Untersuchungen zur Entstehung von Aktiniden im Hochtemperaturreaktor

The actinides, especially the long lived alpha emitters, generated in a fuel cycle, demand a safe storage of the nuclear waste due to their high contribution to the total radioactivity. In this work it has been investigated whether a possible limitation of actinide production can be achieved in the inner fuel cycle by means of proper arrangements and strategies. Concerning this problem a mathematical comparison of different HTR fuel cycles indicates that the Th-U cycle is the most suitable since it has relatively good conversion rate. A special feature of the thorium cycle is that an almost negligible small fraction of 100 ppm of Th-230 in Th-232 produces a considerable amount of U-232. This being itself a strong alpha emitter, it serves as the mother substance of further alpha emitters like Th-228 and Ra-224 leading to a high level of y-radiation. A combined HTR system of a conventional reactor and a near breeder has been investigated mathematically regarding its radioactive waste. The elements protactinium, neptunium, americium and curium as well as a 1% loss of thorium, uranium and plutonium pass into the waste during fuel reprocessing. However, due to the simultaneous operation of both reactors such an alpha waste presents only a moderately higher level of radioactivity than that of the natural uranium used for this purpose. Furthermore, calculations have shown that in case nuclear energy is exclusively applied to meet the demand of the world population, by the help of described strategy the permanently growing nuclear waste would never reach the present level of radioactivity caused by all the natural uranium reserves