Abstract:The long-term safe operation of nuclear facilities poses severe challenges to the performance stability of internal concrete structures exposed to prolonged neutron irradiation. This study aims to reveal the damage mechanisms of different neutron fluences on the macroscopic mechanical properties and microstructure of concrete under realistic irradiation conditions. The main conclusions are as follows. Mechanical test results show that the compressive strength gradually decreases with increasing neutron fluence. SEM observations indicate that, under relatively low neutron fluence, the number of pores increases in the cement paste and interfacial transition zone. Since the neutron fluence is lower than the threshold required to induce aggregate cracking, no obvious cracking of aggregates is observed, and the damage is mainly manifested as microstructural deterioration of the cement paste and interfaces. XRD results show that some crystalline peaks in the mortar gradually intensify with increasing cumulative neutron fluence, indicating changes in the phase composition of the mortar. This phenomenon may be related to long-term irradiation-induced heating, moisture migration during service, and water loss from the cement paste.
