The detectability of the Wigwam underwater nuclear explosion by the radionuclide stations of the International Monitoring System

Highlights: • The detectability of the 1955 Wigwam nuclear explosive test has been investigated. • The radionuclide inventory and atmospheric transport has been modelled. • High probability of detection at Wake Island, Guam and Alaska monitoring stations. - Abstract: The Comprehensive Nuclear-Test-Ban Treaty (CTBT) bans all nuclear explosions, including those detonated from an underwater nuclear explosion. To improve the understanding of the radionuclide signatures of such an event, and whether it would be detectable under the verification regime of the CTBT, the 1955 Wigwam underwater nuclear explosive test has been modelled. Inventory calculations and atmospheric transport modelling has been performed to estimate the activity at the radionuclide stations (RN) of the International Monitoring System (IMS). This has utilized reported release values (0.92%) and meteorological data from the event. The research shows that there is a high probability that Wigwam would have been detectable at U.S. IMS stations at Wake Island (RN77) at 8.4 d, Upi, Guam (RN80) at 10.7 d and Sand Point, AK (RN71) at 13.7 d. At these locations, the majority of IMS relevant radionuclides were fission products, such that additional radionuclides from the seawater activation had largely decayed before reaching the stations.