Dr. Olander et We. Wang, THERMODYNAMICS OF THE U-O AND ZR-SYSTEMS AND APPLICATION TO ANALYSIS OF FUEL LIQUEFACTION DURING SEVERE ACCIDENTS IN LIGHT-WATER REACTORS, Journal of nuclear materials, 247, 1997, pp. 258-264
Citations number
26
Categorie Soggetti
Nuclear Sciences & Tecnology","Mining & Mineral Processing","Material Science
Severe accident modeling requires knowledge of the heat effects accomp
anying simultaneous dissolution of UO2 and fusion of Zircaloy to form
the U-Zr-O melt. Estimation of the enthalpy changes must rely chiefly
an data from the U-O and Zr-O binary systems. The partial molar enthal
pies of oxygen in the pure liquid metals are determined by application
of Sieverts' law. The Sieverts' law constant is obtained by deriving
the complete relationship between the oxygen pressure, the O/M, ratio
of the solid or Liquid phase and temperature from the pure metal M to
the dioxide MO2. This assessment utilizes the integral constraint invo
lving the Gibbs free energy of formation of the compound MOC and the v
ariation of the oxygen pressure p, over the entire composition range.
Once the p-C-T relationship has been established, the enthalpy changes
on dissolving UO2 and alpha Zr(O) into the U-Zr-O melt are computed.
The heat effects of fuel/cladding dissolution in a severe accident are
applied in a liquefaction model based on kinetic control by the avail
able heat from fission product decay. In addition to the portion of th
e decay heat reaching the inner cladding surface, the rate of melting
of the cladding depends on heat flow to its outer surface from steam o
xidation or radiation from other parts of the core. Depending on the r
elative importance of these two heat inputs to the cladding, time to m
elting is from 100 to 400 s and the fraction of the fuel dissolved var
ies from 5 to 20%. (C) 1997 Elsevier Science B.V.