System Identification and Ranking Table (SIRT) for chemical thermodynamics of severe accidents

Journeau, C.*; Bechta, S.*; Komlev, A.*; Kurata, Masaki ; Ogi, Hiroshi  ; Matsumoto, Toshinori ; Mohamad, A. B. ; Barrachin, M.*; Quaini, A.*; Guneau, C.*; Bottomley, D.*; Ito, Ayumi*

Within the second phase of the OECD/NEA project on Thermodynamic Characterisation of Fuel Debris and Fission Products Based on Scenario Analysis of Severe Accident Progression (TCOFF-2), a Systems Identification and Ranking Table (SIRT), has been derived from the usual PIRT and adapted to chemical thermodynamics and material science. Firstly, a draft list of systems of interests has been distributed to TCOFF-2 partners. After review, a final list of 154 systems has been considered. Then system ranking has been carried out. Two series of figures of merit have been considered: importance for safety including the contribution to severe accident phenomena and to fission product behaviour and source term as well as needs for further R&D, based on the lack of existing data and the needs to improve relevant existing thermodynamic databases (mostly NUCLEA and TAF-ID). Each participating organization provided ranking of the systems for these Figure of Merits. Relevance to safety has been organized in 10 columns: Classical LWR / High BU, High enrichment fuel/ Fukushima Daiichi, TMI2, Chornobyl/Near-term ATF cladding (Cr-coated Zry)/ Near-term ATF cladding (FeCrAl) /Long-term ATF cladding (SiC) /Advanced fuels (UN, U-Si) /Advanced Modular Reactors / Post-Accident Leaching). Received rankings have then been agglomerated and averaged. A dedicated finalization meeting has been held in June 2023 in which the systems having the highest relevance and the largest needs for improvement have been considered. It must be noted that some systems for which there is a rather good knowledge, like (U,O, Zr) have not been selected, nor systems in which thermodynamic results are very hard to attain due to kinetics effect such as (U,H,O). After some system grouping, consensus have been reached on a list of 20 systems (13 linked to current or near-term fuels and 7 linked to longer-term fuels) having the highest priority.