Neutron irradiation of modern KU-1 and KS-4V fused silica

Investigations performed in the late 1990s showed Russian KU-1 and KS-4V fused silica demonstrated the smallest degradation of transmittance among all quartz materials considered for ITER vacuum windows in visible range under neutron and gamma irradiation. Following a ten-year hiatus, production of KU-1 and KS-4V was recently restarted. New manufacturers claim their products meet previous standards and agreed to transfer samples to Kurchatov Institute for radiation testing. Both grades met total impurity content and unirradiated transparency requirements. Samples were irradiated with fast neutrons to fluences of 6 × 1016 and 1019 cm−2. These fluences significantly exceed the expected fluence for ITER vacuum windows. The visible range transmittance of both KU-1 and KS-4V decreased by 3–5% (5–25%) after lower (higher) fluence, respectively. Their transmittance was dramatically reduced in the UV range. In the visible range, the KU-1 material performed slightly better than the KS-4V material.