The question of what should be done with spent nuclear fuel still awaits a satisfactory and generally acceptable answer. The easiest way to recover the U and Pu in LWR spent fuel is the complete coprocessing, which yields a pure U + Pu product with a total fissile content of 1.4 to 1.5 weight percent. For fueling a LWR with that U + Pu mixture, it is necessary to blend it with a fissile makeup; whereas such mixture can be directly used to fuel a CANDU reactor. Another scenario in the same context is the so-called DUPIC, direct use of PWR spent fuel in CANDU. This study focuses on burnup analyses of these two recycling scenarios in a PWR-CANDU tandem system. Supplementary burnups achievable in CANDU-6 are computed using the full-core geometry and nonlinear reactivity model with MONTEBURNS, and based on those, natural U requirement and nuclear resource utilization are estimated. It is found that significant additional burnups can be attained in CANDU-6 in both cases, and this reflects meaningful reductions on natural U requirement and gains on nuclear resource utilization. Since fission products and minor actinides (Np, Am and Cm, mainly) are not present in CANDU fuel in the complete coprocessing, all the positive effects are more pronounced in that case, as expected. (C) 2016 Elsevier Ltd. All rights reserved.