The trapping behavior of hydrogen and its isotope in F82H ferritic/martensitic Steel

Full text of publication follows: For the development of fusion reactor materials, the characterization of trapping and releasing behavior of hydrogen and its isotopes is one of the key issues considering the influences on plasma parameters and tritium inventory. furthermore the injected hydrogen and helium atoms cause problems for the materials such as embrittlement or tritium retention. Recent movements show the consideration of using low-activation ferritic steels for both structural materials and the first wall. On the other hand, ferritic steels are also a candidate material for liquid-cooled high power spallation target for accelerator driven system (ADS), whereas the issues on the material development is also the hydrogen and helium atoms produced by high energy proton bombardments. F82H ferritic/martensitic steel is one of a candidate alloys for the first wall of fusion reactors and also for the container of spallation target for ADS. In the present work, the trapping behavior of deuterium in F82H under irradiation were studied using thermal desorption spectrometry (TDS) and TEM. The specimens were first irradiated with 1 MeV He+ ions at RT, 400 deg. C and 600 deg. C, and then the additional irradiations were performed with 325 keV D2+ ions at RT. After the irradiations, thermal desorption of D2 and He under heating with a ramping rate of 1 K/s were measured with high resolution quadruple mass spectrometer. At the same time, the samples for the microstructural study by TEM were prepared using focused ion beam system (FIB) from the same specimens. Pre-irradiation with helium ions caused remarkable effects on the trapping of injected deuterium. Normally most of the injected deuterium is desorbed between 100 deg. C and 300 deg. C for the case without helium irradiation. Meanwhile, additional large desorption occurred around 300 deg. C for the case with helium irradiation at 600 deg. C in this study, and the total amount of trapped deuterium was significantly increased. According to the TEM observation, the helium bubbles with the size of around 8 nm were densely formed by the pre-irradiation of helium. The additional desorption around 300 deg. C can be explained by the stress field around those highly pressurized helium bubbles acting as a trapping sites for deuterium. (authors)