ORNL-4191 - the Molten Salt Energy Technologies Web Site

The assembly was segmented into shield plug,
connector, and loop container regions. Sections
of the gas addition and gas sample tubing and
sections of the salt sample line from these re-
gions were obtained for radiocheniical analysis.
The loop container region was opened; no evi-
dence of salt leakage from the loop was seen.
Several sections of the gas addition and sample
lines and of the salt sample line were taken. The
loop was then pressurized wit.h dry argon, and
bubbles from a leak-detecting fluid indicated the
crack on the top of the core outlet tubing near the
core.
During these operations, the core region was
kept at 300°@ in a furnace when not being worked
on to keep radiolytic fluorine from being generated
in residual salt, although the salt inventory was
only about 2 g. The loop was cut into three
segments - gas separation tank, cold-leg return
line, and core - and was transferred to the High-
Radiation-Level Examination Laboratory for
further cutup and examination. There the Hastel-
loy N core body was removed, and the graphite
was cut into upper and lower sections with thin
sections removed at top, middle, and bottom for
metallographic examination.
Samples of loop metal were taken such that
surfaces representing all regions of the loop were
subiiiitted for both radiochemical and metallo-
graphic examination. In total, some 16 samples
of loop metal, 8 of the salt sample line, 11 of the
“hot” gas sample tubes, and 9 of the “cold” gas
additiori tube were submitted for radiochemical
analysis. A dozen specimens of metal from the
loop, some of which contained parts of several
regions of interest, have been subjected to metal-
lographic examination. The results of these
analyses and examinations are described in sec-
tions which follow.
Small amounts of blackened salt were found in
the gas separation tank near the outlet, in the
core bottom flow channels, and in the first few
inches of salt sample line near the core. A droplet
also clung to the upper thermocouple well in
the file1 channel. The total residual salt in the
loop did not appear to exceed the inventory value
of 2 g.
The penetration profiles of the various fission
prodiicts in graphite were determined by collecting
concentric thin shavings of core graphite from
representative fuel tubes for radiocheiiiical analysis.
For this purpose a graduated series of
185
broaches or cylindrical shaving tools were designed
by S. E. Dismuke. Fourteen broaches permitted
sampling of the core graphite fuel channels
( v4 in. ID) to a depth of 45 mils, in steps nominally
ranging from 0.5 mil for the first few mils in
depth up to 10 mils each for the final two cuts.
In some cases, two or three cuts were collected
in the same bottle in order to reduce the number
of samples to be analyzed.
A sample bottle was attached directly below the
hole being sampled, and the broach with shaved
graphite was pushed through the hole into the
bottle from which it was subsequently retrieved
after brushing into the bottle any adhering graphite
particles. The bottle was closed, a new bottle
clipped into place, and the next larger broach used
For each bottle, all the graphite sample was
weighed and dissolved for radiochemical analysis.
Total recovery from given holes ranged from 94
to 111% of values calculated from the broach diameter
and graphite density. The higher values
were almost entirely due to high initial cuts, indicating
fuel channels narrower than the nominal
0.250-in.-diam, irregular original holes, or in some
cases, some salt adhering to the surfaces. Since
penetration depth should be measured from the
original surface, actiial depths were calculated
from the cumulated weight of material actually
removed. Forward, next-to-forward, next-to-rear,
and rear fuel tubes, in top and bottom sections,
were sampled in this way; a total of 76 such
samples were submitted far analysis.
Graphite was also shaved from the outer surface
of the core cylinder in four samples to a depth of
19 mils. In addition, eight by 3/,-in. core
drillings were taken of the interior central part of
the graphite.
Samples of loop metal taken from the core outlet,
gas separation tank inlet and outlet ends,
cold leg, and other regions were subjected to
metallographic examination. This examination
defined the nature of the break in the core outlet
line and gave evidence of some carburization
and corrosion of loop metal surfaces.
Bottom and top inner surfaces of the core outlet
tube near the core are shown in Figs. 15.4 and
15.5. These photographs give a metallographic
view of the break in this tube. ‘The break appears