Provided herein is a method for operating a slurry polymerization reaction system to reduce, inhibit, and/or prevent fouling in the polymer recovery and separation apparatus, including one or more portions of a high pressure flash tank. The method generally comprises polymerizing a monomer feed in a slurry polymerization reactor in the presence of catalyst and diluent to produce a polymerization effluent; continuously discharging at least a portion of said polymerization effluent from the reactor through a discharge valve; combining a catalyst poison stream with the polymerization effluent downstream of said discharge valve, wherein the catalyst poison stream comprises a catalyst poison that is a gas at standard conditions; and flashing the combination of polymerization effluent and catalyst poison stream in a first flash tank.