Fuel cycle options for optimized recycling of nuclear fuel

Abstract

The accumulation of transuranic inventories in spent nuclear fuel depends on both deployment of advanced reactors that can be loaded with recycled transuranics (TRU), and on availability of the facilities that separate and reprocess spent fuel. Three recycling strategies are explored in this study: (1) Recycling in thermal Light 'Water Reactors (LWR) using CONFU technology (COmbined Non-Fertile and UO2 fuel), (2) recycling of TRU in fast cores of Actinide Burner Reactors (ABR), and (3) recycling of TRU with UO2 in self-sustaining Gas-cooled Fast Reactors (GFR). Choosing one fuel cycle strategy over the others involves trade-offs that need to be quantified. The CONFU, ABR, and GFR strategies differ from each other in terms of TRU loading in the reactor, net TRU incineration, capacities of recycling facilities needed, technology option availability, and flexibility. The CONFU and GFR are assumed to achieve zero net TRU incineration, while the ABR is a net consumer of TRU. The TRU loading is greatest in GFR and lowest in CONFU. While both CONFU and ABR require separation (of TRU from U) and reprocessing (recycling of TRUs from fertile-free fuel), the GFR is designed to, in equilibrium, recycle TRU+U after extraction of fission products only. It is assumed that thermal recycling is available in the short-term (2015), as opposed to recycling in fast reactors (2040). Finally, thermal recycling is the most flexible as either CONFU batches or regular LWR uranium batches can be loaded; the issue of running out of TRU fuel is therefore irrelevant for this option. A fuel cycle simulation tool, CAFCA II - Code for Advanced Fuel Cycles Assessment - has been developed. The CAFCA II code tracks the mass distribution of TRU in the system and the cost of all operations.

(cont.) The code includes a specific model for recycling plants deployment; as an industrial process occurring in facilities with given capacities and investment requirements. These facilities may operate with a minimum target capacity factor during the lifetime of the plant. The deployment of these facilities is also constrained by a user-specified ability to add recycling capacity within a given time interval. Finally, the CAFCA II code includes a specific model for recycling prices as a function of plants nominal capacities, which reflects the economies of scale that go with increasing the nominal capacity of recycling plants. Our first case-study identifies the optimal choice of fuel cycle option and recycling plants capacities as a function of the deployment of advanced fuel cycle technologies over the next hundred years and under the assumption of the US demand for nuclear energy growing at a 2.4% annual rate. Key figures of merit for comparison of the strategies are the reduction of TRU interim storage requirements, the maximization of TRU incineration, the minimization of the size of the fleets of recycling plants and fast reactors, and the fuel cycle cost. We found that it is not possible to minimize simultaneously (1) the construction rate of advanced reactors and advanced spent fuel recycling facilities, and (2) the construction rate of U02 spent fuel separation facilities. The latter was found to be more constraining than the first for purposes of TRU inventories reduction. We found also that reactor technologies with zero net TRU destruction rate can achieve total depletion of TRU inventories is spent fuel interim storage at a lower fuel cycle cost and with fewer recycling facilities than reactor technologies that incinerate TRU; the lower fuel cycle cost is achieved at the expense of a lesser reduction of total TRU inventories.

(cont.) Finally, we found that, if the construction rate of advanced nuclear technologies is large enough, the later introduction date of fast recycling schemes compared to thermal recycling schemes is not discriminatory, with regards to the reduction of TRU inventories in interim storage by 2100. The potential of multi-lateral approaches to the nuclear fuel cycle has recently been widely acknowledged. Cited benefits include cost attractiveness following from economies of scale, proliferation resistance and collaborative and more efficient nuclear waste treatment strategy. CAFCA II has been developed to quantify these trade implications for the back-end of the fuel cycle Three bi-lateral scenarios of partnerships have been examined between two regions: first a scenario where the "Fuel-leasing/fuel take-back" concept is implemented, second a scenario with "Limited Collaboration" at the back-end fuel cycle, where spent fuel recycling and advanced fuel fabrication are externalized in countries that have these technologies, and third a scenario of "Full Collaboration", under which two regions fully collaborate at the fuel cycle back-end: spent fuel inventories and advanced fuel cycle facilities are co-owned and comanaged. Our second case-study concentrates on optimizing the choice of (1) fuel cycle option, (2) spent fuel recycling plant capacities, and (3) partnership scenario by analyzing the implications of these choices for the LWR-CONFU, LWR/ABR, and LWR/GFR strategies. The nuclear fuel cycle is simulated in a two-region context from 2005 to 2100 under the assumption that one region represents the US growing at a 2.4% annual rate and the other region represents Brazil, Indonesia, and Mexico growing at a 7.4% annual rate until 2080, and at 2.4% afterwards.

(cont.) We found that a US partnership with Brazil, Mexico, and Indonesia, could be advantageous to the reduction of TRU storage in both regions if the construction rate of UO2 spent fuel separation plants would be larger than one 1,000 MT/yr plant every two years after 2050. We found also that, from the point of view of the spent fuel recycling industry, use of largest recycling plants with the lowest construction cost per unit of installed capacity becomes optimal only with multi-national approaches to the fuel cycle back-end.