ORNL-TM-3863 DESIGN AND OPERATION OF A FORCED-CIRCULATION CORROSION TEST FACILITY { MSR-FCL-1) EMPLOYING HASTELLOY N ALLOY AND SODIUM FLUOROBORATE SALT W. R. Huntley P. A. Gnadt MASTER QISTRIBUTION OF THIS DOCOWENT 1S ORLMIT 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, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. & 3 «d ) ORNL-TM- 3863 Contract No. W-Th05-eng-26 - Reactor Division DESIGN AND OPERATION ” | OF A FORCED-CIRCULA TEST FACILITY (MSR-FCL-1) EMPLOYING Hfzstgglgggxz 128 o ATIOY AND SODIUM FLUOROBORATE SALT W. R. Huntley P. A. Gnadt W ——————me— N O T | CE This report was prepared as snt 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, of their employees, makes any warranty, express or implied, or assumes any legal lisbility of responsibility for the accuracy, com- pleteness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights, JANUARY 1973 OAK RIDGE NATIONAL LABORATORY Oak Ridge, Tennessee 37830 operated by UNION CARBIDE CORPORATION | | | for the i U.S. ATOMIC ENERGY COMMISSION DISTRIEUTION OF THIS DOCUMENT 1S UNLIMITE ” A o iii CONTENTS ABSTRACT veveeevvovaceassassssssossasssosasvasssassssnacsassassas 1. INTRODUCTION ...... s sesseassaseasscssarnanse ceeescerssesnas 2. DESIGN AND FABRICATION ..cvvecevascssccssccacccaasnses ceeenas 2.1 Design Criteria .....ccec0vcee resesstesastnsesensnans . 2.2 General Design Information ............ e eeeen 2.3 Detalled Design and Fabrication ..........ccccceeneee 2.3.1 Heater ...ccecevcececscsnccsnccoass Coeteraacae 2.3.2 COO0ler ...iieevscocrorsassonsncsonns trreevnane . 2.3.3 Salt pump «csvevcceness ceseesseavesscasessarsnce 2.3.4 Salt sampler ....... Cereereceneseatacttareaana 2.3.5 BF; system .......000000e ceeenereanaa ceeaese .o 2.3.6 Fill and drain ta8nK ...cevererertvccnnnccannes 2.3.7 ‘Corrosion specimen design ..... ceseseasssenene 2.3.8 Electrical system ......... ceeeens ceeseeiraans 2.3.9 Instrumentation and control ..........cc00cue 2.4 Quality ASsSUTance .......oeeeeeeees R Ceeeeionenans 3. OPERATING EXPERIENCE s veuvuvencnsensnnensnnrnennenrenenes 3.1 Heat Transfer Performance of Sodium Fluoroborate .... 3.2 BFy Handling ........ ceesecernas ceceessaccsorassereans 3.3 Salt PUmp OPETBtLON we.eeneenenenenennenenencnsenenns 3.4 Corrosion Specimen Removal ......ccveeeveennn. ceeeeas 3.5 Salt Sampling ..veeeeeseccrenseroonaessanasnnonsonnns 3.6 Summary of Corrosion RESULLE ...ceeeessvnsessasosnnns CONCLUSIONS e v evenennnsnncncnsnsnnenenenennses RECOMMENDATTONS s ¢« e e eeeseaensocanencnensassosnensesancnsnsns ) APPEND]X A- MSR-FCL-l FIIOWSHEE.P oaco.-co-oooo--oo-coccoooco.ocov APPENDIX B. MSR-FCL-1 CONTROL SYSTEM DESCRIPTION AND OPERATING PROCEDURES_FOR‘UNATTENDED OPERATION .ecvececscnes APPENDIX C. MSR-FCL-1 SALT SAMPLING FROCEDURE .,.}............ r § W O O N0 PP - A FE R R R OEW N D PR EFREFFFEFERBRIRIRLLELE 5B O\ w 1) v ACKNOWLEDGMENT The fabrication end operation of the test loop were the joint responsibility of the ORNL Metals and‘Ceramics Division and the ORNL Reactor Division. The authors wish to thank the many personnel who alded in the design, installation, operation, and posteoperational examination of this test. Special thanks are extended to the following personnel who were instrumental in the success of the experifient. H. E. MCCoy, Metals and Céramics Division, and R. E. MacPherson, Reactor Division, for thelr guidance of the test program. J. W. Koger, Metals and Ceramics Division, for metallurgical analy- sis throughout the program. H. C. Savage, Reactor Chemistry Division, for guidance of loop operation during the latter portion of the test period and for the Control System Description of Appendix B. E. J. Breeding, R. D. Stulting, and L. C. Fuller, Reactor Division, for their contribution to the detailed design of the system. % " 7h DESTIGN AND OPERATION OF A FORCED-CIRCULATION CORROSION TEST FACILITY (MSR-FCL-1) EMPLOYING HASTELLOY N ALLOY AND SODIUM FLUOROBORATE SALT W. R. Huntley P. A, Gnadt - ABSTRACT A forced-circulstion loop (MSR-FCL-1) was assembled and operated to evaluate the compatibility of standard Hastelloy N with sodium fluoroborate—sodium fluoride eutectic (NaBF,-8 mole % NaF) coolant salt at operating conditions expected in the Molten-Salt Reactor Experiment coolant circuit. The salt velocity in 1/2-in.-0D, 0.042-in.-wall tubing was nominally 10 fps. Hastelloy N corrosion specimens were exposed to the circulating salt at temperatures of 950, 1030, and 1090°F. The test has operated more than 10 000 hr at these conditions and tests are continuing. This report is mainly concerned with the design, fabrication, and operation of the facility. Special problems related to accommodating the BFs vapor pres- sure of the salt were resolved, and the sodium fluoroborate demonstrated heat transfer characteristics that could be approximated by conventional correlations such as the Dittus- Boelter equation. Corrosion rates generally decreased with opergting time; for example, the lowest coérrosion rate ob- served for the 1090°F corrosion specimens during a 2900-hr test interval was equivalent to 0.0003 in. of uniform materisal removal per year. : Kezgprds: molten salt, corrosioh, sodium fluoroborate, Hastelloy N, design, operation, centrifugsl pump, mass trans- fer, heat transfer, MSRE, unattended operation. 1. INTRODUCTION The sodium fluorcborate (NEBF;—S mole % NaF) salt mixture is of interest as a coolant for the secondary circuit of molten salt reactors because of its low cost (~$0. 50/Ib) and relatively low melting point (725 F) Screening tests in thermal-convection loops® indicate no seri- ous problems due to reactions between the salt and the proposed reactor containment material, Hastelloy N. 3. W. Koger and A. P. Litman, MSR Program Semiannu. Progr. Rep. Feb. 28, 1969, ORNL-4396, p. 2L6. The forced-circulation.loop'described here (MSR-FCL-1) represents a more sophisticated test of the compatibility of the candidate salt and Hastelloy N. High coolant velocities were used, and the design thermsl gradient was applied to the system. The results from this test will assist in the evaluation of the corrosion resistance of the Hastelloy N containment material and the mass transfer interactions of the contain- ment material and salt. Detailed metallurgical results will be presented separately._ ' 2. DESIGN AND FABRICATION 2.1 Design Criteria The MSR-FCL-1 test was designed to evaluate the use of sodium fluoro- -boratez salt in contact with Hastelloy N alloy containment material at conditions simulating the secondary-coolant (high-temperature side of the ~ steam generator) circuit of molten-salt reactors.' One objective of the test was to develop the technology associated with the new salt by using it in a relatively complex operating system. - ‘The BFy vapor pressure of the sodium fluordborate salt is higher (e.g., 1h1 mm Hg at the maximum loop temperature of 1090°F) then the vapor pressure of other salts developed for use in molten—salt reactors. Accommodating the BFy vapor pressure of the salt at elevated temperature in MSR-FCL-~1 was a major design prdblem, since BF; is a noxious gas and' s design to provide adequate ventilation for personnel protection was required. An existing system desigr® was used as a basis for MSR-FCL-1. Cen- tringal pumps, air blowers, electrical transformers, and miscellaneous _control equipment used in previous corrosion tests of this type were ®Unless otherwise indicated the term sodium fluorcborate will be used in this report to designate the NaBF,—8 mole % NaF eutectic mixture. 8J. L. Crowley, W. B. McDonald, and D. L. Clark, Design and Opera- tion of Forced-Circulation Testing Loops with Molten Salt, ORNL-TM-SQB (May 1963). Yy 0 oy LL] <) availsble. The reuse of the availsble instrument and conmtrol design and the existing equipment resulted in a system of limited flexibility; how- ever, these design features had been previously tested and funds were only available for minimum redesign and fabrication of new equipment. The hydraulic characteristics of the ekisting pump were g specific limit- ing factor on loop performance. ' The facility was originally designed to operate for 10,000 hr and to provide a maximm bulk fluid salt temperature of 1125°F, a bulk fluid AT of 275°F at a velocity of T 1/4 fps (3 gpm), and a total heat input ‘of 94 kW. However, the ioop was not operated st these conditions. After the originél design was completed and before the loop fabrication was complete, the test conditions were changed to more nearly match the tem- perature profile of the coolant circuit of the Molten-Salt Reactor Experi- ment (MSRE), which was then operating. This modificetion to program plans was a prelude to the proposed introduction of sodium fluorcborate into the secondary-coolant circuit of the MSRE; The test facility was operated at a maximum bulk fluid temperature of 1090°F, a bulk fluid AT of LLO°F at a velocity of 10 fps (4 gpm), and a total heat input of 53 kW. Corrosion specimens were introducéd into the system at appropriate " locations to obtaln accurate weight change, chemistry change, and metal- lographic data. Periodic removal and reinsertion of the specimens were specified at approximately 2000-hr intervals. Salt sampling at approxi- mately 500-hr intervals was specified to permit chemical analyses nec- essary for chargcterization of corrosion processes occurring during operation. | Protective instrumentation end an auxiliary power supply were pro- vided in an attempt to prevent sccidental freezing of the'salt.due to lose of normal electricai supply or & pump stoppage. Originally this proteétive system was to be continuously monitored by facility operators; however, evening and night shift operator coverage’fias discontinued during the latter part of the operating period and the facility had to be modified for unattended operation. 2.2 General Design Information A simplified schematic drawing of the test loop is shown in Fig. 1, and an isometric drawing of the equipment is shown in Fig. 2. A complete flowsheet is included as Appendix A. Sodium fluoroborate is discharged downward from the salt pump (model LFB) at a_temperatfire of 950°F and at a flow rate of 4 gpm. The salt enters the first of two heat input sections and is heated to 1030°F; flows over three Hastelloy N metallurgical speci- mens; continues through the second heat input section, where the bulk fluid temperature is increased to 1090°F; and:flows.over three additional metallurgical specimens before being cooled‘in 8 hesat exchanger to 950°F. The cooled salt then flows over two more metallurgical specimens before returning to the inlet of the pump. S | ‘ The sglt inventory is stored in a sump tank located below the primary piping system. A high-purity helium gas blanket is maintained above the salt surfaces in this tank and in the pump to minimize salt.contamination. A dip leg in the sump tank allows the liquid salt to be forced by helium overpressure into the circulating system. The sump tank is designed to contain approximately twice the salt volume to be circulasted. A freeze valve serves to isolate the salt in the circulating system from the sump”’ tank inventory. This valve consists of a cooling air line installed around the 1/h+in.-0D, 0.035-in.-wall tubing connecting the sump tank to the circulating system. Piping of the circulating system is principally 1/2-in.-0D by 0.042-in.-wall Hastelloy N tubing. No direct flow measuring equipment is provided in the circulating- salt system; provisions are made to measure the flow calorimetrically. Three calibrated Chromel-Alumel thermocouples are installed at both the inlet and exit of one of the heater sections. By determining the thermal losses from this section at several temperature levels with no salt in the system, it is possible to obtain the net electrical heat input during operation. Flow rates can then be calculated from the net electrical n power input and the ohserved temperasture rise in the salt as it passed through the hesgter. ' Engineering parsmeters of the system are shown in Teble 1, and com- position and physical properties of sodium fluoroborate'are shown in Table 2. | | o H ORNL-DWG €8-279TR2 SALT SAMPLE LINE AJUSTO SPEDE 5 hp MOTOR — _ QIL LINES [[ TO PUMP GAS LINES 050 *F TO _ PUMP / METALLURGICAL OPERATING "/ SPECIMEN PRESSURE 7 psig 1030 *F LFB PUMP RESISTANCE HEATED SECTION 1090 °F METALLURGICAL SPECIMEN FINNED COOLER BLOWER METALLURGICAL SPECIMEN /HEATER LUG (TYPICAL) Y o /‘-' RESISTANCE HEATED SECTION 950 °F FREEZE VALVE E)—— AIR VELOCITY 10 fps FLOW RATE - 4 gpm ! SUMP I o Fig. 1. Simplified schematic of molten-salt corrosion test loop. wd ORNL-LR-OWG 64T40RA METALLURGY SAMPLE 10 kva POWER SUPPLY - {DETAIL A) {MAIN POWER) 1600-amp BREAKER DETAIL A METALLURGY SAMPLE LFB PUMP OUTLET DETAIL B | 10kva POWER SUPPLY lll (COOLER PREHEAT) 7~ DUMP TANK Fig. 2. Molten-salt corrosion testing loop and power supplies. »h 43 ay «) &) Table 1. Selected engineering data for MSR-FCL-l Based on actual operéting conditions Materials, temperatures, and velocities Tubing and specimens Standard Hastelloy N Nominal tubing size 1/2 in. OD, 0.042 in. wall Total tubing length 57 £t Bulk fluid tempersture (max) 1090°F Bulk fluid temperature (min) 950°F Bulk fluid AT 140°F Flow rate ' Lk gpm Iiquid velocity A 10 fps Cooler heat transfer Heat load at finned cooler 180,900 Btu/hr (~53 kW) Iiquid Reynolds number B 45,000 Iiquid film heat transfer coefficient ~2000 Btu hr-t ££22 (°F)-? Iength of finned 1/2-in.-OD cooler coil . 26 fit Coolant gir flow 995§cfm Coolant air AT 185 °F ~ Pumping requirements System AP at 4 gpm 57.5 psi (65 ft) Required pump speed 5000 rpm Salt inventory being circulated Volume in pump bowl 85 in.® Volume in tubing 46 in.® Total volume ‘ ) 131 in.%® Total weight 8.81 1b - Miscellaneous Surface to volume ratio for circulating 7 in.2/in.3 salt ' : : Volume of dump tank - - . 274 in.8 The possibility of leakage of BF, gas through the rotating mechani- cal face seal of the pump or from the valvés:and'fittings in the pump seal oil lines exists. To protect pefSonnel from this noxious gas, & ventilated cabinet is provided to enclose the LFB pump and the‘gas sys- 1 tem. An induced draft blower exhausts the air from the cabinet through ducts to the roof of the building. Table 2. Composition and physical properties of sodium fluoroborate Composition (mole %) NeBF, ; 92 NaF . | 8 Approximate molecular weight 10k Approximate melting point (°F) 125 8 10,656 Vepor pressure; log,, P (mm Hg) = 9.02h4 — -—ffi At 1090°F 140 At 950°F . , ’ | 29 Densityt’ (1b/ft3)'= 141.4 — 0.0247t ( °F) | | At 1090°F o 11h.) At 1020°F -~ 116.2 At 950°F 117.9 Viscosity P (1b £t hrl) = 0.2121 exp —E%QET At 1090°F 2.86 At 1020°F 3,23 At 950°F 3.7 Heat capacity © [Btu 1v1(°F)"!] 0.360 Thermal conductivity & [Btu hrlft1(°F)~1] At 1090°F 0.23 At 1020°F 0.235 At 950°F | - 0.2k 83. Cantor et al., Physical Properties of Molten-Salt Reactor Fuel, Coolant, and Flush Salt, ORNL-TM-2316, p. 33 (Egust 1960). : S Cantor, MSR Program Semignnu. Progr. Rep. Aug. 31, _._2J2 ORNL-4449, pp. 1547, ®A. S. Dworkin s MSR Program Semiannu Progr. Rep Feb. 29, J . W. Cooke, MSR Program Semiannu. Progr Rep. Aug. 31, 1969, ORNL-LL4Lg, p. 92. | N a o} o) In addition, a sheet~metal enclosure 1s provided around the salt ,plplng and hegt exchanger to protect operating personnel from gross - liquid leakage. The system piplng is considered sufficiently reliable to preclude the need for special exhaust ventllatlon from this enclosure for protectlon against BF, leakage.. Favorable ventilation conditions exist in the test areas, which has a 50 ft-high ceiling and continuous exhaust ventllation The test loop is shown in Fig. 3 durlng installation of the heaters and thermocouples. Figure 4 shows the. completed 1nstallatlon | 2.3_'DEtailed Design and-Fabrication '2 3 1 Heater The heat input into the salt is accompllshed by resistance ‘heating ‘two sections of the system piping, each approximastely 105 In. long. Voltage is applied between two lugs attached to the ends of each heated - length of pipe. Control is_common to both of the heat input sections f2.3.2_'Cooler' Heat is removed from the system by a heat exchanger composed of an air-cooled, 26-ft-long, 19-in.-diam coil of 1/2-in.-0D by 0.0k2-in.-wall tubing to which 1/16-in.-thick circular nickel fins are attached (see Fig. 3). These fins are brazed to the tubing with Coast Metals 52 fur- nace braze alloy. The finned coil is 1n31de a, sheet-metal housing which ‘ serves as the coollng alr duct. The salt side pressure drop, as. llmited by the capacity of the salt 'rpump, prohiblts the use of & longer heat exchanger c01l Variations in fin dlameter and spacing are. used to provide a hlgher heat flux at the 'dhot end of the,oooler. This.geometry creates a flattened salt wall tem- perature:profile whichlmakesapOSSible'maximum heat-removal‘without cooling the wall at,the cold end of‘the unit below the 725°F melting point of the salt. [This feature was importafit during the design stages, when the expected drop in the bulk fluid temperature was from 1125 to 850°F. It 10 N o 0 W - 2 o I Q f heaters and ther- tallation o ins Test loop assembly during ig. 3. -mocouples. F o} 5 o) o PHOTO 75688 T Fig. 4. Corrosion test loop installed in test stand. 12 became less important when the proposed operating conditions were changed to simulate the Molten-Salt Reactor Experiment coolant circuit tempersture profile (1090-950°F).] | The cooler is resistance heated during preheating of the loop. This resistance heat system is alSo used to keep the salt above the melting point during loss of normal Building power. ,Hastelloy N lugs are installed at the inlet, midpoint, and exit of the coil for attachment of three electrical leads. The lugs project through holes in the air duét to give access to the electrical connections. During a loss of normal power the voltage is supplied to the central lug of the coil from a diesel-generstor unit used for emergency electrical supply. o A hinged door, provided on the air exit side of the cooler housing, is closed to reduce the heat losses during preheating and is equipped to close autdmatically during & power outage. The top side of this door and the four sides of the air plenum are insulated with Johns Manville Kaowool thermal insulation to further reduce the heat losses. This insu- lation is also used to plug the holes where the electrical lugs penetrate the air duct. Air to the cooler 1s supplied through appropriate‘ducting'by a model 200-A-1 Americen blower with a 3-hp 1725-rpm motor which provides & maximum air flow of 3200 efm air through the ductwork; However, in normal operation the alr flow required is about 1000 c¢fm. A throttling damper is provided to regulate the flow. Selected engineering data on the actual performance of the cooler are shown in Tgble 1, along with other engineering parameters of the system. 2.3.3 Salt pump The salt pump, model LFB, used in this corrosion test is shown in Fig. 5. It is a centrifugal sump pump desighed et ORNL and features a downward discharge. The pump has an overhung vertical shaft, two greése- sealed ball besrings, and an oil-lubricated mechanical face seal above the salt liquid level and just below the lower ball bearing. Shaft and seal cooling are provided by oil which flows downward through the hollow [ N ) ) 13 ORNL—LR—DOWG 30958 " 3=—oIL IN N1l bl 23'/2in. SPARK PLUG | PROBE FACE SEAL - AN i OIL OUTLET — 1 ‘ .i i | IS / H == A LIQUID LEVEL— l eve 4 U] Y i SALT INLET——EZ2 “, [\ l. IMPELLER VANE +—— ey, i - lDISCHARGE 9Y/5 in.—— Fig. 5. Molten-salt pump (model IFB). 14 shaf% through a rotary seal. The oil leaves through holes in the shaft located Jjust above the top side of the mechanical face seal. The pump requires a gas purge as described in Section 2.3.5. Pump performance data taken with water are shown in Fig. 6. The model LFB salt pump was selected for this particular test since several pumps were available and over 400,000 cumulgtive hours of successful operation had been experi- enced in many previous applications at Oak Ridge National Laboratory. The head capability of the pump is somewhat lower than desired, and the acceptance of this limitation.resulted in 8 maximum liquid velocity of 10 fps. The pump tank contains the only free liquid surface in the circu- lating system during normal operation with the dump tank isolated by = freeze valve. The pump is located at the highest point in the flow cir- cult, and the pump tank acts as a liquid expansion volume. The liquid level in the tank is indicated by two spark plug probes which have Hastelloy N extensions welded to the center electrodes to make contact with the liquid salt at preset elevations. A salt sampling apparatus is provided at the pump tank, as described in Section 2.3.4. 2.3.4 Salt sampler A cross section of the moltén-salt sampler is shown in Fig. 7. It is used to remove salt samples from the pump tank at approximately 500- hr intervals during the test program. (The test loop operation is not interrupted during sampling.) The sampler consists of a dip tube with a small copper bucket attached on the lower end which is lowered into the molten salt in the pump tank. Vacuum and inert-gas back-filling con- nections are provided so that the sampler assembly can be attached to or removed from the pump tank-without contaminating the salt inventory. A Swagelok fitting with Teflon ferrules acts as the packing giand on the 1/4-in.-0D dip tube. The Swagelok nut is loosened, as required, to per- mit raising or lowering of the dip tube. The original bucket design had a cépacity of about 2 g of sodium fluoroborste. A second separate com- partment which holds about 0.5 g was added later to provide a separate sample for an oxygen analysis. " N & [ 1) Fig. 6. 15 ORNL-LR-DWG 65065A 110 { "--__k.-‘. \ | 100 \“\ r 80 S 6000 rpm 80 70 @ e, s - ”\ = ® 2 o . | w \$ 5000 rpm I - ; 50 ¢ : e \ 40 "-\“ T~~¢ 4000 rpm 30 0~_.__ B . 20 — ¢ 3000 rpm {0 0 0 1 2 3 4 5 6 7 Performance characteristics of the LFB salt pump in water. FLOW (gpm) 16 ORNL -DWG €8-2796R SWAGELOK FITTING BUCKET: VACUUM CONNECTION 4 22T, oz REr SAMPLE REMOVAL SECTION CORNECTION PERMANENT LOOP ASSEMBLY BALL VALVE LFB PUMP AN B §|§ __ MAXIMUM LIQUID LEVEL o *L§ TTTMINIMUM LIQUID LEVEL TG R Fig. T. Cross section of a molten-salt sampling device. ok " " 17 2.3.5 BFa system A relastively complex tubing system is provided to supply He-BF, mixtures for use in purging shaft seal oil leskage from the salt pump. A simplified schematic of the system is shown in Fig. 8, and the com- plete system is shown in the flowsheet of Appendix A. Special pressure regulators from Matheson Company with chemically coated nickel bodies and Monel diaphragms are used on gas cylinders containing BFy . These materials are used to resist attack by HF 1in case of moisture contami- nation of the BFa gas. All gaskets, valve packings, or soft valve seats were of Teflon or Kel-F, which are also resistant to attack by HF. A standard 200-f‘t.3 capacity gas cylindér supplies a gas flow of about 80 cc/min to the reference side of a thermal conductivity cell; the gas flow then continues on to the pump. The gas flow to the pump is used to purge seal oil leakage from a catch basin and carry it to an oil trap, from which the o0il can be drained manually as required. The gas flow then returns to the thermal conductivity cell, where a comparative meagsurement is made to detect any change of BF; concentration in the helium. It was originally thought that a 3% mixture of BF; and helium (for a 950°F pump bowl temperature) would be necessary for the purge flow through the seal oil leakage catch basin of the salt pump. This require- ment was brought sbout by the fact that the seal oll leakage catch basin and the gas space above .the salt level in the pump are interconnected, and thus s possible path for loss of BFg'from the salt is creagted. The use of a purge-gas mixture having the same composition as the gas in the pump bowl would preclude removal of BF; and a resultant change in salt composition. However, it was found in actual operation, as discussed . in Section 3.2, that the use of He-BF; mixture was unnecessary. Since the loss of BF; from the pump in a pure helium purge was too low to Justify the COm?lications attending BF, addition, a pure helium purge was used throughofit most of the tesf. Most of the seal purge system is fabricated of 1/k-in.-OD by 0.035-in.-wall copper tubing. DBrass compression fittings are used exten- sively. Check valves are used to preclude BFé.backflow into helium supply lines or backflow of atmospheric moisture into the BF; -He vent lines. Fig. 8. 18 ORNL-DWG 68-2795 FLOW Ha0 L . INDICATOR CONDENSER e I l/ ) | ~ THROTTLE oIL SALT VALVE TRAP Y ~\ SEAL PURGE TO PUMP \ GAS AND THERMAL OIL FROM CONDUCTIVITY CELL PUMP SEAL * FLOW INDICATOR THROTTLE VALVE PRESSURE GAGE PRESSURE REGULATOR HELIUM-BF3 MIXTURE SUPPLY Molten-salt forced-circulation corrosion loop — simplified schematic — LFB pump seal purge systemn. w » 19 2.3.6 Fill and drain tank The fill and drain tank is fabricated from a 23 3/16-in. length of Hastelloy N, 5-in., sched-40 pipe with 1/2-in.-thick flat heads. The five pipe risers located on the cylindrical surface of the tank provide for salt addition and removal, spark plug level indication, and gas pressurization. A drain line is provided at the bottom of the tank as an additiohal path for salt removal. 'The tank is electrically insulated from ground to prevent the flow of electrical current from the main loop tubing, which is resistance heated during certain periods of off-normal operation. 2.3.7 Corrosion specimen design Corrosion specimens (see Fig. 1) are used to monitor corrosion rates at the points of maximum, minimum, and intermediate bulk fluid tempera- tures. The Hastelloy N specimens are approximately 2 5/8 in. long, 0.250 in. wide, and 0.030 in. thick. A total of eight specimens are mounted in the three locations. Details of the corrosion specimens design and mounting arrangement are shown in Fig. 9. The specimens are mounted on the Hastelloy N stringers, inserted into the l/2—in. tubing, and tack welded into position. The section of 1/2-in. tubing containing the specimens is then butt welded into the system piping. 2,3.8 Electrical system The electrical power system is shown schematically in Fig. 10. Power is- supplied to the test facility from a 460-V, thrée-phase, delta- connected building supply. A separate connection from a diesel-generator provides emergency power to some of the equipment in the event of & failure to the normal building supply. Upon'failure of the normal supply voltage, the diegel-generator is automatically started, and an automatic transfer switch connects the emergency power éupply to thé facility. When normal pofier becomes avail- able, the automatic switch returns the system load to this supply. The heat input for normal operation is provided by two resistance- heated sections. Voltage is supplied to these sections through a INSERT TAB AND THEN TACK WELD STRINGER 20 ORNL-DWG 68-4294R TACK WELD CORROSION SPECIMEN TO INNER SURFACE OF TUBE Fig' 9. Molten-salt test loop corrosion specimens. 21 LU 13.8kV/460V 200, 1000 kVA 3¢ TRANSFORMER o NORMAL POWER BUS DISCONNECT SWITCH I | - 110 kVA SATURABLE REACTOR 110 kVA 4 20/40-76V {600A AUTOMATIC OPERATED CIRCUIT BREAKER ) 1 MAIN LOOP ! HEATER H —————— _— ORNL-DWG 72-9802 DIESEL ? GENERATOR T EMERGENCY - POWER BUS 1H K—I-\UTOMI&TIC TRANSFER SWITCH ) o—+ N CIRCUIT N/ \—/ 'BREAKER 3kVA 3kVA 25kVA 460/115V 460/115V - 460/230-115V ) S5hp 3hp 3hp LUBRICATION LIGHTING INSTRUMENT AUXILIARY PUMP COOLER EXHAUST PUMP AND POWER HEATERS MOTOR BLOWER BLOWER MISCELLANEOUS MOTOR MOTOR " N . Fig. 10. Schematic of electrical power system. 22 saturable reactor, which in turn supplies g 110-kVA high-current trans- former. Temperature is controlled on these sections by a variation in the impedance of the saturable reactor. During normal operation the circuit breaker, shown in Fig. 2, is closed and the electrical potential is applied between the two sets of lugs (A&B, C&D). This circuit bresker is opened manually to permit pre- heating of the piping system (except cooler) and is sutomatically opened to provide heat to all the system piping (except cooler) under emergency conditions. When the circuit bresker is open, the electrical potential is applied between lugs A and C, and the resulting two parallel electri- cal resistance heating circuits keep the system temperature above the freezing point of the salt. Power measuring instrumentation is provided to determine the heat input to the system. A separately controlled resistance-heated circuit is provided for preheating the cooler. When normal power is lost, autométicrcontrols also apply electric potential to this section of piping to prevent freez- ing of the salt. | Additional electric supply sources are provided for the salt pump motor, lube oil pumps, the cooler blower motor, the BFg cubicie exhaust blower, instrument power, and miscellaneous lighting and auxiliaries. 2.3.9 Instrumentgtion and control The salt pump is driven by a 5-hp 440-V motor connected to a variable-speed magnetic clutch. The clutch output torque is delivered to the pump by V-belts. The speed of the coupled units is regulated by varying the supply voltage to the magnetic coupling. The normal supply is from an electronic unit furnished with the magnetic clutch. In the event of the loss of the normal clutch control voltage, the loop is automatically placed in a standby (preheat) condition. Pump speed is measured by a tachometer built into the magnetic clutch, and alarms are provided for low and high speed. The pump speed is checked with a "Strobe" light at the beginning of each test run to insure that the desired speed is obtained. ~ The loop temperatures are controlled by a Leeds and Northrup "Speedomax-H" controller, which senses changes in loop temperature and i N L 1] 23 transmits a signal to the saturable reactor to increase or decrease voltage applied to the two resistance-hegted sections of the piping. Controls are also provided to close the outlet dsmper on the radiator air duct, stop the blower motor and the salt pump, and transfer the main heat input to the preheat mode in the event of any of the following off- normal conditions: 1. low clutch speed, 2. 8alt high tempergture, 3. salt low temperature, - h. loss of normal power to the facility, 5. low lube oil flow to the salt pump. Bypass switches are provided around most of these instruments to facili- tate startup and to provide a means of testing the workability of the control system during normal operation. 2.4 Quality Assursance ~Although the desgign of the salt circulating system was essentially the same as had been used on a previous program, it was reviewed by the _ORNL‘Pressure Vessel Review Committee. Complete histories of the Hastelloy N used in the pressure-containing portion of the loop were documented, except for the salt pump, which had been febricated and assembled in accordance with ORNL Reactor Division Standard Procedures in force at the time. Although records of the mate- rials or welding were not available, the administrative procedures in effect at the time of fabrication providéd assurance .of the integrity of the pump. Since many of these pumps had been operated and hundreds of thousands of hours of experience with this type of equipment had been accumlated, it was felt that the reliability of the units was suffi- ciently established to warrant their use without complete documentdtion. The inspection of the materials used to fabricate the salt-containing - portions of the system other than the pump included ultrasonic tests and dye-penetrant checks in accordance with ORNL Metals and Ceramics Division specifications MET-NDT 1 through L. 2L WEIding of components and assembly into the system were conducted in accordance with Metals and Ceramics Division specification PS-23, = -25, and -35, which include welder qualification procedures, weld joint design, and welding parameter limitations. Welds were inspected by x- ray examination and dye-penetrant methods stated in Metals and Ceramics Division specification MET-WR 200 and 201. Material and cleaning requirements invoked during fabrication in- cluded degreasing with perchloroethylene vapor, followed by water and alcohol rinses. Before each part fias welded into the system, it was agaln wiped with an alcohol-sosked cloth. Both the part and the cleaning cloth were visually exsmined for evidence of foreign materisal. All cleanliness, material, and weld inspections were made by person- nel other than those having the responsibility for febrication and assem- bly. Weld reports, which included the inspections and materials certifi- cations, are on file with the Inspection Engineering Department. Helium lesk tests were made on the completed piping assenbly prior to installation of the pump rotary assembly into the pump bowl. Lesk testing was done in accordance with ORNL Inspection Engineering Quality Assurance Procedure T. No detectable lesks were observed. All wiring was given a terminal-to-terminal check prior to energizing. Each control function was checked manually to insure that the protective schemes were operating properly prior to filling of the system. Operational procedures, including sbnormal condition procedures, were prepared to assist the operators. A complete description of the operation of the control system was prepared (see Appendix B), and train- ing sessions were conducted for the personnel 3. OPERATING EXPERIENCE The test loop has been operated for 10,335 hrjat design conditions ~ for an additionsl 1135 hr at off-design temperature. A chart of the operating history is shown in Fig. 11. For most of this time the system was operated at 1090°F meximum bulk fluid temperature and 950°F minimum bulk fluid temperasture. Figure 12 is & typlcal temperature profile of the system. The inner wall temperatures are estimsted from heat transfer calculgtion. - 25 _ ORNL-DWG 72- 9803 Il OPERATION AT DESIGN CONDITIONS | CONSTRUCTION OR REPAIR [ ] sHAKEDOWN DESIGN STARTED I | I | I ! ADDED SALT TO DUMP TANK 660 hr , ISOTHERMAL " OPERATION REMOVED METALLURGICAL 10,335 hr TOTAL TIME AT DESIGN CONDITIONS 1135hr TOTAL TIME AT U/ /S ISOTHERMAL CONDITIONS s l CONSTRUCTION LOOP REACHED PUMP OIL SALT LEAK DUE STARTED DESIGN BEARING FIRE TO OVERHEATING ~ CONDITIONS FAILURE 351 hr AUTOMATION ISOTHERMAL OF LOOP OPERATION I l [ l i [ [ JULY JAN JuLy JAN JULY JAN JULY JAN 1967 1968 ' 1969 : 1970 1971 Fig. 1l. Operating history of test loop. 26 ORNL-DWG 69-2535 | FRST | | SECOND | [ FINNED IHEATER | | HEATER | COOLING COIL '] [ | m m TO go? s — @ P—H+H+H|—I—H—|+I—H—1-P+H-H—®-——pump s T 1 | @ METAL COUPON LOCATION i | —— LIQUID TEMPERATURE l | ——— INNER WALL TEMPERATURE 1300 |—i | ; [ | ] i | | i ! 1200 i — E | b _ 1 ' | - 1 — 1100 e & 1ot T r” ! @ 1000 ———+ | —+- ~=——] E ! | ] TS eI e § 900 ' t i | = | | I - 800 —1 | | ! | | . 700 — L | | | | 600 L | | | 0 10 20 20 40 50 60 LENGTH (ff) Fig. 12. Temperature profile of molten-salt forced-circulation cor- rosion loop, MSR-FCL-1, at typical operating conditions. Y ] w) a ") 27 After raising the sodium fluoroborate from the sump tank into the salt piping proper and establishing the freeze valve, the system is started. The salt pump is started and the speed is adjusted to approxi- mately 5000 rpm. The main power is transferred to the two resistance- heated piping sectioné by closing the circult bresker, and the loop tem- perature is increased by adjusting the temperature controller. The sys- tem differential temperature is established by starting the blower and adjusting the damper in the air system duct. For the initial startup a flushing charge of salt was run in the salt piping for 478 hr, after which it was discarded and the working charge of salt was installed. The reliability of the system during the initial 10,000 hr of op- eration was very good, but after this time seversl difficulties were encountered. A pump bearing failure occurred, resulting in damage to ‘the pump impeller. Chips were rubbed from the impeller and deposited in the sglt piping. Extensive repairs to remove these chips from the loop piping were necessary. In addition, fatigue failuré of an oil line resulted in an oil fire, requiring extensive repairs. Subsequently, the loop piping was ruptured during an inadvertent overheating transient cagused by a defective control thermocouple and ah operator error during the replacement of the thermocouple. Table 3 lists the interruptions that occurred during the operation period, over half of which (15) were due to problems with component auxiliaries such as the pump rotary oil seal and drive motor and the blower shaft bearings. Replacement bearings in the blower and blower drive motor were reguired about every six months. 3.1 Heat Transfer Performance of Sodium Fluorcborsate | Since no published heat transfer dsta were available for the sodium fluoroborate salt, the heat transfer characteristics of sodium fluoroborate were measured in the MSR-FCL-1. Provisions for these heat transfer mea- surements were not part of the originsl design criteria, and the tests were made with existing instrumentation which was not highly sophisticated. Also considerable uncerfiainty'ekisted in available physical property data, particularly on viscosity and thermal conductivity; so the sbsolute acéu- racy of results obtained is questionable. 28 Teble 3. MSR-FCL-1 operational interruptions Number Item of | failures Rotary oil seal (Deublin) leskage 5 Salt pump bearing failures 3 Drive motor and clutch problems 6 'Air blower.besrings 2 Instrfifient mal functions 6 Electrical system difficulties L 0il line fatigue failure at pump rotary seal 1 - Other mechanical problems 2 Total 29 The heat transfer dats were obtained in one -of the resistance-heated: sections of the loop piping. This section was 105 1n. in length and O.hlo in. in inside dismeter. The tubing inside diameter was determined by micrometers, and wall thickness measurements were made with a model 1L Bronson Vidi-gage. The flow rate through the tubing was measured calori- metrically by observing the power input and the temperature rise of the salt. Heat losses at various temperatuie levels had bheen determinéd pre- viously. The specific heat data for thé salt presented in Table 2 was among the better defined physical property data and had an uncertainty of 29, The flow velocity was calculated using salt density data with an uncertainty df 5%. Powei input meaéurémenté were madé fiith instruments of iO.S% accuracy. | | - The temperature measurements were made with 1/16-in.-OD stainless- steel-sheathed,'insulated-Junction, Chromel-Alumel thermocouples. Bulk fluid,temperatures at the heater inlet and exit were each measured by three calibrated thermocouples. Ten thermocouples located along the 105-1in. length were used to obtain the wall temperature in the heated region. ") n *y 1) 29 All thermocouples were electrically insulated from the tubing wall to preclude an electrical path along the stainless steel sheaths, since all portions of the plping were above ground potential during resistance heating. Two layers of quartz tape provided electrical isolation from the piping and also served to thermally insulate the thermocouples from the pipe wall. The ends of the thermocouples were installed in a 180° arc around the quartz-tape-covered tube and held in place with a band of shimstock spot welded to itself. Two inches of "Hi-Temp" diatomaceous egarth formed the thermal insulation for the piping. The detail on ther- mocouple installation is presented to emphasize that the configuration was not ideal for accurate temperature measurehent. The error between insulated thermocouples and thermocouples installed directly on the pipe wall was later determined to be less than 10°F. The overall AT from pipe wall to bulk fluid ranged up to 100°F, so the thermocouple error of 10°F represents about a 10% uncertainty. Performance data were obtained at heater inlet temperatures from 974 to 1060°F and heater exit temperatures from 1038 to 1170°F. The Reynolds modulus ranged from 5500 t0751,h00, and heat fluxes ranges from 15,750 to 160,000 Btu hr ' ft™2. The measured heat transfer coefficients ranged from 267 to 2130 Btu hr 1 £ft72 (°F)™'. The data obtained correlated well with the Dittus-Boelter equation as shown in Fig. 13 (using recently determined physical prOperty values from Teble 2). Although no statisti- cal anslysis has been made, it is estimated that the error in the mea- surements is less than 20%. These heat transfer data constituted the first demonstration that sodium fluoroborate performs as an ordinary heat transfer fluid. 3.2 BF; Handling The LFB salt pump was designed to operate with approximately 80 ce/ min of helium purge through the pump shaft seai region to remove traces of oil leaking through the rotating face seal (see Fig. 5). The vapor pressure of the NaBF, component of the salt mikture, as shown in Fig. 1k, produces a BFy partial pressure above the salt level in the pump bowl. Since the helium purge tends to carry some of the BF; out of the system, 30 3 ORNL-DWG 68-13483R HEATED SECTION Z/D RATIO=256 © EXPERIMENTAL DATA )0.8 Mo (T',,O'T =0, 023(~Rl o' ' ; 103 2 5 104 2 5 i0° REYNOLDS NUMBER Fig. 13. Heat transfer characteristics of NaBF,-NaF (92-8 mole %) flowing in 0.410-in.-ID tube. 31 L2 ORNL-DWG 72-9804 {000 500 200 |- 8 o o n o .} BFy VAPOR PRESSURE (mm Hg) 10 n 10,656 r{*r) . loqio P=9024- 1 800 900 1000 1100 1200 1300 TEMPERATURE (°F) . Fig. 1k, Vapor pressure of NaBF,-NaF (92-8 mole %). (From ORNL- T™™-2316. ) | | & 32 it is possible to change the salt composition by gradual depletion of the volatile constituent. As indicated by the NaBF,~NaF phase diagram (Fig. 15), the freezing point of the salt mixture changes drastically with a change in composition néar the eutectic. Therefore this problem needed further consideration. The helium purge, as originally installed, was through the seal re- gion of the pump, which was loosely coupled through an annulus around the pump shaft to the helium gas space above the salt level in the pump bowl. It was assumed that BFs; vapors from the salt mixture would diffuse up the shaft annulus into the seal region and be carried gway by the purge gas. To avoid the problem of BF; depletion in the salt mixture, a system was installed to permit blending BFs; into the helium purge to produce a BF; concentration in the purge gas equivalent to the concentration in the pump bowl. Thus, no net loss of BFs in the system would occur. The possibility of chemical interaction of the BFy in the purge gas with the oil in the seal region also had to be considéred, and preliminary tests were run to see if a problem existed. The amount of BFy in helium ~ required to sustain the 92-8% salt mixture was calculated to be 1%, with a pump bowl temperature of 850°F, or 3% with the pump at 950°F. Mixtures of these two gases were prepared by adding the proper asmount of BF; to bottles containing helium; however, confirmstory analyses for the concen- tration of BFy in helium were unsuccessful. Checks with commercisl sup- pliers of mixed gases revegled that there were no economical methods for determining the BF; concentrations in helium in the 1 to 3% range. The BF; gas adsorbs on the walls of analytical equipment, resulting in gross inaccuracies in analytical results. Attempts at confirmatory analysis were abandoned, and the concentrations were assumed to be those predicted by the mixing calculations based on volume, temperatures, and pressures. Tests were conducted to examine the effect of mixtures of 1 and 3% BF; in helium of the Gulifspin 35 pump oil under conditions which would simulate its use in the pump seal-oil purge system. The results for the 1% BF; mixture indicated that the seal leakage o0il would not be affected deleteriously by contact with the mixture. Some discoloration and an increase in acidity were noted in the oil after only a few hours of exposure to the gas mixture; however, viscosity changes over a long L1} ) TEMPERATURE (°C} 33 ORNL-DWG 67-9423A 1000 g 8 3 8 500 H 3 300 200 NaoF 20 - 40 60 80 NGBF4 NaBF, (mole %) Fig. 15. The system NaF-NaBF,. 3L period gave no reason to suspect that the small passages of the pump seal purge system would become plugged with degraded oil. Results of two separate room-tempersture tests of approximately one week's duration using the 3% BF; mixture with an oil leskage flow rate of 10 cc/day and a gas flow rate of 80 cc/min indicated that the seal oil purge line would probably become plugged during loop operation; thus use of this 3% mixture for purging was abandoned. A black sludge,lformed in the test setup which simulated the pump catch basin, eventually plugged a 1/8-in.-diam port (see Fig. 16). In these tests the oil removed from the test gpparatus was extremely acidic, with g pH from 1.0 to 1.5. Attempts to determine the composition of the oil sludge were unsuc- cessful. Infrared spectrophotometrié exafiination indicated that traces of water were probsgbly removed from the piping system by the sparging gas and that the acid formed by the BF; -water reasction had attacked one or more of the ingredients of the oil to form the sludge. Thé BFs also produced, either as products of degradation or by direct addition to some component or components, new materials not found in unexposed oil. No further effort was made to characterize the degraded oil. To eliminste BF; in the seal purge stream and the resulting oil deg- radation, the purge route through the pfimp bowl was changed to provide a pure helium purge gas flow down the pump shaft. It was thought that by providing this purge, helium could be used to remove the legkage oil from the oil catch basin in the pump and the helium flow down the shaft would deter (except for back diffusion) the BFy vapor from reaching the oil. This purge path required the addition of a new outlet gas 1line from the pump bowl and a new line for BFy addition into the pump bowl. The BF addition was required since the helium flow down the shaft and across the BF; vapor space in the pump would carry off BF vapors in even greater quantities than had been anticipated with the purge only through the face séal region. After one day of operation the outlet line from the pump 'vapof space plugged with reaction products from the salt, oil, and BFj. As’ an expedient, a decision was made to return to the original design for purging the pump seal with no BF; addition to the purge stream. The helium was connected to the pump seal purge line, and the effluent was carefully monitored for BF; contaminstion. Measurements from the thermal 35 - | - - - PHOTO 7590 , o { | I 1 | INCHES | Fig. 16. Sludge formation from polymerization of Gulfspin 35 oil after one week's exposure of 3% BFj;—He mixture at room temperature. 36 conductivity cell indicated that the helium gas (80 cr? /min) leaving the pump oil cgtch basin was contaminated with approximately 0.08% BFy . This indicated that the amount of BF; removed from the NaBF, salt during the scheduled 10,000-hr operation would not significantly alter the salt com- positidn. Had the BF; depletion been significantly high, plans were to replenish the BF; by intermittent gas additions to the salt. During calibration of a thermal conductivity cell which was to be used to measure the concentration of BFy in the effluent line from the seal purge line, a 1/h-in.-OD copper tubing vent line plugged. A 3% mixture of BE, in helium had been purged through the conductivity cell and vented to atmosphere in a ventilastion system. Reaction products of ‘moist alr and BF; completely sealed the end of the tube and stopped the seal purge (see Fig. 17). An scidic solution was found in the vertical line immediately adjacent to the discharge end of the tube, evidently formed when the BFy gas came in contact with moisture in the air. Acid was also formed on the ventilation hood in the vicinity of the BF-He vent. Enough acid was present to form droplets on the lower edge of the hood, which demonstrated that a suitable BF; "serubber" is required for future systems where long-term, reliable venting of significant BF; con- centrations must be maintained. The low BFa concentration in the helium purge from the final con- figuration of the shaft seal purge system resulted in little acid accu- mulation at the gas purge line outlet. Inversion of the purge line out- let port and the addition of a bucket-type catch basin helped to reduce the plugging problem at the end of the purge line. No accumulation of acid on the air exhsgust ducts was visible, but acid reaction products were noted at the end of the purge line. As the buildup of these products was noted, the open end of the copper tubing was either cleaned or cut off. 3.3 Salt Pump Operation The major problems to be resolved by the use of the model LFB pump in this test program involved (1) the effect of the BFy partial pressure on the oil in the seal leakage catch basin and (2) the bearing and oil seal performance at 5000 rpm for sustained periods of operation. The i i i * " . 37 i PHOTO 76078 , Fig. 1T. | Typical plugging formation where BFj3—He mixtures are vented to atmosphere. R ) B B 38 problems relating to BF; reactions with the Gulfspin 35 oil in the pump are described in Section 3.2. In addition the bearing and seal lifetime was a point of concérn.since a pump of this type had not been used in applications requiring thouSahds of hofirs of operation at the relatively high speed of 5000 rpm. A series of idéntical pumps had been operated at speeds around 3000 rpm and had demonstrated adequate reliasbility dur- ing about 450,000 hr of operation.® Normal operstion conditions for the pump were as follows: Salt inlet temperature, °F 950 Salt flow rate, gpm | 4 Pump speed, rpm _ 5000 Coolant oil Gulfspin-35 Coolant oil temperature, °F 110 Pump tank pressure, psig - 7.0 Pump tank cover:gas | Helium Purge gas for seal leaksge Helium Purge gas flow rate, ce/min 80 The pump was removed for routine maintenance at approximately 2000« hr intervals to install new bearings. These bearings have a relatively short lifetime expectancy of about 4000 hr at 5000 rpm. Normally this maintenance period coincided with removal of the corrosion specimens from the loop piping. However, three bearing failures occurred during opera- tion despite the bearing replacement schedule. The polymerizgtion of oil in the catch basin by reaction with BF; was no problem during the 2000-hr operating periods. The leaking seal 0il was darkened by contact with the BF; and & black coating formed on the bottom of the catch basin, but no significant plugging occurred. This could be s problem, however, in a-systém where”periodic removal and cleaning are not possible or perhaps where higher BF; concentrations are: present. The seal oll catch basin at the conclusion of g typical 2000-hr run is shown in Fig. 18. 4J. L. Crowley, W. B. McDonald, and D. L. Clark, Design and Operation of Forced-Circulation Testing Loops with Molten Salt, ORNL-TM-523, p. 9 (May 1963). * 3y 39 Fig. 18. Typical appearance of the seal 0il catch basin of the salt pump after 2000 hr operation (model LFB pump). 40 The seal oil leakage rate has averaged approximately 1 ce/day (see ‘Pgble L4). The leakage rates were higher than average during short periods neéar the end of the test, for reasons that were not discernible. ‘Teble 4. Seal oil leakage rates in salt pump removed operation - (cc/day) 12-9-68 13 3.5 10-18-68 9 2. o-14-69 58 - 0.3k 3-25-69 39 10.51 T-22-69 - 1ok - 0.17 10-22-69 . 80 0.27 12-17-69 38 1.05 1-29-70 43 0.81 h-2h-T0 66 10.58 10-16-T0 . sl 0.90 - 10-19-710 3 20.0 1-11-71 L ol.0 1-12-T1 1 30.0 aAverage leak rate = 1 cc/day. The seal leakage 0il is highly acidic due to its contact with BFj; tests with litmus paper showed a pH of 1 to 1.5. Analytical results of oll samples revesgled small amounts of dissolved boron. | The mechanical faée seal appeared in good condition upon disassembly at the end of each operating period. Although there were no indications of impending trouble, the seal was changed as a precsutionary measure during each pump maintenance cycle. The upper bearing normally showed evidence of loss of most of its internal lubricant (grease); the lower S L] k1 bearing usually appeared in excellent condition, but both bearings were replaced routinely. The upper bearing is affected by the drive belt tension and operates under s heavier radial load then the lower bearing. The condition of the upper bearing was ample evidence that when the salt pump 1s belt driven, operation at 5000 rpm for 2000-hr periods was a maximum practical service limit. - ' The sodium fluorcborate drained easily from the rather complex ge- ometry of the salt pump. Normal draining procedure consisted in circu- ,'lating the salt at 1000°F and turning the pump at about 1000 rpm as the ‘1iquid level was lowered. Typical appearance of the salt-wetted portions ‘of the pump after a 2000-hr test period is shown in Figs. 19 and 20. The white deposits are traces of frozen sodium fluoroborate salt. 3.4 Corrosion Specimen Removal Corrosion specimens,are‘normally-xemoved for examination at approxi- 'metely 2000-hr intervals, but when operating problems were encountered - they were removed more frequently. TneZSalt inventory was drained into the sump tank, and the piping was cooled to room temperature prior to specimen removal. An argon purge flow was maintained through the loop during specimen removal to mlnimize air contamination of the inner sur- ~ faces of the remaining piping Tubing cutters were used to remove the tubing that contained the specimens. Immediately after the specimens were removed the open ends of the piping -rere sealed to allow slight argonflpreSsurization;of the system while the specimens were cleaned and inspected; o "_ | The specimen stringers were retrieved from the tubing after grinding the tack weld which joined them to the inner tubing surface. The grinding was done carefully so that the specimens could be reinstalled in the same tubing from which'they'were recovered, _The specimens were cleaned of residusl salt droplets by placing them in warm distilled water for sbout 1 hr followed by ethyl alcohol washings and air drying. Specimen weights were then measured and weight changes calculated. | 1 i 42 Fig. 19. Appearance of the salt pump bowl after draining 1000°F at conclusion of 2000-hr run (model LFB pump). PHOTO 96313 salt st 0 43 PHOTO 9631tA Fig. 20. Typical salt deposits remaining on support structure and heat baffles of LFB pump after draining salt at 1000°F at conclusion of 2000-hr run. L 3.5 Salt Sampling Salt samples were taken at the start of the test and at about 500~-hr intervals thereafter. The salt was analyzed prior to operation in MSR- FCL-1 (Teble 5); the original salt charge contained high concentrations of metallic impurities (Fe, Ni, Cr, Mo). The changes in concentration of these impurities have been rather erratic with time, probably due to inadvertent moisture contamination of the salt inventory. Some general trends were observed in the salt analyses after several thousand hours of operation. For eiample,‘the chromium concentration increased from 66 to ~250 ppm and thereafter remained at that generai level, the iron concentration dropped from LOT7 ppm and remained at sbout 70 ppm, and the nickel and molybdenum concentrations were reduced to less than 10 ppm. Table 5. Analysis of sodium fluoroborate salt prior to operation in MSR-FCL-1 Na - 21.8%‘ B 9.14% F 67.9% Cr 66 ppm Fe 407 ppm Ni 53 ppm Mo 41 ppm H,0 ~400 ppm® 0 ~400 ppm aAnalysis questionable. A cross-sectional view of the salt sampler is shown in Fig., 7. A copper bucket is attached to the lower end of the sampler assembly, and the assembly is then attached to a hydrogen furnace so the bucket is in the heated zone, and the bucket is fired in hydrogen at 1100°F for 30 min. After firing, the bucket is protected at gll times by an argon-atmosphere while being moved to the test stand. The sampler container and holder is C. hs attached to a Swagelok coupling on the pump tank riser. The volume be- tween the two closed ball valves is evacugted and back filled with helium at least four times before the ball valves are opened to lower the sample bucket into the pump tank. The bucket is held below the liquid surface for several minutes to insure filling, after which it is raised above the lower ball valve and allowed to cool for 30 min. Tt is then withdrawn to a position above the upper ball valve, and the valve is closed. The top portion of the assembly, including the upper ball valve, is disengaged, and the sample is removed from this assembly within a dry box. The de- tailed sampling procedure is given in Appendix C. 3.6 Summary of Corrosion Results The weight changes of the corrosion specimens in MSR-FCL-1 are plotted in Fig. 21 for the entire operating period. The corrorion rate gradually decreased during the first 9500 hr of operation. The specimens operating at the highest temperature (1090°F) showed the greatest weight loss, which was equivalent to a uniform metal removal rate of 0.001 in./year after 9500 hr. The lowest corrosion rate occurred during a 2900-hr period (6700 to 9600 hr), when the weight loss rate was equivalent to 0.0003 in./year; Corrosion rates would probably be reduced if more highly purified salt wére used., Operation difficulties after 9600 hr resulted in an undetermined amount of air and moisture inleakage to the salt system. The drastic effects of this inleakage are shown by the sharp increase in the weight change at a salt exposure time of 10,000 hr. This behavior is similar to that experienced in a £hermal convection test loop' when wet air came in contact with the salt due to a defective cover gas line. CONCLUSIONS A materials compatibility loop was assembled and operated for 10,000 hr to investigate corrosion of Hastelloy N by sodium fluoroborate. Automatic controls adequate to prevent damasge to the system due to upsets during unattended periods of operation were developed and applied. WEIGHT CHANGES (mg/cm?) 20 L6 ORNL-DWG T7i-4938R - 10 950*F I {030°F -20 =30 -40 1090°F 0 2000 4000 6000 8000 10,000 12,000 Fig. 21. Weight changes of removable standard Hastelloy N speéimens in flowing sodium fluoroborate (MSR-FCL-1). » b7 Corrosion specimens and salt samples were routinely removed for analysis. , An existing salt pump design and available components were success- fully adapted for salt cificulation, Operation of the salt pump, model LFB, at 5000 rpm for 2000-hr periods is a maximum practical servicé con- dition for the grease-lubricated bearings when the pump is belt driven. Degradation of the salt pump seal leakage oil due to contact with low concentrétions of BF; has not been a problem at a salt temperature of 950°F during 2000-hr operating periods. In the LFB pump geometry, diffusion of BFs vapors from the pump bowl gas space to the seal region is sufficiently restricted that the BF, concentration does not become critical. Thus purge flows to prevent this diffusipn are not necessary. This results in a greatly simplified purge gas systém. Heat transfer performance of the sodium fluorcborate agrees well with standard heat transfer correlations. Sodium fluorcborate exhibits good drainability at about 1000°F. In well-ventilated areas relatively simple ventilation and shielding enclosures may be used for low-temperature BF; tubing and gas panels because of the visual warning provided by the "white smoke" which forms from the reaction of BF; with molst air. Sodium fluoroborate is easlly contaminated by air when in the molten state, and great care to prevent air inleskage is required in all phases of operation. | The corrosion rate of Hastelloy N specimens at 1090°F averaged sbout 0.001 in./year during 9500 hr of operation and was reduced to sbout 0.0003 in./year during the last uninterrupted 2900 hr of operation. The corrosion rate increased sharply with air inleskage. | - RECOMMENDATIONS :A new system design should be provided for future tests to achieve ~ improved pump capsbility and relisbility, higher salt flow velocity, and a more flexible, rapid specimen removal technique. Future tests should be designed to allow corrosion specimen re- moval without dumping the salt inventory. This would prevent dilution L8 of the circulating sslt inventory with the salt remailning in the dump tank an& simplify interpretation of the corrosion processes. ' The design of future salt corrosion test loops should provide an emergency heating system which will allow the pump to be stopped with- out subsequent free21ng of the salt. A sultable BF; "scrubber" must be developed for future sodium fluoroborate pump systems, so that BFy vent lines cen be operated for long periods without plugging, acid formation, or back diffusion of vater vapor into the salt system. The effect of sodium fluoroborate purity on corrosion rate should be determined in future pumped corrosion test facilities. Techniques for conbtrolled purification of the salt will be required. + k9 Appendix A MSR-FCL-1 FLOWSHEET w dnm ngv 19 ag MAIN DL TO ANNULUS SPECImIN LI NEATER Lve ~nEATER U8 'C” " EQUIPMENT |DENTIFICATION EQUIPMENT LOCATION RI& MOUNTED oK GASCONTROL PANEL AT REAR OF & Ab-CoNTAOL PANEL N VENTILATED CUBICLE fa PANEL MOUNTED !O NOT PANEL MOUNTED ' EXAMME OF RAUVIAMENT DEMANKTION § S EQUISMENT LOCATION By —RQUIPMENT IOENTIECATION VEA RQUIRMENT MUMBEA SUMTER b Suen Caromt Convoranen FLOW SHEET 0% e+ e 51 -Appendix B MSR-FCL-1 CONTROL SYSTEM DESCRIPTION:AND OPERATING PROCEDURES FOR UNATTENDED OPERATION CONTROL SYSTEM DESCRIPTION The control system of MSR-FCL-1 was revised during July and August 1970 to permit unattended operation of the loop during evening and night :Shift'periods. ‘This deseription-is intended to assist in the operation of the loop and to provide guidance in the event of any difficulties en- countered during operation. ‘ The automatic control system is designed to transfer the loop opera- tion from "design," or normal, conditions to "isothermal," or standby, conditions in the event design limits are exceeded or a malfunction of equipment occurs. | ‘The principal changes in the control system are (1) the circulating pump is shut off in the event of an alarm condition, (2) loss of pump iube and cooling oil flow is included as an alarm condition that will transfer the loop to "isothermal," or standby, condition, and (3) a con- trol was added to automatieally provide the proper amount of heat to ‘maintain the salt inventory molten with the pump off. -Normal Operation In the normai (design) mode of opefation; tfio-seotions of‘piping between the pump dlscharge and cooler 1n1et ‘are heated by direct re51s- .tance_heat. This heat is removed in the finned cooler to prov1de a temperature dlfference in the circuit. An -LFB pump circulates the molten salt, and a constant speed blower W1th a manually adjusted damper provides ~ air flow for heat removal from the flnned cooler. During normal operation 7;the follOW1ng conditions exist: L R ) | 1. _salt is. carculatlng in the lOOp and the pump is on- ’ 2."the pump 1Ubr1cat1ng and cooling 011 is flow1ng, 3. the two d1rect-res1stance-heated sections are supplled with- sufflclent power to provide the desired temperature rise in the salt; o2 . the air blower is on and the cooler housing door (top of cooler housing) is open to provide sufficient cooling to reduce salt tem- peratures to desired level; | 5. the cooler direct resistance heater is off. Standby Operation The loop is preheated by direct resistance heating during standby operation except in the pump bowl section and the dump tank region, which are heated by Calrod electric heaters. Direct resistance heat for normal and standby operation is applied through three separaste control systems. The two main heater sections (used for normal operation) are supplied from one control system, and resistance heating of the entire loop (used for standby operation) is controlled by a second control system. The cooler is preheated by the third separate resistance hea#-control_system. During normal (design) operation this heat will not be applied. With a loss of salt circulation, the cooler hester circuit and loop resistance heater circuit along with the pump bowl heat will maintain the salt in- ventory sbove the freezing point. During standby operation the following conditions exist: , - : ! - o 1. salt is not circulating; the pump is off (Note: