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ORNL-TM-2213.txt
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T e
"\
\‘l‘
ORNL TM-2213
1'\; ; 1
Contract No. W-7405-eng-26
CHEMICAL TECHNOLOGY DIVISION
Process Design Section
LEGAL NOTICE
This report was prepared as an account of Government sponsored work, Neither the United
States, nor the Commission, nor any person acting on behalf of the Commiasion:
A. Makes sny warranty or representation, expresaed or implied, with respect to the accu-
racy, completeness, or usefulness of the information contained in this report, or that the use
of any information, apparatus, method, or process disciosed in this report may not infringe
privately owned rights; or ’
B. Assumes any liabilities with respect to the use of, or for damages resulting from the
use of any information, apparatus, method, or process disclosed in this report.
As used in the above, ‘‘person acting on behalf of the Commission® includes any em-
ployee or contractor of the Commission, or employge of such contractor, to the extent that
such employee or contractor of the Commission, of employee of such contractor prepares,
disseminates, or provides access to, any information pursuant to his employment or contract
with the Commission, or his employment with such contractor, ’
DESIGN OF AN ENGINEERING-SCALE, VACUUM DISTILLATION
EXPERIMENT FOR MOLTEN-SALT REACTOR FUEL
W. L. Carter
R. B. Lindauer
L. E. McNeese
'NOVEMBER 1968
‘OAK RIDGE NATIONAL LABORATORY
Odak Ridge, Tennessee
operated by
UNION CARBIDE CORPORATION
| for the | -
- | .. U.S. ATOMIC ENERGY COMMISSION
ESTRIBUTION OF Tdis QOCUMENS €5 Mmtm
-
e X (»
a) &
vee
1
CONTENTS
PREOPERATIONAL INSPECTION ===mmmmmmmmmmmmmmmmmne mmmmmmmmeme e
Page
ABSTRACT . e ————— ]
INTRODUCTION ~- e e e e 2
DESIGN CRITERIA AND FEATURES ~=======m=m=m—mmm—mmmmmm e e oo é
Basic Design Requirements ==~=====m==—m=mm——emmmmc oo oo 6
Material of Construction =—=====-======- mme s 7
EXPERIMENTAL PROGRAM ====mmmmmmmm e e e e e e 8
‘Nonradioactive Operation =====m==m==mmmm e e e e e e 8
Radioactive -Operation ===~======——===eeccmeemm e - ——————— 10
METHODS -OF OPERATION ==~amemmmmm e e e m e e e e 10
~Semicontinuous Operation ========ememmemmimm e e e e ————— 1"
Batch Operation ===——=m===mmmemmem oo e e e 11
DESIGN OF EQUIPMENT =—-==m===mmmemam e mm e e e e oo 14
Feed Tank ~=====m==memmannaaa- e ————————— e = 14
Condensate Receiver ==—===—=======-mmesm—m— e m e oo e oo m e 16
Still and Condenser =—==msmmmmemmcmec— e 19
Cold Trap =========mm===- -——— e e e e e 27
- Vacuum Pump: e 27
Sampler =~-- e : - 30
Heaters =—=~=~—===cecea=- o e . e e e 8 e 0 30
Thermal Insulation ====—=====cmmmmme e e e e e oo e e 33
METALLURGICAL CHARACTERIZATION OF HASTELLOY N =--=====-=-=-- 33
Creep-Rupture Properties =—=-========mmmmmmmm e oo oo oo 34
Ductility ————- o S 34
Metallographic Examination ====—========-- ' - 38
STRESS ANALYSIS —=s—cmemmmmm e e e mc s e m e e e e e e e mwmm e 38
" Vacuum Still and Condenser =—====—===c====ux - e e 38
Feed Tank and Condensate Receiver =======~ - —emmme= 39
" INSTRUMENTATION =---=cmemmcmem e e e - e e e s 39
Temperature Measurement ———=========v==--- e -- 40
Temperature Control =====m=mmecmm e e e e e e 40
Temperature. Annunciafors ==========m==e = - ————————— e e 48
Pressure Measurement ======me=me—cnm oo e e e e 48
Pressure Control ===~=====meee=u= - ———————————— s 49
Liquid Level Measurement and Control =----==~=======ac-- —————— 49
51
iv
" CONTENTS (continued)
. Page
EQUIPMENT INSTALLATION ==<r—ecmmeeeommees ———————— Y
Unitized Construction ======emeaeemaeax —————————— ———— - 52
Hood Installation =====weeemmmeercemeea mm——— s -=- - 52
- Cell Installation e m—————— ——— -—- 52
FINAL DI'SPOSIT-ION e 55
ACKNOWLEDGEME NTS -- m———————————— rmm—mnm————— 55
REFERENCES - - ——————————— —————————————————— 57
APPENDICES ——— e e ———————————e 59
~ Appendix A Physical Properhes of Hastelloy N ~===m=aa—am- — 61
Appendix B Physical Properties of LiF, BeFy, ZrF4, and Thelr i
. - Mixtures and MSRE Salt A =m==mmeemcm e caacaeae 66
Appendix C Estimation of Pressure Drop for Salt Vapor in the
| Still=Condenser System ======-- cmm——— 72
Appendix D Estithation of Time to Heat Condensate Receiver and
- ‘Feed Tank to Operating Temperatyre ====~===~-= wo——— 79
‘Appendix E Estimation of Heat Rejection Rate By Condenser =~===== 90
Appendix F Stress Analysis of Vacuum Still and Condenser ~——----- 95
-Appendix G Specifications for Heaters for Vacuum Distillation ==~- 1M
Appendix H Equipment Drawmgs —m——mme . ——— m—m——————— -—- 116
)R "
b
N
5o
;\
")
P
\ifl ;‘L;) ‘
DESIGN -OF AN ENG.NEERING-SCALE, "VACUUM DISTILLATION
EXPERIMENT FOR MOLTEN-SALT REACTOR FUEL
W. L. Carter
R. B. Lindaver
L. E. McNeese
ABSTRACT
Experimental equipment has been designed for an engineering=- -
scale demonstration of vacuum distillation of molten-salt reactor fuel.
The distillation is carried out at about 1000° C and 1 mm Hg to
separate LiF-BeF, carrier salt from less volatile fission products,
primarily the rare earths, Uranium tetrafluoride is not present
during the distillation. - The experiment is designed for continuously
feeding a molten-salt-fission=product mixture into a still at the
same rate that distillate is being removed, thereby concentrating
fission products in the still. Also, the still may be operated batch-
wise to give large concentration factors. Frequent sampling of the
~ distillate furnishes data on the separation between carrier and fission
products as a function of concentration in the still bottoms.
‘The equipment consists of a 48-liter feed tank, a 12-liter
still, a 10~in. diam x 51-in. condenser, a 48-liter condensate receiver,
plus associated temperature, pressure and level control instrumen-
" tation. All vessels and parts contacted by molten salt are made of
Hastelloy N. The unit is electrically heated by shell-type, ceramic
heaters.
About 90% of the experimental program will be devoted to
. nonradioactive operation using mixtures of LiF, BeF,, ZrF,, and
selected rare earth fluorides. The experiment will be concluded
by distilling a 48~liter-batch of uranium-free spent fuel from the
~ Molten-Salt Reactor Experiment. o |
INTRODUCTION
- This report describes the design and proposed use of experimental equipment
to demonstrate vacuum distillation of fuel carrier salt from a .molten-salt reactor.
The purpose of this experiment is to demonstrate the feasibility of distilling a large
portion of the carrier from contained fission product fluorides. - Vacuum distillation
is the key step in one method of processing a molten-salt breeder (see Fig. 1)
because it separates the bulk of the valuable LiF~BeFy carrier from less volatile
fission products, primarily the rare earths, and recovers this carrier salt for recycle
to the reactor. Feasibility of dnshllmg fluoride salts was established in batch,
laboratory experiments by Kelly this design is of an experiment that will demon-
strate the operation on an engineering scale.
In the interest of simplicity, fabrication time, and economy, no attempt was
made in this experiment to reproduce the actual operating conditions, such as
high internal heat generation rate in the molten salt, or to use a still design of the
type to be used in a processing plant for a breeder. Such advances are the next
logical step after an engineering~scale demonstration. However, it is the purpose
of this experiment to show that molten salt, containing fission products, can be fed
continuously to the still at the rate at which it is being distilled, with the simul-
taneous accumulation of fission products in the bottoms. Furthermore, the still can
be operated batchwise to concentrate fission products in some small fraction of the
salt volume. In this way the still meets a requirement of a still for processing
breeder fuel since large fission product concentration factors are necessary to mini~
mize the amount of carrier salt discarded as waste.
The experiment is designed to obtain throughput data and relative volatility
data between rare earth fluorides and the carrier components of molten salt fuel,
which are LiF, BeF,, and ZrF4. Zirconium fluoride will not be a component of
breeder reactor fu % but it is mcluded here because the still will be operated with
salt of the composition of the Molten-Salt Reactor Experiment (MSRE), which is
65 mole % LiF, 30 mole % BeF,, and S mole % ZrF4. Progress of distillation is
followed by sampling the flowing condensate at several times during the course of
an experiment. Samples can be removed under vacuum without interrupting the
run and will be analyzed to determine the amount of separation being obtained
~ between components being fed to the still. It is also possible to sample the contents
of the still, but this necessitates interrupting the run during the time a sample is
being removed. .
The experimental program is in two parts: About 90% of the time will be
- devoted to nonradioactive operation, and the remaining 10% to radiocactive
operation in distilling a-small quantity of fuel carrier salt from the MSRE, The first |
phase is expected to log about 500 hr of operation. The same equipment will be u
used in the radicactive experiment after being thoroughly inspected at the conclusion
of nonradioactive operation. Radioactive runs will be carried out in an MSRE cell
(¥
&
‘] t:) & l‘.» i* 7 ({‘ b !
ORNL DWG. 66-82 R2
] F, Recycle
NoF { MgF.
OREES, SORBER
'REACTOR f | v UFg+Fp |
o Ee | . [+voLaTiC
BLANKET. g
~\_ | FLuornaTOR FP'S
\LiF-BeFy-UFy 7 ~ 550°C
F2. |
LiF-BeFa-UFa o SPENT
5 T | - LiF+BeF, NaF + MgF,
\ | o ond VOLATILE FP's
Off |
Gas
‘ | 0.5-Imm Hg
*-Make-Up | »1000°C
_ |LiF-BeFy-UF,
. | REDUCTION
T ~ 600°C
y
FUEL
MAKE -UpP Y v
DISCARD WASTE
FOR REMOVAL RARE EARTHS
OF VOLATILE IN LiF
FP'S
Fig. 1. Principal Steps in Processing Irradiated Fuel from a Molten Salt Reactor.
4
on a 48-liter batch of uranium=-free MSRE fuel that has been decayed at least
two months.
Components of the experiment are a feed tank (48 liters), still (12 liters),
condenser, condensate receiver (48 liters), associated temperature_and pressure
instrumentation, and o vacuum system. The still, condenser, and receiver are
fabricated as a unit. The vessels are mounted in an angle~iron frame, which is
3 x 6 x 7 ft high, allowing transport of the entire facility as a unit once
instrumentation, power, and service lines have been disconnected. . The equupment
is heated by shell-type electric heaters which are enclosed in 4 to 8 in. of thermal
insulation. - |
An experimental run is carried out by charging a molten mixture of carrier
salt and fission product fluorides into the feed tank, which is held at a temperature
slightly above the salt liquidus, which is 450°C for MSRE carrier salt. Concurrently
the still, condenser, and condensate receiver are heated and evacuated, and the
~ space above the liquid in the feed tank is evacuated. The final pressure is adjusted
to about 0.5 atm in the feed tank and 0.2 to 5 mm Hg in the rest of the equipment,
depending upon the desired operating pressure. When the still temperature reaches
900°C, a 12 liter charge is forced into the still through a heated line; and the
temperature is raised to the operating temperature range of 950 to 1000°C.
The still pot is the highest point of the system and is an annular volume surround-
ing the top of the condenser (see Fig. 2). Salt vapors flow into the top of the
condenser and condense along its length by losing heat to the surroundings. Freezing
is prevented by supplying the necessary external heat to keep the condenser surface
above the liquidus temperature. In leaving the condenser the distillate passes
through a small cup from which samples can be removed for analyses. Sampling can
be done under vacuum without interrupting an experiment.
Liquid-level instrumentation in the still allows control of feed rate to correspond
to the distillation rate, which is estimated to be 400 to 500 em3 distillate per hour.
Determining the actual distillation rate for molten-salt systems is an important part
of this experiment.
All vessels and lines that contact molten salt are. fabricated of Hastelloy N.
In the region of the still and upper section of the condenser, the normal use témper-
" ature for this alloy may be exceeded by as much as 200°C. Consequently, the
vessels are to be examined thoroughly by dimensional, radiographic, and ultrasonic
methods before and after nonradicactive operation.
Provision is made for hanging test specimens of candidate metals of construction
in the still. The materials that will be tested are:
»
4B
w
W
.
2t
2D
VENT ~——
STILL
| | CO!‘E~I¥E<%L Vol.=12 liters
‘——&‘:::::::::::fl~ Peimm Hgq
' T=1000°C -
ARGON INLET
S 1]
'I. ‘i
) b
ORNL DWG 66-10952Ri1
5
NN
&
A
CONDENSERSY
10" in. Dia. x 51 in.
CONTAMINATED FEED—=—-=x
LiF. = 65.6 mole % E i
BBF2329.4 n " 3
ZrFpe 50 " " |
FISSION PRODUCTS ¢
P S RN LY, 5
RO 3 AN
CONDENSATE TANK
Vol. =48 liters
P20.5 mm Hg
T=500°C
Vol. = 48 liters
P=6 psia
Tx500°C
Fig. 2. Vacuum Distillation of LiF-Ber-ZrF4.
COLD TRAP
TR DECONTAMINATED
SER LiF -BeFp -ZrF,
-6
1. ‘Hastelloy N (referee sample of still composition)
2. Moly TZM (a Ti-Zr-Mo alloy)
3. Haynes Stellite No. 25
4. Graphite (grade AXF-SQBG, isptropic) |
5. Ni-18 Mo=0.2 Mn-0.05 Cr |
Samples will be removed and inspected at the end of nonradioactive operation.
DESIGN. CRITERIA AND FEATURES
Basic Design Requirements
- |
Factors which influenced ':equipment design included the following:
1. The total operating time and the total volume of salt distilled during
- operation with irradiated material should be sufficient to conclusively
demonstrate the feasibility of molten=salt distillation.
2. Operation with irradiated material should be preceded by successful
operation with unirradiated material.
3. The same equipment should be used for work with irradiated and
unirradiated materials.
4. The equipment size should be compatible with space suitable for
containment of Bef, during nonradioactive operation.
Other factors of importance included:
1. Either semicontinuous or batch operation should be possible.
2. Condensate samples should be taken during an experiment without
upsetting operating conditions.
3. The latent heat of condensation of the molten—salt vapor should be
removed from the condenser by loss of heat to the surréundings.
4. The pressure drop in the passage connecting the vaporization and
condensation surfaces should be low.
~ o
The experimental program will consist of both nonradioactive and radicactive
- operation, with the former being about 90% of the program. Nonradioactive
operation will be carried out over a period of three to six months in the
e
Lo
wo
vy
"
<
7
Unit Operations Section, and then the equtpment will be moved i in jg_fg_ to the
MSRE site to demonstrate vacuum distillation of irradiated MSRE carrier salt. |
Equipment size was governed by the space in an available hood, and the overall
installation is limited to about 6 x 3 x 8 ft in length, width, and height
respectively. Unitized installation of all components within a supporting frame-
work was designated to facilitate transport between sites. Radioactive operation
will be carried out in the spare cell of the MSRE.
The duration of the radioactive experiment is an important factor because of
the technological significance that can be associated with a conclusive demonstration
using recently irradiated fuel. For this purpose, an operating period of 10 to 14 days
was considered adequate, and, during this time, 48 liters of the fuel carrier salt will
be distilled.
Another design feature is that provision be made for sampling the condensate
stream at any time during the course of a distillation experiment. This requirement
is made so that the composition of the still vapor can be measured as a function of
still composition and/or temperature. Condensed vapors flow contindously through
~ a cup at the condenser outlet (see drawing M~12173-CD-011D in the Appendix)
from which a 10-g sample can be taken by lowering a thimble into the cup. The
sampling operation is carried out at the operating pressure, causing no interruption
or upset in the run.
Simplicity of design and ease of operation were primary considerations in
planning this experiment. The only auxiliary systems are the necessary heaters,
instruments, and vacuum equipment. Vapor condensation is brought about by
radiative and convective heat loss to the surroundings, obviating the need for an
auxiliary, high-temperature cooling system. This somewhat limits the maximum
distillation rate, the calculated range being 350 to 500 cm3/hr with 3.5 to 4~in.
insulation around the condenser.
Material of Construction
All major pieces of equipment and connechng lines are built of Hastelloy N.
This material has excellent resistance to corrosion by molten LiF-BeFy=ZrF, mixture
at the lower temperatures (500 to 700°C) of the experiment. A limited amount of
data at the higher operatlng temperatures (200 to 1000° C) indicate that the
corrosion resistance is probably quute good at these temperatures. This characteristic
“of Hastelloy N will be evaluated in the distillation experiment.
The still and condenser, which will be exposed to the higher temperatures, are -
constructed of 3/8-in.~thick plate to allow for uncertainty in the strength of Hastelloy
N in the neighborhood of 1000°C. The ASME Unfired Boiler and Pressure Vessel
‘Code makes no provision for the use of this alloy for service above 700°C. This
8
design is based on the creep data of McCoy* and the stress analysis of Hahs and
Pickel,* which substantiate the use of this equipment for an operating time up to
- 1000-hr duration. At no time will the unit be exposed to a positive internal
pressure, the largest AP being 1 atm external pressure.
Use was made of on-hand material from the MSRE stockpile of Hastelloy N
plate, sheet, tubing, rod, and pipe. Design and fabrication changes were made
- to conform to the available material, For example, cylindrical vessels are made
of rolled and welded plate instead of the more obvious choice of using standard
pipe if it were available; directional changes are made with mitered joints because.
- pipe fittings were not available; some nozzles are made of tubing or drilled rod
when a more conventional choice would have been standard pipe.
EXPERIMENTAL PROGRAM
The vacuum distillation experiment will be carried out in two phases. The
first phase will consist of a large number of nonradioactive experiments to thoroughly
evaluate the still, obtain operating experience, and gather data that are pertinent
to the distillation process. The second phase will be a 10 to 14 day demonstration
in which irradiated carrier salt of the Molten Salt Reactor Experiment will be
distilled in a cell at the MSRE site.
Nonradioactive Operation
- The experiment is described by the simplified flow diagram presented in Fig. 2;
a detailed flowsheet is given in Appendix H, Drawing No. E~12173-CD-012D.
The system consists of a feed tank, still, condenser, condensate receiver, cold trap,
vacuum pump, and auxiliary instrumentation for controlling pressures, temperatures,
and liquid level. All vessels and lines are heated with ceramic, clam-shell-type:
heaters or Calrod-type elements. |
Initially the system is purged and filled with argon to remove oxygen, .and all
vessels are heated to about 500°C. A 48-liter charge of molten LiF-BeFy=ZrFy
of MSRE carrier salt composition containing a fission product fluoride is then put
into the feed tank, and the entire system is evacuated. Pressure above the salt in
the feed tank is adjusted to about 5 psia, sufficiently low to prevent salt from being
pulled into the still when the still is at full vacuum. The evacuation is continued
*H. E. McCoy, Metal and Ceramics Division; C. A. Hahs and T. W. Pickel,
General Engineering Division. See later sections of this report treating the
metallurgical study and stress analysis.
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until the still, condenser, and condensate receiver are at the desired operating
pressure of 0.2 to 2 mm Hg. Concurrently with the evacuation, the still
temperature is raised to about 850°C, the temperature at which the salt charge
has a vapor pressure of around 1 mm Hg. The condenser temperature is adjusted
100 to 200°C lower than the still temperature to facilitate condensation of the
salt vapor without solidification. Condenser heat is applied in four zones so that
a high-to-low temperature gradient can be maintained down its length, The
condensate receiver is heated to 500 to 550°C, a temperature that will keep the
condensate molten but not cause undesired vaporization into the vacuum system.
When all parts of the sysfem have reached the desired temperature ond pressure,
12 liters of the feed salt are transferred through a heated line into the annular
section of the still by pressurizing the feed tank with argon. The gas is added
slowly through a capillary, and a liquid-level device, which senses the upper level
in the still, stops the argon addition when this level is reached. The still
temperature is controlled so that the vapor pressure of the salt is near 1 mm Hg; and,
as distillation progresses,changing the salt composition, this temperature is allowed
to increase to keep the vapor pressure at about 1 mm Hg. Pressure at the condenser
exit is held at about 0.5 mm Hg. The calculated distillation rate is about 350 ml/hr.
The liquid-level instrument in the still is set to detect a low level that
corresponds to vaporization of 2 liters and to begin argon flow into the feed tank to
push more salt into the still. The upper-level setting stops the addition, and this
cyclic operation is repeated throughout the run. Smoother, more continuous
operation can be obtained by regulating the argon flow to the feed tank to be very
near the predicted vaporization rate so that salt flows into the still at about the
same rate that it is being vaporized.
In leaving the condenser, the condensate flows through a small cup that is
centered beneath a sample tube. A 4~cm3 sample is obtained by lowering a
1-1/2-in. by 3/4=in.~diameter thimble into the cup. Sampling is done under
‘operating conditions with no interruption in the experiment; a double-valve
arrangement (shown schematically in Fig. 2) permits removal of a sample from the
system without upsetting the still pressure. The sample cup is continuously flushed
with fresh condensate, giving a sample that is representative of the still vapor at
the time the sample is taken. -
Flnally, the condensate collects in a receiver from whu:h it mrght be recycled
~ for subsequent experiments. Level-detecting instrumentation allows an independent
check of distillation rate. The condensate receiver can be sampled for a cumulative
analysis only if the run is terminated because the tank must be pressurized to force
the salt out the drain line. The vacuum line passes through a baffled trap cooled
by liquid nitrogen to remove particulates or vapors that might clog the vacuum pump.
- The still residue cannot be withdrawn during the course of an éxperiment. A
dip tube is provided for draining all but about 154 em3 from the conical bottom
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section when a positive pressure is applied above the liquid surface. However, if
desired, all liquid fed into the still may be evaporated. The maximum still temper-
ature (1000°C) is high enough to vaporize the least volatile component (LiF) of the
carrier but considerably below the point at which rare earth fluorides have a
significant vapor pressure. Fission product fluorides, which the carrier salt contains
during some runs, are allowed to accumulate in the still. A flush salt can be used
to purge the still between different types of experiments. |
Because of the toxic nature of beryllium, nonradicactive experiments are
carried out in a hood, and all work areas are monitored for beryllium contamination.
Containment is based on maintaining adequate air velocities at all hood openings.
Radioactive Operation
At the conclusion of the nonradioactive experiments, the equipment will be
moved intact to the spare cell at the MSRE site for a similar experiment using
irradiated salt. Distillation is carried out in the same way as described above;
however, all operations must be remote. A 48-liter batch of LiF-BeFo-ZrF
MSRE carrier salt, which has been fluorinated to remove uranium and volatile fission
products, will be transferred from the chemical processing cell through an existing
pipe line into the feed tank. The salt will then be distilled over a period of
- 10 to 14 days. Frequent samples will be withdrawn for analysis. It is anticipated
that the extensive operating experience with nonradioactive experiments will allow
specifying operating conditions to obtain maximum decontamination and trouble-free
operation.
The cell ventilation system is used for disposol of gases from the experiment.
This system contains the necessary fllters for removing activity from the gas before
exhausting it to the atmosphere.
METHODS OF OPERATION
The distillation system can be operated in either of two modes: semicontinuous
operation followed by batch operation or batch operation with heel retention. These |
methods are not necessarily the best for MSBR processing; they are, however, well’
suited for demonstration of molten salt distillation at the MSRE site,
Instrumentation for measuring liquid level in the still includes a liquid-level
probe which operates when the still inventory is between 10 and 12 liters and a
level probe which operates when the still inventory is between 0.78 and 6 liters. |
Salt can be fed to the system continuously or intermittently; however, no provision is g
made for removing liquid from the vaporizer during the operation. During a given
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run, the total salt volume which will be distilled by either method of operation is
approximately 48 liters.
Semicontinuous Operation
For semicontinuous operation, the still will-be charged with 12 liters of MSRE
fuel salt (65 mole % LiF—30 mole % BeFy—5 mole % ZrF4) containing rare earth
fluorides. An additional 36 liters of fuel salt will then be fed to the still at a rate
equal to the desired distillation rate. The liquid volume in the still will be main-
tained between 10 and 12 liters during this period. After feeding 36 liters of salt,
the salt feed will be stopped and vaporization will be continued until the salt liquid
volume is 0.78 liter.
The variation of BeFy concentration in the condensate and the fraction of rare
earth flyoride vaporized are shown in Fig. 3 for this mode of operation. The liquid
volume in the still was assumed to be perfectly mixed and the relative volatilities of
- BeF, and rare earth fluoride were assumed to be 4.0 and 5 x 1074, respectively.
The BeF, concentration in the condensate is observed to decrease from an initial
valuve of 67 mole % to 35 mole % at the end of semicontinuous operation and then
to drop sharply to essentially zero during batch operation. The fraction of rare
earth vaporized is seen to continuously increase to a value of 0.0018 at the end of
operation. Approximately 98.5% of the salt fed to the still will be vaporized.
Batch Operation
For batch operation with heel retention, the still is charged initially with
12 [iters of MSRE fuel salt containing rare earth fluorides. Vaporization is then
carried out until the liquid volume in the still is 0.78 liter. Fuel salt (11.22 liters)
will be fed to the still to yield a total liquid volume of 12 liters and the above
sequence repeated. Four cycles of batch operation with heel retention can be
- carried out with 48 liters of salt.
The variation of BeF, concentration in the condensate and the fraction of rare
earth fluoride vaporized is shown in Fig. 4. The liquid volume in the still was
assumed to be uniform in concentration and the relative volatilities of BeF, and
rare earth fluoride referred to LiF are assumed to be 4.0 and 5 x 10-4, respectively.
The fraction of rare earth fluoride vaporized is based on the total quantity of rare
“earth fluoride which has been fed to the still during a given cycle. The BeF,
concentration is observed to decrease from an initial value of 67 mole % to
essentially zero during each cycle. The fraction of the rare earth fluoride vaporized
after four cycles is 0.0027. Approximately 98.2% of the salt fed to the still will be
vaporized..
MOLE FRACTION BeF, IN VAPOR
12
ORNL DWG. €7-3678