ORNL-4191 - the Molten Salt Energy Technologies Web Site

Shortly after full power operation was reached on
March 14, the radiation monitor on the charcoal
trap in the container sweep-gas line increased to
18 mr/hr. Some 8 hr later a further increase to
-3.4 r/hr was noted. No further increase occurred
until March 17, when the radiation from the
charcoal trap increased rapidly (over a period of
-3 hr) to -100 r/hr, indicating a significant
leakage of fission products from the loop. At this
point the loop was retracted out of the high-flux
region to a position at 1 to 2% of the highest flux,
and the fuel salt in the loop was frozen by reducing
the loop temperatures to -400°C in order
to prevent possible saIt leakage from the loop.
As a result of these actions, the charcoal trap
activity decreased to 1 r/hr over a 15-hr period.
From March 17 to March 23, 1967, the loop was
operated in a retracted position at 1 to 2% of full
power, and the fuel salt was kept frozen at a
temperature of 350 to 4OO0C, except for brief
periods of melting to determine the location of
the leak. It was concluded that the fission prod-
uct leak was in the vicinity of the gas separation
tank and that loop operation could not be con-
tinued. Three fuel salt samples were removed
from the loop during this period.
Beginning on March 27, 1967, the fuel salt was
drained from the loop by sampling to facilitate the
removal of the loop from the reactor and subse-
quent examination in hot-cell facilities. By this
procedure the fuel salt inventory in the loop was
Ou t-of-Pile
Flush
Solvent salt
In-Pile
Preirradiation
Solvent salt
Fueled salt
Retracted-fuel removala
Total
179
reduced from 151.6 g to 2.1 g, requiring ten sam-
ples (12 to 25 g per sample). On April 4, 1967,
the ORR was shut down, and on April 5, 1967, the
loop package was removed from the reactor into a
shielded carrier and transferred into a hot cell
without difficulty .
During the in-pile operating period, fuel salt
containing enriched uranium was exposed to re-
actor irradiation for 1366 hr at average fission-
power densities up to 150 w/cc in the graphite
core fuel channels. For both out-of-pile and in-
pile operating periods, various salt additions and
removals were made, including samples for analy-
sis. During the in-pile period, the reactor power
was altered appreciably 38 times, and the distance
of the loop from the reactor lattice, that is, the
loop position, was changed 122 times. Thus, the
equivalent time at full loop power during fueled
operation was 547 hr, while the ORR was operated
for 937 hr. Table 15.1 summarizes the operating
periods under the various conditions for molten-
salt loop No. 2.
Details of some of the more significant observa
tions made during operation and results of hotcell
examinations and analyses are given in
sections which follow.
15.3 OPERATING TEMPERATURES
The salt in the loop was kept molten (> 490OC)
during all in-pile operations until it was frozen on
Table 15.1. Summary of Operating Periods for In-Pile Molten-Salt Loop 2
Operating Period (hr)
Total Irradiation
77.8
171.9
73.7
343.8 339.5
1101.9 937.4
435.0 428.3
2204.1 1705.2
Full Power
Dose Equivalent
Salt Additions and Withdrawals
Additions Samples Salt Removal
7
5
1
136.0 1
547 .o 2
11.2 0
- -
694.2 16
aMaintained at 350 to 4OO0C (frozen) except during salt-removal operations and fission product leak investiga-
tions.
1
1
2
2
3
4
-
13
13
0
0
0
0
9
-
22