Research On The Resident Hydrogen Isotope Removal Technology In Chinese RAFM Steel

Reduced activation ferritic martensitic (RAFM) steels are commonly thought to be the first candidate structure materials for the future demonstrational nuclear fusion or nuclear fusion power plant due to their good resistance to high dense irradiation, high heat conductivity with low thermal expanding coefficient and low irradiation caused swelling. The retention and removal of deuterium and tritium in two types of domestically developed RAFM steels nominated as CLAM and CLF-1 were investigated in this work.The metallurgical structure of the two types of steel is obtained by optical microscope. The result shows that the CLAM steel is ferritic and the CLF-1 steel is ferritic based with large amount of martensite and the grain size of CLF-1 steel is smaller than CLAM steel. The calculating results according to the deuterium diffusive constants in the two types of RAFM steels show that the concentration of deuterium can be saturated of 7.43wppm and 5.7wppm at 500℃,500kPa and 5h in CLAM and CLF-1 steels, respectively. While a subsequent aging for 0.5h at the room temperature can cause a significant loss of deuterium up to 23% and 51% in CLAM steel and CLF-1 steel, respectively. The thermal desorption result shows that there is only one peak at about 300℃ for CLAM steel, with an activation energy of 21kJ/mol. And there are two peaks at 300℃ and 500℃ for CLF-1 steel with the activation energies of 31kJ/mol and 94kJ/mol respectively. The hydrogen trap site of grain boundary and dislocation is the reason of the low temperature peaks with lower activation energy, and the activation energy of CLF-1 sample is higher than CLAM is because of the smaller grain size and more paths for atoms to travel. The trap site of defects together with MC precipitates is the reason of high temperature peak in CLF-1 with higher activation energy.The removal of retained deuterium in Chinese RAFM steels were investigated by thermal desorption and hydrogen exchange approaches. The removal efficiencies were obtained by quantitatively testing the amount of remaining deuterium in the thermal desorption spectrums. The results show that for the CLAM, deuterium removal efficiency is 93% at 100℃ for 2h. And it can be improved up to 98% with an elevation of the temperatures. The hydrogen exchange method improves the deuterium removal efficiency by 3% at lower temperatures. At higher temperatures, the heat effect is the main reason of deuterium release so that the hydrogen exchanging has low contribution to the deuterium removal efficiency. For CLF-1steel, because the deuterium trapped in low activation energy hydrogen trap sites could be re-trapped in high activation energy of hydrogen trap sites, bothmethods show low removal efficiency at 100℃. However, the deuterium removal efficiency can still attain at 94% at high temperatures.The tritium removal experiment results show that the detritiation efficiency of both CLAM steel and CLF-1 steel are quite low at 200℃ due to very low tritium retention concentration as ppb level. After hydrogen introduced or elevation of the temperatures, the detritiation efficiencies for CLAM and CLF-1 steels can still be up to 92% and 75%, respectively. The detritiation efficiency for CLAM steel is higher than that for CLF-1 steel at the same tritium removal process.