Environmental concerns: entrainment

Entrainment is the term used to describe the process by which organisms get drawn into the water extraction system with the flow of water. In power stations entrained organisms pass through the condenser circuit and are discharged back to the environment.

During passage through the cooling system, the entrained organisms suffer sudden changes in pressure and temperature and may suffer mechanical damage. Agents such as chlorine that are added to prevent biofouling may also hurt them. It is now widely recognised that the entrainment of fish eggs and larvae can be an important impact that should be minimised.

The reduction of entrainment at direct-cooled power stations must overcome considerable difficulties, and has yet to be fully demonstrated at large volume intakes. Wedgewire screens with a slot width of 1 mm can be placed at intakes, and providing the water velocity is kept sufficiently low they will exclude the majority of fish eggs and larvae. But, they will still allow many members of the plankton to be entrained. More recently, geotextiles such as the Gunderboom system have been trialled in the Hudson River estuary.
Pisces have considerable expertise in the applicability of these technologies and we are internationally recognised as experts in this field - please contact us.

Ongoing monitoring programs: Monitoring of entrainment, fish impingement (including salmon/trout smolts), water quality, and the causes and impacts of CW discharge foaming, at a number of UK power stations.
Intensive entrainment studies: We have designed and installed a fully automated and computer-controlled entrainment sampler, capable of sampling up to 25 litres/second in hourly units over a 24-hour period. The sampler has been used in evaluating fish egg, larvae and plankton entrainment in a UK nuclear station.
Planning: We have provided expertise on entrainment and fisheries issues for the construction of a large nuclear power plant in the United Arab Emirates.

The effects of power station entrainment passage on three species of marine planktonic crustacean, Acartia tonsa (Copepoda), Crangon crangon (Decapoda) and Homarus gammarus (Decapoda). Bamber, R.N. and Seaby, R.M.H., (2004). Marine Environmental Research 57 (2004) 281–294. Download report (223 kb PDF).

We have considerable experience in evaluating methods of entrainment avoidance; Pisces can provide advice and expertise on the full range of environmental and operational issues - please contact us for further information and assistance.