HELIUM CIRCULATOR DESIGN CONSIDERATIONS FOR MODULAR …

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GA-A--18566

DE87 003847

HELIUM CIRCULATOR DESIGN CONSIDERATIONS FOR MODULAR HIGH

bY C. F. McDONALD and M. K. NICHOLS

This is a preprint of a paper to be presented at the 32nd International Gas Turbine Conference, May 31 through June 4, 1987, Anaheim, California, and to be published as an ASME Paper.

Work supported by Department of Energy

Contract DE-AC03-84SF11963 T h i s document is

GA PROJECT 6300 DECEMBER 1986

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

HELIUM CIRCULATOR DESIGN CONSIDERATIONS FOR

MODULAR H I G H TEMPERATURE GAS-COOLED REACTOR PLANT

C o l i n F. McDonald and Michael K. Nichols

GA Technologies Inc .

San Diego, C a l i f o r n i a

AESTR. LCT

: f f o r t s are i n p r o g r e s s t o develop a s t a n d a r d m d u l i r h i g h tempera ture gas-cooled r e a c t o r (MHTGR) p l a n t t h a t is amenable t o d e s i g n c e r t i f i c a t i o n and s e r i a ! product ion . The MHTGR r e f e r e n c e des ign , based on a itearn c y c l e power convers ion system, u t i l i z e s a 350 MJ(t) a n n u l a r r e a c t o r c o r e w i t h p r i s m a t i c f u e l e l e m e i t s . F l e x i b i l i t y in power r a t i n g is a f f o r d e d by u t i 1 i : i n g a m u l t i p l i c i t y of t h e s tandard module. The c i rcu!a tor , which is an e l e c t r i c motor-driven helium comprssor, is a key component i n t h e primary system of t h e ni tc lear p l a n t , s i n c e it f a c i l i t a t e s thermal energy t r a n s ' e r from t h e r e a c t o r c o r e t o t h e s team g e n e r a t o r ; and, 'rence, t o t h e e x t e r n a l tu rbo-genera tor set . This paper h i g h l i g h t s t h e he l ium c i r c u l a t o r des ign cons ider - a t i o n ; f o r t h e r e f e r e n c e MHTCR p l a n t and i n c l u d e s a d i s c u i s i o n on t h e major f e a t u r e s of t h e turbomachine concei t t , o p e r a t i o n a l characteristics, and t h e technol - ogy bitse tha t e x i s t s i n t h e U.S.

AGR AVR CAD FSV HTGR I A IS1 MHTGR NASA NSSS PCRV THTR U.K. D

D S

g Had J N

NOMENCLATURE

advanced gas-cooled r e a c t o r Arbe i t sgemeinschaf t Versuchsreaktor computer a ided des ign F o r t S t . Vrain h i g h tempera ture gas-cooled r e a c t o r i n t e g r a t e d approach i n - s e r v i c e i n s p e c t i o n modular h i g h tempera ture gas-cooled r e a c t o r N a t i o n a l Aeronautics and Space Adminis t ra t ion n u c l e a r s team supply system p r e s t r e s s e d c o n c r e t e r e a c t o r v e s s e l Thorium Hochtemperatur Reaktor United Kingdom compressor t i p d iameter , m ( f t )

D. Had' 25 s p e c i f i c diameter

dV a c c e l e r a t i o n due t o g r a v i t y , m / s 2 ( f t / s 2 ) a d i a b a t i c head, m ( f t ) mechanical e q u i v a l e n t of h e a t , f t - l b / B t u r o t a t i o n a l speed , rpm

N . 6 S p e c i f i c speed - Had*75

compressor i n l e t p r e s s u r e , MF'a(psia) head c o e f f i c i e n t mean b lade speed, m/s ( f t l s ) compressor i n l e t vo lumetr ic f low, m 3 / s

( f t 3 I s ) a x i a l v e l o c i t y f low c o e f f i c i e n t en tha lpy r i s e a c r o s s compressor, k J / k g ( B t u l l b ) tempera ture r i s e c o e f f i c i e n t p r e s s u r e r i s e a c r o s s compressor, kPa ( p s i ) c o n s t a n t (3.1416)

1. INTRODUCTION

The MHTGR program is a c o o p e r a t i v e government- i n d u s t r y e f f o r t t o develop an i n n o v a t i v e , advanced, second g e n e r a t i o n n u c l e a r power p l a n t t h a t is s a f e , r e l i a b l e , and economical, w i t h minimal r i s k t o t h e ovner; and, w i t h g r e a t l y improved p u b l i c acceptance . P u b l i c concerns have focused on t h e p o t e n t i a l f o r a c c i - d e n t s w i t h r a d i a t i o n consequences t o nearby communi- t ies , on e s c a l a t i n g power c o s t s , and on waste d i s p o s a l impacts on t h e environment. I n d u s t r y concerns have focused on t h e enormous s i z e of a u t i l i t y ' s investment burden i n l a r g e n u c l e a r p r o j e c t s , on u n c e r t a i n t i e s a s s o c i a t e d w i t h p r o j e c t schedules and c o s t s , and on u n c e r t a i n t i e s i n load demands. The MHTGR program addresses a l l o f t h e s e concerns , wi th p a r t i c u l a r emphasis on meeting p r o j e c t e d u s e r requirements. The MHTGRs t o l e r a n c e t o wi ths tand h igh tempera tures and i ts i n h e r - e n t l y h i g h thermal i n e r t i a has been e x p l o i t e d t o des ign a r e a c t o r sys tem t h a t e l i m i n a t e s i t s r e l i a n c e on a c t i v e engineered s a f e t y f e a t u r e s and o p e r a t o r a c t i o n s . The MHTGR i s p a s s i v e l y s a f e and e x h i b i t s benign or q u i e s - c e n t c h a r a c t e r i s t i c s .

This paper b r i e f l y addresses t h e des ign cons idera- t i o n s f o r t h e helium c i r c u l a t o r f o r t h e MHTGR. The c i r c u l a t o r i s an e l e c t r i c motor-driven helium compressor t h a t f a c i l i t a t e s thermal energy t r a n s f e r from t h e r e a c t o r c o r e t o t h e steam genera tor by c i r c u l a t i o n of helium i n t h e primary c i r c u i t . I n t h e MHTGR, t h e c i r - c u l a t o r is not a s a f e t y - r e l a t e d component. The helium

c i r c u l a t o r concept , s e l e c t e d f o r more d e t a i l e d des ign , has taken advantage o f i n t e n s i v e c i r c u l a t o r s t u d i e s performed f o r t h e RTGR program over t h e l a s t twu decades, an e s t a b l i s h e d technology base (which is d i s - cussed i n t h i s paper ) , and proven c i r c u l a t o r f e a t u r e s fron: a u t i l i t y opera ted HTGR p l a n t . Advantage has been taken of an emerging t r i b o l o g y technology, namely active magnetic bear ings , t o e s t a b l i s h a des ign concept i n which t h e p o s s i b i l i t y of l u b r i c a n t i n g r e s s i n t o t h e r e a c t o r primary sys tem has been obvia ted .

The c i r c u l a t o r f o r t h e MHTGR is i n s t a l l e d i n one of t.ie two ( j u x t a p o s i t i o n e d ) s t e e l v e s s e l s t h a t , when coupled with a c o a x i a l d u c t , forms t h e nuc lear s team supply system. The hel ium compressor, t o g e t h e r wi th t h e ,klectric motor d r i v e , is submerged i n t h e r e a c t o r p r i m t r y sys tem ( i . 0 . no d r i v e - s h a f t p e n e t r a t e s t h e s t e e l v e s s e l ) . S i n c e t h e c i r c u l a t o r is an i n t e g r a l p a r t of t h e r e a c t o r primary system, a b r i e f d e s c r i p t i o n of ttie modular MHTGR is included. The MHTGR is i n t h e e a r l ? d e s i g n s t a g e and t h i s paper h i g h l i g h t s t h e major desi::n c o n s i d e r a t i o n s ( i n c l u d i n g compressor aero- dynainics, mechanical des ign , bear ings , motor d r i v e , and mach:ine o p e r a t i o n ) f o r t h e c i r c u l a t o r . The c i r c u l a t o r is rtigarded a s s t a t e - o f - t h e - a r t technology; and, i n t h e desi;:n p r o c e s s , advantage has been t a k e n from t h e oper- a t i n ] : exper ience of t h e a x i a l f low c i r c u l a t o r (Fig- u r e .) i n t h e F o r t S t . Vrain p l a n t . As w i l l be out - l ine i l i n la ter s e c t i o n s , t h e MHTGR c i r c u l a t o r r e f l e c t s chan1;es from t h e F o r t S t . Vra in u n i t i n t h e a r e a s of comp:'essor d r i v e (electric motor i n s t e a d of s team t u r - b i n e and bear ings ( a c t i v e magnetic bear ings i n s t e a d of wa te i ' l u b r i c a t i o n ) . These changes were p r i m a r i l y made t o s : .mplify t h e machine arrangement and t o ensure t h a t h i g h a v a i l a b i l i t y g o a l s a r e me t .

Fig. 1. Helium C i r c u l a t o r f o r Fort S t . Vrain P lan t

2. MITGR PLANT CONCEPT

1 d e s c r i p t i o n of t h e MHTGR has been presented pre- v i o u s l y (1); t h u s , on ly t h e major f e a t u r e s a r e high- light.:d here . The r e f e r e n c e MHTGR p l a n t c o n s i s t s of four i d e n t i c a l 350 M W ( t ) r e a c t o r modules and two turbo- gener . i to r s e t s t o achieve a p l a n t ou tput of 558 MW(e). The f , , l lowing d i s c u s s i o n d e s c r i b e s an i n d i v i d u a l modul,:.

2

The primary system components a r e contained i n two s t e e l v e s s e l s , a s shown on Figure 2. These j u x t a p o s i - t ioned v e s s e l s a r e connected by a c o a x i a l CKOSS duct and t h e e n t i r e nuc lear s team supply system (NSSS) i s i n s t a l l e d i n a below grade s i l o . The c o r e , r e f l e c t o r , and a s s o c i a t e d suppor ts and r e s t r a i n t s a r e loca ted i n t h e r e a c t o r v e s s e l . The r e a c t o r i s an assemblage of p r i s m a t i c g r a p h i t e b locks , s tacked on a support s t r u c - t u r e . The a c t i v e r e a c t o r c o r e has an annular geometry. Cont ro l rods , which o p e r a t e i n t h e s i d e r e f l e c t o r i n n e r and o u t e r reg ions , a r e d r i v e n by mechanisms loca ted i n p e n e t r a t i o n s above t h e r e a c t o r v e s s e l . The f u e l e l e - ments i n t h e annular c o r e a r e s i m i l a r t o those used i n t h e F o r t S t . Vrain HTGR power p l a n t .

LSTEAM I GENERATOR

Fig. 2. E leva t ion V i e w of Nuclear Steam Supply System f o r MHTGR

The steam g e n e r a t o r , which has as i t s major component a h e l i c a l tube bundle, is contained and supported i n a s e p a r a t e s t e e l v e s s e l . The main helium c i r c u l a t o r i s a var iab le-speed , e l e c t r i c motor dr iven a x i a l f low compressor; and, is mounted above and i n l i n e with t h e steam genera tor . A r e a c t o r shutdown cool ing system, which c o n s i s t s of a small hea t exchanger and c i r c u l a - t o r , is loca ted i n t h e lower p o s i t i o n of t h e r e a c t o r v e s s e l .

The gas flow p a t h w i t h i n t h e i e a c t o r c i r c u i t i s as fol lows. During normal o p e r a t i o n , helium flows down- ward through t h e annular p i i s m a t i c r e a c t o r c o r e ; and, from t h e core o u t l e t plenum, t h e hot helium i s t r a n s - por ted , v i a t h e inner s e c t i o n of t h e c o a x i a l duct-, t o

t h e steam g e n e r a t o r v e s s e l . The gas flows down, over t h e i e l i c a l bundle , counter t o t h e upflowing water / stean i n s i d e t h e s team genera tor tubes . The cooled gas l e a v s s t h e s team g e n e r a t o r bundle a t t h e bottom and f lows upward, i n an annular passage (surrounding t h e stean g e n e r a t o r o u t e r shroud) , t o t h e top mounted c i r - c u l a r o r . The c i r c u l a t o r d i scharges hel ium (now a t t h e h i g h s s t p r e s s u r e i n t h e system) t o t h e plenum a t t h e t o p ,f t h e steam g e n e r a t o r v e s s e l . The f low is t h e n r o u t s d through t h e o u t e r annulus of t h e c o a x i a l duct t o t h e Lower p o r t i o n of t h e r e a c t o r v e s s e l . The gas then f lows upward, through t h e passages i n t h e o u t e r graph- i t e r e f l e c t o r , t o t h e t o p of t h e c o r e , where it is t u r n s d r a d i a l l y inward; and, then , down through t h e c o o l m t channels i n t h e p r i s m a t i c f u e l e lements; t h u s , complet ing t h e primary c i r c u i t loop.

3. iELIUH CIRCULATOR REQUIREMENTS

The I n t e g r a t e d Approach is being used i n t h e development o f t h e des ign and des ign documentation f o r t h e WTCR. It is an organized and s y s t e m a t i c development of p l a n t f u n c t i o n s and requirements , determined by top-iown d e s i g n performance and c o s t t r a d e - o f f s t u d i e s and ana lyses , t o d e f i n e t h e o v e r a l l p l a n t systems, sub- systems, components, and human a c t i o n s . This approach is aimed a t c o n t i n u a l l y d r i v i n g t h e requirements t o a p o i n t where a procurement s p e c i f i c a t i o n can be prepared f o r each component; i n t h i s case, t h e c i r c u l a t o r . The a c t u a l requirements f o r t h e c i r c u l a t o r r e p r e s e n t a com- prehens ive l i s t i n g ; and, Table 1 sunnnarizes t h e s a l i e n t requirements . These have formed t h e b a s i s f o r t h e c i r - cu la t o r des ign .

TABLE 1 CIRCULATOR SALIENT REQUIREMENTS

LIESIC MIFEATURES

cincu . m n OPERI T l O l

HAVE A8111TV TO PERFORM REOUIREO SURVflLLAlCE AN0 IS1 TO THE GREATEST ExnnT PRACTICAL WITH MACUIME o s i n A m i n i

* CIRCULATOR ASSEMBLY OESlGl m FAClllTATt REMOVAL A I 0 REPLILEEMEIT

* MEET P L A l l AVAILABILITY REOUlRfMElTS i_ 1008 FULL POWER IIOURS PER YEAR

n-880 31

4 . IIELIUM CIRCULATOR DESIGN

4 .1 . Compressor Aerodynamic Design

Based on t h e aforementioned requirements , ana lyses were Performed t o e s t a b l i s h a compressor geometry t h a t meet:; t h e systems performance. The c i r c u l a t o r boundary

3

c o n d i t i o n s a r e noted on t h e nuc lear s team supply s y s t e - hea t ba lance (diagram shown i n F igure 3 ) . A quick com- p u t a t i o n i n d i c a t e d t h a t a s i n g l e s t a g e a x i a l f low com- p r e s s o r represented a p r a c t i c a l s o l u t i o n . A slow-speed c e n t r i f u g a l compressor would not be aerodynamical ly a t t r a c t i v e and would e x h i b i t a very l a r g e d iameter . A c o n f i g u r a t i o n wi th only two b lade rows was s e l e c t e d wi th t h e r o t o r s ahead of t h e s t a t o r ; t h u s , e x h i b i t i n g a degree of r e a c t i o n between 50% and 100%. I n t h i s b l a d - ing arrangement (wi thout i n l e t and e x i t s w i r l ) t h e r o t o r s impart t h e energy i n t o t h e g a s , i n t h e form of v e l o c i t y ; and, t h e t r a i l i n g s t a t o r s recover t h i s energy by r e t u r n i n g t h e gas v e l o c i t y t o a x i a l . This b lad ing approach, demonstrated s u c c e s s f u l l y i n t h e F o r t . S t . Vrain c i r c u l a t o r , has t h e fo l lowing advantages: (1 ) minimizes number of p a r t s ; ( 2 ) reduced r o t o r weight ; (3 ) reduced bear ing span; ( 4 ) good e f f i c i e n c y i n hel ium environment, s i n c e Mach number e f f e c t s a r e not a f a c t o r ; and, (5) f low c o n t r o l f a c i l i t a t e d by speed change, r a t h e r t h a n by v a r i a b l e i n l e t guide vanes.

Fig. 3. Nuclear s team supply system hea t balance diagram f o r one 350 M W ( t ) MHTGR module

An i n i t i a l assessment showed some s i m i l a r i t y between t h e des ign c o n d i t i o n s f o r t h e MHTGR compressor and t h e For t . S t . Vrain c i r c u l a t o r (2). The requi red p r e s s u r e r i s e was near i d e n t i c a l f o r t h e two machines, bu t t h e h igher gas d e n s i t y i n t h e MHTGR y i e l d s a much reduced a d i a b a t i c head. A pre l iminary aerodynamic des ign of t h e compressor was performed us ing a computer code developed by GA Technologies based on w e l l e s t a b - l i s h e d des ign methods, such a s those presented i n NASA SP-36 (5). A summary of t h e major aerodynamic d a t a i s g iven on Table 2 . A t t h i s e a r l y s t a g e of t h e des ign , paramet r ic s t u d i e s of t h e major v a r i a b l e s were not con- ducted; b u t , r a t h e r , a des ign was s e l e c t e d t h a t had a c c e p t a b l e aerothermal and s t r u c t u r a l loadings . Since t h e compressor i n t h e For t S t . Vrain c i r c u l a t o r has e x h i b i t e d a t t r a c t i v e performance c h a r a c t e r i s t i c s , t h e i n i t i a l geometr ies s e l e c t e d f o r t h e MHTGR r e f l e c t a high degree of s i m i l a r i l y , a s i l l u s t r a t e d on Table 3 . A simple c a l c u l a t i o n of s p e c i f i c speed ( N , ) and s p e c i - f i c diameter ( D s ) ; parameters , which a r e i n d i c a t i v e of aerodynamic acceptance ( 4 ) , showed t h e des ign to be i n t h e regime of high e f f i c i e n c y f o r a s i n g l e s t a g e a x i a l flow compressor, as shown on Figure 4 . Addi t iona l p o i n t s shown on t h i s a r r a y a r e f o r o t h e r s i n g l e s t a g e a x i a l f low c i r c u l a t o r s t h a t w i l l be d iscussed i n a l a t e r s e c t i o n covering technology bases .

I O

B -

1 -

D

d E 9 " L - -

. I -

1 -

TABLE 2 ASROTHEWDYNAMIC PARAMETERS FOR HELIUM COMPRESSOR 0 OELYARVA HlGR ClRCULImR

I -

- DESIGN OATA

I IELIUM FLOW RATE. KGISEC IlBlSECl

INLET TEMPERATURE. "CPFI

I NLET PRESSURE, MR IPSIAI

I:IR~ULATOR PRESSURE RISE, KR IPSIOI

I ww CONTROL

ilDlABATlC HEAD. M IFTI I IIFFUSER EFFICIENCY, %

I IIFFUSER AREA RATIO

I IVERALL EFFICIENCY. % 1TOlAL.TO.STATICI

IlOTOR SHAFT POWER, KWdHP)

I OMPRESSOR TIP OIAMETER. MM 1lN.l I:LAOE HEIGHT, MM 11N.l I IUBlTlP RATIO

'I I P SPEED. MlSEC IFTlSECl

I>XIAL VELOCITY, MlSEC IFTISECI

I DTATlONAl SPEED. R P M

I LOW COEFFICIENT, VnIUm I IEAN ROTOR SOUOllV I mOR ASPECT RATIO

I IEAN ROTOR MACH NUMBER

I OTOR DIFFUSION FACTOR I M A X I

I EGREE OF REACTION

1 EMPERATURE RISE COEFFICIENT. 3 U J m 2

! PEClFlC SPEED. Ns ! PEClFlC DIAMETER. Os

I EA0 COEFFICIEMT. HsdlU'lg

I ESlGM TECHNOLOGY

PARAMETER

158 13481 255 14911

6.29 19121

91 113.21

VARIABLE SPEED ORWE

1618 153091

80

0.35 80

3210 143021

889 135.01 88.9 13.51

0.80

289 19471

125 14111

6200

0.48

0.31

1.66

0.21

0.42

0.85

0.29

311

0.80 0.13

NOT OPTIMIZE0

H--8E 014)

With o p e r a t i o n i n a h igh p r e s s u r e environment, b l a d e gas bending s t r e s s is an important c o n s i d e r a t i o n and, r o t o r and s t a t o r stress l e v e l s were s e l e c t e d t h a t are commensurate w i t h t h e f u l l , 40 y r , l i f e t i m e requirement . The b l a d e t i p speed of l e s s t h a n 1000 f t l sec is modest compared w i t h modern compressor technol - ogy and is on t h e o r d e r of 2OX less t h a n t h e F o r t S t . Vra in c i r c u l a t o r t i p speed. The b lade s o l i d i t i e s ( i . e . r a t i o o f c h o r d l p i t c h ) s e l e c t e d a r e not n e c e s s a r i l y optimum; b u t , t h e y d i d y i e l d a mean r o t o r d i f f u s i o n of 0 .4C. which is on t h e conserva t ive s i d e and should result i n a compressor w i t h a c c e p t a b l e c h a r a c t e r i s t i c s (i.e., e f f i c i e n c y , s u r g e margin, etc.) . While not opt imized a t t h i s e a r l y s t a g e of des ign d e f i n i t i o n , t h e compressor concept is regarded a s being t e c h n i c a l l y sound and d e f e n s i b l e .

TABLE 3 AXIAL FLOW HELIUM CIRCULATOR COMPARISON

Fig. 4. Curve a r r a y showing s p e c i f i c speed and diameter r e l a t i o n s h i p for a x i a l f low compressor

4 . 2 . C i r c u l a t o r Mechanical Conf igura t ion

The c i r c u l a t o r assembly is i n s t a l l e d i n t h e top p lane of t h e steam genera tor v e s s e l , a s i l l u s t r a t e d on Figure 5 . The electric motor is submerged i n t h e sys- t e m and forms an i n t e g r a l p a r t of t h e compressor r o t o r . The r o t a t i n g assembly (F igure 6 ) is f u l l y f l o a t i n g on a set of a c t i v e magnetic bear ings , backed up wi th a set of a n t i f r i c t i o n c a t c h e r bear ings . The c i r c u l a t o r i s i n s t a l l e d wi th t h e compressor impel le r s e c t i o n extend- ing i n t o t h e s team g e n e r a t o r v e s s e l . Helium from t h e s team genera tor e x i t ( a t t h e system lowest tempera ture) e n t e r s t h e compressor, v i a a c y l i n d r i c a l s e c t i o n . Af te r compression, t h e gas e x i t s from t h e d i f f u s e r sec- t i o n and sweeps t h e upper p o r t i o n of t h e v e s s e l p r i o r t o e n t e r i n g t h e o u t e r annulus of t h e c r o s s duc t .

IMSlRUNE~lAlIOI IllElliACE INPIULl

YA61EllC RAOlAl BEAR110

COMPRESSOR smmn

H-64311)

F i g . 5 . Helium circulator assembly for MHTGR

4

OVEl IALL LENliTH

MAGNETIC r BEARING SPAN

I 9 2 IN.) 2 . 3 m

UPPER CATCHER BEARING

RADIAL MAGNETIC BEARING

AXIAL MAGNETIC BEARING

I- 8 8 9 MM OIA 4 135.00 IN. OIAI n-81 o(i31

RADIAL MAGNETIC BEARING LOWER CATCHER BEARING

AXIAL FLOW HELIUM COMPRESSOR

Fig. 6. C i r c u l a t o r r o t a t i n g machinery assembly

The c i r c u l a t o r assembly c o n s i s t s of t h e fo l lowing com )orients :

1. Electric mto r / compresso r r o t o r assembly. 2 . Compressor s t a t o r and d i f f u s e r assembly. 3 . E l e c t r i c = t o r s t a t o r and i n t e r n a l s t r u c t u r a l

4. Helium-to-water h e a t exchanger. 5 . Two r a d i a l and one double a c t i n g a x i a l ,

a c t i v e magnetic bear ings . 6. Two angular c o n t a c t ( r a d i a l - a x i a l ) . c a t c h e r

bear ings . 7 . Hermet ica l ly s e a l e d connec tors f o r e l e c t r i c

power, c o o l i n g water, helium b u f f e r , magnetic b e a r i n g c o n t r o l s and ins t rumenta t ion .

The c i r c u l a t o r / m o t o r c a v i t y is f i l l e d w i t h p u r i f i e d he l ium purge flow, a t a p r e s s u r e s l i g h t l y h i g h e r t h a n t h e r e a c t o r system. The r e s u l t a n t s m a l l f low through t h e l a b y r i n t h system prevents t h e primary c o o l a n t from e n t e r i n g t h e e l e c t r i c motor c a v i t y and contaminat ing t h e motor. magnetic b e a r i n g s is assured by t h e helium-to-water h e a t exchanger, which sur rounds t h e motor s t a t o r . When t h e machine is r o t a t i o n a l , two c o o l i n g f a n s ( i n t e g r a l l y mounted on t h e s h a f t ) g e n e r a t e helium f low through t h e motor, around t h e magnetic bear ings , and through t h e h e a t exchanger, where t h e hea t from e l e c t r i c a l and r o t o r windage l o s s e s is d i s s i p a t e d . The helium p r e s - S U L ~ is h igher t h a n t h e cool ing water . This a l l e v i a t e s the p o t e n t i a l f o r water i n g r e s s i n t h e u n l i k e l y event of a t u b e leak .

SUppOKtS.

Cooling of t h e motor and

Primary f l o w c o n t r o l is provis ioned by t h e v a r i - a b l e speed motor c a p a b i l i t y ; and, t h e c i r c u l a t o r i s r e q u i r e d t o o p e r a t e over t h e range of 310 rpm ( 5 % ) t o a maximum 6820 rpm (110%). Pre l iminary r o t o r dynamic a n a l y s e s have shown t h e assembly t o e x h i b i t s t i f f c h a r a c t e r i s t i c s ; namely, t h e maximum r o t a t i o n a l speed is below t h e f i r s t c r i t i c a l speed, by a c o n s i d e r a b l e margin.

Upstream of t h e compressor i m p e l l e r , a f l o w - a c t u a t e d check v a l v e is incorpora ted i n t h e c y l i n d r i c a l duc t . This v a l v e i s o l a t e s t h e h e a t t r a n s p o r t system from t h e r e a c t o r v e s s e l when t h e c i r c u l a t o r i s not o p e r a t i o n a l ( i . e . p r e v e n t s n a t u r a l c i r c u l a t i o n f low of h o t gas e n t e r i n g t h e steam g e n e r a t o r ) . The v a l v e con- s is ts of t w o s e m i - e l l i p t i c a l p l a t e s which a r e he ld open by t h e c i r c u l a t o r dynamic head; and, c l o s u r e i s e f f e c - t e d by g r a v i t y . A helium j e t mechanism, t o a s s i s t i n c l o s i n g t h e v a l v e ( a s a back-up), i s included i n t h e des ign . D e t a i l s of t h e c i r c u l a t o r mechanical des ign f e a t u r e s a r e g iven i n Table 4 .

TABLE 4 MECHANICAL DESIGN FEATURES OF HELIUM CIRCULATOR

AREA

MACHIRE LIFE, VEARS ASSEMBLY CONFIGURATION HmOR DRIVE R m O R WEIGHT, KG ILBSI SHAFT DIAMETER, MM IIY.1 RADIAL BEARING TYPE TURUST BEARllG TVPE MAX. THRUST LOAa K G (LEI AT 0 RPM AT 6200 RPM MAX. RADIAL LOAD, KG l lB l MAGNETIC BEARllG SPAN, MM 111.1 CATCHER BEARING GEDMETRV CATCHER BEARING MATERIAL CATCHER BEARING LUBRICATION OVERALL MACHINE ASSEMBLY DIAMETER. M IFTI OVERALL ASSEMBLY LENGTH, M IFTI OESIGN STATUS TECHNOLOGY STATUS

H-880l61

PARAMETER

40 SUBMERGED IN REACTOR SYSTEM VARIABLE SPEED SYNCHRONOUS MOTOR 1722 160001 222 18.751 ACTIVE MAGNETIC BEARINGS ACTIVE MAGNETIC BEARINGS

2955 165001 DOWN 5000 111 0001 DOWN 1182 17.0001 2337 1921 DUPLEX BALL BEARING METALLIC ORVFILM 2 4 18 01 3 66 112 01 PRECONCEPTUAL STATE OFTHE ART

4 . 3 . C i r c u l a t o r Bear ing(s ) System

I n t h e l a s t t h r e e decades, t h e d e s i g n e r s of c i r c u - l a t o r s f o r gas-cooled r e a c t o r s have had t h e o p t i o n of gas , o i l , or water l u b r i c a t e d bear ings . The use of gas b e a r i n g s i n HTGR p l a n t s o r t e s t f a c i l i t i e s has been l i m i t e d t o r a t h e r small machines: ( 1 ) Dragon, t h e p ioneer HTGR p l a n t i n t h e U.K. ( 5 ) ; and, ( 2 ) c i r c u l a - t o r s i n helium test loops ( 6 ) .

The mainstay of t r i b o l o g y f o r r o t a t i n g machinery i s o i l l u b r i c a t i o n f o r many types of bear ings . Circu- l a t o r s wi th o i l - l u b r i c a t e d bear ings have performed w e l l i n t h e fo l lowing gas-cooled r e a c t o r p l a n t s : ( 1 ) Peach B o t t o m 1 ( t h e f i r s t HTGR opera ted i n t h e U.S.); ( 2 ) t h e t w o German helium r e a c t o r s , AVR ( I ) , and THTR ( E ) , and t h e many carbon d ioxide cooled r e a c t o r s opera ted i n t h e U.K., (2). For t h e F o r t S t . Vrain p l a n t , water bear - ings and s e a l s were s e l e c t e d a s being compatible w i t h t h e s e l e c t i o n of s team t u r b i n e and p e l t o n wheel d r i v e s .

The emergence i n t h e e a r l y 1980s of a new and demonstrated technology i n t h e bear ing f i e l d , namely a system i n which t h e s h a f t i s l e v i t a t e d by a magnetic f i e l d and p o s i t i o n a l l y sensed and c o n t r o l l e d by an e l e c t r o n i c system, o f f e r s t h e des igner an a d d i t i o n a l

o p t i o n f o r new p l a n t des igns . magnet ic b e a r i n g system is t h a t it e l i m i n a t e s t h e pos- s i b f l i t y of sys tem contaminat ion by l u b r i c a n t i n g r e s s . Addi t iona l b e n e f i t s a r e h i g h l i g h t e d on Table 5 .

The major advantage of a

TABLE 5 ADVANTAGES OF ACTIVE MAGNETIC BEARINGS

IINLIMITEO BEARING SERVICE LIFE (NO CONTACT OR WEAR SURFACES) IllGH ROTATIONAL SPEED CAPABILITY I LlMlNATlON OF SYSTEM CONTAMINATION BY LUBRICANT INGRESS liEDUCED BEARING FRICTIONAL LOSSES i LlMlNATlON OF LUBRICATION SYSTEM AND COMPLEX SEALS \'IBRATION FREE OPERATION (ABILITY TO PASS CRITICAL SPEEDS) IUGNMENT AN0 BALANCING SIMPLIFICATION I:ONTINUOUS MONITORING OF ROTOR STATUS llEDUCE0 MAINTENANCE I'OTENTIAL FOR HIGH RELIABILITY

H-E 8017)

Act ive magnetic b e a r i n g s a r e w e l l understood (a t h r m g h l2) and, as w i l l be d iscussed i n t h e s e c t i o n on technology bases , have been deployed i n h igh speed i n d u s t r i a l r o t a t i n g machinery. The p r i n c i p l e is q u i t e b a s i c , as shown on Figure 7 ; namely, t h a t by us ing a s t a t i o n a r y e lec t romagnet ic ( s t a t o r ) and a r o t a t i n g f e r - rous m a t e r i a l ( r o t o r ) , t h e s h a f t is suspended i n a mag- n e t i c f i e l d whi le main ta in ing an a c c u r a t e p o s i t i o n under v a r y i n g loads and speeds. This can be accom- p l i s h e d g iven a smal l space (he l ium gap) between t h e s t a t o r and r o t o r and proper e l e c t r o n i c c o n t r o l of t h e electromagnet . I t is t h e i n t r o d u c t i o n of an e l e c t r o n i c c o n t r o l system, f o r real-time s e n s i n g and p o s i t i o n i n g of t h e s h a f t displacement , t h a t has made t h e a c t i v e magnet ic b e a r i n g system a r e a l i t y f o r a wide range of engineer ing a p p l i c a t i o n s .

ELECTROMAGNET

'POSITION SENSOR

H-731171

Fig. 7 . Magnetic bear ing - p r i n c i p l e of o p e r a t i o n s

The a c t i v e magnetic bear ings c o n s i s t of two f u l l y redundant c i r c u i t s , which inc lude s e n s o r s , e lectromag- n e t s , and e l e c t r o n i c c o n t r o l s . As shown on Figure 5 , p r o v i s i o n is made f o r accommodating both r a d i a l and

a x i a l loading i n t h e magnetic bear ing system. The t h r u s t b e a r i c g has adequate margin of overload c a p a c i t y t o r e a c t a l l g r a v i t a t i o n a l ( i n c l u d i n g s e i s m i c ) and aerodynamic a x i a l loads . Key elements i n t h e system a r e t h e e l e c t r o n i c s e n s i n g and c o n t r o l of t h e l e v i t a t - i n g s h a f t . u r e 8 . I n d u c t i v e s e n s o r s , used t o d e t e c t t h e exac t r a d i a l and a x i a l l o c a t i o n of t h e r o t o r , p rovide p o s i - t i o n feedback t o t h e c o n t r o l e l e c t r o n i c s . As with t h e b e a r i n g s , t h e s e n s o r s r e q u i r e a f e r r o u s r o t o r and a wound f i e l d s t a t o r . The s e n s o r s u t i l i z e t h e hel ium gap between t h e r o t o r and t h e s t a t o r for t h e i r response s i g n a l genera t ion . As t h e hel ium gap i n c r e a s e s or d e c r e a s e s , t h e inductance of t h e sensor i n v e r s e l y changes. t i o n provides t h e p o s i t i o n s i g n a l requi red f o r c l o s e d loop servo c o n t r o l of t h e bear ing system. e l e c t r o n i c s a r e r e q u i r e d t o process t h e p o s i t i o n s i g n a l and power t h e a p p r o p r i a t e bear ing c o i l s . redundant magnetic bear ing systems a r e t o t a l l y sepa- r a t e d . One of t h e magnetic bear ing systems is s u p p l i e d v i a an u n i n t e r r u p t i b l e power supply , backed-up by b a t - teries, whi le t h e o t h e r sys tem is suppl ied from t h e p l a n t electrical power supply. n e t i c bear ing is a noncontact bear ing , some means mst be provided a s a backup t o ensure t h a t no harmful r o t o r - t o - s t a t o r c o n t a c t occurs i n t h e u n l i k e l y event t h a t bo th pr imary and secondary e l e c t r i c a l power sources are l o s t . The primary f u n c t i o n of t h e c a t c h e r bear ing sys tem is t o prevent mechanical c o n t a c t between t h e r o t o r and t h e s t a t i o n a r y p a r t s while r o t a t i n g , b u t they may be u t i l i z e d , on a l i m i t e d b a s i s , t o prevent c o n t a c t d u r i n g t r a n s p o r t a t i o n and i n s t a l l a t i o n . During normal machine o p e r a t i o n , t h e r o t a t i n g i n n e r r a c e s of t h e c a t c h e r b e a r i n g s a r e not i n c o n t a c t w i t h t h e b a l l bear ings and w i t h t h e o u t e r bear ing r a c e s , which a r e s t a t i o n a r y ( i . e . , t h e c a t c h e r bear ing hel ium gap is h a l f of t h e v a l u e i n t h e magnetic s e c t i o n ) . When t h e c a t c h e r bear ings a r e a c t u a t e d by t h e r o t o r drop, t h e i n n e r r a c e s move a x i a l l y causing c o n t a c t w i t h t h e b a l l s , which t h e n a c c e l e r a t e t o t h e i n n e r r a c e ve loc- i t y . The s m a l l mass i n e r t i a of t h e b a l l s a t t r i b u t e s t o minimum skidding; and, w i t h t h e use of a dry f i l m l u b r i c a n t on t h e b a l l s , damage is avoided. The mag- n e t i c bear ing system is regarded a s s t a t e - o f - t h e - a r t ; b u t , des ign v e r i f i c a t i o n (by t e s t i n g ) of t h e c a t c h e r bear ing system is necessary.

A schematic on t h i s a s p e c t i s given on Fig-

This v a r i a t i o n i n inductance wi th s h a f t loca-

Cont ro l

Two f u l l y

S ince t h e a c t i v e mag-

ELECTROllC

SVSTEM SVSTEM COlTROL ntnuinc

, ' IFA I I IYC .. .

SENSOR SIGNAL

H-731(91

Fig. 8. E l e c t r o n i c schematic diagram for magnetic bear ing system

4 .4 . E l e c t r i c Motor Drive

The helium compressor is dr iven by a v a r i a b l e speed e l e c t r i c mtor submerged i n a helium environment.

6

S t i d i e s l e d t o t h e s e l e c t i o n of a 3210 kW(e) (4302 hp) v a r i a b l e speed, n o n s a l i e n t p o l e , v e r t i c a l synchronous mo:or. I t has a b r u s h l e s s e x c i t e r t h a t embodies a s o l i d s t a t e r e c t i f i e r designed for v a r i a b l e speed oper- a t i o n . These s e l e c t i o n s were based p r i m a r i l y on con- s i t l e r a t i o n s of system performance and r e l i a b i l i t y . E f f i c i e n c y , power f a c t o r , and r o t o r dynamics were t h e m o ; t s i g n i f i c a n t sys tem performance parameters , and des ign and f i e l d o p e r a t i n g exper ience wi th s i m i l a r d r i v e systems were t h e r e l i a b i l i t y c o n s i d e r a t i o n s .

The motor speed c o n t r o l l e r ( l o c a t e d o u t s i d e t h e r e a c t o r system) is a s o l i d - s t a t e a d j u s t a b l e f requency p o m r supply w i t h output r a t i n g s compatible wi th motor o p s r a t i n g and s t a b i l i t y requirements over t h e e n t i r e spaed range. The synchronous motor and c o n t r o l system a r a regarded as s t a t e - o f - t h e - a r t and s i m i l a r t o equip- m e l t i n o p e r a t i o n (e .g . , l a r g e b o i l e r water feed pump d r l v e s ) . The r o t a t i n g d iodes , h e r m e t i c a l l y s e a l e d i n t h 2 s h a f t , are n o t perce ived a s a problem (a l though t h e d i r l e c t r i c c o n s t a n t in hel ium is a f a c t o r ) ; b u t , some detelopment may be requi red .

5 . CIRCULATOR OPERATION

A n impor tan t c o n s i d e r a t i o n i n t h e MHTCR p l a n t program has been t h e a t t e n t i o n given t o meeting t h e a v a i l - a b i l i t y goa ls . The most s i g n i f i c a n t d a t a base f o r c i c c u l a t o r performance and r e l i a b i l i t y is t h e gas- c o J l e d r e a c t o r exper ience in t h e U.K. where s e v e r a l m i l l i o n s o f o p e r a t i n g hours have been accumulated on suimerged electric motor d r i v e n c i r c u l a t o r s . I n r e c e n t y e a r s , t h e a v a i l a b i l i t y of t h e s e machines has been very high. As o u t l i n e d below, c o n d i t i o n m n i t o r i n g , main- t e i a n c e , and machine replacement f a c t o r s were consid- e rzd i n t h e des ign d e f i n i t i o n of t h e c i r c u l a t o r assembly.

5 . !. Condi t ion Monitoring

Advantage w i l l be taken of d i a g n o s t i c systems be tng developed f o r advanced i n d u s t r i a l and a i r c r a f t g a l t u r b i n e s where cont inuous monitor ing w i l l i n d i c a t e t h , ? c o n d i t i o n of t h e r o t a t i n g machinery. Instrumenta- t i , m w i l l i n c l u d e (1) acce lerometers f o r v i b r a t i o n de :ec t ion ; (2) measurement of c i r c u i t a c o u s t i c s ; (3) t empera tures i n v a r i o u s l o c a t i o n s ; ( 4 ) measurement

m e w s of f i b e r o p t i c devices ; and, ( 6 ) monitor ing f o r r a l i o a c t i v i t y i n t h e motor c a v i t y . t h t s e w i l l b e d i a g n o s t i c i n s t r u m e n t a t i o n i n suppor t of t h , magnetic bear ing system and e l e c t r i c motor d r i v e .

5 . 1 . C i r c u l a t o r Removal and Replacement

of t h e b lad ing performance; ( 5 ) v i s u a l observa t ion by

In a d d i t i o n t o

I f t h e machine d i a g n o s t i c system i n d i c a t e s t h a t a s e r e r e problem has developed, p r o v i s i o n has been made f o r complete removal and replacement of t h e e n t i r e c i r - c u l a t o r assembly, inc luding t h e shutof f va lve . The conple te c i r c u l a t o r assembly can be removed from t h e t o 3 of t h e s team g e n e r a t o r and i n s t a l l e d i n a l eak- t i s h t s h i e l d e d cask. With a crew of f o u r , it has been es:imated t h a t a c i r c u l a t o r assembly could be replaced i n 48 h a f t e r r e a c t o r shutdown and cooldown.

6 . CIRCULATOR TECHNOLOGY

S i g n i f i c a n t c i r c u l a t o r technology bases e x i s t from which t h e MHTGR can b e n e f i t , namely ( 1 ) d a t a and exper ience from o p e r a t i o n a l p l a n t s and ( 2 ) u t i l i z a t i o n of new and emerging technologies . In t h i s paper , i t is only p o s s i b l e t o h i g h l i g h t t h e technology bases ; par - t i c u l a r l y those i n t h e U.S., Federa l Republic of Ger- many, and t h e U . K . A comparison of f e a t u r e s f o r repre-

s e n t a t i v e contemporary c i r c u l a t o r s i s given i n Table 6 . The p o r t r a y a l of t h i s d a t a does not n e c e s s a r i l y imply t h a t p r i v a t e des ign know-how and technology from a l l t h e i n t e r n a t i o n a l sources i s a v a i l a b l e for a new pro- j e c t , bu t it does show t h a t a formidable c i r c u l a t o r d a t a base f o r t h i s component e x i s t s , and t h a t on ly minimal r e s e a r c h and development f o r t h i s component i s necessary f o r t h e next g e n e r a t i o n of gas-cooled reac- t o r s . below.

S i g n i f i c a n t technology bases a r e summarized

TABLE 6 CIRCULATOR DESIGN FEATURES COMPARISON

.... . 1 _ _ _ _ _ _ _ _ _ _ . I I "......I... I ".....,".., I n.c..l,"..,

6.1 . U.S. C i r c u l a t o r Technology

From t h e aerodynamic s t a n d p o i n t , t h e r e is a high degree of s i m i l a r i t y (shown on Table 3 ) between t h e For t S t . Vrain hel ium compressor and t h e MHTGR machine. The compressor r o t o r f o r t h e MHTGR main c i r c u l a t o r resembles t h e FSV compressor (F igure 9 ) , which has demonstrated good performance. The r o t a t i n g assembly ( w i t h e l e c t r i c motor d r i v e ) w i l l be s impler than t h e s team t u r b i n e d r i v e n FSV machine. The c i r c u l a t o r s i n t h e F o r t S t . Vrain p l a n t have opera ted f o r over a quar - t e r of a m i l l i o n hours and from t h e t r i b o l o g y s t a n d - p o i n t , t h e performance has been good; and, o p e r a t i o n has been f r e e from r o t o r v i b r a t i o n , and no damage has been done t o t h e w a t e r bear ings . I n t h e FSV p l a n t , t h e c i r c u l a t o r i s a s a f e t y - r e l a t e d component; and, t o ensure o p e r a t i o n of t h e machine under a l l p o s t u l a t e d events ( b o t h wi th t h e s team t u r b i n e and p e l t o n wheel d r i v e s ) , water must be p r e s e n t i n t h e bear ing c a r - t r i d g e . I n some c a s e s , t h e high water p r e s s u r e i n t h e bear ings has been incompatible wi th primary system con- d i t i o n s and water i n g r e s s has occurred. The FSV p l a n t c i r c u l a t o r s have e x h i b i t e d good performance and t h e aforementioned problems have been assoc ia ted wi th a combination of f a c t o r s involv ing t h e a u x i l i a r y systems, coupled loops , c o n t r o l complexi ty , and s a f e t y r e q u i r e - ments. The problems a r e a l l overcome i n t h e p r e s e n t design.

I n suppor t of commercial HTGR p l a n t development i n t h e mid 1970s, a f u l l s c a l e pro to type c i r c u l a t o r f o r t h e Delmarva p r o j e c t (13 t o E) was b u i l t and s u b j e c t e d t o l i m i t e d t e s t i n g t h a t v e r i f i e d t h e water and bear ing s e a l performance. The major f e a t u r e s t h a t were d i f f e r - e n t from FSV were (1) a dedica ted supply and dra inage system f o r each c i r c u l a t o r and, ( 2 ) i n c o r p o r a t i o n of a j e t pump a c t i v a t e d dra inage system to f a c i l i t a t e removal of water from t h e bear ing c a r t r i d g e .

In 1985 , a t h i r d gcnera t ion bear ing n n d s e a l cnr - t r i d g e w a s t e s t e d to address t h e water i n g r c s s proolern

7

wit11 t h e a d d i t i o n of a shaft-mounted pump and modif ica- tiolis t o t h e d r a i n and s e a l systems. t h e tests was p o s i t i v e , and it was concluded t h a t water bea : ings r e p r e s e n t a v i a b l e o p t i o n f o r follow-on c i r i :u la tors .

The outcome of

The two and one-half decades of c i r c u l a t o r activities. in suppor t of t h e l a r g e HTGR p l a n t s , rep. :esents a v a l u a b l e d a t a base f o r t h e MHTGR.

H-880116)

Fig. 10. Helium c i r c u l a t o r f o r German THTR-300 p l a n t ( c o u r t e s y of H R B )

B r i t i s h CO,, Magnox, and AGR s t a t i o n s . Many c i r c u l a t o r s (over 150) of v a r i o u s types ( c e n t r i f u g a l , a x i a l , and mixed f low) have been b u i l t f o r v e r t i c a l and h o r i z o n t a l i n s t a l l a t i o n s (submerged and e x t e r n a l

Fig. 9 . F o r t S t . Vrain hel ium c i r c u l a t o r r o t a t i n g machines) , and t h e accumulated opera t ing t i m e i s i n t h e millions of hours. Most of t h e B r i t i s h machines are designed f o r c o n s t a n t speed o p e r a t i o n wi th f low c o n t r o l

C i r c u l a t o r Technology in t h e Federa l Republic of by means of v a r i a b l e geometry i n l e t guide vanes (B t o Germany - 21) . A v e r t i c a l c i r c u l a t o r assembly f o r t h e Har t lepool

AGR is shown on Figure 12.

machinery showing a x i a l f low compressor

6 .2 .

The two small c i r c u l a t o r s i n t h e AVRI p l a n t have o i l - l u b r i c a t e d bear ings and t h e compressor is a s i n g l e c e n t r i f u g a l s t a g e . These machines wi th submerged e l e c - t r i c motor d r i v e s have opera ted w e l l f o r over 100,000 h and exper ience gained was appl ied t o t h e hel ium c i r c u - l a t c r s f o r t h e follow-on p r o j e c t .

The c i r c u l a t o r assembly f o r t h e THTR-300 p l a n t is s h o t n on Figure 10 and d e t a i l s a r e given i n Refer- ences 8 and s. The c i r c u l a t o r r o t o r , d r i v e motor wi th c o o l e r s and shut -of f and c o n t r o l va lve ( i n c l u d i n g i ts d r i v e ) , are i n t e g r a t e d i n one i n s e r t a b l e assembly. The s i n g l e - s t a g e r a d i a l compressor r o t o r is mounted on t h e motor s h a f t i n an overhung p o s i t i o n . The s h a f t bear - ings are l u b r i c a t e d and cooled by oil. The e lec t r ic motcr d r i v e is submerged i n a hel ium environment. A t t h e t i m e of w r i t i n g t h i s paper , t h e THTR-300 p l a n t has opera ted a t 100% power.

With s e l e c t i o n of a c t i v e magnetic bear ings f o r t h e MHTGR, a p a r t i c u l a r l y germane d a t a source is t h e s m a l l hel ium c i r c u l a t o r o p e r a t i n g i n a high temperature i n s u l a t i o n t e s t f a c i l i t y i n Germany (u). This c i r c u - l a t o r , w i t h a s i n g l e s t a g e a x i a l compressor, embodies a c t i v e magnetic bear ings and d e t a i l s a r e given on Table 6 ; and, t h e assembly is shown on Figure 11. Opera t ion of t h i s machine was i n i t i a t e d i n September 1982 and has opera ted s u c c e s s f u l l y f o r approximately l1,COO h. No f a i l u r e s in t h e magnetic bear ing system have occurred and t h e b a l l bear ing c a t c h e r system has not been deployed ( i . e . , no r o t o r drop has been expe r i e n c e d ) . 6.3. C i r c u l a t o r Technology i n t h e United Kingdom

The most e x t e n s i v e technology d a t a base f o r gas cooled r e a c t o r p l a n t c i r c u l a t o r s i s i n t h e U . K . , where Fig. 11. Opera t iona l helium c i r c u l a t o r with magnetic man) c i r c u l a t o r s have been b u i l t and operated f o r t h e bear ings ( c o u r t e s y of H R B )

a

H-810117l

Fig. 12. CO2 c i r c u l a t o r assemblies f o r Har t lepool AGR ( c o u r t e s y of James H o d e n and Company)

While t h e c i r c u l a t o r s i n t h e B r i t i s h r e a c t o r s a r e desjgned f o r o p e r a t i n g i n a carbon d ioxide environment, most a s p e c t s of t h e technology can be regarded a s a p p l i c a b l e f o r t h e MHTGR. imptoving machine r e l i a b i l i t y is very b e n e f i c i a l t o t h e MHTCR c i r c u l a t o r . For example, i n t h e Hinkley Poin t B AGR p l a n t , t h e t o t a l c i r c u l a t o r running hours is apptoximately one m i l l i o n , wi th over 62,000 h on t h e l e a d machine. The a v a i l a b i l i t y has been 99.4%. which means t h a t t h e c i r c u l a t o r s or t h e i r a n c i l l a r y system accounted f o r o n l y 0.6% loss of r e a c t o r ou tput , over t h e per iod 1978 t o 1985.

6.4.

Experience gained towards

I n d u s t r i a l Rota t ing Machinery Technology Transfer

The u t i l i z a t i o n of a c t i v e magnetic bear ings , i n high speed i n d u s t r i a l r o t a t i n g machinery, is an impor- t a n t d a t a base; p a r t i c u l a r l y n a t u r a l gas compressors (a to 25). where e l i m i n a t i o n of a l l contaminant i n g r e s s t o t h e p i p e l i n e system is important . Mult i - megawatt gas compressors, wi th l a r g e r o t o r s , have been r e t r o f i t t e d w i t h a c t i v e magnetic bear ings and have per - foraed s a t i s f a c t o r i l l y . An example of a h igh speed compressor (13,000 rpm), wi th about t h e same power requirement a s t h e MHTGR c i r c u l a t o r [approximately 4 Mk(e)] , embodying a c t i v e magnetic bear ings , is shown on Figure 13. Monitoring t h e progress of t h e s e h igh p r e s s u r e a p p l i c a t i o n s w i l l l i k e l y y i e l d d a t a t h a t could be b e n e f i c i a l t o hel ium c i r c u l a t o r s .

7. SUMMARY

While s t i l l in t h e conceptual des ign s t a g e t h e hel ium c i r c u l a t o r concept presented i n t h i s paper has a sound technology base , and has been conserva t ive ly

designed based on e s t a b l i s h e d p r a c t i c e . A high degree of confidence can be expressed regard ing meeting a l l of t h e demanding c i r c u l a t o r requirements , i n a c o s t - e f f e c t i v e manner.

The hel ium c i r c u l a t o r des ign concept o u t l i n e d h e r e was not designed i n an i s o l a t e d manner: r a t h e r , it was designed a s an i n t e g r a l p a r t of t h e p l a n t primary sys- t e m . The I A t h a t has been used is a s y s t e m a t i c method of ensur ing t h a t t h e evolv ing p l a n t and component des igns a r e guided by t o p - l e v e l economic and s a f e t y goa ls . The I A is a v a l u a b l e t o o l f o r e s t a b l i s h i n g and defending a well-developed nuc lear p l a n t design.

H--63911)

Fig. 13. C e n t r i f u g a l gas compressor wi th a c t i v e magnetic bear ings ( c o u r t e s y of I n g e r s o l l - Rand Company)

An o v e r r i d i n g c o n s i d e r a t i o n i n t h e des ign of t h e helium c i r c u l a t o r was t h e goa l of e s t a b l i s h i n g a s imple concept c o n s i s t e n t w i t h meeting t h e requirements , w i t h p a r a m u n t importance being placed on meeting a v a i l a - b i l i t y goa ls . The fol lowing p o i n t s were observed i n t h e c i r c u l a t o r des ign process:

1. The des ign embodies f e a t u r e s and c h a r a c t e r i s - t i c s t h a t have evolved from a c t u a l c i r c u l a t o r o p e r a t i n g exper ience ( b o t h p o s i t i v e and nega- t i v e c o n s i d e r a t i o n s . ) Where a p p r o p r i a t e , t h e des ign was made s impler . For example, a submerged e l e c t r i c motor d r i v e was adopted, t o avoid a s h a f t p e n e t r a t i o n through t h e v e s s e l and t h e a t t e n d a n t complex high p r e s s u r e s e a l s .

2 . Primary emphasis was p u t on machine a c c e s s i - b i l i t y f o r i n s p e c t i o n , r e p a i r , replacement , e t c . This is manifested i n c i r c u l a t o r i n s t a l l a t i o n on top of t h e s team g e n e r a t o r v e s s e l .

3. As a p p r o p r i a t e , f o r a second e r a nuc lear power p l a n t , new and emerging technologies were f a c t o r e d i n t o t h e design. An example of t h i s was t h e s e l e c t i o n of a c t i v e magnetic bear ings , t h i s being i n concer t wi th t h e goa l of e s t a b l i s h i n g a bear ing system t h a t obvi - a t e s l u b r i c a n t i n g r e s s i n t o t h e r e a c t o r c i r - c u i t , and has high r e l i a b i l i t y .

4. Design of the circulator was made with adher- ence to the fact that a significant worldwide technology base exists and should be taken advantage of.

In closing. the helium circulator concept presented in this paper is regarded as state-of-the-art, fron both design and technology standpoints. cycle MHTGR plant could be deployed in the near term (i.e.. mid 1990s) without a major need for fundamental research. Remaining key areas of emerging technology (for example, the use of magnetic bearings in the circulator) will require modest programs of design verifi- cation. As outlined by Dean (1). the key to near deployment of the MITGR is in international cooperative efforts; and, this would be particularly germane for the circulator.

8 . ACKNOWLEDGMENTS

The steam

The authors would like to thank the U.S. Depart- ment of Energy, for approval to publish this paper. Thanks are also expressed to the management of GA Tech- nologies Inc. for permission to write and present this circulator work, which was supported by the Department of Energy, San Francisco Operations Office Contract DE-A:03-84SF11963. inclasion of photographs of rotating machinery hard- ware, and the authors are appreciative to all concerned.

This paper has been enhanced by the

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REFERENCES

Dean, R. A. and Johnston, T. A., 1986, "Develop- ment of the Modular HTGR in the U.S.A.," Paper presented at ENC-6 Conference, Geneva, Switzerland. Yampolsky, J. S., 1971, "Circulators for Helium Cooled Reactors," Nuclear Engineering International. "Aerodynamic Design of Axial-Flow Compressors, " National Aeronautics and Space Administration Publication, NASA SP-36, 1965. Balje, 0. E., 1981, "Turbomachines - A Guide to Design, Selection, and Theory," Wiley-Interscience Publication. Van Z i j l , N. A., and Eggman, J., 1967, "Totally Enclosed Blowers with Gas Lubricated Bearings," Proceedings of Institution of Mechanical EnKineers, Vol. 181. Young, M. C., and A. 0. White, "Gas Bearing Circulators for High Temperature Gas-Cooled Reactor Component Flow Test Loop," ASME Paper No.

"The Circulators for the Julich Reactor," The Brown Boveri Review, JunelJuly 1963. Cramer, H. et al., 1972, "Components of the THTR 300 Heat Transfer System," Paper 38, Proceedings on Component Design in High Temperature Reactor Using Helium as a Coolant, Institution of Mechanical Engineers.

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Habermann, H., and Brunet, M., 1984, "The Active Magnetic Bearing Enables Optimum Damping of Flexible Rotor," ASME Paper No. 84-GT-117. Anton, E., and Ulbrich, M., 1985, "Active Control of Vibration in the Case of Asymmetrical High-speed Rotors by Using Magnetic Bearings," ASME Paper No. 85-DET-28. Habermann, H., and Brunet, M., 1985, "The Active Magnetic Bearing Enables Optimum Control of Machine Vibrations," ASME Paper No. 85-GT-221. Cavallaro, L. and Yampolsky, J., 1974, "Design and Development of a Steam Turbine Driven Circulator for High Temperature Gas-Cooled Reactors," Nuclear Engineering and Design, 26, pp. 135-157. Yampolsky, J., et al., 1972, "Design of Steam Turbine Driven Circulators for High Temperature Gas-Cooled Reactors," ASME Paper 72-WAINE-20. Barbat, V. J., et al., "Development of Steam Turbine Driven Circulator for High Temperature Gas-Cooled Reactors," ASME Paper 72-WAINE-21. "THTR-300 Coolant Gas Circulation Insertable Module," THTR-Kernkraftwerk Project Information 8, April 1975. "Facility for Fatigue Testing of Thermal Insulation," BBC Review, 6, Vol. 72, June 1985. Fraser, W. M. 1966-67, "Trends in Design of Blowers for Gas-Cooled Reactors," Paper 12, Proceedings of Institution of Mechanical Engineers, Vol. 181, pp. 120-128. Thorn, J. D. et al., 1963, "Main Circulators," Jousnal of the British Nuclear Energy Society,

Fraser, W. M., 1968, "The Submerged Circulator Unit for Gas-Cooled Reactors," Paper En-1/36, ENEA Symposium on the Technology of Integrated Primary Circuits for Power Reactors. Paris. "Howden in the Nuclear Power Station Industry," Howden Journal, No. 18, October 1980. Hustak, J., et al., 1985, "Active Magnetic Bearings for Optimum Turbomachinery Design," paper presented at Bently Nevada Symposium on Instability in Rotating Machinery, Carson City, Nevada. Schoeneck, K. A., 1985, "The Application of Gas Seals and Magnetic Bearings to Centrifugal Compressors," paper presented at Pacific Coast Gas Association Transmission Conference, Spokane, Washington. Foster, E. G., et-al.. 1986, "The Application of Active Magnetic Bearings to a Natural Gas Pipeline Compressor," ASME Paper No. 86-GT-61. Cataford, G. F., and Lancee, R. P., 1986, "Oil Free Compression on a Natural Gas Pipeline," ASME Paper No. 86-GT-293.

NO. 59 pp. 321-326.

pp. 165-172.

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