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Comparative study of plutonium burning in heavy and light water reactors.

Conference ·
OSTI ID:977018

There is interest in the U.S. and world-wide in reducing the burden on geological nuclear fuel disposal sites. In some disposal scenarios, the decay heat loading of the surrounding rock limits the commercial spent fuel capacity of the sites. In the long term (100 to 1,500 years), this decay heat is generated primarily by actinides, particularly {sup 241}Am and {sup 241}Pu. One possible approach to reducing this decay-heat burden would be to reprocess commercial spent nuclear fuel and use intermediate-tier thermal reactors to 'burn' these actinides and other transuranics (plutonium and higher actinides). The viability of this approach is dependent on the detailed changes in chemical and isotopic compositions of actinide-bearing fuels after irradiation in thermal reactor spectra. The intermediate-tier thermal burners could bridge the commercial water-cooled reactors and fast reactors required for ultimate consumption of the transuranics generated in the commercial reactors. This would reduce the number of such fast reactors required to complete the mission of burning transuranics. If thermal systems are to be used for the transmutation mission, it is likely that they would be similar to or are advanced versions of the systems currently used for power generation. In both the U.S. and Canada, light- and heavy-water-cooled thermal reactors are used for power generation in the commercial nuclear sector. About 103 pressurized- and boiling- light water reactors (PWRs and BRWs) are deployed in the U.S. nuclear industry while about 18 CANDU (heavy-water-cooled) reactors are used in the Canadian industry. There are substantial differences between light and heavy water-cooled reactors that might affect transmutation potential. These arise from differences in neutron balance of the reactors, in neutron energy spectra, in operational approaches (e.g., continuous refueling enhancing fuel burnup), and so on. A systematic study has been conducted to compare the transmutation potentials of CANDU and PWR systems using (U,Pu)O{sub 2} mixed oxide fuels. First, we examine and compare the isotopic evolution of plutonium-containing fuel under irradiation in these reactor types to understand the physics processes involved. The core-physics parameters to be compared for these systems are generated using two-dimensional lattice physics models for a single fuel assembly that is representative of the whole-core (e.g., using the linear reactivity model). Results from a parametric study of the discharge burnup as a function of the Pu fraction in the initial heavy metal are presented for each system. The Pu consumption level, minor actinides buildup level, and the masses destroyed per unit energy generation are summarized and compared. In addition, assessment results for a simple plutonium recycling concept in realistic CANDU and PWR cores are presented. In these cases, plutonium from commercial spent PWR fuel will be separated and burned in realistic intermediate thermal burner reactors using (U,Pu)O{sub 2} mixed oxide fuel. The spent fuel from this thermal burner will be separated and the resulting Pu will be burned in a second pass through the thermal burner reactor. The resulting transuranics are assumed to then be burned in a fast burner reactor. The impact of using the spent fuels of these systems on the core performance of the fast burner reactor and the required numbers of the various reactor types will be discussed.

Research Organization:
Argonne National Laboratory (ANL)
Sponsoring Organization:
USDOE; AECL of Canada
DOE Contract Number:
AC02-06CH11357
OSTI ID:
977018
Report Number(s):
ANL/NE/CP-58667
Country of Publication:
United States
Language:
ENGLISH