Numerische Berechnung des Tritium-Verhaltens von kugelhaufenreaktoren am Beispiel des AVR-Reaktors

For a predefined number of core regions the production and distribution of tritium, broken down according to the different tritium sources, is described using linear differential equations. The procedure is based on an ORNL programme written for high-temperature reactors with blocktype fuel elements. The programme areas dealing with the bond of the tritium fraction passing from the gas phase into the graphite due to recoil were revised for the purposes of a pebble bed. More recent results concerning the adsorption of tritium in graphite have been incorporated in the computer algorithm. A special problem in connection with programme development arose from the complex time dependence of tritium sources in the different core regions due to the possible repeated circulation of spheres. This problem was solved by determining fictitious storage times for the various types of spheres on the basis of known neutron doses.Calculations carried out on the AVR-reactor and compared with measured values showed a good agreement. Parameter studies with differing Li-contents of the spheres demonstrated a highly sensitive response of the system in this respect. Investigations relating to the inhibiting effect of hydrogen on tritium permeation revealed that the retention factors ascertained experimentally cannot be fully effective in practical reactor operation