Self-pumping impurity by in-situ metal deposition Page: 3 of 24
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High energy particles (deuterium, tritium, and helium) impinging on mate-
rial surfaces are known to become trapped within the material up to saturation
levels which depend on the particle species and energy, the type of material,
and the material temperature. Passive helium removal using this approach was
first examined for a short pulse experimental reactor [1,2], but saturation
limits the effective pulse length for power reactors. By continually plating
the surface, however, it may be able to achieve long burn times (>6 mo) with a
relatively imple system. A conceptual view of this approach is shown in
fig. 1. A key requirement for this application is for the material to trap
helium much better than hydrogen. It has been demonstrated experimentally
that nickel preferentially traps helium , and that se/eral other materials
(iron, vanadium, niobium, and tantalum) are believed to be capable of prefer-
ential trapping. The selective trapping in certain metals is a result of the
negligible solubility of helium compared with the relatively high solubility
of hydrogen in the lattice. The injected helium will diffuse through the
lattice until it reaches a nearby trapping site where it can come out of solid
solution. Hydrogen, on the other hand, remains in solid solution until it
diffuses to the surface and escapes. Thus, the material surface can act as a
selective helium pump. However, helium trapping occurs only up to a satura-
tion level, typically lO^-lO^/cm2, after which it is released at the same
rate it is injected. In order to be used as a pump in a tokamak reactor, a
fixed trapping surface would have to be regenerated after every pulse by ,uch
means as thermal spiking. By continuously plating the surface, however, much
longer bum pulses, suitable for a commercial power reactor, may be feasible.
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Brooks, J.N. & Mattas, R.F. Self-pumping impurity by in-situ metal deposition, article, July 1, 1983; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc1088326/m1/3/: accessed June 17, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.