Hensaen, J., et al., "Facility for Fatigue Testing of Thermal HELIUM COMPRESSOR AERODYNAMIC DESIGN Insulation,* BBC Review, 6. Vol. 72, June 1985. CONSIDERATIONS FOR MHTGR CIRCULATORS Cataford, G. F., and R. ¥. Lancee, "Oil-Free Compression on a Natural Gas Pipeline,- ASHE Paper 86-GT-293, 1986. C.F. MCDONALD GA Technologies, Inc., Foster, E. G-, et al., "The Application of Active Magnetic Bearings San Diego, California, to a Natural Gaa Pipeline Compressor," ASMS Paper 86-GT-61, 1986. United States of America Uptigrove, S. 0., et al., "Economic Justification of Magnetic Bear ings and Mechanical Dry Seals for Centrifugal Compressors," ASME Abstract Paper 87-GT-174, 1987. Compressor aerodynamic design considerations for both the main and shutdown cooling circulators in the Modular High-Temperature Gas-Coc Ted Reactor (MHTGR) plant are addressed in this paper. A major select' topic relates to the impeller type (i.e., axial or radial flow), a:.J the aerothermal studies leading to the selection of optimum parameters are discussed. For the conceptual designs of the main and shutdown cooling circulators, -oppressor blading geometries were established and helium gas flow paths defined. Both circulators are conservative by industrial standards in terms of aerodynamic and structural loading, and the blade tip speeds are particularly modest. Performance characteristics are presented, and the designs embody margin to ensure that pressure-rise growth potential can be accommodated should the circuit resistance possibly Increase as the plant design advances. The axial flow impeller for the main circulator is very similar to the Fort St. Vrain (FSV) helium compressor which performs well. A significant technology base exists for the MHTGR plant circulators, and this is highlighted in the paper.
1. INTRODUCTION
Details of the circulator configurations (Ref. 1) that are respon sive to the system requirements (Ref. 2) have been addressed as separate topics, and this paper focuses on aerodynamic design considerations for the compressor impellers in the two circulators. Both axial and radial flow impeller compressors have been utilized in gas-coole-l reactors (Refs. 3 to 6), and there are no firm ground rules that mandate the best type. The compressor cannot be designed in an isolated manner, but must In the case of the FSV plant and the units developed for Delmarva, be integrated in the reactor system to satisfy requirements in the areas the following factors led to the selection of an axial flow impeller: of thermal-hydraulics, gas-flow path compatibility, drive type, and (1) low pressure rise characteristic of the prismatic core, (2) compati possible future pressure-rise growth potential. Two circulators are bility with high speed steam turbine drive, and (3) requirement to mini- addressed in this paper, and the considerably different requirements and raize the machine diameter for vertical installation within the pre- criteria led to the selection of different impeller types; namely, an stressed concrete reactor vessel. axial flow compressor for the main circulator and a radial flow con figuration for the small shutdown cooling machine. The studies leading In reviewing Che technology bases, it is clear that the radial flow to the selection of the two compressor types are the focal point of this compressor is dominant in the gas-cooled reactor field, and its simplic paper. ity is perhaps its greatest attribute. In the conceptual design of the MHTGR plant, there was no attempt to "force-fit" a given circulator con 2. CIRCULATOR BACKGROUND figuration into the reactor circuit. The following sections highlight the results of studies to identify the most optimum type for the two la the ^irst generation of carbon dioxide-cooled plants (Magnox circulators in the MHTGR plant based on an annular prismatic reactor Reactors) built in the United Kingdom (Ref. 5) and France (Ref. 7), the core. modest levels of circuit pressure loss were compatible with the selec tion of a single-stage axial flow compressor. Various electric motor 3. MAIN CIRCULATOR and steam turbine drives were used for these machines. With the intro duction of the AGR commercial power plants, the higher resistance in the 3.1. INSTALLATION carbon dioxide circuits were beyond the capability of a single-stage axial flow compressor, and the choice lay between multistage axial or As illustrated in Fig. 1, the main circulator is installed in the radial flow compressors. The simplicity and ruggedness of the radial top head ot the steam generator vessel. The main circulator facilitates impeller was a deciding factor in the selection of this type of machine transfer of reactor thermal energy to the steam generator. The system (Ref. 8). is capable of decay heat removal in pressurized and depressurized modes of operation. The selection of reactor coolant also has an effect on the circula tor design, and in the case of the aforementioned units the very dense 3.2. REQUIREMENTS carbon dioxide yielded low values of adlabatic head (i.e., pressure rise/density). In the early helium-cooled reactors (Dragon, AVR, Peach Comprehensive requirements for the circulator have been discussed Bottom 1), the circulator head rise favored the selection of radial flow previously (Ref. 2), and boundary conditions necessary for the design of compressors. In the case of the circulators for commercial pebble bed the circulator are given in Table 1. reactors, the very high circuit resistance associated with this type of reactor core essentially dictated the use of radial flow compressors (Ref. 9). , CMIMt MD OUNII MIUtMK TABLE 1. MAIN CIRCULATOR DESIGN REQUIREMENTS nanuiHMs • PROVIDE HELIUM FLOW OF 348 LB/SFC (158 Kg/SEC! • PROVIDE HELIUM PRESSURF RISE OF 13.2 PSI (91 kPa) • PROVIDE CAPABILITY TU CIRCULATE HELIUM FOR PRESSURIZED AND /^ DEPRESSURIZED SYSTEM CONDITIONS • FLOW CONTROL BY VARIABLE SPEEO MACHINE MAW CIMUUIOH • ENSURE STABLE OPERATION OVER WIDE SPEED RANGE (5V110K) SIMM GtmiuiM • INCORPORATE PRtSSURE RiSE GROWTH CAPABILITY VISSil • INSTALL CIRCULATOR IN LOW TEMPERATURE PART OF CIRCUIT • BASE DESIGN ON ESTABLISHED AND PROVEN TECHNOLOGY • ESTABLISH MACHINE ENVELOPE TO FACILITATE REMOVAL AND REPLACEMENT IN SPACE ABOVE STEAM GENERATOR VESSEL • STRESS LEVELS TO 3C COMMENSURATE WITH 40 YEAR LIFE REQUIREMENT
was necessary to accommodate the high system pressure loss. Details of the radial flow machine are given in Fig. 2.
In performing scoping studies on compressors, a particularly useful relationship involves the portrayal of data on a specific speed-diameter array, the approach having been developed by Balje (Ref. 10). An exam Fig. 1 Main Heliun Circulator Installed in Heat Transport Loop ple OL" this relationship for radial compressors is given on Fig. 3, ar.d the obvious goal is to establish aerodynamic parameters to give a design 3.3. AXIAL VERSUS RADIAL FLOW COMPRESSOR AERODYNAMIC CONSIDERATIONS solution in the regime of high efficiency. Data points for operational machines are superimposed on the island array. In many cases, there are A summary of *he major factors In the selection of the impeller physical limitations (e.g., dr? sr speed, envelope constraints, etc.) type is given in Table 2. Early in the comparative study, it Mas con that do not permit operation in the island of maximum efficiency; never cluded that both types could meet the system requirements, the designs theless, the compressor performs well. The array should be regarded as being based on demonstrated and proven technology. A first step towards indicating whether a r dial, mixed, or axial flow machine should be selected. 3.3.1. Radial Flow Impeller As an initial point (in the center of the efficiency island), a Initial studies of a pebble bed variant of the MHTGR confirmed the specific speed and diameter of 100 and l.S (in the units stated), res 111 findings of similar work done in Germany that a radial flow compressor pectively, would yield an impeller diameter of 1676 mm (66 in.) and A m
TABLE 2. AXIAL OR RADIAL COMPRESSOR FOR HELIUM CIRCULATOR
CONSIDERATION AXIAL FLOW COMPRESSOR RADIAL FLOW COMPRESSOR
DESIGN STATUS CONCEPTUAL DESIGN CONCEPT EVALUATED
MEETING DESIGN PRESSURE RISE SINGLE STAGE ADEQUATE SINGLE STAGE REQUIREMENT 1112 PSD
PRESSURE RISE MARGIN CAPABILITY CAN BE ACCOMPLISHED WITH SINGLE STAGE SINGLE STAGE HAS CAPABILITY FOR MUCH 115* ABOVE DESIGN) HIGHER PRESSURE RISE (WEll SUITED TO PBR PLANT)
EXPERIENCE/TECHNOLOGY COMPRESSOR VERY SIMILAR TO FSV IMPELLER INDUSTRIAL COMPRESSORS • MAIN C.nrjLATOR FOR 250 MWIl] THAT PERFORMS WELL MOOULAR PBR PLANT CONCEPT
PERFORMANCE SELECTEO AXIAL COMPRESSOR NEAR OPTIMUM LARGE OIAMETER IMPELLER, ANO LOW — W - 252 LB/SEC 1114 Kg/SEC) 9,0F PARAMETERS SPEED FOR EFFICIENT OPERATION — Tin " * I2S5*>CJ — P t - 1050 psi 17.24 MPn) PRIMARY SYSTEM GAS FLOW PATH SELECTED FLOW DIRECTION THROUGH IMPELLER GAS FLOW PATH RESULTS IN THRUST ANO ou — Ap - 33 psi 1228 KPa) COMPATIBILITY GREATLY REDUCES THRUST BEARING LOAD ROTOR WEIGHT BEING ADDITIVt
MACHINE ENVELOPE WEIGHT COMPACT SMALL OIAMETER MACHINE ASSEMBLY INCREASED DIAMETER (WEIGHT • RADIAl IMPELLER ASSEMBLY) — DIAMETER, 33.2 IN. (843 mm) SIMPUCITY/RUGGEONESS DEMONSTRATED IN FSV SIMPLE ROTOR. VERY RUGGEO — SPEED, 5240 RPM — POWER, 6800 HP [5073 kWle|] DESIGN CONSERVATISM MACHINE WElt WITHIN STRESS LIMITS CONSERVATIVE HOW SPEED)
MEETS SYSTEM REQUIREMENTS YES YES
CAS-COOIED REACTOR EXPERIENCE FSV PEACH BOTTOM. AVR. THTR
EARLY MAGNOX PLANTS ICO;) 116 MACHINES BUILT FOR AGR (CO;)
OVERALL SUMMARY COMPATIBLE WITH REACTOR SYSTEM RADIAL COMPRESSOR WEll SUITED TO PLANTS (SUCH AS THE PEBBLE BEO COMPRESSOR SIMILAR TO FSV UNIT THAT REACTOR) Will HIGH CIRCUIT PRESSURE PERFORMS WELL LOSS NEAR OPTIMUM Fig. 2 Initial Radial Flew Circulator for 250Wt Pebble Bed Reactor
rotational speed of 2000 rpm. Bearing in mind the requirement for a compact machine asseubly to facilitate ease of removal and replacement 3.3.2. Axial Flow Impeller (Ref. 1), such a compressor would not be practical from the installation standpoint. A parametric array showing the Impact of impeller diameter From the onset of the study, it was quite clear that the compressor and speed is given on Fig. A. Considering envelope constraints, an requirements were similar to those for Fort St. Vrain (Table 3). While impeller diameter of 1118 mm (44 in.) with a rotational speed of the FSV circulator has experienced operating problems (Ref. 11), the 3600 rpm was tentatively selected. With a specific speed and diameter impeller performs well, and there was an obvious incentive to take of 180 and 1.0, respectively (see Tab)* 3 and Fig. 3), such a radial advantage of this. Since helium flow control is accomplished by vari flow machine is considered viable, but as will be discussed below, it is able speed (as opposed to variable inlet guide vane geometry), there is physically larger than a comparable axial flow machine. no obvious incentive to have a stator ahead of the rotor; in fact, it is too A MHTGR - SHUTDOWN COOLING CIRCULATOR DESIGN i.i «i \ V^^nf \ so - 0 RAOIAl HOW 12 _— LINE! OF CONSTANT VARIANT FOR lie. IPICIFIC DIAMETER 350 MW{I) MHTGR ,0 40 M MAIN CIRCULATOR — •"• EFFICIENCY ISLANDS RADIAL FLOW CIRCULATOR a- 3.0 A T" T»'^ \ \ \ \ \^"*" FOR 260 MWdl PEBBLE 41 — BED REACTOR ,0 %i , LINES OF CONtTANT CIRCULATORS IN - / SPECIFIC SPIED I HELIUM REACTOR I -L» V ;X«w^ \ ^\ -^ir PLANTS 1000 < O ORAGON " 1^^^ IM 10 0 PEACH BOTTOM 1 \ \ / \ \*^«»«^i* II *te.\ \x \ \ JV" «^*-i_ H N/V7 D AVR THTR OS o \^"V^J\/\\^? p H»d'/4 N = BPM H«4 = FT-LB/LB V AGR CO; CIRCULATOR FOR °S 3 V = FT 'SEC D = FT "/T \ /\"^F^fer VMTT COMPARISON 3ioo ^*<^^ y \ \ \ 0 3 J_ _L _L_ _J_ - \ 10 60 100 300 600 100G ROTATI0 MAI \ / \ \ '« SPECIFIC SPEED, N, WIO II '" \ / \ »» \ / \ ^ nmuni Fig. 3 Specific Speed-Diameter Array for Radial Flow Compressor - Y ,J /^ - 4000 II
desirable to minimize the number of stages. As in the case of the FSV
compressor, a rotor-before-stator configuration was selected, and the • DESIGN POINT • PHESSURIZED OPERATION velocity diagram is shown on Fig. S. In this zero inlet and exit swirl — 3600 flPM — W - 348 LB/SEC arrangement, the rotors impart the energy into the gas in the form of a — TIP DIAMETER, 44 IN. — T,, - 491"F velocity, and the trailing stators recover this energy by returning the — OUTLET ANGLE, 40 DEGREE — Pout - 926 ptii gas velocity to the axial direction. — Ap - 13.2 pii
A preliminary aerodynamic design of the compressor was performed Fig. 4 Parametric Array for Main Circulator Radial Compressor
using a computer code developed by GA Technologies based on well- complexity as the plant design advances), could a tingle-stage axial established design methods, such as those presented in NASA SP-36 compressor accommodate this?" (Ref. 12). The aerothermodynamic parameters for the axial flow machine are given on Table 4. A study was performed to address an obvious ques From the compressor map shown on Fig. 6, It was concluded that the tion, "If the system pressure loss was to Increase (as a result of added 119 proposed design had adequate surge margin, as was demonstrated in the TABLE 3. COMPRESSOR COMPARISON FOR HELIUM CIRCULATOR
COMPRESSOR TYPE AXIAL FLOW RADIAL FLOW
MHTGR MAIN FSV MHTGR MAIN THTR COMPRESSOR DESIGN CIRCULATOR CIRCULATOR CIRCULATOR CIRCULATOR
HELIUM FLOW. LB/SEC 346 276 DATA 112 INLET TEMP. »f 491 742 AS 482 INIET PRESSURE. PSIA 9118 6*6 FOR AXIAL 651 PRESSURE RISE. PSI 13.2 14.0 FLOW 180 INIET DENSITY. LB/FT^ 0 366 0.213 COMPRESSOR 0.216 VOLUMETRIC FLOW. FTl/SEC 972 1.304 514 AJNABATIC HEAD. FT 6.310 9,466 11,890 IMPELLER O/O. IN 360 210 44 Oil) 354 SPEED. RPM 6.200 9.550 3.600 5.600 TIP SPEED, FT/SIC 947 1.167 191 865 SPECIFIC SPEED. N, 311 360 180 111 SPECIFIC OIAMETER. 0, 010 0.64 1.0 1.35 NUMBER OF STAGES 1 1 1 1 POWER, HP 4.250 5,300 APPROX. 4.600 3,083 STACGER ANGLE PRESSURE — RISE GROWTH • 25% Ap INCREASE CAN BE • GOOD GROWTH CAPABILITY RADIAL CAPABILITY ACCOMMOOATEO WITH SINGLE STAGE CAN ACHIEVE MUCH AXIAL STAGE INCREASED AOIABATIC HEAD
(•IVAIUE SEIECTEO FOR CONCEPTUAl DESIGN. RECOGNI2ING ENVELOPE CONSTRAINT. FOR OPTIMAL RADIAL ROTOR COMPRESSOR PRAMETERS l« •. N, = 100, D, - 1.5) THE COMPRESSOR DIAMETER AND SPEED WOULD BE 66 RELATIONSHIPS FROM VELOCITY DIAGRAM IN AND 2000 RPM. RESPECTIVELY, AND NOT PRACTICAL FROM INSTALLATION STANDPOINT. Vi I 1 FLOW COEFFICIENT TM dl TM ill + TH ..I
STAGE TEMPERATURE RISE T - 7* (TM tfl - TM rill -7— U' U I J Cf
ROTOR DIFFUSION FACTOR 0' - II - £~ + ' C">" (TM ill - TM (121 CM ill C 1 AXIAL VELOCITY Vi DEGREE OF REACTION R - — (TM 01 + TM M\
'PARAMETER MUTING TO AERODYNAMIC LOADING IN AN AXIAL FLOW COMPRESSOR. THE DlfHJSO* FACTOR IS AN INDICATION OF BOUNDARY LAYER GROWTH ON THE SUCTION SIOE OF THE BLAOC. WHEN 3 > 0 10 THERE IS EVIDENCE OF BOUNDARY LAYER SEPARATION.
'ITOR BEFORE STATOR TYPE I HO INIET AND EXIT SWIRLI Fig. 5 Velocity Diagram for Axial Flow Conpressor TABLE 4. AEROTHERMODYNAMIC PARAMETERS FOR HELIUM COMPRESSOR
DESIGN DATA PARAMETER
HELIUM F10« RATE. KGJSEC IIBISEC) ISO 1341) IMET TEMPERATURE. *Ct*F) 255 (4911 miET PRESSURE. MP* IPSIAI 0.29 1912) CIRCULATOR PRESSURE RISE. KPa (PSIDI 91 113.2)
FlOW CONTROl VARIABLE SPEEO DRIVE ADIAMTIC HF.AO M IFT) 1111153091 OIFFUSER EFFICIENCY. % 10 V OlfFUSER AREA RATIO 0.24 OVERALL EFFICIENCY. % (TOTALTO STATIC) 79.2 MOTOR SHAFT POWER. KWWHP) 3170 (4250) COMPRESSOR TIP DIAMETER. MM UN.) 019 I3S.0) BIAOE HEIGHT. MM UN 1 01.9 13.5) HUBITIP RATIO 010 TIP SPEED. M1SEC IFT/SEC) 219 1947) AXIAL VELOCITY. MSEC If TISECI 125 14111 ROTATIONAL SPEED Ai»M 8200 FLOW COEFFICIENT. ValUa 0.40 MEAN ROTOR SOLIDITY 1.02 ROTOR ASPECT RATIO 1.22 MEAN ROTOR MACK NUMBER 0.21 ROTOR DIFFUSION FACTOR (MAX) 0.42 DEGREE OF REACTION 0.15 Helium Flow W>/fl/^ (lb/sec)
1 TEMPERATURE RISE COEFFICIENT. AHIUK 0.29 SPECIFIC SPEED N. 311 Fig 6. Main Circulator Conpressor Map (Normal Pressurized Operating Condition) SPECIFIC DIAMETER. Dt 0.10 HEAD COEFFICIENT. HafU'lt 0.19 DESI6N TECHNOLOGY BASED ON PROVEN TECHNOIOGV factor exceeds 0.60 (Ref. 14). From Fig. 7 it can be seen that with a maximum rotor diffusion factor of 0.42 the design has conservative Load FSV machine. The results of the pressure rise growth potential are ing. Without exceeding the D value of the FSV compressor (which hat> shown on fig. 7. A parameter that is Indicative of aerodynamic loading good characteristics), the compressor could be rebladed within the »ame in an axial flow compressor Is the diffusion factor, which is indicative annulus and rotational speed to give about 17 psi rise (28Z increase). of the extent of boundary layer growth on the suction side of the blade. The attendant power increase would, of course, necessitate a larger In comparing the NASA design method with that of Howell (Ref. 13), it electric motor envelope. It is likely that by blade geometry/speed can be seen from Fig. 8 that the diffusion factor is a strong function optimization a single-stage compressor could be designed for a presHure of gas deflection (for a given solidity). There is evidence of boundary rise of over 20 psi, and indeed this waa demonstrated for the Delmarva layer separation on the suction surface of the airfoil if the diffusion plant. IIMIT MPMSEMTUI8 MHMOMV IA»E« SIMMTHW CURVES DRAW FOR y//////////////////v/////y//////Y//////Y/y////////^^^ SOLIDITY (C/SI - 10 • 14 0.70 HOWELL'S STALL 060 DEFLECTION LINE
050 DEFLECTION 0.40 r- HOWELL'S NOMINAL SUGGESTED AERODYNAMIC DEFLECTION LINE s LOADING 1IMIT FOR tt 0.30 SINGlt-STABI AXIAL (•OX OF STAt.ll s COMPRESSOR CONCEPTUAL s DESIGN 0.20 LINES OF GAS OUTLET ANCLE /Jj 0.10
0 ?4k A» 6MWTM POTENTIAL 20 30 40 50 60 70 FOR REILAOEO COMPRESSOR WITH SAME ANNUM* SEOMI1RY GAS INLET ANGLE 0, J_ -L
t« It "DEFINEO AS 0 = |l - (Cot PRESSURE RISE. u r Fig. 8 Comparison of Howell's (U.K.) and NASA Diffusion Factor Methods of Defining A COMPRESSOR OESIGN POINT PRESSURIZED OPERATION Axial Compressor Aerodynamic Loading — TIP DIAMETER, 35 IN — W - 348 IB/SEC — NUB DIAMETER. 28 IN. — Tia - 49I«F with the FSV machine on Table 6. An overall view of the circulator — SPEED. 6200 RPM — P0U| - 925 ptia — A major change from an earlier design variant (Ref. 15) involved a 3.4. REFERENCE COMPRESSOR DESIGN change in the gas flow direction through the Impeller. In the reference design (Fig. 10), the helium flow is downwards through tl.a compressor Based on the aforementioned studies, the single-stage axial flow blading, and the upward aerodynamic thrust (4500 lb) partially offsets variant was selected, it being concluded that it best satisfied the the downward rotor weight (6500 lb) to ease the requirements on the requirements. A. strong factor in this selection was the near commonal catcher thrust bearing. In the previous design, as would be the case ity with the FSV compressor Impeller, a view of which is shown on for a radial flow impeller concept (as in Fig. 2), the thrust and weight Fig. 9. Aerodynamic data for the MHTGR axial compressui. blading is would be additive, this resulting in more demanding requirements on the given on Table S, and the major parameters and features are compared catcher bearing. TABLE 5. AERODYNAMIC DATA FOR AXIAL COMPRESSOR BLADING RADIAL POSITION ROOT TIP IMPELLER DIAMETER, M (INI 711 (21.01 IIS (35.0) HUB/TIP RATIO 010 AXIAL VELOCITY. m/SEC (FT/SEC) 12t (4111 125(411) BLADE SPIED. m/SEC (FT/SEC) 231 (7HI 211 (147) FIQW COEFFICIENT. Vi/U 0.M 043 ROTOR BUOE CHORO, mm (INI 12 0 11.23) 65 1 (2.59) STATOR BUOE CHORO, mm (IN.) Ml 12.53) 64.3 (2.53) ROTOR SOUOW, C/S Ml 012 BUOE HEIGHT, mm (INI III (3 SI ROTOR ASPECT RATIO 1 20 ROTOR MACH NUMBER 0.11 023 ROTOR DIFFUSION FACTOR 0.40 0 33 STATOR OIFFUSION FACTOR 0.45 0.41 OECREE OF REACTION Oil 0.11 MEAN ROTOR INIET ANGIE •4 3 14.3 MEAN ROTOR OUTLET ANGLE SSI 55.1 MEAN STATOR INIET ANGLE 311 31.1 MEAN STATOR OUTLET ANGLE 0 0 MEAN ROTOR STAGGER ANGLE 514 51.4 MEAN STATOR STAGGER ANGLE 12.4 12 4 NUMBER OF ROTOR BUDES 35 NUMBER OF STATOR BUOES 37 BENDING STRESS. MPi <•») 1 ROTOR BUOE 34 7 (S.000I STATOR BUDE 34 7 (5,0001 ROTOR CENTRIFICAl STRESS, MPi <>»l 70.2 (10,110) MAX. COMPRESSOR IMPELLER EFFICIENCY, X 1175 Fig. 9 Fort St. Vrain Circulator Rotating Assarctoly DIFf USER EFFICIENCY. % 10 0 (0.24 AREA RATIO) OVERALL EFFICIENCY (INCLUOING MFFI, % 712 1 NOTES: 1) ROTOR BEFORE STATOR (2ERO INLET ANO EXIT SWIRL). 2) NASA (5 SERIES PROFILE 3) DESIGN METHODOLOGY AS FOR FSV COMPRESSOR. SHUTDOWN COOLING CIRCULATOR 4.1. INSTALLATION A.2. REQUIREMENTS As shown on Fig. 12, the shutdown cooling circulator Is Installed Comprehensive requirements for the circulator have been discussed ln_ the bottom head of the reactor vessel. This small circulator (not previously (Ref. 2), and boundary conditions necessary for the design of safety-related) Is used to provlds rapid cooling of the reactor system the circulator are given in Table 8. (for refueling, maintenance, repair, etc.) If the main loop la unavail able. The system Is capable of decay heat removal In pressurized and depressurlsad modes of operation. 123 124 TABLE 6. HELIUM CIRCUuATOR FEATURES COMPARISON 0 EOF CHINON A MAIN CIRCULATOR FOR 7 TWO-STAGE AXIAl HAIMI/PARAMETER FORT If VRAM MHTGR COj CIRCULATOR MODULAR HTGR PLANT MHTGA SHUTDOWN _ KfUUM HOW. ««/UC IU/SIC) IH urn 1MOOI •11 TEMPI RATIMK. *C l«f)l 1*4 l?4M 251 (4*1) MUI PRESSURE. Mfa IPSA) 4.T) I444I • II (111) PRESSURE MM. IN into) Hi (14II •1 11)11 AOMOAtK MAO. M IFTt HIS IMUI 1*11 IIMSI CIRCULATOR OMUTATIOK VERTICAL VERTICAL COMPRESSOR T»PE AXIAl AXIAL COMPRESSOR DRIVE STEAM TUAMNE ELECTRIC MOTOR HOW CONTROL VARIAIlt SPEIO VAAIAItE SKEO SKI 0. HTM MM •100 POWER, KWM) iitrt JIM (MOD 3141 (4IH) TOROJK. M-«| in III Ml 121341 4IIIMMI COMPRESSOR EFFICIENCY. % III lit WKUn TIP DIAMETER. MM HMD Ml III) Mt (») MAM KKII!. MM (l«S) III HJU 1*1 Oil NUMOEA W ROTOR I4S.0E1 11 li TIP SKEO. MV3EC IFT/SECi »i mm 111 (Mil WAFT DIAMETER, MM IIW WATER-LURRKATEO ACTIVE MAGNETIC REARMSS MAMHS SPAH, MM (Ml HI 122) HIT IMI •EARMM CAPACITY RAOMl/lEARtNS. M Uil till (15*01 2041 (4MW THRUST. K| lit) HU IU.OM) MM Itl.tMt FIRST CRITICAL SKf 0. MM 1%) I3.M0 1141) TIM (111) MOSU PROTECTION CAPARRJTY «1 YES SAKTV CLASS SAIETV CUSS HON-SAFETY i L__i_J _J i i_J i : i_ IACKUPORW PfHON WHEEL •A io 30 to too 300 MO looo 3000 cooo :oooo MACMtM IMIAIUTION m KM III LOW COMI TOP Of STEAM GENERATOR VESSEL MACMMK STATUS OMRATtMAI l>IM.MM HOURS) OMCEPTU.H OtSWN SPECIFIC SPEE0. Nl Fig. 11 Specific Speed - Diameter Array for Axial Flow Compressor TABLE 7. MAJOR PARAMETERS FOR SELECTED HELIUM CIRCULATOR • SINGLE STAGE AXIAL FLOW COMPRESSOR • IMPELLER DIAMETER 35 IN. {889 mm) 1 BlA0E GEOMETRIES VERY SIMILAR • ROTATIONAL SPEED 6200 RPM J TO FSV COMPRESSOR • TIP SPEED 947 FT/SEC 1289 m/SEC) • CONSERVATIVE STRUCTURAL DESIGN • POWER 4250 HP (3169 kW(tl) • CONSERVATIVE AERODYNAMIC LOADING COULD ACCOMMODATE UP TO 25% INCREASE IN CIRCUIT RESISTANCE • GOOO SURGE MARGIN OVER WIOE FLOW RANGE • CONCEPTUAL DESIGN CLOSE TO OPTIMUM FOR MAXIMUM EFFICIENCY • OVERALL MACHINE DIAMETER 8.0 FT 12 4 ml • OVERALL MACHINE LENGTH 20.0 FT (6.1 ml • ASSEMBLY WEIGHT 30 TONS 127,220 Kg) • MACHINE ASSEMBLY CAN BE REAOTLY REMOVED ANO REPLACED IN SPACE ABOVE STEAM GENERATOR VESSEL • DESIGN BASED ON EXISTING AND PROVEN TECHNOLOGY • EXTENSIVE INDUSTRY EXPERIENCE FOR COMPRESSOR 0ESIGN ANO FABRICATION for MHTGR 4.3. AXIAL VERSUS RADIAL FLOW COMPRESSOR AERODYNAMIC CONSIDERATION:? A summary of the major factors in the selection of the impeller type are given on Table 9. Since the circulator is located near thit bottom of the below-grade silo (Ref. 1), a dominant consideration in the early phase of the design was to minimize the machine size (paruicu- SERVICE WAIfcft larly the diameter, since this impacts the size of the removal cask). OUT Initial focus was on a high-speed axial flow machine, and a design was J^£ established. This design was not viewed as being conservative and would involve considerable extrapolation from the FSV data base; accordingly, studies of a lower-speed radial compressor were undertaken, and various aspects of the resulting comparison are given in the following sections. HEAT / SCS EXCHANGER CIRCULATOR 4.3.1. Axial Flow Impeller In reviewing the machine operating envelope, it was quickly deter mined that the depressurized mode (with very low gas density) gave the Fig. 12 Small Circulator Installed in Shutdown Cooling Loop TABLE 9. AXIAL OR RADIAL COMPRESSOR FOR SHUTDOWN COOLING CIRCULATOR TABLE 8. SHUTDOWN COOLING CIRCULATOR DESIGN REQUIREMENTS CONSIDERATION AXIAL FLOW COMPRESSOR RADIAL FLOW COMPRESSOR DESIGN STATUS INITIAL DESIGN CONCEPT CONCEPTUAL OESIGN • PROVIDE HELIUM FLOW OF 6 36 LB SEC U 89 Kg/SEC) MEETING DESIGN PRESSURE RISE 2 AXIAL STAGES NEEOEO SINGLE STAGE REQUIREMENT 10.71 piil • PROVIDE HELIUM PRESSURE RISE IDEPRESSURIZED) OF 0.71 PSI I4.9 kPa) PRESSURE-RISE MARGIN YES. WITH 2 STAGE YES • PROVIDE CAPABILITY TO CIRCULATE HELIUM FOR DEPRESSURIZED AND CAPABILITY 125% ABOVE DESIGN) PRESSURIZED SYSTEM CONDITIONS EXPERIENCE/TECHNO'30V EXTRAPOLATION FROM SINGLE- INDUSTRIAL MACHINE STAGE FSV MACHINE • FLOW CONTROL BY VARIABLE SPEED MACHINE PERFORMANCE ALTHOUGH NOT OPTIMIZFP POWER CONCEPT Will NEED SUGHT • ENSURE STABLE OPERATION OVER WIOE SPEED RANGE (bS-100%) ABOUT 200 HP (ISO >W(«I| INCREASE IN POWER SIMPUCITV/RUGGEDNESS HAVING 2 STAGES A00J SIMPLE ROTOR • INCORPORATE PRESSURE RISE GROWTH CAPABILITY COMPLEXITY • INSTALL CIRCULATOR IN LOW TEMPERATURE PART OF CIRCUIT DESIGN CONSERVATISM HIGH SPEED MACHINE WITHIN LOWER SPEED. MORE STRESS LIMITS CONSERVATIVE CONCEPT • BASE DESIGN ON ESTABLISHED AND PRCVEN TECHNOLOGY MEETS SVSTEM REQUIREMENTS VES YES • MINIMIZE MACHINE ENVELOPE TO FACILITATE REMOVAL AND REPLACEMENT IN SPACE MACHINE ENVELOPE ASSEMBLY DIAMETER MINIMI2E0 1 FOOT {0 3 ml INCREASE ON BELOW REACTOR VESSEL FOR EASE OF REMOVAL ASSEMBLY DIAMETER ACCEPTABLE • STRESS LEVELS TO BE COMMENSURATE WITH 40 YEAR LIFE REQUIREMENT OVERALL SUMMARV DESIGN MEETS REQUIREMENTS SIMPLER OVERALL MACHINE EXTRAPOLATION FROM EXISTING CONSERVATIVE PARAMETERS DATA BASE SLIGHTLY INCREASEO ENVELOPE NOT CONSERVATIVE DESIGN most severe compressor requirement In terms of adiabatlc head as shown •PIIO. RPM LIMIT REPRESENTING on Table 10. With a head rise on the order of 50% greater than for the tOUNOARV LAYER M,Mi 0 7* SEPARATION •I SINGLE STAGE DATA FSV machine, it became clear that the design pressure rise requirement of 0.71 psi could not be realized with a single-stage axial flow com • M [_ ^yyvyj-yyvi SPEED, «PI pressor. The impact of number of stages on the blade loading factor (D) . 0„, FOR FSV MM is shown on Fig. 13. A two-stage design was selected based on an impel • to ler diameter of 737 mm (29 *n.) and a rotational speed of 10,000 rpm. With a diffusion factor of around 0.4, the blade loading is very conser 0.4* vative. The resultant specific speed and diameter of 381 and 0.75, res pectively, gives a machine In the island of maximum efficiency as shown on Fig. 11. A layout of the circulator assembly embodying a two-stage 0 20 axial flow compressor is given on Fig. 14. DESIGN APPR0X 21% • 10 VALUE OESIGN MARGIN 4.3.2. Radial Flow Impeller As a starting point In the study, an observation of Fig. 3 would • M 0 70 indicate that to be in the center of the maximum efficiency island, the PRESSURE RISE. Mi A OESIGN POINT 0ATA FOR — SYSTEM DEPRESSURIZED TWO STAGE AXIAL FLOW — Ap — 0.71 psi SHUTDOWN COOLING — N = 10,000 RPM TABLE 10. COMPRESSOR COMPARISON FOR SHUTDOWN COOLING CIRCULATOR CIRCULATOR "Up 29 IN. COMPRESSOR TYPE AXIAL FLOW RADIAL FLOW Fig. 13 Axial Flow Ccnipressor Aerodynamic Loading MMTGR MHTGR THTR 2 STAGE 1 STAGE fSV MACHINE MHTCR CIRCULATOR COMPRESSOR DESIGN DESIGN CONCEPT (FOR COMPARISONI CONCEPT (FOR COMPARISONI specific speed and diameter should be on the order of 100 and 1.5, res MACHINE STATUS CONCEPTUAL 0ATA POINT OPERATIONAL CONCEPTUAL OPERATIONAL pectively. An example of a machine in this regime is the radial flow DESIGN OESIGN compressor for the THTR plant circulator. NUMSER OF STAGES 2 1 1 1 1 PRESSURE RISE, pai 0 71 IM 14.0 071 II 0 HELIUM FLOW. LI/SEC 111 OS 271 os 112 INLET TEMP. «F 240 240 742 210 412 For the design valve of pressure rise (i.e., 0.71 psi), an effort 0UTIET PRESSURE. M» 140 14.0 700 140 519 INLET DENSITY. IR/FT^ 000701 0 00701 0213 000701 0211 VOLUMETRIC FLOW. FT^/SEC III 111 1304 191 514 was expended to investigate the impact of major parameters on a radial ADIARATIC HEA0. FT 94IS 14.500 10170 14.500 11.190 flow compressor, and data are portrayed on Fig. IS. Without regard to IMPELLER 0/0. IN 210 290 210 310 354 SPEE0. NPM 10.000 10.000 9550 5400 5100 envelope constraint, the first iteration in the design process would be TIP SPEED. FT/SEC 1215 1215 1147 lis IIS to select specific speed and diameter values consistent with operation SPECIFIC SPEE0. N, 311 235 310 123 111 SPECIFIC MAMETER. 0, 0 75 011 0S4 1 22 1.35 in a high-efficiency regime. This would yield a low-speed machine POWER. MP 207 ISO 5300 220 3013 PRESSURE RISE CAPAIUITY SINGLE STAGE AXIAL IIMITE0 TO AI0UT OS ill LOW SPEED RADIAL HAS CAPABILITY [e.g., 4400 rpm with a 1194-mm (47-ln.) diameter impeller], with a PRESSURE RISE TO 6IVE HIGH PRESSURE RISE machine envelope much greater than the aforementioned axial flow TWO STAGE AXIAL HAS CAPARILITY TO 0 JO pu I > 0.9 Mi) (APPRO < 2SX MARGIN A80VE OESIGN VALUE! variant. IIMI Df CONSTANT _ TIP tPEEO. FT/SIC ^ MM A / SPECIFIC iPfio / Nl - IM IM .iiNit or /CONSTANT _ ACCEPTAOlf \ / SPECIFIC OPERATING tag 1 1 MAMCTER,D> ENVELOPE » . •to \ \ X If. Ni - lit REGIME FOR •"•^«_JLt*—• - HION EFFICIENCY VI S\\\/ A it}* • DESICN DATA OPERATION ^^^ \S \N| —»"It-— YV Jih. I ••* — DEPflESSURIZEO OPERATION — W - 1.36 LB/SEC — T - 240«F «M^^*A,/\ yWn ta — P m - 14 »si M 0 ~ «M 4^T~ \^Jk y\ X / / / — A» - 0.71 psi iV /An uoo -5^ 3r^/ \ *'** "\^*>f^t^ \ una ~^T \S\jt ,218 1 SPEED "Z^^^C \ OUTIET M ANGll (Jj - Mat—^^\ S« CCOMITRV IIUCTU INSTRUMENTATION WlfMACE COOUNG WATER INTERFACE ION -«*C FOR UVOUT IOISERVINS MACHINE ENVELOPE RESTRAINT) Fig. 14 Initial 2 Stage Axial Flow Shutdown Cooling Circulator Concept For concept layouc pucpoaes a machine was selected with an impeller Fig, 15 Parametric Array for Radial Compressor diameter of 965 om (38 in.) and a rotational speed of 5400 rpm. From Fig. 15 it can be seen that this selection is still within the accept two-stage axial compressor (since it involves considerable extrapolation able envelope, although slightly outside of the maximum efficiency from the proven FSV impeller), and (2) it takes full advantage of -he island (Fig. 3). Such a radial compressor has the potential for at good European experience with radial flow compressors in gas-cooled least a 251 in pressure rise. reactors. 4.4. REFERENCE COMPRESSOR DESIGN Detailed aerod} lamic design of the radial flow compressor remains to be done, but sufficient analyses and design work have been performed There were essentially two factors that led to the selection of the to identify the major parameters and features. A representative layout radial flow machine: (1) the desire to avoid using a high tip speed, of the circulator is shown on Fig. 16. Striving for maximum efficiency 128 TABLE 11. MAJOR PARAMETERS FOR SHUTDOWN COOLING CIRCULATOR • RADIAl FLOW COMPRESSOR SHUTOFF VALVE (OKN) • IMPELLER DIAMETER 38.0 IN. (965 mml j VERY SIMILAR TO THTR (COONTERWEIGHTEO TO • ROTATIONAL SPEED 5400 RPM J WANT CIRCULATOR CtOSE) HOW FROM SCS HEAT EXCHANGER • TIP SPEED 895 FT/SEC (273 m/SEC) • CONSERVATIVE STRUCTURAL DESIGN • PCWER 220 HP (164 kW(»l] • CONSERVATIVE AERODYNAMIC LOADING COULD ACCOMMODATE UP TO 25% INCREASE IN CIRCUIT RESISTANCE • DESIGN NOT OPTIMIZED FOR MAXIMUM EFFICIENCY (MACHINE USE WILL BE INTERMITTENT DURING PLANT LIFE) BUT RATHER FOR MINIMUM ENVELOPE • OVERALL MACHINE OIAMETER 4 FT (1.23 m) • OVERALL MACHINE LENGTH 9.6 FT (2.93 ml • MACHINE ASSEMBLY CAN BE READILY REMOVED AND REPLACED IN SPACE AVAILABLE 8EL0W REACTOR VESSEL • DESIGN BASED ON EXISTING AND PROVEN TECHNOLOGY • EXTENSIVE INDUSTRY EXPERIENCE FOR COMPRESSOR DESIGN AND FABRICATION INDUCTION 5. SUMMARY MOTOR ORIVE In surveying the over 200 circulators that are operational (or have MA6NFTIC THRUST operated) in gas-cooled reactors, a variety of impeller types (radial, •EARING mixed, and axial flow) and drives (electric motor, steam turbine) can be CATCHER observed. In the case of applications involving the p'unoing of dense MOTOR CAVITY carbon dioxide (i.e., ACR plants), or helium in HTRs with a high circuit PRESSURE BOUNDARY resistance (i.e., pebble bed reactor), the choice of a radial flow com pressor is quite clear. This paper has addressed the choice of compres Fig. 16 Radial Flow Shutdown Cooling Ci -culator Concept sor type for the MHTGR with a low circuit resistance characteristic of the prismatic core. The following results were obtained from the circulator design studies; is not a strong requirement for this machine, since its service will be • Axial Flow Compressor Well Suited :ror Main Circulator intermittent, and will be called upon to operate in the rare event that the main loop is unavailable. Major parameters for the selected machine Impeller similar to FSV compressor which performs well. are given on Table 11. Near or optimum for maximum efficiency. Has pressure rise growth potential. TABLE 12. COMPRESSOR AERODYNAMIC PARAMETERS/NOMENCLATURE Well suited to pressure loss in prismatic reactor. c BLADE CHORD V INLET VOLUMETRIC FLOW, FT3/SEC Conservative aerodynamic and structural loading. D IMPELLER DIAMETER. FT • V» AXIAL GAS VELOCITY, FT/SEC SPECIFIC DIAMETER, D. HAD°"/V» FLOW COEFFICIENT ". v»/um Sifeple machine with no variable geometry tenures. °m« MAXIMUM DIFFUSION FACTOR P INLET GAS DENSITY, LB/FT3 Had ADIABATIC HEAO, AP/p FT-LB/LB • Ap PRESSURE RISE, LB/IN.2, LB/FT2 Good surge margin over wide flow range. N ROTATIONAL SPEEO, RPM qad HEAO COEFFICIENT Selected flow direction through impeller results in thrust «• SPECIFIC SPEED, N • v'v/Had0'* P| INLET PRESSURE, LB/IN.2 W loading partially offsetting rotor weight (eases thrust S BLADE SPACING MASS FLOW, IB/SEC c/s SOLIDITY T1 INLET TEMPERATURE, °F bearing requirements). u BLADE TIP SPEED, FT/SEC AH ENTHALPY RISE, Btu/IB "m MEAN BLADE SPEEO, FT/SEC AH/Un, TEMPERATURE RISE COEFFICIENT * Radial Flow Compressor Ideal for Shutdown Cooling Circulator 9 ACCELERATION DUE TO GRAVITY, FT/SEC2 J MECHANICAL EQUIVALENT OF HEAT, FT-IB/Btu Cp SPECIFIC HEAT, Blu/IB°F Established machine envelope facilitates ease of removal/ 'VARIABLE PARAMETERS IN AERODYNAMIC STUDIES replacement. Not optimised for nnnHmiim efficiency (machine has ACKNOWLEDGMENT intermittent service). The author would like to thank the U.S. Department of Energy for - Has pressure rise growth potential. approval to publish this work, which was supported by San Francisco Operations Office, Contract DE-AO03-84SFU963. - Simple straightforward small machine. - Conventional by industry standards. REFERENCES McDonald, C. F., M. K. Nichols, and J. S. Kaufman, "Helium Circula The compressor aerodynamic designs were performed using established tor Design Concepts for the Modular High-Temperature Gas-Cooled and validated computer codes. A high level of confidence exists that Reactor (MHTGR) Plant," paper presented at IAEA Circulator Special the compressors will perform as predicted. With the well-established ists Meeting, San Diego, California, December 1, 1987. technology base* the need for a compressor development program is not Baccagllni, G. C, et al., "Systems Engineering Requirements foreseen. A well-established vendor infrastructure exists for the Impacting MHTGR Circulator Design," Ibid. design and fabrication of both machine types. The nomenclature is Fraser, W. M., "Trends in Design of Blowers for Gas-Cooled Re.ic- included on Table 12. tors," Paper 12, in Proceedings of Institution of Mechanical Engi neers, Vol. 181, 1966-67, pp. 120-128. U. "Rotating Machinery for Gas-Cooled Reactor Application," United States Atomic Energy Commission Report TID-7631, April 1962. Goudy, L. J., and R. D. Teire, "The Development of Compressors and MAIN GAS CIRCULATOR FOR VG-400 REACTOR PLANT Drives for Gas-Cooled Reactors," in Proceedings of Symposium on Gas-Cooled Reactors," The Franklin Institute Monograph No. 7, May F.M. MITENKOV, V.I. KOSTIN, E.G. NOVINSKU, 1960, pp. 254-276. A.I. KUROPATOV, A.N. PROTSENKO, V.P. SMIRNOV, A. Ya. STOLYAREVSKIJ "Rotating Machinery for Gas-Cooled Reactor Application," United I.V. Kurchatov Institute of Atomic Energy, States Atomic Energy Commission Report TID-7690, November 1963. Moscow, Union of Soviet Socialist Republics Strub, R. A., "Gas Circulators for French Power Reactors," Paper 10, in Proceedings of Institution of Mechanical Engineers, Abstract Vol. 181, 1966-67, pp. 120-137. Principle parameters and operating conditions Thorn, J. D., et al., "Main Circulators," Journal of the British Nuclear Energy Society, 1963, pp. 165-172. of the main gas circulator (MGC) in 3r~400 reactor plan: Stoelzl, D., "Twenty-Five Years of Brown Boveri Experience in are presented. Development, Design, and Fabrication of Circulators for HTGR," Brief MG0 design deacription and experimental paper presented at IAEA Circulator Specialists Meeting, San Diego, California, December 1, 1987. work scope are given. Balje, 0. E-, "A Study of Design Criteria and Matching of Turbo- machines," ASME Journal of Engineering for Power, January 1962, pp. 103-114. 1. INTRODUCTION Brey, H. L., "For. St. Vrain Circulator Operating Experience," paper presented at IAEA Circulator Specialists Meeting, San Diego, Important design features of 3r~400 reactor California, November 30, 1987. "Aerodynamic Design of Axial Flow Compressors," National Aeronau plant are integral lay-out of the main primary circuit tics and Space Administration Publication, NASA SP-36, 1965. components in a preatre3sed concrete reactor vessel and Howell, A. R., "Fluid Dynamics of Axial Compressors," Proceedings helium coolant use /!/. Main gas circulator is one of of Inst, of Mech. Engineers, Vol. 153, 1945. Lieblein, S., et al., "Diffusion Factor for Estimating Losses and the key plant components, effecting the reactor lay-out Limiting Blade Loadings on Axial Flow Blade Compressor Elements," and its long availability. iatlonal Advisory Committee for Aeronautics Report NASA RM E53D01, Pour MGCa are allowed in the reactor plant. -^53. Circulators are high energy consumption components - up McDonald, C. F., and M. K. Nichols, "Helium Circulator Design Con siderations for Modular High-Temperature Gas-Cooled Reactor Plant," to 5% of the plant rating, due to high circulator capa ASME Paper No. 87-GT-138, 1987. city. That is why the choice of the optimum circu lator gas path configuration substantially effects both