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2.4 Neutron flux distribution<br />

One radial flux distribution corresponding to the mid-plane and two axial flux distributions<br />

corresponding, respectively, to the centre of the target and the fuel zone were requested. Considerable<br />

differences between the participants are observed, especially for the radial neutron flux distribution<br />

and for the axial flux distribution in the target zone. In particular, ENDF-based results (ANL and RIT)<br />

estimate by far the lowest neutron flux through the target. The discrepancies are also significant in the<br />

fuel region, where differences in flux level and in peak flux position appear. These discrepancies can<br />

be partially explained by the different level of sub-criticality: a system with a lower k eff<br />

needs more<br />

external neutrons in order to maintain the chain reaction. This results in a more peaked axial flux in<br />

the target, at the interface with the duct, and a displacement of the axial flux peak in the fuel towards<br />

the upper part of the core.<br />

An additional study was performed with ERANOS in order to assess the impact of the k eff<br />

value<br />

on the neutron flux distribution. By modifying appropriately the ν values for reproducing the k eff<br />

values submitted by the participants, neutron flux distributions were recalculated for each participant.<br />

From these distributions, spatial dependent correction factors were obtained. Finally, the neutron flux<br />

distributions supplied by the participants were rescaled for the reference k eff<br />

value of 0.95 using these<br />

spatial dependent correction factors. The rescaled neutron flux distributions are presented in Figures<br />

6, 7 and 8 and refer to the equilibrium core.<br />

Figure 6. Axial flux distribution in the target region; results scaled to a k eff<br />

value of 0.95<br />

1.6E+16<br />

1.4E+16<br />

Neutron Flux<br />

1.2E+16<br />

1E+16<br />

8E+15<br />

6E+15<br />

ANL<br />

CIEMAT<br />

KAERI<br />

PSI/CEA<br />

JAERI<br />

RIT (JEF)<br />

RIT (ENDF)<br />

SCK-CEN<br />

4E+15<br />

2E+15<br />

0<br />

0<br />

10<br />

20<br />

30<br />

40<br />

50<br />

60<br />

70<br />

80<br />

90<br />

100<br />

110<br />

120<br />

130<br />

140<br />

150<br />

160<br />

170<br />

180<br />

190<br />

200<br />

Axial position (cm)<br />

388

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