Abstract
Submerged-arc welds in Magnox RPVs are expected to show substantial shifts in ductile-to-brittle transition temperature (DBTT), due to their high copper content, and also because of a contribution from intergranular fracture. For structural integrity arguments, the fracture toughness of irradiated welds is predicted by applying an irradiation shift in DBTT to a start-of-life toughness curve. The shift is obtained from a trend curve derived from Charpy impact data. An uncertainty allowance is obtained by combining uncertainty contributions in start-of-life fracture toughness and shifts, including a contribution from uncertainties in neutron dose. Through-thickness samples were removed from four submerged-arc welds in a decommissioned Magnox RPV at Trawsfynydd. Fracture toughness tests were made on pre-cracked Charpy geometry specimens made from the samples, in order to compare the measured toughnesses with those predicted for irradiated material. Specimens were tested from several positions along the welds and also at four different through-thickness locations with dpa doses varying by a factor of more than 2. The paper presents the results of nearly 400 toughness measurements and demonstrates that the prediction methodology is sound.
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