UPDATE 1-Mississippi reopened after towboat collision

(Recasts, updates with Mississippi River reopened, no barge sunk, Valero refinery unaffected)

HOUSTON, May 19 (Reuters) - The U.S. Coast Guard closed the Mississippi River south of Memphis, Tennessee, for several hours Tuesday after a vessel collision set 26 barges adrift.

The Coast Guard reopened the river 15 hours after shutting it, following recovery of barges set free by the collision of two towboats and a channel survey showing no barge had sunk.

Valero Energy Corp (VLO.N) said its 195,000 barrel per day refinery in Memphis was unaffected. "It would have to be a lengthy closure," said Valero spokesman Bill Day.

The Coast Guard said vessel traffic was halted between Mile Marker 595 (958 km) and Mile Marker 640 (1,030 km) after a predawn vessel collision near Helena, Arkansas.

Memphis is at Mile Marker 736 (1,184 km), nearly 100 miles (161 km) north of the accident scene, a Coast Guard spokeswoman said.

The collision involved the towboats Golden Eagle and Mary Ann. There were no reports of injuries or pollution but investigation continues, the news release said.

The Coast Guard originally said one barge may have sunk near the accident scene.

Valero's Memphis plant receives crude oil by pipeline, so its feedstock supply would not be affected by shutdown of the river, Day said.

The plant ships some products by barge on the river, but most of its output travels by truck, Day said. (Reporting by Bruce Nichols; Editing by David Gregorio)