ORNL-3124.txt

 

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ORNL=-3124
UC-25 — Metals, Ceramics, and Materials

 

“
s 0

- INOR-8-GRAPHITE-FUSED SALT

COMPATIBILITY TEST

R. C. Schulze
W. H. Cook

R. B. Evans lll
J. L. Crowley

    
  
 

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DOCUMENT COLLECTION

LIBRARY LOAN COPY
DO NOT TRANSFER TO ANOTHER PERSON

If you wish someone else to see this
document, send in name with document
and the library will arrange a loan.

 

 

 

OAK RIDGE NATIONAL LABORATORY
operated by

UNION CARBIDE CORPORATION
for the

U.S5. ATOMIC ENERGY COMMISSION

 
 

$1.00

Printed in USA. Priee __~ ., Available froem the
Office of Technical Services

Department of Commerce
Washingten 25, DL C.

 

 

 

 

LEGAL NOTICE

This report wos prepored as on oceount of Government sponsored work., Neither the United States,

nor the Commission, nor any person acting on behalf of the Commission:

A. Mokes ony warranty or reépresentation, expressed or implied, with respect to the accuracy,
completenass, or usefulness of the informotion cantained in this report, or that the use of
any Infermation, opparatus, methed, or process disclosed in this report moy not infrings
privataly awnad rights; or

B. Assumes any licbilities with respect to the use of, or for domages resulting from the use of
any information, apporatus, method, or process disclosed in this repart.

As used in the obove, ""person octing on behalf of the Commission'" includes any employee or

contractor. of the Commission, or amployese of such contractoer, 1o the extent thar such employes

or controctor of the Commission, er employee of such contracier prepores, disseminates, or
provides access to, any information pursuent te his employment or contract with the Commission,

or his employment with such centractor.

 

 

 

 
 

 

ORNL-312k4

Contract No. W-T405-eng-26

METALLURGY DIVISION

INOR-8-GRAPHITE-FUSED SALT COMPATIBILITY TEST

R. C. Schulze and W. H. Cook

Metallurgy Division

R. B. Evans, IIT, Reactor Chemistry Division

Je L. Crowley, Reactor Division

DATE ISSUED

jUN 1 - 1961

OAK RIDGE NATIONAIL LABORATORY
Cak Ridge, Tennessee
Operated by
UNION CARBIDE CORPORATION
for the
U.5. ATOMIC ENERGY COMMISSION

TR

3 Y456 O3L437L O
e 5 1 A AR B8 O 0 AL Do b8t i 500+ e i ms

INOR-8-GRAPHITE-FUSED SALT COMPATIBILITY TEST

R. C. Schulze, R. B. Evans, III,l Je Le Crowley,2 and We. He Cook

ABSTRACT

For the purpose of evaluating the compatibility of graphite and INOR-8
in a dynamic fluoride fuel medium, INOR-8 Forced Convection Loop No. 9354-5
was operated 8650 hr. The loop operated at a maximum temperature of 1300°F
and circulated a fluoride fuel of the system LiF—BeFE—UFM. Post-test
examinations of the graphite and loop components revealed no apparent

corrosion or carburization problems.
INTRODUCTION

Design studies have indicated that potentially large gains in the con-
version or breeding ratioc of molten fluoride reactor systems can be realized

3

by the incorporation of a graphite moderator and/or reflector. Such a concept

requires that graphite, together with other structural materials comprising
the reactor vessel, be in direct contact with the molten fluoride fuel mixture.
Problems which potentially arise from this arrangement are penetration of the
pores of the graphite by the molten salt, carburization of the structural
material, and possible reactions between impuritles contalined in the graphite

and the molten salt.

 

lReactor Chemistry Division
2Reactor Division

3Report on Fluid Fuel Reactor Task Force, TID-8507, pp. 92-8L (Feb., 1959).

 
 

Since graphite is inherently porous,u a strong probability exists that
this material will be infiltrated by the fuel salt. There are four major
reasons why this penetration, if severe, would be detrimental: (1) increased
reactor fuel inventory, (2) danger of hot spots in the graphite assembly,
(3) fission product retention, and (&) spalling of the graphite because of
differential thermal expansion between it and the fused salt. This fourth
condition could arise if the salt were allowed to freeze in the pores of the
graphite and were subsequently melted.

An additional problem resulting from the incorporation of graphite
relates to the carburization and resultant embrittlement of the structural
material. Presently, the structural material that has shown most promise
for use with molten fluoride systems ig INOR-8, whose composition is shown
in Table 1. Studies up to this time have shown INOR-8 to be susceptible to
carburization when placed in static sodium-graphite systems at temperatures

as low as lEOO"F.(ref 5)

However, static tests containing INCR-8, graphite,
and salt mixture LiF-BeF —UF, (60-37—1 mole %) at temperatures up to 1300°F

have given no evidences of INOR-8 carburization in periods as long as

12 000 by, (FeT 657

The third problem area associated with the use of graphite 1s that of
reactions between the fuel salt and impurities contained in the graphite.
The most serious reaction to be considered is that of uranium-tetrafluoride
and oxygen reacting to form uranium dioxide, a product which is relatively
insoluble in molten fluoride mixtures of the type considered for present

salt reactor concepts. The precipitation of UO if it occurred, would pose

2)
a serious hot-spot problem in any stagnant region of the reactor core.
Up to the time of the subject experiment, studies concerning these

salt-metal-graphite compatibility problems had been limited to static systems.

 

Porosity ranges from 15 to 30% by volume in present commercial grades.
5MSRP Quar. Prog. Rep., Jan. 31, 1959, ORNL-268L, p. T6.
6MSRP Quar. Prog. Rep., July 31, 1959, ORNL-2799, p. 59.
87D. H. Jansen and W. H. Cook, Met. Ann. Prog. Rep., July 1, 1960, ORNL-29808,
D.22C.

 

 

 

 
 

_3_

T+t was felt advisable to complement these studies with a compatibility test

in which the flow and temperature conditions of the molten fuel mixture closely
simulated those of proposed reactor systems. This report describes the results
of such an experiment which was conducted jointly by members of the Metallurgy,

Reactor Chemistry, and Reactor Divisions.

TEST EQUIPMENT AND METHODS
Loop Design

A forced-convection loop of the type employed for investigations of the
corrosion properties of fused fluoride mixtures was modified to permit the in-
corporation of graphite at the point of maximum fluoride temperature. The loop,
designated 93545, consisted of a centrifugal pump, two resistance heater sections,
the container of graphite, a cooler section, and drain tank which were assembled
as shown in Fig. 1. The entire loop and pump bowl were fabricated of INOR-8.

The tubing used for the loop was 3/8-in.—o.d. by 0;035—in. wall. The drain tank,
which was isolated from the circulating salt mixture during operation, was of
Inconel, and tThe pump rotary element wetted parts were fabricated of Hastelloy B.
The nominal compositions of Hastelloy B and Tnconel are shown in Table 1.

The grephite container, completely constructed of INOR-8, was installed in
a horizontal position at the outlet of the second heater leg (Fig. 1). Gas
entrapment in the container was prevented by placing the inlet at the lower
portion of the end plate and the outlet at the upper portion of the opposite
end plate, as shown in Figs. 1 and 2.

Figure 2 shows the INOR-O container filled with graphite rods before the
cover was attached. The container, fabricated from 0.060~in. sheet, was in the
form of a rectangular box ol in. long by 2_1/2 in. square. Orifice plates were
placed at the ends to hold the rods in place and to distribute the flow to the
spaces between the rods. Baffles were also welded in between the orifice plate

and the end of the container to 9id in the distribution of flow.

 

8J. L. Crowley, W. B. McDonald, and D. L. Clark, "Design and Operation of
Forced-Circulation Corrosion Loops with Molten Salts," Paper presented at A.N.S.
Meeting, Gatlinburg, Tennessee, June 17, 1959.
UNCLASSIFIED
ORNL- LR~ DWG 39365R

  
   

GRAPHITE CONTAINER

\SAMFLE LEG

FREEZE VALVE

  
  

DRAIN TANK

Fig. 1. Molten Salt Corrosion Loop No. 9354-5 Containing Graphite
Specimens. Showing thermocouple and specimen locations.

-
-
Table 1. Nominal Compositions of Various Nickel-Base Alloys

 

Composition (wt %)

 

Alloy N1 Mo Fe Cr C S1 Mn !

\J1
Inconel 72 min -- 6.0~10.0 14,0-17.0 0.15 0.5 1.0 max -
INOR-8 bal 15.0-18.0 5.0 max 6.0-8.0 0.4-0.8 0.35 max 0.8 max
Hastelloy B bal 26.0-30.0 h,0=7.0 1.0 max 0.05 max 0.03 max 1.0 max
Hastelloy W bal 25.0 5.5 5.0 -- - --

 

 

 
UNCLASSIFIED
PHOTO 30631

 

Fig. 2. Graphite Container Before Installation in Loop.

 
 

-7 -

The graphite test specimens consisted of thirty-two 1/2-in.-diam rods
and eighteen 3/16-in.-diam rods, each 11 in. long. These specimens were of a
low—permeation9 type graphite, National Carbon Grade GT-123-82. Measurements
made by the Materials Compatibility Laboratory indicated that the average bulk
density of the "as-received" graphite was 1.91 g/cc. This is 84.2% of the
theoretical density of graphite.lo’ll

Before the graphite rods were installed, they were calipered and welghed
by the Reaction Processes Group of the Reactor Chemistry Division. Figures 2
and 3 show the horizontal array in which the graphite rods were stacked. opace
was maintained between each of the rods and the sides of the box by means of
0.035-1in.-diam Hastelloy W (nominal composition listed in Table 1) wire spacers

wound around the 1/2-in.-diam rods. These spacers were staggered along succegsive

layers of rods so that a flow area between the rods was maintained.
Operating Procedures

Because of the ability of graphite to contain relatively large amounts of
sorbed gases, it was necessary to outgas the rods before loop operation was
initiated. Outgassing of the graphite was accomplished after the loop was
insulated and installed in its facility. A description of the method by which
the graphite was outgassed 1s given in Appendix A.

Upon completion of the outgassing process, the loop was filled with the
salt mixture LiF-BeF —UF) (62—37—1 mole %). This first fill was utilized as
a cleaning fluid and circulated approx 12 hr at 1200 to 1250°F. After dumping
and refilling with a second salt charge, the loop was placed on the AT con-
ditions shown below.

Maximum salt-metal interface
temperature 1300°F

Maximum salt and salt-graphite
temperature 1250°F

 

91n this report, 'permeation! refers to impregnation of the graphite with
o fluoride salt and 'permeability! refers to the rate of gas flow through
graphite.

O
The theoretical density of graphite is 2.27-2.28 g/cc.

Llvaeneral Properties of Materials," The Reactor Handbook, 3(1), 136,
AECD-3647 (March, 1955). -

 
UNCLASSIFIED
ORNL-LR-DWG 440884

 

 

\

\

 

.

N
\

\

A\
Ry ,//, ,
S %,,,7//%//

3\

A

   

 

Numbering Scheme for Positioning Graphite Rods.

Fig. 3.
- 9 -

Minimun salt temperature 1100°F
AT 200°F
Reynolds No. 2200

Flow rate 1 gal/min
Pressure on graphite 12.9 psig

The calculations made to determine the pressure on the graphite along
with other loop statistics are shown in Appendix B.

The averages of loop temperatures, which were recorded once per day, are
shown in Fig. 4. External heat was applied to the graphite contalner during
operation to maintain the temperature at the outlet (TC No. 11) approximately
egual to the temperature at the inlet (TC No. 9). The maximum wall temperature
of the container, as recorded by TC's No. 7 and No. 8, was maintained at 1300°F.

The loop operated under the specified polythermal conditions for a total
of 8950 hr. In addition, minor troubles encountered during the course of
operation caused the locp to operate 78 hr isothermally. Upon termination,
the loop was placed on isothermal operation and the salt was drained through
a sampling tube into a pot. A trap was placed in the line between the loop
and the pot, in order to obtain a specimen ol the after-test salt for chemical
analysis. Along with providing an after-test specimen of the salt, draining
the loop facilitated the removal of the graphite rods and loop specimens for
examination. A sample of the before-test salt was also submitted for chemical
analysis. A chronology of the events that affected the performance of the
loop is in Appendix C.

EXPERIMENTATL RESULTS AND DISCUSSION
Procedure for Ixamination

The box containing the graphite rods was removed at the conclusion of
loop operation and opened by grinding through top of the container. A portion
of the after-test graphite rods was submitted to the Analytical Chemistry Group
for determination of any physical or chemical changes, and the remainder of the
rods was examined metallographically for any microscopic changes by the

Metallurgy Division.
TEMPERATURE (°F)

41300

1250

1200

1150

1100

1050

1000

UNCLASSIFIED
ORNL-LR-DWG 32366

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LUG LUG  LUG LUG GRAPHITE
2 o 5 5 CONTAINER COOLER
ST ND
B n 1STHEATER i 2NPHEATER
P | | |1
O o< M < N O W Tqm < m O
© © © N o o - O o b
b | l
@
AVERAGE TEMPERATURE
° e OF CONTAINER WALL
o Y
Vo r\
/ ~
A /,/ \\
'~
® // \\
/// N
p— N
~
// o N
4 Z \\\
// N
, ~
/7 \\
& ___ ./ U
@ @
A LUG TEMPERATURE
® WALL TEMPERATURE
NOTE: DASHED LINE DRAWN THROUGH WALL TEMPERATURES o
WHERE LOOP WAS INSULATED AND UNHEATED TO
INDICATE FLUID TEMPERATURES
0 100 200 300 400 500 600

CISTANCE FROM PUMP EXIT (in.)

Fig. 4. Average Wall Temperatures for INOR-8 (with Graphite Insert)
Loop No. 9354-5,
 

- 11 -

Specimens of the loop components were also removed from positions
indicated in Fig. 1 and were examined metallographically for evidence of
carburization and attack by the fluoride mixture. Samples of the galt cir-
culated were submitted to the Analytical Chemistry Group for optical microscopy,

x ray, and wet chemical analyses.
Graphite Analyses

Chemical Analysis.- Machined increments of graphite specimens were sub-

 

mitted for chemical analysis. Successive cuttings, 1/32 in. in depth, were
taken from two of the larger diameter rods until center portions of less than
3/16-in. diam were left. These portions and "gas-received" impervious graphite
"planks! were then ground to -100 mesh in a mortar and pestle, which was
thoroughly scoured with Ottawa Sand according to the recommendations of the
Analytical Chemistry Division after each grinding. All graphite samples were
qubmitted for an analysis of the uranium and beryllium concentrations. Two
machine cuttings, 1/32 in. in depth, were taken from four additional rods.
These results are given in Table 2 with the beryllium and uranium concentrations
graphed as a function of penetration depth in Fig. D. Only a very slight mi-
gration of salt to the center of the graphite is noted.

Physical Analysis.- Macroscopically, there was no change in the rods. None

 

of the samples was broken or distorted and, except for the bottom layer of rods
that was covered with solidified melt, the salt did not adhere to the graphite,
as shown in Fig. 6. The weight and dimensional changes observed for the rods
after contact with circulating fluorides are listed in Table 3. The dimensional
changes for the thirteen 1/2-in.-diam rods corresponded to an average loss of
less than 0.5 mil in diameter which approximates the probable error of the mea-
surements. Otherwise, there was no evidence of erosion. Weight losses, which
ranged from negligible to 0.05% and averaged 0.02%, could be attributed to de-
sorption of residual gases from the graphite. No statistically significant
differences were noted in the thirteen 1./2-in.-diam rods as compared with the

eight 3/16-in.-diam rods for which weight data were available.

 
- 1o -

Table 2. Analyses of Machine Cuttings from Graphite Rods

 

 

Rod Cutting pemn Theoretical” Actual
No. No. T Be U/Be U/Be
8 1 30 125 0.573 0.240
0 9 175 0.051
b 10 <1 -
11 1 PP 125 0.176
D 10 110 0.091
14 1 ol 75 0.320
2 28 105 0.267
23 1 17 125 0.136
2 <1 60 0.017
a 5 < 1 -
18 a, 8 < 1 -
1 50 170 0.294
D 15 130 0.115
3 15 125 0.120
b 12 100 0.120
5 10 65 0.154
6 13 105 0.124
7 <1 50 0.020
&8 13 140 0.093
9 5 165 0.030
16 <1 <1 1.000
11 6 105 0.057
10D <1 <1 -
Center 100 125 0.800
31 b 5 <1 -
1 20 165 0.121
2 18 140 0.129
3 ol 120 0.199
L 20 85 0.235
5 20 75 0.267
6 20 80 0.250
7 17 55 0.310
8 < 1 80 0.013
9 < 1 95 0.011
10 < 1 <1 1.000
11 < 1 90 0.011
Center 70 170 0.411
b < 1 < 1 -

 

®Based on chemical analysis at original salt batch, nominally
LiF—BeF —UF, (62=37=1 mole %).

Samples machined from "as-received" material.

 
URANIUM, BERYLLIUM CONCENTRATION (ppm)

 

UNCLASSIFIED

ORNL-LR—DWG—41131A

 

 

 

|
ROD 31

 

 

BERYLLIUM

 

 

 

 

 

 

 

 

 

 

 

 

 

e

 

 

 

 

 

URANIUM

A

 

 

 

 

 

 

200 |
ROD 18
oo |3 |
«—BERYLLIUM
120 ””,7
A ‘r
a0 %
URANIUM /
0—..._.__. /
0 D °
—40
8 12
0 /32 /32

 

X O—~

 

 

 

 

DEPTH (in.)

4
/32

8
/32

Penetration of an Impervious Graphite by LiF—BeFQ-UFu.

16
732

_E-[_.

 
Fig.

Graphite Container After Test.

UNCLASSIFIED
Y-3033%

 

-1-{-[...

 
of the Graphite Before and After Salt Exposure

Table 3.

- 15 -

 

Weight and Dimensional Changes

 

 

 

 

 

Before Exposure After Exposure Net
Rod Welght Diam Welght Diam Change Percent
No. (&) (in.) (&) (in.) (s) Change
Tmpervious Graphite Rods (1/2-in. diam)
1 Lost
3 Lost
6 68.0555 0.498 68.0397  0.496 -0.0158  -0.02
8 68.0571 0.498 68.0438  0.497 -0.0133  -0.02
9 68.5709 0.502 68.5572  0.501 ~0.0137 -0.02
11 68.4152 0.500 68.4096  0.500 -0.0056  -0.01
14 68.7779 0.499 68.7639  0.500 -0.0140  -0.02
16 67.7389 0.496 67.7205  0.495 -0.0184  -0.03
18 68.2650 0.498 68.2517  0.497 -0.0133  =0.02
20 Lost
21 68.5801 0.500 68.5793  0.500 -0.0008 0.00
23 67.9828 0.497 67.9703  0.496 -0.0125  -0.03
26 68.2956 0.499 68.2911  0.500 -0.0045  -0.01
28 68.6806 0.501 68.6666  0.501 -0.0140  -0.02
29 67.8522 0.499 67.8352  0.498 -0.0174  -0.03
31 67.9389 0.499 67.9169  0.498 -0.0220 -0.04
Tmpervious Graphite Rods (3/16-in. diam)
2 9.1095 9.1082 -0.0013  -0.01
L 9.1236 9.1228 -0.0012  -0.01
6 9.4826 9.4810 -0.0016  -0.02
8 9.0329 9.0352 +0.0021  +0.02
10 9.3176 9.3126 ~0.0050  -0.05
12 8.7251 8.7372 +0.0121  +0.1h4
14 9.0932 9.0930 -0.0002 0.00
16 9.5142 9.5098 -0.004L  -0.05
18 9.0149 9.010L4 -0,0045  -0.05

 
 

R T AR A TR RS SR R e S A e e e e SR AT T e e e e A e T i ST AT e e 1T e,

- 16 -

Metallographic Examination.- Additional post-test physical examinations

 

were made by the Materials Compatibility Laboratory of the Metallurgy Division.
Only a single specimen of this material, a 1/2-in.-diam x ll-in.-long graphite
rod, was avallable for establishing the "as-received" characteristics of the
graphite rods. Iowever, comparisons of the microstructures of samples from
this rod and samples from tested rods indicated that samples were relatively
uniform in structure.

The typical microstructures of the graphite in the "as-received" and
after-test conditions are compared in Fig. 7. In both conditions the
graphite characteristically exhibited small, uniform, and widely scattered
volds. DBecause of the extremely small size of the voids, it was not possible
to identify fuel in them by simple microscopic examination.

Both the 3/16-in.-diam and 1/2-in.-diam rods had radial laminations or
cracks in sections transverse to the axes of the rods, Fig. 7. The laminations
were 0.010 to 0,075 in. long and approx 0.001l in. wide in a 3/16-in.-diam rod
and were 0.030 to 0.150 in. long and 0.001 to 0.C02 in. wide in 1/2-in.diam
rods. There appeared to be fewer laminations in the 3/16-in.-diam rods than
in the 1/2-in.-diam rods. The majority of the laminations began and terminated
inside the rods. Only a few extended to the curved surfaces of the rods. The
test apparently had no effect on the laminations.

Finally, comparisons of the microstructure of the transverse and longi-
tudinal sections of tested rods with those of the "as-received" material indi-
cated that no attack or erosion had occurred in the tested rods. This
observation is in agreement with the weight measurements of the specimens
discussed previously.

Discussion.- The grade GT-123-82 of graphite was an experimental graphite
that was fabricated especially for this particular test. The prime objective
was To produce a low permeation graphite. The manufacturer utilized his
technology for meking the low permeation graphite but the actual fabrication
of grade GT-123-82 was not part of his research for the development of grades
of low permeation graphite. The small diameters, 3/16 and 1/2 in., of the
graphite rods probably made the reduction of the permeation easier. Therefore,
it is not known if the structure of grade GT-123-82 could be duplicated in

larger shapes applicable for reactor usage.

 
Fig. T.

diam Rods (a) As-Received and (b) After a Qne-Year Exposure to LiF-BeF

lUnelassified

Low Permeability Graphite:

(62-37-1 mole %). As polished. 100X

Typical Microstructure of 1/2-in.-

o UFy,

Unclassified

 

-LT'
 

   

- 18 -

Assuming this particular grade of graphite could be duplicated for the
shapes required for use in a reactor, the small amount of salt that permeated
the graphite in the loop is not entirely representative of the permeation of
the graphite in a reactor, in that the pressure on the graphite in a reactor
would be approximately three to four times as great as the 13 psig experienced
in the loop test. At thilis time, there is not sufficient data to make an ex-
trapolation for the percentage of the bulk volume of (T-123-82 that would

be permeated by salt in the reactor.
Examination of Loop Components

Loop Specimens.- Metallographic examination of specimens from the first
and second heater legs indicated negligible attack to have occurred in these
sections, based on the absence of surface pitting or subsurface voild forma-
tion. The general appearance of the surfaces of these specimens can be seen
in Figs. 8 and 9. Similarly, no evidence of attack (i.e.,surface attrition)
was found in the specimens removed from the unheated segments of the loop, the
tubing connecting the pump to the first heater leg, the unheated bend connecting
the two heater legs, and the cooler coil. The condition of the cooler coil
surfaces is shown in Fig. 10. Neither the cooler coil nor other cold leg
regions of the loop exhibited detectable mass transfer deposits.

As evidenced in Figs. 8, 9, and 10, the metallographic appearance of
the loop specimens gave no indication of surface carburization, carbide pre-
cipitation being no heavier at the exposed surfaces than below.

However, an extremely thin film was found to be present on all the
specimens examined from the pump exit up to the entrance of the box containing
the graphite rods. This film appeared as a continuous second phase which ex-
tended below the exposed surfaces of the specimens to thicknesgses ranging up
to 1/3 mils. The thickness of this film appeared to increase linearly along
the affected length of tubing, increasing in thickness from approx 1/10 mil
at the pump outlet to 1/3 mil at the end of the second heater leg. As can be
seen in Figs. 8 and 9, there is no evidence of a transition or diffusion zone

between the film and the base metal.

 
 

Unelassgified

T-17667

 

 

00T

 

.oo8

 

009

 

010

 

211

 

 

 

 

 

 

Fig. 8. Appearance of Specimen Removed from End of the First Heater
leg. Etchant: 3 parts HCl, 2 parts H,0, 1 part 10% Chromic acid. 250X

Unclassified
=) £
T-17467

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s

 

 
   
 

1 T
INCHES
1 1

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g : e ; 007

 

 

 

 

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Fig. 9. Appearance of Specimen Removed from End of the Second Heater
250X

er
Leg. Etchant: 3 parts HCl, 2 parts HEO’ 1 part lflfi Chromic acid. 50

 
 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 10. GCeneral Appearance of Coocler Coil. Etchant: 3 parts HC1,
2 parts H,0, 1 part 10% Chromic acid. 250X

 
 

 

- 21 -

Graphite Container.- Metallographic examination of specimens removed from

 

the entrance and exit of the graphite container revealed no attack and no
evidence of carburization. As in the case of the specimens removed from the
loop, a very light surface film was found along the interior surfaces of the
box (Fig. 11).

As a check for carburization, hardness tests were made on two after-test
specimens removed from the entrance and exit ends of the box top and on an
"as-received" specimen of the box. As shown in Table L, the results of these
measurements corroborate the apparent absence of carburization in that the
after-test specimens exhibited the same range of hardness as found in the
"as-received" specimen.

Hastelloy W Spacer Wires.- As described previously,l2 0.035-in.-diam

 

wires circled each of the graphite rods stacked in the container to maintain
a fixed flow amulus between each of the rods. Since these spacer wires were
in direct contact with graphite, they were examined particularly for evidence
of carburization. Metallographic examination of the after-test wires showed
them to have a microstructure distinctly different from that of the "as-
received” material, as shown in Figs. 12 and 13.

Hardness determinations, which utilized a Tukon Hardness Tester, indicated
hardnesses from 411 to L35 DPH in the before-test specimens and from 435 to
L69 DPH in the after-test specimens. Since Hastelloy W is subject to aging
at the temperature range to which it was exposed, a hardness increase for this
material would be expected with or without carburization. However, the analyses
also showed that the carbon content had increased significantly from a before-
test level of 0.028% to an after-test level of 0.055%.

Analysis of Corrosion Film.- As noted above, a continuous second phase
was observed along the exposed surfaces of various loop components thicknesses

up to 1/3 mil. The comparative hardnesses of the film and parent metal in

 

lg"Test Equipment and Methods” p. 7 of this report.
iy

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|._-'.r
09

l11. Specimen Removed from Top of Box Containing Graphite

L
L ol 17 3 | [ %
Etchant: 3 parts HCl, 2 parts H_ 0, 1 part 10% Chromic acid. 250K

==2

fo

 
 

- 23 -

 

 

 

Table 4. Hardness Measurements Made on Top of Graphite Container
Hardness (DPH)
oide Exposed oide Exposed
Top of Box to Air to Salt
Salt Entrance 201 201 178 177 177
Salt Exit 188 180 178 178 177
As-Received 201 201. 194 194 170

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 12. As-Received Microstructure of Hastelloy W Spacer Wires.
Etchant: 3 parts HCl, 2 parts HEO, 1 part 10% Chromic acid. 250X

 

 

 

Fig. 13. Typical Microstructure of Hastelloy Spacer Wires After Test.
Etchant: 3 parts HCl, 2 parts HEO, 1 part 10% Chromic acid. 500X

 
 

- 25 -

specimen No. 11, on which the thickest layer was found, were determined using
a Bergman Microhardness Tester and a l1-g load. On the basis of the 1l-g load,
the film was found to have a VHEN of 518, while the Vickers hardness number for
the parent metal was 269 (Fig. 1Lk). A check of the base metal using the Tukon
Hardness Tester with a 200-g load indicated a VEN of 218. Thus, the absolute
magnitudes of the hardness values yielded by the Bergman tester would appear
to be slightly high; nevertheless, they demonstrate that the film is approxi-
mately twice as hard as the parent metal.

Because of the minute thickness of this film, difficulty was encountered
in quantitatively determining its chemical composition. However, gualitative
analyses of the film were obtained using material which was "scrubbed" from
the inside surface of specimen No. 5 (Fig. 8) through the use of a corundum
slurry and a glass rod. The specimen was welighed before and after scrubbing
+o determine the amount of material removed. The resultant mixture of slurry
and metal, together with an unused sample of the slurry as a blank, was then
submitted Tor spectrographic analysis. Results of analysis by this technilque

are shown in Table 5.

Table 5. Analyses Made of Surface Films

 

Composition (wt %)

 

 

Specimen Ni Cr Fe Mo Other
As-Received 71.66 6.99 L.85 15.82 0.68
No. 5 80.0 1.5 14,5 4.0 —-
No. 11 67.0 - 0.6 21.6 10.8

 

A semiquantitative analysis of the film was algso carried out by use of
an electron-beam microprobe.l3 This analysis was accomplished by aiming the

electron beam directly on the inside diameter surface ol specimen No. 11 (Fig.9)

 

13MSRP Quar. Prog. Rep., July 31, 1960, ORNL-3014, p. 56,
INCHES

02

 

oca

 

T50X

 

 

Fig. 1h. Microhardness Measurements Made on Specimen Removed from
Second Heater Leg. Etchant: None. 750X.

 
 

- 27 -

>

which excited an area of 1.96 x 10 cm2 at the surface to a depth of approx
L p. The characteristic x rays emitted by the film were then spectrographically
analyzed. The results obtained from this technique are also shown in Table 5.
Both types of analyses indicated the film to be composed primarily of
nickel. In the sample from specimen No. 5, iron appeared to have increased
relative to the base-metal composition while chromium and molybdenum appeared
to have decreased. In contrast, the analyses of specimen No. 11, obtained by
means of the microprobe, showed an enrichment of molybdenum along with apparent
depletion of chromium and iron.
At best, these results provide a semiquantitative picture of the chemical
composition of the films. Because of inherent errors involved in the analyses

"scrubbings" from specimen No. 5, the estimated accuracy of

obtained on the
the results is within + 20% of each individual cfl.etermination.l)‘L A few of

the contributing errors involved are: (1) tramp elements in the abrasive,

(2) residual fluorides on the surface of the specimen, and (3) tramp elements
in the glass rod used as the scrubber. In the case of the analyses obtained
for specimen No. 11, the errors are less easy to resolve. An immediate indi-
cation of some error is afforded by the fact that the percentages of nickel,
chromium, iron, and molybdenum do not add up to 100%. To assure that the
deviation was not associated with residual fluorides remaining on the surface,
the specimen was cleaned with an ammonium oxalate solution and then reanalyzed.
The ammonium oxalate solution has been found to dissolve fluoride salts quite
effectively without disturbing alloys composed predominantly of nickel. The
results of this reanalysis, as shown in Table 5, showed no difference from the
orlginal analysis. Thus, the failure of nickel, chromium, iron, and molybdenum
%o add up to lOO% is believed to have resulted from scattering or absorption

losses, which would also introduce some error in the reported relative amounts

of these components.

 

IHM. M. Murray, Analytical Chemistry Division, to R. C. Schulze, personal

communication, September, 1960.
 

- 28 -

Chemical Analyses of Salt.- Chemical analyses of the salt circulated in

 

the loop after test are shown in Table 6. Except for an expected increase in

Table 6. Chemical Analyses of Salt Mixture
Before and After Operation

 

 

wt % Theoretical@ ppm
Sample Taken U Be U/Be U/Be Fe Cr Ni
Before Test 4,87 8.37 0.582 0.767 235 135 5
After Test
Loop L.97 9.77 0.509 330 550 25
Sump 4.59 9.55 0.480 460 585 85

 

aCalculated for LiF-—BeF,-UF) (62=37=1L mole %).

chromium concentration, these analyses show little change from the analyses
of the concentration of impurities in the before-test salt. As shown in
Table 6, chemical analysis of the after-test salt revealed no measurable
pick-up of carbon. FExamination of the after-test salt was also made under
the petrographic microscope and x-ray diffraction unit to detect the presence
of oxide compounds within the salt. These analyses showed the salt to be
apparently unaffected by impurities contained in the graphite; however,
analysis of the salt by wet analytical methods indicated the presence of

3400 ppm of oxygen.

CONCLUSIONS

Excluding the possible irradiation effects and keeping in mind the
other differences that have been pcinted out for the pump loop and a reactor,
there were useful data generated by the pump-loop test. The compatibility of
the three-component system, salt-graphite-INOR-8, at slightly above the
reactor operating temperature for a relatively extended period of time was

demonstrated. The test indicated that:
1. There was no corrosion or erosion of the graphite by the flowing salt.

2, There was very little permeation of the graphite by the flowing salt,
and the permeation that occurred was uniform throughout the graphite

rods.

 
 

- 29 -

3. The various INOR-8 loop components exposed to the salt were not

carburized.

4. The INOR-8 components exposed to the salt and graphite were
negligibly attacked.

5. With the possible exception of oxygen contamination, the salt
appeared to have undergone no chemical changes as a result of

exposure to the graphite test specimens.
ACKNOWLEDGMENT

The authors wish to thank J. H. DeVan who made many pertinent and
helpful suggestions concerning the experimental work and the preparation of
this report.

Thanks are due to the following individuals and groups for their

contributions:

W. H. Duckworth for the operation of the experiment,
M. A. Redden for the preparation of loop-component specimens,
The Reactor Chemistry Division, especially F. A. Doss and W. K. R. Finnell,

The Analytical Chemistry Division, especially C. F. feldman, M. M. Murray,
and W. F. Vaughn,

The Metallography Group of the Metallurgy Division, and particularly
C. E. Zachary.
 

 

 

 

 

 
 

APPENDIX A

PROCEDURE FOR OUTGASSING GRAPHITE AND CLEANING LOOP

e O R R AR
 

 

8 o e, 1 X

 

b SR R

 

   

 

 

 
 

- 33 -
PROCEDURE FOR OUTGASSING GRAPHITE AND CLEANING LOOP

After the entire loop was insulated and installed in its facility, the
pump rotary element was removed and the bowl was sealed in preparation for
outgassing of the graphite.

Outgassing of the graphite was accomplished by first holding a vacuum
on the loop for 48 hr at room temperature and then gradually heating both the
loop and container to between 1000 and 1100°F while still under vacuum. After

3

reaching this temperature range, a vacuum of less than 5 x 10 ° mn Hg was
maintained on the system for 24 hr, following which the system was pressurized
with argon and allowed to cool. The cover, used to seal the pump bowl, was
removed and the pump rotary element installed while maintaining flow of argon
from the opening. The loop was then heated under a positive argon pressure
and filled with the salt mixture LiF—BeF,-UF) (62—37—L mole %). This first
£i11 was utilized as a cleaning fluid and circulated approx 12 hr at 1200 to
1250°F before being dumped. The loop was then refilled with the operating

charge.
 

 

  

Sy

B R

 

 

   
   
 
   

 

 
 

APPENDIX B

PRESSURE CALCULATIONS FOR SALT IN GRAPHITE CONTAINER
             

   

 
_.3‘7_
PRESSURE CALCULATIONS FOR SALT IN GRAPHITE CONTAINER

Using a pump performance curve for the LFB pump and the physical
properties of the salt mixture LiF-—BeF ~UF) (62—37—1L mole %), the flow con=-

ditions of the test were estimated as follows:

Reynolds number, N_ = pdv 2, 180 where p = 123 1b/ft at 1100°F
o d = 0.0254 ft

v = 4,84 ft/sec
L= 0.00692 1b/ft-sec

Flow head at discharge of pump,

2
1V 6L
htotal = T 3 —g =21.5 ft., where T = fi; = 0.029

1 =50 Tt
d = 0.254 ft

v = 4.84 ft/sec

Flow head at 5&% of length of the loop at the inlet to the graphite

container.

h(inlet) = 0.54 (21.5) = 11.6 ft

Estimated pressure of molten salt at the graphite container (neglecting
vertical height difference and assuming a 3-psig cover pressure on the

pump suction).

Blinlet)P o .

P = —~ I - 12.9 psig in the container.

Other statistics of the loop and container are as follows:
Volume of molten salt No. 130 in circulation 121 in.3
Surface of INOR-8 exposed to salt 1023 in.2
Geometric surface of graphite exposed to salt 683 in.2

Ratio of graphite to INOR-8 surface 0.67
                

 

     
 

APPENDIX C

CHRONOLOGY OF LOOP OPERATION
 

 

     

 

 
 

5-9-58
5.10-58

5-28-58

6-23-58

8-5-58

8-15-58

8-22-58

11-7-58

1-15-59

3-16-59

4-17-59

2-20-59

i e o it i e

- 41 -
CHRONOLOGY OF LOOP OPERATION

The AT cperation was started.

The loop was placed on isothermal operation 3 hr for pump motor
work.

The loop was placed on isothermal operation for 24 hr while
alterations were being made to controller.

The loop was placed on isothermal operation 18 hr for repairs on
pump motor.

Power fallure caused cooler to become partially frozen, but the
plug was thawed successfully and the loop resumed operation. Only
the cooler temperatures dropped below the melting temperature of
the salt (approx 850°F). 'The first heater section reached 1500°F
momentarily when power was reapplied suddenly. Loop operated 23 hr
isothermally.

The loop was placed on isothermal operation for 4 hr as precautionary
measure during a plant fire.

The loop was placed on isothermal operation for 1 hr for pump motor
work.

The loop was placed on isothermal operation for 2 hr after momentary
power outage.

The loop was placed on lsothermal operation for 1 hr after momentary
power outage.

The loop was placed on Isothermal operation for 1 hr to replace
broken pump drive belt.

The loop was placed on isothermal operation for 1 hr for pump

motor work.

The loop was terminated after 8 928 hr of operation at AT' conditions.
The loop was drained through the sample leg while on isothermal
operation.

Total Hours AT Operation - 8 850

Total Hours Isothermal Cperation - 78
 

o e

 

  

 
5L4—58.

o8.
93-100.
101.
102.
103.
10L—680.

DISTRIBUTION

Biology Library 63.
Health Physics Library 6l
Metallurgy Library 65.
Central Research Library 66.
Reactor Division Library 67.
ORNL Y-12 Technical Library, 68.
Document Reference Sectilon 69.
Iaboratory Records Department 70.
Laboratory Records, ORNL R. C. T1.
G. M. Adamson, Jr. T2.
D. 5. Billington 73.
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D. A. Douglas 88.
R. B. Evans, III 89.
J. H Frye, Jr. 90.
W. R. Grimes 91.
C. 5. Harrill 92.
M. R. Hill 23.
A. Hollaender ok,
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R. G. Jordan (Y-12) %.
W. H. Jordan 97.

EXTERNAL DISTRIBUTTION

D. E. Baker, GE Hanford
D. Cope, AEC, ORO
Ersel Evans, GE Hanford

J. Simmons, AEC, Washington

D. K. Stevens, AEC Washington
Given distribution as shown in TID- 1500 (16th ed.) under Metals, Ceramics,
and Materials Category (75 copies - 0TS)

ORNL-312%

Metals, Ceramics, and Materials

mtr_l':UO"—|L|POPHQPO:_E.’MEEUM':UU"GELIWH:D_OSM’;U"—IZO

TID-1500 (16th ed.)

Keim

Kelley

Tane

Livingston

. MacPherson

Manly

McHargue

Miller

Miller

Morgan

Murray (K-25)
Nelson

Patrlarca

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pEOPHEEFPEHEBDEEESS

. E. Stansbury (consultant)
. A. Wilhelm (consultant)