On Monday, a testing error knocked Pilgrim Nuclear Power Station’s cooling system offline for 40 minutes. This is the system that cools the reactor in the event of an emergency. Plant technicians testing another system apparently applied heat to the wrong switch, shutting it down. Read more from the Cape Cod Times >>

Then today, it was reported (also in the Cape Cod Times) that Pilgrim powered down (97%) to meet the required temperature limit for the discharge going into Cape Cod Bay. Pilgrim’s NPDES permit, required under the Clean Water Act, allows Pilgrim to use up to 510 million gallons daily from Cape Cod Bay for cooling. The permit also requires the water discharged back to the Bay  be no more than 32 degrees F hotter than the ambient temperature in the Bay. Learn more about thermal pollution from Pilgrim >>

Usually this happens during the height of the summer, but what would cause the discharge water to be so warm in March?

It is through to be associated with the hundreds of condenser tubes that we repaired and plugged last month, according to Entergy. The Nuclear Regulatory Commission (NRC) also suggested it could also be related to marine life, such as seaweed and clams, blocking up the heat exchange.

If this is the case, Pilgrim could  carry out chlorination of the cooling water or superheated backwash operations. Chlorination is used as a form of bio-fouling to control bacterial and algal slime that builds up on the internal pipes, especially in the hot summer months.  Thermal backwashes are done approximately 4x per year to clean pipes and screens that get clogged with marine life. Pilgrim is permitted to discharge water 120⁰F hotter than the ambient temperature of Cape Cod Bay during these operations.

Pilgrim is expected to remain powered down for another day.