RRFM 2009 Transactions - European Nuclear Society

All described fuel elements were calculated separately because of their different irradiation
history. The irradiation power of each FE at some specific location was calculated by relation
given below [7]:
Total Thermal Power
P
irr
=
x P f
Number of FE
Where total thermal power of TRIGA Vienna is 250 kW and P f is power factor .The values of
P f are 1.0, 0.9, 0.8, 0.7, 0.6, 0.5 and 0.5 for A, B, C, D, E, F and G ring of the core
respectively.
3 Results and Discussions
The comparison of calculated and measured results has been given in table3 & figure 5. The
reasons these deviations between have been discussed in this section one by one.
FE number
Burn up
(MWh)
Cal. Activity (Bq)
Cs-37/cm
Meas. Activity (Bq)
Cs-137/cm
Percent difference
(%))
2196 25,68 1.351E+09 1.362E+09 0.8200
2077 30,912 1.715E+09 1.597E+09 6.8790
2156 58,08 3.519E+09 3.600E+09 2.2979
2124 69,24 4.588E+09 4.440E+09 3.2127
Tab 3: Comparison between Calculated and measured results
Fig 5: Comparison of ORIGEN2 calculations and gamma spectroscopic measurement
First, the reactor has been operating since 1974 with mixed core, using three different types
of fuel elements. Due to the mixed core composition, the accuracy of calculated burn-up
varies significantly from element to element [1]. Second, the basis of the calculation (i.e.
MWD) was taken from log books and because of long history of the fuel elements since
1962; some operational uncertainties in the log books may cause these variations in the
accuracy. Third, the PWR libraries of ORIGEN2.2 have been used for this TRIGA fuel
element model which have its own contribution in these deviations for example, it can also be
seen in figure 5 that with increasing the burn up, difference between calculations and
measurements increases showing that PWR library for TRIGA reactors is well valid in lower
burn up regions.
The spectrometric analysis provides the Cs-137 axial distribution for given fuel
elements. As mentioned that Cs-137 production is proportional to BU therefore applying this
axial distribution of Cs-137, the axial burn-up distribution of each measured TRIGA fuel
element can be predicted with reasonable accuracy.
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