OECD/NEA Benchmark Calculations for Accelerator Driven Systems

2.4 Neutron flux distribution
One radial flux distribution corresponding to the mid-plane and two axial flux distributions
corresponding, respectively, to the centre of the target and the fuel zone were requested. Considerable
differences between the participants are observed, especially for the radial neutron flux distribution
and for the axial flux distribution in the target zone. In particular, ENDF-based results (ANL and RIT)
estimate by far the lowest neutron flux through the target. The discrepancies are also significant in the
fuel region, where differences in flux level and in peak flux position appear. These discrepancies can
be partially explained by the different level of sub-criticality: a system with a lower k eff
needs more
external neutrons in order to maintain the chain reaction. This results in a more peaked axial flux in
the target, at the interface with the duct, and a displacement of the axial flux peak in the fuel towards
the upper part of the core.
An additional study was performed with ERANOS in order to assess the impact of the k eff
value
on the neutron flux distribution. By modifying appropriately the ν values for reproducing the k eff
values submitted by the participants, neutron flux distributions were recalculated for each participant.
From these distributions, spatial dependent correction factors were obtained. Finally, the neutron flux
distributions supplied by the participants were rescaled for the reference k eff
value of 0.95 using these
spatial dependent correction factors. The rescaled neutron flux distributions are presented in Figures
6, 7 and 8 and refer to the equilibrium core.
Figure 6. Axial flux distribution in the target region; results scaled to a k eff
value of 0.95
1.6E+16
1.4E+16
Neutron Flux
1.2E+16
1E+16
8E+15
6E+15
ANL
CIEMAT
KAERI
PSI/CEA
JAERI
RIT (JEF)
RIT (ENDF)
SCK-CEN
4E+15
2E+15
0
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Axial position (cm)
388