ORFL-L5TT Contract No. W-7L0S5-eng-26 CHEMICAL TECHNOLOGY DIVISION UNIT OPERATIONS SECTION LOW-PRESSURE DISTILLATION OF A PORTION OF THE FUEL CARRIER SALT FROM THE MOLTEN SALT REACTOR EXPERIMENT J. R. Hightower, Jr. L. E. McNeese B. A. Hannaford H. D. Cochran, Jr. This report was prepared as an account of work | sponsored by the United States Government, Neither ' the United States nor the United States Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, com- pleteness or usefuiness of any information, apparatus, product or process disclosed, or represents that iis use would not infringe privately owned rights. AUGUST 1971 OAK RIDGE NATIONAL LABORATORY Oak Ridge, Tennessee operated by UNIOK CARBIDE CORPORATION for the U.S. ATOMIC ENERGY COMMISSION s ey T e renmomm e AT o Tl d il e g R T T TN : S . Loeew @AW Sule bl ; A e e e iii CONTENTS ABSTRACT . . ¢ ¢ v v 4 o & &« « o o & INTRODUCTION .« + & ¢ o o v o o o« o « DESCRIPTION OF EQUIPMENT . . . ¢ ¢ + « ¢ o o« « o « o 2.1 Process Equipment . . . ¢« + ¢« ¢« ¢ & o « o 2.2 Instrumentation . 2.2.1 Measurement and Control of Temperature 2.2.2 Measurement and Control of Pressure 2.2.3 Measurement and Control of Liguid Level 2.2.4 Radiation Instrumentation . . . . . 2.2, Instrument Panel . 2.3 Condensate Sampler . . 2.4 Location of Equipment at the MSRE . . . . . . . . DESCRIPTION COF DISTILLATION OPERATICN . . . . . & EXPERIMENTAL RESULTS . . . ¢« « « o ¢ & L.l Summary of Experimental Data . . . . . . . . . L.2 Material Balance Calculations . . . . . « . . 1.3 Results of Relative Volatility Calculations . 4.4 Possible Explanations of Calculated Results . h.4.1 Entrazimment of Droplets of Still-Pot Liguid 4,h.2 Concentration Polarization . h.h.3 Contamination of Samples L,h.k TInaccurate Analyses .« « ¢« « o o & « o CONCLUSIONS & & & & ¢ ¢ o o o s o o o o o « o s + o ACKINOWLEDGMENTS . . . . . v ¢« ¢« ¢« ¢ ¢« ¢ o o o« « & REFERENCES . « & o o« o ¢ o ¢ o s o o o o = 10 10 12 13 15 15 17 20 20 8. APPENDIX: ANALYSES OF SAMPLES FROM THE MSRE DISTILLATION EXPERIMENT . . ¢ & & ¢ ¢ & ¢ o o o s o o o o ........... LOW-PRESSURE DISTILLATION OF A PORTION OF THE FUEL CARRIER SALT el FROM THE MOLTEN SALT REACTQOR EXPERIMENT J. R. Hightower, Jr. L. E. McNeese B. A. EHannaford H. D. Cochran, dJr. ABSTRACT An experiment to demonstrate the high-temperature low=pressure digtillation of irradisted Molten Salt Reactor Experiment (MSRE) fuel carrier salt has been successfully completed. total of 12 liters of MSRE fuel carrier salt was distilled in 23 hr of trouble~free opersation with gtiil- pot temperatures in the range 900-980°C and condenser pres- sures in the range 0.1-0.8 torr. ZEleven condensate samples were taken during the course of the run at intervals of approximately 90 min and were subsequently analyzed for Li, Be. 7r, 13T¢s, 957y, 1lbbce, 14Tpy, 155my, 91y, 90sy, and 89gr. Effective relative volatilities, with respect to Li¥, for Be and Zr were in good agreement with wvalues measured previously in the laboratory. Effective rela- tive volatilities for the slightly volatile materials lthe, 9ly, 908r, and 898r were found to be much higher than values measured in the laboratory. The high values are believed to be the result of contamination from other MSRE salt samples, although concentration polarization may have also been a contributor. The effective relative vol- atility for 13Tcs was found to be only 20%, cr less, of the value measured in the laboratory: no explanation of this discrepancy is available. Although the effective relative volatilities for the lanthanides were found tc be higher than anticipated, the values observed would still allow adequate recovery of TLiF from waste salt streams by distillation. 1. INTRODUCTION Low-pressure distillation may be required in order tc recover valuable carrier salt components from waste salt streams coming from the fuel processing plant of a mclten-salt breeder reactor (MSBR). Typically, TLiF would be vaporized and recovered, leaving & ligquid heel . more concentrated in the less volatile lanthanide fission products (as fluorides). This heel would then be discarded. The final stage of g three-phase experimental program to study and demonstrate the feasibility of distillation for decontaminating carrier salt components of lanthanide fission products is described in this report. The experimental program included measurements of relative volatilities of several lanthanide and alkaline-earth fluorides in mixtures of LiF and Bng, Ls2 the opera~ tion and testing of a large single-stage still using fuel carrier salt from the Molten Salt Reactor Experiment (MSRE) with simulated fission prod- ucts ", and, as described here, a demonstration of the distillation process using irradiated fuel carrier salt from the MSRE. The operation of the distillation equipment with unirradiated salt had the following objectives: (1) obtaining operating experience with large, low-pressure, high-temperature distillation equipment; (2) in- vestigating entrainment rates and separation inefficiencies due to con- centration gradients in the still pot; (3) measuring distillation rates under a variety of conditions; and (4) uncovering unexpected difficulties. The objectives of the demonstration distillation of the irradisted MSRE fuel carrier salt were: (1) to provide MSBR fuel processing technology with a process tested with fuel salt from an operating resactor, (2) to provide information (not available from the laboratory investigations) on relative volatilities of fission preducts, and to give a general confirmation of predicted fission product behavior, and (3) to uncover unexpected difficulties associated with radioactive operation. In the nonradicactive tests, six 48-liter batches of salt that had the composition of the MSRE fuel carrier salt and contained NdF3 were distilled at condenser pressures below 0.1 torr¥ and at a still-pot temperature of 1000°C. Whereas these tests indicated areas in which further engineering development was required, they also indicated that decontsmination from lanthanide fluorides by distillation was feasible. The still that was used in the nonradicactive tests was also used to distill the radiocactive salt (containing no uraniuvm) from the MSRE. This operation and its results are described in the secticns that follow. 2. DESCRIPTION OF EQUIPMENT 2.1 Process Eguipment The equipment used in the MSRE Distillation Experiment included a 18-1iter feed tank containing s salt charge from the MSRE to be distilled, a 12-liter still from which the salt was vaporized, a 1l0-in.-diam by 51-in.-long condenser, and a 48-liter condensate receiver. This equip- ment is only briefly described here; a more complete description is given elsewhere.3 The feed tank, shown in Fig. 1, was a 1/2-in.-diam by 26-in.-tall right circular cylinder made from 1/L-in.-thick Hastelloy N. It was designed to withstand an external pressure of 15 psi at 600°C. The condensate receiver, shown in Fig. 2, was a 16-in.-diam by 16-1/2-in.- tall right circular cylinder having sides of 1/b-in.~thick Hastelloy N and a bottom of 3/8-in.-thick Hastelloy N. It was designed to withstand an external pressure of 15 psi at 600°C. %¥1 torr is 1/760 of a standard atmosphere. ORNL DWG. 66-10983 Np INLET — 3 O.DaI9GA. TUBE !f M ; / ; ; FEED INLET ; TI7 - 3 ]fir ! I T i) i 70.0.x15 GA. TUBE | il 1 | | i I I | | ! i |- | i ! 1t I H I | i | 10y 111 | I I 1 ' | 11 s i | ' it i1 ' I I 1l ! | Hi 1 ! ! f.l | | : i i Hi | | ) | ! 153 0D i 1! ' . o i3 1.D. 1l | | 72* TYR ' g g | o i ‘ N o 2 { nlfl ! E H | Hy I [ I Iy 1] I it | ! i { i i | [i] : [ I L | i I I i | i1y | | H 1 | i . 4 y b \ I \ it f £ M i \ =3l | : E“‘\%;—:h‘_fl_ { 'II'H-ERMOCOUPLE WELL ; = i 3 0:D.x19 GA. TUBE J ; FEED OUTLET —- : 20.0.118 6A. TUBE i PLAN VIEW r fl Fig. 1. Molten Salt Distillation Experiment. Schematic diagram of feed tank. ST ORNL DWG. 66-10984 & VACUUM LINE (" SCH. 40 PIPE THERMUCOUPLE WELL % ©.0.x.042 WALL TUBE @— THERMOCOUPLE WELL 30.0.2.042 WALL TUBE 30.0.x.042 WALL TUBE THERMOCOUPLE VIELLA@ > — FUEL DIP LINE & Ny ADD'N, 20.0.x.072 WALL TUBE I3 SCH. 40 PIPE l&'mloo'& LEVEL PROBE TUBE P . . - . _ >~ / - /i . N 7 I,:/";.A / WO gl - 7 N ‘\\‘l“. ,’/,i i P ) T _ ’ \;‘L"- R ]!.: il N | /1 iyl R | il Byoa Heov i | \w/ | 0 o 1 : ol | ! i ! I . ) 30° - L P l ‘ | N o | | ! i il | | [ o | : 1! I | | T ol I | K : b | 1 i | \ 1 I I : L ! ] kR ! e —la i |11 b ! “ = i | i | e 16 Ie.o. L o + sgLo. || P ! v : 1 | ! L : 11 | | ‘ | S 3 : | al v " ; : Vol I £ E'[ ; i [ bho H l ! I I | . )l Lis Fig. 2. Molten Salt Distillation Experiment. ©Schematic diagram of the condensate receiver. The still snd the condenser are shown in Fig. 3. The still pet consisted of an annular volume between the vapor line and the outlet wall, and had a working volume of about 10 liters. Both the still and the condenser were made of 3/8-in.-thick Hastelloy N and were designed for pressures as low as 0.05 to 1.5 torr. The design temperature for beth the still pot and the condenser was 982°C. The feed tank., the still pot, the condenser, and the receiver were mounted in an angle iron frame to facilitate their transfer between Bldg. 3541, where the nonradiocactive tests were carried out, and the MSRE site. ©Since the equipment was to be installed in a cell only slightly larger than the equipment frame, the thermocouples, the heaters, the insulation, and most of the piping were added before the equipment was placed in the cell. TFigure 4 is a photograph of this equipment (without the insulation). A stainless steel pan to catch melten salt in the event of a vessel rupture was placed around the bottom of the frame. Because large gquantities of iron and nickel particles were expected tc be present in the fuel storage tank (FST) at the MSRE (as a result of the chemical processing of the fuel salt), a porous metal filfier was installed in the feed tank fill line downstream from the freeze valve in line 112 (see Fig. 5). The Inconel filter medium consisted of ap- proximately 28 in.2 of Huyck Feltmetal FM 284 having a mean pore size of 45 u. To prevent particulates from reaching the vacuum pump, Flanders High Purity filters were installed in the vacuum lines from the feed tank and the receiver. These filters were tested and demonstrated to ORNL DOWG, 66-10983 HERMOCOUPLE WELL 14270.0. TUBE %19 GA.-- ¢ O LEVEL PROBE - v—— FEED LINE 13 5CH. 40 PIPE : , 34*0.0.1.072 WALL . - HANGER ! BRAGKET LEVEL PROBE I35CH. 40 PIPE ~— DRAIN & SPECIMEN HOLDER THERMOCQUPLE WELL. 172°0.0. TUBE %19 GA. 172°0.0. TUBExXIS BA, VIEW A=} SAMPLE TUBE k5 SCH. 40 PIPE Fig. 3. the vacuum still and condenser. Molten Balt Distillation Experiment. Schematic diagram of PHOTO 93564 Fig. 4. Molten-Salt Distillation Equipment Before Installation in Spare Cell at MSRE. ST iy Al o ke o VW — — ARGON Iii ORNL DWG 70-6280 SUPPLY FREEZE vaLve. 1 | "z MOLTEN SALT FILTER FUEL STORAGE TANK "=} FEED —1| TANK ARGON SUPPLY PRESSURE MEASUREMENT ™ _r - AND CONTROL HCV -2 E - & - VACUUM HCV—9 ACUU -3 I i L LEVEL FILTER [ ] MEASUREMENT — AND CONTROL ! I - ! SAMPLER a - i i CONDENSER 4 | CONDENSATE | RECEIVER Fig. 5. Simplified Flow Diagram of MSRE Distillation Experiment. 10 effectively remove 99.997% of 0.3-u particles. The hcusings for these filters can be seen in Fig. 4 on two of the larger lines at the right- hand side. A1l valves and piping that did not ccntact the molten salt were made of stalnless steel and were housed in a sealed steel cubicle containing pressure transmitters and two vacuum pumps— one to evacuate the reference side of g differential pressure transmitter, and the other to evacuate fhe distillation process vessels. The valve box, with its front and rear cover plates removed, is shown in Fig. 6. This box completed the second- ary containment around piping and instrumentation when its lower plates were bolted and sealed in place. With the box under a pressure of 15 in. B O, the leak rate was 0.1 cfh. During operation, the pressure in the box 2 never exceeded 0.5 in. H. 0, and the lesk rate was negligible. 2 2.2 Instrumentaticn 2.2.1 Measurement and Control of Temperature Temperatures were measured and controlled over two ranges: 500-600°C for the feed tank and the condensate receiver, and 800-1000°C for the still and the condenser. Platinum vs platinum - 10% rhodium thermocouples were used for the high~temperature measurements, whereas less expensive Chromel-Alumel thermocouples were used on the feed tanks, condensate re- ceiver, and salt transfer lines. FEach of the thermocouples {total, 60} was enclosed in & 1/8-in.-diam stainless steel sheath; insulated junctions were used. Five 12-point recorders were available for readout: twc for the Pt vs Pt - 10% Rh thermocouples, and three for the Chromel-Alumel thermocouples. MSRE Fig. 6. Containment Box for Instruments Distillation Experiment. and Valves Used in the PHOTO 92843 T 12 There were a total of nine individually heated zones on the feed - tank, the still, the condenser, and the receiver. The heaters for each of these zones were independently controlled by a Pyrovane "on-off" con- troller; the voltage to the heaters was controlled by Variacs. Heaters on the various salt transfer and argon lines were manually controlled by "on-off" switches and Variacs. 2.2.2 Measurement and Control of Pressure Pressure measurements over three ranges were required: 0 to 15 psia for monitoring system pumpdown at the start of the run, for monitoring system repressurization at the end of the run, and for contrclling salt transfer from the fuel storage tank; 0 to 10 torr for suppressing vapori- zation while the salt was held at operating temperature in the still; and C to 1 torr during distillation. Absclute-pressure transducers(Foxboro D/P cells with one leg evacuated) covering the 0- to 15-psia range were used to measure the pressure in the feed tank and in the still-condenser-receiver complex. An MKS Baratron pressure measuring device with ranges of 0-0.003, 0-0.01, 0-0.03, 0-0.1, 0-0.3, 0-1, 0-3, and 0~10 torr was used to measure very low pressures in the condensate receiver. The system pressure was controlled in the 0.l1- to 10-torr range by feeding argon to the inlet of the vacuum pump. The Baratron unit produced the signal required for regulating the argon flow. It was necessary to ensure that an excessive internal pressure did not develop in the system since, al operating temperature, a pressure in excess of 2 atm would have Deen unsafe. This was accomplished by using an absolute-pressure transmitter in the condenser off-gas line to monitor .......... 13 the system pressure. When the pressure exceeded 15 psia, the argon supply was shut off automatically. 2.2.3 Megsurement and Control of Liguid Level The difference in the pressure at the outlet of an argon-purged dip tube extending to the bottom of the vessel and that in the gas space above the salt was used to measure the depth of the salt in both the feed tank and the condensate receiver. Twe conductivity-type level probes were used in the still for measur- ing and controlling the liquid level. These probes essentizlly measured the total conductance between the metal probes {that extended into the molten salt)} and the wall of the still; the total conductance was a func- tion of the immersed surface area of the pro‘be,5 The conductivity probes (see Fig. 7) were similar to the single-point level prcbes that were used in the MBSRE drain tanks. Tests have shown that the range of such an instrument is limited to approximately 30% of the length of the signal generating section. A 6-in. sensing probe was used to control the liquic level between points that were 1 in. and 3 in. below the still-pot overflow; a longer sensing probe wag used to measure very low levels of liquid in the still pot. Metal disks were welded to the conductivity probes to aid in their calibration. These disks provided abrupt changes in the irmersed surface ares of each probe at known liguid levels. During operation, the signal from a probe changed abruptly when the salt level reached one of the disks. The liguid-level controller for the still pot was a Foxboro Dynalog circular chart recorder-controllier, which consists of a 1-kHz ac bridge-type 1h ORNL-DWG 67-4776R1 TOP VIEW SIGNAL AMPLIFIER AND LEVEL INDICATOR EXCITATION SOURCE A X\ SIGNAL LEADS HEAD COVER FOLDED EXCITATION SECTION CONTAINMENT VESSEL _ BUOSSOSOOOOONINNY / | _ e N N N N N e N N N R s e N S A R S AN AN A S A A S AR R R A Y A Y DISKS TGO AID CALIBRATION Fig. 7. OSimplified Schematic of Conductivity-Type Liquid Level Probe for Still Pot in MSRE Distillation Experiment. 15 _____________ measuring device using variable capacitance for rebalance. The proper control action {see Sect. 3) was accomplished by having a variable dead zone imposed on the set-point adjustment mechanism. With the controller set for the desired average liquid level, the argon supply valve to the feed tank was opened when the level indicator dropped 3% below the set point and was closed when the level indicator rose 3% above the set point. 2.2.4 Radiation Instrumentation Ionization-chamber radiation monitors were mounted on process lines in three locations: one on the filter in the feed tank vacuumn line, one on the filter in the receiver vacuum line, and one on the liquid-nitrogen trap in the receiver vacuum line. The two monitors on the filters were shielded from the radiation field in the cell by an 18-in.-thick barytes concrete bleck wall and indicated the level of radiocactivity for each filter. The monitor on the liguid-nitrogen trap was not shielded from the radiation field produced by the process vessels and thus registered the general level of radiation in the cell. Two Geiger-Muiller tubes, which were attached to the valve box, monitored the vacuum pumps. They were set to sound an alarm when the radiation level reached 1 mR/hr at a point about € in. from the pumps. 2.2.5 Instrument Panel The instrument panel, from which the process was controlled, con- tained the temperature controllers, the pressure and level reccorders and controcllers, the valve operation switches, the electrical power supply controls, the temperature and pressure alarms, and four of the five temperature recorders. This panel is shown in Fig. 8. The fifth it F ig. 8. Instrument Panel for MSRE Distillation Experiment. R PHOTO 89322 91 17 e temperature recorder and the radiation measuring instrumentation were mounted in other cabinets. 2.3 Condensate Sampler The condensate sampler was the most important item of equipment for obtaining information from the distillation experiment. The sampler was 233U patterned after the equipment that had previously been used to add to the fuel drain tanks and to take salt samples from the drain tanks. Modifications of this design were made to allow the sampler to be evac- uated to about 0.5 torr so that condensate samples could be withdrawn without disturbing the operation of the still. Figure 9 shows a cutaway diagram of the sampler. The main components of the sampler were: (1) the containment vessel in which the samples were stored; (2) the turntable inside the contaimment vessel, which allowed the sample capsules to be aligned with the handling tool and also with the removal tool; (3) the capsule handling tool, with which empty capsules were sttached to the cable tc be lowered into the sample reservoir; and (L) the reel assembly, with which capsules were lowered and raised. The following sequence was used in collecting a condensate sample. With valve HV-62 (see Fig. 9) closed and the containment vessel at atmos- pheric pressure, the sample handiing tool was raised to the highest position. As shown in Fig. 9, the cable was attached about 20 in. from the top of the tool so that, when the cable was reeled to the highest position, the top end of the tool protruded through valve HV-66 and the samples on the turntable could pass under the lower end of the tool. 18 ORNL DWG 69-4945 s VACUUM PUMP FILTER— Fig. 9. Cutaway Diagram of Condensate Sampler for MSRE Distillation Experiment. ............ 19 With the tool at its highest position, an empty capsule was rotated underneath the lower end of the tool. The tocl was then lowered onto the stem of the capsule and locked in place by an adjustment at the end of the tool protruding through HV-66. The tool and the attached capsule were raised again, the turntable was rotated until the sampling notch was located underneath the tool, and the tool was lowered below valve HV-66. Valve HV-66 was then closed. At this time, the vacuum pump was turned on, and the containment vessel was evacuated to about 0.5 torr. When the pressure in the containment vessel reached 0.5 torr, valve HV-62 was opened and the sample handling tecol and the empty capsule were low- ered until the sample capsule rested on the bottom ¢of the sample reservoir at the end of the condenser. The tool and capsule were then ralised above valve HV-62, which was subseguently closed. Next, the containment vessel was pressurized to atmospheric pressure with argon. Valve HV-66 was then opened, and the sample handling tocl was raised to its highest position. Finally, the empty samplie holder was rotated underneath the sample handling tool, and the sample was lowered into its holder and re- leased from the tool. The process was repeated by raising the sample tool again, rotating another sample capsule undernesth it, etc. The turntable was designed to contain 11 sample capsules. After the samples had been collected, they were stored in the containment vessel. At the end of the experiment, they were removed for analysis. A blower, which drew air into the top of the line at the reel assem- bly to prevent radioactive particles from escaping into the operating area, was provided for the parts of the operation requiring HV-66 to be open. The air handled by the blower was filtered and exhausted into the cell. 20 The sample capsules were standard 10-g MSRE sample capsules, each of which was fitted with a key for attaching to the sample handling tool. Figure 10 shows one of these capsules. The three wire ribs on the stem ensured that the capsule would remain vertical in the capsule holder on the turntable. ¥igure 11 is a photograph of the sampler during installsation at the MSRE. 1In this photograph, the unloading tube has been capped off, and the turntable operating handle is not in place. The ring of lead bricks around the sampler forms the base for the radiation shield, which is fitted over the containment wvessel. 2.k ILocation of Equipment at the MSRE The éistillation unit was installed in the spare cell at the MSRE site; the sampler., the valve box, and the instrument panel were placed in the high bay area above the cell. Figure 12 shows a schematic diagram of the spare cell, while Fig. 13 shows a photograph of the unit in the cell before the cell cover was put in place. 3. DESCRIPTION OF DISTILLATION OPERATION The transfer of salt from the fuel storage tank (FST) to the feed tank was initiated by evacuating the feed tank, which contained about 2 liters of unirradiated salt, tc gbout 1.5 psia. Prior to the transfer, freeze valve FV-112, located between the FST and the feed tank for the still (see Fig. 5), was heated and opened. (Salt had previously been frozen in the feed line to the still pot in order to isolate the feed Fig. 10. Experiment. ~ PHOTO 95933 Condensate Sample Capsule Used in the MSRE Distillation Tc 22 PHOTO 94943 Fig. 11. Condensate Sampler for MSRE Distillation Experiment. 23 ORNL DWG 68-{30R1 SAMPLER HIGH BAY AREA o °° o ollP I:, o o 3'_0'::, : EESCF; : ioo ° o :&:\oo. l 0% o ° o:o °°°co'--F'EXED e 0% % ollgpe °.%2p e SUPPORT °l PLUG *eNs-BARYTES b o ¥ CONCRETE ® : N BLOCKS > — ol {'-0" FROM FUEL LINE 4 STORAGE & 0 TANK h fi gg&%rEN ° o ° ELEV. 840'-0" <7 FILTER o f e Yo o I 00,00 — [~ 6 © ° 4 STILL &g Pleec '-:5_',6? :’°° o e ¢ YA e ° ) Do < S i .()-( ° : 04 °° ‘.‘q g © o 0 35 o ° LAy 0: ol fees CONDENSER — Q s eo] /g ELEV. 83¢'-0" 5 X L W v v v L) = : o8l © 2% S0%ns 00 %0 » CONDENSATE RECEIVER ‘0‘,(.’0"o °°°o°°:°:°:°:°°o°°o "0c °°°°°o go "000 °°°o°°°.°o-°°.°°°°°°°: °o°:°° 0% o ¢ Fig. 12. South Elevation of MSRE Spare Cell, Showing Distilliation Unit and Sampler Locations. 24 QRNL PHOTO 94840R FiL’FER fificz:, VER TG HCV 4 fi& _ VALVE BQK FILTER IN FEED TANK - VACUUM LINE EXPANSION ok Bt - . JG NT : TR B amEBER. 0000 e RS S - - SAMPLER - VACUUM PUMP’ - ~SA PL,E . 3 v_%;{:uum LINE BLOWER £ FILTE FOR SAMPLER - VENTILATION LiQ N, TRAP C@ND&NS»&TE REEE VER | DUITS FROM . PROCESSING STILL POT __ : DRAIN LINE ™ § JUNCTION BOXES | a@x;%‘ FOR THERMOCOUPLE POWER LEA FILTER IN FEED TANK FilLk LINE (LINE 442) L LINE M2 PENETRATION | i (FROM FUEL STORAGE TANK) - ® N Fig. 13. Molten Salt S5till Installed in Spare Cell at MSRE. 25 S tank from the cther process vessels.) After 12 liters of salt had been transferred from the FST, the pressure of the feed tank increased from about 4 psia tc atmospheric pressure over a period of about 2 minj; this indicated that gas was being transferred from the feed tank through the salt charging line. More salt could not be transferred from the FST even though the bubbler in the FST indicated that additional salt was present. Only one further attempt at salt fransfer was made because of the potential danger of blowing the trapped salt out cf the freeze valve; this would have made it impossible to obtain a seal between the feed {tank and the fuel storage tank. After we had established that & tight seal could be made, we decided to proceed with the experiment using the salt already transferred, even though its volume was much less than the anticipated volume (48 liters). To start the distillation experiment, the still-pot feed line was thawed, all process vessels were evacuated to 5 torr, and the still pot was heated to 900°C. The valve between the feed tank and the vacuum pump was then closed, and argon was introduced into the feed tank to increase the pressure to about 0.5 atm; this forced the salt to flow from the feed tank into the still pot. When T liters of salt had been transferred to the still pot, the condenser pressure was reduced to 0.2 torr to start the distillation of salt. At this point, control of the liquid level in the still pot wes switched to the automatic mode. In this mode, salt was fed to the still pot at a rate slightly greater than the vaporization rate. The argon feed valve to the feed tank remained open {forcing more salt into the still pot) until the liquid level in the still rose to a given set point; the valve then closed and remained closed until the liquid 26 level decreased to a second set point. In this manner, the salt volume in the still pot was maintained near T liters. As the salt vapor passed through the condenser, heat was removed from it by conduction through the condenser walls and the insulaticn and by convection to the air in the cell. The condenser was divided into three heated zones, the temperatures of which could be contrclled sepa- rately when condensation was nct occurring. A sharp increase in tempera- ture above the set points near the condenser entrance, as well as a gradual temperature rise near the end of the condenser, accompanied the beginning of distillation. Operation of heaters to keep the temperature of the condenser abové the liguidus temperature of the condensate was not necessary during vapcr condensation. In this part of the run, the still- pot temperature was slowly increasing; and, since the concentrations of volatile BeF2 and Zth were still fairly high, the vaporization rate was alsc increasing. An abnormally high temperature at the end of the con- denser indicated that the capacity of the condenser would be exceeded. By raising the condenser pressure to 0.8 torr, the distillation rate was reduced sufficiently to maintain the condenser temperature near T00°C, an acceptably low temperature. When the contents of the feed tank (7 liters) had been depleted, the salt in the still feed line was frozen; then & total of 4 of the 7 liters of salt in the still pot was distilled by batch distillation. At this point, the still-pot temperature was 980°C. As the more volatile mate- rials were vaporized from the still pot, the condenser pressure was re- duced from 0.8 torr to 0.1 torr in order to maintain a fairly high distillation rate. When the condenser pressure could not be decreased .......... 27 o further, the distillation operation was terminated by increasing the pressure in all the process vessels to atmospheric pressure and turning off the power to all the heaters. The semicontinuous distillation phase lasted for 8.3 hr; the average distillation rate during this pericd was 0.57 liter/hr. The duration of the batch distillation period was 13.8 hr; the average distillation rate for this pericd was 0.36 liter/hr. Eleven condensate samples were taken during the run at approximately 90-min intervals. At the end of the experiment, radiation readings of these samples ranged from L R/hr at contact (the first sample) to 500 mR/hr at contact (the last sample). After the still had been allowed to ccol down, a2ll electrical and thermocouple leads to the still were cut and all pneumatic instrument lines from the valve box were disconnected. The sampler was dismantled and sent to the burial ground; the projecting end of the sample line was . flanged. Valve handle extensions were cut flush with the floor of the high bey ares. The process vessels and the valve box were allowed to remain in place. 4. EXPERIMENTAL RESULTS 4.1 Summary of Experimental Dats In order to determine the capability of the distiliation equipment for separating fission products from the carrier salt, we measured the following quantities in the course of this experiment: the concentration of 811 the major and most of the minor components in the feed salt to the still, the concentration of each component in the condensate as it left 28 the still pot, the volume of liquid fed to the still pot, and the vclume i of ligquid collected in the receiver. An estimateT was made of the con- centration of each fission product whose concentration in the feed salt was not measured. The estimate was based on the production rate of each fission product in the MSRE and assumed that all the precursors of a given fission product remained in the salt. This seemed to be a fairly gcod assumption for isotopes having no long-lived gaseocus precursors. All the concentraticns were converted to mole fractions; the mole fractions of radicactive materials were caiculsted as of May 7T, 1969. The volumes were determined by measuring the weight of liquid over the end of & bubbler, dividing by & salt density of 2.2 g/cm3 to obtain the depth of liquid, and multiplying this value by the cross-sectioconal area of the particular vessel to obtain the velume. We assumed that the mass density of the liquid was independent of composition and that the wvolume of liquid in the still pot could be calculated by subtracting the volume . of condensate collected from the total volume of salt fed to the still from the feed tank. Assuming that molar volumes can be added (which is e fairly good assumption for fluoride salts), we calculated mass densities for liquids in the concentration range seen in this experiment and found only & 5% varistion; hence, our assumption of constant density appears to be acceptable. The analyses of all the condensate samples are reported in the Appendix. 4.2 Material Balsnce Calculatiocns One of the mcst concise ways to express the separation performance of the distillstion equipment is to convert the condensate analyses tc effective 29 S relative volatilities with respect to LiF. The effective relative = volatility of component i with respect to LiF is defined as: . - v,/ X, - . . = s 1-LiF = ypip/¥p;p where y = mole fraction in the condensate, x = mole fraction iIn the still pot. Although the composition of each component in the still pot was not meas- ured directly during the run, the data allowed the composition of the still pot to be estimated from a material balance for each component. In this section, we derive the material balance eguations and outline the calculational procedure. For the semicontinuous mode of operation, a differential mole balance for component i gives: £,dI - y,dO = dM,, (2) where I = total moles fed to the still pot, 0 = total moles removed from the still poct, Mi = moles of component i in the still pot, fi = mole fraction of component i in the feed, v, mole fraction of component i in the condensate. Since volume was the measured quantity, we can make the following substitutions: &Vin al = N ’ (32) ot f Ve 30 40 = {(3p) where Vin = volume of salt fed to the still pot, liters, out = volume of condensate collected, liters, partial molar volume® of component j, liters/mole. v, J When we substitute the quantities in Eq. (3) into Eg. (2), we obtain: f Vi AV, - V=AM (k) j=lfjvj ) b.v Integration of Eq. (L) yields Vout fl Vi | in N dVout =M (5) f.v, Y.V, j=1 J J g;l Jd d C where the conditions V, =V =M, = 0 at the start of the experiment in out i vere used. The compositlion in the still pot can be determined by solving for Mi for each component. This eguation is valid up to the point where Vout = 5.07 liters (the end of the semicontinuous distillation). If Mi moles of component i are present in the still pot and dMi moles of component i are vaporized during the batch distillation, the mole fraction of ccmponent i in the vapor is given by dM. i ¥pssumed to be independent of the composition of the liquid. 31 similarly, for component j (i # 3), My v v, = (1) <7 o aM k=1 1k From Hgs. (6) and (7), we obtain the expression dMi de . (8) i J or Y5 dM. = dM.o (9) 1 Y. J J Assuming that the partial molar volumes v, are independent of the composi- tion of the liquid (as before), we multiply both sides of Eg. (9) by vy and sum both sides over all 1 to obtain the following equation: n T Loa do Vi T Wopsny 50 o yvy) (10) i= i___}zl . J where Vstill = volume of salt in the stiil pct, liters. Sclving Eq. (10) for de vields: 73 de = Tm" dvstill' (11) PY.LV, e Integrating Eq. {11) yields: Vstinn ’ Y, M, =M, + / i Oy N Vsti11 12) vV 1). The high correla- tion of the scatter of the calculated effective relative volatilities of different slightly volatile fission products is consistent with the hypothesis that entrainment occurred. Although there was some evidence of entrainment during the non- radiocactive operation of the still,h the considerably lower rate of distillation of the MSRE saltmakes entrainment by the same mechanism less likely. Therefore, some cther reason for entrainment in the radio- active operation should be sought. Evidence of a salt mist above the salt in the pump bowl at the MSRE and also sbove .salt samples removed from the MSRE has been reported;8’9 the studies have indicated that these mists are present over radicactive salt mixtures but not over non- radioactive mixtures. According to the reported data, either a mist concentration (grams of salt per cm3 of gas) or a rate of formation of mist (grams of salt per second) could be calculated. Entrainment rates sufficiently large to explain the results of this experiment could only be obtained by assuming that the gas space above the salt contained salt ............... mist having the same concentration as that seen in the studies, instead L3 Y of by assuming equal mist formation rates. However, the concentrations calculated from the data were scarcely adeguate to explain the entrained fraction that must have occurred. Furthermore, both the mist formation rate and the concentration of the mist would be expected to decrease with decressing decay power density in the liquid. ©Since the salt used in the distillation experiment had a much lower decay power density than the salt examined for mist formation {400 days of cocoling for distilla- tion feed, as compared with less than 30 days of cooling for salt samples tested for mist formation), it seems unlikely that the mist concentra- tion would have been high enough to explain the high relative volatili- ties for the slightly volatile fission products. In addition to the argument against the entrainment hypothesis just rgivena not all the discrepancies, for example, the variations in the 89Sr/90 Sr activity ratio of and the low wvalue for the effective volatility 137 . of Cs, would be explained by the entrainment hypothesis. L. 4.2 Concentration Polarization Concentration polarization would cause the effective relative vola- tilities of the slightly volatile materials to be higher than the true relative volatilities. As the more-volatile materials were vaporized from the liquid surface, the slightly volatile materials would be left behind at a higher concentration than in the liquid Just below the sur- face. In turn, the vapor-phase concentration of these slightly volatile - materials would increase, since further vapcorization would cccur from & liguid with successively higher concentrations of slightly volatile materials. Thus, since effective relative volatilities were based on average concentrsations in the still pot, the vapor concentration would Ll be higher than that corresponding to the average liquid concentration, e and the calculated effective relative volatility woculd be higher than the true relative volatility, if the concentrations at the surface of the liquid were higher than average. Similarly, concentration polariza- - tion would cause the effective relative veolatilities of components with relative volatilities higher than 1 to be lower than their true relative volatilities. If mixing or diffusion did not reduce the concentration gradient in the liquid, then the separation performed by the still would be adversely affected. As noted in ref. 4, the extent to which concentration fiolarization affects the effective relative volatility of a particular component depends on the dimensionless group D/vL, which qualitatifiely represents the ratio of the rate of diffusion of & particular component from the vapor-liquid interface intc the bulk of the still-pot liquid to the rate at which this material is transferred by convection to the interface by liquid moving toward the vaporization surface. In this ratio, D is the effective diffusivity of the component of interest, v is the veloccity of liquid moving toward the interface, and L is the distance between the interface and the point where the feed is introduced. The occurrence of concentration polarization is suggested by the sharp rise, at the beginning of the run, in the effective relative vola- tilities of lthe, 1)'L'T‘r"’rnl, 155Eu, and, possibly, 91Y and. 9OSr. This rise would correspond to the formation of the concentration gradient at the beginning of the run. The effective diffusivities of NdF3 in the still pot, calculated from results of the nonradicactive experiments,h ranged - L from 1.4 x 10 = to 16 x lO_LL cmg/sec. They form the basis for estimating b5 - the magnitude of the concentration polarization effect in the radioactive operation. During the semicontinuous operation at the MSRE, the liquid velocity resulting from veporization averaged 2.2 X 10'h cm/sec and the depth of liguid above the inlet was approximately 9.4k em. If cne assumes that the effective diffusivity of the fission products in the still pot during the MSRE Distillation Experiment was in the same range as that seen during the nonradiocactive tests, the observed relative volatilities of the slightly volatile materials would be only 2.0 to 18 times the actual relative volatilities, and the observed relative volatility of 137Cs would be 0.011 to 0.021 times its true value (in each case, assuming that the true relative volatilities were those given in refs. 1 and 2). Although concentration polarization may have been present in the work with radicactive salt, the effect was less important than that needed to account for the discrepancies between observed relative volatilities and what we consider to be the true values. Concentration polarization would not explain the variation in the ratio of the activities of 89Sr and 9OSr between samples. 4. L.3 Contamination of Samples The possibility that the condensate samples were contaminated during preparation for analysis is suggested by the extreme variation in the ratio of 89Sr and 90 Sr activities between samples. Although routine precautions against sample contamination were taken in the hot cells - where the capsules were cut open, no special precautions were taken. (The same manipulators that are used to handle MSRE salt samples were employed for opening these condensate samples.) If it is assumed that the scurce of the contamination was a sample from the MSRE taken just L6 before the condensate analyses were sent to the hot cells, then the - amount of radicactive material necessary to result in the observed values 89 90 3 of the ratio of Sr and Sr activities was in the range 10-6 to 10~ g per gram of sample. Prevention of such a low level of contamingtion is extremely difficult. Other observations that csn be explained by assuming that the samples were contaminated are the high relative volatilities of the slightly vol~- atile fission products and the high correlation between the variation of calculated relative volatilities of different fission products. On the other hand, the low relative volatility for 13TCS is not explained by this hypothesis. L. k. Inaccurate Analyses 95 137 1l 90 89 The analyses for ir, Cs, Ce, or, and Sr were made by proved, reliable methods and are considered toc be accurate within i_B%. 147 91 The analyses for Pm and Y are thought tc be less reliable but, 155Eu was difficult; nevertheless, accurate to within i_lO%, Analysis for therefore, the results are only approximate and their accuracy is open to question.lo 1Lk : . The analyses for Ce, which were made by gamma scanning and by radiochemical separation technigues using separate portions of the con- densate samples, appeared to be accurate. Good agreement was obtained between the two sets of analyses. T 5. CONCLUSIONS The following conclusions were drawn from the results obtained in the experiment described above. The separation of fuel carrier salt from the lanthanide fission products was demonstrated by processing 12 liters of fuel salt from an coperating reactor. Although the volume of salt that was processed was less than anticipated, gll the important featureé of the operation were adequately tested. The operation of the equipment for this run was smooth and trouble-~free. The effective relative volatilities for BeFo, and ZrF) (based on both natural zircenium and fission product 952r) agreed with previous laboratory measurements. lSTCS . The upper limit of the relative volatility of effective in this run, was found tc be only about 20% of the value measured in the laboratory. We cannot adequately explain this discrepancy in terms of the occurrence of liquid entrainment, concentration polarization in the still, or condensate sample contamination. The effective relative volatilities for the lanthanide figssion products lthe and 1MTPm were unexpectedly high. The effective relative volatility cof lthe was about 56 times that indicated by previous measurements. No previous measurements for lhTPm were agvailable; however, the relative volatility 1s thought to be close to that of CeF3. It is believed that the discrepancy between observed values and previous measurements is, in part, due to sample contamination. Even if the relative volastilities of the lanthanides are as high as seen here (v0.0l), adequate recovery of [LiF from waste salt streams by distillation is still possible. L8 If the relstive volatilities of the rare-earth fluorides were as high as 0.01, only 3% of the rare earths would be volatilized during vaporization of 95% of the TLiF in a batch distillation. 6. ACKNOWLEDGMENTS The authors gratefully acknowledge the help of the following pecple in the installation, operation, and analysis of the MSRE Distillation Experiment: P. N. Haubenreich, R. H. Guymon, P. H. Harley, A. I. Krakoviak, and M. Richardson, of the Reactcr Division; R. W. Tucker of the Instrumentation and Controls Division, R. B. Lindauer of the Chemical Technology Division; J. H. Moneyhun of the Analytical Chemistry Division; R. 8. Jackson of the Plant and Equipment Divisicon; and R. 0. Payne, V. L. Fowler, J. Beams, F. L. Rogers, E. R. Johns, and J. C. Rose, technicians in the Unit Operations Section of the Chemical Technology Division. kg oo 7. REFERENCES 1. J. R. Hightower, Jr., and L. E. McNeese, Measurement of the Relative Volgtilities of Fluorides of Ce, La, Pr, Nd, Sm, Eu, Ba, Sr, Y. and Zr in Mixtures of LiF and BeF P ORNL-TM-2058 (January 1968). 2. F. J. Smith, L. M. Ferris, and C. T. Thompson, Ligquid-Vavor Equilibris in LiF=-BeF,. and LiF-BeF, ~ThF, Systems, ORNL-4L415 (June 1969). < o i 3. W. L. Carter, R. B. Lindauer, and L. E. McNeese, Design of an Engineering-Scale Vacuum Distillation Experiment for Molten Salt Reactor Fuel, ORNL-TM-2213 (November 1968). 4. J. R. Hightower, Jr., and L. E. McNeese, Low-Pressure Distillation of Molten Flucride Mixtures: Nonradioactive Tests for the MSRE Distillation Experiment, ORNL-LL3Lk (January 1971). 5. M. W. Rosenthal, MSR Program Semiann. Progr. Rept. Feb. 28, 1967, ORNL-L119, p. T6. 6. M. W. Rosenthal, MSR Program Semiann. Progr. Rept. Feb. 28, 1969, ORNL-4396, p. 2k. 7. E. L. Compere, ORNL, personal communication, July 1, 1969. 8. M. W. Rosenthal, MSR Program Semiann. Progr. Rept. Feb. 29, 1968, ORNL-L254, p. 100. 9. M. W. Rosenthal, MSR Program Semiann. Progr. Rept. Feb. 28, 1969, ORNL-L4396, p. 1i5. 10. J. H. Moneyhun, ORNL, personal communication., Feb. 9, 1970. 51 ......... 8. APPENDIX : ANALYSES OF SAMPLES FRCM THE MSRE DISTILLATION EXPERIMENT 53 Table A-1. Analyses of Samples from the MSRE Distillation Experiment . Component, Salt Volumes Associated (w6 %) (v %) (vt %) (ais min"lg™l) (ais min"lgl) (ais min-lgl) (ais min-lg-l) (ais min-lg=1) (dis min-lg-1) (ais min-Ye-1) (aie min-lgl) Fed Collected Fuel storage tank-1 — — — 1.79 x 109 3.1k x 1010 3,48 x 109 — — 3.11 x 107 — . (Date analyzed) (h/2k/69) (k/25/69) (k/24/69) (L/24/69) Fuel storage tank-2 10.6 5.67 13.39 1.62 x 109 3.21 x 1010 3,75 x 107 — — 3.35 x 107 — — (Date analyzed) (5/1/69) (5/1/69) (5/1/69) (4/29/69) (5/2/69) (4/30/69) (4/29/69) Condgnsate samples 3.88 11.1k 15.66 1.53 x 107 6.83 x 10° <2.6 x 10° <8 x 103 6.5h x 10° <2.1 x 10° 2.10 x 107 9.4 x 10° 7.9 0.42 -2 Y67 8.48 12.05 1.39 x 107 1.21 x 108 1.53 x 107 N1k x 102 1.18 x 108 <5.2 x 106 5.15 x 107 6.k9 x 108 10.0 1.93 -3 6.86 10.39 10.04 1.14 x 109 2.39 x 108 2,78 x 107 ~3.0 x 107 1.4h x 108 8.54% x 106 1.61 x 107 3.93 x 109 11.2 2.96 - 7.24 9.76 10.09 1.17 x 109 1.97 x 10° 2.23 x 107 A2.1 x 107 1.32 x 106 5.76 x 106 1.3% x 107 3.53 x 109 12.6 3.81 -5 8,15 10.00 10.48 1.24 x 107 8.09 x 107 8.85 x 10° A1.0 x 10° 6.14 x 10° <2.5 x 10° 2.49 x 107 3.1k x 10% 13.% : 4.35 -6 7.05 9.93 10.49 1.21 x 107 2.89 x 10° 3.20 x 107 n3.L % 107 1.81 x 10° 8.93 x 108 1.08 x 107 .61 x 109 13.6 %.95 - 7.82 9.24 10.53 1.16 x 10° 1.99 % 108 2,16 x 107 n2.5 x 10° 1.15 x 106 8.57 x 100 1.91 x 107 1.66 x 107 13.8 5.80 -8 8.77 8.148 9.83 1.17 x 10° 3.01 x 10° 3.08 x 107 3.3 x 107 1.60 x 10° 8.75 x 106 3.38 x 107 5.91 x 108 13.8 6.3k -9 9.80 T.66 8.71 9.78 x 108 4.63 x 108 5.98 x 107 n5.5 x 10° 2.29 x 106 1.56 x 107 3.59 x 107 4,06 x 108 13.8 6.89 -10 13.02 5.11 8.26 9.4k x 108 h.75 x 108 6.27 x 107 . 6.6 x 10° 6.01 x 106 2.37 x 107 1.69 x 107 2.63 x 108 13.8 7.%9 -11 13.28 5,20 8.11 9.25 x 100 .91 x 108 6.90 x 107 n8.1 x 10° k.10 x 108 3.04 x 107 .2 x 107 .96 x 108 13.8 7.85 (Date analyzed) (5/21/69) (5/23/69) (5/23/69) (5/21/69) (7/21/69) {7/2/69) (10/8/69) (9/30/69) (7/8/69) (7/8/69) (5/21/69) aDuplicate samples differed by a factor of 4 or more. 55 UC-80 — Reactor Technology INTERNAL DISTRIBUTION 1-3. Central Research Library 84-85. J. R. Hightower, Jr. 4-5. MSRP Director's Office 86. H. W. Hoffman 6. ORNL — Y-12 Technical Library 87. R. W. Horton Document Reference Section 88. W. H. Jordan 7-41. Laboratory Records Department 89. P. R. Kasten 42. Laboratory Records, ORNL R.C. 90. C. W. Kee 43. R. K. Adams 91, M. J. Kelly 44, G. M. Adamson 92. 8. S. Kirslis 45, J. L. Anderson 93. J. W. Koger 46. C. F. Baes 94, R. B. Korsmeyer 47. C. E. Bamberger 95. A. 1. Krakoviak 48, C. J. Barton 96. T. S. Kress 49. H. F. Bauman 97. J. A. Lane 50. S. E. Beall 98. R. B. Lindauer 51. M. J. Bell 99. A. P. Litman 52, E. S. Bettis 100. M. I. Lundin 53. R. E. Blanco 101. H. G. MacPherson 54. F. F. Blankenship 102. 3. C. Mailen 55. J. 0. Blcomeke 103. H. E. McCoy 56. R. Blumberg 104, L. E. McNeese 57. E. G. Bohlmann 105. A. S. Meyer 58. G. E. Boyd 106. R. L. Moore 59. J. Braunstein 137. D. M. Moulton 60. M. A. Bredig 108, J. P. Nichols 6l. R. B. Briggs 109. E. L. Nicholson 62. S. Cantor 110. A. M. 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