Estimation Of Permeability Of Tritium In The Materials Of Molten Salt Reactor Based On Hydrogen Isotopes

Molten salt reactor (MSR) was identified as a candidate for the Generation IVnuclear reactors. In MSR, the fuel salt contains a large quantity of lithium, whichcould produce tritium by neutron absorption. Tritium diffuses easily through thestructural materials and transfers to the steam system and the atmosphere at hightemperatures, which could cause harm for environment and human body. Thus,tritium must be controlled. In order to effectively control tritium in molten salt reactor,it is necessary to research the permeation behaviors of tritium in the candidatestructural materials of MSR. As tritium is one of hydrogen isotopes, their chemicalcharacteristics are similar. As tritium is radioactive, the results of permeationexperiments for hydrogen and deuterium could be used to simulate tritium permeationbehavior in the structural materials.In this study, the experiment materials are Hastelloy N, GH3535, HastelloyC-230and Hastelloy C-276. With the method of gas driven permeation, hydrogen anddeuterium were used to simulate the permeation process of tritium and theirpermeabilities in these materials were examined at the temperature range of400700oC. The fluxes of hydrogen and deuterium are proportional to the square root of thegas pressure. During increasing of the temperature, the balance time of hydrogenisotopes to permeate are shortened. Their permeabilities are a little different in thesealloys and they are increased with increasing experimental temperature. Therelationship between the permeability and the reciprocal of the temperature is suit forArrhenius formula. At the experimental temperatures, the ratios of the permeabilitybetween hydrogen and deuterium in these materials are all close to1.4, which isconsistent with the classical diffusion theory. As the thickness of the sample is0.92mm, it almost has no influence on permeability. The permeabilities of hydrogenisotopes are very close in GH3535and Hastelloy alloy N, which is in the same order of magnitude with the permeabilities of hydrogen isotopes in Hastelloy alloy C-230and Hastelloy alloy C-276. According to the theory, pre-exponential factors for tritiumpermeation in these materials are1.1×1071.6×107mol·m1·s1·Pa1/2and activationenergy are5962kJ mol1.