The use of advanced fuel cycles in CANDU is supported by more than 50 years of R&D. A number of facilities at AECL’s Chalk River Laboratories have supported, and continue to support, the development of advanced fuel cycles. Advanced fuel laboratories have been used to develop advanced bundle designs and LEU, MOX and thorium fuels, used either for irradiation testing in the NRU fuel irradiation loops or for reactor physics measurements in the ZED-2 reactor. Freon loops have been used to characterize bundle thermo-hydraulics. A variety of microscopes and hot cell facilities have been used to characterize the behaviour of advanced fuels and materials.

Prototypical irradiations have been carried out under CANDU reactor coolant conditions in the fuel irradiation loops in the NRX (National Research

Experimental) and NRU reactors. Thorium fuel irradiation took place early in the development of the CANDU reactor in the prototype NPD (Nuclear Power Demonstration) reactor. CANDU thorium, LEU and MOX fuels have been irradiated to burnups greater than 40 MWd/kg HE. Figure 11.6 shows a demountable bundle, which was developed for experimental fuel irradiation in the loops in the NRU reactor. The outer elements of this bundle can be removed, replaced with other elements, and the irradiation continued.

The ZED-2 reactor at the Chalk River Laboratories (Fig. 11.7) is a zero-energy critical facility, which has been used for the measurement of reactor physics parameters for a variety of CANDU advanced fuel cycles, including LEU, MOX and thorium. In ZED-2, CANDU fuel bundles are suspended in CANDU-type fuel channels hanging vertically from beams across the top of the core. The reactor provides a great deal of flexibility in the types of fuels, coolants, fuel channels and lattice pitches that can be examined.

Boczar (2003) has described AECL’s strategy for the development of advanced fuels and fuel cycles.

11.2 Sources of further information

I AEA (2002) is a comprehensive description of the CANDU and other heavy water reactors. Chapter 6 describes the state of the art on advanced fuel cycles at that point in time.

The Canadian Nuclear Society (CNS) (www. cns-snc. ca) has a list of conferences and conference papers sponsored by the CNS, including the Annual CNS Conference and the regular CNS International Conference on CANDU Fuel.

The Canadian Nuclear FAQ website (www. nuclearfaq. ca) contains much information on CANDU technology, as does the CANTEACH website (http:// canteach. candu. org).