Uranium fuels, heavy element separation

Heavy Element Separation for Thorium-Uranium-Plutonium Fuels... 

The heavy water reactor was developed in Canada and is known as the CANDU reactor. The D2O is used as both coolant and moderator. The relative moderating efficiency of various materials is given in Table 7.11. Because of the superior moderating property of D2O, it is possible to use natural uranium as the fuel in the form of UO2 pellets in zircaloy tubes. This makes the CANDU one of the best designed reactors in the world. The coolant cycle and the moderator are separate flow circuits shown in Fig. 7.6. The fuel elements in the pressure tubes and the D2O flow is shown in Fig. 7.7 where the coolant is at about 293°C and 100 atm pressure. The moderator is at lower temperature. The efficiency is rated at 29%. ... 

On chemical separation of the uranium from the irradiated thorium, the is, of course, removed along with the It does not itself represent a serious radiation hazard and, since it has a long half-life, the buildup of its daughter Th in the extracted uranium is relatively slow. Consequently, it is possible to avoid the need for heavy shielding and remote handling of the recycle U provided that the fabrication of the fresh fuel elements is done within a short time of the separation of the uranium from the irradiated fertile material. 

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