Contributions to the Ar background by research reactor operations.

Radioargon has been identified as a useful nuclide for verifying compliance with the Comprehensive Nuclear-Test-Ban Treaty. Use of Ar to identify a nuclear explosion requires quantification of contributions to the Ar background at a potential measurement site. A method of estimating Ar release activities using isotopes of radioxenon and radioargon has been developed in this paper. Numerical solutions to the system of equations describing air-activation in a reactor were used to determine ratios of release activities for Xe/Xe, Xe/Xe, and Ar /Ar as function of irradiation time and off-gas residence time prior to measurement and release. Published radioactive noble gas effluent data for the High Flux Isotope Reactor, HFIR (ORNL) from the year 1996 to 2010 were compiled as a test data set to predict the Ar release on a yearly basis. An average Ar release rate of 1.86 × 10 Bq per year was calculated. The estimated release rate was used as a source term for atmospheric transport to run a test case for Ar release over a typical HFIR operation cycle. Results showed that ground-level concentrations of Ar did not exceed the minimum detectable concentration for a Ar field measurement system beyond the immediate vicinity of the release point. [ABSTRACT FROM AUTHOR]