** Viva Energy falls as much as 0.4% to A$2.640; set to lose most since Jan. 2

** Fuel supplier's Geelong refinery in Victoria experienced power outage on Jan. 12 due to an external interruption to supply

** Co says outage led to unscheduled shutdown across all units

** Adds it would take between one and two weeks to resume normal production

** Stock on track for third consecutive session of losses

** VEA up 0.8% YTD as of last close

(Reporting by Rajasik Mukherjee in Bengaluru)

((Rajasik.Mukherjee@thomsonreuters.com;))