CRACK GROWTH SAFETY ASSESSMENT OF OVERLAY WELD ON THE O SEAL FOR CONTROL ROD DRIVE MECHANISM

摘要

As a key device, the Control Rod Drive Mechanism (CRDM) is of great important for the safety operation of the nuclear reactor, where the pressure shell of CRDM is exposed to the primary loop pressure, and is installed on the head of the reactor pressure vessel by the Ω seal. During the operation cycle of the reactor, cracks may be induced on the Ω seal weld by primary water stress corrosion cracking which is the major factor leading to leakage of coolant and impacting the safety of the reactor. Therefore, the Ω seal is required to be repaired to maintain structural integrity and safety by using the evaluated overlay weld technology. Based on fracture mechanics, this paper investigates the crack growth safety assessment of the overlay weld structure on the Ω. seal of control rod drive mechanism, induced by the operation fatigue and stress corrosion, and the evaluation is completed by the standard code. The calculation method and assessment results can be a reference for the overlay weld structure design and safety evaluation of the Ω seal in CRDM.