RRFM 2009 Transactions - European Nuclear Society

FISSION INDUCED SWELLING AND CREEP OF URANIUM-
MOLYBDENUM ALLOY FUEL *
G.L. HOFMAN, YEON SOO KIM
Argonne National Laboratory
9700 S Cass Ave, Argonne, IL 60439 – USA
A.B. ROBINSON
Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-6188 – USA
ABSTRACT
Detailed analysis of metallographic sections taken from miniplates that were
irradiated as the RERTR-6, -7 and -9 tests in the ATR has shown that the apparent
fuel swelling contains a significant fuel creep component. Equations for both fission
induced swelling and creep for U-Mo alloy fuel are presented.
1. Introduction
It is a common observation in the analyses of the postirradiation metallography of dispersion
miniplates, as well as full-size plates, that the meat swelling close to the side rails of the
plates is significantly diminished. This effect is particularly pronounced in our RERTR
miniplate tests where one side of the plates faces the ATR core, resulting in a rather large
transverse flux, or fission-rate, gradient in the plates with values peaking at the very edge of
the fuel meat that faces the ATR core.
Although the effect is obvious, it has been difficult to quantify in dispersion fuel because of its
complex microstructure that includes variations in fuel volume fraction and the presence of
variable fractions fuel-Al matrix interdiffusion. Monolithic miniplates do not have these
drawbacks, and this paper presents the analysis of the edge effect using the metallography
on mini plates from tests RERTR-6, 7 and 9.
2. Analysis
Figure 1 shows the location of the transverse metallographic section taken from each plate
and Fig. 2 the micrograph of one of these sections. The taper in the fuel foil at the edges
close to the side rails is very clearly evident. A transverse fission density profile, derived from
γ-ray scanning and physics calculations, is shown in Fig. 3. Using these profiles and our fuel
swelling correlation, the calculated swelling is plotted in Fig. 4 together with the profile
measured on the micrographs from a miniplate from each of the three tests. As expected, the
swelling at the tapered end of the fuel foil is substantially less than predicted.
In fact, it is much lower than swelling due to solid fission products. This and the evidence that
the fission gas porosity does not vary appreciably along several millimeters from the foil edge
(see Fig. 5) rule out, at least to the first order, an effect on the fuel swelling per se.
* Work supported by US Department of Energy, Office of Global Threat Reduction, National Nuclear Security Administration
(NNSA), under Contract DE-AC-02-06CH11357. The submitted manuscript has been authored by a contractor of the U. S.
Government under contract NO.DE-AC-02-06CH11357. Accordingly, the U. S. government retains a nonexclusive royalty-free
license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.
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