Biological Testing of Geiger MultiDisc™ Rotary Screens at Salem Generating Station

PSEG Nuclear, LLC installed a Geiger MultiDisc™ rotary screen with a fish collection and return system in the Salem Generating Station intake structure in 2006 and conducted biological testing of the pilot installation through November 2010. The modifications were intended to improve the capabilities of the cooling system to handle the high detrital load present in the Delaware Estuary during certain periods of the year. Latent impingement mortality (“LIM”) and entrainment length-frequency data for the rotary screen were collected for comparison to the existing long-term data on impingement/entrainment mortality of the other eleven Ristroph-modified traveling screens (6.35 x 12.7-mm woven wire mesh). Biological testing was conducted with both 8.0-mm and 9.5-mm drilled plastic plate panels on the MultiDisc™ rotary screen. Results for the 8.0-mm mesh indicated higher LIM values than for the Ristroph screens. In order to estimate expected entrainment losses associated with the rotary screen, transfer factors were computed for each species/length class using the ratio of concentrations behind the rotary screen to concentrations behind a Ristroph screen. By applying these transfer factors to entrainment concentrations measured behind the Ristroph screens, and applying the measured rotary screen LIM values to impinged organisms, PSEG was able to estimate the combined impingement and entrainment losses for an overall comparison of a Ristroph screen to the rotary screen. The estimated impingement/entrainment losses were converted to biomass using a Production Foregone Model to determine that the average combined biomass loss (with entrainment survival) through the 8.0-mm mesh rotary screen would be slightly less than through a Ristroph-modified screen. The LIM and entrainment length-frequency data from biological testing of the 9.5-mm mesh are currently being analyzed and these results, including an estimate of combined impingement and entrainment losses using a Production Foregone Model, will be presented for an overall comparison of biological effects.