The 4th SINQ Target Irradiation Program (STIP-IV) was performed in 2004 and 2005. More than 1000 specimens from about 40 kinds of materials were irradiated up to 27dpa and 2300appm He in the temperature range of 80–550°C. The majority of specimens were irradiated in helium gas environment. Some specimens were irradiated in contact with lead and lead–bismuth eutectic. Neutron radiography inspections on specimen and target rods were performed before and after irradiation, which revealed some interesting features of the target rods with thermal couples. Neutronic calculations were performed using the proton distribution profile obtained by γ-mapping on the beam window of the AlMg3 target container after irradiation. Irradiation parameters of the specimens such as proton and neutron spectra and fluxes, heat deposition, irradiation dose in terms of displacement damage (dpa), helium and hydrogen concentrations were calculated. Most of the specimens were retrieved. But, more than 360 tensile and TEM specimens were lost due to a leak in a specimen rod occurred during irradiation.

In the European EUROTRANS/DEMETRA program, the synergistic effect of radiation damage and helium on microstructure and mechanical properties of two 9Cr 1Mo ferritic/martensitic (FM) steels T91 and EM10 was evaluated after irradiation in SINQ targets. In addition, the helium induced effect was investigated using helium implanted specimens. The results demonstrate that helium can induce significant embrittlement effect in FM steels as shown by the tremendous increase in ductile-to-brittle transition temperature, the great reduction in ductility and fracture toughness at>∼15dpa and 1000appm He and the occurrence of intergranular fracture mode. Further, high-density helium bubbles can produce pronounced hardening effect.

In this work metallography investigations and microhardness measurements have been performed on 15 ferritic/martensitic (FM) steels and 6 weld metals irradiated in the SINQ Target Irradiation Program (STIP). The results demonstrate that all the steels have quite similar martensite lath structures. However, the sizes of the prior austenite grain (PAG) of these steels are quite different and vary from 10 to 86μm. The microstructure in the fusion zones (FZ) of electron-beam welds (EBWs) of 5 steels (T91, EM10, MANET-II, F82H and Optifer-IX) is similar in respect to the martensite lath structure and PAG size. The FZ of the inert-gas-tungsten weld (TIGW) of the T91 steel shows a duplex structure of large ferrite gains and martensite laths. The microhardness measurements indicate that the normalized and tempered FM steels have rather close hardness values. The unusual high hardness values of the EBW and TIGW of the T91 steel were detected, which suggests that these materials are without proper tempering or post-welding heat treatment.

The present work aims to investigate the susceptibility of ferritic/martensitic steels of different strength to the embrittlement of liquid Pb–Bi eutectic (LBE). Slow strain rate tensile (SSRT) tests on specimens of the T91 steel in three tempering conditions at 500, 600 and 760°C were conducted in Ar and in LBE at temperatures between 150 and 500°C. For the specimens tempered at 760°C (the normal tempering condition) the susceptibility of the steel to LBE embrittlement appeared at temperatures between 300 and 450°C. With increasing the strength of specimens by lowering the tempering temperature, specimens tempered at 600 and 500°C demonstrated more pronounced embrittlement effects, reflected by wider and deeper ‘ductility-troughs’. The results suggest that ferritic/martensitic steels with higher strength are more susceptible to LBE embrittlement. The LBE embrittlement effects can be attributed to the decrease of fracture stress resulted from the ‘weakening inter-atomic bond’ by LBE contacting at crack tips.

The susceptibility to liquid metal embrittlement (LME) of the T91 steel was studied by performing 3-point bending tests in liquid lead–bismuth eutectic (LBE), and for comparison, in argon (Ar) atmosphere as well. The specimens of T91 with different heat treatments were tested to access the hardening effect on the fracture toughness of the steel after exposure in LBE. The results showed that the fracture toughness of steel was reduced by contacting with LBE. The susceptibility of T91 to LBE embrittlement increased with the hardening of the steel introduced by heat treatments.

Specimens of ferritic/martensitic (FM) steels T91, F82H, Optimax-A and the electron beam weld (EBW) of F82H were irradiated in the Swiss spallation neutron source (SINQ) Target-3 in a temperature range of 90–370°C to displacement doses between 3 and 12dpa. Tensile tests were performed at room temperature and the irradiation temperatures. The tensile test results demonstrated that the irradiation hardening increased with dose up to about 10dpa. Meanwhile, the uniform elongation decreased to less than 1%, while the total elongation remained greater than 5%, except for an F82H specimen of 9.8dpa tested at room temperature, which failed in elastic deformation regime. At higher doses of 11–12dpa, the ductility of some specimens recovered, which could be due to the annealing effect of a short period of high temperature excursion. The results do not show significant differences in tensile properties for the different FM steels in the present irradiation conditions.

The wide application of 316-type austenitic stainless steels in existing spallation targets requires a comprehensive understanding of their behavior in spallation irradiation environments. In the present study, EC316LN specimens were irradiated in SINQ targets to doses between 3 and 17.3 dpa at temperatures between about 80 °C and 390 °C. Tensile tests were conducted at room and irradiation temperatures. The results demonstrate that the irradiation induced significant hardening and embrittlement in the specimens. The irradiation hardening and embrittlement effects show a trend of saturation at doses above about 10 dpa. Although the ductility was greatly reduced, all specimens broke with strong necking, which indicates a ductile fracture mode.

Martensitic steel T91 will be used for the liquid lead bismuth eutectic (LBE) container of the MEGAPIE target. The irradiation assisted LBE corrosion and embrittlement effects on the behaviours of T91 steel have been studied by performing the LiSoR experiments, where T91 steel was irradiated with 72MeV protons to doses up to 0.2dpa at temperatures above 300°C in flowing LBE with or without mechanical stress. Tensile tests on the T91 steel after irradiation demonstrated that the irradiation assisted LBE embrittlement was not evident at such a low irradiation dose. The irradiation produced small defect clusters and dislocation loops were observed in the inner tensile-stressed specimens (ITS-specimens) of LiSoR-3 and LiSoR-4. The main features of the dislocation structure in the ITS-specimen of LiSoR-2 and the test-section tubes (TS-tubes) were dislocation tangles and dislocation networks, and small defect clusters and dislocation loops were hardly observed due to the high irradiation temperatures. The TEM observations support the results of the tensile tests.

The embrittlement effect of liquid lead–bismuth eutectic (LBE) on martensitic steel T91 has been studied by performing slow-strain-rate tensile (SSRT) tests in static LBE with about 1wppm oxygen at temperatures ranging from 250°C to 425°C. Two groups of samples were used. Group-I samples with microcracks on the lateral surfaces indicated clearly LBE embrittlement effect at temperatures ⩾300°C, while Group-II samples without microcracks did not show the effect. The LBE embrittlement effect occurred after the necking of specimens started. The yield and ultimate tensile strengths and uniform elongation were not affected. SEM observations showed the specimens ruptured in a brittle fracture mode when the embrittlement occurred. It is concluded that the requirements for the susceptibility of LBE embrittlement effect on the T91 steel are: surface cracks or flaws, wetting and a certain level of stress concentration at crack tips.