Analysis of Reactivity and Temperature Transient Experiments at the AVR High-Temperature Reactor

In the Arbeitsgemeinschaft Versuchsreaktor high-temperature reactor low-enriched fuel elements have been loaded for several years, replacing about half of the initial highly enriched uranium-thorium fuel. This changeover is accompanied by an elaborate experimental program wherein changes in the neutronics and thermohydraulics behavior of the system are monitored. Within this program reactor transients are induced by means of either circulator speed reduction or control rod movement. The resulting transients in neutron flux and temperatures are recorded and used as a basis for detailed theoretical analysis. Working groups at several institutions have carried out transient calculations using different dynamic codes. The results are presented and differences are discussed. In general, the experimental values were reproduced in a very satisfactory way.