Study on the effect of high temperature on the pore structure and closed-pore gas release behavior of nuclear-grade graphite IG110

As one of the fourth-generation nuclear energy systems, the Very High Temperature Gas cooled Reactors (VHTRs) face significant challenges related to material corrosion and radionuclide generation caused by impurity gases in the helium coolant. Among these, carbon-14 ( 14 C), produced by nitrogen activation in fuel elements, is a key source term. Its generation is closely linked to the evolution of the closed-pore structure in the graphite matrix under irradiation and high-temperature conditions. This research focuses on nuclear-grade graphite IG110. Through high-temperature vacuum isothermal simulation experiments, combined with Mercury Intrusion Porosimetry (MIP) and Gas Expansion Porosimetry (GEP), the evolution of the material's pore structure within the temperature range of 25–1100°C was systematically characterized. Online gas chromatography was employed to monitor the release patterns of H 2 , O 2 , CO 2 , and N 2 during high-temperature processes. The results indicate that IG110 graphite exhibits excellent high-temperature pore stability, with minimal fluctuations in open porosity and closed porosity (ranges of only 1.31% and 0.50%, respectively). The high-temperature nitrogen release curve shows three distinct peaks, with the second release peak (590–840°C) identified as resulting from closed-pore rupture. Quantitative calculations reveal that only 0.409% of the original closed pores opened. This research clarifies that high temperature (up to 1100°C) has a weak effect on the evolution of micrometer to millimeter-scale closed-pore structure accessible by GEP, providing experimental evidence for 14 C source term assessment in VHTRs. Note that potential changes in nano-scale porosity (e.g., Mrozowski cracks) were not captured by the techniques used and warrant separate investigation.