Microbial Corrosion of a Process Water Cooling System in a Nuclear Power Generating Unit

A 316 stainless steel plate heat exchanger of a process water cooling system failed due to microbial corrosion during operation at a nuclear power station. A detailed failure analysis was done on the heat exchanger plate and described in this paper. The results established that inadequate chlorination has resulted in the infestation of the heat exchanger unit by corrosion and biofilm forming bacteria and caused the breakdown. Optical microscopy revealed concentric ring patterns on the SS- 316 plate, which is typical of sulphate reducing bacteria which induced microbial corrosion. SEM EDAX showed the presence of significant sulphur peak. XRD and Raman spectroscopy analysis showed the presence of FeS2 peak. Various observations recorded in the study were characteristic to typical microbial corrosion failure, particularly by SRB. The paper further highlights the remedial measures taken to prevent microbial corrosion by optimizing biocide dosing and water chemistry changes in the power plant.