Severe accident research at the Transuranium Institute Karlsruhe: A review of past experience and its application to future challenges

• Severe accident research at the Transuranium Institute, Karlsruhe has been reviewed.
• Large (Phébus, TMI-2) and smaller tests have improved understanding of core degradation.
• Cladding/structural materials interaction and attack of fuel are important in degradation.
• Formation and composition of molten fuel pool in the lower bundle was reproducible.
• This mechanistic knowledge has greatly assisted severe accident modelling.

With the current situation in Japan one should examine previous research into severe accidents and the current state of European severe accident research to assess what are the priorities for research for existing and future nuclear reactors.The European Commission’s SARNET 2 (Severe Accident NETwork of Excellence) programme and its SARP (Severe Accident Research Priorities) assessments have been made and have outlined the future needs as seen from the EU point of view.There is already considerable research that will be very valuable in analysing and guiding the investigation and remediation activities at Fukushima Dai-ichi. This includes investigations into previous major accidents and international severe fuel damage projects. Facilities using analogue materials are able to analyse large-scale behaviour of materials, while smaller-scale testing of irradiated fuel for detailed property measurements are important for mechanistic studies. The final (and very important) aspect is application of this information to formulate codes to model the identified mechanisms and also to have their predictions validated by the data.This paper will take examples from the Transuranium Institute’s (ITU Karlsruhe’s) contribution to projects such as the TMI-2 accident investigation and the Phébus PF bundle and fission product deposit investigations as well as some of the smaller scale testing and modelling support that ITU has performed over the last 20 years. This will show what has been learnt about fuel and structural material degradation and formation of molten materials, fission product release, and subsequent behaviour. Finally some severe accident research perspectives following Fukushima are proposed.