Connecticut Yankee (USA)

Map of Connecticut Yankee

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580 MW PWR constructed by Westinghouse; operation started in 1968, shut down in 1996; decommissioning will be completed in 2004.

Facilities in Connecticut Yankee

plantreactor typconstruction startoperation startshut down
Connecticut YankeePWR196219681996

After shutdown for the refueling outage nitrogen was found under the RPV head which had displaced about 20.000 liters of water from the core to the pressurizer. Workers discovered that the nitrogen from the volume control tank had leaked through a valve, forming a buble at the top of the vesselectrical The reactor vessel level indication system was disconnected, when opening of RPV started. Workers were relying on a less sophisticated indication system.
Besides this fault it was found that one of the two RHR pumps was inoperable. Another incident occured when a valve which was thought to be closed was not fully closed and 1100 liters spilled into containment.


Plugged SG tube found ruptured during refuelling outage: crack greater than 25 mm long and the tube had bowed about 10 mm; rupture was located between the tube sheet and the first support plate.
Reduction in the number of tubes beeing plugged from 160 in 1989 to 25 in 1995 and the sludge removed from the secondary side of all 4 SG weighed only 120 kg versus 420 kg in 1989.


Shutdown of the plant caused by failure of ESSW cooling EDGs and RHR. Degradation of welds in underground and inaccessable part of the system.


Leak in a 350 mm extraction steam line


243 fuel rods in 88 assemblies have developed throughwall cracks caused by metal flakes left over from a job done on the thermal shield during the last outage. (Repairs on the fuel rod costs: $9million) During the inspections 26 cracks inside the PRZ were discovered; Three of them extending through the inner cladding to the 140 mm carbon steel base.