In Canada's long-term waste management documentation spent fuel is referred to as "used nuclear fuel" or "used reactor fuel", which is an appropriate term.
George Stanford discusses some fuel recycling options. An strategy to be added to this list is the use of CANDU/LWR synergism, driven by the simple fact that spent (used, irradiated, long-in-the-tooth, put-out-to-pasture) LWR fuel is still enriched in U-235, relative to natural uranium, and therefore can still produce energy in a CANDU reactor. A brief overview of this option is given in the following extract from a recent paper of mine (full text at
http://www.magma.ca/~whitlock/cnf/brat_fuel.htm):
"CANDU/LWR Synergism
"Although little incentive exists for the extraction of fissile material from spent CANDU fuel, based upon its low fissile concentration, the opposite is true for spent LWR fuel. Depending upon initial enrichment and burnup, spent LWR fuel contains about 0.9 wt% U-235 and 0.6% fissile plutonium.
Since the U-235 content exceeds that of natural uranium, CANDU technology offers the unique option of uranium recycling without reenrichment. This "recovered uranium" (RU) fuel cycle would have all the benefits of SEU fuel cycles described above, and would extract at least 25% more energy from the mined uranium going into the LWR fuel cycle. Compared to reenriching the RU for use in an LWR, about twice as much energy can be extracted by burning it without reenrichment in a CANDU reactor.
"Twice the energy can also be extracted from burning LWR-recycled plutonium in a CANDU reactor, compared to using an LWR. In general, therefore, CANDU technology is an efficient vehicle for the recovery of fissile material at the back end of the LWR fuel cycle.
"The remaining material after fissile-material recovery would be the actinide and fission-product waste. Responding to international interest in the destruction of actinide waste in reactors, CANDU fuel cycles that burn this material have been studied (Chan, 1997; Verrall, 1998). An "inert-matrix" carrier using SiC has high thermal conductivity, leading to low fuel temperatures and other safety benefits. The absence of uranium precludes the creation of additional plutonium and higher actinides, and leads to high net destruction rates. Studies using the unadjusted mix of plutonium and actinides from spent LWR fuel show a net destruction efficiency of 60% for the total actinide inventory, and 90% for the fissile inventory.
"In addition to its high neutron economy, the CANDU reactor's on-power refuelling capability is key to the success of this process. With no uranium in the initial fuel mix, reactivity drops rapidly and must be matched by an increased fuelling rate. The refuelling strategy can be optimized by shuffling bundles within and between channels.
"CANDU technology offers another unique option for the back end of the LWR fuel cycle, which completely avoids the need for wet reprocessing and fissile-material recovery. The "DUPIC" fuel cycle, or "direct use of spent PWR fuel in CANDU", utilizes the non-separated, non-enhanced waste product of LWRs directly as CANDU fuel (Keil, 1992).
"The transfer from LWR to CANDU can be literally "direct", involving only the cutting of spent LWR fuel rods to CANDU length (~50 cm), resealing (or double-sheathing), and reengineering into cylindrical bundles suitable for CANDU geometry.
"Alternatively, a dry reprocessing technology has been developed which removes only the volatile fission products from the spent LWR fuel mix (Lee, 1998; Sullivan, 1998). After removal of the cladding, a thermal-mechanical process is used to reduce the spent LWR fuel pellet to a powder, which is then sintered and pressed into CANDU-sized pellets.
"The DUPIC process is much simpler than conventional wet-chemistry techniques for reprocessing, and promises to be cheaper. It presents a significant anti-proliferation benefit as well, since radioactive fission products and fissile material are not separated. In addition, since the heat load of spent DUPIC fuel is similar to that of the original spent LWR fuel, disposal requirements do not increase. However, since approximately 50% more energy can be derived from LWR fuel by burning it as DUPIC fuel in a CANDU reactor, the disposal cost is expected to be lower than either spent LWR or CANDU fuel (Baumgartner, 1998).
"Between the extremes of conventional reprocessing and the DUPIC fuel cycle, a spectrum of options exists. The CANDU reactor's high neutron economy offers many options for exploiting the CANDU/LWR synergism, allowing customization to meet local requirements and capabilities. Pursuing these various options requires international cooperation, such as the Canada-South Korea partnership that has pioneered the DUPIC process. South Korea has a fleet of both LWR and CANDU reactors, and can thus benefit from the synergism within its existing nuclear infrastructure (Lee, 1998)."
[J.J. Whitlock, "The Evolution of CANDU Fuel Cycles and Their Potential Contribution to World Peace", IYNC 2000, Bratislava, Slovakia, April 2000, published on The Canadian Nuclear FAQ at
http://www.magma.ca/~whitlock/cnf/brat_fuel.htm]
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Jeremy Whitlock
"The Canadian Nuclear FAQ": www.ncf.ca/~cz725