IRRADIATION-INDUCED DIMENSIONAL CHANGES OF H-327 FUEL ELEMENT GRAPHITE.

Samples of production grade H-327 fuel element graphite have been irradiated in six capsules at fast fluences and temperatures which cover the proposed service conditions of the material in the Fort St. Vrain High-Temperature Gas-Cooled Reactor.This material exhibits no observable changes 21 2 in structural integrity at fast neutron fluences of 8 to 9 x 10 n/cm (E > 0.18 MeV).Furthermore, when fabricated in the current HTGR fuel block configuration, the material will not experience expansion in the radial direction within the proposed range of service conditions.Damage gradients due to variations in radial fluence and the stress relaxation effects that result are discussed in terms of a creep constant for the material which is shown to be similar to the broad band values derived for all graphites.