(Adds details of the unit's capacity and background)
SEOUL, Aug 10 (Reuters) - GS Caltex, South Korea's second-largest oil refinery, said it has shut a heavy oil upgrading unit after a fire mishap on Thursday.
The blaze, which is now under control, broke out in the heavy oil upgrading unit or Vacuum Residue Hydrocracker (VRHCR), at GS Caltex's Yeosu refinery, located in southwest of Seoul.
GS Caltex has a combined 274,000 barrels-per-day of heavy oil upgrading capacity to convert fuel oil into more expensive and cleaner fuel such as gasoline and diesel.
The fire hit the refiner's 66,000-bpd hydrocracker, the spokesman said.
No casualties have been reported, the spokesman said, adding that the cause and damage to the unit were still being assessed.
He said it was too early to tell if there would be any impact on the refinery's operations.
A week ago, GS Caltex shut its No.2 Aromatics plant after a fire occurred at an electrical substation in the refinery.
GS Caltex, equally owned by GS Energy Corp, a unit of GS Holdings and U.S. oil major Chevron Corp, runs a 790,000-bpd refinery in Yeosu. (Reporting by Jane Chung; Editing by Joseph Radford and Sherry Jacob-Phillips)