Study of creep deformation of irradiated zircaloy cladding by isothermal heating of irradiated PHWR fuel pins in temperature range 700°C–900°C

Abstract

Fuel pins removed from actual irradiated fuel bundles discharged from Pressurised Heavy Water Reactors (PHWRs) have been used for experimental study of high temperature creep deformation as functions of cladding temperature and internal fission gas pressure. Experiment consisted of localized heating of 100 mm long segment of the fuel pins in a furnace in inert atmosphere at temperatures 700 o C, 800 o C, 850 o C and 900 o C for 10-15 minutes. The internal pressure and the total void volume in the fuel pins were estimated by puncture test on sibling pins from the same fuel bundle. After the heating experiment the diameter of the pin along the length was measured to obtain the diameter increase due to high temperature creep. Analysis of the experimental data for fuel pins with internal pressure 0.55 ± 0.05 MPa, provided the following empirical correlation for creep rate of the cladding as a function of temperature:Creep rate (s -1 ) = 2.23 x 10 10 x exp (-305500/RT), for temperatures in the range of 800 o C -900 o C, where, R is gas constant, 8.314 J/mol K and T is temperature in K. For fuel pins with different internal fission gas pressures, the correlation obtained for the cladding strain as a function of internal pressure (at room temperature) was Cladding strain = 118.22 x 10 -3 exp (0.53P), for temperature = 900 o C where, P is the internal pressure in MPa at room temperature. This paper presents the details of the experiment and the results.