A growing number of foreign residents in Korea who have contributed to the National Pension Service (NPS) for only short periods are using a loophole in the retroactive payment system to secure old-age pension benefits, with Chinese nationals accounting for a significant share of such cases, insiders at the state pension operator said Friday. The cases are fueling scrutiny of the scheme, which was originally intended to expand pension coverage for people with interrupted careers, and prompting calls for reform. Under current measures, individuals must have at least 10 years, or 120 months, of contributions to qualify for a monthly old-age pension. The back-payment system allows people who were exempt from paying pension premiums for certain periods to pay those missed premiums later in a lump sum. The payments are then added to their contribution records. The system was introduced in 1999 to help people maintain their pension rights after career interruptions caused by unemployment, marriage, childbirth and other circumstances. Up to 119 months of missed contributions can be paid retroac