ABSTRACT 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.
INTRODUCTION The purpose of this paper is to describe the development and resolution of a biological fouling incident in the main condenser at the Callaway Generating Station of the Union Electric Company, in Fulton Missouri. The station operates a single unit PWR plant generating 1238 MWe at full load.
During the analysis of this problem, the authors found two very good sources of information on the subject of condenser biofouling. Both of these were proceedings of symposia conducted by EPRI. The first was held in Atlanta, Georgia, in March of 1979. The second was held in Buena Vista, Florida in June of 1985. Although both of these conferences were held some time ago, both contained a number of valuable papers which were useful in providing information on this subject. Despite the valuable information found in these and other sources, we found that the analysis of this problem was difficult and the actual root cause of the problem was not completely clear until much analytical work had been done on the deposit and on the results of our clean up program.
Specifically, the authors found a great deal of ambiguity in the data that the system produced in the early stages of the problem development. It was not immediately clear that there actually was a problem and, after it became clear that a problem did exist the cause of the problem, whether inorganic deposition or biofouling was not easily defined.
If there is a general theme of this paper, it would be the application of Murphy?s Law to the operation of a nuclear power plant condenser cooling system. This is not to imply that there was anything comical about this event, this is a very large system and it is very expensive to operate if the condenser is not clean. There was never any danger that this kind of a problem could threaten the ability of the system to control the generating process. The only danger was the potential for decreased heat rate due to fouling of the condenser. There was also a concern that the problem would get much worse and would ultimately require an acid cleaning of the unit.
The problem developed in a way that was not expected. It required the confluence of a number of different factors to take hold. Once the problem began, the implications of its continued development were serious. However, the early data did not conclusively define the cause of the problem. Without a root cause of the fouling problem a treatment approach would be difficult to develop. The ultimate goal of this paper is to provide others with the insight developed from this problem and to make future problems easier to diagnose and treat.