Room-temperature microindentation behaviour of LWR-fuels, part 1: fuel microhardness

Comments on the threshold porosity for fission gas release in high burn-up fuels

“…This comes from a Monte Carlo calculation, in which the rim structure is simulated by distributing variable amounts of 1 lm (or larger) hole-cubes (pores) in a finite mesh of 0.5 lm solid-cubes (grains) [4]. However, these results contradict our experimental observations and supporting calculations using Ronchi's percolation model for regular arrangement of pores [8], both indicating low pore-interconnection probability for the rim material up to high porosity fractions [2,9].…”

“…However, the more thoroughly the rim material and related processes are characterized, the less probable seems a high fission gas release (FGR) from this part of the fuel. Support for this are the ostensible closed character of the rim porosity [2] and the predominance of thermally released gases (i.e. of non-rim origin) in the rod freevolume [1].…”

“…However, fine-grained and porous materials do not always exhibit large open areas. For example, closed cell solid foams, a class of materials to which the fuel rim would belong [2], can sustain considerable pore fractions (>80%) under sealed conditions [5]. Therefore, the surface-to-volume ratio (S/V) increase postulated in Ref.…”

Detailed characterisations of high burn-up structures in oxide fuels

“…The porosity measured in this agglomerate was about 50%. Such swelling and deformation properties (see [29]) certainly explains the decrease in the fabrication porosity in UO 2 rim areas.…”

Nanoindentation tests for TiO2, MgO, and YSZ single crystals

“…The mechanical properties of the irradiated fuel have been measured in a post irradiated experiment (PIE). For example, the Vickers and Knoop indentation tests for the irradiated nuclear fuels have been performed [1,2]. Against this background, we consider the application of the nanoindentation for the mechanical properties evaluation of the irradiated fuel, because the system and equipment are small enough to set up in a hot cell.…”