Elastic properties of severely degraded fuels

The decommissioning of nuclear power plants subjected to a nuclear accident is a crucial activity for post-accident recovery and remediation of the affected areas. To achieve this objective, safe and successful removal of the fuel debris is required, but the accomplishment of this task needs the conception, design and construction of adequate tools and new procedures. The Three Mile Island Unit 2 (TMI-2) experience has taught that the success of such operations is related to adequate knowledge of the fuel debris’ physical and mechanical properties; hence these properties must be accurately investigated. The present work focuses on the determination of corium’s elastic properties by using acoustic methods. The Young’s modulus was determined for prototypic corium produced during the FARO experiments at the Joint Research Centre Ispra and for compounds synthesised at the Joint Research Centre Karlsruhe; the acoustic microscopy was also applied to corium samples extracted from the TMI-2 nuclear reactor, and to “lava” sampled at the Chernobyl Nuclear Power Plant. The study shows a slight decrease in Young’s modulus caused by the increase in zirconia content for the prototypic corium and comparable values in the case of TMI-2 core rocks. In this scenario, the specimen of Chernobyl brown lava constitutes an exception due to its lower Young’s modulus, in comparison with prototypical corium or the In-Vessel accident corium.