High neutron economy and good fuel utilization make the CANDU reactor complementary to LWRs, since the used fuel from the latter has more than enough fissile material to fuel a CANDU reactor. One such fuel cycle is RU from reprocessed LWR fuel. The use of RU in a CANDU reactor is simpler, more economical and derives more energy than would be obtained by re-enrichment followed by irradiation in an LWR. RU could be used as-is in a CANDU reactor, where a U-235 level of 0.9% would result in a burnup of about 14 MWd/kg HE. Alternatively, a simpler option would be to down-blend the RU with depleted uranium (DU) from enrichment plant tails to form ‘natural uranium equivalent’ (NUE) fuel. This would make use of DU, which otherwise is of little value, while the reactor licensing and operation would be essentially unchanged from the use of natural uranium. A demonstration irradiation of 24 CANDU NUE bundles successfully took place in 2010 in two separate channels at the Qinshan Unit 1 CANDU reactor in Haiyan, China (Jioa et al, 2009).

DUPIC (Direct Use of used PWR fuel In CANDU) is another example of a CANDU fuel cycle that is synergistic with the LWR. Used LWR fuel has about 0.9% U-235 and 0.6% fissile plutonium, giving a total fissile content of around 1.5%. The high neutron economy of the CANDU reactor results in the ability to use that material without removal of fission products. DUPIC involves thermal/ mechanical processing of used LWR fuel to convert the LWR pellets into new CANDU pellets, without selective removal of isotopes. In the DUPIC process, the cladding is first removed. The LWR pellets are then subjected to a series of oxidation and reduction cycles, which convert the pellets to powder, which can then be milled, if necessary, before the powder is pressed and sintered into new CANDU pellets. The pellets are loaded into new CANDU fuel sheaths. Of course, the energy derived from the used LWR fuel is not as great as it would be if some or all of the fission products were to be removed. However, the process has a high degree of proliferation resistance, is simpler and is expected to be more economical than conventional reprocessing. AECL and the Korean Atomic Energy Research Institute (KAERI) collaborated on the DUPIC cycle, along with the US Department of State. In AECL, three full-length CANDU DUPIC fuel elements were fabricated from used LWR fuel, and successfully irradiated in the NRU (National Research Universal) reactor (Floyd et al., 2003).

Whether or not DUPIC becomes commercialized, it is illustrative of the unique recycling opportunities between LWR and CANDU reactors.