Darlington (Canada)

Map of Darlington

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4 units CANDU 880 MW (PHWR) , constructed by AECL; operation started between 1990 and 1993.

Facilities in Darlington

plantreactor typconstruction startoperation startshut down
Darlington-1CANDU 880 (PHWR)19821992
Darlington-2CANDU 880 (PHWR)19811990
Darlington-3CANDU 880 (PHWR)19841992
Darlington-4CANDU 880 (PHWR)19851993

Relief valve failure on a fueling machine spilled about 10.000 liters of heavy water into the reactor vault. Leak was stopped after 32 hours, The defective fueling machine had to be exchanged.


Shut down when level of iodine-131 in heavy water coolant indicated a pin-hole leak in fuel bundle sheating. Inspection revealed a end-plate crack in 1 bundle.


Damaged fuel bundle firstly prompted utility to cut back operations to about 65% of capacity in December 1990 was removed. Subsequent inspection of the retracted fueling machine turned up pellets and fragments from one or two fuel pencils (there are 37 fuel pencils in one fuel bundle and 13 bundles in a pressure tube). Investigation showed that the fuel bundle had sustained damage to the end plate which holds the pencils in position. This was the first time such end-plate damage has occured in Candu. Further inspections identified cracks in some fuel bundle end-plates. The cracking of fuel bundle end plates is believed to be caused by hammering vibrations of primary cooling pumps under certain startup conditions. Unit-1 was examined for fuel failures, too.


During pre-commercial testing: generator shaft cracked . The crack is more than a foot long and extends from holes drilled in the rotor for the generators electrical leads. Unit was shutdown because of high vibrations emanating from the generators shaft. Commisioning delayed. Rotor from unit-4 still under construction, shall be used, but modifications are necessary to relieve stresses that caused the cracked shaft.


Contaminated heavy water inadvertently put in instrument line of the main heat transport system, Exposed workers to tritium. The heavy water contained 6,5 GBq/l