Russia’s large-scale military mobilization on Ukraine’s border has grim historic precedents.

But should the Kremlin pull the trigger, it will encounter a hazard that no invading army has ever faced before: 15 nuclear power reactors, which generate roughly 50% of Ukraine’s energy needs at four sites.

The reactors present a daunting specter. If struck, the installations could effectively become radiological mines. And Russia itself would be a victim of the ensuing wind-borne radioactive debris. Given the vulnerability of Ukraine’s nuclear reactors and the human and environmental devastation that would follow if combat were to damage them, Russian President Vladimir Putin should think again about whether Ukraine is worth a war.