RRFM 2009 Transactions - European Nuclear Society

In this case the size of pores in all the regions is within a range of 140 nm to 1100-1400 nm,
this means that all the regions of specimen #74-2 (taken from the pillowing area) have pores,
whose smallest size is by ~40 nm less than that in #74-1. The data obtained for all the
regions of #74-2 obey the poly-extreme dependence N i =f(D i ) and the corresponding curves
have some maxima, i.e. two are in the areas remote to the crack, two are at the crack mouth
and three are in the area near the crack. This may imply that the pores in the fuel particles in
the regions remote from the crack can consist of two poly-dispersed systems with their own
distribution over sizes and even three such systems can exist in the regions close to the
crack. This manner of the distribution over sizes can be either a cause or a predecessor of a
crack formation as well as a consequence of its formation in the fuel meat matrix.
All different patches of specimen #74-2 reveal a common peculiar feature, i.e. the changing
of pore parameters (a mean size, a total quantity and a volume) while approaching the crack
(Fig. 3). This feature distinguishes specimen #74-2 from specimens #73 and #74-1 in spite
of the fact that their burn up values are close. According to these data the mean size of
pores decreases from 455 to 390 nm, the total amount increases from 1.18·10 9 to
1.96·10 9 mm -3 and the volume grows from 0.103 to 0.129 mm 3 /mm 3 when approaching the
crack (from a distance of 5 mm to ~300 µm).
With further moving towards the crack (to a distance of ~30 µm), the mean size is still
decreasing and the total amount increases by ~10 %, while the volume reduces by ~20 % to
reach a value 0.109 mm 3 /mm 3 .
Fig. 3. An influence of a fuel particle position relative to a fuel meat crack on a mean size
(d), volume (V) and quantity (N) of pores in fuel particles
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