Evaluation of Calvert Cliffs Unit 2 leaking pressurizer heater sleeves and nozzle

During a normal refueling outage, leakage was detected at the annuli between some of the Unit 2 pressurizer heater sleeves and the pressurizer shell and at one of the Unit 2 vapor space instrument nozzles. Destructive examination of a heater sleeve showed that the cracks were intergranular. The grains near the inside surface were heavily cold worked. The key fabrication difference between Unit 2 heater sleeves which developed primary water stress corrosion cracks and Unit 1 heater sleeves which did not develop cracks was that the inside diameters of the Unit 2 sleeves had been reamed prior to welding the sleeves into the pressurizer shell. The conclusions from failure analysis were that the cracking was primary water stress corrosion cracking and the heater sleeves cracked primarily as a result of high tensile residual stresses resulting from cold work followed by welding, and the susceptibility of the low yield strength (36 ksi (248 MPa)) instrument nozzles was increased by the extensive rework