A performance estimate for the detection of undeclared nuclear-fuel reprocessing by atmospheric 85Kr

To test the sensitivity of using atmospheric 85Kr to detect undeclared separation of plutonium from irradiated nuclear-reactor fuel, measurements of atmospheric 85Kr taken in Tsukuba, Japan are analyzed to determine: (1) a lower limit of detection for discovering anthropogenic 85Kr emissions, (2) the probability of detecting plutonium separation at the Tokai Reprocessing Plant, and (3) the extent to which these results can be generalized to other sites. A LLD of at least 3.4σ = 0.14 Bq/m3 with a theoretical false-positive rate of 0.05% is recommended for safeguards' purposes. At this threshold, the continuous separation of 100, 300, and 900 g equivalent weapon-grade plutonium per day was found to correspond to 10%, 50%, and 80% probability of detection, respectively. The smallest detected concentration was for the continuous separation of 45 g/day, with a probability of detection of about 0.6%. It was found that the detection rate is determined predominately by the weather.