1. magnetic confinement - ENEA - Fusione

3. FUSION TECHNOLOGY 77
3.5 Neutronics
Fig. 3.12 - Measured dose
rate in the cavity centre.
[3.33] P. Batistoni et al.,
Experimental validation
of shutdown dose rate
experiment. Final report
of ITER Task T-426,
FUS-TN-SB-NE-R-002
(2001)
[3.34] P. Batistoni et al.,
Fusion Eng. Des. 58-59,
613 (2001)
[3.35] P. Batistoni et al.,
Benchmark experiment
for the validation of shut
down activation and dose
calculation in a fusion
device, presented at the
Int. Conf. on Nuclear
data for Science and
Technology (ND2001) and
accepted for publication
in J. Nucl. Sci. Technol.
Sv/h
10-3
10-4
10-5
10-6
Background inside the cavity
Measured dose rate (G-M)
Measured dose rate (TLD)
Background dose rate in the cavity
1 day 7 day 1 month
10-7
+ + +
10-5 10-4 10-3 10-2 10-1 100
Time after irradiation (years)
assembly was irradiated
long enough
to create a sufficiently
high level of activation
for monitoring by
dosimeters and other
radiation detectors
after shutdown. Provision
was made for
the cooling time
assumed necessary
before allowing
personnel access. The
objective of the
experiment was to
validate the present
dose rate calculations in a typical and complex shield geometry. It was started in 2000
and completed in 2001 in collaboration with the Technical University of Dresden
(TUD) and Forschungszentrum of Karlsruhe (FZK).
The mockup was irradiated with 14-MeV neutrons for three days at the FNG. The
resulting dose rate was measured for about four months of cooling time by two
independent experimental techniques (fig. 3.12). Other useful measurements, such as
the neutron spectrum, decay gamma-ray spectrum, dose-rate distribution and some
relevant activation reaction rates inside the mockup, were performed [3.33-3.35].
The experiment was then analysed with a rigorous, two-step method (R2S), i.e.,
using the neutron transport code MCNP-4C and the activation code FISPACT, and a
direct, one-step method (D1S), approximate but more straightforward, with an ad
hoc modified version of MCNP used in the nuclear analysis of ITER. The FENDL-2
nuclear data libraries (FENDL/MC-2 for the neutron flux calculation and
FENDL/A-2 for the activation calculation), which are the ITER reference libraries,
were used for both methods. The European libraries EFF/EAF-2001 and the Japanese
libraries JENDL-FF/JENDL-3.2(A) were used with R2S.
The analysis showed that the dose rate measurement inside the mockup is well
predicted by R2S and by all the nuclear data library packages: in the comparison in
figure 3.13, all the computed vs. experimental (C/E) values are close to unity within
the total uncertainty, with the exception of some under-estimations found at about 1
day of decay time.
Fig. 3.13 - C/E dose rate
in the cavity centre.
C/E
1.6
R2S/EFF/EAF2001
1.4
R2S/EEN-2
R2S/JENDL
D1S (FENDL-2/A)
1.2
1.0
8 . 10-1
6 . 10-1
4 . 10-1
10-4 10-3 10-2 10-1
Time after irradiation (years)
100
The approximate
D1S method with
FENDL-2 is also
in good agreement
with
measurements
and gives values
slightly but
systematically
lower than R2S.
This may be due
to the fact that
minor nuclides,
contributing to
the total dose
rate at the