TCOFF-2 is the second phase of the NEA joint project Thermodynamic Characterisation of Fuel Debris and Fission Products Based on Scenario Analysis of Severe Accident Progression now running until 2027. 

The first phase focused on analysis of reactor-related aspects of the Fukushima Daiichi Nuclear Power Plant. The current phase builds on the knowledge acquired and also includes studies on other reactor and advanced technology fuels (ATF), as well as other fuel designs. The project brings together 12 organisations from Canada, France, Germany, Japan, Sweden, United States and the European Commission. 

The aim of TCOFF-2 is to improve models and underpinning data on the material interactions and their role in the various potential phases of the severe accidents. The ultimate goal is the integration of such models into severe accident simulation codes to increase their accuracy, including in respect of the extent of potential radioactive release. This improvement will be driven by state-of-the-art knowledge of the thermodynamic properties of the relevant combinations of materials. 

The NEA convened TCOFF-2 Programme Review Group (PRG) and Management Board (MB) meetings in Tokyo, Japan, on 30 June – 1 July 2026 to review progress of its activities. The meetings were hosted by the Central Research Institute of Electric Power Industry (CRIEPI) and held after the 15-Year Fukushima Daiichi Accident International Workshop hosted jointly by the Nuclear Damage Compensation and Decommissioning Facilitation Corporation (NDF), the Nuclear Regulation Authority (NRA) of Japan and the NEA. 

The meeting gathered 40 participants and progress was reported from each of the five principal tasks of TCOFF-2:

Prioritisation of the material science issues related to severe accident study 
Improvement of the materials science knowledge regarding fuel core degradation and fission product release (UO2-Zr and ATF)
Implementation of improved knowledge for the simulation of the accident behavior (UO2-Zr and ATF)
Extension of the leaching experimental database to better evaluate mid- and long-term stability of degraded cores 
Training and education (including partnership with the NEA Nuclear Education, Skills and Technology Framework)

Sessions also featured updates from supplementary R&D projects: 

Thermochemistry of fission product phases with a long-term radiological impact: experimental studies of the Ba-Sr-Cs-Mo-O system – Prof. Anna Smith (TU Delft) 
Experimental characterisation of representative corium samples under severe accident conditions – Morgan Collins and Prof. Markus Piro (McMaster University) 
Modelling heavy actinide solute trapping during solidification with data from the CNL cold crucible experiments – Dr Mike Welland (McMaster University)
In situ high-temperature XRD/XAFS study of phase equilibria for hypo-stoichiometric region in U-Zr-O system – Prof. Ayumi Itoh (Science Tokyo)
The effect of FeO and ZrO2 on the phase equilibrium of CaO-SiO2-Al2O3 simulant of the SiO2-rich concrete at 1673 K – Dr Ryoto Nakazawa (Science Tokyo) 
Oxidation of Cr-coating layer by steam in accidental conditions: gaseous phase of Cr-Cs-O system description using Knudsen effusion mass spectrometry + Thermodynamic evaluation – Dr Ioana Nuta (CNRS)

More information and next steps

Further details on TCOFF-2 can be found on the dedicated web page and information about the partnership with the NEA Nuclear Education, Skills and Technology (NEST) Framework is available on the NEST page.

A dedicated TCOFF-2 special session will be organised at NuMat2026: The Nuclear Materials Conference in Halifax, Canada, from 21 to 24 September 2026. In this session, the key outcomes of the TCOFF-2 project will be presented, providing an opportunity to disseminate and discuss the project’s achievements within the broader international nuclear materials community.

The next TCOFF-2 project review meeting is planned to be held in Aix-en-Provence, France, in February 2027.