Melting Temperature of Irradiated Fast Reactor Mixed Oxide Fuels.

Abstract

The melting (solidus) temperatures of irradiated mixed oxide fuels were measured and the compositions of the fuels on the temperature measurement date were calculated. The fuels contained about 29wt% Pu initially and were irradiated up to 124GWd/t in the experimental fast reactor JOYO. A melting temperature correlation was obtained by an experimental regression analysis using 21 measurements:where Tm is the expected melting temperature (K), XI the plutonium fraction (Pu/(Pu+U)) and X z the americium fraction (Am/(Pu+U+Am)) at the measurement, and XB the burnup (GWd/t). The equation shows that the melting temperature decreases by 5, 4, and 3 K per 10 GWd/t at 50, 100 and 150 GWd/t, respectively. The effects of actinides, such as Pu and Am, on melting temperature could be explained by an ideal solution model. However, the decreases caused by soluble fission products could not be well explained in terms of the ideal solution model. KEYWORDS: melting t e m p e r a t u r e , m i x e d o x i d e f u e l , fast reactor, irradiated fast reactor oxide fuel, solidus temperature, t h e r m a l arrest, experimental regression analysis, ideal solut i o n , burnup dependency, s a t u r a t i o n of temperature decrease, a m e r i c i u m f r a c t i o n , actinides

Melting Temperature of Mixed Oxide Fuels for Fast Reactors.

“…2) For evaluating the melting temperature lowering from stoichiometric MOX that would be accountable solely to soluble FPs, we derived the deviations T Sol.FP from the measured T meas shown by that calculated using T Sol.MOX of Eq. (2), T Sol.O/M of Eq.…”

“…3). While melting temperature lowering accountable to the presence of soluble FPs cannot be explained simply on the basis of ideal solution model, 2) assuming a pseudoternary system UO 2 -PuO 2 -FPsO 2 , the values of T m (FPsO 2 ) and h f (FPsO 2 ) were derived by curve-fitting.…”

“…Available literature 2,3) gives empirical solidus equations for irradiated (Pu 0.29 U 0.71 )O 2 fuels, together with the actinide compositions at the time of melting temperature measurement, but which, besides being limited to the above-cited fuel composition, does not take account of the effect on melting temperature brought by differences in the O/M ratio.…”

Liquidus Temperature of Irradiated Mixed Oxide Fuels for Fast Reactors

“…1) While many reports have been published on the solidus temperature and on equations for deriving the solidus for irradiated MOX fuel, [2][3][4][5] the only study on measuring its liquidus is that reported by Reavis et al 6,7) The present study aims at filling this gap by deriving the liquidus temperature equation of irradiated MOX fuel using as basis the solidus temperature equation in various reported studies. [8][9][10][11][12][13][14][15] Derivation of the equation proceeded in three steps, making reference to published reports where available: (1) Derive the liquidus temperature equation for unirradiated stoichiometric MOX fuel [8][9][10] and evaluate liquidus temperature lowering brought by the presence of Am and by the alteration herewith of fuel stoichiometry (oxygen-to-metal ratio (O/M) ratio), applying the procedure adopted previously for deriving the solidus temperature equation.…”

Melting Temperature of Simulated High-Burnup Mixed Oxide Fuels for Fast Reactors

“…For example, changing oxygen potential and increasing burnup can cause transition between groups (2) and (3), and between groups (1) and (3). Since soluble FPs tend to reduce the melting temperature, the oxides dissolved in the matrix, group (1), cause the greatest effect on the melting temperature; the other two precipitates, groups (2) and (3), have small effects on the matrix. The gases and other volatile FPs, group (4), have little or no effect on melting temperature.…”