ML20214N318

Microbiological Analysis of Oyster Creek Corrosion Samples

ML20214N318
Person / Time
Site:	Oyster Creek
Issue date:	02/02/1987
From:	Mathur C YORK COLLEGE OF PENNSYLVANIA, YORK, PA
To:
Shared Package
ML20214N301	List: ML20214N297 ML20214N318 ML20214N332
References
NUDOCS 8706020135
Download: ML20214N318 (13)

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MICROBIOLOGICAL ANALYSIS OF OYSTER CREEK CORROSION SAMPLES i Prepared by Carolyn F. Mathur, Ph.D.

York College of Pennsylvania i

For GPU Nuclear Corporation 2 February 1987 WR618MaE88li[

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SUMMARY

The purpose of this study was to determine if microorganisms are involved in the corrosion process occurring in the Oyster Creek drywell. The criteria used include: 1)-presence of viable cells in or around corroded areas; 2) presence of-conditions at the site that are believed to promote microbiologically influenced corrosion (MIC); and 3) presence of specific types of microbes that have been associated with corrosion in other systems.

Four sand or corrosion samples adjacent to metal plugs removed from the Oyster Creek plant drywell were analyzed for microbes that could be influencing the corrosion occurring in that area. Viable bacteria were found in all samples. Cells were observed closely adhering to the corrosion materials, and a variety of microbial types were isolated. The temperature, chemistry, and environment were all conducive to microbial growth. However, we did not detect significant numbers of the types of bacteria believed to play a dominant role in microbiological 1y influenced corrosion. _

We did not detect sulfate reducing bacteria, Gallionella organisms, or Pseudomonas (slime formers). Some ' filamentous types and spore-formers were present. We concluded that microbes probably played a role in the early s'tage of the corrosion, but are not likely the most important factor at this time influencing the corrosion rate in the most heavily wasted metal areas. We recommend future monitoring for MIC (microbiologically influenced corroston) and w

the eventual implementation of corroston control procedures that-

also inhibit microbial growth.

METHODS Four of seven core plugs taken from the Oyster Creek drywell on December 6 and 7, 1986, were analyzed for the presence of microorganisms that could be involved in microbiologically influenced corrosion. Corrosion or sand material taken from directly behind each of the metal plugs was transferred to a sterile plastic bag in preparation for analysis.

SAMPLE PREPARATION Part of each sample was suspended at a 10% concentration in sterile water and incubated with the vital stain INT (p-iodonitratetrazoluim phosphate) and substrate for-one hour. The samples were fixed in formalin and transported to York for microscopic analysis.

Another part of the sample was suspended in sterile water and used for innoculated into SRB (Sulfate Reducing Bacteria) media and for standard plate counts. Representative colonies were isolated and characterized from each sample.

MICROSCOPIC ANALYSIS Samples were stained with fluorescein isothiocyanate (FITC) and, analyzed using a Zeis epifluorescence microscope. The total cell counts were done on the FITC stained cells, while the percent viable cells (aerobic) were quantitated by counting cells positive for INT. Samples were microscopically examined for bacteria that can be associated with corroston.

1 RESULTS Table 1 includes a physical description of the sample material and a brief description of its microscopic appearance, cultured results and other relevant information. Samples 1, 4, and 5 were associated with wastage, while sample 2 had only pitting. The sand from sample 5, however, was not directly adjacent to the metal plug.

Table 2 gives the total cell counts (FITC cells / gram), the percent viability (as measured by INT staining), the standard plate count (as colony forming units / gram), and the SRB growth results. The cell counts and viability were at levels reasonable for soil samples. The lower counts and viabilities in the corrosion material samples inoicate less microbial activity here, compared to the straight sand materials. It could also mean more anaerobic organisms were present in the corrosion samples. The SRB culture results indicate that little, if any, sulfate reducing bacteria were present. These are believed to play a role in some carbon-steel corrosion processes. No Gallionella, a microbe associated with steel corrosion, was detected by visual inspection. Many small vibrio shaped cells were observed closely adhering to the corrosion material from the Bay 19 samples.

Table 3 contains information on some of the dominant colonies of bacteria isolated from the standard plate counts. A variety of Gram positive and Gram negative rods were detected.

Pseudomonas, an organism sometimes associated with corrosion, was not detected. Some filamentous forms, sometimes seen with corroston, were observed. Gram posttive score formers were

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Table 1 Physical and Microbial Descriptions Sample Physical Description Microbial Description 1-19C corrosion corrosion product;- material dominant- in wastage sample; slight growth in SRB media; long Gram positive and Gram negative rods: 50% of population -

aerobically viable 2-15A dry sands pitting long and short rods, both Gram positive and Gram 1 negative some filamentous types; no growth in SRB media 71% aerobically viable 4-19A corrosion variety of rod-shaped-Gram product; positive and Gram negative-wastage cells; short'vibroid cells closely attached to corrosion strands; may be Gallionella but could not confirm; 40% aerobically viable 5-11A wastage; moist sand Gram positive taken from area spare forming rods; weak distant growth in SRB media;1 74%

from corrosion aerobically viable material 6

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Table 2 l Bacteriological Results From Core Plug Samples Collected From Oyster Creek Drywell on December 6'and 7, 1986 Sample FITC SPC (cfu/g) . SRB (culture-cel1s/q results)

(% viable) 4 1-19C 5x 10' (50) 3x 10* little growth 2-15A 1: 107 (71) ~2 x ~ 10* negatise 4-19A 6x 10* '(40) 4x 10' negative 4

5-11A 4x 107 (74) 1x 10" little growth.

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Table 3-Descriptions of Colonies Isolated From Oyster Creek Samples Sample Colony Moroh. Gram Stain Misc.

(5)11A-1 white, irregular gram + rods + spore (5)11A-2 white, irregular'

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gram + rods + spore (2)15AD-1 clear, g r aru ' + . rods - oxid, - cat irregular, large with + motility.

spreading long thin fi1 aments (2)15AD-2 med. white dry, long Gram - + oxid, + cat irregular . rods + motility (1)19C-E med. clear white long Gram - oxid, + cat-colony, rods + motility concentric (1)19C-F same as 19C-E long Gram - - oxid, + cat rods + motility (1)19C-G med. clear white long Gram + - oxid, +. cat oblong, muccid rods + motility (4)19A-1 small Gram -

fat - oxid, + cat clear white rods with pointed ends (4)19A-2 bright Gram + med - oxid, + cat yellow smooth rods singles. - motility pairs, clumps (4)19A-3 small same as 19A-1 - oxid, + cat clear white (4)19A-4 tan, wrinkled, med. to long + oxid, - cat dry Gram -

rods + motility singles & end to end pairs

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DISCUSSION AND CONCLUSIONS Microorganisms are one of several factors that can influence corrosion rates in metals, such as carbon-steel. Specific organisms such as the sulfate reducers (SRB's) and Gallionella can be active in the corrosion process, but Microbiological 1y Influenced Corrosion (MIC) probably involves a complex system of different microbial types. The presence of cells not obviously-involved in corrosion can stimulate the growth of forms that can contribute to the electrochemical changes occurring. To evaluate MIC in a given system, a variety of factors need to be considered. In the samples reported on here from the Oyster Creek drywell, MIC probably has played a role, especially in the-earlier stages. However, MIC does not appear to be the primary cause of the corrosion that is currently occurring.in the heavily wasted samples (i.e. from Bay 19). It should be noted that the relatively non-corroded samples (i . e. Bay 15) show signs of early MIC activity, based on tha type of. small pitting that is occurring and the general conditions of the sandbed environment.

RATIONALE FOR ABOVE CONCLUSIONS '

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1. Moisture, dirt, and the alternating l wet and dry i condi tions that have been and are occurring in the sandbed adjacent to the metal are generally conducive to MIC. Water serves as a source of the microbes and of the nutrients needed by them. The materials above the sand (i.e. firebar D) contain protein and other nutrients that could be carried tnto the sand and allow for the qrowth of eartous microbes. Water serves as a-

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reactant in microbial metabolism and in corrosion. It can spread-the microbes and corrosive oroducts throughout the system.

2. The presence of sulfates and chlorides in the water that passed through the sand bed and -the differential concentrations j of chlorides in the crevices of the corroded metals. indicate the-possibility of MIC.

3. Black corrosion deposits are frequently associated with MIC.

4. Previous studies (i . e. Vermont Yankee Nuclear Power Plant) 4 indicate that MIC involving Gallionella was most significant early in the corrosion process, and that the influence of

microbes on the corrosion rates reduced considerably over time.

5. The presence of microbes in the sand adjacent to the metal

and in close contact with the corrosion materials itself indicates some microbial influence on the corrosion process. The presence of microbes in sand is expected, and because of moisture and other conditions, such as temperatures-of 110=F in which many microbes can grow, their numbers could increase. We detected little, if any, SRB's in the samples, and no Gallionella were observed. Although these two organisms can play a role in corrosion, their absence does not necessarily rule out MIC as a factor to consider. Unidentified microbial cells were observed closely attached to the corrosive materials from the Bay 19 l samples. However, the microbial cell counts were not that high, and this, along with our snability to detect large numbers of 4

organisms beli eved to be directly involved with MIC, indicates d

that MIC is not a major force affecting the corrosion rate at l

this Ltme. MIC should, however, be considered when control l

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RECOMMENDATIONS

1. Recheck areas again for MIC during future analyses for corrosion rates. Note especially the areas which had relatively litle wastage, as some of these showed pitting and signs of the early stages of MIC.

2. Consider corrosion control mechanisms that would also be antibacterial, such as elevated temperatures, drying, flushing with a biocide gas or liquid, improved drainage, or cathodic protection.

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