Report No. BMI-1396 UC-81 Reactors — Power (TID-4500, 15th ...

R e p o r t No. B M I - 1 3 9 6

U C - 8 1 R e a c t o r s — P o w e r ( T I D - 4 5 0 0 , 15th E d . )

Contract No. W-7405-eng-92

M L - l - l A C O R E S T U D I E S W I T H T H E G C R E C R I T I C A L A S S E M B L Y

b y

R i c h a r d A . E g e n W i l l i a m S. Hogan D av id A . D i n g e e J o e l W. C h a s t a i n

N o v e m b e r 27 , 1959

B A T T E L L E M E M O R I A L I N S T I T U T E 505 King A v e n u e

C o l u m b u s 1, Ohio

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.

TABLE OF CONTENTS

Page

ABSTRACT . . . . . . . . . . . . . . 1

INTRODUCTION 1

DESCRIPTION OF THE M L - l - l A CRITICAL ASSEMBLY. 2

Core S t ruc ture and Fue l -E l emen t Lat t ice 2

Fue l -E lemen t Construct ion 5

RESULTS OF EXPERIMENTS WITH THE M L - l - l A CRITICAL ASSEMBLY . . . 5

Cri t ical Core Configuration , 5 Reactivi ty Worth of P e r i p h e r a l Fuel E lements . 7 Power -Dis t r ibu t ion Measu remen t s 8 Flux-Dis t r ibut ion Measu remen t s 10 Latracell Flux Measure inen ts 13 Tempera tu re Coefficient of React ivi ty . . . . . . . . . . . . . . . . 13 Void Coefficients of Reactivi ty . . . . . . . ' 20 Reactivi ty Worth of M L - l - l A Mock-Up Control-Blade Assembly 22

FUEL-ELEMENT-REPLACEMENT STUDIES 22

lA Fue l -E lemen t Studies 22 GCRE-1B-10T Fue l -E l emen t Studies 27

Power -Dis t r ibu t ion Measuremients . . . . . . . . . . . . . . . 27 Flux Measu remen t s 29

DISCUSSION 31

Cri t ical Configurat ion, 31 Resul t s of Flux and Power M e a s u r e m e n t s 31 Reactivi ty Worth of M L - l - l A Mock-Up Control -Blade Assembly . . . . . 31 Void Coefficient of React ivi ty . 32 lA Fue l -E lemen t Studies 32 IB Fue l -E lemen t Studies 32

R E F E R E N C E S . . . . . . . . . . . . . . . . . . . . . . . 33

M L - l - l A C O R E STUDIES W I T H T H E G C R E C R I T I C A L A S S E M B L Y

R i c h a r d A . E g e n , W i l l i a m S. H o g a n , D a v i d A. D i n g e e , a n d J o e l W. C h a s t a i n

Critical-assembly studies were conducted to provide physics and engineering data to aid in developing the Mobile Low-Power Reactor (UL-1).

The UL-l-lA core was critical with 59 elements containing 17, 906.71 g of uranium-235, and had an excess reactivity of 0.381 x 10~ tsk/h at a moderator temperature of 24.91 C. The ratio of maximum element power to core-averaged power n'as approximately 1.09. The ratio of maximum to core-averaged thermal flux was approximately 1.10. At an 18-deg separation, the shutdown worth of the cadmium-covered control-blade mock-up was 1.14 x I0~ Ak/k for a 69-element core. Radial and upper axial reflector-moderator void coefficients were -0.59 ± 0.07 and -0.366 - 0.015 x 10~ Ak/k per in., respectively.

Two lA production fuel elements were evaluated in the critical-assembly core. The results predict that the production elements tested contained roughly the same fuel as the critical-assembly element and an additional 772 g of stainless steel equivalent on the average. Radial power and neutron-flux distributions were measured in a 19-pin IB fuel element. Fairly uniform distributions were observed. Data to evaluate the thermal utilization of this element were obtained.

I N T R O D U C T I O N

A e r o j e t - G e n e r a l N u c l e o n i c s i s d e v e l o p i n g a t r a n s p o r t a b l e g a s - c o o l e d n u c l e a r p o w e r p l a n t f o r the A r m y R e a c t o r s B r a n c h of t he A t o m i c E n e r g y C o m m i s s i o n . To a i d in t h i s d e v e l o p m e n t a con t inu ing s e r i e s of c r i t i c a l - a s s e m i b l y e x p e r i m e n t s h a s b e e n in p r o g r e s s a t B a t t e l l e ' s N u c l e a r R e s e a r c h C e n t e r for the p a s t 2 y e a r s .

The d e v e l o p m e n t a l p r o g r a m i n c l u d e s the o p e r a t i o n of a g a s - c o o l e d w a t e r -m o d e r a t e d t e s t - r e a c t o r f a c i l i t y , t he G a s C o o l e d R e a c t o r E x p e r i m e n t ( G C R E ) , at t he N a t i o n a l R e a c t o r T e s t i n g S t a t i on in I d a h o . The i n i t i a l g r o u p of c r i t i c a l - a s s e m b l y s t u d i e s w a s c o n d u c t e d to p r o v i d e e n g i n e e r i n g a n d p h y s i c s d a t a for the c o n s t r u c t i o n of t he G C R E . S e v e r a l c o r e c o n f i g u r a t i o n s w e r e s t u d i e d l e a d i n g to a c o r e for the G C R E w h i c h w i l l h a v e suf f i c ien t e x c e s s r e a c t i v i t y to m e e t p o w e r , l i f e t i m e , a n d o p e r a t i n g r e q u i r e m e n t s b u t w h i c h can b e a d e q u a t e l y shu t down w h e n the c o o l a n t r e g i o n s a r e f looded d u r i n g f u e l - e l e m e n t r e m o v a l . T h i s i n i t i a l s e r i e s of e x p e r i m e n t s i s s u m m a r i z e d in B M I - 1 2 8 8 . (1)

A s e c o n d g r o u p of s t u d i e s w a s u n d e r t a k e n to p r o v i d e i n f o r m a t i o n for e v a l u a t i n g s p e c i f i c d e s i g n p r o b l e m s a n d to a i d in o p t i m i z i n g a n d d e v e l o p i n g a d v a n c e d c o n c e p t s of t he G C R E . D u r i n g t h e s e s t u d i e s t he U n i f o r m R a d i a l P o w e r D i s t r i b u t i o n C o r e (URPD) w a s i n v e s t i g a t e d . T h i s c o r e d e p a r t e d f r o m the u n i f o r m f u e l - e l e m e n t s p a c i n g of p r e ced ing c o r e s ; a n o n u n i f o r m l a t t i c e s p a c e w a s d e s i g n e d to g ive a m o r e u n i f o r m r a d i a l p o w e r d i s t r i b u t i o n . The r e s u l t s of t h i s s e c o n d g r o u p of s t u d i e s a r e r e p o r t e d in B M I -1306 . (2 )

(1) References at end of report.

2

After concluding the s tudies per ta in ing to the GCRE, a s e r i e s of exper iments was under taken to provide physics and engineering information on the Mobile Low-Power Reactor (ML-1) a prototype of the por table Army Gas-Cooled Reac tor . Originally, the ML-1 r eac to r design incorpora ted lA fuel e lements a r r anged in a nonuniform fuel-element spacing ( s imi la r to that used in the URPD core studied e a r l i e r ) . Designs subsequent to the exper iments r epo r t ed he re in incorpora te a reduced core length and use uranium oxide p ins . These changes were r equ i red to significantly reduce the weight of r eac to r plus shield. The lA fuel e lement is desc r ibed in the next sect ion.

In the M L - l - l A studies (a designation to differentiate these studies from la te r studies using oxide p ins , designated M L - l - l B ) , flux and power dis t r ibut ions were m e a s u r e d , a mock-up s c i s so r - ac t i ng cont ro l -b lade a s sembly was ca l ibra ted , and the reac t iv i ty effects of voids at r e f l e c t o r - m o d e r a t o r in ter faces w e r e invest igated.

In addition, fue l - e l emen t - r ep lacemen t studies were conducted to evaluate p roduction lA fuel e lements and to m e a s u r e neutron-f lux and power distr ibution in a IB e l e ment (oxide pin c lu s t e r ) .

DESCRIPTION OF THE M L - l - l A CRITICAL ASSEMBLY

The main fea tures of the c r i t i c a l - a s s e m b l y facility a r e shown in Figure 1. The stand, con t ro l s , and other de ta i l s a r e fully desc r ibed in BMI-1288. ' ^ ' Several inodifi-cations to the core were r equ i r ed for the p r e sen t r e s e a r c h .

Core S t ruc ture and Fue l -E lemen t Lat t ice

The construct ion and location of the rad ia l and upper axial r e f lec to rs of the ML-l - l A c r i t i c a l - a s s e m b l y core differed from those of the cores previous ly studied. The upper axial re f lec tor was s tee l , 3 -1 /2 in. thick, fabr icated from a 1/2-in. - thick fuel-element positioning plate and two 1-1/2-in. -thick filler p l a t e s . Changes were made in severa l s t ruc tu ra l components to facil i tate removal and to a s s u r e accura te repos i t ioning of the en t i re ref lec tor a s sembly .

The radial ref lec tor was a regu la r hexagon 4 in. thick and 28 in. long formed of refined lead. It was located 1/2 in. from the n e a r e s t fuel e lement . A 1-in. gap was provided in one sec tor for inser t ing the M L - l - l A mock-up control blade assembly into the c o r e .

The core was const ructed so that the bottom of the upper axial ref lec tor was co-planar with the top of the fuel, the top of the lead re f lec tor , and the ful l -water-height posi t ion. The fuel region is 28 in. long and begins 4 - 1 / 2 in. above the bottom aluminum positioning and support p l a t e s , i . e . , t he re is a 4 -1 /2- in . bottom water re f lec tor .

The ML-1-1A core s t ruc tu re provided space for 61 fuel e l emen t s . Figure 2 shows a sketch of the core plan and tabula tes the fuel-eleinent spacings for a symmet ry sec to r . No c r i t i c a l - a s semb ly control rods were located in the M L - l - l A control-blade t e s t sec to r .

• 4 •'.

FIGURE 1. GCRE CRITICAL ASSEMBLY

| | << i» , t ;

mibi'i

Neutron startup sources guide tubes-.

Lead reflector •

ML-1 control-bladi position

© 0 / ' 0© __

Symmetry sector

/©/©0© (® @ 0 (£;"(

m>

0s© © © \0V®©(2

© © © ©

Note: Critical-assembly control-rod positions ore denoted by numbers at the appropriate locotions between fuel elements

A-52447

X - Y COORDINATES FOR SYMMETRY SECTOR

Elemenc Pos i t ion

1

5

14

29

50

4

13

Cooi X., in.

0

Z,375

4 .75

7.388

10,173

1. 188

3.563

•dinate Y, in.

0

0

0

0.025

-0 .299

2.06

2.06

Element Pos i t ion

28

49

12

27

48

26

47

46

Coordinate X , in.

6. 158

9.095

2.375

4.999

7.845

3.673

6.548

5.345

Y , i n .

2.06

1.955

4. 12

4 .07

3.97

6.415

6.515

8.660

FIGURE 2. F U E L - E L E M E N T LATTICE SPACING FOR THE M L - I - I A CORE

5

Fue l -E lemen t Construct ion

The fuel-e lement a s sembly i s shown in Figure 3. Except for the p r e s s u r e tube it is identical to that used in previous c o r e s . The s ta in less s teel p r e s s u r e tube replaced a 0. 058-in. -wall aluminum tube 1. 875 in. in OD.

Burnable poison in the core was s imulated with a 5-in. -wide band of cadmium-plated steel foil (0. 00012 in. of cadmium on 0. 015-in. - thick mi ld steel) wrapped around the insulat ion l iner of each fuel e lement and cen te red 15 in. above the bottom of the fuel.

In rewrapping the fuel cy l inders for these s tud ies , the en r i ched-u ran ium foils (0.001 in. thick, th ree l a y e r s pe r cyl inder) were se lected to min imize fuel-loading va r i a t ions . The average fuel weight per e lement was 303.40 g with a max imum deviation of 2 .01 g and a mean deviation of 0. 7 g from this weight.

RESULTS OF EXPERIMENTS WITH THE M L - l - l A CRITICAL ASSEMBLY

The genera l p r o c e d u r e s used in these studies to de te rmine c r i t i ca l fuel loadings , reac t iv i ty effects^ flux and power distr ibutions^ and t h e r m a l uti l ization a r e the same as those desc r ibed in BMI-1288, ' ^ ' P r o c e d u r e s applicable to exper iments pecu l ia r to this study a r e d i scussed in the following sect ions if they differ from the genera l p r o c e d u r e s .

Exper imen t s with the M L - l - l A c r i t i c a l - a s s e m b l y core were conducted to d e t e r mine ce r t a in c h a r a c t e r i s t i c s of the M L - l - l A co re :

(1) Cr i t ica l fuel loading

(2) Flux and power d is t r ibut ions

(3) React ivi ty wor th of M L - l - l A mock-up control-blade a s sembly

(4) Void coefficient of reac t iv i ty for voids at the m o d e r a t o r - r e f l e c t o r in te r faces .

React ivi ty wor ths were de te rmined e i ther with ca l ibra ted c r i t i c a l - a s s e m b l y control rods or by m e a s u r e d r e a c t o r pe r iods resul t ing d i rec t ly from the exper imenta l change.

Cr i t ica l Core Configuration

The M L - l - l A core was c r i t i ca l with 59 fuel e lements a r r a n g e d as shown in F igure 4. The co re contained 17 ,906.71 g of u ran ium-235 and had an excess react iv i ty of 0. 381 X 10"^ Ak/k at a m o d e r a t o r t e m p e r a t u r e of 24. 91 C.

stainless tube, 1.804 0. D. x 0.020 wall pressure tube

Stainless-321-tube, 1.500 O.D. x0.010 wall insulation liner Aluminum-606IT6-tube, 1.375 O.D. x0035 wall support tube •Stainless-3l6-tube, 1.250 O.D. X 0.040 wall fuel cylinder Stainless-3l6-tube, 1.015 O.D. X 0.040 well fuel cylinder •Stainless-3l6-tube,0.807 O.D.X0.040 wall fuel cylinder Stainless-3l6-tube,0.587 O.D.x0.040 wall fuel cylinder •Aluminum-606116-tube,0.4380.D. X 0.065 wall support mondrel

Positioning spider

Pin

•28.00 ^ -31.00 -37.00 V • 38.00 y

o

Electrical insulation

FIGURE 3. F U E L - E L E M E N T ASSEMBLY

Burnable poison is not shown. All d imens ions a r e in inches .

7

A-32444

FIGURE 4. INITIAL CRITICAL CONFIGURATION OF THE M L - l - l A CORE WITH 59 ELEMENTS

React ivi ty Worth of P e r i p h e r a l Fuel Elements

Fuel e lements were added to two s y m m e t r i c a l core pos i t ions , 58 and 38 (see F igure 4), resul t ing in 60- and 6 l - e l e inen t c o r e s . The excess reac t iv i t i es assoc ia ted with the addition of these e lements a r e s u m m a r i z e d in Table 1. These e lements appear to have different wor ths (cor rec ted to 24. 91 C), 0. 44 x 10"^ Ak/k for the e lement in Posi t ion 58 and 0.48 x 10"^ Ak/k for the e lement in Posi t ion 38. This difference is bel ieved to r e su l t from incomplete con t ro l - rod data for the 59-e lement and 60-e lement core a r r a n g e m e n t s . It was found, for example , that the wor th of Rod 2 i nc rea sed by about 20 p e r cent when a fuel e lement was added to Pos i t ion 58. Rod 4 i nc rea sed in worth by about 10 pe r cent when Posi t ion 38 was filled. (Note the re la t ive posi t ions of Rods Z and 4 and Pos i t ions 38 and 58 in F igure 2. ) For the 60-eleDaent core the Rod 4 cal ibrat ion for the 59-e lement core and the Rod 2 cal ibra t ion for the 6 l - e l e m e n t core w e r e used .

TABLE 1. WORTH OF PERIPHERAL ELEMENTS IN THE ML-l-lA CORE

Number of Fuel Elements

59

60 (element added to Position 58)

61 (elemaits added to Positions 38 and 68)

Fuel Inventory,

g

17,906.71

18,208.56

18,510.96

Excess Reactivity, per cent Ak/k

0.381 at 24.91 C

0.824 at 25.33 C or 0.820 corrected to 24.91 C

1.339 at 28.45 C o: 1.305 corrected to 24.91 C

Worth per

pet Elements cent Ak/k

—

0.44

0.48

8

Power -Dis t r ibu t ion Measu remen t s

With the core in the init ial c r i t i ca l configuration (Figure 4) re la t ive power d i s t r ibut ions were m e a s u r e d in each fuel e lement in the symmet ry sec tor defined by the t r iangle joining Pos i t ions 1 42^ and 46 (see F igure 2).

Aluminum ca tcher foi ls , 1/2 in. wide and 0.001 in. thick, we re wrapped completely around each fuel cylinder of each e lement , 8 in. above the bottom of the fuel. Power d is t r ibut ion was previous ly m e a s u r e d by attaching 1/Z-in. -d i ame te r aluminum catcher foils to d iamet r i ca l ly opposite points on the individual fuel cyl inders (see BMI-1306). After i r r ad ia t ion the foils w e r e folded to fit under scinti l lat ion counters and the f i ss ion-product activity of the en t i re foil was nrieasured. The m e a s u r e d act ivi t ies a r e propor t ional to the total power genera ted in the cylinder at that posi t ion.

The r e su l t s of the r e l a t ive -power -d i s t r ibu t ion m e a s u r e m e n t s a r e shown in F igure 5, The quanti ty, P / P , i s defined as the ra t io of the power developed in a given e lement to the c o r e - a v e r a g e d (radial ly) power as de te rmined from m e a s u r e m e n t s in a symiTietry s ec to r . The c o r e - a v e r a g e d power i s defined a s :

P = ^ , N

where

N | = the number of e lements of type i in the core

N = y N| » total number of e lements in core

Pj 4 = mieasured ca tcher - fo i l act ivi ty on the j th fuel cylinder in the ith e lement .

The data of F igure 5 do not indicate any consis tent p r e f e r r e d var ia t ion of P / P with position except in a radia l d i rec t ion . Nonuniformity of foils and c leanl iness of the adjacent fuel a r e felt to be the pr inc ipal causes of sca t te r in the data . Asymmet ry of the 59-e lement core may a l so contr ibute to apparent a s y m m e t r y of the power d is t r ibut ion.

The max imum ra t ios of local power to c o r e - a v e r a g e d power occur where the la t t ice spacing changes from a uniformi hexagon (Posi t ions 1 through 19) to a nonuniforixi one, i . e . , at Pos i t ions 8 through 19. For compar i son the corresponding data froin the URPD core a r e a lso shown on F igure 5. These values w e r e obtained by averaging the re la t ive power from the two points (mentioned above) on each fuel cylinder and a r e , t he re fo re , only approx imate .

Table 2 l i s t s the re la t ive total power genera ted in each e lement of the sec tor and the percentage of the total power genera ted in each fuel cyl inder . The data indicate that , in genera l , the percentage of total power genera ted in the outer cylinder i n c r e a s e s with Increas ing r ad ius , amd that genera ted in the inner cylinder d e c r e a s e s with increas ing r ad iu s .

Q- IQ- 1,0

0.8

0,6

0,4

Data from ML—I core

Data from URPD core

Note: Numbers designate core position

4 5 6 7

Radial Distance From Core Center, in.

10

FIGURE 5. RADIAL POWER DISTRIBUTION IN THE M L - 1 - lA CORE

Data were obtained with aluminum catcher foil around each fuel cyl inder on the e lements in the indicated core pos i t ions .

10

TABLE 2 . PER CENT TOTAL ELEMENT POWER GENERATED IN EACH FUEL CYLINDER

Fuel-Element Position

1 3 4

10

11 12

23 24

25 26 42

43 44

45 46

Radial Distance From Cote Center,

in.

0

2,37 2.37 4.76 4.12 4.75 7.39 6.45 6,49 7.39

10.18 9.24 8.79 9.30

10.18

1 (Inner)

11.50 11.45 11.50 11.00 11.80 11.65 10.95 11.15 11.20 11.00 10.00 11.20 10.90 12.00 10.66

Per Cent Total Power Generated in Fuel Cylindei

2

18.10 17.10 17.55 16.95 17.30 17.30 17.86 17.10 17.10 16.65 17.40 16.55 15.90 16.00 17.05

Indicated

3

27.20 27.60 26.00 27.10 27.55 25.75 26.70 25.85 27.55 27.70 25.86 26.80 25,15 26,30 25.35

4

(Outer)

43.20 43.85 44.95 45,00 43.60 45,30 44,50 45.95 44.20 44.65 46.70 45.50 48,05 45.70 46.25

Relative Total Power

1.00 1.04 1.06 1.11 1,09 1.05 0.99 1.07 1.01 1.06 0.74 0.87 0.93 0.78 0.73

Flux-Dis t r ibut ion M e a s u r e m e n t s

Axial and rad ia l re la t ive-f lux d is t r ibut ions were m e a s u r e d in the 59-element core with b a r e and cadmium-cove red m a n g a n e s e - i r o n w i r e s located in the center mandre l s of fuel e lements within the s y m m e t r y sec tor defined by the t r iangle through Posi t ions 1, 42, and 46. Axial d is t r ibut ions w e r e obtained in Pos i t ions 1 and 26. Radia l -d is t r ibut ion data were taken 8 in. above the bottom of the fuel in all pos i t ions .

Radial-f lux data a r e shown in F igure 6. The quantity A/A.J. is defined to be the ra t io of the local wire act ivi ty (ei ther b a r e or cadmium covered) to the co re - ave raged (radially) value of the b a r e - w i r e ac t iv i t ies m e a s u r e d in the center m a n d r e l s .

For com.parison the cor responding data from the URPD core a r e also p resen ted . The URPD data m e a s u r e d along two core radi i show a peak in the total flux dis t r ibut ion. The data from the M L - l - l A core indicate a smal l radia l var ia t ion of flux but no peak. The data a lso indicate that the M L - l - l A core configuration reduces the ra t io of m a x i mum to average flux in the cen te r mandre l from 1. 21 in the URPD core to 1, 17.

The axia l - f lux-dis t r ibut ion data a r e p resen ted in F igure 7. The corresponding data from Posi t ion 1 of the URPD core a r e included. The l a t t e r data a r e normal ized to the fo rmer on the b a s i s of equal in tegra l s under the curves shown. The higher values in the M L - l - l A core toward the top of the fuel elemient may be a t t r ibuted to the steel ref lec tor (aluminum in the URPD core ) .

<II<

1.4

1.2

1.0

0.8

0.6

0.4

0.2

, - ^ 3 '

^.Al J Y-radius (Figure 2)

•Along Z-rodius (Figure 2)

Legend ~

•Data from ML-1 core

— — — D a t a from URPD core

Note: Numbers designate core position

Epicadmium activity

i46 —

4 5 6 7

Radial Distance From Core Center, in.

10

C-32452

FIGURE 6. RADIAL-FLUX-DISTRIBUTION DATA IN ML- 1- lA CORE

Data were obtained using manganese - i ron wi res at the cen te r of fuel e lements in indicated coi'e pos i t ions .

m

10 12 14 16 18 20 22

Diitaoce Above Bottom of Core, in.

FIGURE 7. AXIAL-FLUX-DISTRIBUTION DATA FOR THE M L - l - l A CORE

Data were obtaiiied u.sing mangant-oe-iron w i r e s at the center of f .ui e lements in the nidic.ttecl co re pos i t ions .

13

In t race l l Flux M e a s u r e m e n t s

Detailed flux m e a s u r e m e n t s w e r e made within and around the fuel e lements in Pos i t ions 1, IZ, 26, and 45 at a point cen te red 8 in. above the bottom of the fuel. These m e a s u r e m e n t s were made in the 59-e lement core a r r a n g e m e n t shown in F igure 4 using 33 -mi l -d i ame te r m a n g a n e s e - i r o n w i r e s .

The re la t ive posi t ions of both the b a r e and cadmium-cove red w i r e s a r e shown in F igure 8. Wires within the e lement were taped onto the outside of the indicated cyl ind e r s . The m o d e r a t o r w i r e s were held ve r t i ca l ly in special ly cons t ruc ted 1/2-in. - thick polyethylene h o l d e r s . Special t e s t s were pe r fo rmed using p - m e t a l w i r e s (more m a n ganese) to show that the wi re absorpt ion does not affect the r e su l t s significantly. Modera tor w i r e s lie on l ines joining cen t e r s of adjacent e lements and on perpendicular b i s e c t o r s to these l i ne s . In some ins tances additional w i r e s a r e posit ioned to equally subdivide the dis tance between the fuel -e lement p e r i m e t e r and the perpendicular b i s e c to r l i n e s . The number of epicadmium m e a s u r e m e n t s was l imi ted by s t ruc tu ra l r e s t r i c t ions and f lux-per turbat ion cons ide ra t ions .

The background-co r r ec t ed and norma l i zed data a r e p resen ted in Table 3. The data from comparable posi t ions in each of the four fuel e lements show the same genera l radia l var ia t ion as indicated in F igure 6. It may be noted that w i r e s were act ivated in nea r ly identical posi t ions between e lements in Pos i t ions 12 and 26 and Pos i t ions 26 and 45. The normal ized act iv i t ies of these w i r e s a r e not in close ag reemen t . This is bel ieved to be a r e su l t of smal l e r r o r s in posit ioning these w i r e s . A smal l positioning e r r o r can lead to a l a rge difference in act ivi ty because of the seve re flux peaking in the mode ra to r region. Such posit ioning e r r o r s average out over the l a rge number of m e a s u r e d points and a r e not bel ieved to affect the de terminat ion of the average flux in the m o d e r a t o r .

The data from Table 3 w e r e used in calculat ing the rmal -u t i l i za t ion va lues . The per t inent p a r a m e t e r s and data a r e l i s ted in Tables 4 and 5. As in p rev ious calculat ions the flux shape through the fuel plate i s not taken into account . That i s , surface va lues , averaged over the p e r i m e t e r , a r e a s sumed to apply through the cyl inders where m e a s u remen t s w e r e m a d e . A m o r e extensive analys is of the neu t ron-absorp t ion p r o c e s s would be requ i red to p roper ly i n t e rp r e t the data . However, it appea r s that the p re sen t method of data reduct ion demons t r a t e s co r r ec t l y the var ia t ion in core p r o p e r t i e s between the M L - l - l A and URPD core g e o m e t r i e s . F igure 9 shows this compar i son . The c o r e - a v e r a g e d value of t h e r m a l ut i l izat ion for the M L - l - l A core is approximate ly 0. 005 below the URPD core va lue .

Tempera tu re Coefficient of Reactivi ty

In at tempting ce r ta in m e a s u r e m e n t s , it was found that the react iv i ty changes which were being m e a s u r e d w e r e smal l enough to be appreciably affected by m o d e r a t o r -t e m p e r a t u r e changes . To c o r r e c t for these changes , the m o d e r a t o r - t e m p e r a t u r e coefficient was m e a s u r e d for one t e m p e r a t u r e chsmge. This m e a s u r e m e n t was made in a 61-e lement c o r e . The t e m p e r a t u r e change was jus t the na tu ra l change which occu r r ed during the day and hence was smal l (28. 19 to 28. 90 C). The value obtained was

14

A. Support mondral B. Fuel cylinder C. Fuel cylinder D. Fuel cylinder E. Fuel cylinder F. Insulation liner G. Pressure tube

Legend

H. (Positions 1,12, 26) wires that lie midway between G and I

I. (Positions I, 12, 26) perimeter wires

H. a I. (Position 45 only) wires that lie evenly spaced between G and J

J. (Position 45 only) perimeter wires

Position 45

Position 46 /

Position-25

Position 12 Position 27

FIGURE ,s. WIRE POSITIONS FOR FUEL. Ei^EMENTS IN POSITIONS i , 12, Z6. AND 45

Cadmium-cox e red wircb were located at c i rc led points and i r r ad ia t ed separa te ly . Arrows point toward indicated core pos i t ions .

15


-Position 27


Position _.-44

Position 25

Scale: inches

FIGURE 8. (CONTINUED)

16

Wire

Position

0

A-1 2

B-1 2

3

C - 1 2

3

D-1 2

3 4

TABLE 3. RELATIVE INTRA

Position 1

Bare Wire

3,440

3,351

__

3.441

— --

3,798 3,806 3.666

4 ,678 . ---__

Cadmium-Coveced Wire

1135

__ --

1117

----

._ — —

1214

__ --_-

CELL FLUX-D [STRIBUTION D.

Relative Normalized Activity Position 12

Bate Wire

3,477

3.329

--

3,374

3,226

3,468

3 ,684

3.877

--

4,673 4,660

4 .842

--

Cadmium-Covered Wire

1061

— --

.-944

--

__ _. --

__ 1041

1045

__

kTA FROM CO RE POSITIONS SH

Obtained From Position Shown Position 26

Bare Wire

3.155

3,056

—

3,093 3,174

3,076

3,533 3,375

--

4,218 4 ,379

4 ,405 4,412


859

— —

804

._ --

— . . --

899

--818 864

OWN IN FIG URE8

Position 45

Bare Wire

2.394

2,300

2.362

2,400

2,311 2,547

2.658 2,505

--

3,176 2.964

3,413 3,552

Cadmium-Coveted Wire

619

— —

__ 616

—

— — —

648 534

— 678

E-1 2 3

F-1 2 3

4

G-1

2 3 4 5 6

7 8 9

10

11 12

H-1 2 3 4 5

6

I - l 2 3 4 5

6,331 6.145 5.954

7,059

7,179

8,785

8,079

8,010

8,116

7,634

11,926

11,145

11.635

12.598

11,818

10,752

1340

1433

1435

1433

1486

1518

6,261

7,160

7,002

7,538

7.546

7,931

8^369 7,964 8,002 8,618 8,654 8,743 8,845 8.604 8,450 7,758 8,356

12,101

12,922

12,642

14,360

12,931

11,903

11,299

13,099

10,953

13,969

12, 002

1163

1272

1249

1135

1175

1257

1314

1328

1221

6,479

6.425 7,150 6,564 6.102

7,175 7,231 6,840 6,870 6,963 7,367 7.722 7,771 8.023 8,510 7.827 7^782

11,270

10,457

12,265

14,273

14,678

12,638

9,758

12,264

10,345

10,628

11,061

971

995

954

963

980

5,009

4,731

5,632

6,872 6,676 5,367 5,780 4 ,974 5,380 5,372 6,027 6,197 6,882

11,971

9,158

9,221

9,642

12,204

10,164

9.857

740

752

622

849

1065

17

TABLES. (Continued)

Wire

Position

1-6 7 8 9

10 11 12

J-1 2

3 4

5

6 7 8 9

10

Position 1 Cadmium-

Bare Wire Covered Wire

__ __ . . ._ — . . "

.---— — — . . — — -_ --

Relative Normalized Activity

Position 12

Bare Wire

13,672 13,748 15,769

13, 229 14,006 11,072 13,108

— _. — — — . . — .-— —


. -1207 1249

_. 1353

._ —

__ __ — -_ — — — _-_. --

Obtained From Position Shown

Position 23

Bare Wire

11,981 14,226

15,918 13,805 15,640 14,139 13,809

— -. — ._ . . --— . . __ --


— 841

--__

1038 — --

— . . _. ._ ._ _. ._ . -_---

Position 45

Bare Wire

__ . . __ _. . . ._ --

13,407 13,010

7,725 9.149

7,732 8,280 7,734

10,719 10.032

13,269


__ — — ._ _. ._ --

— . . 810

662 634 601

__ 846 898

1017

18

TABLE 4 . PARAMETERS USED IN THERMAL-UTILIZATION CALCULATIONS

Cell Area, i n . ^

Position 1

4 .834

Position 12

5.257

Position 26

6.005

Position 45

6.513

Amount of Indicated Material in Total Cell Volume, per cent

Moderator Aluminum Stainless Steel Uranium~235

47 .91 4 .68

12.26 0.78

52 .23 4 .19

i l . 2 4 0.72

58.06 3.68 9.87 0.63

60.72 3.45 9.24 0.59

Ratio of Material Volume to Fuel Volume

Moderator Aluminum Stainless Steel Uranium-235

Cross-Section Data


61.23 5.85

15.67 1.00

gCj j , _bam_s

0.589 0.204

2 .66 599(b)

72.66 5.76

15.63 1.00

2 , cm~l

0.0196 0.123

0.2217 28.555

92 .41 102.93

5.87 5.85 15 .71 15.67

1.00 1.00

Ratio to Fuel Cross Section

0.000686

0.000431 0.007764 1.00

(a) Corrected for Maxwellian distribution at 25 C. (b) Corrected for n o n - l / v dependence.

TABLE 5. THERMAL-UTILIZATION DATA

Average Relative Thermal Flux in Indicated Material

Moderator Aluminum Stainless Steel Uraiiium-235

Position 1

8633 4000

4351 3591

Position 12

10302

4181 4583 3748

Position 26

10231 4160

4368 3669

Position 45

8037 3112 3461

2752

Ratio of Flux in Material to Flux in Fuel


2 .40 1.11 1.21 1.00

2 .75 1.12 1.22 1.00

2 .79 1.13 1.19 1.00

2. 92 1,13 1.26 1.00

Calculated Values of Thermal Utilization 0.799 0.776 0.755 0.734

0.82

Core Rodius, in.

F I G U R E 9. T H E R M A L UTILIZATION IN T H E M L - l - l A CORE

zo

(1 . 04 ± 0. 045) X 10-4 Ak/k pe r C at Z8.75 C^ where the uncer ta inty r e p r e s e n t s the m a x i mum deviation observed . In reducing reac t iv i ty data, this value was applied over a t e m p e r a t u r e range of "'ZB to 30 C.

For compar i son , previous t e m p e r a t u r e coefficients m e a s u r e d at Z8.75 C were; 0. 82 X 10-4 pe r C for the Clean Core and 0. 66 x 10-4 pe r C for the Lead-Reflected C o r e . f l )

Void Coefficients of React ivi ty

During operat ion of the M L - l - l A power r e a c t o r , gamma heating in the s t ruc tu ra l r e f l ec to r s m a y lead to nucleate boil ing of the m o d e r a t o r at the m o d e r a t o r - r e f l e c t o r in te r face . Tes t s were made to es t ima te the reac t iv i ty effects of such voids at radial and axial in te r faces using the 61-e lement c o r e .

Since the fuel region extends up to the uppe r - r e f l ec to r sur face , voids at this s u r face may have a not iceable reac t iv i ty effect. Since a 4 - 1 / 2 - i n . wa te r ref lector s epa ra t e s the lower gr id plate from the core voids at this location would have a much smal l e r effect. Consequently, the void effect was m e a s u r e d only at the upper re f lec tor . The voids w e r e a s sumed to be homogeneously d is t r ibuted over the surface of the re f lec tor , and were s imulated by making smal l reduct ions in the height of the m o d e r a t o r .

Over the range of wa te r heights 66.486 to 66.888 in. , the react iv i ty effect of changes in wa te r heights was constant at - 0 . 366 ± 0, 015 x 10"^ Ak/k pe r in. at 28 C. Measu remen t s were made below 66.888 in. to e l iminate men i scus p rob lems p resen t nea r the full wa te r height, 67. 211 in.

At the m o d e r a t o r - r a d i a l re f lec tor in terface the voids were again a s sumed to be homogeneously d is t r ibuted . Readily available void-containing or - s imula t ing m a t e r i a l s (aluminum, Styrofoam) w e r e unsuitable because of phys ics and engineering cons ide ra t ions . Fo r the sake of expediency, polyethylene was used to s imulate i n c r e a s e s in hydrogen density or "negative vo ids" . Assuming a l inear re la t ionship between small changes in hydrogen density at the in terface and the assoc ia ted reac t iv i ty effects, p o s i tive void effects can be pred ic ted by extrapolat ing the effects of i nc reased hydrogen dens i t i e s . Accordingly, reac t iv i ty effects of 0 - , 0 . 0 6 0 - , and 0. 120-in. th icknesses of polyethylene at the ent i re m o d e r a t o r - r a d i a l ref lec tor interface were m e a s u r e d . The r e s u l t s a r e shown in F igure 10. A value of - 0 , 59 ± 0. 07 x l O ' ^ Ak/k per in. (-2. 32 ± 0. 3 X 10-4 Ak/k pe r mm) of void was obtained.

The solid line is the resu l t of a l e a s t - s q u a r e ana lys is of the data (excluding the spur ious value at 0. 060 in. of polyethylene). The data were t e m p e r a t u r e co r r ec t ed to 27.81 C. The m e a s u r e m e n t s w e r e repea ted using the th ree th icknesses of polyethylene. Each th ickness change r equ i r ed the fuel e lements and uppe r -ax ia l - r e f l ec to r a s sembly to be reiTioved from the c o r e . This d i sa s sembly and r e a s s e m b l y of the core could have introduced smal l unknown reac t iv i ty changes and may have been respons ib le for some of the sca t t e r in the data . This i s , however^ only conjecture^ and at this t ime the wide sca t t e r indicated in F igure 10 i s unexplained.

o

xf

r

> to

0.08 -0.06

Equivalent Void Thickness, cm A-32534

FIGURE 10. REACTIVITY WORTHS OF POLYETHYLENE SHEETS PLACED AT THE MODERATOR-REFLECTOR INTERFACE IN THE M L - l - l A CORE

22

Reactivi ty Worth of M L - l - l A Mock-Up Control-Blade Assembly

The power r e a c t o r will be control led with s c i s so r s l i ke control b l ades . M e a s u r e men t s w e r e made to de te rmine the reac t iv i ty wor th of a pa i r of these blades as a function of the i r separa t ion angle . B a r e and cadmium-cove red (0. 020- in . - th ick cadmium) b lades were invest igated.

The const ruct ion and locat ions of the mock-up blade assembly with r e spec t to the core center l ines a r e shown in F igure 11. The b lades a r e s ta in less s tee l , 3 in. wide, 14 in. long and va ry in thickness from 0. 625 in. to 0, 125 in. When located in the core in a pa ra l l e l posi t ion (zero separa t ion angle) the b lades were separa ted by 1/2 in. The blades w e r e cen te red 13 in. above the bottom of the fuel between Posi t ions 47 and 48 pa ra l l e l with the adjacent l ead - re f l ec to r face (see F igure 2),

All m e a s u r e m e n t s w e r e made in a 6 l - e l e m e n t core by noting the change in p o s i tion of ca l ibra ted c r i t i c a l - a s s e m b l y control rods r equ i red to main ta in cr i t ica l i ty for va r ious angle separa t ions of the b l ades . The r e s u l t s of the t e s t s a r e shown in Figure 12, Because of the size of the b lades the cal ibra t ion of the c r i t i c a l - a s s e m b l y control rods was checked frequently; no changes w e r e observed throughout the t e s t s . In genera l , for each configuration of the mock-up blade a s sembly two or m o r e cr i t ica l conditions were obtained with the ca l ibra ted c r i t i c a l - a s s e m b l y control r ods . In analyzing the data it was poss ible to r e l a t e a reac t iv i ty change due to a new blade configuration to those assoc ia ted with all other configurat ions. Thus , many checks on the reac t iv i ty effect of any single mock-up cont ro l -b lade configuration were avai lable .

The length of the mock-up b lades made it imposs ib le to r e t r a c t them fully into the ref lec tor ( i . e . , to a 180-deg separa t ion angle) . The 180-deg separa t ion configuration was mocked up for the cadmium-cove red case by filling the cadmium sheath with an equivalent weight of s teel sheet and placing this package in the 1-in. -wide slot in the lead. This separa t ion angle was not duplicated for the b a r e b l ades .

The l imi t s shown at each data point of F igure 12 indicate the upper and lower values obtained from many checks and should not be in te rp re ted as a probable e r r o r . In the analys is of these data no co r r ec t i ons for w a t e r - t e m p e r a t u r e var ia t ion were applied as they were smal l comipared to the total blade w o r t h s .

F U E L - E L E M E N T - R E P L A C E M E N T STUDIES

The c r i t i ca l a s sembly was used to check reac t iv i ty of lA production fuel e lements to detect g r o s s e r r o r s in fabr icat ion. Also , a IB- type fuel e lement which contained 19 UO2 fuel pins was studied to aid in predic t ing the per fo rmance of this e lement .

lA Fue l -E l emen t Studies

An a t tempt was i-nade to use the c r i t i ca l a s sembly to de termine the fuel and neutron-abso rbe r (actually s ta in less s teel equivalent) content of production lA fuel e l emen t s .

Note: Blades centered 13 in. above bottom of fuel. Material is stoinless steel.

'Intersection of core T. or y-oxis

of Figure 2 A-32449

FIGURE 1 1. CONSTRUCTION OF ML- I- lA CONTROL. BL/vDES

-10

Q .

-0.2

4^

20 30 40 50 60

Half-Angle Separation of Control Blodes, deg

70 9 0 100

A-32446

FIGURE 12. SHUTDOWN WORTHS OF M L - 1 - lA CONTROL Bi^ADES AS A FUNCTION OF TIlElR AXGU1.AR SEPARATION

25

The p o w e r - r e a c t o r e lements were shipped to Bat te l le by Aero je t -Genera l Nucleonics . The production e lements w e r e longer ove r - a l l than the c r i t i c a l - a s s e m b l y mock-up e lements because of the special end fi t t ings. For use in the exper iments they were cut off so that the bottom of the fuel was aligned with the bottom of the c r i t i c a l -a s sembly fuel.

In additioiij the p o w e r - r e a c t o r e l ements had other significant differences from the i r c r i t i c a l - a s s e m b l y coun te rpa r t s . These w e r e ;

(1) The fuel was in the form of a d i spe r s ion of uranium dioxide in s ta in less s tee l . The fuel-plate th ickness was 45 mils^ made up of 33 m i l s of core and 12 m i l s of cladding. The total e s t imated fuel loading of the p o w e r - r e a c t o r e l ements is given in Table 6. The nominal outside d i a m e t e r s of the fuel cy l inders were 1. Z6. 0.94j 0 .75 , and 0. 53 in; these values compare respec t ive ly with the following values for the c r i t i c a l - a s s e m b l y e l emen t s : 1. 25, 1 .01, 0 . 8 1 , and 0.59 in,

(2) The p o w e r - r e a c t o r e lement contained s a m a r i u m oxide burnable poison (about 0, 1 g in each e lement ) . The poison was in the form of a d i spers ion of s a m a r i u m oxide in a thin s teel band 6 in. wide affixed to the inside of the outer insu la t ion- l iner tube. The 6-in. s a m a r i u m oxide band was 1 in. below the fuel center l ine. The corresponding cadmium-band mock-up on the c r i t i c a l - a s s e m b l y e lements is 5 in. wide and is cen te red 1 in. above the fuel center l ine . This difference in posi t ion a r i s e s from the fact that the c r i t i ca l a s sembly mocks up the inver ted power r e a c t o r .

(i) An outer insulat ion l iner (zirconium) and insulat ion m a t e r i a l (Therinoflex) were p r e s e n t on the p o w e r - r e a c t o r e l e m e n t s . These w e r e not mocked up in the c r i t i c a l - a s s e m b l y e le inen ts .

(4) The ends of the p o w e r - r e a c t o r e lements contained s ta in less s teel s t ruc tura l p ieces which a r e absent in the mock-up e l emen t s .

In conducting these s tudies it was a s s u m e d that for a given core posit ion, and for approximate ly uniform axial d is t r ibut ions of fuel and s tee l , a l inear re la t ionship exis ted between the defect in fuel a n d / o r s teel weight compared with a s tandard c r i t i c a l - a s s e m b l y e lement and the resu l t ing reac t iv i ty change assoc ia ted with the r e ac to r . It was further a s s u m e d that s imi l a r re la t ionships would hold with the fuel e lement ent i re ly covered with a 0. 010-in. - thick cadmium s leeve .

With these assmxiptions, the following equation can be wr i t t en :

ApB = a g AMf + b g AMgg , (1)

Apc = ^C ^ ^ f + ^C AMss ,

where

A/j = change in reac t iv i ty due to defect m fuel or s teel weight

AMf - fuel defect, g

26

A M s s - s t e e l d e f e c t , g

a a n d b = c o e f f i c i e n t s t o b e d e t e r m i n e d

S u b s c r i p t s B a n d C d e s i g n a t e b a r e a n d c a d m i u m - c o v e r e d e l e m e n t s , r e s p e c t i v e l y .

T h e c o e f f i c i e n t s w e r e d e t e r m i n e d b y l o a d i n g f u e l e l e m e n t s w i t h k n o w n d e f e c t s of f u e l a n d s t a i n l e s s s t e e l a n d o b s e r v i n g t h e r e s u l t i n g r e a c t i v i t y c h a n g e w i t h t h e e l e m e n t b a r e a n d c a d m i u m c o v e r e d . T h e s e m e a s u r e m e n t s w e r e m a d e i n P o s i t i o n 26 i n a 6 1 -e l e m e n t c o r e . M e a s u r e m e n t s w e r e i n i t i a l l y a t t e m p t e d i n P o s i t i o n 1 , b u t w i t h t h e 1 0 -m i l - t h i c k c a d m i u m s l e e v e c o v e r i n g t h e c r i t i c a l - a s s e m b l y f u e l e l e m e n t t h e c o r e w a s n o t c r i t i c a l . T h e m o c k e d - u p b u r n a b l e - p o i s o n b a n d w a s p r e s e n t o n t h e c r i t i c a l - a s s e m b l y e l e m e n t o n l y d u r i n g t h e c a d m i u m - c o v e r e d t e s t s .

T h e r e a c t i v i t y d i f f e r e n c e w a s m e a s u r e d b y c a l i b r a t e d c r i t i c a l - a s s e m b l y c o n t r o l r o d s ; t h e d a t a w e r e c o r r e c t e d f o r m o d e r a t o r - t e m p e r a t u r e c h a n g e s u s i n g a t e m p e r a t u r e c o e f f i c i e n t of r e a c t i v i t y of 1 . 0 4 x 1 0 " ' * A k / k p e r C . T h e c o r r e c t e d r e a c t i v i t i e s w e r e f o u n d t o b e r e p r o d u c i b l e t o w i t h i n 1 t o 2 x 1 0 - 5 A k / k .

T h e e q u a t i o n s r e s u l t i n g f r o m t h e s e c a l i b r a t i o n s a r e :

AMf a 0 . 7 3 1 X 1 0 ^ [ ( 0 . 0 3 8 ) A p B + ( 0 . 4 2 7 ) A p c _ J

A M g s = 0 . 7 3 1 X 106 [ ( - 2 . 3 4 ) A p g + ( 9 . 6 6 ) ApQ J

E q u a t i o n (2) w a s a p p l i e d t o r e a c t i v i t y m e a s u r e m e n t s f o r a c r i t i c a l - a s s e m b l y fue l

e l e m e n t of k n o w n c o m p o s i t i o n , d i f f e r e n t f r o m a s t a n d a r d e l e m e n t , a n d t w o s p e c i a l e l e

m e n t s s u p p l i e d a n d d e s i g n a t e d b y A G N a s C E - 1 a n d C E - 2 .

T h e r e s u l t s of t h e s e m e a s u r e m e n t s a r e s u m m a r i z e d i n T a b l e 6 . T h e l a r g e

a p p a r e n t s t a i n l e s s s t e e l d e f e c t i n E l e m e n t s C E - 1 a n d C E - 2 i s p r o b a b l y d u e t o t h e

b u r n a b l e - p o i s o n s a m a r i u m o x i d e b a n d w h i c h w a s p r e s e n t o n t h e s e e l e m e n t s . T h e

a m o u n t of c a d m i u m u s e d t o s i m u l a t e t h i s b u r n a b l e p o i s o n i n t h e c r i t i c a l - a s s e m b l y e l e

m e n t s ( a p p r o x i m a t e l y 0 . 4 g ) i s a c t u a l l y a s t r o n g e r a b s o r b e r t h a n t h e s a m a r i u m of t h e

p r o d u c t i o n e l e m e n t s ( a b o u t 0 . 1 g ) , ( F r o m t h e r e s u l t s of v a r i o u s c r i t i c a l c o n d i t i o n s ,

w i t h o u t t h e c a d m i u m s l e e v e , i t h a s b e e n f o u n d t h a t t h e c a d m i u m b a n d i n P o s i t i o n 26

r e p r e s e n t s a s h u t d o w n w o r t h of a p p r o x i m a t e l y 5 x 10"** A k / k , ) U s e of c a d i n i u m b a n d s i n

TABLE 6. FUEL AND STEEL CAUBRATION RESULTS

(2)

Mf Specified^ AMf Specified, AMf Calculated, Mgs Actual, AMgg Actual, AMjs Calculated,

g i s i i S Element

ML-l-iA standard 303.47 0.00 element

ML-l-lA with extra 403.82 100.35 fuel and stainless

GCRE-CE-l(b) 313.6(c) 10.03(c)

GCRE-CE-2(b) 313.0(c) 9.53(c)

105.90

-3.8

2,3

2474(a)

2866

0.00

392 388

748

796

(a) Includes weight of pressure tube. (b) GCRE elements were inserted in ML-1 element pressure tubes. (c) These values represent the specified loading and are not known to be correct.

27

cal ibrat ing to obtain the constants for Equation (2) would not have given c o r r e c t r e su l t s in t e r m s of s ta in less s tee l , and by introducing a different absorbing m a t e r i a l would probably have made the r e s u l t s m o r e difficult to i n t e rp r e t .

GCRE-1B-10T F u e l - E l e m e n t Studies

The GCRE-1B-10T fuel e lement was cons t ruc ted of 19 uranium dioxide fuel pins clad with Inconel X in a t r i angu la r -p i t ch lat t ice as shown in F igure 13. The 7 cent ra l pins contained UO2 enr iched to 48, 53 pe r cent and the 12 outer pins contained UO2 enr iched to 24. 48 per cent. The total weight of u ran ium-235 in the e lement was 377, 62 g. The cladding consis ted of an 0. 030-in, -wal l Inconel X tube 0, 164 in. in ID by 30. 985 in. long. These tubes w e r e furnished with top and bottom plugs of Inconel X and with a lumi num s p a c e r s for center ing the fuel in the tube.

The fuel consis ted of cyl indr ical uranium dioxide pel le ts 0. 250 in. long which were s tacked inside the tube to give a total fuel length of 22.75 in. The fuel region was cen tered 17.920 in, from the top of the pin a s sembly . Most of these pel le ts contained a cent ra l void l a rge enough to allow a 0. 004-in, -wa l l - th ickness aluminuin tube 0. 040 in. in OD to be inse r t ed into the center of the fuel pin after a s sembly . These aluminum tubes extended out of the fuel region to the top of the pin a s sembly . They acted as ho lders for manganese -copper w i r e s which w e r e used for making flux m e a s u r e m e n t s .

Five of the pins were cons t ruc ted such that the i r fuel regions were in th ree separable segments . One of these was a capsule 0. 50 in. long that was machined to connect to the other two sect ions of the pin with a slip fit. The capsule was centered 2, 284 in. below the center of the fuel region. The fuel in the top segment contained the aluminum tube mentioned above, but the fuel in the capsule and bottom segment did not. The remain ing fourteen pins w e r e a s sembled as one p iece . The cent ra l aluminum tube extended the en t i re fuel length in these p ins .

For these studies the GCRE- lB- l i ^T pin bundle was placed in a c r i t i c a l - a s s e m b l y -e lement insulation l iner and s ta in less s teel p r e s s u r e tube; the cadmium band was r e moved from the insulat ion l i ne r . The e lement was located in Posi t ion 1 in the init ial 59-e lement configuration of F igure 4. The fuel region of the IB-li^T element was centered ver t ica l ly at the fuel midplane of the M L - l - l A c r i t i c a l - a s s e m b l y fuel e l e m e n t s . As a r e su l t , the fuel region began 7 -1 /2 in. above the bottom re f lec tor .

Power -Dis t r ibu t ion Measu remen t s

Power -d i s t r ibu t ion m e a s u r e m e n t s were obtained by counting the f i ss ion-product activity in each of five fuel capsu les . The capsu les w e r e 0. 50-in. -long fuel-pin seg men t s from Pins 1, 4, 7, 9, and 15 (see F igure 13). The mieasured act iv i t ies of the i r r ad ia t ed capsules were c o r r e c t e d for decay, background, and act ivi t ies p r e sen t p r i o r to i r rad ia t ion . Relat ive p in- to-p in power r a t io s were calculated d i rec t ly froin these co r r ec t ed ac t iv i t i es . These ra t ios a r e l i s ted in Table 7. The low value obtained for Pin 15 may be a r e su l t of the proximity of the s ta in less s teel guide tubes for the neutron s tar tup source (note source tubes shown in F igure 2).

Critical assembly element pressure tube (insulation liner included but not shown)

To center of Position 2 -*-

To center of Position 3

Boundary of unit cell of Position I

To center of Position 5

/ To center of Position 7

Notes: I. All flux points in moderator

lie on radii spaced 15 deg opart.

2. Points 34, 35, and 36 lie midway between other moderator points on the same radii.

2 3. Moderator area is 2.278 in. .

A-32455-

05

FIGURE 13. POSITIONS OF INTRACELL FLUX MEASUREMENTS FOR GCRE-18 FUEL ELEMENT IN POSITION OF M L - l - l A CORE

29

TABLE 7, RELATIVE FUEL-PIN POWER FOR GCRE-1B-1<^T FUEL ELEMENT

Fin Power Ratio Relative to Pin 1

1 1.00 4 1.10 7 1,14 9 1.12

15 LOO

F l u x M e a s u r e m e n t s

M e a s u r e m e n t s w e r e m a d e i n t h e G C R E - l B - l i p T e l e m e n t t o p r o v i d e d a t a o n t h e d e t a i l e d i n t r a c e l l a n d t h e a x i a l t h e r m a l - f l u x d i s t r i b u t i o n . I n a d d i t i o n , d a t a w e r e o b t a i n e d r e g a r d i n g p o s s i b l e n e u t r o n s t r e a m i n g b e t w e e n f u e l p i n s . T h e i n f o r m a t i o n w a s o b t a i n e d b y i r r a d i a t i n g 2 5 - m i l - d i a m e t e r p - m e t a l (~80 w / o m a n g a n e s e - 2 0 w / o c o p p e r ) w i r e s .

T w o s e p a r a t e i r r a d i a t i o n s w e r e p e r f o r m e d i n t h e c o u r s e of t h e s e e x p e r i m e n t s .

In t h e f i r s t i r r a d i a t i o n t h e f o l l o w i n g w i r e s w e r e p r e s e n t i n a n d a r o u n d t h e e l e m e n t :

(1) F u l l - l e n g t h w i r e s in the c e n t e r p o s i t i o n in a l l a p p l i c a b l e fuel p i n s .

(2) P r e c u t 1-in. - l o n g w i r e s in the m o d e r a t o r a t a p o s i t i o n c e n t e r e d 18. 55 in . above the b o t t o m of the ox ide fue l . The a r r a y i s s h o w n in F i g u r e 13 .

(3) P r e c u t 1-in. - l o n g w i r e s on the c i r c u m f e r e n c e of s e l e c t e d fuel p i n s . T h e s e w e r e a l i g n e d w i t h t he p in a x i s a n d s p a c e d 90 deg a p a r t a s shown on F i g u r e 13 . T h e s e w i r e s w e r e p l a c e d a t 18. 55 a n d 5. 05 i n . above the b o t t o m of t h e fue l .

The a x i a l w i r e s in the c e n t e r s of the p i n s w e r e cut in to 1-in. s e g m e n t s a t h e i g h t s c o r r e s p o n d i n g to t he c i r c u m f e r e n t i a l w i r e s , 18, 55 and 5 . 0 5 i n . a b o v e t h e b o t t o m of t he fue l , a n d a t one a d d i t i o n a l h e i g h t , 1 2 . 0 5 i n . T h e n o r m a l i z e d a c t i v i t y of t h e s e t h r e e w i r e s a n d t h e w i r e s f r o m (2) a n d (3) a b o v e a r e g i v e n in T a b l e 8. T h e y p r o v i d e a c o m p l e t e t o t a l - a c t i v i t y d i s t r i b u t i o n in a p l a n e 18 . 55 i n . a b o v e the b o t t o m of the fuel a n d a d d i t i o n a l d a t a a t 5 . 0 5 in . c o n c e r n i n g p o s s i b l e n e u t r o n s t r e a m i n g . The d a t a f r o m 1 2 . 0 5 i n . above the b o t t o m of the fuel s e r v e a s a c h e c k on the g r o s s r a d i a l d i s t r i b u t i o n of flux w i t h i n t he p i n s .

The s e c o n d i r r a d i a t i o n w a s p e r f o r m e d to g a t h e r d a t a for c a d m i u m - c o v e r e d w i r e s so t h a t t he d a t a a t 1 8 . 5 5 i n . cou ld b e c o r r e c t e d to t h e r m a l - n e u t r o n d i s t r i b u t i o n s . F i g u r e 13 s h o w s the p o s i t i o n s w i t h i n a n d a d j a c e n t to t h e e l e m e n t w h e r e t h e s e e p i c a d m i u m w i r e s w e r e l o c a t e d . D u r i n g t h i s s a m e r u n f u l l - l e n g t h b a r e w i r e s w e r e i r r a d i a t e d in the c e n t e r of P i n s 3 and 19. T h e s e l a t t e r d a t a i n d i c a t e t h e a x i a l f lux d i s t r i b u t i o n ( u n c o r r e c t e d fo r e p i c a d m i u m a c t i v i t y ) . D a t a f r o m t h e s e c o n d i r r a d i a t i o n a p p e a r in T a b l e 8 .

TABLE 8. RELATIVE INTRACELL FLUX-DISTRBUTION DATA FOR GCRE-1B-1# ELEMENT

Pin

1

1 1

1

1 2

2

2

2

2

3 4

5

5

5 5

5

6

7

8 9

10

10 10

10

10

11

12

13 14

15 16

16

16 16

16

17 18 19

Radial Distribution

In Element Center at Indicated Position of Wire

PositionCa)

CP

1

2

3

— CP

5 6

7

8

CP

CP

CP

9 10

11

12

CP

CP

CP

CP CP

13 14

15

16 CP

CP

CP

CP

CP

CP

17 18

19 20

CP CP

CP

Total

1621 2364

2318 2274

2258

1678

2238

3052

3558 3282

1708

1706

1635

2427

3135 3147

2489

1676

1689

3113

3026 3267

3221 5071

6218

4369

2968

3039

2968

2818 2850

2878 3240 3610

5742

5340

3008 3087 3162

Above Bottom of Fuel

18.55 In. 1 Epicadmimn

— 873

— 926

. . — — 945

999

943

— — . . — 983

1016 962

— — — . . —

1002

1139 1091

. . — -_ — — — . . 994

1135

1205

. . — . . —

2.05 I n . , Total

1941

--— — —

2064

— — — —

2067 2072

2026

— — — —

2033

. . 3704

3606 3914

. . — .-—

3628

3653 3589

3466 3313

3468

--— — —

3593 3595 3624

5.05 I n , , Total

__ 2804

2694

2711 2624

2014

2674

3352 4021

3748 2034

. . 1958

~ — . . —

1992

. . 3589

— 3869

— --— —

3559

3581 3466

3486

--3526 4041

6738

6281 3959

3523 3690

3759

Pia

2

2

2

2 2

3

4

5

5

5

5

5

6

7 8

9 10

10 10

10

10

11 12

13 14

In Moderator at 18 .55 In. Above

Bottom of Fuel Position

21

22

23

24

25 26

27

28 29

30

31

32

33

34

35

36

37

38

39 40

41

42

43 44

45

46

47

48 49

Tota l

7,357 7.490

7 ,666

7,472

7,542

7 .623 7 ,444

7,462

7 .421

7.533

7,545 7 ,401

7 ,044

11,726 11.909

10,974

9,860

11,834

12,496 11.208

10.817

11,968 12,836

11,127 10.330

10,875

11.967

10,968

10,178

Epicadmium

— — — —

1377

— — — — „

1328

. .

. . — — —

1369

— 1331

— 1363

— 1400

__ 1307

— 1267

" 1298

Axial Distribution

Center Position of Wire Above

Bottom of Fuel,

in.

0.375

1.375

2.375

3.375 4.375

5.375 6.375

7.375 8.375 9.375

10.375

11.375

12.375

13.375

14.375

15.375

16.375

17.375

18.375

19.375 20.375

21.375

22.375 23.375

24.375

25.375

26.375

27.375

28.375 29.375

Pin 3 .

Total

1640

1729 1852

2040

2115

2257 2324

2311 2384

2305

2346

2315 2244

2185

2228 2109

2039

1846

1493 1550

1595

1559 1535

4597

2989

2637

1221

523 243 114

Pin 19,

Total

3201

3103

3345

3663

3821

3897

4076

4235 4241

4191 3984

3899

3922 3820

3798

3699

3507 3102

2850

3013

2979 2840

2869

5119

4636

2892

1152

533

239

89

(a) CP indicates center of pin. See Figure 13 for location of other positions.

31

DISCUSSION

C r i t i c a l C o n f i g u r a t i o n

The M L - l - l A c r i t i c a l - a s s e m b l y c o r e s t r u c t u r e d i f f e r e d f r o m p r e v i o u s l y s t u d i e d c o r e s in the c o n s t r u c t i o n a n d l o c a t i o n of t he r a d i a l a n d u p p e r a x i a l r e f l e c t o r s . The r a d i a l r e f l e c t o r w a s a r e g u l a r h e x a g o n , 4 i n . t h i c k and 28 i n . l o n g , f o r m e d of r e f i n e d l e a d . The 3 - 1 / 2 - i n , - t h i c k u p p e r a x i a l r e f l e c t o r w a s m a d e of s t e e l . The top of t he l e a d w a s c o p l a n a r w i t h t he t o p of t h e fuel a n d t h e f u l l - w a t e r - h e i g h t p o s i t i o n .

E x c e p t for p r e s s u r e t u b e s , t h e fuel e l e m e n t s w e r e i d e n t i c a l to the p r e v i o u s l y u s e d G C R E - 1 c r i t i c a l - a s s e m b l y e l e m e n t s . A s t a i n l e s s t u b e r e p l a c e d a s l i g h t l y l a r g e r a l u m i n u m p r e s s u r e t u b e .

The M L - l - l A c o r e w a s c r i t i c a l w i t h 59 e l e m e n t s c o n t a i n i n g 1 7 , 9 0 6 . 7 1 g of u r a n i u m - 2 3 5 , and h a d an e x c e s s r e a c t i v i t y of 0. 381 x 1 0 " ^ Z\k/k a t a m o d e r a t o r t e m p e r a t u r e of 2 4 . 9 1 C.

R e s u l t s of F l u x and P o w e r M e a s u r e m e n t s

F l u x and p o w e r m e a s u r e m e n t s show i n c r e a s e d u n i f o r m i t y of t h e r a d i a l d i s t r i b u t i o n s w h e n c o m p a r e d w i t h t he p r e v i o u s l y s t u d i e d U R P D c o r e . The r a t i o of m a x i m u m e l e m e n t p o w e r to c o r e - a v e r a g e d p o w e r w a s a p p r o x i n n a t e l y 1, 09 . P e r c e n t a g e s of t o t a l e l e m e n t p o w e r g e n e r a t e d in e a c h fuel c y l i n d e r w e r e m e a s u r e d . T h e d a t a i n d i c a t e d a s l i gh t v a r i a t i o n of t h e s e p e r c e n t a g e s w i t h r a d i u s j t h e p e r c e n t a g e g e n e r a t e d in the o u t e r fuel c y l i n d e r i n c r e a s e d s l i g h t l y w h i l e t h a t in t h e i n n e r fuel c y l i n d e r d e c r e a s e d s l i g h t l y w i t h i n c r e a s e d r a d i u s .

The r e l a t i v e t h e r m a l - f l u x m e a s u r e m e n t s i n d i c a t e a r a t i o of m a x i m u m to c o r e -a v e r a g e d flux of a p p r o x i m a t e l y 1. 10. D e t a i l e d i n t r a c e l l m e a s u r e m e n t s w e r e m a d e to a i d in t h e r m a l - u t i l i z a t i o n c a l c u l a t i o n s . R e s u l t s a r e shown in T a b l e 9.

TABLE 9. THEimAL UTILIZATION(a) AS A FUNCTION OF CORE POSITION

Position 1 Position 12 Position 26 Position 45 Calculated Values of

Thermal Utilization 0,799 0,776 0.755 0.734

(a) Note text for interpretation of data leading to tabulated values. See Figure 2 for element positions.

R e a c t i v i t y Wor th of M L - l - l A M o c k - U p C o n t r o l - B l a d e A s s e m b l y

The r e a c t i v i t y w o r t h a s a func t ion of b l a d e - s e p a r a t i o n ang l e w a s m e a s u r e d fo r a i n o c k - u p of the M L - l - l A s c i s s o r l i k e c o n t r o l b l a d e s . B o t h b a r e a n d c a d m i u m - c o v e r e d s t e e l b l a d e s w e r e i n v e s t i g a t e d . A m a x i m u m v a l u e of a p p r o x i m a t e l y - 1 . 14 x 1 0 " ^ A k / k a t a n 18 -deg s e p a r a t i o n w a s o b t a i n e d fo r c a d m i u m - c o v e r e d b l a d e s . T h e m a x i m u m v a l u e for t he b a r e b l a d e s w a s m e a s u r e d a s - 0 . 41 x 1 0 " ^ A k / k a t a 1 0 - d e g s e p a r a t i o n . The

32

m e a s u r e m e n t s w e r e made in a 6 l - e l e m e n t core containing 18,510,96 g of u ran ium-235 and having an excess reac t iv i ty of 1. 300 x 10"^ Ak/k at 23, 19 C,

Void Coefficient of React ivi ty

Void coefficients of reac t iv i ty w e r e m e a s u r e d at the rad ia l and upper axial r e f l e c t o r - m o d e r a t o r in t e r faces . At the upper axial r e f l ec to r , a void was introduced by lowering the wa te r height, A reac t iv i ty effect of - 0 , 366 ± 0. 015 x 10"^ Ak/k per in. at 28 C was m e a s u r e d .

At the m o d e r a t o r - r a d i a l re f lec tor in terface polyethylene was used to de te rmine void coefficients. As a r e su l t of the m e a s u r e m e n t s an approxiinate react iv i ty effect of - 0 . 59 ± 0. 07 X 10~2 Ak/k per in. is p red ic ted for a uniform void at the m o d e r a t o r -rad ia l re f lec tor in te r face . The methods and assumpt ion used in measu r ing this value a r e d i scussed in the text .

lA F u e l - E l e m e n t Studies

The ML,-1-1A cr i t i ca l a s s emb ly was used in an at tempt to detect g r o s s e r r o r s in the fabricat ion of lA product ion fuel e l e m e n t s . The ca l ibra ted react iv i ty effects of known defects in fuel and s ta in less steel loadings in a s tandard c r i t i c a l - a s s e m b l y fuel e lement were used to ca l ib ra te two lA production fuel e l emen t s , CE-1 and C E - 2 . The r e su l t s p red ic t that the production e lements t es ted contained roughly the same fuel as the c r i t i c a l - a s s e m b l y e lement and an additional 77 2 g of s ta in less s teel equivalent on the ave rage . These r e s u l t s a r e tabulated below.

TABLE 10. lA PRODUCTION-ELEMENT CALIBRATION

Element

CE-1

CE-2

A M / * ) Specified, g

10,03

9.53

A M / * ^ Measured, g

-3,8

2.3

AMg/^) Specified, g

_.

—

Mlss^*) Meabuted, g

748

796

(a) Difference in mass of fuel (f) and stainle.>s steel equivalent (ss) with respect to critical-assembly fuel element.

IB F u e l - E l e m e n t S t u d i e s

P o w e r a n d n e u t r o n - f l u x d i s t r i b u t i o n s w e r e m e a s u r e d in a 19 -p in IB fuel e l e n i e n t in t he c e n t e r p o s i t i o n of the M L , - 1 - 1 A c o r e . P i n - t o - p i n p o w e r r a t i o s i n d i c a t e a f a i r l y u n i f o r m r a d i a l d i s t r i b u t i o n i n c r e a s i n g f r o m the c e n t e r p in to a v a l u e of about b e t w e e n 1. 10 a n d 1. 14 in the s e c o n d r i n g of 6 p i n s a n d showing a s l i g h t d e c r e a s e to a v a l u e b e t w e e n 1. 12 to 1.00 of the c e n t r a l v a l u e in t he o u t e r 12 p i n s . The t h e r m a l flux b e h a v e d s i m i l a r l y . D a t a w e r e o b t a i n e d w h i c h m a y b e u s e d to e v a l u a t e the t h e r m a l u t i l i z a t i o n for t h i s fuel e l e m e n t .

33 and 34

REFERENCES

(1) Dingee, D. A . , Ballowe, W. C. , Klingensmith, R. W. , Egen, R. A . , Jankowski F . J . , and Chastain, J . W. , "GCRE Cr i t i ca l -Assembly Studies" , BlvII-1288 (September 10, 1958).

(2) Dingee, D. A . , Ballowe, W. C. , Egen, R. A . , Jankowski, F . J . , and Chastain, J. W. , "Fu r the r Studies With the GCRE Cri t ica l Assembly" , BMI-1306 (December 29, 1958). Confidential,

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