Fuel transient deformation

A micromechanical model for the secondary creep of elasto-viscoplastic porous materials with two rate-sensitivity exponents: Application to a mixed oxide fuel

“…The dependence of the creep rate on stress is described by the superposition of a linearly viscous flow and of a power-law creep relation. In the proposed models the maximal temperature in the range of validity is about T max ≈ 2000 K. A high temperature enhancement of the model was then proposed by Slagle et al (1984) who added a third term to increase the accuracy of the model up to T max = 2900 K. The final unidimensional constitutive relation of Slagle et al (1984) reads as follows:…”

“…The matrix surrounding the pores is considered as isotropic and its viscoplastic behavior is described by a strain-rate potential including two creep mechanisms, diffusion creep and dislocation creep. The constitutive relations for the matrix are derived from the phenomenological strain rate identified for MOX fuel in a creep test by Slagle et al (1984). This potential is described by two power-law functions with two different rate-sensitivity exponents.…”

Viscoplastic behavior of a porous polycrystal with similar pore and grain sizes: Application to nuclear MOX fuel materials

“…Reference Houston et al (1970) 10-17 1100-1330 1.95-1.98 3-15 90-94 22 - Evans et al (1971) 7-70 1475-1625 1.95-2 4-23 88-94 0-100 - Routbort et al (1972) 7-110 1400-1675 1.83-1.99 10-47 95-97 25 65-93 Routbort and Voglewede (1973) 69 1500-1600 1.883-1.994 5-44 90-97 22/25 30-93 Slagle et al (1984) 2.2-6.5 2175-2640 1.89-1.92 25 88-93 25 93 Caillot et al (2004) 40-80 1535 -5.5 95-96 6-10 -Table 1: Creep tests on MOX pellets where σ is the compressive stress, T the temperature, O/M the oxygen-to-metal ratio, d the grain size, and ρ the pellet density.…”

“…The dominant creep mechanism for this regime seemed to be the dislocation motion (dislocation glide and dislocation climb can occur). Then, creep tests were performed on MOX pellets (Houston et al, 1970;Evans et al, 1971;Routbort et al, 1972;Routbort and Voglewede, 1973;Slagle et al, 1984;Caillot et al, 2004) and, similarly to UO 2 , two regimes were observed. Some features on the compression tests are reported in Table 1.…”

“…Stresses are between 7 MPa and 110 MPa. Temperatures are between 1100 • C and 1700 • C, with the exception of (Slagle et al, 1984) in which tests are performed at temperatures higher than 2000 • C, representative of extreme temperatures which could be encountered in a fuel during a postulated RIA (Suzuki et al, 2008).…”