Case Study
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Biofouling and MIC in a Nuclear Power Plant's Closed Cooling Water Systems
A nuclear power plant's closed cooling water loop chemistries were experiencing erratic and rapid drop in pH, formation of nitrogen gas, and loss in heat transfer efficiency of associated heat exchangers. Multiple attempts were made to readjust corrosion inhibitor and pH levels to bring the affected systems back under operational guidelines but was unsuccessful. Biofouling was suspected when thick sludge was found built up within the tubes of the affected heat exchangers.
Altran's ABC Kits, for biofouling and microbiologically influenced corrosion (MIC) detection, were used to characterize the sludge and test results showed that it was predominantly composed of biofilm containing iron and manganese depositing bacteria.
This prompted the client to re-dose their systems with biocide, however, the effect was only minimal against the established biofilms and system chemistries soon fell out of operational compliance.
When biocide re-dosing and chemistry adjustment failed to bring the systems back into compliance, Altran Solutions was hired to investigate the situation by performing a review of the client's biofouling control program. Altran Solutions' review of the systems' chemical and microbiological data histories, biocide and chemical treatment regimes and operating procedures, and data from ABC Kit testing, revealed that the monitoring practices employed by the client were not accurately determining biocide and microbial levels. The client was using commercially available colorimetric and biochemical test kits to determine biocide and microbial levels in bulk cooling water samples. The kits were found to be inadequate for determining either bioburden levels or antimicrobial efficacy.
Altran made recommendations for getting the affected systems cleaned from biofouling deposits, alternative analytical and microbiological methods for monitoring chemical and microbial levels, and optimizing their treatment practices.
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| Biofouled Heat Exchanger (Heavy Slime) |
Slime Analysis Indicates Iron Depositing Bacteria Present |