ORNL-4191 - the Molten Salt Energy Technologies Web Site

133
Table 9.9. Comparison of Aqueous Chelotiny Agent with HN03 Leach for Removing Geposited
Fission Products from Graphite and Hastelloy
._.._._. __I..._ ~... .__. .
Disintegrations per
Exposed
Minute in Total Sanrple
Samplea
in - 9 9 ~ ~ 0 132TC. 103Ru 95%,
Gas CGB V
A
T
Liquid CGB V
A
T
Go s Hastelloy N V
A
T
Liquid Hastelloy N V
A
T
x 10'O
4.6
1.7.5
6.35
4.60
3.24
7.84
4.65
0.21
4.87
2.24
1.51
3.75
% 1o'O
2.99
32.1
35.1
2.99
2.25
5.24
5.89
70.2
76.1
1.99
15.5
17.5
x io9
0.15
1.19
1.34
0.154
3.00
3.15
0.12
0.07
0.66
0.73
*V represents leaching in aqueous chelating solution; A represents leaching in acid; T represents total,
Since this solvent dissolves salts but not
metals, these observations may possibly indicate
that 99M0 and "Nb are present as oxidized
species (fluorides?), while tellurium and tuthenium
are present as metals. Wiping with a
cloth removed larger fractions of 'OM0 and "Nb
than of activities such as '32Tt?, I3'I, y5Zr,
I4'Ba, and 89Sr which penetrated the graphite.
The depmition of fission products on pyrolytic
graphite (see Table 9.10) in the gas phase was
similar to that on CGB graphite, although 132Te
deposited to a smaller extent on the pyrolytic
graphite. In the liquid phase, 9yM0 and '"Te
deposited slightly more heavily on pyrolytic
graphite than on the CGB.
The deposition of "Nb was markedly heavier
on Hastelloy N in the liquid phase than in the gas
phase. Tellurium-132 and '"Ha deposited more
heavily on the metal exposed in the gas phase.
Other isotopes deposited similarly on metal in
the two environments.
When metal and graphite were exposed to the
gas phase, somewhat mote '32Te, I3'I, arid
95Zr deposited on the metal. When both were
exposed to the liquid phase, less "Mo, 14'Ra,
and 89Sr and more 'j2Te and 13LI deposited on
the Hastelloy. The deposition per square centimeter
of R given isotope varied by less than a
x 10'
4.3
0.89
5.23
0.13
4.47
1.49
, 3.5 for 1"3R~, 14.0 for loiRu, 95 for
95Nb, and 56 for "Zr. A similar comparison of
the activities on the Hastelloy N specimens from
the two exposures (Tables 9.6 and 9.10j J ves
ratios of 20 for "Mo, 6 for '32Te, 170 for 103Ri~,
400 for '*'IRU, 7.5 for "Nb, arid 30 for 9sZr. The
ratio of full-power exposure times is 417; the ratio
of total exposure times is, of course, considerably
greater. Both sets of activity ratios may be biased
high since the sample holder in the 8-hr exposute
may have intercepted a sii;able fraction of
the depositing activities.
Examination of the ratios given above shows
that only deposition of "'Ru 011 Hastelloy N
proceeds at approximately the same rate for 8
as for 3340 full-power hours. However, the
measured deposit of a given radioactive nuclide
actually reflects the deposition rate only
over the last two or three half-lives of exposure
time for that nuclide. Thus the measured ac-