1276 3。6 1278 3。9

1484 2。9 1486 3。3

1651 2。9 1653 3。2

1858 2。9 1861 2。8

BeO 13。6 wt%

278 66。8 300 68。0

480 41。1 500 38。0

688 25。1 700 25。0

904 16。9 900 17。5

1099 13。3 1100 12。5

1280 10。0 1300 11。0

1489 8。0 1500 9。0

of 5000 W/m2 was applied to one end of the geometry。 Then temperatures were applied corresponding to the temperatures at which measurements were made on the specimens having the range of 278 K to 1653 K。 The ANSYS cases were then solved stepwise at each temperature value。

The results from the ANSYS calculations and thermal mea- surements for the UO2/BeO ceramic composite fuel were com- piled into data tables。 Table 2 shows the comparison between ANSYS code predictions versus experimental data。 The error in the measured data ranges within a few tenths of a W/mK for each data point。 The results from ANSYS compare well, with the measured results often being within this measurement error range。 The overall curve trend is the same with the difference in thermal conductivity being one W/mK to a few tenths of a W/mK difference between the two data sets。

FEM THERMAL MODEL OF UO2/PIP-SIC COMPOSITE

After establishing the accuracy of the ANSYS code to cal- culate effective thermal conductivities of two-phase structures with a minor phase being continuous, the next step was to use the ANSYS grid geometry calculation to predict the thermal conductivity of the UO2/PIP SiC composite。

Figure  1   Silicon carbide thermal conductivity curves。

The Starfire PIP SIC specimens were reportedly fabricated using powder and a polymer palletizing method, and thermal diffusivity and specific heat were measured to be 50  W/m-K at 300 K [7, 16]。 Although this data was not published, two known SiC thermal conductivity curves for 94% TD sintered SiC and 97% TD refractory SiC have values near that of the Starfire SiC [8]。 Figure 1 shows these data。 Although the two curves differ in values, the overall shapes are similar。 An average between the two curves was then used to generate a general data trend with temperature。 This trend was then applied to the 50 W/m-K at 300 K data point to produce a probable thermal conductivity curve for Starfire SiC consolidated in this way。 It is interesting to note that the higher density sintered products have lower conductivity than the PIP-produced SiC。

Other curves were then generated for densities of 50 to 100%TD using the Maxwell equation [17] assuming that the porosity is composed of randomly distributed spherical voids in the SiC phase。 The resultant SiC thermal conductivity curves are shown in Figure 2, which shows the important effect of density on the conductivity。