Prime pagine RA2010FUS:Copia di Layout 1 - ENEA - Fusione

072
progress report
2010
activity varies from 5.25×10 12 Bq/kg in stainless steel to 5.2×10 13 Bq/kg in C10700, maximum dose rate and
decay heat are 1.2×10 4 Sv/h and 9.6 W/kg in Spinel. After 50 years from the shutdown peak specific activity,
dose rate and decay heat are 7.6×10 9 Bq/kg, 102 mSv/h and 0.08 mW/kg respectively in CuCrZr. At medium
cooling times the activation of CuCrZr is higher than of that C10700 (the maximum ratio is 2) because of
Cobalt. Except at very short cooling times, the insulator activation is lower than that of conductor and SS
components and is dominated by the impurities. Copper resistivity increase at the shutdown varies in the range
33.6–276.7 pΩm (resistivity of pure copper is 17 nΩm, at T=20°C) due to transmutation in Ni, Co and Zn.
In the more shielded segments, the activation and transmutation are about one order of magnitude lower than
the peak. The impact of the front manifold on the activation of the poloidal components is within a factor 2
and depends on the material and cooling time. The complete inventory is provided to perform the safety
analysis and waste classification [3.12, 3.13].
Neutron and gamma spectra behind ITER blanket modules and in divertor
The installation of sensors behind ITER blanket modules and in the divertor region is under study. For this
reason, knowledge of the radiation field (i.e. neutron and secondary gamma spectra) is required. For this scope
3–D radiation transport simulations have been performed using MCNP5 code with FENDL2.1.
Z axis
6
4
2
-1
-4
Profile
Neutron and gamma fluxes and spectra have been calculated in
forty–five positions (fig. 3.36) assuming neutron production
from a 500 MW DT plasma. The positions of the detectors in
outboard regions have been varied toroidally to evaluate the
impact on the radiation field of the port plug and the shielding
capability of the blanket modules.
In the divertor region, the maximum total neutron flux is found
in the dome zone (5.5×10 13 n/cm 2 /s) and the minimum one is
found at the bottom of the outer vertical target. The gamma
flux varies between 5.7×10 12 γ/cm 2 /s and 3.6×10 13 γ/cm 2 /s.
Behind blanket modules, maximum fluxes are calculated in the
gaps between the central outboard modules (7.9×10 12 n/cm 2 /s
and 4.6×10 12 γ/cm 2 /s). The fluxes drop of one order of
magnitude at the top of the machine.
The effect of the difference between port plug and blanket
module is moderate. In fact, in the equatorial port zone the
toroidal variation is ≤12% on the neutron flux and ∼25% on the
gamma flux. The effect is higher in the upper port zone (within
a factor 2).
The poloidal behaviour of the neutron flux follows the neutron
R axis
current profile except in the regions close to the equatorial
Figure 3.36 – Positions of the detectors midplane. This is mainly due to the variability of blanket’s
shielding thickness. The radial profile of the flux is very
sensitive to blanket front attenuation: by moving the detectors
located close to the midplane 8 cm toward the plasmas, the neutron flux doubles as compared to the reference
position [3.14].
Neutronic analysis of ITER divertor rails
Nuclear heating for a 500 MW DT plasma, helium production and dpa at end–of–life have been calculated
in several positions of the divertor rails and surrounding components by using the MCNP5 code in a three
dimensional geometry. Maps in two poloidal inner and in five poloidal sections are provided.
Higher values of nuclear heating, He production and dpa are found in the inner zone, especially on the top
corner of inner cover plate because of the streaming through the gaps between cassettes, values are shown in
figure 3.37. In the most irradiated outboard zone the obtained values are lower by one order of magnitude as
compared to the inboard quantities.