Russian billionaire Yury Antipov and his wife have been detained in connection to a fraud investigation, the state-run news agency TASSreported Monday, citing law enforcement sources. The news came on the same day that the billionaire’s steel plants in the city of Chelyabinsk were seized by the Russian government, with prosecutors arguing that the plants had been illegally privatized after the collapse of the U.S.S.R. in the early 1990s. “Antipov, the owner of the Chelyabinsk Electrometallurgical Plant, has been detained as part of a criminal fraud investigation,” a law enforcement source told…