Regulation and control method and system for three-loop cold start low-power stage of sodium-cooled fast reactor

The invention discloses a low-power stage regulation and control method and system for three-loop cold start of a sodium-cooled fast reactor. The method comprises the following steps: monitoring and acquiring reactor power Pn, evaporator sodium side outlet temperature T, evaporator water side outlet pressure P and feed water flow Q of three-loop cold start of the sodium-cooled fast reactor in a current state; according to the obtained reactor power Pn, the evaporator sodium side outlet temperature T, the evaporator water side outlet pressure P and the feed water flow Q, whether the operation conditions of all the operation stages of sodium-cooled fast reactor three-loop cold start are met or not is judged; if the operation condition of the sodium-cooled fast reactor three-loop cold start operation stage is met, the working condition parameters of the sodium-cooled fast reactor cold start low-power stage are adjusted according to a regulation and control method corresponding to the operation stage, the operati