KYIV, Ukraine (AP) – Ukraine’s nuclear energy operator says Russian forces have performed secret work at Europe’s largest nuclear power plant. The activity could shed light on Russia’s unsubstantiated claims that Kyiv’s forces are preparing a “provocation” involving a radioactive device. Ukrainian nuclear operator Energoatom said Tuesday it “assumes” the Russians are preparing “a terrorist act using nuclear materials and radioactive waste” stored at the plant. It says the destruction of containers of spent nuclear fuel would lead to a radiation accident and the contamination of several hundred square kilometers (miles) of adjacent territory. Ukraine has dismissed Moscow’s claim as an attempt to distract attention from the Kremlin’s own alleged plans to detonate a dirty bomb.