Irradiation Damage in Inorganic Insulation Materials for ITER Magnets: A Review

摘要

A literature search on the irradiation resistance of inorganic insulators for theITER toroidal field superconducting magnets is reported. The materials included Al2O3, AlN, MgO, porcelain, SiO2, MgAl2O4, ZrO2, and mica. No in situ measurements of the 4-K compressive, shear, and electrical breakdown strengths after 4-K neutron irradiation were retrieved. Limited optical and thermal property measurements made on these insulators after cryogenic irradiations indicate that recovery occurs in ceramic oxides at ambient temperatures. Host atom amorphization has been demonstrated in Al2O3 at 77 K, but was not successful at 300 K. Apparently, host ion amorphization does not occur in most ceramic oxides at 300 K. Amorphization has evidently not been attempted in AlN, MgO, or MgAl2O4 at 77 K. Silicate-bonded structures, such as mica, porcelain, and silica, do amorphize at ambient temperature and are, at present, considered unacceptable unless proven otherwise by in situ electrical and mechanical property testing after 4-K irradiation. Zirconia, even if stabilized, will probably transform under neutron irradiation and is, therefore, considered unsuitable. Mica layers delaminated under low energy electron bombardment. Natural mica layers are porous, owing to spontaneous and induced tracks from U impurities. Tracks caused a decrease in electrical breakdown strength. Simulation of neutron irradiation by other radiation species is also reviewed in this report.