Mechanical strength of various cyanate ester/epoxy insulation systems after fast neutron irradiation to the ITER design fluence and beyond

To ensure secure operation of the magnet coils, the insulation system must keep its mechanical strength over the whole plant lifetime in a gamma and fast neutron radiation environment. Recent results on cyanate ester (CE)/epoxy blends demonstrated their mechanical integrity after irradiation to the ITER design fluence of 1 x 1022 m-2 (E > 0.1 MeV). For economic reasons, the cyanate ester content should be kept as low as possible due to the higher price compared to traditional epoxy resins. Therefore, the optimal composition of cyanate ester and epoxy is of great importance. In this study R-glass fiber/Kapton reinforced cyanate ester/epoxy blends with different epoxy resins and epoxy content were investigated. Short-beam shear and static tensile tests were carried out at 77 K prior to and after irradiation to a fast neutron fluence of 1 x 1022 and 2 x 1022 m-2 (E > 0.1 MeV), which was done in the TRIGA reactor (Vienna) at ambient temperature (340 K). In addition, tension-tension fatigue measurements were performed in the load- and strain- controlled mode to simulate the pulsed operation conditions of ITER