The effective thermal convductivities developed here provide a method fo rpredicting (with a high level of confidence) a "best estimate" of peak cladding temperatures fo rspent nuclear fuel (SNF) assemblies in a dry environment. This paper describes the development of effective thermal conductivies for PWR and BWR assemblies as a methodology for performing SNF container thermal analyses. Over-predicting SNF cladding temperatures due to excessive conservatism can constrain container design and limit the capacity of potential design concepts. The analyses performed here indicate that the discrete SNF models are more accurate and realistic than other approaches for predicting SNF cladding temperatures. Further, the efective thermal conductivities, calculated using the SNF model results, wre found to be primarily a function of temperature, generally not a function of assembly heat load, and suitable for predicting best-estimate temperatures of PWR and BWR SNF assemblies in fill environments of helium, vacuum, nitrogen, and argon.
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