Allowable peak heat-up cladding temperature for spent fuel integrity during interim-dry storage

To investigate allowable peak cladding temperature and hoop stress for maintenance of cladding integrity during interim-dry storage and subsequent transport, zirconium alloy cladding tubes were hydrogen-charged to generate 250 ppm and 500 ppm hydrogen contents, simulating spent nuclear fuel degradation. The hydrogen-charged specimens were heated to four peak temperatures of 250 degrees C, 300 degrees C, 350 degrees C, and 400 degrees C, and then cooled to room temperature at cooling rates of 0.3 degrees C/min under three tensile hoop stresses of 80 MPa, 100 MPa, and 120 MPa. The cool-down specimens showed that high peak heatup temperature led to lower hydrogen content and that larger tensile hoop stress generated larger radial hydride fraction and consequently lower plastic elongation. Based on these out-of-pile cladding tube test results only, it may be said that peak cladding temperature should be limited to a level < 250 degrees C, regardless of the cladding hoop stress, to ensure cladding integrity during interim-dry storage and subsequent transport. (C) 2017 Korean Nuclear Society, Published by Elsevier Korea LLC.