CLAIRTON, Pa. - United States Steel Corp. has proposed a $1 billion plan to upgrade one of its coke-making facilities - the country's largest - with technology that would reduce emissions.

The Pittsburgh company said the improvements at the Clairton plant would ensure the long-term viability of its Mon Valley Works operations, create more than 600 construction jobs, and ensure thousands of existing jobs. The Mon Valley Works operations employ more than 3,000 people.

Coke is a fuel used in steel production. It is made by baking coal in ovens to remove impurities, a process that has been known to cause pollution.

The project would include the construction of two coke batteries, or sets of ovens, to replace aging ones and the rehabilitation of other batteries. Some batteries may be 50 or more years old.

The plan would cut the number of coke ovens by 235 and reduce by 30 percent the number of openings through which emissions might pass, said John Surma, U.S. Steel's chairman and chief executive officer.

The improvements also may include construction of a power-cogeneration plant to supply electricity to the Mon Valley Works, which includes Clairton and two other facilities.

The Clairton plant remains critical not only to the Mon Valley Works but the success of the entire corporation, Surma said. He said the capital investment program, which hinges on the granting of environmental permits and approval by U.S. Steel's board of directors, would be the largest in the company's history.

"That's a significant investment even for a company the size of United States Steel Corp.," Surma said.

The Clairton plant's coke goes to U.S. Steel's nearby Edgar Thomson steel plant and to factories in Indiana, Michigan, Illinois and Alabama.