CHAPTER 8 COMPONENT DEVELOPMENT* 8—1. INTRODUCTION The reliability of equipment for handling radioactive fuel solutions and suspensions 1s considerably more important in homogenecous than i heter- ogeneous reactors becanse the residual radioactivity of such equipment after shutdown of the reactor precludes direct maintenance. The possi- bility of failures of individual components in a homogeneous reactor, moreover, 1s considerably increased by the corrosive or erosive nature of the media being handled and the temperature fluctuations encountered during startup and shutdown operations. The technical feasibility of cir- culating-fuel reactors is so dependent on the behavior and reliability of mechanical components that there is little likelihood that large-seale plants will be built before the performance of each piece of equipment has been adequately demonstrated. In this regard, the development of satisfactory valves, feed pumps, mechanical joints, and remote-maintenance equipment for large-seale plants appears to be most difficult. The component development work at ORNL has been directed primarily toward equipment for use in the Homogeneous Reactor xperiment (HRE-1) and the Homogeneous Reactor Test (IIRE-2). Although the HRI-2 has both a core and a blanket, most of the components in these two systems are identical and designed for use with solutions rather than suspensions. Since suspensions, or slurries, have not been used in either of the ho- mogeneous reactors built by ORNL, the slurry equipment problems have received less attention than corresponding solution problems. Much of the solution technology can be applied to slurries, although additional difficulties such as the settling tendency of slurries, their less ideal fluid-flow behavior, and their erosiveness must be taken into consideration. The following pages give descriptions and illustrations of the aqueous reactor components which have been selected and developed for use at ORNL. *By 1. Spiewak, with contributions from R. D. Cheverton, C. . Gabbard, E. C. Hise, C. G. Lawson, R. C. Robertson and D. 8. Toomb, Oak Ridge National Laboratory. 408 8-2] PRIMARY-SYSTEM COMPONENTS 409 Alternate Inlet Qutlet A Frc. 8-1. Conceptual design of two-region reactor with slurry blanket. Arrows indicate directions of slurry flow, 82, PrIMARY-SYsTEM COMPONENTS 8-2.1 Core and blanket vessel designs. Core hydrodynamies. TFlow tests have been conducted on a variety of spherical vessels simulating solution-reactor cores which have been selected to mcet the following criteria; (1) Heat removal from all points must be rapid and orderly to prevent hot spots from being generated. (2) Radiolytic gas formed from water decomposition cannot be per- mitted to collect in the reactor. (3) The pressure drop should be low. (1) The core tank should be maintained at a low temperature to prevent excessive corrosion rates. Three geometries which satisfy the above requirements have been in- vestigated. The first, straight-through [1], involves diffusing the inlet flow through sereens or perforated plates [2] to achieve slug flow through the sphere. The second, mixved [3], involves generating a great deal of turbu- lence and mixing with the inlet jet so that the reactor is very nearly iso- thermal. The third, rotational [4], is somewhat between the first two; the fuel is introduced tangentially to the sphere and withdrawn at the center of a vortex, at the north and south poles. 410 COMPONENT DEVELOPMENT [cHAP. 8 In the straight-through core, used in HRE-2, the flow enters upward through a conical diffuser containing perforated plates. The number of perforated plates is determined by the ratio of sphere diameter to inlet-pipe diameter. In general, this ratio will be smaller for a larger reactor, resulting in fewer plates and better performance. The velocity distribution leaving the plates can be made to conform approximately to the flux distribution of the reactor. As a result, the isotherms in the core are horizontal, and the temperature rises smoothly toward the outlet at the top. The gas bubbles rise upward at a velocity greater than that of the liquid and are removed with the liquid. The over-all pressure drop is about 1.5 to 2.0 inlet-velocity heads. The core tank is cooled by natural convection. In the mixed core, illustrated in Tig. 81, the inlet and outlet are con- centric at the top of the sphere. The inlet jet coincides with the vertical axis of the sphere and 1s broken up when it hits the bottom surface. Tixeept for the cold central jet, the bulk of the core is at outlet temperature. The veloeity of eddies is great enough so that the gas bubbles travel along with the liquid. The pressure drop is about 1.0 to 1.5 inlet-velocity heads. The core-tank surface is maintained at a temperature very close to that of the core fluid by the high turbulence. In the rotational core, used in HRE-1, the flow pattern tends to produce isotherms which are vertical cylinders. These are perturbed by boundary- layer mixing at the sphere walls. The temperature generally inereases in the direction of the central axis, which is at outlet temperature. The gas bubbles are centrituged rapidly into a gas void which forms at the center axis and from which gas can be removed. The gas void is quite stable 1n cores up to about 2 ft in diameter, but in larger spheres the pumping re- quirements to stabilize the void are excessive [5]. The pressure drop through a rotational core is a function of the particular system, but is usually above 5 inlet-velocity heads. Slurry blanket hydrodynamics. The suspension contained in the blanket vessel must be sufficiently well dispersed to assure that a maximum of the core leakage neutrons are absorbed within the blanket, the neutron reflec- tion from the blanket to the core remains steady, and the transport of fluids through regions of high heat generation are sufficient for heat re- moval. The primary flow is taken through a jet eductor where the flow rate is amplified and forced through a spherical annulus containing the high heat generation region surrounding the core. It appears that amplification gains of 2.5 are attainable. The outlet may be located either (1) concentric with the bottom inlet or (2) at the top. Configuration (1) has the advantage of high circulation rates in the region outside the shroud. Configuration (2) has the advantage of better natural circulation in the event of a cir- culating-pump stoppage. Also under consideration is a swirling flow pattern similar to the rota- tional flow which was described under cores. 8-2] PRIMARY-SYSTEM COMPONENTS 411 Reactor pressure vessels. Three principal types of stresses should be con- sidered in designing the pressure vessels of one- or two-region reactors: (1) Stresses resulting from the confined pressure. (2) Thermal stresses resulting from heat production, and consequent temperature gradients in the metal. (3) Stresses introduced by cladding if used. Because of the uncertain residual stresses introduced during fabrication, this factor has not been taken into account in the past. The construction material can be chosen on the basis of corrosion re- sistance and structural and thermal properties with little regard for nuclear propertics. Carbon steel with a stainless-steel cladding was selected for use in the HRE-2. Usually the pressure-vessel wall is thin in comparison with the inner radius of the vessel; the “thin-wall” formulas for calculating pressure stressex are then applicable [6]. For precise calculations the general equa- tions [7] for vessels with any wall thickness should be used. Thermal stres=es are superposed on the pressure stresses and can be approximated by conventional formulas for hollow eylinders and spheres [8]. Solution of the stress equations depends upon a knowledge of the radial temperature distribution, which, in turn, depends upon the manner in which heat Is generated in the metal wall and upon the temperatures at the mner and outer surfaces. Ileat is produced in the metal by the following Processes: (11 The absorption of gamma rays arising from neutron capture, from fiz 4 101234 Bellows Seal // 3 inches /,/*;/’ 77— Integral S Flanged Body o 347 SS Body 77 T With Integral Seat —~—— 273 in,— TQOOO psi Inlet Pressure (a) (b) Fic. 8-17. (a) HRE-2 letdown valve. (b) HRE-2 low-pressure valve. side of the throttling orifice and thus under less strain. A seat integral with the valve body is used to avoid the difficult problem of leakage around removable seats. Stellite No. 6 and type 17-4 PH stainless steel plugs have been used, since these very hard materials are corrosion resistant in uranyl- sulfate solutions below 100°C and resist erosion due to flow impingement. The primary bellows seal, 13-in. OD by 7 /8-in. ID and 32 in. long, is mechani- cally f-=med of three plies of 0.0085-in. type—-347 stainless steel stock. The bellows seal assembly i1s in two sections, welded together, because the bellows length needed for the 1/2-in. stroke cannot be manufactured in a single section at this time. An average bellows life of 50,000 5/8-in. strokes has been obtained at 500-psi with this assembly. The stem 1s of hexagonal stock and fits in a similarly shaped guide to prevent a torque from being applied to the bellows. The leak-detecting tap between the bellews and the secondary graphited-asbestos packing seal affords a means of detecting a bellows leak, while the asbestos gland prevents gross leakage of process fluid in case of bellows failure. 8-3] SUPPORTING-SYSTEM COMPONENTS 447 The valve, which was supplied by the Fulton Sylphon Division of Robert- shaw-Fulton Controls Corporation, is rated for 2500-psi service with the flow introduced under the seat; however, the downstream pressure is limited to 500 psi by the bellows seal. The valve has a €, (flow coeflicient) of 0.1. The reversible-action operator, supplied by The Annin Company, has a, 50-in? effective area. It is rated for a maximum of 60 psi air operating pressure. The action illustrated is spring-closed, air-to-open; however, by a simple interchange of parts, the actuator operation can be reversed. The actuating bellows is made from type—321 stainless steel and was formed by the Stainless Steel Products Company. The stem guide bushing is brass. The largest valve used in the HRE-2 is the blanket dran valve, which has a 1-m. port and a C'y of 10. The valve and operator were supplied by Fulton- Sylphon. The operator supplies a maximum force of 5440 Ib, and the full stroke 1s 3/4 in. The only two process valves in the HRE-2 which operate with full system pressure on the bellows seal are those which are used to isolate the reactor from the chemical plant. The bellows used here, supplied by Fulton- Sylphon, are rated at 2000 psi and 300°C. The low-pressure HRE-2 valves are novel in that ring-joint grooves are integral with the valve body, as illustrated in Iig. 8-17(b). Long bolts at the corners of the valve body hold the companion flanges; the valve is replaceable with the disassembly of only one set of bolts. The main problems encountered in HRE-2 valves have been valve stem misalignment and corrosion of valve plugs. Valve trem materials. In uranyl sulfate service, stainless steel seats are used with type 17-4 PH stainless steel or Stellite plugs. The latter material is uzeful only below 100°C and where only a small amount of oxygenated- water service i1s anticipated with a high pressure differential across the valve. In slurry service, metallic trims such as those above have been satis- factory for low-pressure valves but unsatisfactory for long life in high- pressure service. Ceramic materials appear promising, but little experience has been obtained to date. A gold-gasketed valve has been developed for tight shutoff of gases. The gasket 1s placed into a groove machined in the valve plug, which mates with a tongue machined into the seat. This type of trim has also given ex- cellent results in one hot uranyl-sulfate loop application. Slurry service valves. In addition to the erosiveness of slurries, other problems are introduced by their tendency to settle out in the primary bellows seal or at stem guiding surfaces, thus interfering with valve action. This may be avoided by purging slurry from the bellows compartment with distilled water. It is hikely that the hydrodynamic design of slurry valves 448 COMPONENT DEVELOPMENT [cHAP. 8 Asbestos Tape PV IIIII S S B FIPIE S ST N T ',[ g il { - g ey 2 Thermocouples 1TH;E) \l[ & - \ &_’4’."{_’_' T T T T T T A T T T T T T T T e T e e SIS Sl ."."Ti Conax Gland Fic. 8-18. Differential thermal expansion valve to control gas flow in the HRE-2. may be revised to make entry of solids into the bellows compartment improbable. Slurry throttling has been accomplished by use of long tubes or capil- laries. These have the disadvantage of fixed orifices, in that continuous flow control 1s not possible. Special gas-metering valve. An ORNL-developed* differential thermal- expansion metering valve is used to regulate the flow of oxygen gas to the HRE-2 high-pressure system [50]. The required flow is very small and is difficult to control by conventional mechanical positioning methods. The valve shown in Fig. 8-18 utilizes the difference in thermal coefficient of expansion of tantalum and stainless steel to effect flow control. The tan- talum plug is used to avoid any possibility of an ignition reaction between the oxygen gas and the metal, the temperature of which for a flow of 2000 std. ec/min with a 400 psi differential can reach 300°C. The design incor- porates all-welded construction and is covered with a waterproof protective housing. The resistance heating element and thermocouple are duplicated to ensure continuity of service. 8-3.9 Sampling equipment. Operation of an aqueous homogeneous re- actor requires that numerous samples be taken in maintaining control of the chemical composition of the solutions. Because of the radioactivity associated with these fluids, standard sampling equipment must be modi- ried, or entirely new apparatus must be devised for taking the samples. Examples of sampling equipment presented here were designed for use on the HRE-2 at ORNL. Samples of liquid and suspended solids will be taken from the high- and low-pressure systems of the HRE-2. Solution from the high-pressure system is reduced in temperature and pressure from 300°C and 2000 psl to approximately 80°C and 1 atm by a cooler and throttling valve before *17.S. Patent 2,610,300 (1952). [Assigned to the U.S. Atomic Energy Commis- sion by W. W. Walton and R. C. Brewer.] 8-3] SUPPORTING-SYSTEM COMPONENTS 449 - .. ¢ Valve 5t Loading . ave Stems I Tube 7 T }\\. - ] i@t @ Universal Joint e - / Plan “ (With Carrier Removed) R fi.fi i 04 812 N L Tos . —=r—Valve Stem _ _ Inches f\k g5 Packing Gland v | | A : : ' \ \1 Carrier | _ B e Vent A i Bellows L Positioning Handle ! 1 f ... < . - 11| E Overflow ~— (it - | | _ Stop | Sample Isolation Chamber ‘ ‘ Cooling Coil i i ‘ Flask Holder Loading Plunger Tube — Needle Holder Needle Isolation L Chamber™} s ——— Sample Yalve i Rubber Top of Flask +——Tubing Disconnect Diaphragm Holder ™ . Transfer . -~y Mechanism Air . Cylinder |_.Differential Pressure Cell Receptacie Fia. 8-19. (a) HRE-2 sampling facility. Flask holder has just been lowered through the loading tube. It is then moved under the isolation chamber by the transfer mechanism. (b) HRE-2 sampler head, shown in the position of transferring sample to the receptacle. entering the sample station. There, a sample of 4 to 5 ml is isolated and removed for analysis [51]. Figure 8-19(a) shows the general assembly of the sampling facility. Virtually all the mechanism is suspended from a shield plug. Personnel shielding is provided by a 2-ft depth of lead shot and water in the plug. The loading tube is sealed by a plug valve to maintain a slight vacuum in the housing. Threaded backup rods extending through the plug are em- 45() COMPONENT DEVELOPMENT [cuap. 8 ployed to make the final connections with reactor piping after the plug assembly is lowered into its housing. Each sampling facility contains two isolation chambers: one for isolating samples from the high-pressure system and the other for obtaining samples from the low-pressure system. Each chamber in the station is served by a common loading and manipulating device. When a sample is being taken, solution from the desired system is al- lowed to flow through its isolation chamber until a representative sample is obtained. The isolation chamber is then valved off. An evacuated sample flask is placed in the holder and lowered through the loading tube to the transfer mechanism. The assembly is then indexed under the proper isolation chamber, where the flask holder is raised by an air cylinder until contact is made between the isolation-chamber nozzle and the inverse cone of the carrier head (Fig. 8-19h). Further hfting of the flask holder causes the hypodermic needle to puneture the rubber diaphragm. The sample is then discharged into the flask by opening the valve on the chamber. When the sample is in the flask the procedures are reversed, and the flask holder is removed into a shielded carrier for transport to the analytical laboratory. Electrical contacts indicate positive positioning of the flask holder under the isolation chamber and closure of the isolation-chamber nozzle. A third sampling station for the HRE-2, identical to the fuel and blanket facilities except for larger passages and a modified isolation chamber, is employed for sampling a fuel stream in the chemical processing facility. This stream has the order of 50 times the solids concentration of the other streams being sampled. 8-3.10 Letdown heat exchanger. The purpose of the letdown heat ex- changer is to conserve the sensible and latent heat of the solution-steam- gas mixture removed in the gas separator prior to discharging it to the dump-tank system. It is necessary also to cool the letdown stream to below 100°C hefore it reaches the letdown valve to minimize corrosion of the valve trim. The thermal design of the exchanger is conventional [52]. In the HRE-2 stainless-steel triple-pipe unit, 400,000 Btu/hr arc removed from the letdown stream into the countercurrent fuel feed stream, the pressurizer purge-water stream, and a cooling-water stream. The unique feature of the design deals, with the flow geometry of the letdown stream [53]. To promote cfficient flow of the two-phase mixture through the letdown valve, it is necessary to prevent flow separation of the two phases. This is done by utilizing the annulus of the exchanger, with weld-bead spacers every 3 in. to promote turbulence. The velocity of the letdown stream is not permitted to fall below 5 ft/sec for any pipe lengths above 1 ft anywhere between the gas separator takeoff and the letdown valve. 8-3] SUPPORTING-SYSTEM COMPONENTS 451 During the transit from reactor operating temperature to 100°C in the letdown heat exchanger, fuel solution must go through the temperature range 175 to 225°C at which stainless-steel corrosion resistance passes through a minimum. This suggests that after several years leakage would occur between the feed and letdown streams. This problem can be ecireum- vented by substitution of titanium for stainless steel. 8-3.11 Freeze plugs. Several reactor installations have employed freeze plugs on liquid-carrying process lines to assure absolute leaktight shutoff. Lines up to 4 in. in diameter have been frozen with a simple wrap-around coil of copper tubing when there was no flow in the pipe other than the convective currents set up by the freczing process. It is conceivable that leaktightness in very large lines might be achieved by refrigerating the passages of valves to freeze a relatively small amount of liquid at the valve seat. This freezing technique is most helpful in reducing the spread of contamination during maintenance. The most efficient frecze-jacket design is one which provides an annular space around the process pipe and allows direct contact of the refrigerant with the pipe. This is generally considered undesirable, however, from the standpoint that if process fluid should leak into the refrigerant, activity would be carried outside the shielded area. I'reeze jackets consisting of tubing wound around the process pipe perform noticeably better if soldered or welded to the process pipe; filling the interstitial space with poured lead also appears to be o worth-while refinement for lines difficult to freeze. Tubing 5/16-in. in diameter has been used on 1/4- to 1/2-in. standard pipe sizes; 3/8-in. tubing on 3/4- to 13-in. pipe sizes, and 1,/2-in. tubing on sizes up to 4 in. Clamp-on, or clamshell, types of freeze juckets were developed for the HRE-2 for temporarily freezing certain lines, On the HRE-2, stainless-steel refrigerant tubing is used for permanent freeze jackets on hines which normally operate at or above 350°F. Copper tubing, which is oxidized more readily in air, is used for lower temperature lines. A jacket length of 3 to 4 pipe diameters has been demonstrated to be optimum:. Freezing times of a few minutes for 1/2-in. and smaller lines and up to several hours for 3- and 4-in. sizes have been obscerved when the refrigerant temperature is in the —20 to —40°F range and with flows through the jacket of 3 to 5 gpm. Insulation outside the freeze jacket materially aids in the ability to freeze lines with particularly high heat load, such as those subjected to gamma heating. If the freeze jacket must be operated sub- merged, such as for underwater maintenance, it has been found that pro- tecting the jacket from convection water currents by means of aluminum- foil wrapping aids materially in the freezing process. 452 COMPONENT DEVELOPMENT [caaPp. 8 8-4. AuxiLiARY COMPONENTS 8-4.1 Refrigeration system.* Refrigeration is required in the HRE-2 for operation of freeze plugs and cold traps. The refrigeration system con- sists of a primary loop, which is not irradiated, and a secondary liquid eir- culating system which enters the shield. A two-stage primary mechanical refrigeration system is employed in the HRE-2. Refrigerants commonly used in such a system are the halogenated hydrocarbons, provided that the primary refrigerant remains outside the reactor shield. Breakdown of this series of refrigerants under radiation has been observed to have the serious effects of forming phosgene gas and in- soluble tarry polymers, thus creating conditions corrosive to stainless steel. Carbon dioxide 1s probably the best refrigerant for use in an irradiated direct-expansion system, but it must be used at high pressure. Choice of a secondary refrigerant to be circulated through radioactive equipment is difficult in that the fluild must not only meet the obviously desirable properties of having a low freezing point, suitable viscosity, low vapor pressure, noncorrosiveness, nontoxicity, and nonflammability, but it must also be resistant to radiation damage, not contain chloride ions which might promote stress-corrosion cracking of staimnless steels, and not evap- orate to insoluble residues. Misecibility with water would be advantageous if underwater maintenance techniques are employed in that if some refriger- ant escapes, there is less impairment of vision and a film is not left on equipment when the water is drained. After considering many possible secondary refrigerants, Amsco 125-82, an odorless mineral spirit resembling kerosene in its physical properties, was selected for the HRE-2. Its performance to date has been quite satis- factory. In addition to the primary refrigeration system used to maintain a central supply of chilled Amsco, it was useful for short-term maintenance operations at the HRE-2 to have also a portable rig, consisting of an in- sulated tank and circulating pump. Chilling was accomplished by floating blocks of COs-ice directly in the liquid; secondary refrigerant tempera- tures of about —75°F were maintained with a circulation rate of about 4 gpm and with an ice consumption rate of 75 to 100 Ib/hr. 8—4.2 Oxygen injection equipment.f Oxygen is needed in the high- pressure fuel system to maintain chemical stability of the uranyl-sulfate solution and to reduce corrosion of the stainless steel container. This oxy- *Based on material furnished by R. C. Robertson. fMaterial submitted by K. C, Hise. 8-4] AUXILIARY COMPONENTS 453 gen may be introduced most conveniently into the fuel feed stream, at either the suction or discharge of the feed pump. As a result of operational experience, high-pressure injection has been found to be more flexible and to give better feed-pump performance. The oxygen system requires a high-pressure gas supply and a metering device. The first supply used in the HRE-2 was a converter manufactured by Cambridge Corp. of Lowell, Mass. This has been replaced by high- pressure cylinders, which have considerably lower operating costs. Oxygen compressors may be desirable to recirculate contaminated oxygen and are being investigated. Metering is accomplished with a thermal valve (de- scribed earlier) controlled by a capillary flowmeter. Oxygen converter. The HRE-2 oxygen generator is designed to convert liquid oxygen to the gaseous state and deliver it to the fuel and blanket high-pressure systems at pressures up to 3000 psig. The capacity of the generator 1s 0.47 {3, or 30 Ib of oxygen, when 909 filled with liquid. This will permit delivery of approximately 21 1b of oxygen gas at 3000 psig and 70°F. This pressure is automatically maintained over a flow range of from 0.01 to 0.7 Ib/hr. The oxygen generator consists of an insulated high-pressure container, with an electric heater and automatic pressure and temperature controls. The high-pressure inner vessel 1s fabricated of type-304 stainless steel. Charging of the converter with liquid oxygen is a manual operation. The labor of charging and the inefficient utilization of oxygen are disadvantages of this unit. High-pressure cylinders. The HRE-2 is now using 300-liter high-pressure cylinders which are commercially charged to 2400 psi and are used down to 2000 psi. A hank of three eylinders will last for about two days of normal operation. This system involves no waste of gas, since the cylinders are recharged from 2000 psi to 2400 psi, with very little operator attention or hazard. Oxygen compressors. High-pressure low-capacity laboratory-type oxygen compressors have recently become commercially available. Pressure Products Industrics, of Hatboro, Pa., produces a compressor having a stainless-steel diaphragm hydraulically actuated in a contoured chamber by a reciprocating drive. A single-stage machine capable of compressing approximately 0.8 sefm of Oy from 500 psi to 2500 psi has been purchased and placed in service in the HR'T mockup. Although there have been some difficulties with the hydraulic plunger packing, it has been generally satis- factory. A three-stage machine capable of compressing 2 sefm of contaminated oxygen from atmospheric pressure to 2500 psi is being designed. The diaphragm heads will be located remotely with respect to the drive, as is done in diaphragm feed pumps. 454 COMPONENT DEVELOPMENT [cHAP. 8 85. INsSTRUMENT COMPONENTS* The instrumentation and controls systems for aqueous homogeneous reactors are similar to those used in modern high-pressure steam power and chemical plants. However, problems attendant on radiation damage to insulations, the difficulty of performing maintenance or replacement operations, the requirement for the absolute leaktightness and the very high reliability of components necessary for safety and plant operability have required considerable development of special components. 8-5.1 Signal transmission systems. In a typical control loop the pri- mary and final control elemets are in a radioactive area isolated from the control room by a vapor container and a concrete radiation shield. Electric. Advantages for electric transmission under these conditions include the ease of readjusting system zeros and spans from the control room and the ability to sense motion from weld-sealed transmitters without the use of flexure seals such as bellows and torque tubes. The speed of information transmission, the ease of switching signals, and the ability of the sensing elements to operate over wide temperature ranges may also be important. Disadvantages of the electrical system include the possible radiation damage to insulations and the present unavailability of a cheap, reliable linear-power actuator for control valves. Pneumatic. Advantages of a pneumatic system include the utilization of all-metallic radiation-resistant construction for the transmitters and valve actuators by the use of metallic bellows, bourdon tubes, and con- voluted diaphragms. The advantages of the high state of commercial development, low cost, reliability, miniaturization, and ease of paralleling of receiving elements are considerable. A disadvantage of the penumatic system is the tubing transmission line, which affords a path out of the radiation enclosure for contaminated fluids or vapors in case of a release of radioactivity coupled with a line break. HRE-2 system. A combined electric-pneumatic system (described in Article 7-4.8) is used in HRE-2. In the control room, electric signals from primary variable sensing elements (temperature, flow, liquid level, pressure, etc.) are converted by transducers to penumatic signals, and these are used to actuate miniature pneumatic display instruments and pneumatic valves in the reactor. The escape of radioactivity through air lines is prevented by the automatic closure of “block’” valves within the vapor-contained area, on a signal of the release of radiation. Radiation damage to primary elements is avoided by the use of inorganic electrical insulations such as glass, ceramics, mica, magnesium oxide, and magnesium silicate. Electric control actions are derived from the pneumatic signals by pressure switches. These switches are simple devices in which diaphragm deflection opens or *Material submitted by D. S. Toomb. 8-5] INSTRUMENT COMPONENTS 455 Waterproof Coil Housing A_E/(DifferenfiolTrcmsformer) 3 T T' | Piston Position Sensing Coil Magnetic Piston With Stainless Steel Sheath i Helical Permanent Magnet Yoke Suspension Springs Copper Damping Ring Sheathed in Stainless Steel L 7 VoporTcp<‘f‘_i‘ S | - ‘W\ 3 R 7 e T 77 e ¥ v o 14 in, 1 “ 5 é% Displacer (*'Float’") - \\ N ’ v ;. V/ ? % ;’%,-‘ R ¥X§§§L\\\\\\K§\ Low Level Tap . N Fic. 8-20. HRE-2 float-type level indicator (covers a 5-in. range at psi-2000 operating pressure). closes an electric snap-acting switch. Electric interlock control of the penumatic signals to final control elements is achieved by the use of solenoid-actuated pilot valves. 8-5.2 Primary variable sensing elements. Liquid-level transmatters. Knowledge of liquid levels in reactor systems and loops is eritical for main- taining the proper balance of liquid and vapor in pressurizers and storage tanks. It is desired also to be able to maintain accurate inventories of the hazardous and valuable fluids which are contained. 456 COMPONENT DEVELOPMENT [cHap, 8 There are a large number of liquid-level sensing devices in use, since no one device has been developed which satisfies all the criteria of precision, rapid response, insensitivity to temperature and pressure, and utility of its signal for control functions. Devices which have been used at ORNL are described in the following paragraphs. (1) Displacement or Float Transmitters, The ORNIL-developed dis- placement transmitter, used to control HR¥-2 pressurizer level, consists of a 5-in.-long displacer suspended by two helical springs (Fig. 8-20). An extension rod above the springs positions a magnetic piston in the center of a differential transformer. Troublesome vibration of the float is damped by the action of the field from permanent magnets on a one-turn copper ring. The only nonwelded closure is the ring-joint flange, which makes the unit easily replaceable. The differential transformer is a compact, highly sensitive, linear device which is commercially available. The most satisfactory instrument system for the differential transformer is a high-frequency oscillator-amplifier phase-sensitive demodulator carrier system which provides the necessary sensitivity and stability and eliminates phase-motion ambiguity associated with the null voltage. Float transmitters of this type have also been built with cantilever springs, with floats up to 47 in. long, and with hydraulic damping vanes attached to the hottom of the float in lieu of the magnetic damping [34]. They have given excellent service in continuous control applications. However, the displaccment transmitter is quite sensitive to fluid densities, and the springs exhibit some changes in properties with temperature. The best spring material tested to date is Isoelastic spring alloy supplied by John Chatillon and Sons, which may be gold-plated for supplementary corrosion resistance. Hollow spherical floats, lighter than water, have also been used at pres- sures below 600 psi. Magnetrol, Ine., makes a unit in which float position is transmitted magnetically. Moore Products Company supplies a level alarm where float position is transmitted mechanically through the all- welded housing by a flexible shaft. (2) Differential-Pressure Cells. D/P cells have been used successfully in HRE-1 and in loops as level transmitters. The variable liquid leg is compared to a reference level maintained by condensation or liquid addi- tion. Since the density of water is temperature-dependent, the temperature of the primary systemn and the lines to the D/P cell must be known for accurate level measurement. (3) Weigh Systems. For obtaining an accurate inventory of IHRI-2 storage tanks, they are weighed with pneumatic weigh cells. This was found to be the only feasible method of measuring the quantity of liquid in long, horizontal storage tanks. Piping to the tanks is kept flexible by 8-5] INSTRUMENT COMPONENTS 457 the use of horizontal L and U bends. A pneumatic system is selected pri- marily because taring can be done remotely with balancing air pressures, and components are less susceptible to radiation damage. The pneumatic load cells, which are supplied by the A. H. Emery Corporation, have an accuracy of 1/10%; however, when used in a system with solid pipe con- nections to the weighed vessels, an accuracy of 19 of full load results. (4) Heated Thermocouple Wells. Heated thermocouple wells have been used for liquid-level alarm or control. The thermocouple junction is normally held a few degrees above the vapor temperature; as the liquid level surrounds the probe, the increased heat transmission to the fluid from the probe lowers the thermocouple signal output [55]. Several wells must be used for control purposes. This system gives rather sluggish response. (5) Capacitance Probe. An aluminum oxide capacitance probe, manu- factured by Fielden Instrument Division, has been recently received by ORNTL but has not vet been evaluated. This instrument senses the dielectrie constant of the medium it contacts. Its ceramic-to-metal seal is rated at 2000 psi and 636°F. This type of instrument may prove useful in water or slurry service. Differential Transformer o . - Cast Aluminum Position Adjustment \{.. Electrical Housing Core Guide Bearing i lTerminaI Strip B Differential Transformer Core Motion Sensing Element |- Stainless Steel Bourdon Tubes ‘\ ;Mognefic Core "0 . . a Differential Transformer a . Retaining Spring ! Core Drive Rod 2 Scale In ; Inches 3 - 4 | Stainless Steet 57 Safety Housing Fie. 821. Bourdon-tube pressure transmitter in safety housing. Sensing ele- ment, twin Bourdon tubes; range, 0 to 2500 psi; test pressure, 3750 psi; accuracy, + 19, of range; transmission, electrical; fabricated by the Swartwout Company. 458 COMPONENT DEVELOPMENT [cHAP. 8 Magnetic Piston Cased T In Stainless Steel Differential Pressure Sensing Diaphragmgy: Electrical Cable Gland 1.9 ] 2 3 4 5 ¢ 7 L Piston Motion Sensing Coil Scale In Inches - Loy Differential Pressure Transmitter ol SN ) [Foxboro Company) L T ! T Autoclave Disconnect Fitting L apillary | AN F16. 8-22. Capillary flowmeter, used to meter small gas or liquid streams, shown with high-pressure seal-welded differential-pressure transmitter. (6) Fluid Damping Transmitters. The Dynatrol transmitter, manu- factured by Automation Products, Inc., is an interesting possibility for use as a fluid damping transmitter. It contains a vane exposed to the process system and vibrated through a pressure housing by alternating- current excitation of a solenoid. The degree of damping, which is dependent on the area of the vane covered with liquid, is measured by a second sensing coill. No test experience with this transmitter is yet available. Unusually difficult level-sensing problems are introduced when it is desired to measure or control the true level of a slurry or a boiling liquid. Most proven devices are density-sensitive, and the mean density of two- phase systems 1s usually unknown. Of the level transmitter types cited above, none appears adequate for continuous-range indication. IFor spot indication, float, capacitance, and Dynatrol transmitters are promising. Pressure and differential-pressure measurement. Bourdon tubes of weld- sealed 347 stainless steel are used for pressure transmission in the HRE-2. Most suitable for reactor use are units contained within secondary pressure housings, such as the 2500-psi pressure transmitter shown in Fig, 8-21. Baldwin cells have been widely used for accurate pressure measurement in loops. Bellows or diaphragm differential-pressure cells have been used to meas- ure pressure differentials with full-scale sensitivity of 25 in. of water to 125 pst. A typical D/P cell with electric transmitter is shown in Fig. 8-22, Pressure transmitters are usually tied into the steam or water portions of aqueous homogeneous systems to reduce the probability of plugging or other damage. Where it is necessary to connect a D/P cell into a slurry system, the pipe connection is regularly purged with 10 to 30 cc/min of water. Large vertical piping connections with the transmitter mounted above the primary piping have also been used. Diaphragm transmitters mounted flush with the pipe surface are being developed for slurry applica- tions. 8-5] INSTRUMENT COMPONENTS 459 Flow transmitters. Tlow measurements are made in high-pressure lines by sensing the pressure drop across a calibrated orifice or venturi, or by the transmitting variable-area type of flowmeter. The latter meter resembles a Rotameter with float position transmitted electrically. It has the ad- vantage of being an in-line element but is not readily applicable to large flows. Another system for metering and controlling small liquid and gas flows in the HRE-2 is illustrated in Fig. 8-22. The pressure drop across the metering capillary is measured by the differential-pressure transmitter and the output signal is calibrated in terms of flow. The “snubbing” capillary is used to prevent the sudden application of pressure to the inlet side of the differential-pressure transmitter, which would cause undesirable zero shift. A technique widely used in the HRIE-2 for metermg purge flows 1s a “heat balance” flowmeter in which a known amount of heat is added or extracted from the process stream and the temperature change noted. Temperature measurement. 'The most commonly used method of tempera- ture detection in the HRE-2 is the thermocouple measurement of vessel and pipe wall temperaturcs; the couples are spot-welded directly to the wall and then covered with insulation. When faster response is desired, thermocouples are spring-loaded into thin thermowells. Chromel-Alumel wire is generally used because its resistance to corrosive attack by moisture is better than that of iron-constantan alloys. Thermocouple wire insulated by compressed magnesium oxide powder and housed in various alloy tubes is available from the Thermo Electric Company. Another commonly used wire supplied by the Claud 8. Gordon Company is insulated as follows: each strand is coated with phenol formal- dehyde varnish and Fiberglas-impregnated with a silicone alkyd copolymer, and the entire wire is Fiberglas-impregnated with a silicone alkyd co- polymer. Sound transmitters. Waterproof microphones are attached to pumps to monitor bearing and check-valve noises. 8-5.3 Nuclear instrumentation in the HRE-2. The purpose of the nu- clear instrumentation in homogeneous reactors is to provide neutron-level measurement and the gamma monitoring of auxiliary process lines and control areas for the detection of radioactive leaks (see Article 7—1.8). Gamma radiation measurement. Gamma monitors for detecting process leaks, manufactured by the Victoreen Instrument Company, consist of a simple one-tube, three-decade logarithmic amplifier sealed within the chamber head and a remote-contact-making meter and multipoint recorder. These detectors can be remotely calibrated by exposing a radioactive source on the actuation of a solenoid-operated shielding shutter. All channels are 460 COMPONENT DEVELQPMENT [crAP. 8 Fluorethene Insulator . Y O lNifrogen Gas e & . _rAquadag Surface Guard Ring o TR ‘ %’” v ] LT il | | b RG 59-U Coaxial | Cables : i s B Y ¥ . W 7 T % \l {4 Kovar Seals g Sl i ~ \\ Positive Electrode \Signcl Electrode \Aluminum Housing Brass Ground Rod ™Fluorethene !nsulator 1 0 1 2 3 4 Scale In Inches Fia. 8-23. High-level gamma ionization chamber. Effective volume, 120 cm3; electrode spacing, 1/8 in.; performance, 20 ua, chamber saturated at 100 volts at radiation level of 3 X 107 r/hr; design temperature, 130°F. duplicated, and control action is initiated only upon a simultaneous signal from both channels to minimize false “‘scrams.” However, a signal from either channel is annunciated. For monitoring control areas for personnel protection, more stable and accurate vibrating-condenser types of elec- trometers are used. The cell air monitors, which provide an alarm in case of a leak of radio- active vapor from the reactor system, are installed in an instrument cubicle. Cell air is circulated through a 2-in. pipe from the reactor tank, past the enclosed monitors, and then back to the cell. The blower is sized so that only 5 sec is required for cell air to reach the radiation monitors. A high-level gamma ionization chamber, developed at ORNL [56], is used to measure cell ambient radiation levels up to 107 r/hr (Fig. 8-23). This measurement is needed to evaluate the effectiveness of shielding, to assay the rate of radiation damage to reactor components, to measure radiation levels during maintenance operations, and to provide data for future reactor designs. The chamber is of inexpensive construction and is discarded upon failure. 8-5.4 Electrical wiring and accessories. Copper-clad compressed mag- nesium-oxide spaced and insulated electrical cable is very desirable for service in extremely high-temperature, radioactive, or wet areas because no organic material subject to cracking and outgassing is used in the insula- tion. A waterproof disconnect, designed to be broken remotely to permit the removal of reactor electrical equipment, is used with this type of cable. The electrical connectors are terminated inside the disconnect with a multiple-header ceramic-to-metal seal, voids being filled with magnesium- 8-5] INSTRUMENT COMPONENTS 461 oxide powder. The outside guides are tapered to simplify remote main- tenance. Long insulators are used on the connecting terminals to minimize leakage currents after submersion. The cable is available in a varted num- ber of conductors and sizes, from single to seven conductors in a copper sheath, as wire sizes No. 16 AWG to 4/0 AWG, from the General Cable Company. The hermetic end seals are available from the Advanced Vacuum Products Corporation or Permaseal Corporation. A compression seal designed around an inorganie material, magnesium silicate, is used to seal wires at conduit terminations. These seals are supplied by the Conax Company. A similar device but utilizing a glass- to-metal seal is manufactured by the Stupakoff Ceramic and Manufactur- ing Company. For the windings used on the motion-sensing coils of instruments, 30- gage anodized aluminum wire supplied by the Sigmund Cohn Company has successfully withstood temperatures up to 300°C and radiation ex- posure of 6 X 10'7 nvt fast neutron and 1 X 10% r gamma without failure. The only electrical insulation on the wire is that afforded by the oxide film on the aluminum. This wire must be handled carefully to avoid abra- sion and is suitable only for low-voltage use. For lower temperatures, the Ceroe magnet wire available from the Sprague Electric Company has been used very sucecesstully. 162 COMPONENT DEVELOPMENT [cHAP. 8 REFERENCES 1. P. H. Harurey, Straight Through ITRT Core Model Test, USAT.C Report CF-54-9-129, Oak Ridge National Laboratory, Sept. 22, 1954, 2. 1. Seiewaxk, Preliminary Destgn of Screens for the Inlet of the ISHR Core, T'SAEC Report CF-52-10-181, Oak Ridge National Laboratorv, Oct. 18, 1952, W. D. Bamxes and BE. G. Prterson, Trans. Am. Soc. Mech. Engrs. 73(3), 467 (July 1951). 3. L. B. Lesem and P. H. Harney, Scale-up of Mernate HRT Core, USAEC Report ARECD-3971. Oak Ridge National Laboratory, Mav 7, 1954, L. B. Lesem and I. Serewak, Aternate Core Proposal for the HRT, USAEC Report CTF-54-1-80, Oak Ridge National Laboratory, Jan. 28, 1954, 4. ¥. N. PreBres and H. J. Garsrr, Studies on the Swirling Motion of Water within a Spherical Vessel, University of Tennessee, Report 8-370, January 1956, 5. L. B. Lesesm et al., Hydrodynamie Studies in an Fight-foot Sphere Utilizing Rotatron Flow, USAEC Report ('F-53-7-29, Oak Ridge National Laboratory, July 20, 1953. 6. 8. TrvosuENko, Strength of Materials, 2nd ed. New York: D, Van Nostrand Co., Inec., 1940. (Part I1, pp. 160, 162) 7. 8. Trvosuexko and J. N. Goopier, Theory of Flasticity. 2nd ed. New York: McGraw-Hill Book Co., Tne., 1951, (pp. 59, 359} 8. 8. TrvmosuexNko and J. N, Goonier, Theory of Elasticity. 2nd ed. New York: MceGraw-Hill Book Co.. Ine., 1931, {(pp. 412, 418) 9. I.. G. ALEXANDER, Fstimaiton of Heat Sources tn Nuclewr Reactors, A.1. Ch. E. Journal 2: 177 (June 1956). 10. R. H. Crapyman, Analysis of Spherical Pressure Vessel Having an Fnergy Source Within the Wall, USAEC Report ORNL-1987, Oak Ridge National Lab- oratory, Oct. 26, 1954, 11. L. F. Brensor et al.. Welding J., N. Y., 35, 997-1006 (October 1956). W. R. Garr, Nucleonies 14(10), pp. 32-33 (October 19306). 12. .. C. Movxyers, Long-term Run of Westingliouse 4001-1 Pump, USAEC Report CF-57-9-1, Oak Ridge National Laboratory, Sept. 3, 1957. 13. R. B. KorsMEYER et al., in Homogenecous Reactor Project Quarterly Progress Report for the Period Inding Jan. 31, 1955, USAEC Report ORNL-2493. Oak Ridge National Laboratory, 1958, 14. H. A. Ru~prLL et al., I'nvestigation of Effect of Seal Configiration on Mixing Flow and Radiation Damage tn HRT-Type Circulating Pumps. USALE.(C Report CF-57-10-48, Oak Ridge National Laboratory, Oct. 10, 1057, 15. J. C. Movers, Long-term Run of Westinghouse 1004-1 Pump. USALC Report CF-57-9-1, Oak Ridge National Laboratory, Sept. 3, 1957. 16. R. B. KorsMEYER et al., in Homogeneous Reactor Project Quarterly Progress Report for the Period Ending July 31, 1957, USALC Report ORNL-2379, Oak Ridge National Laboratory, Oct. 10, 1957. (p. 59) 17. R. B. KorsMuEYER et al., in [Homegeneous Reactor Project Quarterly Progress Report for the Period Ending Jan. 31, 1958, USALEC Report ORNL-2493, Ouk Ridge National Laboratory, 1958. REFERENCES 463 18. H. A. RunpeLu et al., Tnvestigation of Effect of Secal Configuration on Mixing Flow and Radiation Damage in IIRT-Type Circulating Pumps, USAEC Report CF-57-10-48, Ouk Ridge National Laboratory, Oct. 10, 1957, 19. W, J. Finax and 1. Gra~ver, Final Reports on Union Carbide Nuclear Company Contract No. W35X-31312, Phase 1, Foster-Wheeler Corp., Nov. 15 and Dec. 15, 1956. 20. J. C. Griess et al.. Solution Corroston Group Quarterly Report for the Period Ending July 31, 1957, USAEC Report CF-57-7-121, Oak Ridge National Laboratory, July 31, 1957. (p. 33 ff) 21. C. H. Secoy, Aqueous [Fuel Systems, USALC Report CEF-57-2-139, Oak Ridge National Laboratory, Feb. 28, 1957, 22. C. Micurrson, ITRT Modified Pressurizer Design, USALEC Report CI- 56-5-165, Oak Ridege National Laboratory, May 25, 1956, 23. Boiler Construction Code, Section I, Power Boilers, American Society of AMechanical ngineers (1956); ASA Code for Pressure Piping, B31.1-1935. 24, K. L. Haxso~n and W. E. Jausyax, An Fealvation of Piping Analysts Methods, USALEC Report KAPL-1384, Knolls Atomic Power Laboratory, Aug. 10, 1955. 25. M. W. Krnrose Cosmeany, Design of Piping Systems. 2nd ed. New York: John Wiley & Sons, Inc., 1956. 26. M. 1. Lu~pix, HRT High Pressure System Piping Line Deflections and Reactions on Fquipment Nozzles, USAEC Report CF-55-8-83, Oak Ridge Na- tional Laboratory, Aug. 10, 1955. 27. W. R. GavrL ct al., In Homogeneous Reactor Project Quarterly Progress Report for the Period Ending Apr. 30, 1957, USAEC Report ORNL-2331, Oak Ridge National Laboratory, Aug. 14, 1957, (pp. 22-25) 28. B. Drarrrand H. C. RoLurr, Design and Development of a ! 5-in. Tifanium to Stainless Flange, USAEC Report CF-57-11-140, Oak Ridge National Labora- torv, Nov. 27, 1957, 29. J. A. Harvorp, Development of the Pipe-line Gas Separator, USAEC Report ORNL-1602, Oak Ridge National Laboratory, Nov. 2, 1953. 30. P. H. Haruey, Performance Tests of [TRT ['uel Solution Evaporator and Entrainment Separator, USATC Report CF-534-10-531, Oak Ridge National Laboratory, Oct. 13, 1954, 31. WestiNGgHOUsE ELEcTtric CORPORATION AND PENNsSYLVANIA POWER AND LigrT Conmpany, 1957. [Unpublished. 32, 0. A. FarBrr, Bubble and Slug Flow in Gas-Liquid and Gas (Vapor)- Liguid Solid Mixtures, Research Progress Report on Subeontract N.996 to REED of Oak Ridge National Laboratory, 1957. 33. R. V. BatLey et al., Transport of Guases Through Liguid-Gas Mixtures, USAEC Report CF-55-12-118, Oak Ridge National Laboratory, Dee. 21, 1955. 34. C. L.Segaser, HRT Entrainment Separator Design Study, USALCReport CF-54-7-122, Oak Ridge National Laboratory, July 23, 1954. 35. R. &, Aven, IHTRT Recombiner Condenser Design, USAEC Report CF-54- 11-1, Oak Ridge National Laboratory, Nov. 1, 1954, 36. 0. A. Hovaen and K. M. Watsox, Chemical Process Principles, Vol. 111, New York: John Wiley & Sons, Inc., 1947, (pp. 902-910) 464 COMPONENT DEVELOPMENT [cHAP. 8 37. J. A, Ransonorr and 1. Seiewak, in Development of Hydrogen-Oxygen Recombiners, USAEC Report ORNIL-1583, Oak Ridge National Laboratory, Oct. 22, 1953, (p. 40) 3%. P. H. Hawwey, [ligh-pressure Recombination Loop Progress Report, USAEC Report CF-57-1-90, Ouk Ridge National Laboratory, Jan. 4, 1957. 39. J. A, Ransonorr and . Seiewax, in Development of Ilydrogen-Oxygen Recombiners, USATIC Report ORNL-1583, Oct. 22, 1953, (pp. 48-56) 40. 1. K. Namna, Natvral Ciurculation Recombiner Report, USAEC Report CF-56-9-27, Oak Ridge National Laboratory, Sept. 10, 1956. 41. P. H. Harrney, High-pressure Recombination Loop Progress Report, USAEC Report CF-57-1-90, Oak Ridge National Laboratory, Jan. 4, 1957. 42. T. W. Lrrann, Design of Charcoal Adsorbers for the HRT, USAEC Report CF-55-9-12, Oak Ridge National Laboratory, Sept. 6, 1955, 43. I.. B, ANpErsoN, Oak Ridge National Laboratory, 1955. Unpublished. 44. ). S. Cuuver and C. B. Granay, High-pressure Diaphragm Pumps for Reactors, in Safety Features of Nuclear Reactors; Selected Papers from the 1st Nuclear Engineering Science Congress, December 12-16, 1955, Cleveland, Ohio. New York: Pergamon Press, 1957. (pp. 225-230) 45, C. H. GaBBanp, Diaphragm Feed Pumps for Homogeneous Reactors, 4th Fngincering and Science Conference, Held in Chicago, Illinois, March 17-21, 1958. (Preprint 74) 46. R. BLuumsira ot al., Diaphragm Feed Pump Development Program Progress Report, USAEC Report CI-56-10-114, Oak Ridge National Laboratory, Oect. 29, 1956. 47. Ohio State University, Union Carbide Nuclear Company, Contract No. 81X-44934. 48. A. M. BiruuNgs, Control Valves for the Homogeneous Reactor Test, 4th Nuclear Engineering and Science Conference, Held in Chicago, Illinois, March 17-21, 1958, (Preprint, 149) 49. A. M. Bruuinas, Life Tesis of Stem-sealing Bellows for HRT Valves, USAEC Report CF-58-3-39, Oak Ridge National Laboratory, Mar. 17, 1958. 50. D. 8. Tooums ct al., in Homogeneous Reactor Project Quarterly Progress Report for the Period Inding Jan. 81, 1957, USAEC Report ORNL-2272, Oak Ridge National Laboratory, Apr. 22, 1957. (p. 34) 51. B. A. Han~narorn, HRT Sampler Development, USAEC Report CF-57- 1-87, Oak Ridge National Laboratory, Jan. 22, 1957, 52. R. VaNn WinkLE, Fuel Let-down Heat Exchanger, USAEC Report CF-54- 9-143, Oak Ridge National Laboratory, Sept. 20, 1954. 53. C. D. Zersy, Design of Smoothly Flowing Gas and Liquid JMaxtures, TSAEC Report CF-51-10-130, Oak Ridge National Laboratory, Oect. 11, 1951. 54, D. 8. Tooms et al., in Homogeneous Reactor Project Quarterly Progress Report for Period Ending Apr. 30, 1956, USAEC Report ORNL-2096, Oak Ridge National Laboratory, May 10, 1956. (p. 32) 55. D. 8. Tooums et al., in Homogeneous Reactor Project Quarterly Progress Re- port for Pertod Ending July 31, 1956, USAEC Report ORNL-2148(Del.), Oak Ridge National Laboratory, Oct. 3, 1956. (p. 67) REFERENCES 465 56. D. 8. Toowms et al., in Homogeneous Reactor Project Quarterly Progress Re- port for Period Ending Jan. 31, 1957, USAEC Report ORNL-2272, Oak Ridge National Laboratory, Apr. 22, 1957. (p. 35)