The 1986 Chernobyl nuclear disaster in Ukraine was caused by a flawed Soviet reactor design and mistakes made by the plant's untrained operators. During a test with safety protocols deactivated, a series of errors caused a power surge and steam explosion, destroying the reactor and releasing massive amounts of radiation across Europe. Over 4,000 deaths are expected from long-term health effects, though the full consequences are unknown. The disaster highlighted issues in the Soviet nuclear program and had wide-ranging environmental and political impacts.