Measurement of pellet and clad dimensional changes in the Halden Reactor

The dimensional changes occurring in oxide fuel and cladding are measured during reactor operation using fuel and clad elongation detectors and diameter gauges. Analysis of data obtained during carefully controlled start-up ramps, staircase ramps and during hot standby has provided information on the following; The mechanism of pellet axial extension; The mechanism of the onset of PCMI; The mechanism of clad elongation in rods with flat and dished ended pellets; Fuel densification rates; Solid fission product swelling rates; The mechanisms of ridge formation in rods with flat and dished ended pellets; The mechanisms of clad strain relaxation by slippage and fuel creep; The mechanism of axial clad stress relaxation; The formation of permanent ridges. (Author)