Reloadable graphite creep facility for tensile or compressive experiments

An irradiation test consisting of four experimental periods was prepared to evaluate the creep characteristics at elevated temperatures and to high fast neutron fluences of a special core graphite for the High Temperature Reactor. The material is a cylindrical stressed sample which is surrounded by a number of unstressed half-shell reference pieces. All the samples are irradiated at about 9000C in four consecutive steps leading to a total fast fluence of 1.0, 2.0, 3.5, and 5.5 x1021n.cm-2 (DNE). Irradiations are carried out in core positions of the High Flux Reactor of the Euratom Joint Research Centre at Petten/The Netherlands. To meet the experimental requirements a Graphite Creep Facility was designed and manufactured which enables the creep samples to be subjected to either tensile or compressive loads during the irradiation merely by changing the specimen can assembly. The load control modes can be either (a) steady tensile or compressive, or (b) continuous cycling at predetermined rates. The facility is re-loadable out of the thimble and the specimen can may be removed during reactor shut-down to permit intermediate dimensional measurements or replacement of the specimen. The paper describes special design features of the Creep Facility e.g. (a) specimen stressing mechanism, (2) load control system, (3) reloadability, and concludes with a description of the measuring apparatus which detects the dimensional changes of the stressed samples and the unstressed reference pieces. Experimental results of the first irradiation step are presented. (Auth.)