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etween runs contain enough uncertainty that an
error of this magnitude could be lost. Thus the
shift in rod position cannot he assigned to either
the beginning or end of run 12. Even with this
uncertainty in residual reactivity, the zero-power
results fall within a very narrow band, whicii
derrionstrates the continuing good performance of
both the reactor system and the reactivity-balance
calcitlation.
MAL EFFECTS OF OPERATION
C. H. Gabbard
Radiation Heating
Reactor Vessel. - The temperature differences
between certain thermocouples on the reactor
vessel and the reactor inlet temperature are monitored
by the computer io determine whether there
is any evidence of a sedimentation buildup in the
lower head or on the core support flange. In the
previous semiannual report,' it was stated that
these temperature differences had increased. Fullpower
data were reviewed from runs 6 through 12,
and it now appears that the increase reported is
within the data scatter. The average temperature
differences for run 6 were 2.11 and 1.51°F/Mw
for the core support flange and the lower head,
respectively, and were 2.205 and P.5S°F/Mw for
run 12.
Fuel Pump Tank. - An unexplained downward
shift in the temperature of the upper pump-tank
surface was inentioned in the previous semiannual
report. Past data for the pump-tank temperature
and for the heat removal by the oil system were
reviewed to determine if a better thermal coupling
could have developed between the pump tank and
the shield-plug oil cooler. No evidence of increased
heat removal by the oil system was found.
The temperature distribution remained essentially
the same throughout run 11, with pump operation
continuing without cooling air. When the reactor
was taken to power in run 12, the full-power temperature
distribution had shifted downward another
15 to 30°F, and the pump tank continued through
'MSX Program Semiann. Progr. Rept. Feb. 28; 1967,
ORNL-4119, p. 19.
'Ibid., p. 18.
22
the run at the lower temperatures. The tempera-
tures at zero power were consistent with the run
11 zero-power data. This would seein to indicate
that less fission product activity was being re-
leased in the pump tank. The lower temperatures
are not detrimental to the operation or to the life
of the pump tank,
Thermal Cycle History
The accumulated thermal cycle history of the
various components sensitive to thermal cycle
damage is shown in Table 1.2. Approximately 63%
of the design therinal cycle life of the fuel system
freeze flanges has been used to date; 54% had
been used at the time of the previous semiannual
report.
Temperature Meosurernent
Sa It Systems. -- Approxiinately 330 thermocouples
are used to tne'asure the temperatiire at various
locations on the fuel and coolant circulating salt
systems. Only two thermocouple wells are pro-
vided, one each in the coolant radiator inlet and
outlet pipes. The remaining thermocouples are
attached to the pipe or vessel walls. The thermo-
couples on the radiator tubes are insulated to pro-
tect them from the effects of the high-velocity air
that flows over them during power operation; the
others are not insulated and thus are subject to
error because of exposure to heater shine aild to
thermal convection flow of the cell atmosphere
within the heater insulation. In March 1965, with
the fuel and coolant systems circulating salt at
isothermal conditions, a complete set of readings
was taken from all the thermocouples that should
read the temperature of the circulating salt. A
similar set of data was taken in June 1967 at the
start of run 12. The results of the two sets of
measurements are shown in 'Table 1.3. Compari-
son of the standard deviations for the radiator
thermocouples with those for the other thermo-
couples shows the effect of insulation on reducing
the scatter. Comparison of the sets of data taken
ovei two years apart shows very little change,
certainly no greater scatter. Figure 1.9 shows
that the statistical distribution of the deviations
31bid., p. 20.