ORNL-CF-61-12-50.txt

UCN-2383
(3 11-80)

OAK RIDGE NATIONAL LABORATORY
Operated by

 

UNION CARBIDE NUCLEAR COMPANY

Division of Union Carbide Corporation

Post c? Box X CENTRAL FILES NUMBER

Oak Ridge, Tennessee _

  

 

 

 

DATE: December 26, 1961 COPY NO. éii/

SUBJECT: MSRE -~ Analog Computer Simulation of the
System With a Servo Controller

TO: G’O Ao CI'iS-ty

FROM: 0. W. Burke

ABSTRACT

One purpose of this study was to determine whether the fuel salt

-~ temperature inside the reactor could be controlled with a closed-
loop servo controller. An "on-off" type controller was demonstrated
using four different control signals. The stability of the system

/ when using the controller was of primary interest.

These studies indicated that the system was stable for large and
relatively fast power demand changes when using the controller with
any one of the four control signals.

NOTICE

This document contains information of a preliminary nature
and was prepared primarily for internal use at the Oak Ridge
- National Laboratory. It is subject to revision or correction
. and therefore does not represent a final report. The information
N is not to be abstracted, reprinted or otherwise given public
dissemination without the approval of the ORNL patent branch,

Legal and Information Control Department.
CONTENTS

I. Introductionecseccococecosceoceecoososocococasso
IT. Description of the System Simulated secoceecoecse
IIT. Description of Controllerecececcoccccccocccocsoss
V. Description of the Control Signals Used cecoo
A. Control Signal No. 1, €, ccccccecooocssos

B. Control Signal No. 2, €
C. Control Signal No. 3,62 coeecccecccsoss

€,

® 0 06 60 © 060 0 0 06 © 06 0 O 0 o

D. Control Signal No. L
Vo Procedure and Res-tfl.ts’0.000000000000000000000

© © 0 0 ¢ 6 0 6 0 0 0 0 0 00

l. Basic Flow Diagram of MSRE System ococeoceee
2. Identification of Temperature Symbols....
3. MSRE Design Point Data_as of 12-13-60....
L. Generator Circuit for &/ ...ccccccoccsccs
5. Generator Circuilt for'f; ccoeescccocococe
6. Generator Circuit fOr€, eeceeccecoccccs
7. Generator Circuit forEL_ cocoeccoscoccee
8. Control Signal €, , Nuclear Power and
Mean PFuel Temperature in Reactor vs.
TiME cococooeocecccocscesossscooscoococcoonocosocos
9. Control Signal é&,, Nuclear Power and
Mean Fuel Temperature in Reactor vs.
TIiME ceeceococcsocsessosscoscoscooocsocoooccss
10. Control Signal 6; , Nuclear Power and
Mean Fuel Temperature in Reactor vs.

Time © 0 0 © O © O @ ©6 & & 06 ¢ 0 6 © ¢ 0 6 06 & 06 0 00 0 O © 0 0 00 © 0 0O 0

11. Control Signal 6;, Nuclear Power
andT VSo Timeooooooooooooooooooooooo
OI"
BibliOgraphy ©6 000006006 0©00O0O0O0O0CS6 066 060O0OCO0COOCO0O0OS O00O0COCO0 OO0

Distributign e 06 6 6 6 0 0O 8 0 0O © 6 06 ©0 @ © & 0 © 6 0 0 @ 0 06 06 060 06 0 6 ©0 0 0 ©0 © ¢ 0 o

O\

I
—~J

9-10
11-12
13

14

15

16

17

18

19
20

22-23
IT.

III ©

Introduction: It is desirable to provide a controlier for con-
trolling the fuel temperature inside the reactor. There are many
control conceptg that would do the job.

 

The decision was made to try a simple "on-off" controller. E. R.
Mann of the Instrumentation and Controls Division proposed four
control signals which have definite possibilities and suggested
that they be demonstrated on the analog computer. This report
covers the analog computer demonstrations.

Description of the System Simulated: A schematic flow sheet of the

MSRE system is shown in Figure 1., The temperature symbols are identi-
fied in Figure 2.  The design information used in these studies is listed
in Figure 3. The analog computer diagram is filed in the Engineering and
Mechanical Division print files on Drawings 40331 and L0332,

 

The simulation of the thermal system and nuclear system as used in these
studies has been discussed in previous preliminary reports.~ There were
two changes, however, that were significant. The temperature coefficient
of reactivity of the graphite was changed from:

2x10% 6k to -6x10° Sk
K-OF K-°F

and the total secondary salt looP transit time was changed from 13
seconds to 24.2 seconds.

Description of Controller: The controller simulated was a simple
"on-off" servo controller. The rod drive motor was a constant speed
motor, driving the rods at a constant velocity sufficient to change
the reactivity at a rate of:

 

0002 O K
K-sec.

For the sake of simplicity, the rod worth was considered to be linear
throughout the range used in these studies. The "time constant” of the
controller was assumed to be 50 milliseconds. This "time constant" is the
time required for the rod speed to attain 63% of full speed subsequent to
receiving a demand signal to move the rods. The "dead band" of the con-
troller was I 20F,

Description of the Control Signals Jsed: The four different control
signals used with the above described controller were as follows:

 

A. Control Signal No. 1,€&,

 

The egquation expressing éi is as follows:

IR e 4 )
where,
G = control signal gain factor or amplification factor.
m, n, and a are coastants that may be varied at will.

@ = neutron flux

 

To = Fuel salt temperature at the reactor outlet.

T
T;] = TFuel salt temperature at the inlet to the reactor.

r t
g(t) = )\.J[acb - (To:l - ‘I’J - g (t)] dt

r r
0 - L.

This can be considered as a'"rese% mechanism." t:_yfifxffflwfivfi
Tsp - The desired mean fuel temperature in the reactor.

The controlled variable in E} is the mean fuel temperature in the

reactor, Té] + TQJ » This variable appears only in the
r T

 

2

second term of the contrcl signal. If this term alone is used as
the control signal, the system 1s unstable.

The first terflliILGV can be considered as a high frequency band
pass stabilizing mechanism. It merely compares the rate of pro-
duction of nuclear power to the rate of addition of heat to the
fuel salt as it passes through the reactor. Note that for steady
state operation:

ddgg(t)}O =A.2[a 9 _(TOL- Tj]r>- g(t)] o
g (t)=2a ¢ - <§é]r - Ti}é)

This insures that the first term:flnf) will be zero for steady state
operation whether the term:

b (- o)

is zero or not. For this reason, the constant, "a'", does not have

to be reset for various power levels. thf) exceeds the dead band

_)_J__J
positively, rods will be inserted and iféi exceeds the dead band
negatively, rods will be withdrawn. The analog computer diagram
used to obtain 6} is shown in Figure L.

The temperature sensing elements are thermocouples attached tc the
walls of the pipes containing the fluids whose temperatures are to

be measured. There is a time lag between the time at which a change
in temperature of the fluild occurs and the time at which this change
is reflected in the thermocouple output signal. This time lag varies
with different thermocouple designs, pipe wall thicknesses, etc. The
time constant for this lag in the salt temperature thermocouples was
designated as'f£ and was considered to be 5 seconds.

-

=% #
¥ o G2 Ko
i

The time constant of the g(t) circuit wag%éhosen agt 10 times that
of the thermocouple. This lorgtime constant was necessary in order
to get "reset action" and still not interfere with the stabilizing
effect during transients.

The other three control signals are quite similar to €, and only
their differences fromfi will be pointed out in the following
descriptions of these signals.

Control Signal Nooza,el, o

 

The equation expressing€ is as follows:

%67;: m a ¢ - fa(Tc;la‘ T;Ja>~ g(t) p+ n (TOJT+ TJJ)--TSP

where,

f, = air flow rate across the radiator

TO = outlet air temperature from radiator
Ja

Ti = 1inlet air temperature to radiator
J a

 

The time constant used for the alr temperature sensing elements
was 2.5 seconds and that used in the g(t) circuit was 25 seconds

(T3 = 2.5and A}, = 0.04).

Note that the controlled variable is the same as forf& . The
stabilizing portion of the control signal is now formed by comparing
the rate of production of power in the reactor to the rate of re-
moval of power from the secondary salt by the alr flowing across

the radiator. Note that a multiplier is required in this circuit.

-5 -
The analog computer diagram used to f@rmulateé; is shown in Figure 5.

C. Control Signal No. 3363 o

 

The equation expressing €

%63 nia ¢ - (] JS>- 'g(fl + n (Tc]r+ Tflr>’2Tsp

secondary salt temperature at the radiator inlet

=
I

H
I

secondary salt temperature at the radiator outlet

 

—_ S

The controlled variable is the same as that 1n€ andC . The
stabilizing circuit is formed by comparing the rate of power production
in the reactor to the rate of power loss of the secondary salt as it
flows through the radiator. No multiplier is required since the flow
rate in the secondary salt system is constant.

The "time constant" potentiometer settings are the same as those used
in €, . The analog computer diagram used to obtain €, is shown in
Flgure 6.

D. Control Signal No. 4,€, .

 

The equation describing €

L€, { b (] - t)} (] )

This control signal is the same as €3 except that a different con-
trolled variable is used. The outlet fuel temperature from the
reactor is the controlled variable. The analog computer diagram
used to deriveé; is shown in Figure 7.

Procedure and Results: The system without a controller was shown to be
unstable subsequent to any appreciable perturbation. The system was also
shown to be unstable when using the controller with only the second term
in the above control signals.

 

The stability of the system with the gbove controllers was checked sub-
sequent to large changes in the power demand or load. The changes in the
load for the four runs, each using one of the four above described control
signals to the controller, were not precisely equal in magnitude and rate
of change. The change in load was accomplished by manually turning a
potentiometer. Also, no attempt was made to get optimum settings for M
and N in each case. Therefore, the results cannot be compared quantita-
tively. In later runs linear ramp load changes will be used, and optimum

-6 -
values of M and N used, so that wortrollers can be compared. Record-
ings of the controlled variliable and the neutron flux were made subssgquent
to a load change, while uging each of the four control signals to the
controller. The conditiong for these runs were ag follows:

A U81ng;€' as the control signal, M, as shown on the computer
diagram, wag set at 877 (qutg arbitrarily) and N was set at
0.5, The load, or the heat removal rate by the air across the
radiator, was se+ at approximately 2 megawatt and the system
permitted to stabilize. The load was increased from %'mw to
10 mw in 15 seconds, approximately at a constant rate. The
curves obtained are shown in Figure 8. On all the curves only
a relatively short time is shown. It can be seen that the curves
are converging, which indicates stability.

B. U31ng;€' as the control signal, M, as shown on the computer
dlagram,was set at 0.877 and N set at 0.5. The load was changed
from approximately 1.6 mw to 10 mw.in 17 seconds. The resguiting
curves are shown in Figure 9.

C. [knr@;f' as the coatrosl signal, M, as shown on tha computer
dlagramfl was set at 0.25 and N was set at 0.5. The load was
changed from approximately 1.6 mw to 10 mw in 13 seconds. The
resulting curves are shown in Figure 10.

De Using € 4 @8 the control signal, M, as shown on the computer
diagram, was set at 0.50 and N was set at 1.00. The ioad was
changed from approximately 1.6 mw to 10 mw in 11 seconds. The
resulting curves are shown in Figure 11.

The conclusion reached wag that the system would be stable using the con-
troller with any of the four control signals.

It should be pointed out that th= congtants M and N on the actual in-
stallation could be changed ov=r a congiderable range. No attempt was
made to get the optimum settings on the computer, due to time limitations.
ORHL-LR-D—wg. 64899

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

UNCLASSIFIED
PUMP
PUMP s e |
g | 200 GAM. Tes s, | "
- =
.T’:‘P‘/j Tes ‘ ¥
& v
‘ A T |
‘T;]R .T;z ‘ & -Tg TS3
- Tee _ t | AtrR —
'T,'Ja .,:j £ T ™ ]
a —* ————
—
, | L
REACTOR | 'T;j; s s
- | , RADIATOR

F1G. 1 BASIC Flow DIAGRAM OF MSRE SYSTEIM
 

Figure 2

TDENTIFICATION OF TEMPERATURE SYMBOULS

Te - Circulating fuz2l mean temperature in the reactor corsa.

Tro - Circulating fusl temperaturs at the outlet of the reactor corsz.

Tf3 - Circulating fus=l tzmperature at the inlet to the primary heat
exchanger.

Lel - Circulating fuel mean tempsrature in the primary heat exchanger.

Tf5 - Circulating fuel Temp ture at the outiet of ths primary h=at
exchanger.

Trg - Circulating fusl temperature at the inlet to the reactor cors,

Tg - Mean temperaturs of the graphits in the rsactor z0rz.

Emp - Mean temperature of the metal in the primary heat exchang=r wa.l.

Ty - Mean *temperature of the secondary salt in the primary heat excrangs=r.

Teo - Secondary salt temperaturs at the outlet of the primary heat exchangexz,

Ts3 - Secondary salt temperaturs at ths inlet to the radiator.

Taly - Mean temperaturs of the s=zomdary salt in ths radiator.

Lss5 - Secondary salt tempsraturs at the radiator outlet.

Ts6 - Secondary salt temperaturs ab tos inlet to the primary beat sxzarger

Lo - Mean *temp=raturs of the metal in the radlator.

Thot - Mean circulating fuel temperaturs in the "hot leg' of the primary
system.

Tcold Mean circulating fuel temperaturs in toe "oold leg" of the rrimary
systeto

Tha, - Mear air temperatire in the radlator.

 
Figure 2 (contd.)

Fuel temperature at reactor core inlet.
Fuel temperature at reactor core outlet,
Secondary salt temperature at the radiator inlet.

Secondary salt temperature at the radiator outlet.

Cooling air temperature at radiator inlet.

Cooling ailr temperature at radiator outlet.

= 10 -
Figure 3

’
) - \
MSRE DESIGN POINT DATA AS OF 12—13160

 

Reactor inlet temperature: 1175 O
Reactor outlet temperature: 1225 °F
Mean graphite temperature: (with no fuel absorption) 1230 °F
Residence time in reactor: | 7.63 sec.
Film drop from graphite to fuel: Linear with power
Heat capacity of graphite: 0.425 %EE_

# OF
Prompt ]?’and neutron heating in graphite: 6% of 10 MW
Residence time in piping from reactor outlet to H. E. inlet 3.09 sec.
Residence time in H. E. 2,24 sec.
Heat capacity of metal in H. E. | 200 BTU/°F
Avg. film drop between primary coolant and metal at D. P. 55.2 OF
Avg. drop in metal at D. P. | 56.7 OF
Avg. film drop between metal and secondary coolant at D. P. 26,1 OF

Film drop between primary coolant and metal as function of
flow: See graph, displace curve if necessary so that at 6.2
fps velocity /\T = 55.2 °F.

L .
Mean secondary coolant temperature at D. P. 1062 F

Residence time in piping between H. E. outlet and reactor 9.04 sec.
inlet (including coolant annulus) |

Total circulation time 22,0 sec.
Temperature coefficient of reactivity of graphite: -6 x 10-5CSK/K=OF
Temperature coefficient of reactivity of fuel: -3.3 x 10720 k/k-CF
Melting point of primary coolant: 8up °F

Melting point of secondary coolant: 860 °F

- 1] -
Figure 3 (contd.)

Check points:

 

 

 

N
- Thermal resistances: ft. hr. OF
BTU
. . : _l
o in primary coolant film: 3.28 x 10
| -l
in metal: 3.32 x 10
: . =l
in secondary coolant film: 1.56 x 10
Simulator data for secondary 1loop
Air temperature rise in radiator 200 °F
Air suction temperature 100 °F
Air flow 166,000 cfm
(7.11 x 10°  #/nr)
Heat capacity of radiator L2 BTU/OF
. BTU
Heat capacity of secondary salt 0.57
- # OF
A~
Density of secondary salt 120 #/ft3
Residence times of secondary salt:
in primary heat exchanger 1.75 ség;'{
in piping to radiator 5.20 sec.
in radiator 7.14 sec.
in piping from radiator 10.11 sec.
Total 2L .20 sec.
Residence time of air in radiator 0.0l sec.
Temperature differences in radiator:
in salt film 13.4 CF
. in tube wall 78 .4 OF
in air film (0.7 O
AN

- 12 -
ORNL-LR~Dwg. 64900

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

+7;JF\’ | - H¢t) /‘
5 3 NN
‘ CP w -&- (e =721 —#4)] ‘
+ €,

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

. = o.l(f,g—{)

=&, = M{,a.cp =(Tde- T’T-JR)*?('&)} * N{(.T;JR.'-E]R) -c TSP}

FIG 4. GENERATOR CIRCUIT FOR €,
- 13 - |
ORNL<=LR=DWg .. 64901
Unclassified

- %(t)/l
N

—fa b= £ (T] )~ o)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

| .
SENSe L £,
. TIME . ‘
'T‘,_j , LAG | ( )

S

 

 

 

 

 

 

 

 

 

 

FIG.5 GENERATOR CIRCUIT FORE,.

- 14 -
.

+T;JR ( >

Unclessified
ORNL-LR-Dwg. 64902

1)
I

T A LA "{Qtp ~(n]5-T°]5)~?(t)}

 

l
/gls
G

 

 

 

 

 

 

 

 

 

 

 

+
A,
o
4
©
®

 

 

 

   

 

 

 

 

 

 

| N  SENsoR
+—r;jr? | TimMmfE LAG
Y
7y | |

 

 

 

 

 

 

 

 

| | “{('73.7«"* TL]R)' Z’TS"}
—lo0oV %fi X %7
o

A, = 0-}’ ('Cll"s3

Le =mfad-(T- -r;]s)__?cfl} + N{(Te] T ) =2 Ter

G €3

FIG.6 GENERATOR CIRCUIT FOR €3.

- 15 -
ORNL-LR-Dwg . 64903
Unclassified

- |

L
Ts
Trine LA fad ~(1,~ 7)) - 1#)f
Ae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

-D )
+ ¢ a
—O—
|
SENSOR /"T'
“TTIME LAS /)
_, 0 o
+ -T”JIP Z . \\, -+ 64
\. | \\
L
G

 

~/ooVv

Ao E 0. (6"})

Loe, = m{acp -'(72]3.“73]5)‘?(‘&)} + N (T = Tsr)

FIG.7 GENERATOR CIRCUIT FOR €,.

- 16 =
(°F)

121

in Reactor

1200

1190

Mean Fuel Temp.

Nuclear Power (mw)

0

Elapsed Time from Start of Transient (sec.)

- 17 -

ORNL~LR-Dwg. 6490k

 

"w
v
%,
%fi:’,

3 ¥

M b
1220

(°F)

1210

in Reactor

1200

1190

Mean Fuel Temp.

10

Nuclear Power (mw)

O

Elapsed Time from start of Transient (sec.)

 

- 18 -

ORNL~LR-Dwg. 64905
Unclassified

 
(°F)

in Reactor

Mean Fuel Temp.

Yuclear Power (mw)

1210

1200

1190

Elapsed Time from Start of Transient (sec.)

- 19 -

ORNL~-LR-Dwg. 64906

 
ORNL~LR-Dwg. 614907

e
/,/

50

D

1

 

 

 

 

 

1O o

can 3

—— e e fea

— e egeeies
i ; .

e g e v} o g ek i = e

1

Jamcd

TS T
“ O

o .D.w,w

 

20 -

Flapsed Time from Start of Transient (sec.)
)

VO

BIBLIOGRAPHY

O. W. Burke, MSRE - Preliminary Analog Computer Study—
Flow Accident in Primary System, ORNL CF 60-6-110
(June 27, 1960)

 

O. W. Burke, MSRE - Analog Computer Simulation of a
Loss of IFlow Accident in the Secondary System and a
oimulation of a Controller Used to Hold the Reactor
Power Constant at Low Power Levels, ORNL CF 60-11-20
(Nov. L, 1960)

O. W Burke, MSRE - An Analog Computer Simulation of
the System for Various Conditions - Progress Report
No. 1, ORNL CF 61-3-42 (March 8, 1961)

- 21 -
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17.
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26.
27.
o8.
29,
30.
31.
32.
33.
3,
35.
36.
37.
38.
39.
LO.
b1,
Lo,
L3,
Ly,
L5,
L6.

MSRP Director's Office

G
L.

® ® e * . ®

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HgegdsQ2nd ey OndidEROdE P OEH D >EH= D>

M.
G

. B.
. Bender

. Bettis

. Bettis

. Billington
. Blankenship
. Boch

GEGQE = nNnH

Adamson
Alexander
Beall

Bohlmann

. BOlT

Borkowski

. Brandon
. Bruce

. Burke

. Cole

Conlin
Cook
Cristy
Crowley
Culler
DeVan
Doss
Douglas

. Dunwoody

. Epler

. Ergen

. Ferguson

. Fraas

. Frye

. Gabbard

. Gallaher

. Greenstreet

Grimes
Grindell

. Guymon

Harley
Harrill
Haubenreich
Hise

. Hoffman
. HOlZ

Howell

. Jarvis

Jordan

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B. S. Weaver

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