What was found
(CAN) FLIGHT NR1179DURING REFUELING A FUEL VALVE CIRCUIT BREAKER POPPED. RESETTING WAS NOT SUCCESSFUL (C/B POPPED AFTER VERY SHORT TIME). MAINTENANCE REPLACED L/H REFUEL/DEFUEL SHUTOFF VALVE, S/N ON AV24B1318D-1, S/N OFF RN20152. AIRCRAFT GROUND CHECKED SERVICEABLE AND AIRCRAFT RETURNED TO SERVICE.CIRCUIT BREAKER POPPED AGAIN IN FLIGHT AND CREW ELECTED TO RETURN TO BASE - AIRCRAFT LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTION FOUND THE NR1 FUEL VALVE CIRCUIT WAS SHORTING OUT - ENGINEERS REPLACED THE REFUEL/DEFUEL SELECTOR PANEL AND GROUND CHECKED THE SYSTEM AS SERVICEABLE. AIRCRAFT RETURNED TO SERVICE WITH NO FURTHER INCIDENTS TO REPORT.