Hydride blister features in Zircaloy-2 pressure tubes removed from Pickering units 1 and 2: A selection of micrographs

Following the failure of the pressure tubes in channel G16 in Pickering Unit 2 (P2G16) sections of it and other pressure tubes removed from Pickering Units 1 and 2 were examined to study the blisters that led to the failure. Several tubes were removed for examination before the decision was made to replace all of the Zircaloy-2 tubes with Zr-2.5Nb tubes. Additional work on the Zircaloy-2 tubes was stopped at this time. The examination carried out on the tubes at AECL CRL included a visual inspection of the outside surface looking for blisters, followed by optical metallography of the transverse and axial sections that contained the blisters. The micrographs are of blisters found in pressure tubes removed from Pickering units 1 and 2. The micrographs document principal features found associated with the blisters in the pressure tubes not to cover all the details of blister growth and of crack initiation and growth. The pictures found within the report were to give an appreciation of the different stages that happen after the pressure tubes come into contact with the calandria tubes. 32 figs