The Root Cause Analysis of the Bolt Fracture in the Nuclear Power Plant Essential Service Water System Available to Purchase

When inspecting in the nuclear power plant, the bolt of the 001/004 pump in Essential Service Water system was found fracture. The bolt in 001 pump had ever fractured before, and it had been replaced. In this paper, the material, microstructure, energy dispersive spectrometry and mechanical check calculation of the bolt are analyzed. The result shows, the bolt breakage is for stress corrosion cracking, the corrosion element is Cl⁻. When the martensitic stainless steel is in the heat treatment, the temperature is improper control, which causing the Cr element distribution changed. So the ability of material to resist corrosion becomes poor which is the root cause of the bolt fracture.