For lead‐cooled fast reactors and accelerator‐driven subcritical systems, the surface corrosion behavior of candidate structural materials in lead–bismuth eutectic (LBE) is a key issue, which determines whether the material is applicable. The candidate materials of two typical MAX phases, Ti3SiC2 and Ti3AlC2, were immersed in static LBE with saturated oxygen concentration at 500°C for up to 3000 h. The corrosion behaviors of Ti3SiC2 and Ti3AlC2 were analyzed by scanning electron microscope, energy‐dispersive X‐ray, X‐ray diffraction, and Raman spectra. The experimental results showed that elements interdiffusion between LBE and sample matrix occurred on both Ti3SiC2 and Ti3AlC2 surfaces, which led to the formation of the diffusion layer. The dominant component of the diffusion layer is PbTiO3, which makes the corroded surface fragile in a stress environment. Besides, there were differences in structures of corroded sample surfaces between Ti3SiC2 and Ti3AlC2. The corrosion layer of Ti3SiC2 consisted of two layers, while only one single layer formed on Ti3AlC2 surfaces. The stable oxide layer consisting of SiO2 and TiO2 can protect Ti3SiC2 samples from further LBE corrosion and maintain the integrity of the surfaces. For Ti3AlC2 samples, it is hard to form a continuous Al2O3 protective layer, thus no stable oxide layer was detected on the corroded surfaces. Compared with Ti3AlC2, Ti3SiC2 showed better corrosion resistance in LBE.

After a loss of coolant accident (LOCA) in a pressurized water reactor (PWR), the chemical environment inside containment is complex; there is a potential trend for some materials to be corroded by high-temperature alkaline water.The subsequent corrosion products may be recirculated through the sump strainers using the emergency core cooling system (ECCS), and ultimately transported into the reactor core. This phenomenon would aggravate the blockage and head loss across the fuel assembly, thereby prohibiting decay heat transfer. To analyze the potential impact of "chemical effects" on flow resistance in the fuel assembly, the specific test loop was established and a series of analysis tests were performed. Four types of chemical precipitates were used in the tests: AlOOH, NaAlSi 3 O 8 , Ca 3 (PO 4 ) 2 , and Zn 3 (PO 4 ) 2 . This study concluded that the AlOOH precipitates could effectively increase pressure drop across the fibrous bed. The final head loss could also be affected by the physical and chemical characteristics of precipitates, such as the particle size, settling rate, and chemistry. K E Y W O R D Sblockage, chemical effects, LOCA, metal corrosion, pressure drop

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