to safety issues. And that will only happen if we assume an active role in large EU research projects.’ START: Loading of the new, fast reactor BN-800 at Beloyarsk. Photo: Rosenergoatom

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