ORNL-2106 - the Molten Salt Energy Technologies Web Site

ANP PROJECT PROGRESS REPORT
Fig. 3.4.26. Corner Tube from Air Exit Face of
NaK-toAis Radiator PWA No. 2 as Viewed in the
Direction of the Air Flow. 75X. Reduced 36%
prior to installation. It may be noted, however,
that the radiator as redesigned retained the bottom
flanged plate, a top plate, and the four support
members. During the brazing cycle the NaK tubes
were brazed to these members, and a relatively
rigid condition resulted at each of the five trans-
verse sections across the radiator matrix. Local
differences in rates of heating and cooling, par-
ticularly between the air inlet face and the
remainder of the radiator during blower startup,
could therefore bring about the development of
tensile loading. This condition could be partially
relieved by slicing the support members and plates
in a manner similar to that utilized during dis-
section for metallographic examination, as shown
in Fig. 3.4.21.
The development of tensile forces alone, how-
ever, cannot be assigned the full responsibility
for failure. The incidence of numerous incipient
fractures in this radiator has been related to the
presence of a support member or heavy plate.
Over 13,000 tube-to-fin joints have been examined
1 94
metallographically without the observation of a
single incipient fracture. The differences in mass
and thermal conductivity of the support members
and plates as compared with the high-conductivity
fins could result in significant differences in
heating and cooling rcites during cyclic operation.
These differences could create lateral forces that
could be responsible for the initiation and propa-
gation of fractures in brazed joints between tubes
and support members in any portion of the radiator.
EXAMINATION OF FUEL-TO-NaK HEAT
EXCHANGER AFTER SERVICE
G. M. Slaughter
Tests of the fuel-to-NaK heat exchanger, desig-
nated as IHE-3, were terminated as a result of
the detection of a leak in a tube bundle after a
total of 1794 hr of operation in the temperature
range 1100 to 150U'F. There was a temperature
differential imposed on the heat exchanger for
1015 hr of this total time, and 21 thermal cycles
were applied over this period.
The NaK inlet and NaK outlet headers of the tube
bundle that leaked were separated from the heat
exchanger to facilitate examination and inspection.
Top and bottom views of the inlet header are
shown in Figs. 3.4.27 and 3.4.28. The general
location of the failure is evident in Fig. 3.4.28,
in that a dark reaction product can be distin-
guished from the lighter solidified fuel mixture.
Forty tubes in the area of the failure were indi-
vidually inspected with a dye penetrant and a
Borescope, and at least five tubes were found to
contain obvious cracks. The NaK inlet header
after dissection with an abrasive cutoff wheel
"UCUIIIFIE~
v.1-
Fig. 3.4.27. Top of NaK Inlet Header of Fuel-to-
NaK Heat Exchanger IHE-3 Showing Tube Welds.
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.