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.