ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN NUCLEAR REACTOR AND CLOSED-CYCLE GAS TURBINE POWER PRODUCTION A PROPOSAL FOR A 50 MW NUCLEAR REACTOR DEVELOPMENT PROJECT By H. A. Ohlgren June 15, 1955

TABLE OF CONTENTS Page 1.0 ABSTRACT 3 2.0 INTRODUCTION 4 3.0 DESCRIPTION OF THE NUCLEAR POWER GENERATION AND THE CLOSED - CYCLE GAS TURBINE 6 3.1 Description of the Nuclear Reactor 6 3.2 Description of Closed-Cycle Gas Turbines 10 4.0 SCOPE AND DIVISION OF WORK 12 5.0 PRELIMINARY BUDGET COST FIGURES 13 APPENDIX I - DESIGN STUDY 60 MW CLOSED —CYCLE GAS TURBINE 14 NUCLEAR POWER PLANT 2

1.0 ABSTRACT One of the most promising technological developments for production of power from a nuclear reactor is a high-temperature reactor operating in conjunction with a closed cycle-gas turbine. This report presents a proposal for designing, constructing, and operating a nuclear power producer which is capable of generating 50 megawatts of reactor heat power and 25,000 kilowatts of electrical power. The reactor is a modification of the liquid metal fissioning reactor developed by Brookhaven. The closed-cycle gas turbine is basically one developed by Escher Wyss, Zurich, Switzerland, and introduced in the United States by the American Turbine Corporation. It is believed that a reactor core coupled with a closed-cycle gas turbine offers great promise for basic research, development, power production demonstration, and competitive economics. The proposed reactor turbine combination is capable of demonstrating efficiencies in excess of 40 percent and power costs of 7 mills/kwh. 3

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2.0 INTRODUCTION It is proposed to design., erect, and operate a 50 megawatt nuclear reactor in conjunction with a closed-cycle gas turbine for the production of.electrical power. This endeavor is suggested as a joint activity between the University of Michigan under the general supervision of its Engineering Research Institute., and organizations and agencies who will provide the initial funds and operating costs for a long-range continuous development program. The development project would have included'in its physical equipment and facilities a closed-cQycle gas turbine installation, necessary buildings and auxiliary facilities for fue'ls make-up, water processing equipment., start-up power, instrument air supply, and laboratories for routine radiochemical analysis. This proposal considers that the facility will be located within reasonable proximity to the University of Michigan. Such location not only allows maximum use of the facility for education, and a wide variety of research,, but also has the great advantage of accessibility'-to -scores of faculty., staff, and graduate students representing skills in a wide variety of scientific and engineering fields. Such location also makes it possible to supplem ent new physical research equipment with the use of a variety of facilities in many of the now-existing laboratories of the University of Michigan. In addition to the technical and scientific investigations., it is expected.-that this facility would provide major means by which business management problems, legal problems, and social problems can be coordinated with technological progress. From the engineering studies which have been conducted to date., it is believed possible to engineer and construct a development reactor facility with a closed-cycle gas turbine for an initial cost between $6,000,000 and $7,,000,000. Estimates of costs for operating the facility indicate expenditures of about $2.,000.,000 per year for a period of between five to ten years. Thus, the commitment to this development project in the form of capital funds will range between $15,,000,,000 and $25,,000,000. In this proposal there is describe d the general plan for the nuclear power generating plant and its attendant facilities., It is proposed to construct a reactor power plant with a closed-cycle gas turbine which has the characteristics shown in Table I. TABLE I Reactor Power 50 megawatts (maximum) Reactor Fuel U-235 dissolved in bismuth metal Reactor Pressure Atmospheric Reactor Temperature Range 6500C to llOO0C Gas for Turbine Helium Cycle -. -,4. Temperature 90/11I000

The general flow plan of the reactor cycle integrated. with a closed.-cycle gas turbine power gererator is shown in Figure I. The core of the reactor power unit is fueled with uranium-235. This uranium-235 is dissolved in bismuth metal and as a homogeneous metal solution is cir~culated through a critical geometry. It is believed. that by resolving the problems involved. in prod~uction of heat power from the core of such a reactor possibilities exist in ex-tending the work to evaluate converter reactors., breeder reactors, as well as packaged. power generating -units. Possible field~s of application consist of mobile propulsion, stationary power generation, closed-cycle gas turbine propulsion of merchant ships, and remotely located packaged. power generating units. In addition the peacetime uses of radiochemicals and nuclear interactions in fields of chemical reactions, petroleum, biological work, medicine', foods,, metallurgy., etc., can be investigated. at a wide range of levels of temperature and. radiation activities.

3.0 DESCRIPTION OF THE NUCLEAR POWER GENERATION AN~D THE CLOSED CYCLE GAS TURBINE The Babcock and. Wilcox Company, coordinated. with the efforts of many industrial organizations and. the Brookhaven National Laboratory, has indicated. that a liquid. metal fissioning reactor requires a working experiment before many of the questions for using such a reactor for power generation can be finally determined. The optimum experiment i's defined as one which provides useful design data on mass transfer, heat transfer, effects of radiation poisoning, handling of fission products, reactor specific power, critical mass and geometry, control and. safety, as well as proving itself to.be a competi'tive nuclear reactor for power generation. The employment of a closed-cycle gas turbine in which conventional fuel is used for providing energy to gases has been under development by Escher Wyss Ltd., Zurich,, Switzerland. In this country., serious consideration to closed-cycle turbines for power generation is being given by the American Turbine Corporation and Westinghouse Electric Corporation. Due to recent developments in nuclear reactors', heat transfer equipment, turbomachinery, and materials engineering', the combination of nuclear power with a closedcycle gas turbine appears within reach of practicality and'indicates tremendous improvement over any-other program for nuclear power. 3.1 Description.of the Nuclear Reactor The nuclear reactor which is proposed for this development project is the core portion of a stationary power plant. It is believed. that'if the problems for the core-can be resolved mn apIctosfth core as such as well as the core integrated with added reactor designs can cover a wide range of applications. The reactor core is a liquid metal homogeneous system. The system consists of solutions of uranium in molten bismuth circulating through a critical geometry. The research and development for this type of reactor has been and will continue to be done at Brookhaven National Laboratory. Recently, a group of industrial study teams have cooperated. with Brookhaven National Laboratory to achieve a practical concept of the reactor system. The reactor system consists of a critical mas-s and geometry, of a solution of bismuth and. uranium, with attendant heat exchangers for transferring the heat from the circulating uranilum-bismuth to a gas such as helium for operation of the closed-cycle gas turbine. A circulating pump is provided to maintain proper velocities of the bismuth-uranium solution through the critical geometry. From the experimental work done, it appears that the reactor can operate over a range from 6000C to 11000C depending upon desired power output. In general,, the higher the temperature of operation the more efficient will be the power pz'oduction.

A portion of the circulating uranium-bismuth solution i's by-passed through a degasser device which permits removal of a large portion of the gaseous fission product poisons. As nuclear fuel is consumed, from time to time it will be necessary to add known quantities of fissionable material to the reactor core. Control of the reactor i s essentially automatic since concentration of uranium in the bismuth is known at all times. From preliminary design calculations made for this reactor, Table II indicates a summary of the preliminary design data. (Table II on next page). The proposed reactor offers great advantages and improvements over other proposed power reactors. Some of the advantages which can be achieved are: 3.1.1 The reactor is small and compact with high specific power. 3.1.2 The system is self-regulating and-controlling., thus eliminating control rods in the core. 3.1.3 Temperature levels ra.nging from 4500C to lJ1000C might be achieved, thus producing available energy-at levels that give substantial improvements in overall cycle and power efficiency. 3.1.14 The heat transfer rates for bismuth to helium are high, thus requiring small heat exchange surfaces to transfer energy to the closed cycle gas loop. 3.1.5 The materials of construction for the reactor are in advanced stages of development., thus assuring that a development reactor of this size can be firmed within specified limits. 3.1.6 The critical configurations are dimensionally less for the reactor core', thus requiring a minimum of shielding. 3.1.7 The development project, as a power producling reactor, offers excellent promise for packaged power plants and mobile power propulsion. The general objectives of building and operating a reactor at the designated power level are to develop and improve the following areas:3.1.8 The demonstration of safe handling of bismuth-urani'um solutions over a wide range of temperatures. 3.1.9 The development of a proven system for degassing fission product poisons. 3.1.10 The demonstration of long-term continuous power production wi~thout removing reactor fuels from the circulating loop.

TABLE I I SUMMARY OF PRELIMINARY DESIGN DATA Power- 50 MW heat = 47,400 BTU/sec. Net Electrical 20 MW Reactor Size 2' =p 6.3 ft.3 Piping 10" cp = 6.3 ft.3 Heat Exchanger 22 ft.3(3o% for Bi) = 7.0 ft.3 Total System Volume 19.6 ft.3 Critical Mass 3.28 Kg. - U-235 Total uranium 10 Kg. Total bismuth 11,9000# Bismuth flow rate 2820 #/sec. or 18410 gpm AT Bismuth hoo0 F. Burn-up 50 g./clay Sp.,Power - Core 15,200 KWI/Kg. Sp. Power - System 5~,000 KW/Kg. Min Temperature for solution 41200 C. Max. Temperature for solution Limited. by materials of construction or boiling point of bismuth 14O00 C. Cp Neutron flux =-6 x 1014 neutrons/cm2 /sec. Coolant Helium at 1000 psi Helium f low 265,000 #/hr. AT - 514.10 F. Helium temperature in 8860 F. Helium temperature out 14oo0 F. Helium specif ic heat 1.25 BTU`/# 20F Helium film coefficient at AP 1.2 1200 F./h./t P ~ ~ ~.% BUh.f./ Approximate Size of Heat Exchanger 2650 tubes 3/8"1 CP x 10' x 1/411 ID 100 # heliumn/hr./tube Tube Bundle Cross-Sectilon 3' x 18" Helium insid~e-bismuth shell sid~e Temperatures These temperatures Bismuth Core Inlet 5860 C - 11820 F.) can be reduced. by Bismuth Core Outlet 7860 C. =141500 F.) sacrificing some Helium in 8860 F. )thermal ef fi1ciency. Helium out 111000 F.) The figures used. ind~icate a thermal efficiency of 4o1.%.

3.1.11 The d~evelopment of full-scale pumping and. the fluid. transfer system. 3.1.12 The improvement of method~s of heat transfer and. materials of construction. 3.1.13 The d~emonstration of sustained. power levels und~er safe and. stable cond~itions.3.1.14 The evaluation of the circulating fuel and. stud~y method~s of continuous sid~e-stream removal of fission prod~ucts and. rad~iochemicals. 3.1.15 The evaluation of the performance of molten bismuth solutions.over wid~e ranges of temperature d~rops, isotopic build~ups,, and. fluid. mechanics and. transfer problems. 3.1.16 The d~emonstration of the economics of a highly efficient power plant. Xt is believed. that if these general objectives can be achieved., results of such d~evelopment may accomplish the following: 3.1.17 The packaged. power plant, which'is particularly good. from the stand~point of requiring small amounts of cooling water. 3.1.18 Merchant ship and. s~ea.going vessel propulsion, which appears would. require the smallest volume in shield~ing of any of the presently proposed. reactors and. would. eliminate bulky cond~ensers and. water treatment required. for steamn turbines. 3.1.19 Breed~er reactors, when surround~ing the core writh a suitable blanket,, allow the d~emonstration of breed~ing gains sufficient to sustain a fuels economy within the reactor system as well as prod~ucing fuels for use in other types of fissioning reactors. The inventory of fissionable fuels over long period~s of time is sustained. at a minimum. 3.1.20 The d~evelopment reactor, as a test reactor, appears to be the cheapest way of obtaining a high neutron flux for testing purposes., provid~es a source of rad~iation for many field~s of end~eavor as well as provid~ing field~s of research in neutron physics., nuclear chemistry, fluid. mechanics, materials engineering, rad~iation d~amage, instrumentation and. control. Thus, such a d~evelopment reactor'is a necessary implement and. ad~ditive to the Phoenix Memorial Project,, sponsored. research in ind~ustrial nuclear power, and. pure acad~emic research.

3.2 Description of Closed-Cycle Gas Turbines The American Turbine Corporation has conducted considerable development for applications of closed-cycle gas turbines in the United States. The adaption of a closed-cycle gas turbine to a nuclear reactor makes possible the use of temperatures of nuclear fission at high levels, resulting in power production at high efficiencies. The use of an inert gas as a power plant working fluidexchanging heat with a molten metal such as a bismuth-uranium solutioneliminates the problemof a remotely operated turbine. The closed-cycle gas turbine system consists of a dual stage turbine unit with necessary intercoolers. The plan in obtaining such a closedcycle turbine would be to work closely with the engineering designs being achieved by Westinghouse Electric Corporation, the American Turbine Corporation, as well as the developmental activities of Escher Wyss Ltd., of Zurich, Switzerland. Present considerations have selected helium as the working fluid. Other possibilities are air, argon, carbon dioxide. From many viewpoints, however, helium offers specific advantages in heat transfer, does not become radioactive, and permits direct operation and maintenance of the turbine equipment. The closed gas loop consists of flowing the gas through a specially designed heat exchanger in which it exchanges heat with the molten bismuth-uranium solution. Thus, the gas flowing through this heat exchanger is raised to a temperature as high as 15OF and a pressure of about 1000 psig. The gas exhausting from this heat exchanger flows to the high pressure turbine stage which effectively drives the compressor which recompresses the gas for return to the reactor heat exchanger. The helium exhausts from the high pressure turbine after partial expansion and flows to a low pressure turbine. The turbine drives a 3600 RPM power generator. The gas exhausted from the low pressure turbine is cooled'in a recuperator exchanger and intercooler and flows to the first stage compressor driven by the high pressure turbine. The partially compressed gas flows through a second interchanger'into.the final compressor which is driven also by the high pressure turbine. This compressor returns the gas in a closed loop at about 880 0F to the reactor heat exchanger. For a more detailed explanation of this closed-cycle gas turbine, please refer to the report "Design Study 60 MW Closed-Cycle Gas Turbine Nuclear Power Plat," which is attached to this proposal as an appendix. These dat, prepared by the American Turbine Corporation., indicate that efficiencies between 4i0 and 4~5 percent might be achieved by combining a reactor of this type with a closed-cycle turbine. It would be expected that the closed-cycle turbine and the auxiliary generating and heat exchange equipment would be provided to the project by one of the licensors of the American Turbine Corporation'.

The general development problems in this field are numerous. If helium gas is selected as the working fluid for the closed..cycle gas turbine, consideration of investigations of helium as a diffusi~ng gas into metal become a relative ly important problem. The design and development of mechanical seals to. contain the working f luild, the optimization of heat transfer surface., and the general characteristics of an optimum closed cycle gas are needed before assured performance for power generation can be achieved. In the event other fluids such as carbon dioxide, air, or argon are selected, measurements of degrees of radiation and amounts of shield for safe operation would be required. It is believed that through the operation of a closed cycle gas turbine in conjunction with the nuclear reactor, measured improvements in-gas turbine design for this specific purpose can be achieved and many advantages demonstrated over the nominal steamn cycle turbine presently being considered.

4.O SCOPE ADDl DIVISION OF WORK This proposal contemplates the engineering, construction, and. opera tion of a nuclear power plant in conjunction with a closed-cycle turbine'und~er the general supervision of the University of Michigan. The fund~s necessary to erect and. construct this facility as well as the costs involved. in d~evelopment programs and. operations research would. be provid~ed. to the University of M4ichigan by others. Professor H. A. Ohlgren will be the Project Supervisor. He has had. many years of experience'in the field~s of nuclear reactors,~ nuclear pby~ics, rad~iochemicals., shield~ing problems, and. fuels recovery. Assisting Professor Ohlgren will be a key group of faculty ad~visors in conjunction with full-~ time staff people for the operation of this specific d~evelopment program. Grad~uate and. und~ergrad~uate stud~ents will be employed. on a part-time basis so that effectively between 10 to 15 technical man years will be consumed. in the operation of this d~evelopmental facility.

.*0 PRELIMINARY BUDGET COST FIGURES The work and investigations conducted to date on this type of system are not adequate to predict accurately the total investment required. One of the first steps in this, type of a program would be to conduct engineering studies in sufficient detail to permit establishment of a more firm budget.' Order of magnitude estimates, however, have been made. In evaluating costs of a reactor core, heat exchange equipment., auxiliary systems, instruments, buildings., gas turbines, generation and switch gear equipment,, the estimates which have been completed to date indicate a magnitude between $6.,ooooo an 700000 as the amount needed to engineer and construct this type of a development project. The operating costs including allowances for development and improvement are anticipated to approach $2,000,,000 per year. It is believed that a program for a period of between 5 to 10 years is needed to demonstrate adequately this principle of utilizing atomic power for efficient power production.

APPENDIX I

Design Study

ATC -54-12 Design Study 60 MW Closed Cycle Gas Turbine Nuclear Power Plant TABLE OF CONTENTS Page 1 -Summary......1 04. - I D000a001 2 -Introduction............... 2 3 -Power Plant Cycle............. 4 4- Design Assumptions.............11 5 -Turbomachinery...............14 6 -Heat Exchange Apparatus......*9.. 23 7 -General Arrangement............26 8- Control System........ D*- ae&4 PD 29 9 -Xenon Removal....e*9o**9o.***32 Appendix I - Cycle Analysis.3

ATO -54 -12 Design Study 60 MW Closed Cycle Gas Turbine Nuclear Power Plant 1.0 Summary This report covers the design of the power generating equipment of a closed cycle gas turbine nuclear power plant having the following characteristics: Output at generator terminals 60 MW Cycle pressure 1000 psia Cycle temperature 90/14000F Reactor output 148.5 MW Heat rate 8460 BTUJ/KW Hr. Helium flow rate 12.5 Lbs/KW Hr. Reactor design is not covered in this report, it would, however, be a graphite moderated enriched fuel reactor designed for conversion or breeding and its requirements were taken into account in the selection of the power plant cycle and plant operating conditions as summarized above.

- 2 - ATC-54I-12 2.0 Introduction The closed cycle gas turbine power plant using fossil fuel fired heaters has been under intensive development by the firm of Escher Wyss Ltd. of Zurich, Switzerland and their licensees for the past fifteen years. The idea of a power plant using a gas as a working fluid is not new but its development as a practical power plant has only been possible during recent years due to current developments in turbomachinery, heat transfer apparatus and high temperature materials. Adaption of this power plant cycle to a nuclear reactor makes possible the use of the temperature resulting from nuclear fission at a high level, resulting in a power plant of high efficiency. Use of an inert gas as a power plant working fluid and reactor coolant removes the problems of chemical attack on power plant components in the transport of heat from the reactor to the point of conversion into mechanical energy and since there is no phase change in the reactor coolant there is no necessity of providing for secondary containment of the reactor in event of gross temperature excursions. Heat distribution in a closed cycle gas turbine power plant is illustrated in Figure 1 which shows the gas flow path super-imposed on a compressor/turbine assembly.The gaseous working fluid is compressed in a compressor, heated

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- 3 - ATC-54-12 bine, giving up energy in expansion to drive the compressor and produce useful power. The energy input required is reduced, or the efficiency of the plant is increased, by transfer of heat from the gas after expansion to the gas after compression in a recuperator. Unavailable energy from the process is rejected in a precooler, thereby restoring the gas to its initial temperature before compression. The system is closed and the process is one of continuous flow. Load changes are effected by varying the pressure level of the system, bypassing the compressor, or both. Efficiency is substantially constant over a wide range of loads as the temperature differences remain constant as do gas velocities and peripheral speeds of the turbomachinery. Efficiency is affected by changes in sink temperature but out120 - -T put can be held constant TEMEN"' i I00 by changes in system pres- j - / -- - sure level as shown in,o ~,, I. Figure 2. L0 40 - 0 20 40 60 60 I00 120 Figure 2 Part Load Efficiency

- 4 - ATC-54-12 3.0 Power Plant Cycle This power plant has been designed using helium as the working fluid and reactor coolant, due to its zero neutron capture cross section and its good heat transfer characteristics. Major equipment items are the machinery set, heat transfer apparatus and control system. The machinery set consists of a two-stage axial flow compressor set with intercooling between stages driven at constant speed by a high pressure turbine. Helium leaves the high pressure turbine after partial expansion and flows directly to a low pressure turbine directly connected to a 3600 RPM generator of 60 MW output. Heat transfer apparatus is of the extended surface type, plate fin, or finned tube, depending upon the application. The control system consists of a master regulator to maintain constant system pressure with a low pressure receiver-high pressure accumulator system and transfer pump. A flow diagram of the complete power plant cycle, including control and helium purification system is shown in Figure 3. Table I lists the state points at the inlet to all pieces of machinery and heat transfer apparatus as well as a heat balance of the power plant. The basic principles of design of a closed cycle power plant require the extensive use of heat transfer surface for the recuperation of heat available in the working fluid after

H.P.RECEIVER' TRANSFER L.P.ACCUMULATOR COMPRESSOR MAKE -UP SUPPLY CONTROL I COMPRESSOR I BY-PASS VALVE I LOAD POWER TURBINE REACTOR INTERCOOLER BY-PASS VALVE PRECOOLER XENON TRAP RECUPERATOR FIG. 3- FLOW DIAGRAM

TABLE I State Points & Heat Balance W = 790,000#/Hr = 219#/sec. Point at inlet T(~R) AT Rc-Re E(%) P/P1 P(Psia) P Q(CFS) +MW -MW 1 LP Compressor 550 120 1.55 1.000 426.289 760 34.7 2 Intercooler 670 120 0.75 1.550 661.368 596 34.7 3 HP Compressor 550 120 1.55 1.538 656.445 494 34.7 4 HP Recuperator 670 676 1.50 2.382 1015.565 388 196 5 Reactor 1346 514 1.50 2.345 1000.279 787 148.5 6 HP Turbine 1860 240 1.48 2.310 985.1975 1110 69.4 7 LP Turbine 1620 218 1.51 1.56 665.153 1435 63 8 LP Recuperator 1402 676 2.25 1.033 440.1175 1870 196 9 Precooler 726 176 1.00 1.010 430.231 950 50.8 Rejected to oil 1.5 Electrical Losses 1.5 Net Output 60

- 5 - ATC-54-12 expansion. The high system pressure at which a closed cycle gas turbine power plant operates, coupled with the fact that the working fluid is uncontaminated by products of combustion, makes attainment of this objective relatively easy to accomplish through the use of heat transfer surface having flow passages of small hydraulic diameter and/or the use of extended or interrupted surface. All fossil fuel fired closed cycle power plants built to date use air as the.working fluid. The use of helium with its different gas properties makes necessary the reevaluation of the generally accepted cycles as used with air. Compared to air, helium exhibits a considerable improvement in heat transfer properties, the film coefficient being about 180% higher under the same conditions of pressure level, pressure drop and passage geometry. This is illustrated in Figure 4, being a plot of film coefficient at various system pressure levels at constant relative pressure drops (AP/P) for helium and nitrogen flowing in a one inch diameter tube having an l/d of 100. Since air is composed of 75% nitrogen there is no noticeable difference in the heat transfer properties of air or nitrogen. This improvement in helium film coefficient over that of air results in heat transfer equipment approximately 55% of the size required for air, or where the equipment is the same

100 o - - 80 IaJ w 60 a~~~~~~~~~~~~, z or 7 0 40 2 0o w 10 (020 100 200 400 600 800S 1000 2000 4000 FILM COEFFICIENT BTU/HR/FT/OF VARIATION OF FILM COEFFICIENT WITH PRESSURE FOR CONSTANT AP/P FLOW IN TUBE 100" LONG AT 1000 OF NITROGEN HELUM FIG.4.

- 6 - ATC-54-12 size, an appreciable increase in the quantity of heat that can be transferred, the exact amount depending upon the effectiveness of the surface with air. For example, if the recuperator in the air cycle machine has an effectiveness of 80%, the same surface will have an effectiveness of 86% in a helium cycle. If the effectiveness in an air cycle machine is 90%, which is more of the order used in a closed cycle power plant, the same surface will have an effectiveness of 95% in a helium cycle machine. On the other hand, the high specific heat of helium (1.25 BTU/#) makes the design of the turbomachinery difficult, the number of stages required for the same temperature rise being roughly proportional to the specific heat, or compared to air, in the approximate ratio of 5:1 (1.25:.24). However, a cycle analysis will show that the compressor temperature ratio required for maximum cycle efficiency decreases with increasing recuperator effectiveness and this fact is made use of in the design of a closed cycle plant using helium as a working fluid, trading static heat transfer surface for stages of turbomachinery. In order for any closed cycle nuclear power plant to be attractive economically it is necessary that it be a high temperature machine, i.e. operate at cycle temperatures in excess of approximately 12000F. All experience to date with closed cycle power plants has been at cycle temperature from 1250 to 1300~F as dictated by limiting

ATC -54-12 -7 - tube wall temperature in a fired air heater. In a nuclear plant this restriction is removed and turbine inlet temperature is only limited, within reason, by reactor outlet temperature. However, our present experience would limit such temperature to about 15000F for a power plant of conservative design. In establishing a cycle for a helium plant, the value of 1300, 1350 and 14000F cycle temperature was assessed against a 13000 cycle temperature with 100 and 2000 reheat. Referring to Figure 5, there are three ways in which reheat can be applied in such a plant. The first is the use of dual reactors, each having a single flow circuit. These reactors would have the same outlet temperature but slightly different inlet temperatures. Their outputs would be roughly of the same order. An alternate would be the use of a single reactor with a DUAL REACTOR SINGLE FLOW dual flow circuit. On first inspection it would seem that it would be desirable to use DUAL F LOW an annular core taking the heat required for compressor drive from one half and the heat for power from the other SINGLE REACTOR SINGLE FLOW half. However, such a scheme Figure 5. Reheat Systems

- 8 - ATC-54-12 would appear to be unduly complicated from the standpoint of ducting required. A simple solution to the problem, from the standpoint of the reactor, is by the use of a single reactor with a single flow and a reheat exchanger. In such a scheme the reactor outlet temperature is in excess of the first turbine temperature, the working fluid temperature being reduced by a reheat exchanger as shown. Cycle studies are identified by the initial turbine inlet temperature and the amount of heat used in the second or power turbine. For example, a 13000 cycle with 1000 reheat would be a cycle wherein the initial turbine temperature was 1300~F and its discharge temperature raised 1000F in a reheat exchanger. Thus the reactor outlet temperature would be 1300 + 100 or 14000F. A comparison of cycle efficiencies of reheat and nonreheat plants is given in Figure 6 using reasonable polytropic efficiencies for the turbomachinery and taking pressure losses in the two types of systems into account. It will be seen that there is little difference in efficiency between a 1400~ non-reheat and a 13000/2000 reheat plant. Since the latter shows its optimum efficiency at a 3:1 pressure ratio compared to a 2.5:1 for the non-reheat plant and also involves the use of a reheat exchanger it is believed that the problems involved in designing a 14000 non-reheat plant are less than those of a 13000/200~ reheat plant. Therefore, a 1400~ non-reheat was chosen for further study.

-9 - ATC-54-12 4 4 C44OO+20E ] 42 - - |2-STAGES 1 ~00.+200' 1 INTE RCOOLING7 / 13000O+2O000OR 1600~ — I00 Figure 6. Cycle Efficiencies 36 36 341 1,,34 3I I 2.0 2.5 R C 3.0 2.0 2.5 Re:5.0 REHEAT 81 NON-REHEAT ONE & TWO STAGE INTERCOOLING iigure 6. Cycle Eff ic ienc ie but at the same time addiAppreciable gains in efficiency (2.4:1 vs. 2.8:1). Since evein a closed cycle power plant are effected by moderate intercooling. The value of single vs. two stage intercooling was assessed and the results are presented in Figure 6. It will be seen that the use of two stage intercooling results in but 1/2% increase in cycle efficiency (42 to 42.5%) but at the same time additional compression ratio is required to achieve this optimum efficiency (2.4.1 vs. 2.8'1). Since even a simple non-intercooled helium compressor will present enough problems at this stage in development, and 42o cycle efficiency will result in substantially 40% efficiency at the generator

- 10 - terminals, we chose to follow the design of a plant with single intercooling. The design conditions selected for the power plant cycle are as follows: Pressure ratio 2.4:1 Pressure losses 7.0% Expansion ratio 2.23:1 Compressor inlet temperature 90~F Turbine inlet temperature 1400~F Recuperator effectiveness 93% Mechanical & electrical losses 5% Working fluid flow 790,000 Lbs/Hr.

- 11 - ATC-54-12 4.0 Design Assumption The current state of the art of design of turbomachinery of high stage loadings indicates that it is possible to obtain polytropic stage efficiencies of 89% in compression and 88% in expansion. While stage efficiencies of turbines would normally be higher than compressors for the same work per stage, in an effort to reduce the numiber of stages in the turbine to an acceptable level the work output per stage is about three times that of the compressor stage. This accounts for the lower turbine stage efficiency. Figure 7 is a plot of adiabatic turbine and compressor efficiency vs. pressure ratio and are the values used in the final cycle analysis. Com9? pression work is equally.90 a IN EXPANSION divided between the high and low pressure compressor and each has a pressure ratio of.88 1.55:1 resulting in an overall pressure ratio of 2.4:1. Pressure losses in the plant have been assessed at 7%, resulting in an overall.8e4 4 I 1.0 2.0 3.0 expansion ratio of 2.4x(1-.07) RC OR Re Figure 7 - Tiurbomachinery = 2.23:1. Pressure losses eff'iciencies. are distributed as follows:

- 12 - ATC-54-12 Intercooler........0.75% HP Recuperator.....1.50% Reactor...........1.50% LP Recuperator.....2.25% Precooler..........1.00% While these pressure losses may appear to be optimistic, it is believed they can be attained with careful design and without excessively large heat transfer surface. R6ferred to an air cycle plant this is the equivalent of a total overall pressure loss of 11%, assigning 5.5% total pressure loss to the reactor which would be the equivalent pressure loss in a fired heater. Compressor inlet air temperature is assumed at 90~F based on 75~F cooling water which can be obtained in most locations where water supply is critical. If such a plant were located where there was an abundant supply of water at say 55 to 60~F, the efficiency of the plant would increase about 2%. A regenerator effectiveness of 93% has been selected for design since a plant of this type would be a base load machine. This is slightly less than the maximum that has been used in closed cycle plants (94% in the experimental Escher Wyss plant of 2000 KW) and is believed to be reasonable for a plant of this type. Helium characteristics are taken from a critical review of available information made by General Electric and are as follows:

- 13 - ATC-54-12 Cp = 1.25 BTU/# y = 1.658 R = 386.2 + =.398 The variation of thermal conductivity, viscosity and Prandtl number with temperature are taken from data of the Oak Ridge National Laboratory and are presented in Figure 8.

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- 14 - ATC-54-12 5.0 Turbomachinery 5.1 Introduction Modern fluid mechanics and gas dynamics (upon which turbomachinery design is based) are founded upon the concepts of perfect fluid, potential flow and real fluid corrections to this flow. Both the theoretical and experimental developments of the science are expressed in terms of kinematic non-dimensional parameters and non-dimensional groups such as Reynolds Number and Mach Number. Therefore, if the effects of these non-dimensional variables are properly applied, much of the existing work on turbomachinery for air can be used for the design of units for another gas, such as helium. The use of helium working fluid results in two major changes, one advantageous and one disadvantageous. The fact that the sonic velocity in helium is about three times that in air results in practical release from Mach number (compressibility) restrictions. Therefore, tip speeds are limited only by structural considerations. On the debit side, the high Cp of helium (about 1.25 against.24 for air) results in a temperature rise per stage of only one fifth that of air for the same blading diagram and enthalpy input per stage (Cp AT). In spite of the low AT per stage, the required number of stages as compared to present day air practice is low. This is because of the low temperature ratios required for

- 15 - ATC-54-12 the nuclear helium plant. Thus, the resulting mechanical design of a nuclear helium machine bears a close resemblance to its air counterpart. In order to give the proposed 60 MW machine performance a strong foundation in reality, the blading and proportions of the set have been closely patterned on existing compressors and turbines. The units chosen were selected as good examples of present day practice for machines now running in. industrial service. The compressor and turbine were designed for and tested in air, with air Mach Number limitations an important factor. The helium design is so closely patterned on the air machines that no attempt was made to take advantage of the release from Mach Number limitations. Hence, there should be a slight unaccounted for performance bonus, which follows the conservative design pattern adopted for this unit with the idea of providing as nearly guaranteed performance as is possible in the preliminary design of an unconventional machine. The tip speed, solidity ratios and blade diagrams are closely patterned after those of the reference machines, often being identical. Hub-tip ratios are similar to those of the models (except where some modifications are needed to match the speed and volume flow of the helium machine). When considering helium as a real frictional fluid

- 16 - ATC-54-12 capable of separation from boundary walls in an adverse pressure gradient, the question of being able to maintain the same blade velocity diagram without flow separation arises. The answer is that for a given velocity diagram, the ability to resist separation is directly proportional to a fractional power of Reynolds Number (Rel/n). Now Re = CL/P, where L is a significant length, V the viscosity and C, the axial velocity through the machine. Now if we assume C is the same for air and helium machines, then e) helium > +i. — air if we expect to utilize the same velocity diagram. Since V takes values in this helium machine roughly 1/3 of that for the usual air machine, then the characteristic length, say blade chord, must be at least 1/3 that of a comparable air plant. This condition is greatly exceeded with the result that this 60 MW plant operates with Reynolds Number higher than the test machines and therefore can be expected to equal or exceed the test efficiency, if all other factors are equal. 5.2 Compressors Both the high and low pressure compressors are discussed at the same time since each has the same overall pressure ratio and blading design. The only difference is the increase in hub-tip diameter ratio and decrease in

- 17 - ATC-54-12 length of the high pressure unit due to the greater density and consequent reduced volume flow in this machine. The blading is the standard free-vortex, axial stator inlet type pioneered by the Escher Wyss AG of Zurich, Switzerland. This type of blading is conservative in concept and application but provides outstandingly high efficiencies and numerous constructional advantages for the many gas turbine and industrial blower installations in service. This blading is especially attractive for a helium machine since the Mach Number restrictions, which provide the limiting conditions for pressure rise coefficient in air, do not apply in the less compressible helium. Both compressor units are based directly upon test data, in air, covered in i. Escher Wyss Report No. TK-45-046, pertinent.9so data being presented in Figure 9. It should be.80 emphasized that this test work represents conserva-.70 _, tive but efficient practice which resulted from.60 U2..6T0 2 many years research and' ~AT FROM TESTS WITH AIR industrial application.50 I, I, 0.4 0.5 0.6 1 0.7 0.8 with this type of machine i'igure 9. Compressor Stage Characteristics

- 18 ATC>54V12 and which has been further proven in service in the years since 1945. Characteristic data for the compressors is presented in Table II and blade velocity diagrams in Figure 10. A typical eight stage compressor rotor having this type of' blading is illustrated in Figure'11. W2 = 1149 C58 W = 868 W Cz =Co= 446 A-C' 317 /- -317 Um= 743 MEAN RADIUS VALUES Figure 10. Compressor veloci ty diagram Fi gure 11. Ph ot ograph of typi1cal comlpressor rotor

ATC-54-12 TABLE II Compressor Data Rotational Speed, N............ 7400 RPM Tip Speed (first stage, max. value) Ut.. 853 ft/sec Mean radius tangential blade velocity, Um.. 743 ft/sec Axial velocity, Ca........................ 446 ft/sec Pressure ratio LP unit..........1.55 Pressure ratio HP unit...............1.55 Overall pressure ratio..................... 2.40 Number of stages, HP unit......................14 Number of stages, LP unit......14 Stage pressure ratio.......................1.0318 ATad per stage.............................7.540F, PS tage 2 &, C m, tPStage 2 Cum.865 m/2 U2 Um Ca.m = Um.60 Adiabatic efficiency assumed for design...... 88% Polytropic (stage) efficiency assumed for design............................ 89% Polytropic (stage) efficiency obtained on test by Escher Wyss with same blading at same operating point................. 91% Hub-tip ratio, LP unit, stage 1...........74 stage 14.........79 Hub-tip ratio, HP unit, stage 1...........82 stage 14 o..,.,....86

TABLE II (cont) ATC-54-12 Compressor Dimensions Rotor tip diameter HP, stage................. 26.4" stage 14.............. 25.7" Rotor tip diameter LP, stage 1................ 25.2" stage 14............ 24.7" Length of LP compressor-rotor.................. 48.7" Length of HP compressor-rotor................ 31.2" Spacing between rotors........................ 24.0" Overall Dimensions, 1st stage LP to last stage HP...................... 103.9"

- 19 - ATC-54-12 The compressors were designed on the basis of constant mean radius for all stages and for the same mean radius velocity diagram at each stage. The radial velocity variations follow free-vortex principles. All non-dimensional coefficients are based upon mean radius conditions and mean radius tangential velocity. Rotor construction is of the multiple disc type with rotor torsional and bending loads carried near the periphery of the discs. The compressors and high pressure compressordriving turbine are housed in a horizontally split case. 5.3 High Pressure Turbine The high pressure turbine supplies the power for operation of the compressors. It is mounted with them as a single shaft, three bearing, self-running turbo-compressor set. No useful output torque comes from this turbine..92 The turbine blading is a hl high efficiency type,.90 also based on Escher.88 Wyss practice, and is a type successfully used T TOTAL HEAD EFFICIENCY in all closed cycle gas turbine power plants AK TEST BLADING.2 TWO STAGES built by this firm to I I.5 6.7.C.8.9 1.0 date. A U/Co diagram of UTI 8/ 9 1 the blading performance Figure 12. Turbine stage characteristics is given in Figure 12.

- 20 - ATC-54-12 Umrn 1050 ] CI =1282 W =1095 C,=480 \ =500 C2= 484 _Cu = 1122 MEAN RADIUS VALUES Figure 13. HP turbine velocity diagram FW~IgueN~ Potgrphoftyicl urin

- 21 - ATC-54-12 Characteristic data for the turbine is presented in Table Ill and blading velocity diagrams in Figure 13. A typical multistage turbine using blading of this type is shown in Figure 14. In this design, multiple disc construction is used for the high pressure turbine. 5.4 Low Pressure Power Turbine The low pressure power turbine is mechanically independent of the compressors and high pressure turbine, and directly coupled to the generator. The power turbine therefore rotates at a constant speed of 3600 RPM and produces the entire useful work output for the plant. The blading is basically the same as that in the HP turbine and derives from the same test data. However, the tip speed is only about 75% that of the HP machine and the gas velocities are reduced proportionally. Characteristic data for the LP turbine is presented in Table IV and blading velocity diagrams in Figure 15. Um = 776 C, =771 W2=791 C0= 300 W1:307 CeC t 304 =l=na 102.4~ A Cu=666 MEAN RADIUS VALUES Figure 15. LP turbine velocity diagram

TABLE III ATC-54-12 High Pressure Turbine Data Rotational Speed, N...........................7400 RPM Maximum blade tip speed (stage 6), Ut. -o.......1186 ft/sec Mean radius tangential blade velocity, Um.......1050 ft/sec Axial velocity, Ca.............................. 480 ft/sec A had.......................................... 56.9 BTU/stage Number of stages........................ 6 Hub-tip ratio, stage 1oo..*.0..*...............82 stage 6.......................77 Number of blades in stage 6........... 112 Centrifugal stress in stage 6 blades (parabolic tapered blades with 3:1 area ratio).................................. 16,860 psi Gas force per blade.................... 73.2 Lbs. Adiabatic efficiency................... 89% Polytropic (stage efficiency)............ 88% High Pressure Turbine Dimensions Rotor tip diameter, stage 1........... 35.7" stage 6......o............ 36.6" Length of rotor............................... 13.3'!

TABLE IV ATC-54-12 Power Turbine Data Rotational Speed, N............................. 3600 RPM Maximum blade tip speed (at stage 14) Ut........ 867 ft/sec Mean radius blade tangential velocity, Um....... 776 ft/sec Axial velocity, Ca.............................. 300 ft/sec Co.............................................. 1057 ft/sec A had*........................................... 22.2 BTU/stage Number of stages.......................o.... 14 Hub-tip ratio, stage 1.........................84 stage 14........79 Number of blades in stage 14.................... 107 Centrifugal stress in stage 14 blades (essentially untapered blades)............... 15,200 psi Gas force per blade............................. 40.4 Lbs. Adiabatic efficiency............................ 89% Polytropic (stage) efficiency............e...... 88% Power Turbine Dimensions Rotor tip diameter, stage................... 53.8" stage 14.......96 0*6 55.2" Length of rotor................... 31.4"

- 22 - ATC-54-12 The power turbine will also be of multiple disc construction. The low values of tip speed and turbine inlet temperature allow comparatively inexpensive material specification. The turbine is a two bearing machine mounted in the same casing with the high pressure compressor turbine set.

- 23 - ATC-54-12 6.0 Heat Exchange Apparatus Efficient heat exchange apparatus plays an important role in the design of a closed cycle power plant. All exchangers operate at an effectiveness of at least 80% and may exceed 90%. This requires that the units be of special design if their dimensions are to be kept within reason. The problem is alleviated somewhat by the fact that the working fluid is clean, thus permitting the use of compact surfaces with flow passages of small hydraulic diameter. Many such surface types have been conceived of in recent years and a large number have been tested at Stanford University in government research. The heat exchange surface proposed for the recuperator of this plant is a welded and brazed plate fin assembly, as manufactured by Griscom-Russell, which has been tested and found to have desirable flow friction and heat transfer properties. Surface characteristics are detailed in Figure 16. The recuperator is composed of two units, each of which contains a rectangular plate fin section 4'2" x 6'..x 17' long. Figure 17 is a drawing showing the recuperator details. Table V lists the recuperator specifications. The LP gas flows directly through the unit in a single pass. The HP gas flows in cross-counterflow, making four passes in its travel through the recuperator. The Griscom-Russell exchanger is essentially a structure comprising a corrugated fin and a flat plate brazed together

.::B i i:...... FIN ATERIAL SA-2O4CAR80N I/2SMOLY.,ii!11ii~ ~..............~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..... FIN THICKNESS.0145 IN. FIN H~~~~~~~~~~~~~~~~~~EIGHT, FFECTIVE.1238 IN.!~ w oil %T, FLAT PLATE.A2 655 IN,4\A.ON_.. AE THICKNE SS.02 2 IN.,'': " FIN PITCHi TREAFNFSEVEER SE IN.TO FLOW.1885 IN. FIN PITCH PARALLEL TO FLOW 5.00 IN. FIN SURFACE / TOTAL SURFACE.7974:25 I N*% EQIAET HYRUICKDNA.S.125 IN..... FIG.~~~~~~~~~~~~~~'% 16 T.CHEA TRA~NSFER.SUFAC

H. p. ouT LLt H.IP.._ _.L..T Ai,-7 1~~F. 17. ARRANGEMENT & DETAILS RECUPERATOR- PRECOOLER

ATC-54-12 TABLE V Recuperator Specifications Helium flow rate, #/sec 214 Duty, BTU/Hr (Total 2 units) 643 x 106 Effectiveness, % 92.3 Service HP LP Temperature in, ~F 210 937 Temperature out, ~F 881 266 %, % 1.5 2.25 Face area/unit, ft2 25.5 25 Number of passes 4 1 Flow length (total), ft 16.8 17 Surface characteristics see Figure 17 Total surface (LP)/unit, ft2 61,500 Prime surface rate, BTU/Hr/ft2 25,800 Ft2 prime surface /KW 0.415

- 24 - ATC-54-12 with a special nickel brazing compound. The corrugated fin material is contained in flattened tubes which are formed by bending sheet metal to the desired shape and heliarc welding the seam at the middle of the circular edge of the tube. After this welding is done, the corrugations are slipped into the tube and corrugations are placed across the tube on the outside. The tubes are then heliarc welded to the specially formed sheets. When the whole structure is assembled, it is coated with brazing compound and brazed in a reducing atmosphere. The brazing compound gives an impervious coating of nickel alloy on all surfaces and adds considerably to the high temperature oxidation resistance of the unit. Design of the recuperator is based on test work performed by the Griscom-Russell Co. Their test work includes studies of the low temperature performance of various fin geometries over a range of Reynolds Numbers; studies of the physical properties of the brazed joint including tensile, bend and fatigue tests; and high temperature performance of completed cells. These latter tests have demonstrated the adequacy of the design at conditions comparable to those of the present application. The Griscom-Russell Co. is presently in the process of manufacture of heat exchangers of this general type on a production line basis. The precooler, a water-cooled heat exchanger which cools the low pressure helium to the compressor inlet temperature is

- 25 - ATC-54-12 simply a continuation of the recuperator with water replacing the high pressure helium. The precooler section is 4'2" x 6' x 3' long. The LP helium flows directly from the recuperator through the precooler to the compressor. The cooling water flows in four-pass cross-counterflow through the unit. Figure 17 shows the recuperator and precooler exchangers as a unit. Table VI lists the precooler specifications. The intercooler is a conventional tube in shell heat exchanger with a folded tube bundle and a divided tube sheet. The bundle is made up of 5/8" tubes on 7/8" equilateral triangular centers. Table VII lists the intercooler specifications. The partially compressed helium flows through the tubes, and water flows across the tubes in the shell. The pressure loss in the intercooler is slightly greater than that allowed in Table I, however it does not significantly affect the cycle analysis.

ATC-54-12 TABLE VI Precooler Specifications Helium flow rate, #/sec 214 Duty, BTU/Hr (Total 2 units) 169 x 106 Effectiveness, %- 92.2 Surface characteristics see Figure 17 Total surface, (He)/unit, ft2 11,000 Prime surface rate, BTU/Hr/ft2 37,700 Ft2 prime surface/KW 0.745 Service Helium H20 Temperature in, ~F 266 75 Temperature out, ~F 90 125 ~, % S2.25 Face area/unit, ft2 25 4.5 Number of passes 1 4 Flow length (total), ft 3 16.8

ATC -54-12 TABLE VII Intercooler Specifications Tube in Shell Exchanger - Helium in Tubes, H20 in Shell Helium flow rate, #/sec 214 Duty, BTU/Hr 115 x 106 Effectiveness, % 88.8 Total surface, ft2 9170 Prime surface rate, BTU/Hr/ft2 12,550 Ft2 prime surface/KW.153 Number of tubes/pass 3020 Length of tubes, ft 9.25 Tube, diameter-gage 5/8" - 16 BWG Tube pitch, inches 7/8 Service Helium H20 Temperature in, ~F 210 75 Temperature out, OF 90 125 C, fi %1.07 Number of passes 2 2 Flow length (total) ft 18.5 18.5

- 26 - ATC-54-12 7.0 General Arrangement A general arrangement of the machinery set and heat transfer apparatus is shown in Figure 18. The high speed compressor and turbine set and the low speed power turbine are arranged in a single case, split on the horizontal centerline. The high speed shaft, consisting of the two compressor stages and the high pressure turbine, is mounted on three bearings, one at each end of the shaft and one between the low and high pressure compressor. This latter is a combined thrust and journal bearing. The low pressure power turbine is located downstream from the high pressure turbine and it is supported on two bearings, the one at the turbine exhaust being a combination thrust and journal bearing. Viscosity or contact type seals are contemplated at the shaft ends in the casing to prevent the escape of helium from the system. Seals of this type are currently being used in compressors handling hydrocarbon gases at pressures far in excess of the pressure levels encountered at the shaft ends of this power plant. Current requirements for the handling of gases in turbomachinery in the process industries nave revived interest in hydrostatic or the so-called "piston bearings", lubricated by the fluid being pumped. An intensive program for the development of this type of bearing for use in closed cycle gas turbines is being formulated and if the development of this bearing type is successful, it will result in a complete reappraisal

F I G. 18. GENERAL ARRANGEMENT 60MW NUCLEAR 4. [ CLOSED CYCLE GAS TURBINE Ii ~-~.5 01a POWER PLANT STARTING MOTOR COMPRESSORS TURBINES t 1T _____________ ~TO GENERATOR (~~~~~~~~~~~~~~~~~~~I /: ACCESSORY G R )/= —I - RECUPERATOAPRECOOLER INTERCOOLER TO REACTOR FROM REACTOR

- 27 - ATC-54-12 of the bearing and sealing system as the use of hydrocarbon lubricants will be dispensed with. The intercooler, between compressor stages, is so designed as to be an integral part of the machinery set, thus eliminating the necessity for external lines and their associated joints which are a source of leakage. The intercooler is a hairpin tube type with helium in the tubes and water in the shell. The tube sheet, to which the tubes are welded, is bolted directly to a mating flange on the bottom of the machinery set casing between the low and high pressure compressors. By suitable diffusers the helium is conducted from the discharge of the low pressure compressor, through the intercooler and back to the high pressure compressor inlet. A cross section through the machinery set and intercooler is shown in Figure 19. Through a system of internal ducting, helium leaving the compressor flows in an annular passage around the high pressure turbine inlet pipe. By this means, openings in the machinery set casing are reduced to a minimum. This pipe, illustrated schematically in section in Figure 19 employs inside out insulation, a method used on all closed cycle gas turbine plants, the use of which permits the outer pipe which is subjected to pressure only, to be fabricated of normal low alloy materials. The inner pipe conducting the high temperature gas stream is unstressed and

L P TURBINE HP TURBINE <-i-2 <_; RA at~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~'~;~2 LP ~~L u HP COMPRESSOR ~0111O~PRESSOR 7' =i., Rn ~ ~~~FIGa~~~~~..... 19 SECTION THROUGH MACH I NERY SET :~~~~. ).C~ ~~''~/ ",;~ ~ ~ MAGI~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~. -~~t.'II E RY SET

- 28 - ATC-54-12 the material need only be selected for its corrosion resistant properties at the temperature in question.

- 29 - ATC-54-12 8.0 Control System The subject plant is designed for base load operation on a network where the frequency (speed) control is from another source. Therefore only power output (pressure level) control is required, together with a means of synchronizing the speed of the output turbine to the reference source at the time of starting. Power, or pressure level control, is effected by addition or withdrawal of working fluid from the circuit. Emergency speed control of the power turbine is effected by bypassing. Helium that is not being circulated in the plant is stored in accumulators for subsequent use, i.e. this is a no-loss system. The accumulator system consists of two (or two groups of) storage bottles; one being the receiver and the other the accumulator interconnected by a transfer pump. In this system the total amount of helium in the power plant and tanks is constant at all times. Leakage losses are made up by addition of helium to the receiver from time to time as required. A simplified diagram of this system is shown in Figure 3. Over the range of power output that this plant will operate, assumed to be + 10% of normal, power output varies directly with system pressure. Therefore, the power output control consists of a set of variable datum pressure reducing valves between the system and the receiver and accumula

- 30 - ATC-54-12 tor tanks, designed to maintain a constant preselected pressure level in the system. An overspeed governor is provided on both the high pressure compressor/turbine set and the power turbine. The governor on the compressor/turbine set is a top speed governor only, tripping a compressor bypass valve when this set exceeds a predetermined speed limit. The governor on the power turbine is designed to come into play only in event of an emergency, the presence of which makes it necessary to shut the plant down. In action, the power turbine governor opens the power turbine bypass valve, immediately reducing the weight flow through the power turbine. Since this reduces the back pressure on the compressor drive turbine, it tends to overspeed, thus activating the compressor bypass valve. Further, the power turbine overspeed governor trips the system pressure regulator, resulting in the discharge of the contents of the system to the receiver. Simultaneously, the control rods are dropped into the reactor reducing the heat input to the system. When the power plant load is dumped and the reactor activity level reduced, a means must be provided to cool the reactor for a period after shut-down. During the normal procedure of shutting off the plant and the emergency condition previously discussed, the compressor/turbine set will circulate helium through the reactor until the minimum self

- 31 - ATC-54-12 running speed is reached. At that time, a secondary motordriven circulating compressor with an auxiliary cooling loop is energized, circulating helium through the reactor until activity is reduced to a point resulting in a safe temperature level.

- 32 - ATC -54-12 9.0 Xenon Removal The working fluid used in this plant is helium which is available commercially at a purity of 99.99%. Impurities consist of argon, carbon dioxide and nitrogen, none of which is in sufficient quantity to be of any concern. There is, however, the possibility of contamination of the system by gaseous fission products, escaping from the reactor fuel elements. The principle volatile radioactive impurity of the fission process is xenon, and removal of the xenon from the working fluid is desirable to reduce the activity of the working fluid to an acceptable level and avoid the necessity of extensive shielding. The xenon can be effectively removed to any degree desired by solidification in a cold-trap. One procedure for accomplishing this would be to withdraw a small stream of helium from the cold end of the compressor intercooler and pass it through a heat exchanger in which it would be cooled to whatever temperature would be necessary to reduce the xenon content to a permissible level. Since the xenon is present in such small amounts, even its complete removal would leave the helium essentially undiminished in amount. This cold helium stream would pass through a turbo-expander wherein its pressure would be dropped to essentially the suction pressure of the compressor. In passing through the expander, the helium would be cooled sufficiently so that it could act

- 33 - ATC-54-12 as the refrigerant for cooling the xenon cold-trap exchanger. A typical flow diagram for this cold-trap system is shown in Figure 20. HELIUM FREE OF VOLATILE I B = FISSION PRODUCTS TO FIRST en,~~~~ ~STAGE COMPRESSOR INLET GENERATOR XENON DEPOSITS HELIUM CONTAINING VOLATILE FISSION PRODUCTS FROM EXPANSION TURBINE COMPRESSOR INTERCOOLER Figure 20. Xenon trap. Since the gas flow required to hold down the xenon concentration in the working fluid of the power cycle is very small, estimated at 1 of the mass flow or about two pounds per second, the dimensions of the cold-trap heat exchanger will be small, as will be the turbo-expander required to provide the cold end AT. The passages of the cold-trap will gradually become plugged with xenon and its decay products and eventually it will have to be replaced by a new unit. The size of this cold trap is such that it can be

- 34 - ATC-54-12 cleaned or disposed of, depending upon which seems to be most desirable in the final design.

- 35 - ATC-54-12 APPENDIX I Cycle Analysis Assumptions - Pressure ratio 1.552 = 2.40 Pressure losses = 7 Expansion ratio = 2.233 Compressor inlet temperature = 90~F Turbine inlet temperature = 1400~F Recuperator effectiveness = 93% Compressor - T1 = 550~R Rc = 1.55:1 r~Rc ( = 1.191 1 - Rc =.191 a Tad = 1050F nc. =.88 A T 120~F T2 = 670~R T3 = 550~R T4 = 670~R TTc = 2 x 120 = 2400~F

- 36 - ATC-54-12 HP Turbine - T6 = 1860~R A Tc = 240IiF T7 = 16200R V e =.888 h Tead = 240/.888 = 270~F T7, = 1590~R ~ = 270/1860 =.145 1 -E =.855 (1 ).398 =.675 Rc = 1/(_-e)2'51 = 1.48:1 LP Turbine - Re tot = 2.233 ReLp = 2.233/1.48 = 1.51:1 i/ReLP =.662 (1/ReLp) 398 =.848 1 - (1/ReLp)'398 =.152 T7 = 1620~R Tad = 246~F T e =.888 ATw = 218~F T8 = 1402~R

- 37 - ATC-54-12 Recuperator - T8 = 1402~R T4 = 670 ~R g t = 732~F rr = 92.3% AT = 734/13 = 56~F T5 = 1402 - 56 = 1346~R Reactor - T6 = 1860~R T5 = 1346~R ZTR = 514~F Precooler T4 = 670~R ATp = 56~F T9 = 726~R T1 = 550 ~R oft = 176~F Cycle Efficiency - ATw = 218~F ATR = 514 ~F = 42.4% Work Rate W = 3415/ATw x 1.25 = 12.5#/KW Hr

- 38 - ATC-54-12 Terminal Conditions & Weight Flow - Generator efficiency = 97.5o Mechanical efficiency = 97.5% Net output = 60 MW Gross output = 63 MW Helium Flow = 12.5x63 = 790,000#/Hr Reactor Load = 790,000x514x1.25 = 148.5 MW 3415 Terminal efficiency = 60/148.5 = 40.4% Plant heat rate = 790,000x514x1.25 = 8460 BTU/KW Hr 60,000 The effect of changes in cooling water S.. temperature and overall 12 relative pressure loss w in cycle efficiency and work rate are shown in 45.. Figure 21. VS.To.~ rS. S. 40 S COOLING WATER TEMP., To- OF 0 50 60 70 8SO 9 35 1 1 1 5 10 15 SYSTEM PRESSURE LOSS, e-% Figure 21. Correction for off-design condition.