Russian authorites are investigating the cause of an explosion at the nation’s largest hydroelectric plant, in southern Siberia. The explosion at a powerplant of the 6,400-MW Sayano-Shushenskaya hydroelectric dam, which was undergoing repairs, killed at least 12 workers and left as many as 64 others missing after lower sections of the plant flooded. News reports initially suspected a transformer exploded during repairs. The 800-ft-high, 3,168-ft-long dam was opened in 1978 and supplies energy to the region’s large aluminum smelters.

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