Actinides chemistry in mixed oxide nuclear fuel


Actinides chemistry in mixed oxide nuclear fuel

Martin, P.; Belin, R.; Robisson, A. C.; Dumas, J.-C.; Scheinost, A. C.

Innovative Mixed OXide (MOX) (U,Pu)O2-x fuels for Sodium Fast neutron Reactors (SFR’s) systems are studied within the framework of GEN-IV nuclear reactor systems. SFRs will also be able to burn long-lived minor actinides (MA) such as Am, Np and Cm. Among MA, americium is of main concern. One solution currently considered is to homogeneously add americium in small amount to the fuel. Because it significantly affects sintering properties as well as irradiation performances, the oxygen to metal (O/M) ratio is an important factor to be considered when designing oxide fuels. Therefore, a thorough knowledge of the correlation between oxygen potential fixed during fuel sintering and O/M ratio is essential. The aim of this work is to follow the chemistry of uranium, plutonium and americium in (U0.750Pu0.246Am0.004)O2-x samples sintered for 4 h at 1700°C in various moisture-added Ar containing 5% of H2 atmospheres Thanks to XAS experiments performed at U, Pu and Am edges, the O/M ratio values were determined and are in very good agreement with those derived from XRD analysis. Furthermore, both XANES and EXAFS results show that O/M evolution in MOX samples is only supported by the reduction of plutonium. Thus, with this methodology, we are able to obtain O/M ratio without further thermal treatment as opposed to TGA. By using thermochemical modeling based on Lindemer and Besmann formalism [1], determination of thermodynamical conditions leading to these O/M values are estimated. Our results are compared to the study of Osaka et al. [2] highlighting a discrepancy between modeled and experimental oxygen potential vs. O/M ratio curve for Am-doped MOX system.

[1] T.B. Lindemer and T.M. Besmann, J. Nucl. Mat. 130, 489-504 (1985).
[2] M. Osaka et al., J. Alloys Comp. 428, 355-361 (2007).

Keywords: Nuclear fuel; Mixed Oxides; XAS

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