This paper documents a biofilm episode in the main condenser of a nuclear power plant. The problem was reversed by the use of oxidizing biocide and a wetting/penetrating agent, along with pH adjustments and other measures. All of the factors leading up to the problem are discussed in detail as are the measures taken to reverse the problem.
The most difficult aspect of the problem was identifying the onset of biofilm buildup. The existing background noise in the back pressure and fouling factor data obscured the early stages of the problem and delayed detection and treatment. Alternative monitoring techniques are discussed
and the treatment and reversal of the problem are completely documented. The rational for differentiating between biofouling and deposition caused by inorganic precipitation are discussed. Keywords: biofilm, condenser fouling, biofilm removal, water treatment, bromine treatment, nuclear power.