[en] A laser ablation decontamination technology which is reportedly effective for a removal of fixed contaminants has been developed for three years as the first stage of the development. Lab scale experimental equipment was fabricated and the process variables have been assessed for determination of appropriate decontamination conditions at the laser wave lengths of 1,064 nm and 532 nm, respectively. The decontamination tests using radioactive specimens showed that the decontamination efficiency was about 100 which is quite a high value. An electrokinetic-flushing, an agglomeration leaching and a supercritical CO2 soil decontamination technology were development for a decontamination of radioactive soil wastes from the decommissioned sites of the TRIGA research reactor and the uranium conversion facilities. The remediation monitoring key technologies such as a representative sample taking and a measurement concept for the vertical distribution of radionuclides were developed for an assessment of the site remediation. Also an One-Dimensional Water Flow and Contaminant Transport in Unsaturated Zone (FTUNS) code was developed to interpretate the radionuclide migration in the unsaturated zone. The chemical gel decontamination process with more effective drying, rheological and decontaminating properties than the existing commercial gel decontamination technology has been developed for a decontamination of the fixed contamination of extremely high radiation facilities. Its performance were verified for the in-situ large scale application through the demonstration test using the radioactive facilities in KNFC contaminated with uranium