Radiation damage and waste management options for the SOMBRERO final focus system and neutron dumps Page: 4 of 6
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dumps and result in a considerable reduction
of the bending angle.
2. Overview of SOMBRERO
In order to validate our methodology we
have reviewed the previous work that was
completed for the KrF-driven SOMBRERO
IFE power plant design.
It has been found that neutron-induced
gamma-ray doses in the final optical or fo-
cusing components were not considered.
Recent work in support of the National Ig-
nition Facility indicates that gamma-ray
doses can be of great importance when esti-
mating the lifetime of optical components.2
It has also been found that the GIMM was
not modeled in order to consider the neutron
scattering in that element, and only 1-D
scaling was performed in order to achieve
the fast neutron flux at the position of the
final focusing mirror. The present work
shows this flux was then underestimated and
that it is essential to perform 3-D calcula-
tions that consider the secondary neutrons
scattered by the GIMM. Another problem
found when trying to predict the expected
lifetime for the optics is the fact that a clear
fast neutron fluence limit has yet to be de-
termined. The SOMBRERO study estimated
the optics lifetime assuming a range of flu-
ence limits. A complete analysis would re-
quire more material data about the fast neu-
tron and gamma-ray fluence limits.
3. Computational methods
3-D neutronics calculations have been
performed using the TART98 Monte Carlo
neutron and photon transport code. The
present work utilized the ENDL neutron
transport and the EPDL photon transport
cross section libraries.45 A point neutron
source was used at the origin emitting neu-
trons isotropically with the SOMBRERO
target energy spectrum. The model includes
the detailed radial build of the SOMBRERO
design at the midplane for the blanket/reflector, which has an overall thickness of 1
m with an inner radius of 6.5 m. The 1.5-m-
thick inner shield and the cylindrical reactor
containment building are included. The
neutron dumps have been modeled using an
aspect ratio (depth divided by diameter) of
unity. The wedges are located 30 m from the
target and are made of pure fused silica
operated at high temperature (around 400
C) to promote self-annealing. A baseline
wedge thickness of 3 cm was used. All the
free space inside the reactor building is
filled with xenon gas at 0.5 torr in order to
protect the first wall from target x-rays and
debris. Dose rates and fluxes from gamma-
rays and fast neutrons have been obtained at
the optical elements. The results for the final
focusing mirrors are reported in cylindrical
zones around the neutron dumps in order to
approximate their location. Only neutrons
with energies > 100 keV are counted in the
fast flux.
The ACAB activation code has been
used with the FENDL/A-2.0 activation cross
section library for subsequent activation cal-
culations.6- Calculations have been com-
pleted assuming 30 full-power-years (FPY)
of irradiation, using a fusion power of 2677
MW. Results have been obtained for cooling
times of up to 100 years. We have reported
the results of waste disposal rating (WDR)
and contact dose rates for the optical ele-
ments and for the neutron dumps and
building shell. For the activation calcula-
tions typical impurities have been included
in the SiO2 used for the wedges and the final
focusing mirror substrate (typical impurities
have been considered8. For the dielectric
coating of the mirrors, calculations have
been performed for two different materials:
MgF2 and ZnS.
4. Results
The neutronics calculations show that
adequate tritium breeding is possible with
5% open solid angle fraction (TBR = 1.16).
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Latkowski, J. F.; Meier, W. R. & Reyes, S. Radiation damage and waste management options for the SOMBRERO final focus system and neutron dumps, article, August 9, 1999; California. (https://digital.library.unt.edu/ark:/67531/metadc626047/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.