Abstract. The Japanese ITER home team played crucial roles in studying radiation effects in diagnostics components, utilizing JMTR, under close collaborations among universities, JAERI and industries. In-situ studies of performance of the magnetic coil showed that the radiation induced electrical conductivity (RIC) is not a problem when a coil is made of a mineral insulating cable (MI-cable). Magnetic measurements could be carried out up to a few M Hz under the ITER relevant irradiation conditions. A JET-bolometer was irradiation-tested in the JMTR. A structure of the bolometer could withstand the 3 irradiation cycles, corresponding to the expected irradiation dose in the ITER. A few technical problems were found, such as increase of electrical conductivity of a gold meander due to nuclear transmutation of gold into mercury. We found that some optical fibers could be used even for visible application near burning plasma with a limited life. For infrared applications, several optical fibers could be found with a life-time far beyond the ITER whole operation period.