\

(J

i b

O A K RIDGE NATIONAL LABORATORY operated by

UNION CARBIDE CORPORATION NUCLEAR DIVISION

for the U.S. ATOMIC ENERGY COMMISSION

ORNL- TM- 2997

COPY NO. -

DATE - Apri l , 1970

EXPERIMENTAL DYNAMIC ANALYSIS OF THE MSRE WITH 23% FUEL

R . C . S t e f fy , Jr.

ABSTRACT

Tests were performed on t h e Molten-Salt Reactor Experiment t o deter- mine the system time response t o s t e p changes i n r e a c t i v i t y , t he neutron- f l u x - t o - r e a c t i v i t y frequency response, and t h e out le t - tempera ture- to- power frequency response. The r e s u l t s of each of t h e s e were found t o agrek favorably with t h e o r e t i c a l p red ic t ions .

The t i m e response tests were performed with t h e r e a c t o r ope ra t ing a t 1, 5 , and 8 MW and s u b s t a n t i a t e d t h e t h e o r e t i c a l p red ic t ions t h a t f o l - lowing a r e a c t i v i t y pe r tu rba t ion t h e system would r e t u r n t o i t s o r i g i n a l p o w e r level more r a p i d l y a t higher power levels than a t lower power l e v e l s and w a s load-fol lowing a t a l l s i g n i f i c a n t power l e v e l s . A noisy f l u x s i g - n a l (caused by c i r c u l a t i n g voids) hampered detailed comparison of t h e experimental r e s u l t s and t h e o r e t i c a l p red ic t ions .

Neutron flux-to-reactivity frequency-response measurements were per- formed us ing per iodic , pseudorandom b ina ry and t e r n a r y sequences. This type of t es t e f f e c t i v e l y prevented much of t he random noise contamination of t h e neutron f lux from e n t e r i n g t h e f i n a l ana lyses and gave r e s u l t s which contained l i t t l e s c a t t e r . t h e t h e o r e t i c a l p red ic t ions and v e r i f i e d t h a t f o r t h e &!,%E, t h e degree of s t a b i l i t y inc reases wi th power level.

The r e s u l t s were i n good agreement wi th

Outlet-temperature-to-Wwer frequency-response measurements were com- pared w i t h similar measurements made dur ing opera t ion w i t h the 23% f u e l and v e r i f i e d t h a t t h e basic thermal p r o p e r t i e s of t h e r e a c t o r system were e s s e n t i a l l y t h e same as expected.

Keywords : MSm, fused salts, r eac to r s , operat ion, r e a c t i v i t y , t e s t i n g , t i m e response, frequency response, s t a b i l i t y , pseudorandom b ina ry sequences, pseudorandom t e r n a r y sequences.

NOTICE This document contains information of a preliminary nature and was prepored primarily for internal use a t the Oak Ridge National Laboratory. It is subject to revision or correction and therefore does not represent a final report.

This report was prepored as an account of Government sponsored work. Neither the United States,

nor the Commission. nor any person acting on behalf of the Commission:

A. Makes any warranty or represmntation, expressed or implied, wi th respect to the occurocy,

completeness, or usefulness of the information contoined in th is report, or that the use of

any information, apporotus, method, or process disclosed in th is report may not infringe

privately owned rights; or

6. Assumes any l iabi l i t ies wi th respect to the use of, or for damages resulting from the use of

any information, apparatus, method, or process disclosed i n th is report.

As used i n the above, “perron acting on behalf of the Commission.’ includes ony employee or

controctor of the Commission, or employee of such contractor, to the extent that such employee

or contractor of the Commission, or employee of such contractor prepares, disseminates, or

provides access to, any information pursuant t o his employment or contract wi th the Commission,

or h is employment wi th such contractor. c

4. I

L

3

CONTENTS

Page

ABSTRACT ............................

INTROllLTCTION ..........................

TRANSIENTRESPONSE. .......................

FREQUENCYRESPONSE. ....................... Neutron Flux to Reactivity .................

Testing Procedure ...................

Analysis Programs ................... Discussion. ......................

Outlet Temperature to Power. ................

CONCLUSION. ...........................

LISTOFREFERFNCES ........................

. 1

- 5

- !I . 12

. 12

. 12

. 13

. 14

. 22

. 25

. 26

-LEGAL NOTICE--------1

I

I

R . C . S t e f fy , Jr.

5

EXFERDENTAL DYNAMIC ANALYSIS OF THE MSFE WITH 23% FUEL

e i t h e

INTRODUCTION

Seve ra l r e p o r t s and a r t i c l e s (References 1 - 6) r e l a t i n t o

t h e t h e o r e t i c a l o r a c t u a l ( o r both) dynamic response of t he Molten Sal t

Reactor Experiment have been publ ished. However, none of t hese has re-

por ted i n a concise form t h e dynamic response of t h e U-233 f u e l e d MSRE.

Reference 4 conta ins much of the frequency-response information r epor t ed

here in , b u t it i s presented i n a lengthy contex t which is p r imar i ly con-

cerned with comparing t e s t i n g s i g n a l s and techniques. The purpose of

t h i s r e p o r t i s t o g ive a b r i e f desc r ip t ion of t h e observed dynamic re-

sponse of t h e U-233 fue led MSRE, compare it with the t h e o r e t i c a l and sug-

g e s t poss ib l e reasons f o r d i f f e rences when appl icable , b u t t o eschew any

lengthy d e s c r i p t i o n of t h e t e s t i n g techniques.

TRANSlENT RESPONSE

A common method of desc r ib ing t h e dynamic response of a s t a b l e sys-

t e m i s t o d i sp l ay the system response t o a s t e p change i n an inpu t v a r i -

a b l e . For a nuc lear r e a c t o r , r e a c t i v i t y i s usua l ly t h e per turbed para-

meter . This type d e s c r i p t i o n ( i . e . d e s c r i p t i o n i n the time domain) has

t h e advantage of an i n t u i t i v e appea l t o people s i n c e we d e a l d i r e c t l y

wi th t i m e i n day-to-day l i v i n g .

i n t h e t i m e domain does have some disadvantages.

ou tput of i n t e r e s t i s contaminated wi th a l a r g e no i se component, t h e p a r t

of t h e output r e s u l t i n g from a s t e p input may be und i sce rn ib l e from t h e

p a r t caused by the no i se .

d i f f e r e n c e i n t h e neutron noise l e v e l between t h e 23%J f u e l loading and

23?J f u e l loading of the MSRF,. (The inc rease i n noise l e v e l w a s due t o

a concomitant i nc rease i n c i r c u l a t i n g void f r a c t i o n and was not an in-

t r i n s i c func t ion of t h e f i s s i l e i so tope . )

However, a n a l y s i s of a system response

Notably, i f the system

The reason f o r making t h i s po in t i s t h e l a r g e

An example of t h e uncont ro l led

4

neutron f l u x during high-power opera t ion f o r each f u e l i s shown i n F ig . 1,

and t h e r e l a t i o n s h i p between t h e f l u x noise and void f r a c t i o n i s r e a d i l y

observable . The void f r a c t i o n estimates which are l abe led on Fig. 1 were

achieved by varying the f u e l pump speed; however, t h e f u e l pump w a s

operated a t f u l l speed (- 1180 r p ) f o r a l l of t h e dynamics tes ts r epor t ed

here

During t h e i n i t i a l approach t o power with t h e 23% f u e l , time re-

sponses of t h e neutron f l u x t o a s t e p change i n r e a c t i v i t y were recorded * ** and a r e shown i n F igures 2, 3, and 4 f o r t he r e a c t o r a t 1, 5, and 8 MW,

r e s p e c t i v e l y . Also shown i n these f i g u r e s are the t h e o r e t i c a l p red ic t ions

f o r s t e p r e a c t i v i t y changes of t h e same magnitudes. The t h e o r e t i c a l c a l -

c u l a t i o n s were performed us ing t h e mathematical model and method descr ibed

i n Reference 2 . The noisy f l u x s i g n a l h inders a comparison of t h e f i n e r

d e t a i l of t he t h e o r e t i c a l and experimental curves, b u t t h e no i se w a s low

enough t h a t sone f e a t u r e s may be compared.

and t k e experirnental curves a r e i n good agreement.

I n general , t h e t h e o r e t i c a l

For t h e 1 - I G case (Figure 2), t h e i n i t i a l f l u x peak w a s s l i g h t l y

higher t h a K t h e theory predicted, then it o s c i l l a t e d below t h e i n i t i a l

l e v e l anE l a t e r increased aga ic w i t h a second peak occurr ing a f t e r about

360 s e e . The t h e o r e t i c a l curves agree t h a t t he change i n power should

'nave re turned t o a p o s i t i v e i n d i c a t i o n a t t h i s t i m e b u t i n d i c a t e t h a t it

should not have been as l a r g e i n magnitude as t h e observed behavior . The

e x t e n t t o which noise contaminat ioc forced the p o s i t i v e i n d i c a t i o n i s not

mcwn

The noise contamination i n the 5-MW case ( F i g . 3) makes it d i f f i -

c u l t t o compere d i r e c t l y t h e exgerimental and t h e o r e t i c a l r e s u l t s . They

ic The o r i g i n a l p l o t of t h e response a t 1 MW w a s made by a d i f f e r e n t

machine than the o t h e r two p l o t s . This accounts f o r t he d i f f e r e n c e i n gene ra l appearance of t h e p l o t s .

-H Full p o w e r w a s taken as 8.0 MW dur ing t h e d a t a a n a l y s i s and w r i t i n g

of t h i s r e p o r t .

7

P . R C L N T

50 60

PYRCENT

50 60

ORNL- DWG 69- 537 t R

LO

10

RCf NT

0

R C F N T

0

40 PLRCENT

50

PERCENT

50 40

1480 rpm 1460 rpm 1420 rpm 4070 rpm <0.1 VOI 70 0.6 VOIYO 0.3 vOI 70 0.1 VOI Yo

235" 233"

R R - 8 4 0 0 CHART (percent of 45 Mw)

F i g . 1. Secti-ons of Nuclear Power Recorder Chart Con t ra s t ing 235U Fuel, Full Flow and Few Bubbles wi th 23% Fuel, Varying Flow and Bubble F r a c t i o n . Conditions i n each c a s e : 7 MW, 12100F, 5 psig, 52 - 56% Fuel Pump Level.

a

+%

ORNL-DWG 70-2922

A-

0.7

0.6

0.5

0.4

a 0.2

0.1

0

- 0.1

POWER LEVEL= 1 Mw -

THEORETICAL EX PE R I M E NTAL

- ---

REACTIVITY INSERTED = 0.0139 'YO 8k/k -

60 120 180 240 300 360 420

TIME AFTER REACTIVITY INSERTION ( s e d

F?g. 2. Response of' t h e Neutron Flux t o a S t e p Change i n R e a c t i v i t y of 0.0139% 8k ,k wi th t h e Reactor I c i t i a l l y a t 1 MW.

9

0.8

0.6

0.4 3 r a 0.2

0

- 0.2

POWER LEVEL = 5 Mw THEORETICAL EX PER I M EN TA L REACTIVITY INSERTED =0.0190% 6k/k

--- - - .

Fig . 3. Response of the Neutron Flux t o a S t e p Change i n R e a c t i v i t y of O.OlgO% 6k/k with t h e Reactor I n i t i a l l y a t 5 MW.

10

are i n gene ra l agreement, b u t d e t a i l e d comparison would be guess-work.

The swells aid r o l l s t h a t occur a f t e r about 1-50 see a r e almost s u r e l y not

d i r e c t l y r e l a t e d t c t h e o r i g i n a l r e a c t i v i t y input s i n c e t h e system set-

t l i n g t i m e a t 5 i s about 1-50 see .

For the r e a c t o r opera t ing a t 8 WG, the f l u x response t o a r e a c t i v i t y

s t e p of 0.0248$ 6k/k i s shown i n Figure 4. The maximum power l e v e l was

reached during the f i r s t second a f t e r t h e r e a c t i v i t y i n p u t . This r a p i d

increase w a s accompanied by a r a p i d inc rease i n f u e l temperature i n t h e

core, which, coupled with t h e negat ive temperature c o e f f i c i e n t of reac-

t i v i t y , more than counter-balanced tine s t e p r e a c t i v i t y input , so t h e power

l e v e l began t o decrease. The temperature of t h e s a l t e n t e r i n g the core

w a s ccns t an t during t h i s i n t e r v a l , and when t h e power had decreased enough

f o r t he r e a c t i v i t y a s soc ia t ed with t h e increased nuc lear average tempera-

t u r e t o j u s t caficel t h e s t e p r e a c t i v i t y input , t he power l eve led f o r a

b r i e f t i m e (from - 6 t o - 1.7 sec a f t e r t h e r e a c t i v i t y i n p u t ) .

a f t e r t h e r e a c t i v i t y increase , t h e ho t f l u i d generated i n t h e i n i t i a l

p w e r increase completed i t s c i r c u i t of t h e loop e x t e r n a l t o t h e core , and

t h e nega t ive temperature c o e f f i c i e n t of t h e s a l t aga in reduced t h e reac-

t ivi;y so t h a t t he power l e v e l s ta r tec , down aga in . A t l a r g e times t h e

r e a c t o r power r e tu rnea t o i t s i n i t i a l l eve l , and t h e s t e p r e a c t i v i t y in-

put w a s counter-balanced by an inc rease i n t h e nuc lear average temperature

i n t h e co re . Fer t h e 5-MW case, a s h o r t p l a t eau w a s probably p re sen t

also, b u t t he xoisy s i g n s 1 ok,scured i t s presence. A t l oxe r powers, how-

ever , t h e slower system response prevented t h e r e a c t o r from reaching the

peak of i t s firs: o s c i l l a t i c n k e f c r e t h e f u e l completed one c i r c u i t of

t h e e x t e r n a l f u e l loop . The p l a t eau t h e r e f o r e d i d not appear i n t h e 1-MW

case a

About 1-7 sec

An inpor t an t c h a r a c t e r i s t i c of t ke MSRE dynamic response w a s t h a t as

the power decreased the r e a c t o r kecame both more s lugg i sh (s lower respond-

ing) and more o s c i l l a t o r y ; t h a t is, a t low powers t h e t i m e r equ i r ed f o r

o s c i l l a t i o n s t o d i e out was much l a r g e r than a t h igher powers, and t h e

f r a c t i o n a l amplitude of t h e o s c i l l a t i o n s (A power/power) was l a r g e r .

11

CRNL-DWG 70-2923

3 E a

1.4

1.2

i ,o 0.8

0.6

0.4

0.2

0

- 0.2

Fig . 4.

POWER LEVEL = 8 Mw --- THEORETICAL

-t -EXPERIMENTAL REACTIVITY INSERTED = 0.0248% 6k/k

I 1 1 1

1

0 20 40 60 80 100 TIME AFTER REACTIVITY INSERTION (sec)

Response of t h e Neutron Flux t o a S t e p Change i n Reac t iv i ty of 0.248% 6k/k with the Reactor I n i t i a l l y a t 8 MW.

12

Neutron Flux t o R e a c t i v i t y

Most of t h e e f f o r t i n experimental ly determining t h e dynamic response

of t he MSREi w a s expended i n determining the neu t ron - f lux - to - r eac t iv i ty

frequency response. One advantage of working i n t h e frequency domain i s

t h a t a per iodic waveform may be cont inuously imposed on a system inpu t

( e .g . r e w t i v i t y , through c o n t r o l rod movement) u n t i l s e v e r a l per iods of

data have been c o l l e c t e d . All of the s i g n a l power of a pe r iod ic s i g n a l

i s concentrated a t harmonic f requencies , and subsequent a n a l y s i s a t a

harmonic frequency very e f f i c i e n t l y e l imina te s most of t h e noise contami-

na t ion which i s usua l ly d ispersed over a wide frequency band. There are

r; ther advantages to wcrking i n the frequency domain, b u t t he more noisy

f l u x s i g n a l w i t h t h e 23?J f u e l loading makes t h i s a s a l i e n t advantage.

Seve ra l s t e p and -pulse t e s t s ( a R r i o d i c t e s t s ) were a l s o at tempted b u t

t h e s e do r o t have t h e s i g n a l energy concent ra ted a t p a r t i c u l a r f requencies

and the system noise w a s l a r g e enough t h a t t h e r e s u l t s contained t o o much

s c a t t e r t o be u s e f u l .

I Test ing Procedure

The pe r iod ic s i g n a l s used i n t h e frequency-response t e s t s were e i t h e r

pseudorandom b ina ry o r pseudorandom t e r n a r y sequences These are par-

t i c u l a r s e r i e s of square wave pulses t h a t were chosen because they evenly

d i s t r i b u t e d t h e s i g n a l power a t t h e harmonic f requencies over a wide f re-

quency range, which permit ted de t e rn ina t ion cf t h e frequency response

over a wide s p e c t r i n wi th only one t e s t . The frequency range over which

we obta ined frequency-response r e s u l t s was from about 0.005 t o 0.8 rad /sec ,

The lower l i m i t w a s se t by t h e l eng th of one per iod of t h e t e s t p a t t e r n

and t h e high-frequency l i m i t was determined by t h e t i m e width of t h e

square wave pulse of s h o r t e s t dura t ion which t h e s tandard equipment would

adequately reproduce. The s h o r t e s t b a s i c pulse width used i n t h e s e tes ts

was 3.0 see . ?he frequency range covered by these t es t s w a s e s s e n t i a l l y

t h e range elver which thermal feedback e f f e c t s are important .

The on- l ine computer, a Bunker-Ramo 340, was programmed t o genera te

t h e sequences by opening and c los ing a set of r e l a y s . Voltage was f e d

through t h e r e l a y s from an analog computer (E lec t ron ic Associates , Inc , ,

Model TR-10).

t r o l rods, which were forced e i t h e r t o fo l low the pseudorandom t e s t pa t -

t e r n themselves o r t o cause the f l u x t o fo l low t h e t e s t pa?;tern.4

cont ro l - rod pos i t i on and t h e neutron f l u x were d i g i t i z e d and recorded

every 0.25 sec on magnetic t ape . The data were r e t r i e v e d from t h e t ape

and s t o r e d on punched cards which could then be processed with t h e ana l -

y s i s programs t o y i e l d t h e frequency-response information.

This vo l tage was used t o determine t h e movement of t h e con-

The

Analysis Programs

Before d iscuss ing each of t he programs used t o analyze t h e data, it

i s p e r t i n e n t t o note t h a t i n some ins tances t h e d i f f e r e n t a n a l y s i s pro-

grams y ie lded markedly d i f f e r e n t r e s u l t s when app l i ed t o t h e same da ta .

It i s beyond t h e i n t e n t of t h i s r e p o r t t o delve i n t o t h e poss ib l e theo-

r e t i c a l explanat ions, b u t t h e i n t e r e s t e d reader may consu l t Reference 4 f o r a more complete t rea t i se on t h e s u b j e c t .

FOURCO. This code d i r e c t l y Four ie r transformed t h e time

The transformed output ( f l u x ) w a s then d iv ided by t h e t r a n s - records .

formed inpu t ( rod pos i t i on ) t o g ive t h e frequency response. This a n a l y s i s

w a s u sua l ly performed on t h e f u l l data record, which would con ta in s e v e r a l

per iods of t h e same waveform, b u t occas iona l ly w a s performed on i n d i v i d u a l

per iods of d a t a wi th t h e s e v e r a l r e s u l t i n g answers then ensemble averaged.

This l a t te r method is denoted FOURCO ENS5MBI;F: on t h e f i g u r e s

- CPSD.3.r6 This a n a l y s i s method u t i l i z e d a d i g i t a l s imu la t i cn of

an analog f i l t e r i n g technique f o r ob ta in ing cross-power s p e c t r a l dens i ty ,

CFSD, func t ions . This code c a l c u l a t e d t h e p c w e r spectrum of the input

s i g n a l and t h e cross-power spectrum of t h e inpu t and output s i g n a l s and

d iv ided t h e cross-power spectrum by t h e input power spectrum t o o b t a i n

t h e frequency response a t each frequency of a n a l y s i s .

t h i s code is an a d j u s t a b l e f i l t e r width about t h e a n a l y s i s f requency.

The key f e a t u r e of

7 C A B .7 The t h i r d c a l c u l a t i o n a l procedure w a s more involved.

The a u t o - c o r r e l a t i o n func t ions of t h e input and output s i g n a l s were calcu-

la ted and t h e c r o s s - c o r r e l a t i o n func t ion of t h e s i g n a l s was c a l c u l a t e d .

14

These were then Fcur i e r transformed t o ob ta in t h e input , output , and

cross-power s p e c t r a . The input power-spectrum w a s then d iv ided i n t o t h e

crcss-power spectrum t o obta in t h e frequency response.

Discuss ion

With t h e f u e l s t a t iona ry , t h e frequency response of t h e zero-power

MSRE w a s e s s e n t i a l l y t h e same as t h a t of any s t a t i o n a r y - f u e l , zero-power,

z3%-fueled r e a c t o r .

c i r c u l a t i n g i s shown i n Figure 5. The magnitude r a t i o ,

seen t o be i n gene ra l agreemect with t h e theory, b u t t h e phase angle i s

c o t i n p a r t i c u l a r l y good agreement. A t t he h igher f requencies f o r t e s t s

a t a l l power l e v e l s , t h e magnitude r a t i o and t h e phase angle were lower

than t h e t h e o r e t i c a l . This i s thought t o have been caused by t h e c o n t r o l

rod not adequately fol lowing t h e t e s t p a t t e r n y e t g iv ing t h e i n d i c a t i o n

t h a t it w a s . The ind ica to r s , which a r e phys i ca l ly loca t ed wi th t h e d r i v e

assembly, accu ra t e ly d i sp lay t h e a c t i o n of t h e rod-drive motors; however,

t h e f l e x i b i l i t y of the c o n t r o l rod makes it doubt fu l t h a t t h e t i p of t h e

rqd, whick i s akout 1.7 f t from t k e d r i v e assembly, reprcduces t h e high

frequency congmnent of t h e rod-drive movement.

The measured frequency response with t h e f u e l no t

fjn/N,.fjk, i s

The res1Alts of a t y p i c a l aero-power t e s t with t h e f u e l c i r c u l a t i n g

a r e shown i n Figure 6. c e l l e n t agreeKent with t h e t h e o r e t i c a l curve, b u t t h e r e s u l t s have been

norrnalized by mul t ip ly ing each experimental va lue by 1.75. The phase

angie da t a w a s i n b e t t e r agreement wi th t h e t h e o r e t i c a l p red ic t ions than

was t h e case f o r t h e non-c i r cu la t ing data, b u t t h e r e i s s c a t t e r i n t h e

r e s u l t s ~

The shape of $he magnitude r a t i o curve i s i n ex-

The need t o normalize some r e s u l t s and no t t o normalize o t h e r s i s

a l s o ccnsidered t o be caused by poor c o n t r c l rod i n d i ~ a t i o n , ~ The nor-

mal,iza%ion w a s no t power dependent s i n c e some da ta d i d and some d i d no t

need normalizat ion a t each power l eve l , and t h e normalizat ion f a c t o r s ,

when they were required, were d i f f e r e n t f o r d i f f e r e n t t e s t s .

A s we mentioned i n t h e introdiAction, s e v e r a l d i f f e r e n t t e s t i n g tech-

niques were used i n ob ta in ing t h e experimental r e s u l t s . An example of

lo4

5

2

5

2

IO2

OR N L - D W G 69 - I 2050

0

- [r

-0

W cn

Q, -30 v

a a I -60

-90 IO-^ 2 5 lo-2 2 5 lo-' 2 5 loo

FREQUENCY ( rad /sec)

Fig . 5 . Neutron Flux- to-Reac t iv i ty Frequency Response of' t h e 23%-Fueled MSRE a t Zero-Power wi th S t a t i o n a r y Fuel .

16

E

2

IO2 0

0

U Q) -30 v

w cn Q 1 - 6 0 a

lo4

5

2

5

-90

f 0 FOURCO . CPSD - THEORY

2 5

ORNL-DWG 69- 12044

10-2 2 5 lo-' 2 FREQUENCY ( r a d /set)

5 loo

Fig. 6. Keutror. F lux- to-Reac t iv i ty Frequency Response of t h e "%-Fueled Y&RE a t Zero-Fower with Ci rcu la t i -ng Fuel .

17

* r e s u l t s 4 obtained us ing a technique

i s shown i n F igure 7. d i c t i o n s , b u t they do l i t t l e toward v e r i f y i n g them e i t h e r , Ce r t a in ly ,

t h e r e s u l t s would have done l i t t l e toward desc r ib ing t h e r e a c t o r f s re-

sponse if the t h e o r e t i c a l response were unknown. These d a t a a r e shown

p r imar i ly t o d i sp l ay t h e system response a t low, b u t s i g n i f i c a n t , power.

A s a t i s f a c t o r y t e s t i n g technique

after the prel iminary tes ts were completed, and it was not convenient t o

r e t u r n t o 1 M W t o perform f u r t h e r t e s t s ,

tween t h e experimental r e s u l t s and the t h e o r e t i c a l p red ic t ions a t both

h igher and lower powers almost i n su res t h a t t h e t h e o r e t i c a l curve i s

very c l o s e t o t h e a c t u a l response, hence t h e 1-MW t h e o r e t i c a l curve may

be taken as t h e a c t u a l response. In addi t ion , t h i s f i g u r e i l l u s t r a t e s

t h e importance of t h e t e s t i n g technique which accounts f o r t he d i f f e r e n c e

i n appearance of t h e r e s u l t s i n Figure 7 and those i n F igures 8 and 9. The s c a t t e r i n t h e r e s u l t s shown i n Figure 7 i s due t o inaccurac ies i n

t h e ind ica t ed cont ro l - rod pos i t i on which were accentua ted by t h e t e s t i n g

technique.

t h a t was u n s a t i s f a c t o r y on t h e MSRE

The r e s u l t s do no t disprove the t h e o r e t i c a l pre-

** f o r t h i s r e a c t o r w a s no t found u n t i l

However, t h e good agreement be-

Typica l r e s u l t s from tes ts which employed t h e most s a t i s f a c t o r y

t e s t i n g technique a r e shown i n Figures 8 and 9 f o r t h e r e a c t o r a t 5 and

8 MW, r e s p e c t i v e l y .

r e t i c a l curves except f o r t h e s l i g h t discrepancy a t t h e h igher f r equenc ie s .

The dip i n t he magnitude-rat io curves a t - 0,25 rad/sec (corresponding t o

a loop t r a n s i e n t time of N 25 sec ) r e s u l t s from temperature feedback from

t h e e x t e r n a l loop. During a pe r iod ic r e a c t i v i t y pe r tu rba t ion a t a f re -

quency of about .25 rad/sec, t h e f u e l i n t h e core during one cyc le r e tu rned

The r e s u l t s are i n e x c e l l e n t agreement wi th the theo-

* This was t h e technique i n which t h e neutron f l u x w a s forced t o fo l low

t o fo l low t h e t e s t p a t t e r n . It w a s necessary f o r t h e c o n t r o l rod t o move almost con t inua l ly dur ing t h i s type t e s t and e r r o r s i n t h e ind ica t ed con t ro l - rod p o s i t i o n caused the u n s a t i s f a c t o r y r e s u l t s . The technique i s b a s i c a l l y sound and could be w e l l u t i l i z e d on a system wi th favorable hardware.

H The technique t h a t gave t h e most s a t i s f a c t o r y r e s u l t s was one i n

which t h e cont ro l - rod p o s i t i o n w a s fo rced t o fo l low t h e t es t p a t t e r n . The rod moved t o a new pos i t i on and then remained s t a t i o n a r y f o r s e v e r a l seconds u n t i l a d i f f e r e n t pulse w a s needed. This minimized cont ro l - rod movement and t h e a s s o c i a t e d e r r o r s .

ORNL-DWG 69-1 2051 io4

5

2

5

2

102 90

60

30 h

0 W U v

u o a cn I a

- 30

- 60

- 90 2 5 !o-2 2 5 io-’ 2

FREQUENCY (rad/sec) 5 ioo

Fig, 7. Neutron Flux-to-Reacti-vity Frequency Response of t h e 23%-Fueled MSRE a t 1 MW.

I

W

W

104 ORNL-DWG 69-12245

102

90

60

h

30 U

w cn

Y

a I O a

-30

- 60 { o - ~ io-2 {O-’

FREQUENCY (rad/sec)

IO0

Fig. 8. Neutron Flux-to-Reactivity Frequency Response of t h e 23%-T-Fueled MSRE at 5 MW.

20

ORNL-DWG 69-42246 t o4

5

2

(o3

5

2

4 O2

ANALYSIS METHODS

0 FOURCO, CABS, CPSD (EACH GAVE S A M E R E S U L T S )

- THEORY

90

0

60

30

0

-30

to-3 2 5 40-2 2 5 jo-’ 2 F R EQU E NCY ( ra d/sec)

IO0

Fig. 9. Neutron Flux-to-Reactivity Frequency Response of the 23%-Fueled MSRE at 8 MW.

21

t o t h e core one per iod l a t e r and, because of t he negat ive temperature coef-

f i c i e n t of r e a c t i v i t y , produced a r e a c t i v i t y feedback e f f e c t t h a t p a r t i a l l y

canceled t h e e x t e r n a l pe r tu rba t ion . The d i p i s obviously present i n the

experimental r e s u l t s as w e l l as i n t h e t h e o r e t i c a l curves; however, t he

d i p i n t h e experimental d a t a i s not as pronounced as t h e theory p r e d i c t s .

S ince t h e magnitude of t h e d i p has been shown2 t o be a func t ion of t h e

amount of s a l t mixing which occurs as the f u e l c i r c u l a t e s around t h e loop,

t h i s d i f f e r e n c e between t h e experimental and t h e o r e t i c a l implies t h a t no t

enough mixing w a s assumed i n t h e t h e o r e t i c a l model. Addi t iona l work wi th

t h e t h e o r e t i c a l model has shown t h a t i f the s a l t t r a n s p o r t i n t h e piping

i s r ep resen ted by a series of 2-sec f i r s t - o r d e r l a g s ( w e l l - s t i r r e d tanks

wi th mean holdup t imes of 2 sec ) r a t h e r than t h e pure delays t h a t were

assumed i n t h e e a r l i e r work, t h e d i p i n t h e experimental and t h e o r e t i c a l

responses are i n good agreement.

Below about 0.5 rad/sec, t h e magnitude r a t i o decreases as the power

i s increased . This s u b s t a n t i a t e s t h e observa t ion drawn from the t i m e

response p l o t s ; t h e degree of s t a b i l i t y f o r t h e MSRE inc reases wi th power

l e v e l . The lower magnitude r a t i o a t t h e higher power l e v e l s over t h e

frequency range i n which thermal e f f e c t s a r e important says, i n e f f e c t ,

t h a t f o r t h e same change i n r e a c t i v i t y t h e f r a c t i o n a l power (A power/power)

change w i l l be l e s s a t h igher power.

The frequency-response curves shown i n t h i s document d i sp l ay t h e

MSREgs frequency response a t seve ra l power l e v e l s . O f course, several

tes ts were performed a t s e v e r a l d i f f e r e n t power l e v e l s , b u t i n o rde r to

keep t h e p re sen ta t ion as s t r a igh t fo rward as poss ib le , we chose t o show

t h e r e s u l t s from r e p r e s e n t a t i v e tes ts . Table 1 summarizes t h e frequency-

response tes t s performed wi th t h e 23% f u e l loading and i n d i c a t e s the

scope of t h e t e s t i n g program which included 28 d i f f e r e n t tes ts of approxi-

mately one-hour du ra t ion each.

f u e l loading are given i n References 4 and 5 . Complete r e s u l t s of theo-

r e t i c a l dynamic ana lyses are given i n References 2, 5 , and 6. Note t h a t

some t e s t s were performed s h o r t l y af ter t h e start of opera t ion wi th 23%

f u e l , and o t h e r s were performed near t h e end of opera t ion wi th 23% f u e l .

There were no ind ica t ions t h a t t h e response of t h e r e a c t o r had changed with

ope ra t ing time.

Other experimental r e s u l t s f o r t h e 233J

22

Table 1

Information Related t o Frequency-Response

Tes t ing of 23%’-Fueled MSRl3

In t eg ra t ed No. of Tes t ing Power Pcwe r Tests

Dates (MW-hrs) Leve 1 Performed

10/15/68 11/7-8168

1/16/69 1 /20 /6 9 2/3/69 2/17/69

2/20/69 3/11/69 4/24/69 5 /26 /6 9*

0

0

86 435

2,390 L, 080

7,220 14,000

19,500

L , 490

100 w 50 w

5Mw 8MW

5Mw 8MW

1 M w

10 kW

8MW 8MW

1

6

3 1

1

1

3 1

2

9

* These t e s t s were performed f o r M . R . Buckner and

T. W . Ker l in of t h e Un ive r s i ty of Tennessee as p a r t of a graduate s t u d i e s program.

Ou t l e t TeKperature t o Fower

DLzring t h e neu t ron - f lux - to - r eac t iv i ty frequency-response t e s t s which

were conducted a t s i g n i f i c a n t p w e r l e v e l s , t h e response of a thermocouple

(TE-100-lA) on t h e o u t l e t pipe w a s a l s o recorded.

included power ( o r more s p e c i f i c a l l y , neutron f l u x ) and o u t l e t temperature

during a time i n which t h e power was va r i ed i n a pe r iod ic waveform. Hence,

t h e outlet-temperature-to-power frequency response could be determined a t

t h e same harmonic f requencies as t h e neu t ron - f lux - to - r eac t iv i ty frequency

The data records then

L

23

response. The r e s u l t s of t h i s determinat ion could then be compared wi th

t h e r e s u l t s of t h e o r e t i c a l p red ic t ions .

The outlet-temperature-to-power frequency-response r e s u l t s from a

t e s t conducted during opera t ion with 235 f u e l as w e l l as two t e s t s per-

formed during opera t ion wi th 23% f u e l are shown i n Figure 10.

mental r e s u l t s of a l l t h r e e t e s t s a r e e s s e n t i a l l y t h e same. This should

be expected s i n c e t h e temperature response t o a given change i n power i s

a func t ion of t h e thermal p rope r t i e s of t h e system, and these were changed

very l i t t l e with t h e change i n f i s s i o n a b l e m a t e r i a l .

The exper i -

Three t h e o r e t i c a l magnitude r a t i o p l o t s are a l s o shown i n Figure 10.

Curve 1 i s t h e a s -ca l cu la t ed curve and curves 2 and 3 a r e t h i s same curve

m u l t i p l i e d by 0.5 and 0.1, r e s p e c t i v e l y . Normalization of t h e t h e o r e t i c a l

by mul t ip ly ing by 0.5 f o r c e s agreement with t h e experimental r e s u l t s a t

low f requencies and mul t ip ly ing by 0 .1 f o r c e s agreement a t high f r equenc ie s .

The reason f o r t h e d iscrepancies between the experimental and t h e o r e t i c a l

have no t been explained leaving t h i s as an area open f o r more a n a l y s i s . It

i s of i n t e r e s t t o note t h a t i n some experimental work” performed by

S , J. B a l l and T . W . Ker l in i n which they at tempted t o determine t h e re-

sponse of ou t le t - tempera ture- to- in le t - tempera ture pe r tu rba t ions , they t o o

found a l a r g e r degree of a t t e n u a t i o n than had been t h e o r e t i c a l l y p red ic t ed .

The phase angle p l o t s shown i n Figure 10 a r e i n good agreement if

t h e t h e o r e t i c a l thermocouple response t o a power pe r tu rba t ion i s delayed

by 0.7 see more than w a s assumed i n t h e o r i g i n a l c a l c u l a t i o n .

de lay g ives a phase s h i f t t h a t changes l i n e a r l y w i t h f requency.)

t h e o r e t i c a l response of t h e thermocouple w a s represented by a 1-sec pure

delay p lus a 5-sec f i r s t - o r d e r l a g . This w a s based on c a l c u l a t i o n s per-

formed by 8. J. B a l l . ”

i n e r r o r by 0.7 sec f o r t h i s p a r t i c u l a r thermocouple depending on i t s

p a r t i c u l a r response c h a r a c t e r i s t i c s and phys ica l con tac t wi th t h e pipe.

Another poss ib l e source of e r r o r i s t h e estimate of t h e l o c a t i o n of t h e

thermocouple on t h e p ipe .

(A pure

The

This r ep resen t s a good estimate, b u t could be

The experimentally-measured outlet-temperature-to-power frequency

response v e r i f i e d t h a t t h e b a s i c thermal p r o p e r t i e s of t h e MSRE were es-

s e n t i a l l y unchanged by t h e change i n f u e l loading . The disagreement

24

too

50

20

I O

5

2

1

0.5

0.2

0.t

0

- 60

- UI W -0

W -J (3 z

v

- I 20

a

a W -180 v,

I a

-240

- 300 10

ORNL-DWG 70-3423

THEORETICAL WITH ADDITIONAL 0.70sec TIME LAG

-3 2 5 10-2 2 5 40-’ 2 FREQUENCY ( rad/sec 1

5 100

Fig. 10. Ou t l e t Temperature-to-Power Frequency Response of t h e MSRE with the Reactor a t 8 MW.

W

between the t h e o r e t i c a l and experimental magnitude r a t i o determinat ions

makes it meaningless t o draw any conclusions about t h e mixing e f f e c t s i n

t h e c i r c u l a t i n g system.

CONCWSION

The dynamic response of t he 23%-fueled MSF8 w a s analyzed by t h r e e

d i f f e r e n t methods, each of which had d e f i c i e n c i e s b u t each of which added

information. The t r a n s i e n t response of t h e neutron f l u x t o a s t e p change

i n r e a c t i v i t y a t var ious power l e v e l s v e r i f i e d t h a t the gene ra l response

of t h e system w a s as an t i c ipa t ed , b u t t h e noisy f l u x s i g n a l made d e t a i l e d

comparison of t h e t h e o r e t i c a l and experimental r e s u l t s d i f f i c u l t . The

shape of t h e experimental ly- determined neutron f lux - to - r eac t i v i t y f r e -

quency-response curves w a s i n e x c e l l e n t agreement wi th t h e t h e o r e t i c a l

curves over most of t he frequency range which w a s r e a l i z a b l e wi th t h e in-

s t a l l e d hardware. There were problems a s soc ia t ed wi th f i n d i n g a t e s t

method which would g ive good r e s u l t s , and erroneous c o n t r o l rod p o s i t i o n

i n d i c a t i o n s n e c e s s i t a t e d normalizat ion of some experimental r e s u l t s . The

o u t l e t temperature-to-power frequency-response determinat ion d id no t agree

we l l wi th theory b u t d id show t h a t t h e b a s i c thermal p r o p e r t i e s of t h e

MSFE w e r e e s s e n t i a l l y unchanged by t h e change from 23% t o 23% f u e l .

A t high powers, t h e MSRE i s a h ighly damped system. It r e t u r n s t o

i t s o r i g i n a l power level r ap id ly w i t h no undershoot o r wallowing. A t

low power l e v e l s , t h e uncont ro l led r e a c t o r tends t o be s lugg i sh and s l o w

i n r e t u r n i n g t o i t s o r i g i n a l power l e v e l .

w a s observed t h a t over 400 see was r equ i r ed f o r t h e f l u x l e v e l t o s t a b i -

l i z e after a s t e p change i n r e a c t i v i t y . In summary, t h e MSFB w a s s t a b l e

a t a l l power l e v e l s and t h e s t a b i l i t y increased wi th power as predic ted .

With t h e r e a c t o r a t 1 Mw, it

26

LIST OF F3FERENCES

1.

3.

4.

5.

6.

7.

a .

9"

10 D

11 0

S. J . B a l l and T. W . Kerl in , S t a b i l i t y Analysis of t h e Molten-Salt Reactor Experiment, USAFX Report ORNL-TM-1070, Oak Ridge Nat iona l Laboratory, (December 1965) .

R. C . S t e f f y , Jr., and P. J. Wood, Theore t i ca l Dynamic Analysis of t h e MSRE with U-233 Fuel, USAEC Report ORNL-TM-2571, Oak Ridge Nat iona l Laboratory ( J u l y 1969).

T. W. Ker l in and S . J. B a l l , Experimental Dynamic Analysis of t h e Molten-Salt Reactor Experiment, USAEC Report ORNL-TM-~~~~, Oak Ridge Nat iona l Laboratory, (October 1966) . R . C . S t e f fy , Jr., Frequency-Response Tes t ing of t h e Molten-Salt Reactor Experiment, USAEC Report O R N L - T M - ~ ~ ~ ~ , Oak Ridge Nat iona l Laboratory (March 1970).

MSR Program Semiann. Progr . Rept. , Feb. 28, 1969, USAEC Report ORNL-4396, Oak Ridge Nat iona l Laboratory.

MSR Program Semiann. Progr . Rept. , Aug. 31, 1968, USAEC Report ORNL-4344, Oak Ridge Nat iona l Laboratory, pp. 46 - 52.

S . J. B a l l , A D i g i t a l F i l t e r i n g Technique f o r E f f i c i e n t Four i e r Transform Calcula t ions , USAEC Report O R N L - T M - ~ ~ ~ ~ , Oak Ridge Nat iona l Laboratory, ( J u l y 1967) .

S. J. E a l l , Instrumentat ion and Cont ro l Systems Divis ion Annual Pro- g r e s s Report, September 1, 1965, USAEC Report ORNL-3875, PP. 126-127, Oak Ridge Nat iona l Laboratory (September 1965) . T. W. Ker l in and J . L. Lucius, CABS - A For t r an Computer Program f o r Ca lcu la t ing Cor re l a t ion Functions, Power Spec t ra , and t h e Frequency Response from Experimental Data, USAEC Report ORNL-TM-1663, Oak Ridge Nat iona l Laboratory, (September 1966) . MSR Program Semiann. Progr . Rept., Feb, 28, 1966, USAEC Report ORNL-3936, Oak Ridge Nat iona l Laboratory.

S o J. B a l l , Personal Commur.ication t o R . C . S t e f f y , Jr., J u l y 24, 1968.

ORNL-TM- 2997

INTERNAL DISTRIBUTION

1, N . J . Ackei*mann 2. R . K . Adams 3. R . G . Affel 4. J, L. Anderson 5. Z . F, Baes 6. S o J. B a l l 7. H. F, Bauman 8. S. E . B e a l l 9. M. Sender

10. E , S. Bet t is 11, R . Blumberg 12. E . G . Bohlmann 13 . C. J. Borkowski 1 4 , G . E . Boyd 15. R . 3. Briggs 16. A , R . Buhl 17. 0. W. Surke 18. D. W. Cardwell 19. F. H . C la rk 20. D, F. Cope, MC-OR0 21. W , B. C o t t r e l l 22. J. L. CrGwley 23. F. L. C u l l e r 24. S. J, D i t t o 250 W . P. E a t h e r l y 26. J. R . Engel 270 E , P. E p l e r 28. D. E . Ferguson 29. L. M. F e r r i s 30. J. K, Franzreb 31. A. Po Fraas 32. D. N . Fry 33. W . K. Furlong 34. C . H . Gabbard 35. A . Giambusso, AEC-Washington 36. 37. A . G , G r i n d e l l 38. R . H . Guymon 39. P. H, Harley 40, W . 0 . H a r m s 41. Po N . Haubenreich 42. A. Houtzeel 43. T. L. Hudson 44. W . H . Jordan

W. R . G r i m e s - G . M. Watson

45 46. 47. 48. 49. 50. 51. 52 * 53 - 54 0

55 56 57. 58 - 59. 60

61-62. 63. 64. 65. 66. 67. 68. 69. 70 * 71. 72. 73 9

74 75. 7 6 .

77-79. 80 a 81 82 83 . 84. 85. 86. 87. 88. 89.

90- 94. 95.

P. R . Kasten R . J. Ked1 T . W . Ker l in H . T . Kerr A . I . Krakoviak T. S. Kress R . C . Kryter Kermit Laughon, AEC-OSR M. I. Lundin R . H . Lyon R . E . MacPherson C . D. Martin C . Lo Matthews, AEC-OSR H. E . McCoy H . C . McCurdy C . K . McGlothlan T. W. McIntosh, AEC-Washington H. A. McLain L. E . McNeese J . R . McWherter A . J . Miller R . Le Moore E . L. Nicholson Lo C . Oakes A . M , Perry H . B. P iper B. E . Pr ince G . L. Ragan J . L. Redford M. Richardson D. R . Ri ley, AEX M. W. Rosenthal H. M. Roth, AEC-OR0 A . W . Savolainen Dunlap S c o t t R . M . Scrcggins , AEC M. Shaw, AEC-Washington W . H . S ides M. J. Skinner W. L. Smalley, AEC-OR0 A . N . Smith I. Spiewak R . C . S t e f f y D. A . Sundberg

28

ORNL-TM-2997

96. 97 - 98. 99 100. 101. 102.

104. 103.

105. 106-107. 108- 109. 110-112 *

113. 114. 115.

INTERNAL DIS TR IBUT I O N

( continued)

J . R . Tal lackson R . E . Thoma D. B. Trauger F. N . Watson, AFX-Washington A . M . Weinberg J. R . Weir M . E . Whatley J. C . White - A . S. Meyer G . D. Whitman Gale Young Cen t ra l Research Library (CRL) Y-12 Document Reference Sec t ion (DRS) Laboratory Records Department (LRD) Laboratory Records Department, Record Copy (LRD-RC) Nuclear Sa fe ty Information Center ORNL Pa ten t Off ice

EXTERNAL DISTRIBUTION

116-130. 131.

Division of Technical Information Extension (M'IE) Laboratory and Un ive r s i ty Div is ion (ORO)