Method for measuring the relative extent of burnout of combustion elements in a pebble-bed high-temperature reactor (htr) and a corresponding device

Abstract

Previous methods for measuring the burn-out of a combustion element from a pebble-bed high-temperature reactor, in particular with high circulation rates, have as a rule an error margin of up to 10%. The inventive method for measuring burn-out is extremely rapid, but nevertheless highly accurate, with an error margin of only 1-2%. The method comprises the following steps: a combustion element is removed from the reactor and transferred to a measuring position; b) the combustion element is subjected to a thermal neutron flux; c) a first detector determines the γ radiation emitted by the combustion element; d) if the measured value exceeds a previously defined first threshold value, the combustion element is fed directly to the reactor, but if the measured value falls below the threshold value, the combustion element is subjected to steps e to f; e) a second detector determines the high-energy radiation above 1 MeV emitted from the combustion element; f) if the measured value exceeds a previously defined second threshold, the combustion element is fed to the reactor, but if the measured value falls below said threshold value, the combustion element is evacuated from the combustion element circuit.

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