Pickering: Fish Nets Are Back in the Water
April 5, 2012
With the arrival of spring, Ontario Power Generation (OPG) has recently reinstalled fish nets near the water inlet used by the Pickering Nuclear Generating Station for cooling the plant. The measure is aimed at substantially reducing the impact of the plant’s activities on aquatic life. The Canadian Nuclear Safety Commission (CNSC) has been closely monitoring how well OPG is meeting established targets.
In 2008, the CNSC raised the problem of fish mortality due to impingement and entrainment as a major issue for OPG to resolve. Impingement affects fish, which die when they are pulled into the screens of the intakes. Entrainment affects eggs, larvae and very small fish that are able to pass through the screens into the cooling system where the water is too warm and pressurized for them. As a result, OPG installed barrier nets in front of water intakes during the spring, summer and fall of 2010.
During 2010, the first year of testing, the net reduced mortality by close to 80 percent. Areas for improvements were identified, however, in response to events involving algae influx and unusually strong lake currents. New design improvements to the barrier nets were implemented by July 2011.
OPG will continue to monitor year-round screen house fish counts and seasonal net performance in 2012 to determine if the new design is adequate. As northern pike are mostly impinged over the winter, OPG has also funded the restoration of the northern pike spawning habitat in the nearby Duffins Creek Marsh.
The 80 percent reduction target for impingement was based on scientific data and agreed to by CNSC staff, other federal regulators and OPG. Other objectives included reducing the mortality of eggs and larvae by a minimum 60 percent target, completing studies on the impacts of the thermal plume and taking appropriate mitigation measures.
Due to the location of the spawning habitat, the thermal plume is only an issue for Pickering B. Several studies on the effects of the thermal plume on whitefish embryo survival have been completed to date. In early 2012, OPG completed a review of 14 potential mitigation options. Environment Canada and CNSC staff are working with the operator to determine a path forward to resolve the issue.
About thermal plume effects
Water from lakes, rivers and oceans is used by all nuclear power plants – and, in fact, most other types of thermal plants – to cool the steam generated to run turbines. The thermal plume is the area the warmer water covers as it spreads out from the plant’s outlet. The environmental impact related to the discharge of warmer water that has served the cooling process is a subject that has been studied by regulators and scientists around the world.
Several effects need to be looked at to determine the overall impact on the local environment. Some lead to harm, others to benefits, and in a number of cases consequences remain uncertain. For instance, some species are very sensitive to sudden changes in temperatures and suffer when reactors are shut down and then restarted. In other cases, a number of “heat-loving” species tend to proliferate near the outlets. Overall, nevertheless, the environmental impact is essentially localized and small.