THE H-1 HIGH TEMPERATURE GRAPHITE IRRADIATION EXPERIMENT

Abstract

A high temperature graphite irradiation experinient was performed in the GETR core to determine the effects of differences in manufacturing, formulation, and graphitization temperatures on radiation-induced eontraction. The experiment was performed at temperatures of 800 to 1200 deg C in an intense fast neutron flux. The maximum integrated exposure of the sample positions was 3.2 x 10?sup 21/ nvt, E> 0.18 Mev, corresponding to approximately 24,000 MWD/AT in a conventional graphite-moderated reactor. All the graphites tested, with the exception of the controls, were needle coke filler, coal tar pitch binder graphites varying mn particle size, graphitization temperature, and impregnation. From theoretical and experitnental considerations, the formulations and treatments were expected to result in a relatively stable graphite in the direction transverse to extrusion. For comparison of the experimental results to existing experience, a conventional graphite, CSF, was used at each irradiation position. The results showed that the graphite most stable to contraction was graphaitized at a high temperature(>3100hC) and made from small particle size (all flour) filler. In all cases, the needle coke graphite contracted at a lower rate than the CSF graphite. Differences attributable to the size of extrusion and/or post graphitization cooling rate were discerned readily. Auxil iarymore » to the purposes of the experiment, the apparent thermnal neutron cross section for Co/sup 58/ (plus Co /sup 58m) was determined. Co/sup 58/ and Co/sup 58m/ are the products of the Ni/sup 58/ (n,p) reaction, which is used widely for fast flux monitoring. Both have large thermal neutron capture cross sections which must be accounted for to prevent error in fast neutron dosimetry. In this experiment, a value was determined for the apparent burn-out cross section of 3750 barns. (auth)« less