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Sodium-cooled fast reactors have formed a multi-level protection system to address the risks associated with nuclear fuel and liquid sodium. The core measures are as follows: The fuel cladding barrier uses chromium-nickel austenitic stainless steel to encapsulate the nuclear fuel, completely sealing the fuel within the cladding tube, fundamentally preventing direct contact between the nuclear fuel and liquid sodium, while ensuring the structural stability of the cladding in a high-temperature sodium environment. The loop isolation design sets up an independent secondary loop sodium system, which isolates the radioactive primary sodium and steam-water loops through an intermediate heat exchanger to prevent the sodium-water reaction caused by the leakage of the steam generator from spreading to the core fuel area. Containment and leakage prevention and control adopt a pool-type integrated structure, integrating all primary-circuit sodium systems into the main vessel, adding a safety guard vessel outside the main vessel, and adding safety jackets to the secondary-circuit pipelines to reduce the probability of sodium leakage to 10⁻⁷/reactor year and avoid leakage of radioactive sodium. Accident protection: A core trap is installed at the bottom of the reactor core to contain molten fuel under extreme core damage conditions and prevent it from breaking through the reactor boundary. It is also equipped with a passive waste heat removal system to prevent core overheating from exacerbating fuel damage. Reactivity suppression design: A sodium cavity structure is installed above the core, and combined with the FAST passive safety device, negative reactivity is automatically introduced when sodium boils/the temperature rises abnormally, to avoid fuel damage caused by abnormal surges in core power.