Research On Water Radiolysis And Corrosion Of Stainless Steel In The Cooling Circuit Of Fusion Reactor

Nuclear fusion is conceived as one of the most promising approach for energy.Water will be used as coolant of future fusion reactors to remove heat generated during operation due to the establishment of complete industry system for developing water-cooled cladding technology.For the sake of safety concerned in the process of developing water-cooled cladding,this thesis investigated the relevant water chemistry issues.The following research results are obtained.1.A model named“Water-homo" for calculating the water radiolysis under fusion condition is developed by addressing the deficiencies in existing models and modifying them accordingly.The model has taken the circulation of coolant into consideration.More reactions and the latest thermodynamic data are utilized in the new model.The LET effect of 14 MeV neutrons is also discussed.Addressing these deficiencies has allowed us to model the radiolytic yields of H2O2,O2 more rigorously.2.The effects of temperature and dose rates on the water decomposition by gamma and neutron are investigated using this model.The calculation results show that,for both gamma and neutron radiation,the yields of water radiolysis products increase as dose rate increases.The yields of molecule species decrease until 150 ? and then increase as temperature increases while the yields of radical species have the opposite trend.The time needed for the molecule species to reach steady state is less in high temperature than in low temperature.For the same dose rate and temperature,gamma radiation has a larger yield of radical species but smaller yield of molecule species than that of neutron.3.We have demonstrated some deficiencies in a previously published simulation result.The water radiolysis calculations in different primary heat transfer systems(PHTSs)are performed.The results show that the maximum concentration of H2O2 and O2 in First Wall and Blanket PHTS are 8 ?M and 1.3 ?M;the minimum concentration are 2.7 ?M and 0,2 ?M,in the Vacuum Vessel PHTS,the maximum concentration of H2O2 and O2 are 1.98 ?M and 0.034 ?M.The results indicate that for ITER,the concentration of oxidizing species in the FW/BLKT PHTS could be efficiently minimized by adding about 5 cc H2 STP/kg H2O in the coolant.4.A new model has been developed,by modifying existing models,to calculate the ECP of recirculation pipes in future fusion power plant.The model takes hydrodynamic conditions and irradiation fields into consideration.The calculated ECP using this model are in good agreement with experimental data under the operating conditions of boiling water reactors(BWR).The model is then applied to operating condition of fusion power plant to investigate the correlation of ECP versus dose rate and coolant velocity.The calculation results show that more positive ECP will be obtained with higher dose rates due to higher yields of oxygen and hydrogen peroxide.Faster coolant velocity will also lead to higher ECP.The effect of hydrogen injection on ECP has also been investigated.The results indicate that about 5?10 mL H2 STP/kg H2O is sufficient to lower the ECP and mitigate the intergranular stress corrosion cracks if the dose rate is below 500 Gy/s.When dose rate is larger than 1000 Gy/s,merely injecting hydrogen cannot reduce ECP below EIGSCC,other assisted water chemistry controlling method is necessary.5.An experimental device is designed and modified for testing 316 stainless steel corroded by pure high-temperature and high-pressure(HTHP)water or adding zinc ion into it.The experimental result shows that the weight gained during 20 days' corrosion is less than 1 mg.A blueish oxide layer is formed on the metal surface.The corrosion product mainly distributes along the crystal boundary.The main ion in the solution are Cr?,very few F? is found.Combining the surface analysis and solution analysis together indicates that the corrosion process can be divided into two steps,the first step is the formation of oxide layer,the second step is the dissolution of oxide accompanied with the release of metal ions into the solution.Higher concentration of Zn will lead to a thinner oxide layer and less dissolution of metal ions,which indicates that Zn is beneficial for suppressing the oxidation of 316 stainless steel in HTHP water.