MERCER02-14
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While anoxia could be achieved by chemical injection, other options, especially biocide water
treatment, appearedmore likely to succeed and be cost-effective.
The injection of sodium hypochlorite, ammonium hydroxide, hydrogen peroxide, Acti-Brom
(sodium bromide) and ClamTrol-CT1 were considered and tested withmixed results. Bulk and
continuous chemical treatment was deemed infeasible for any of the biocides considered and for
chlorine-based water treatment (e.g., sodium hypochlorite). The EPA allows a maximum
concentration of free available chlorine of 0.5 mg L
-1
and average concentration of 0.2 mg L
-1
with only one unit discharging for a maximum time of 2 hours per day, unless the utility can
demonstrate to the Regional Administrator or State (if the State has NPDES permit issuing
authority) that the units in a particular location cannot operate at or below this level of
chlorination (40CFR 423.12 (8)). At these allowable concentrations, hydroidswere damaged but
regrew in laboratory experiments (Stone andWebster Engineering Corp. 1992). However, spot
or pulsed sodium hypochlorite treatment at higher doses in specific areas was deemed feasible
and could be effective. A "wet layup" procedure including a "chemical injection skid to provide
corrosion control" was advised for pipes that were alternatively wet as hydroids grew, then dry
as hydroids die, thenwet again as hydroids break off in the flow and clog systems.
8.1.2. Status ofBiofoulingControl
The Surry Nuclear Power Plant has had success controlling
G. franciscana
, and waterbox
biofouling in general, using a chemical treatment supplied byNALCO. The treatment is based on
liquid injection of sodium hypochlorite (13% specified but actually closer to 10% by the time it
is used) and Acti-Brom (43%) using two one-hour injection times each day. The flow rates of
injection are 300 gal sodium hypochlorite and 70 gal Acti-Brom pumped into the four cooling
water pipe intake cavities, twice a day, per unit. Chemical flow rates are based on the power
plant’s circulating water flow rate of 52,000,000 gph with a total daily chemical usage of 1,200
gal of sodium hypochlorite and 280 gal ofActi-Brom.
A similar approach implemented at CCNPPwould require larger volumes of injected chemicals.
Surry has four cooling water pipes per unit that pump 220,000 gpm each with a total flow per
unit of 880,000 gpm, and a total site flow rate of 1,760,000 gpm. CCNPP has six cooling water
pipes per unit that pump 200,000 gpm each with a total flow per unit of 1,200,000 gpm and a
total site flow rate 2,400,000 gpm. The supply, delivery and handling of such large amounts of
concentrated biocides could present significant cost, logistical and safety concerns. However, a
similar dose and application approach can be achieved by on-site generation of sodium
hypochlorite through electrolysis (i.e., electrochlorination), and if bromide salt levels in ambient
cooling water at CCNPP are naturally high enough, the addition of Acti-Brom may not be
necessary to achieve comparable results.
If this or any other approach is to be implemented, all coolingwater system componentsmust be
mechanically cleaned or the treatment could cause significant sloughing of existing fouling
organism, which could clog the system and trip individual units.
