P~ > OAK ;’R]DGE NATlONAL LABORATORY R s S o b 8 gt ek s e s~ ety g . - 5 et R SR e - Friae v § i T S . ™ ! L “por Ty b e - ; R T prusonrTR e T L 2 S ST i e e oo 1 s IR e O e a i ol e o e S o it | Lo o, Tyt PRTRpre - v N e S | :3foperated by e ST {_f-f-'_-umon CARBIDE CORPORATION ¢ NUCLEAR DWISION Bl L 3 -ui for the_iflfgux.r: ,,_,ff:' R Uas ATOMIC ENERGY COMMISSION ______ C S - ORNL- TM 3303 DATE "_; August 5 1971 _T___i'_'-'FURTHER DISCUSSION OF 1NSTRUMENTATION AND CONTROLS L DEVELOPMENT NEEDED FOR THE MOLTEN SALT BREEDER | j. R R Prevaously pubhshed mformahon (J.R. Tallcckson ’ R. L Moore ; und S J Dlflo, | Efifi_;f-;.,--l'{_f..;.-Insi‘rumem‘c:tu:m and Controls Development for Molten=-Salt Breeder Reactors, ORNL-TM- 1858, May 1967) concerning the development and evaluation of Process instrumentation S -'?"_'_‘app‘hccble to molten-salt breeder reactors: (MSBR) was updated. Areas. where Snstrumenta- v '~ “tion techniques and components tested durmg Operahon of the Molten-Salt Breeder | " Experiment may be applicable to the MSBR are described and recommendation for further - - -~ ... development are stated. In thls study to date, no problems are foreseen that cre beyond o Tl ;ihe present sfate of the art, s 7 S St ST _eywords Developmenf flu:d-f redcfors:fusedsali'smsfrumenfcfion,MSRE, o L, "_j__;__-’_;zy'-iMSBE MSBR reactors S e T L e T e LT -ZIU“cEThls “document ° eontoms mformahon of a prehmmory nature - - .2 and-was_prepared- primarily. for -internal .use at the Ock Ridge Nahonal _ - o 'Luborufory At s sub;ect #o fevmon or correction and therefore does T e "nof represem o finalreport. .. . | : S . o s o T § i g i This report was prepared as an_account of work sponsored by the Uni__fed States Government. Neither the United States nor the United States Atomic Energy Commission, nor any of their 'emplrdyees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or - assumes any legal liability or responsibitity for the accuracy, completeness or- usefylness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. iy % fipl (-) a2 'fl_ &) n 0 0 N Oy AW - S Introduction General Comments Temperature Meosureme nt Pressure Measure ment CONTENTS leferenhal Pressure Measurement " Flow Measuremenf Level Measuremenf ,Salt lnventory Measureme nf - Containment Penetrahon Seals ' Gas-System Control Valves “NOTICE- This report was- piepared 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 . =+ 7} legal . Hability or responsibility for the accuracy; com- ..} pleteness or usefulness of any information, apparatus, | ‘product or process disclosed, or represents that its use =l would not infrmge privately owned rights . BISTRIBUTION OF THIS DOCUMENT IS ENLIMITED Page W O S~ M 11 13 15 16 1. INTRODUCTION In a previous report,® Tallackson, Moore, and Ditto had discussed their evaluation of instrumentation tested during operation of the Molten Salt Reactor' Experiment (MSRE) and its suitability and deficiencies for gpplication to molten-salt breeder reactors (MSBR's).27® Many of the instrument components used successfully in the MSRE will be directly applicable'fo the MSBR. This report summarizes and updates the material covered in the previous (ref. 1) report. The scope of coverage is confined to process instrumentation; it does not cover nuclear instrumentation because recent advancements in the development of high temperature nuclear detectors would make such discussion premature. After these latter developments have been adequately reviewed and evaluated for application to MSBR's, they too will be reported. - 2. GENERAL COMMENTS Although it is reasonable to expect that MSBR process instrumentation. will require designs beyond the present state of the art, no problems are foreseen that could not be resolved by further developme nt of components and techniques. Many instrument components used successfully in the MSRE will be directly applicable to the MSBR. Similarly, experience being gained by the utilities industry with instrumentation of supercritical pressure steam systems will be applicable to the MSBR. MSBR process instrumentation located outside the biologically shielded areas and not an integral part of the containment system can be conventional equipment. Some standard components, however, may require some upgrading, and a strict quality control program will be required to ensure a level of relidbility and performance commensurate with MSBR requirements. 1 J. R. Tallackson, R. L. Moore, and S. J. Ditto, Instrumentation and Controls Development for Molfen Salt Breeder Reactors, ORNL-TM-1856 (May 22, 1971). 2pP. R. Kasten, E. S. Bettis, and R. C. Robertson, Design Studies of 1000-Mw(E) Molten-Salt Breeder Reactors, ORNL-3996 (August 1966). . 2R. B. Briggs, Summary of Objectives and a Program of Developmenr of Molten-Salt Breeder Reactors, TM-1851 (June 1967). - (" ".\ " S All process tnstrumentohon components Iocored wrthm the contommenf cells or as an _integral part of the containment system must. probobly be considered " developmental. - These componenfs are predominantiy primary sensing elements for measurement of flow rates, pressures,. levels, weights, and temperatures in the salt-containing pipes and vessels, in the associated purge and off-gas systems, and in the salt chemical processing facilities. Other such components are final control elements (such as off~gas control valves), leadwire and piping connections to the sensing and final control elements, remotely operated disconnects, and containment penetrotlon seals. . | Present plons,-,fo-,control the temperature of the reactor, drain, and steam= generating equipment by furnace heating will preclude the use of some devices and techniques that were employed successfully in the lower-temperature environ- ment of the MSRE. The physical size of the components and the space available for equipment could restrict otherwise acceptable techniques, such as weighing ~sqalt tanks, and tend to oggrovofe some problem areas, such as insulation shunf - resusfonce in signal cobles., S | Tl'le elecrrrcal conduchvrty of fhe MSBR salts wrll be a srgmfrcont factor in e lecting the type of primary sensing elements that can be used. Although the con- ductivities of MSBR salts are not known with certainty, they are estimated to be about 1 mho/cm--about the same as MSRE salts. If these conductivities were an “order.of magnitude less, some of the MSRE devices could not be used. Conversely, if these conductivities were significantly higher, the existing devices would perform better; and possibly some techniques that could not be used in the MSRE could be - used in an MSBR. For example, srgnrfsconfly I-ngher conduchvrhes would permit use of @ mognehc flowmeter. s , Development of other equrpment and techmques, such as an electr:cul penetration into salt-containing pipes and vessels, would undoubtedly lead to improved instrumentation and new ideas for development. Some development will also be required to adapt 'MSRE ‘control components to fhe hrgh pressures and | ---remperotures in some portsons of rhe MSBR | - e --_3.3-TEMPE-RATUREMEA’SUREMENT:__-'_' R The materials and rechnlques that were used for measurement of MSRE “temperatures should be odequate for most MSBR opplrcohons, although furnace heating of the MSBR reactor cell will create new problems that might require. *further development. It is expected that much of the test data and equipment procurement standards being developed in the LMFBR thermometry program will be applicable to the selection and development of instrumentation for MSBR tempera- ture meosuremenf 6 The reactor cell temperature of ~ 1000°F will require development of in-cell leadwire, disconnects, and containment penetration seals. Additional development ‘will be required to obtain greater measurement ac¢uracy and to ensure long=term (30-year) performance. Development effort could also be profitably applied to methods of thermocouple attachment, to an investigation of radiation pyrometry - techniques, and to measurement of srnall dnfferentml femperafures at elevcfed temperctures. | 4 Although ‘the performance of ‘MSRE thermocouples was very encouraging, improved measurement accuracy and drift stability are needed. Measurement of - small differences between two high temperatures was not satisfactorily accomplished. The accuracy obtained with series~opposed (bucking) thermocouples and extreme care in design and installation was generally adequate for MSRE purposes, but, - without furfher development, it msght be only marginal for the MSBR. - The femperatures of heated pipes and vessels in the MSRE were measured by mmerul-msulated Inconel-sheathed, Chromel-Alumel thermocouples. Results of developmental tests and observation of the field performance of this type of thermocouple indicate that an initial (hot junction) measurement accuracy of +2°F - and a long=term (noncumulative) drift rate of less than 2°F/year can be obtained ~ ot operating temperatures.in a range from O to 1300°F if (1) the thermocouples are carefully selected and calibrated, (2) attention is paid to details during design, fabrication, and installation, and (3) strict quality control is maintained. In particular, the materials must be handled and assembled with cleanliness, the composition of the insulation must be controlled to specified values, and the grode and homogeneity of the thermocouple wire materials must be carefully controlled. To obtain highest accuracy, the design of the sensors and their installation must protect them against stray radiative and convective heat sources which might result in heat transfer to or from the sensor and, thus, biaosed measurements. ~ There is a good possibility that improved accuracy of both absolute and differential measurements of high temperatures in molten=-salt systems can be obtained by using ceramic-insulated platinum resistance thermometers. Several companies have recently marketed resistance thermometers rated for operation at MSBR tempera- tures and higher. Several thermometers rated at 850°C (1562°F) were tested at ORNL for stability.® Although the calibration shifts were excessive in initial thermal cycle tests, it was later demonstrated that these shifts would be decreased to accept- able levels by operating the thermometers at the maximum rated temperature for more than one week. Although the results obtained aofter high-temperature stabilization ¢ Molten-Salt Reactor Program Semiannual Progress Report for Penod Ending August 31, 1967, ORNL-4191, pp. 22-24, 47. ® Molten-Salt Reactor Program Semiannual Progress Report for Perlod Ending August 31, 1968, "ORNL-4344, pp. 94-95. " w' ( o’ . ¥ 7 - were: encourqglng , more data are needed to determine the long-term stability of these devices. The LMFBR Thermometry Program at ORNL mcludes plans for: = repeatmg cmd expandmg these tests. = Multlconductor, gloss-msulated silicone=impregnated, copper-sheathed thermocouple cables used in the MSRE between the in-cell disconnects and the out=of=cell junction boxes will not be usable in the MSBR hlgh-temperature reactor and drain cells, and probably will not be suutable for long-term operation in areas where the radiation level is extremely high (> 100 R/hr) due to insulation degradation “and the effects of radiation-induced outgassing of the silicone-insulating materials. In the MSRE, outgassing produced excessive pressure buildup in organically insulated - cables that were exposed to high radiation and sealed at the containment penetration and the in-cell (dlsconnect) ends. Inorganic-insulated leadwire would be preferred in all high radiation areas in the MSBR.and probably would be mandatory in the furnace-heated cells. In these cells profective sheathing will be required for all in-cell thermocouple wiring. Also for use in these cells, disconnect devices must be developed which will be compatible with the furnace atmosphere and remote ‘maintenance requirements. Multiconductor, mineral-insulated, sheathed-thermocouple ~ cable assemblies probably will be satisfactory for all in-cell leadwire and containment penetration service, but the major problem will be to develop a satisfactory method of sealing the ends of the cable. Although it would be more difficult to develop seals and techniques for installing multiconductor cable through a penetration than for installing a thermocouple through an individual penetration, the advantages to be realized from fewer penetrations required for multiconductor cables would more than | _-|ust|fy the development cost, Other considerations, however, such as maintenance requirements and separation of safety system channels could influence the decision toward use of individual penetratnons, . Both methods need to be studied and evaluated in greater detall The thermocouple attachment technlques used for the MSRE probably will be _, sqtlsfactory for the MSBR, although they were sometimes time consuming and costly.. ~~ Small improvements in these techniques.could yield sugmflcant dividends, because a ~_lorge number of thermocouples wall be requ u‘ed (over 1000 were. mstolled on the o MSRE). Infrared photographlc and rqdlatlon pyrometry devuces mlght enable mappmg _7: "'of temperature contours of . large exposed surfoces (such as the MSBR reactor vessel), possibly by use of a closed-tircuit television camera equipped with an infrared filter. ~ Sucha temperature profile might be determined more accurately by mechanically | maneuvermg a radiation pyromefer to produce a scan pattern similar to the raster - ~ produced on a television scréen. Since the feasibility of these devices would be - . strongly dependent on the physical geometry of the system viewed and of the sur- ‘rounding area, an investigation of their fecmb:hty and the deve lopment of equipment - and techniques should be initiated early in the program. Pyrometric devices whose design is based on usinig the preceding principles are commercnally available, and they may be adaptable to MSBR needs. 8 ~ Ultrasonic devices have been applied recently to measure temperature, and some devices are now available commercially. Although we have not determined the need for such devices in the MSBR, they might be usable for special applications, such as measurement of in-core temperatures. The LMFBR Thermomerry Program also includes investigation of ultrasonic sensors. 4. PRESSURE MEASUREMENT Measurement of pressures in systems not containing molten salfs or hlghly redioactive fluids will not present significant problems. In systems containing molten salts some pressures might be indirectly measurable with MSRE techniques * and others might be directly measurable with NaK-filled transmitters. However, no pressure measuring device is available that is suitable in its present form for . dlrectly mecrsurmg pressures (or dlfferenhal pressures) of fhe fuel salt. o In the MSRE molfen-salf Ioops the pressures were defermmed mdlrecfly by measuring the pressures in gos=purge or supply lines connected to gas spaces in the “drain tanks and pump bowls. This technique will not be usable in the MSBR where - gas purges cannot be tolerated or where high-frequency response is required. Additional work would be required to develop a means of directly measuring salt pressures, since part, or all, of the pressure measuring device would have to be located close to the pressure tap. within the containment vessel and, thus, the device would have to withstand the effects of high temperature, radiation and a varying ambient pressure. In particular, if the reactor and appurtenances are to be heated ~in a furnace, then all pressure transmitter components must be located outside the heated zone or be capable of operating ot the high cell temperatures. NaK-filled pressure transmitters offer the best prospects for direct measurement of cover gas or fluid pressures in molten-salt systems. If this device is to be used, the possibility that a small amount of NaK would enter the system if the seal diaphragm breaks must be acceptable. Additional work will be required to reduce the effects of process temperature on the transmitted signal, to measure pressures > 50 psig at > 1200°F, and, if the transmitting element is to be installed outside the secondary containment, to ensure adequate containment of the reactor system. If the transmitting element is - to be installed inside the secondary containment, the element must be improved to reduce the environmental effects of temperature, radiation, and varying ambient pressure to acceptable levels. Another, but less promising, way to measure pressure directly is to 'possfbly adapt a thermionic diode type of pressure transmitter.® This method is being developed 8 A..J. Cassano and R. E. Engdahl, "Pressure Transducer for,:LiquidrMeral Application," pp. 165-186, Proc. Conf. Application of High-Temperature Instruments to Liquid Metals Experiments, Sept. 28-29, 1965, ANL-7100. w 9 by others for use in high-temperature quu id=-metal systems, and its progress will be followed to determine whether it can be applied to molten=salt systems. 5. DIFFERENTIAL PRESSURE MEASUREMENT As in measurement of pressures, the measurement of differential pressures ~in the MSBR will be more difficult in the systems containing molten salt and highly redioactive liquids and gases, | Except for the coolanf—solt venturi pressure drop meosuremenf (Secr 6), no direct differential pressure ‘measurements were made in salt-containing _equipment of the MSRE. The differential pressure measurements needed to determine molten-salt levels and gas flow rates to and from the molten-salt systems were made on gos lines connected to gas spaces cbove the salt, The performance of the differentlal pressure transmitters for measuring ges flow was satisfactory. Some difficulties were experienced in measuring salt flow rates with ~ the NoK~-filled differential pressure cells during initial operations of the MSRE. 7 The performance of some of these transmitters was satisfactory, but that of others: ~was not, and procurement of oll fronsmurrers was difficult, The problems ossocroted with direct measurement of dtfferenflol pressures in the liquid-filled equipment of the MSBR salt sysrems are similar to those associ=" ated with pressure measurement (Sect. 4); the main difference is that the differential pressure transmitter is not affected by variations in embient pressure and usually is required to megsure much smaller variations in pressures. In applications such as level measurements, where relatively small spans might be required, the effects of variations of ambient temperature, process remperoture, and process pressure on the span and zero of the transmitter are of prime importance and could be the decid- ing factor In determining the sultability of NaK-filled differential pressure trans- mitters for o given application. . If the performance of the transmitters were to be - | improved sufficiently by further development, measurement of level in the drain tanks - might be considered as an acceptable alternative to weighing.. Another, less ‘promising approach to direct measurement of differential pressures in molten-salt systems Is to use thermionic diode l’ype elements presently bemg developed by ofhers for I-he B : 'hqmd metols progroms e 7 Molten-Solf Reactor Progrem Semlonnuol Progress Report for Perlod Endmg | ,August3| i 35 ORNL-3872, p /0. 10 6. FLOW MEASUREMENT Measurement of a variety of flow rates will be required in the MSBR. Most will be conventional measurements of liquid, steam, and gas flows in areas outside the fuel processing and reactor containments. Little development will be required in these applications. However, further development will be needed to obtain satisfactory measurements of salt and off-gas flows. The fuel-salt processing system may also present some special flow measurement problems. The flow rate of molten salt in the MSRE coolant-salt system was measured by a venturi meter section operated at system temperature; the differential pressure was measured by a high-temperature, NaK-filled differential pressure transmitter. The performance was adequate, and this type of system probably would be acceptable for similar service on the MSBR .~ This system was not acceptable for measurement ~of MSRE fuel salt flows, because there was a possibility that NaK could be released into the fuel-bearing salt and possibly precipitate the uranium. This consideration - might not apply to the MSBR, because the volume of NaK is very small compared with the volume of salt. Development would also be required for the venturi, NaK=Ffilled D/P transmitter system for measurement of fuel-salt flow in the MSBR, as menhoned above, Ultrasonic techniques offer promise for molten-salt flow measurement. A commercially available ultrasonic flowmeter is capable of measuring liquid flows in pipes from 1 to 6 in. in diameter. Since this instrument makes use of piezo- electric transducers, it probably will be necessary to use force-insensitive mount techniques (developed by Aeroprojects, Inc., and used in the level probe of the MSRE fuel storage tank) to allow the heat and rodiation=sensitive components to be installed outside the reactor containment and shielding. Such a flowmeter could operate at temperatures > 1300°F and would be compatible with the environmental conditions. It would be of all-welded construction and would not require an electrical or piping penetration into the meter body or the containment vessel. Other devices considered for measurement of molten-salt flow are the turbine and magnetic type flowmeters. Both types can be constructed for high temperature - service and have been used in liquid-metal systems with varying degrees of success. Neither type has been applied to molten-salt service to date; however. The nuclear magnetic resonance type flowmeter might be applicable in the MSBR system and should be investigated. A turbine flowmeter developed for the ANP program operated satisfactorily at 1600°F for a short period before it failed. The major problem with this flowmeter is that the physical properties of the turbine blade and bearing materials must- withstand high temperatures. Perhaps the improved materials now available and lower operating temperature proposed for this service would permit development of a flowmeter of this type for MSBR service. O .yt C’ 1 Magnetic flowmeters have been used extensively at high temperatures (1600°F) in liquid-metal systems and af lower temperatures for the measurement of the flow of many fluids over a fairly wide range of rates. But this type of flowmeter cannot be used for measurement of molten-salt flows in its present form because of consideration of containment, materials compatibility, and molten-salt conductivity, as follows: containment and material compatibility prevent use of ~ electrical lead-through penetrations of the meter body such as those used in con- ventional magnetic flowmeter construction; and the relatively poor (1 mho/cm) - conductivity of the moli‘en salt prevents measurement of the signal voltage at the ovtside surface of the meter body, as is.accomplished with liquid-metal flowmeters. If satisfactory electrical lead-through penetrations could be devised, then magnetic flowmeters for molten=salt service regardless of salt conductivity could be developed. There is o good possibility that such a penetration could be developed by protecting a nearly insoluble insulator material, such s beryllmm oxide, with a frozen-solf film or plug. - - | 7. LEVEL MEASUREMENT Several mei'hods were used successfully for smgle-pomf and continuous mecsurement of molten-salt levels in the MSRE system. All these methods could - be used in the MSBR under sumllar condlhons, although oll hove certain limitations. Molten—sclf levels in the MSRE coolant and fuel-solt pump bowls were measured continuously by bubbler (dip tube) and float level systems. A develop- mental pump installation included a float level transmitter. Two-level, single-" point measurements of molten=salt level in the MSRE fuel and coolant system drain tank were made by conductivity level probes. With the information obtained from these probes, the performance and calibration of the tank weighing systems were checked. The probe signals operated lamps (and other binary devices) that indicated whether the level was above or below two preselected points. An ultra- - sonic probe was used for smgle-pomt measurement of level in the fuel storage ~tank. Except that it is a "one-level" device, the information obtained with ~ the ultrasonic probe is identical to that obtained with the conduchvn'y probe, and information from both probes was used for fhe same purpose. AII of fhe sysfems for meosuremenf of molten-solt Ievel in the MSRE were | developed for a particular service, and further developmenf or redesign would be . required for other oppll_oohoos.r The bubbler systenf is the simplest and the most & Molten=Salt Reocfor Progrom Semlonnuol Progress Report for Period Ending Jan. 31,7963, ORNL-34T9, p. 43. 12 versatile method of measuring molten=-salt level under relatively static conditions of level and cover-gas pressure. This system can be used for narrow or wide ranges of levels, and the vessel modifications required to install the system are simple and inexpensive.. However, since: performance of the bubbler system depends on a steady flow of purge gas through a dip tube, this system can be used only where the purge gas'can be tolerated. Also, the response characteristics of this system depend on the purge flow rate which, in turn, depends on the supply pressure, cover-gas pressure, and other factors. In general, the low purge rate - required for accurate measurement is not compatible with requirements for fast =~ response. Fast changes of cover-gas pressure, such as can occur in the drain tanks and pump bowl during filling and draining operations, can make the system inopera- tive unless there are corresponding changes in the flow rate of the purge gas: A" disudvantcge of the bubbler technique for measurement of levels in systems confam- ing radioactive fluids is that it is necessary to detect and prevent a release of activity through the purge line. Development of a system that would recycle the : purge gas within primary and secondary containments would greatly extend the usefulness of bubbler systems, The float level system® offers the best method of continuous measurement of molten-salt levels over narrow ranges. Such a device would be completely con- tained, have a fast response, and require only electrical penetrations into the secondary containment. Present designs are limited to measurement spans <10 in. Although the span probably can be increased, this device is better suited to - - - low-span than to hngh-—span measurements. The conduchv:ty level prob performed well in MSRE service. ‘Except that redesign of the tank penetration might be necessary to improve containment . and to withstand high temperature ambient conditions in furnace heated areas, = = the present probe design could be adapted to installation in MSBR tanks. Adis-= odvantage of this probe is that the walls of the tube extending into the tank must - be thin, which makes the tubing unsultable in corrosive environments. Since the output signal obtained from the MSRE conductivity probes was much greater than expected, possibly a more rugged and corrosion-resistant single-point probe with a thicker tube wall could be developed. A continuous-type conductivity probe similar to those used in liquid-metal systems also has possibilities. ® MSRE Design and Operations Report, Nuclear and Process Insfrumenfatlon ’ ORNL-TM-729, part IIB, Sect. 6.9 (in preparation). 1°1bid., Sect. 6.10. C. .} . «d 13 Recent dafa on the conduchvnty of molten scnlfs11 have led to a better understanding of the mechamsms that influence the measurement of molten-salt - conductivities and to a possible explanation of the drift characteristics that have deterred development of conductivity probes for application to continuous measurement of molten-salt levels. These data indicate that it might be possible to reduce the drift rates of present developmental designs to acceptable levels | by usmg a l‘ngher excttahon frequency and phcse defechon fechmques. Except for some problems wafh oscnllafor frequency drlft fhe Aeroprolecfs, Inc., ultrasonic level probe! ? hds been dependable and accurate. Development - will be required to improve the main chassis electronics and packaging, and routine redesign and development testing should be sufficient to resolve the remaining’ 'problems. The Aeroprojects single=point ultrasonic level probe is more rugged and corrosion resistant than the conductivity type probe, and, when the remaining problems are solved, this could be the preferred device for smgle-pomt level measurement in msfclllahons where it s ‘applicable. Level measuremeni' by a dlffereni'lal hecd-pressure method was noi' used in _ ‘fhe MSRE because a suitable device for measuring differential pressure was not _available. As discussed previously, if the performance of low-span, NaK-filled, differential pressure transmitters could be improved, this dewce could be consudered for the MSBR. - | _. o With the possable excephon of i'he dlfferenhal (head) pressure mei'hod all methods previously discussed would be compatible with the MSBR design concept of furnace heating the reactor and drain tank cells. The float-type level trans~ mitter should be given great consideration, because its transformer and other | parts could operate at the proposed MSBR sysfem temperatures. Poss:bly, the con- ductivity and vltrasonic probes could be used in a furnace atmosphere in their ~ present form; however, some additional development work on leadwire, penetrations, ~ and disconnects will probably be needed. The effects of temperature on the transmission line characteristics of the- ultrasomc level system must be investigated - before furfher cons:derahon