Progress report on the accelerator production of tritium materials irradiation program Page: 4 of 11
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PROGRESS REPORT ON THE
ACCELERATOR PRODUCTION OF TRITIUM
MATERIALS IRRADIATION PROGRAM
Stuart A. Maloy', Walter F. Sommer , Robert D. Brown2, John E. Roberts2, John Eddleman-, Eugene Zimmermann2, and Gordon Willcutt3
Materials Science and Technology Division', Los Alamos Neutron Science Center2, Technology and Safety Assessment Division'
Los Alamos National Laboratory
Box 1663, MS H 805
Los Alamos, New Mexico 87545
The Accelerator Production of Tritium (APT) project is
developing an accelerator and a spallation neutron source
capable of producing tritium through neutron capture on He-3.
A high atomic weight target is used to produce neutrons that
are then multiplied and moderated in a blanket prior to capture.
Materials used in the target and blanket region of an APT
facility will be subjected to several different and mixed particle
radiation environments; high energy protons (1-2 GeV),
protons in the 20 MeV range, high energy neutrons, and low
energy neutrons, depending on position in the target and
blanket. Flux levels exceed 104/cm2s in some areas.
The APT project is sponsoring an irradiation damage effects
program that will generate the first data-base for materials
exposed to high energy particles typical of spallation neutron
sources. The program includes a number of candidate materials
in small specimen and model component form and uses the Los
Alamos Spallation Radiation Effects Facility (LASREF) at the
800 MeV, Los Alamos Neutron Science Center (LANSCE)
The API' program is designing an accelerator capable of
producing a proton current of around 100 mA in the 1-2 GeV
energy range; optimization studies considering production
needs, plant cost and operations cost will determine the energy
eventually chosen. The protons are directed to a target made of
a high atomic number material such as tungsten. Spallation
reactions produce neutrons as well as protons and other
particles. The neutrons produced have an energy spectrum that
extends to the proton source energy.
Target and Blanket
The primary neutron source is surrounded by a blanket made of
lead which serves both as a neutron multiplier and moderator.
In the blanket, neutrons are captured in He-3 producing on
evaporation tritium and a proton. A back-up concept uses an
alloy of Al 3% Li enriched in Li-6 producing after capture and
evaporation tritium and He-4. In the gas system an on-line
separation plant continuously removes tritium from a flowing
system; in the Li system the alloy is irradiated for a period of
time, removed from the facility and processed in another
facility. Figure 1 shows a schematic cross section of the He-3
target and blanket assembly.
Figure 1: Schematic cross section of an APT target and blanket
assembly. one half of the blanket assembly has been removed
Radiation Environment in the AP' Target and Blanket
Referring again to Figure 1, note that the proton beam enters
the target and blanket assembly through the window module
before interacting with the tungsten neutron source module.
The primary proton beam is restricted in size and does not
directly impinge on the decoupler or other parts of the blanket.
The target and blanket assembly is exposed to the primary
proton beam at an energy of 1-2 GeV. For a beam expanded to
a size of 16 by 160 cm, the proton fluence in nine months of
operation will be about 5.8 x 1021 protons/cm2 for a 100 mA
current and 7.7 x 1021 protons/cm2 for 134 mA; these are the
two likely currents in an operating plant. The leading part of
the tungsten neutron source assembly will also be exposed to
the primary proton beam; the energy of the protons will
decrease as a function of length while passing through the
neutron source assembly. A neutron flux will also be generated
as the beam passes through the neutron source assembly
resulting in a mixed proton and neutron flux. The proton and
neutron energy spectra will also change as a function of
distance into the target. The decoupler region will be exposed
to high energy neutrons with energies up to a few hundred MeV
and protons produced by spallation reactions in the target with
energies in the several tens of MeV range. The remainder of
the targetlblanket assembly including the lead modules,
reflector modules, and shielding will be exposed to a mixed-
spectrum of high and low energy neutrons that varies as a
function of position. Calculations, using high and low energy
transport computer codes including the Los Alamos High
Energy Transport code (LAHIET in the LAH-ET' Code System
(LCS), predicting the flux-spectra throughout the target and
blanket are performed along with optimization studies of the
configuration. Proton fluxes above 1 01/cm2s are expected.
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Maloy, S. A.; Sommer, W. F.; Brown, R. D. & Roberts, J. E. Progress report on the accelerator production of tritium materials irradiation program, article, May 1997; New Mexico. (digital.library.unt.edu/ark:/67531/metadc677857/m1/4/: accessed November 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.