| Popis: |
The fuel elements for the Modular High-Temperature Gas-Cooled Reactor (MHTGR) are to be manufactured from a near-isotropic graphite, such as grade H-451. Low concentrations of impurities, including water vapor, will be present in the helium coolant, primarily because of small, undetected leaks and outgassing of the graphite as temperatures are increased. For economical plant operation, graphite corrosion must not impact the normal fuel-element replacement schedule and must not be the cause of extended reactor-shutdown periods. Graphite corrosion can also affect fission-product release and transport. In general, previous calculations have not shown good agreement with data obtained from out-of-pile and in-pile experiments that involve both transport and reaction phenomena, unless significant adjustments were made to model parameters, including reaction-rate correlations. The currently used reaction-rate correlations were developed from out-of-pile data. Under in-pile conditions, radiolysis of water vapor and neutron-induced damage to the graphite may enhance graphite corrosion. The recently completed irradiation of capsule HFR-B1 provided some unique data for inpile corrosion of H-451 graphite. In this paper, the HFR-B1 graphite-corrosion data are analyzed and compared with model predictions. The present calculations using the out-of-pile rate correlation are in good agreement with the HFR-B1 in-pile data. |
