Zircaloy-2 irradiation creep strain measurement techniques

The extension measuring devices used in the various in-reactor rigs associated with the UK Zircaloy-2 creep programme are described. All tests were performed at temperatures of about 3000C and fast flux levels (>1 MeV) in the range (3-6)x1017 n/m2/sec. The creep rates and total creep strains of uniaxial specimens have been measured using gas gauging techniques. Low creep rates in the range 10-7 to 10-5/h have been determined using a conventional type of gauge to an accuracy of within 10% provided that the specimen is on test for a sufficiently long time. For the measurement of high strains (>1%) a tapered needle gas gauge has been used; reliable strain measurements have been obtained using this device at ambient temperature but at elevated temperature the readings were sometimes found to be in error. The diametral creep strain of small tubes has been determined to within 0.5% using a neutron radiograph technique at reactor shutdown. Provided total strains in excess of a few per cent are expected creep curves can be reliably determined using this method of strain measurement