The Korean research program on nuclear technology requires various in-pile tests to evaluate the safety of currently operating nuclear power plants and develop a future nuclear system. HANARO (High-flux Advanced Neutron Application Reactor) provides a peak thermal and fast flux of 5.0 × 1014 n/cm2 · s (E < 0.625 MeV) and 2.1 × 1014 n/cm2 · s (E > 0.821 MeV), respectively, at 30 MW maximum thermal power. A capsule system has been developed for irradiation tests of nuclear materials and fuels at the core region. Extensive efforts have been made to establish the design and manufacturing technology for various capsules and a temperature control system, which should be compatible with HANARO’s characteristics. The capsule system has been actively utilized for various materials and fuel irradiation tests requested by users from research institutes, universities, and industries. Since 1995, more than 10,000 specimens have been irradiated using the developed capsule system. Presently, new irradiation technologies, such as a high-temperature irradiation capsule for a very-high-temperature reactor and a sodium-cooled fast reactor, and a low-temperature irradiation capsule for a research reactor, are being developed. These technologies will be completed with the development of instruments such as a linear variable differential transformer, a micro-electric heater, and a self-powered neutron detector in the near future, and they will be used for the Generation-IV nuclear system in Korea.