Future requirements of nuclear data for the handling, reprocessing and disposal of spent nuclear fuel

Abstract

This paper considers the decay heat and radiation source terms from a perspective based upon recent validation results for JEFF-3.1. Currently used fuel and reactor systems have sufficient measurements of irradiated fuel to justify safety cases, however until such measurements are available for novel systems these must be studied based upon the accuracy to which important nuclides can be determined from the basic nuclear data, both the individual nuclide concentrations calculated and their uncertainties must be considered and the subsequent effect on operation parameters and costs estimated. It should be noted that future facilities will need to be designed for both the calculated quantities and, typically, twice the uncertainty on the important operational parameters. Any nuclear data which dominates the uncertainties need to be identified as well as any biases so that improvements can be made to the basic nuclear data. An initial study is described considering only thermal reactors and some conclusions made about how these could be extended for novel systems. Currently the majority of commercial nuclear power produc- tion uses two industrially applied fuel cycles that are well quantified for safety and licensed within the nations con- cerned: the once through and the U/UOX/MOX recycling op- tions in thermal reactors. These require the handling, transport and storage of the spent nuclear fuel; and for reprocessing the chemical separation of uranium and plutonium, and storage of the arising wastes in suitable material matrices for disposal. Fuels and wastes from prototype reactors and chemical processing plants, and possible future reactor systems (e.g., GEN-IV, ADS, advanced reprocessing and transmutation tech- nologies) will have to be dealt with by those responsible (e.g., private utilities or Governments) in current and future regu- latory frameworks. These fuels may be considerably different from those currently handled; composed of different materials, be irradiated in different reactors, have different burn-up and cooling; and so will have different requirements for opera- tions and safety. Higher decay heat requires either greater cooling for the fuel, or requires less fuel to be transported, stored or processed at one time in existing facilities leading to greater costs. Similarly, larger or significantly different radiation source terms (gamma-ray and neutron) would lead to similar issues with required shielding, again increasing costs. In addition, these fuels and wastes may be outside of currently accepted parameters for existing facilities and require new facilities to be built to accept them. This paper considers the decay heat and radiation source terms from a theoretical perspective based upon recent val- idation results for JEFF-3.1, ref. (1). Currently used fuel and reactor systems have sufficient measurements of irradiated fuel to justify safety cases, however until such measurements are available for new systems they must be studied based upon the accuracy to which important nuclides can be determined. Both the individual nuclide concentration calculated and its uncertainty must be considered and the subsequent effect on costs estimated. It should be noted that facilities will need to be designed for both the calculated quantity and, typically, twice the uncertainty on the important parameters. Any nuclear data which dominates the uncertainties need to be identified as must any biases so that improvements can be made.