The Hecla–Kemp model's predicted Burevestnik radionuclide signature is an air-activation product, mechanistically distinct from the fission-product isotopes reported after the 2019 Nyonoksa accident

Hecla and Kemp's model of the Burevestnik's radionuclide emissions quantifies only one of three possible source terms they identify — "activated air, activated structural material released by erosion, and—for direct-cycle systems—fission products escaping from the fuel." Their result: "the dominant short-term signature is ⁴¹Ar, which accounts for at least 95% of the activity one hour after production," with ⁸⁵ᵐKr and ¹⁴C as secondary tracers, concentrated "within roughly a kilometer of the vehicle."

This is a neutron-activation signature — air struck by escaping neutrons, not fuel breached. It is a different physical process from what was actually reported after the August 2019 Nyonoksa (Arkhangelsk Oblast) accident, the real-world event most often linked to a Burevestnik failure. There, Rosgidromet reported detecting the short-lived fission products ⁹¹Sr, ¹³⁹Ba, ¹⁴⁰Ba, and ¹⁴⁰La — fission products whose precursors are noble gases (⁹¹Sr from a krypton precursor; the barium and lanthanum isotopes from xenon precursors). Spykman et al. 2021 read this pattern — fission products present, volatile ¹³¹I conspicuously absent — as consistent with a release of only noble gases (Kr/Xe) that then decayed into the detected elements, paralleling the 2010 DPRK event, and reached an overall null result in their own sample search. Either way it is a fission signature, mechanistically distinct from the neutron-activation ⁴¹Ar the Hecla–Kemp model predicts.

The isotope classes differ by production mechanism, not merely by flight phase. Nyonoksa was a ground/recovery accident, and that alone would make it an indirect test of an in-flight prediction — but the deeper reason it doesn't test the Hecla–Kemp signature is that a fission-product leak and an air-activation plume are not the same kind of event to begin with. See question-verify-burevestnik-radioactive-exhaust-corroboration for the tracked verification this bears on.