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more successful at controlling the problems associatedwith
G. franciscana
, but the biocides and
cleaning approaches used can negatively impact coating performance by increasingwear.
While the ultimate goal is to effectively control the problems associated with growth of
G.
franciscana
and other fouling organisms in the CCNPP cooling systems, any single or
combination strategy must not impact fundamental plant operations andmust be cost-effective.
As approaches are added to a fouling control strategy, typically overall complexity, and thus
potential for failures, and costswill increase.
8. CaseStudies
8.1. SurryNuclear Power Plant and
G. franciscana
Surry Nuclear Power Station (on the James River in Surry, VA) conducted a study with the
Virginia Institute ofMarine Science and Stone andWebster EngineeringCorporation in 1992 to
help establish a fouling control program (Stone and Webster Engineering Corp. 1992). Like
CCNPP, themajor contributingmacrofoulerswere hydroids during spring, summer and fall, with
G. franciscana
identified as the primary species of concern. Other macrofouling organisms,
including bryozoans, crabs and barnacles, were also foundwithin their coolingwater systems.
Similarly, the problems related to fouling included reduced flow, increased traveling screen
component failure rates, increased corrosion rates, condenser inlet tubesheet fouling, and heat
exchanger inlet tubesheet fouling. Almost daily cleaning was needed during the late spring
through early fall periods. The final report reviews and summarizes methods used or tested to
control biofouling in various power plants prior to this 1992 study, including coatings, electrical
current/cathodic protection, mechanical, thermal backwash, physical methods including UV,
ultrasounds and acoustics, non-toxic chemicals, freshwater injection, magnetic treatment,
robotics, highwater velocity, biological control, chemical treatment, and asphyxiation. Of these,
mechanical, coatings, chemicals and asphyxiationwere considered and tested for theSurry plant.
8.1.1. Recommendations
The existing "traveling screens"
required upgrades to increase efficacy. The spray wash system
in place at the time did not produce enough pressure to be effective in cleaning fouling off of the
traveling screens because fouling in the pressure lines had reduced pressures from 80 psi to 15 -
20 psi. Specific upgrades recommended for the traveling water screen (TWS) system included:
TWS units with forward and reverse speeds sufficient to dislodge jams; TWS hoods for spray
observation with hood heaters for winter use; and basket lips to remove larger objects (e.g.,
carcasses, shells).
It was also recommended to coat specific areas with Bioclean or another silicone-based foul-
release coating. There were concerns about the coating falling off in sheets if used on the
downstream side of the screens because failure rates had not been tested.
Water treatment options including deoxygenationwere also considered, but it was concluded that
anoxia, as opposed to hypoxia, must be achieved to be effective in controlling
G. franciscana
.
