Computation of diametral deformation of irradiated Zr-2.5 Nb pressure tubes from RAPS-2

The pressure tubes in Pressurised Heavy Water Reactors (PHWRs) are subjected to high stresses, temperatures and fast neutron fluxes which cause changes in dimensions and material properties. To ensure the safe, reliable and economic performance of the reactor, it is important that these changes are known and that the rate of change can be predicted and demonstrated to remain within the design basis. The diametral expansion of pressure tubes due to irradiation creep and growth is an important property that may limit the useful life of the tube. A semiempirical predictive model has been developed to calculate the irradiation creep (diametral) and irradiation growth (diametral) contributions and total diametral change in irradiated pressure tubes. The model can account for variations arising from tube orientation. The sixteen numbers of Zr-2.5Nb pressure tubes (PTs) of RAPS-2 selected had undergone 7.15 Effective Full Power Years (EFPY) of reactor operation. The diametral changes at discrete locations along the length of the pressure tubes are estimated by using the model developed. The maximum of (along the tube length) measured internal diameter data of those fifteen pressure tubes have been compared with those obtained from the model.