Large controlled amounts of helium in uniform concentration in thick samples can be obtained through the radioactive decay of dissolved tritium gas to He3. The term, tritium trick, applies to the case when helium, added by this method, is used to simulate (n,alpha) production of helium in simulated hard flux radiation damage studies

Eash, D. T.

Green, W. V.

Zukas, E. G.

English

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Eash
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'7/CJ6 A,1--*TIlE TIUTIUl\1 ,!:~l!CJ~
Green, with E. G. Zukas and D. T.
Los Alamos Scicnti fie Laboratory
University of California
Los Alamos, New .Mexico 87544
w. v.
Helium is thought to be velj' insolublo ~ n solid metn.ls as it is a noble gas.
When forced in solution in some way, it is trapped in bubbles at high pres~ures.
Small quantities, less tlHm 1 ppm helium atoms per metal atoms nrc sUfficient to modif"
. .
high temperature mechanical propcrties. Just how, and to what c",lcnt properties
like creep ductility will be degraded by large quantities of hellwn (200 ppm increase
PCI' year over 20 years) is lUlknown, but large offects nre likely.
Hellum will be produced in unprccedented amounts in wall matel'jals of proposed
power producing fusion reactor.~, tlle abov€: figure of 200 ppm per year being typical
for such a reactor design, while f.1st breeder fission reactors would produce about
00 3 ppm PCI' year. Hell'illl efreets, tllel'efore, coulc1 be \,el1' important to fusIon
reactor technology.
Large controlled alnOwlts of helium in uniform concentr<ltion throu~hout thick
, .
samples can be readily obtained tlll'ough rncIioactive decay of dissolved trItium gus
to 3He• We coined the namc "tritium trick" when helhun added by thil-. method is
used to simulate (n, ex) production of helium in (r::imulated) hard flux radiation
damagc studies.
Tritium decays to helium with a half life of about 12 years so tlmt about 1/2
percent dccays per month. The only radiation emitted is 0. vcry weak, 12 kcv, beta
. particle. It is too 'Weak to calise significant damage.' Tl'itiulntbefng nn isotope
of hydrogen, is very soluble in many metals. It also d,ffu~es into und out of metals
quickly. Thus tritium can be dissolved, allowed to decay to tllC desired helium
content, and pwnped away selectively relnti-"e to tho 3He• Only 3Ho will remain
to change properties.
*Work lJel'formcd under the auspices of tJ10 U. S. Atmnic Energy Commil:::sion and
Witil tilC support of National Aeronautics nnd Space Admini~trntion.
I
https://ntrs.nasa.gov/search.jsp?R=19720011029 2020-03-11T18:39:31+00:00Z
Published phase diagrams show the amount of hydrogen (am therefore tritiwn)
that will dissolve in various metals at any temperature and pressure. As an
example, at 1000·0 eb~ operating temperatu.re likely ,for some fusion reactor walls)
3
at 1/100 atmosphere pressure of tritium, the He production rate in niobium
(presently the first choice metal for structural parts in the walls of fusion reactx:>rs)
via beta decay will exactly equal the ~e production rate at full power via cn, x ex)
reactions. This amount of tritium in uniform soUd solution would only be 1/4 alOe
As another example, niobium charged at 600·0 under one atmosphere of tlitium
gas will collect 200 ppm heUum in only ten days, thereby allowing accelerated damage
rate studies. The tritium trick should not be difficult, nor expensive, once a
tritium handling facility is available. Initial charging experiments are now in progres
"
We hope in establish how helium diffuses, collects in'bubbles and modifies creep
. '
properties with electron transmission microscopy, internal friction a."d creep
experiments.
ThlJ report wu prepared .. an .CCOllnt of work
.pomored by the Unlled States Oowrnment. NellMr
the Unlled St.te. nor the Unlled St.t.. Atomic I!nUIY
Comm1sslon. nor any of their employ_, nor any of
their c:ontraetOl'l, .lIbc:ontrac:tors, 01' their employ-,
m.u••ny warranty, exprea or lmpUed, or Illumes any
lep! Uabllity or responllbUlty for the .c:euruy, c:om-
pletenell or usefutness of any Information, .pparatua,
prodllc:t or proc:eaa d1lclosed, or "~nts that Its use
woll1d lIot lnfrlnae privately oWMd riabts.


Tritium trick

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