What was found
(CAN) AIRBORNE RETURN. WHILE ENROUTE TO DESTINATION THROUGH 15,000`, THE CREW ADVISED THAT THEY HAVE LOST THE NR 1 HYDRAULIC SYSTEM. THE NR 1 HYDRAULIC QTY QUICKLY WENT TO 0 AND THE PRESSURE WENT TO 0 PSI. THEY RECEIVED ALL ASSOCIATED MESSAGES. ADDITIONALLY, THE EDP RAN FOR 35 MINUTES WITH NO FLUID. THE FLIGHT RETURNED TO DEPARTURE POINT. MAINTENANCE ASSESSMENT/RECTIFICATION FOUND THAT THE NR 1 CASE DRAIN LINE IN THE AFT EQUIPMENT BAY HAD A HOLE CHAFED INTO IT. CONSIDERING THAT THE EDP RAN FOR AN EXTENDED TIME WITHOUT FLUID, IT WAS REPLACED IAW AMM 29-11-01. ACFT HOURS: 26349:11. CYCLES: 20394.