RRFM 2009 Transactions - European Nuclear Society

Similar to the case of stainless steel, the nuclear heating curve in molybdenum still follows
the neutron flux shape. Below the core centreline at positions -7.8 cm, -12.8 cm and -17.8,
where C/E>1, (except for the *F8 tally at -12.8 cm), nuclear heating is overestimated with
relative errors not exceeding 4%, determined from Table 3. Positions -2.8 cm and 2.2 cm
show an underestimation of the nuclear heating values, nevertheless, the relative error
amounts to a maximum of 6%.
Furthermore, above the core centreline, at 7.2 cm, 12.2 cm, 17.2 cm, 22.2 cm and 27.2 cm,
an underestimation of nuclear heating is observed. This occur with relative errors ranging
from a minimum of 13% (at 7.2 cm) increasing in magnitude as we proceed towards the
upper section of the core up to a maximum value of 34%.
Calculated/Experimental (C/E)
Axial Position *F8 F6
-17.8 1.01 1.04
-12.8 1.00 1.01
-7.8 1.02 1.02
-2.8 0.94 0.95
2.2 0.95 0.96
7.2 0.86 0.87
12.2 0.78 0.79
17.2 0.72 0.76
22.2 0.67 0.67
27.2 0.68 0.66
Table 3: Ratio (C/E) of calculated to experimental total nuclear heating in Molybdenum core
calorimeter
4. Conclusions
The total nuclear heating values calculated using the track length estimate and the pulsed
height tally are in good agreement. Below the core centreline, relative errors in nuclear
heating values for stainless steel range from 11% to 16% compared to a range of 1% to 6%
in molybdenum. Above the core centreline, stainless steel exhibits relative errors, from 1% to
19% whereas the relative errors in molybdenum span a wide range, from 5% to 34%.
This variations in the calculated nuclear heating values compared to experimental, can be
attributed to the Z numbers of the two materials being investigated (stainless steel 304 and
molybdenum). For the relatively high Z molybdenum, gamma heating is the most dominant
compared to stainless steel.
While the shape of the nuclear heating curve follows the shape of the neutron flux, the
observation of up to 34% relative errors in the molybdenum still has to be investigated. While
considering all the sources of inaccuracy in both the experiment and the calculations, an
exact agreement between the calculated and experimental values should never be expected.
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