Carbon-14 in waste packages for spent fuel in a tuff repository

Abstract

Carbon-14 is produced naturally by cosmic ray neutrons in the upper atmosphere. It is also produced in nuclear reactors, in amounts much smaller than the global inventory. About one-third of this is released directly to the atmosphere, and the other two-thirds remains in the spent fuel. Both the Environmental Protection Agency and the Nuclear Regulatory Commission have established limits on release of the \ in spent fuel. This is of particular concern for the proposed repository in tuff, because of the unsaturated conditions and the consequent possibility of gaseous transport of l *C as COj. existing measurements and calculations of the C inventory in spent.fuel are reviewed. The physical distribution and chemical forms of the C are discussed. Available data on the release of C from spent fuel in aqueous solutions and in gaseous environments of air, nitrogen, and helium are reviewed. Projected '*C behavior in a tuff repository is described. It is concluded that **C release measurements from spent fuel into moist air at temperatures both above and below the in situ boiling point of water as well as detailed transport calculations for the tuff geological environment will be needed to determine whether the 10CFR60 and 40CFR191 requirements can be met.

Spent fuel performance data: An analysis of data relevant to the NNWSI Project

“…Gas analyses of storage tests of spent fuel stored under inert atmospheres (helium and nitrogen) do not show significant releases of carbon-14. These results support the hypothesis that the observed release under oxidizing conditions is due lo the removal of carbon as COj from the outer surface of the Zircaloy cladding by reaction of the carbon with oxygen in the atmosphere (Van Konynenburg et al, 1986).…”

Strategy for experimental validation of waste package performance assessment

“…Spent Fuel -Leach tests with spent fuel have only been done under saturated conditions [147][148][149][150][151][152][153][154][155][156][157][158][159][160][161].…”

A study of thermally induced convection near a high‐level nuclear waste repository in partially saturated fractured tuff

“…The above estimate therefore indicates that in a partially saturated fractured medium, a strong large-scale convection will only occur in the gas phase, as opposed to the fully saturated case where the fractures will provide pathways for convective liquid flows. This is favorable to the nuclear waste isolation problem, since the possibility that some radionuclides may travel in the gas phase is remote with the notable exception of C •'• [Von Konynenburg et al, 1985Konynenburg et al, , 1986], most of the contaminants that could be released from the high-level nuclear waste packages can only be transported in the liquid phase. Having shown by the above simple estimate that large-scale gas convection phenomena should be induced in a partially saturated medium, we now proceed to a more detailed simulation of the heat and fluid transport on a regional scale.…”