INFLUENCE OF THERMAL-PROPERTIES OF ZIRCONIA SHROUD ON ANALYSIS OF PHEBUS FPT0 BUNDLE DEGRADATION TEST WITH ICARE2 CODE

In the FPT0 test of the PHEBUS/FP program, it was observed that the fr action of liquefied UO2 reached 50%, which is much larger than the exp ected maximum value of 20%. Most of the post-test analyses with variou s computer codes underpredicted the bundle temperature during a late p hase and could not reproduce such a large core degradation. In most of the previous analyses, the shroud thermal conductivity evaluated base d on the Pears' ZrO2 specific heat data and the thermal diffusivity me asured by JAERI was used. However, recent thermal properly data books adopt a lower specific heat than measured by Coughlin and King's at hi gh temperature. The present analyses with ICARE2 showed that the FPT0 bundle behavior could be mostly reproduced by using the shroud thermal conductivity based on Coughlin and King's. If the present calculation is assumed to be correct enough, the shroud thermal conductivity at h igh temperature could be smaller than the current evaluation based on the Pears' data. Since the shroud thermal conductivity has thus a stro ng effect on the bundle behavior, further measurement and evaluation o f the thermal properties of the shroud are highly recommended. (C) 199 7 Elsevier Science S.A.