Background: Reactor drive line is the "lifeline" of reactor control

which performs important safety functions. Purpose: To provide the basis for the drive line design assessment and nuclear power plant safety analysis. Methods: Through analyzing the stress of pressurized water reactor control rod assembly and control rod drive mechanism

established the mathematical model and the motion equation

and then solved by the finite difference method. Results: The program calculated value accords well with the test value of Ling’ao nuclear power plant phase Ⅱ unit hot rod drop. Conclusion: The rod drop time of calculation program based on this method can be used to the safety evaluation when pressurized water reactor is shut down. Abstract