RRFM 2009 Transactions - European Nuclear Society

THE STEREOMETRIC ANALYSIS OF GAS POROSITY OF FISSION
PRODUCTS IN IRRADIATED U-Мo FUEL
O.A. Golosov, S.А. Averin, V.L. Panchenko, M.S. Lyutikova
Institute of Nuclear Materials
Zarechny, Sverdlovsk region, Russia, 624250
ABSTRACT
A stable behavior of U-Mo/Al dispersion fuel under irradiation conditions of research
reactors depends on a U-Mo alloy ability to keep hold of gaseous products of U-235
fission. Numerous investigations of irradiated U-Mo alloys show that a quantity and
size of gas pores in the alloys increase with a fuel burn up. However, up to the
present time changes in the size and quantity of gas pores were mainly analyzed by
their metallographic sections [1, 2].
In paper the results of the stereometric analysis of the volumetric distribution of the
pores of gas fission products in the U-Mo fuel particles irradiated to different burn up
as well as in the sampling areas with abnormal swelling of a fuel meat are described.
1. Introduction
An unstable behavior of dispersion U-Mo/Al fuel under irradiation conditions is the main
problem preventing this fuel from usage in research reactors. When a fuel fission rate and
burn up, dependent on a fuel irradiation temperature, exceed a certain critical threshold, gas
pores are observed to form in a fuel meat and it finally leads to uncontrollable swelling of fuel
elements. This phenomenon seemingly is related to the metal U-Mo fuel, which is unable to
keep hold gaseous fission products (GFP), which can release into the Al matrix. In order to
understand the phenomenon and solve the problem of the uncontrollable swelling rate of fuel
plates the data on the interaction of irradiation parameters with the quantitative
characteristics of the U-Mo fuel GFP pores are required as well as the data on the changes
in these characteristics in the fuel meat areas with a normal and abnormal behavior.
In this paper the data on the volumetric distribution of the gas pores in the U-Mo fuel
irradiated to ~50 and ~97 % burn-up are provided as well as the data on the gas pores
distribution in the abnormal swelling areas located near the fuel meat cracks.
2. Materials and test methods
The fuel element assembly designated “КМ004” was irradiated in the research reactor
IVV-2M, Zarechny. The test specimens were cut out of different areas of a fuel element (FE)
of КМ004 (Table 1).
Ψ 4) , 10 21 Bu 5) , %
Specimen Sampling area L 1) T 2) BOL , 0 C ϕ 3) , 10 14
number in fuel element
f . cm -3. s -1 f . cm -3
135 Top - 48.6 3.80 4.57 49.5
73 Center - 80.2 5.92 7.12 97.3
74-1 Near the center ~5 mm 82.6 5.86 7.06 96.4
74-2-1 Near the center ~1 mm 82.6 5.86 7.06 96.4
74-2-2 Near the center ~300 µm 82.6 5.86 7.06 96.4
74-2-3 Near the center ~30 µm 82.6 5.86 7.06 96.4
1) – a distance from a swelling crack mouth
2) – a fuel cladding temperature at the beginning of tests
3) – a fuel fission rate
4) – a fuel fission density
5) – an equivalent burn-up
Tab. 1: Characteristics of test specimens
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