RRFM 2009 Transactions - European Nuclear Society

Tested fuel assembles are load in the core in chosen position and are reloaded few
times for supporting permissible specific power. One of it is presented in fig. 3.
Irradiation
WL - experimental
channel of water loop
for measurement
of leakage parameter
Fig.3. Arrangement of experimental channel of water loop and FA during
irradiation in a core
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2. Irradiated fuel characteristics
The reached energy release is approximately identical for both irradiated assemblies
with different uranium density in fuel meat. The UO 2 . fuel was irradiated to 60% burn-up and
UMo fuel to ≈30 %.
During the irradiation in the core the maximal power density of 277 kW/l in fuel cell (or about
370 kW/l in fuel element space) has been obtained. It is a typical parameter for research
pool-type reactor.
The test programme included measurements in reactor loop after irradiation.
Leakage parameter (1.3⋅10 -5 ) for pin fuel with UO 2 has remained lower than permissible
value (2⋅10 -5 ) according with test program. However, this result 2,6 times more as WWR-M2
results in case of maximum WWR-M2 energy release.
In WWR-M reactors, the Leakage parameter is used as the operational indicator of fuel
elements non-integrity is the criterion (β), defined as the ratio of the number of fission
fragments leaking out in the coolant to the number of fission fragments generated in the fuel
[3,4]. For stable equilibrium conditions:
V
β = --- , where
q
V - is the leakage out rate of nuclide from the fuel element into the coolant, and
q - is the rate of nuclide generation in the fuel.
The equilibrium activities of five nuclides: 85m Kr, 87 Kr, 88 Kr 135 Xe, 138 Xe are used for
determination of leakage rate (β-value).
PNPI experience shows that the β-increasing from 10 -7 to several units of 10 -6 is normal
effect for aluminium dispersion fuel elements during fuel burnup process.
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