1. magnetic confinement - ENEA - Fusione

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3. FUSION TECHNOLOGY
3.5 Neutronics
Carlo approaches, the numerical tools under development for sensitivity/uncertainty
analysis. Through the
1.3
Nb-93(n,2n) (E
analysis it was possible
1.2
n >10MeV)
to find the reason for
1.1
the underestimation
1.0
(mainly the low value
0.9
of the inelastic cross
0.8
MCNP-EFF-2.4
sections) in FENDL-2
0.7
MCNP-EFF-3.0
DORT/EFF-3.0
and also to check that
0.6
MCNP/FENDL-2
DORT/FENDL-2
the uncertainties in the
0.5
MCNP/JENDL-FF
Total error
cross sections were
0.4
compatible with the
0 10 20 30 40 50 60
experimental findings.
Penetration depth (cm)
C/E
Fig. 3.15 - C/E values for
the neutron flux in the
fusion peak energy range
E > 10 MeV, measured by
the activation technique
using the Nb-93(n,2n)
reaction.
3.5.6 Experimental validation of neutron cross sections for fusion
materials (EAF project)
Chromium is one of the candidate structural materials for a fusion reactor because of
its activation properties. In a relatively short time, pure chromium reaches the
conventional activity and dose-rate limits for disposal and maintenance. In the
framework of the activity for the validation of activation cross sections in the
European Activation File (EAF), a sample of chromium (manufactured by
PLANSEE) was irradiated by the 14-MeV FNG [3.38]. The induced activation was
measured by standard and very low background gamma spectroscopy detectors
(HPGe) located in the Gran Sasso (Italy) underground laboratories.
The sample was irradiated for about six hours at the maximum neutron flux
produced by FNG. The neutron flux and spectrum are well monitored by the
multifoil activation technique. The total neutron fluence at the sample was 4.87×10 12
n/cm 2 ± 3%. After irradiation, the activity was measured for several decay times
ranging from fifteen minutes to three months.
[3.38] M. Pillon, M.
Angelone, Final report
of Task TTMN-002 (5)-
002, Report FUS- TEC-
MA-NE-R-2001 (2001)
The calculations were carried out with the latest version of EAF (2001). The typical
material composition supplied by PLANSEE was input in the EASY code. These
maximum values of impurities were used for the C/E comparison. The
radionuclides not included in the EASY code were determined by measuring their
activity.
The results of the C/E comparison and uncertainty analysis are reported in table 3.II.
The radionuclides in bold are those produced by the impurities in the chromium
sample. The amount is given in Wppm, together with the total uncertainty.
The data in table 3.II show the good quality of the EAF-2001 cross-section data, since
most of the C/E values are, within the uncertainties, close to one. The only exception
is the radionuclides produced by the so-called sequential charge particle reaction
(SCPR), i.e., a two-step reaction like (n,p) → (p,n), which occurs with high-energy
neutrons. These reactions are treated by the EASY system, but in an approximate
way. Another radionuclide which shows a large discrepancy is the V-48 produced by
the reaction Cr-50(n,t)V-48. This is a threshold reaction with the energy threshold
close to the maximum FNG neutron energy, and it is most probable that there are
some errors in the cross-section values near the threshold energy. The experimental
results indicate that these values are overestimated. The high C/E value obtained for
Na24 may be due to the fact that the maximum impurity level for Al and Mg was
used.