Radiation effects on deuterium permeation for PLD alumina coated Eurofer steel measured during 1.8 MeV electron irradiation

Abstract

Tritium permeation through structural materials in future fusion reactors is an extremely important issue due to both radiological concerns and tritium self-sufficiency. In the past many efforts to minimize tritium losses have been made and permeation barriers are considered the best method to reduce them. Alumina is one of the main candidates for such barriers due to its chemical stability and hydrogen isotope permeation reduction factor. In this work pulsed laser deposited (PLD) alumina on Eurofer steel has been studied in terms of deuterium permeation. A reduction factor of about 1000 compared to bare material in the temperature range RT-450 °C was measured. In order to study deuterium permeation during irradiation the Radiation Induced Permeation and Release (RIPER) facility at Ciemat was used. Contrary to expectations the permeation through PLD alumina coated Eurofer was observed to decrease during irradiation. This radiation effect was explained making use of thermostimulated desorption (TSD) experiments. TSD measurements were carried out for both electron irradiated and unirradiated alumina samples and the results showed that radiation induced deuterium back desorption from alumina occurred in this way reducing the overall permeation value during irradiation. Finally, the microstructural study of the irradiated coatings showed that some surface damage appears but not cracking or coating debonding was observed in agreement with the good behaviour observed in terms of deuterium permeation for the irradiated coatings.