Spent fuel storage in the storage pools of nuclear power plants

The pools for storing spent fuel elements in the reactor buildings of nuclear power plants allow the afterheat of fuel unloaded from the reactor for good to decay to a level at which the fuel then can be shipped in special casks. Consequently, these storage pools were designed in Germany in the past so as to accommodate the volume of fuel elements unloaded over approximately two to ten years of operation, depending on the power plant in question before the fuel had to be shipped off. As a consequence of the omnibus law amending the German Atomic Energy Act, which permits direct disposal of spent fuel elements as a legally equivalent alternative to reprocessing, the operators of nuclear power plants have had an opportunity to reassess the nuclear fuel cycle. If the direct disposal option is to be used, this necessitates long-term interim storage of the fuel. This can be achieved, on the one hand, in the storage pools of nuclear power plants and, on the other hand, in separate fuel stores in which the fuel elements can be kept in combined shipping and storage casks. If such relatively sophisticated storage casks are to be loaded economically in nuclear power plants, the afterheat generated by the fuel elements should have decayed as far as possible, as heat removal and radiation dose rate on the surface of the cask are limiting factors. There is yet another aspect, namely the trends towards higher discharge burnups and towards using nuclear recycle fuel. Both measures increase the decay heat produced by spent fuel. In countries where long-term interium storage has been practiced for a long time already (e.g. Spain, Korea), Siemens in the past few years equipped the storage pools of nuclear power plants with compact fuel stores which make optimum use of the storage pools. These innovative two-region stores are being used already in ten of these nuclear power plants. (orig.)