The incident occurred at around 12:54 p.m. (03:54 GMT) in an ADD laboratory building. The explosion, whose cause is still unknown, killed one employee aged over 60. ADD was cited as saying that the deceased had been a contract researcher who was rehired after retirement, Yonhap reported.
Police were cited as saying that the explosion, which destroyed half of the laboratory building, could occur during ammunition-related experiments.
Local authorities are reportedly investigating the circumstances of the incident.
South Korean President Yoon Suk-yeol offered his condolences to the relatives and colleagues of the deceased and ordered a thorough investigation into the cause of the explosion.