Which impurity poses the greatest threat to the system in sodium-cooled fast reactors

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In the liquid metal sodium coolant system of sodium-cooled fast reactors, oxygen impurities are the most harmful impurities to the system. The main hazard is that oxygen directly accelerates the corrosion of structural materials in liquid sodium; it not only promotes the dissolution of metal components in sodium but also participates in reactions to form corrosion products such as NaMO₂, thereby significantly increasing the corrosion rate of these materials. For example, the corrosion rate of platinum in sodium with a high oxygen content can reach nearly 4.6 mm/year, which is much higher than the corrosion rates caused by other impurities. The chain reaction has a wide impact range. The presence of oxygen also indirectly increases the solubility of other impurities such as hydrogen, thereby increasing the risk of material embrittlement. Meanwhile, the oxide impurities formed tend to deposit within the circuit, potentially causing secondary problems such as blockages in the flow channels and reduced heat exchange efficiency. It is therefore the most critical impurity that needs to be controlled in the quality management of sodium-cooled fast reactor coolants.