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AE
-131
AE-131
Measurements of Hydrodynamic Instabilities,
Flow Oscillations and Burnout in a Natural
Circulation Loop
K. M. Becker, R. R. Mathisen, O. Eklind
and B. Norman
AKTIEBOLAGET ATOMENERGI
STOCKHOLM, SWEDEN 1964
AE-131
MEASUREMENTS OF HYDRODYNAMIC INSTABILITIES, FLOW
OSCILLATIONS AND BURNOUT IN A NATURAE CIRCULATION
LOOP
Kurt M. Becker, R« P. Mathisen. O. Eklind and B. Norman
Summary:
The hydrodynamic stability and the burnout conditions for flow
of boiling water have been studied in a natural circulation loop in the
pressure range from 10 to 70 atg. The test section was a round, duct
of 20 mm inner diameter and 4890 mm heated length.
The experimental results showed that within the ranges tested
the stability of the flow increases with increasing pressure, increas
ing throttling before the test section, but decreases with increasing
inlet sub-cooling and increasing throttling after the test section.
The measured thresholds of instability compared well with the
analytical results by Jahnberg.
For an inlet sub-cooling temperature of about 2 °C the measur
ed burnout steam qualities were low by a factor of about 1.3 compared
to forced circulation data obtained with the same test section. At
higher sub-cooling temperatures the discrepancy between forced and natural circulation data increased, so that at At , = 16 °C, the na
tural circulation data were low by a factor of about 2.5.
However, by applying inlet throttling of the flow the burnot
values approached and finally coincided with the forced circulation
data. '
Printed and Distributed in January 1964.
LIST OF CONTENTS
Page
1.0 Introduction 3
2. 0 Apparatus 5
2. 1 Test Section and Power Supply 6
2.2 Instrumentation 6
3. 0 Experimental Procedures 8
4.0 Research Program and Range of Variables 9
5. 0 Results of Preliminary Runs Without SteamSeparator 11
6.0 Results with Steam Separator 12
6.1 Effect of Pressure 12
6. 2 Effect of Inlet Sub-cooling 14
6.3 Effect of Liquid Level 15
6.4 Effect of Inlet Throttling 15
6.5 Effect of Outlet Throttling 16
6. 6 Measurements with Simultaneous Inlet andOutlet Throttling j 7
7. 0 Comparison with Analytical Results a7
Nomenclature 19
Bibliography 20Table 21Figures 22
- 3 -
1.0 Introduction
During recent years a research program concerning the flow
of steam water mixtures in vertical heated channels has been in
progress at the Heat Engineering Laboratory of AB Atomenergi in
Sweden. During the first phases of this program the steady forced
circulation flow was studied, and measurements of pressure drop,
void fractions, heat transfer coefficients and burnout have been
presented in a series of reports (1, 2, 3, 4, 5, 6).
However, in the channels of a nuclear boiling reactor natural
circulation flow is encountered. For this case the driving head is
the difference in density of the steam water mixture inside the
channel and the water in the moderator which also acts as a down
comer. In a system like this it has been observed by many investi
gators that the flow may become unstable and that heavy hydrody
namic oscillations may under certain conditions start to develop.
These oscillations have a great effect on the burnout conditions for
the channel, so that burnout values obtained in a natural circulation
system may only be a fraction of those which one would predict on
the basis of steady state measurer ents. Furthermore the oscilla
tions influence the void volume in the channels and therefore also
the reactivity of the reactor.
It is therefore of major importance for the designer of boiling
reactors to be able to n re diet the onset of flow instabilities in the
fuel elements, and also the nature of the flow and the burnout con
ditions during oscillatory behaviour of the system. During the last
few years the results of a .large amount of work, both theoretical
and experimental, have appeared in published works concerning
this problem. Despite this, present knowledge in the field is not
sufficient for safe and accurate predictions of the hydrodynamic
stability of the flow in boiling water reactor systems.
It was therefore decided to include in our two phase flow research
program a study of the flow in verv'.cal heated channels during natural. ’
- 4 -
circulation. The method of attacking the problem has been to simu
late the reactor fuel element by means of a test section which
is electrically heated. It is desirable to carry out full-scale experi
ments, but such experiments would be very time-consuming and
expensive. In addition, it would be difficult to interprete or analyze
in terms of the basic flow variables, the results obtained in full-
scale test sections consisting of a large number of rods.
We therefore found it quite suitable to start the investigation
by studying the flow in channels of the most simple geometry, such
as round ducts with the purpose of determining the influence on sta
bility and burnout of such basic parameters as static pressure, in
let subcooling, surface heat flux, mass velocity, test section dia
meter, heated length and inlet and outlet throttling. However, it is
planned later on to continue the investigation in annuli and rod
clusters.
The application of the results obtained in a simple geometry
to the design of fuel elements in nuclear reactors is of course quite
problematical. However, simultaneously with the present experi- .
mental study, a theoretical analysis of the problem has also been
conducted, and the analytical results will be reported separately
by Jahnberg (7). Because of the simple geometry the present ex
perimental results may prove to be very useful for testing the
accuracy of the theoretical model, which later on may be applied
to reactor computations.
One should also note that another important physical differen
ce exists between a loop experiment and the conditions encountered
in a reactor. When the flow oscillates in the reactor, the steam
void fraction and the reactivity of the system become time depen
dent. The change of reactivity influences the power which again in
fluences the void fraction. In a loop experiment the above-mention
ed coupling between void fraction and power is not present, nor is
the coupling between different channels.
- 5 -
The present report deals mainly with the measurements ob
tained with a 20 mm inside diameter test section of 4980 mm heat
ed length. Some preliminary measurements obtained with a 10 mm
inside diameter duct of the same length, and in a somewhat different
loop are also included.
2. 0 Apparatus
The flowsheet of the loop is shown in figure 1 and in figure 2
a photograph of the upper part of the apparatus is reproduced.
From the 4890 mm long electrically resistance heated test
section of 20 mm inner diameter the fluid flows through a riser of
36 mm inside diameter and into a steam separator. The details of
the separator are shown in figure 3. The steam water mixture was
discharged radially into the separator through 96 holes in the riser.
The diameter of the holes was 8. 2 mm. From the top of the steam
separator the steam flowed to an aircooled condenser, with a capa
city of 300 kW, and the condensate returned to the bottom of the
steam separator where it mixed w ,th the rest of the water. From
the separator the water flowed through a 51 mm inner diameter
downcomer, passed a preheater and a cooler for adjusting the in
let temperature, before returning to the inlet of the test section.
The downcomer was also supplied with a throttle valve and between
the preheater and the test section a venturimeter was mounted for
measuring the flow rate.
The loop was designed for an operating pressure of 65 atg
and constructed of stainless steel.
For further details of the loop and its exact dimensions we
refer to a previous report (B).
Initially the loop was constructed without a steam separator
in accordance with the flowsheet i i figure 4. Some measurements
obtained with the loop without separator are also included in the
present report.
2. 1 Test section andjpower supply
The test section consisted of a. 20 mm inner diameter stain
less steel duct of 4980 mm heated length. Three copper cylinders,
32 mm outside diameter and 25 mm long were brazed on the test
section at three points, one in the center and one at each end. The
copper electrodes, supplying the power to the test section, were
clamped round the copper cylinders. The power was supplied from
a direct current generator. The maximum available current was
6000 amps, and voltages ranging from 0 to 140 volts could be ob
tained. The two end electrodes were connected to one pole of the
generator, and the central electrode to the other pole. This arrange
ment made it unnecessary to insulate the test section from the rest
of the loop in order to prevent loss of electric power to the other
parts of the loop.
The pressure taps, consisting of 4 mm inner diameter stain
less steel tubes, were welded round 1,. 0 mm diameter holes on the
test section, just below the lower electrode and just above the upper
electrode.
2, 2 Instrumentation
The following quantities were measured.
1. Static pressure
2. Pressure drop over test section .
3. Inlet and outlet water temperatures
4. Power input
5. -Mass flow rate - .
6. Liquid level in the steam separator
7. Wall temperatures at 16 axial positions of the test section
8. Pressure drop over the throttle valve
(
The static pressure in the loop was measured with a precision
calibrated manometer connected to the inlet of the test section.
The pressure drops over the test section and the throttle
valve were obtained by means of D.P. cells.
The fluid temperature measurements were accomplished by
means of copper constantan thermocouples mounted in wells
100 mm deep and with a 3 mm inside diameter. A precision
Cambridge potentiometer was used for measuring the voltages.
The wall temperatures were also measured by means of copper
constantan thermocouples connected to the potentiometer.
The liquid level in the steam separator was measured by
means of a D.P. cell, and is in the present report given as the
height above the lower electrode, where the heating of the test
section starts.
The power was obtained by measuring the voltage over and
the current through the test section. The voltage was measured with
a Goerz precision voltmeter of 1/4 per cent rated accuracy, and
the current was obtained by measuring the voltage over a calibrated
shunt. For the latter measurement a millivoltmeter with a rated
accuracy of l/4 per cent was used.
The mass velocity was measured with a calibrated venturi-
meter. The venturimeter pressure drop was obtained with a D.P.
cell. The accuracy of the flow measurement is estimated at 2 per
cent.
The flow oscillations were observed by studying the time
variations of the mass velocity. The output of the D.P. cell was
coupled to an oscillograph where traces of the oscillations were
obtained. Observations of the oscillations were also possible by
studying the pressure drop over the test section.
~ 8 -
Further, two burnout detectors were installed in order to
prevent the test section from being damaged by overheating when
burnout conditions were reached.
3,0 Experimental Procedures .
Before starting a run the loop was completely filled with de
salinated water, and all ducts connecting instruments to the loop
were degassed.
4 Then a small amount of power was supplied to the test
section. As the temperature of the water increased, the surplus
water due to thermal expansion was discharged from the loop
through a cooler and to the laboratory drain, so that the desired
operating pressure was obtained. The power to the test section was
slowly increased, and as steam started to be generated the dis
charge rate from the loop increased and a water surface in the
loop was formed. This procedure continued until the water surface
had reached the desired level in the steam separator. Then the
first readings of the instruments were taken. After noting the ob
servations the power was slightly increased, the liquid level adjust
ed by discharging more fluid and after about 15 minutes thermal
equilibrium was obtained so that a new set of readings could be tak
en. This procedure continued until the burnout detector shut off the
power, indicating that burnout conditions had been reached in the
test section
As the power increased and the void fraction in the test sec
tion and the riser increased, the driving head, which is equal to the
difference in weight between the fluid in the downcomer and the test
section-including the riser, also increased. This caused the flow
rate to increase. However, one generally reached a point where the
additional driving head due to increased power was not sufficient-to
compensate for the increased friction and acceleration pressure
drops in the test section. Then the mass flow rate started to de-
- 9 -
crease when the power was further increased. Ultimately the pow
er reached a value where the flow became unstable and started to
oscillate. Three cases are actually possible.
1. Diverging oscillations causing burnout
2. Stable oscillations
3. Burnout without oscillations.
For the second case, the amplitude of the oscillations in
creases , if one continues to increase the power, and burnout will
finally be obtained.
For the third case the flow is completely stable until burnout
is obtained, and one would expect the burnout values to be identical
with values obtained during steady state forced circulation.
During the present study all three cases have been encountered.
4. 0 Research Program and Range of Variables
The main part of the present, report deals with measurements
obtained with a 20 mm inner diameter test section of 4980 mm heat
ed length. An examination of the problem revealed that for a fixed
geometry of the loop and the test section the following parameters
may influence the threshold of instability.
1. System pressure
2. Inlet sub-cooling
3. Liquid level in the steam separator.
The critical power may therefore be defined by the func
tion.
(q/A)Cr = f(P- & "gut' H) (1)
The mass velocity, m/F, and the steam quality x are not
included since the6 3 parameters a'>; determined when the parame
ters in eq. 1 are fixed. In addition to the parameters in equation 1
- 10 -
it was decided also to study the effects of changing the geometry of
the loop. The geometrical changes employed were throttling of the
flow before or after the test section.
The performance of the loop permitted the static pressure to
be varied between 10 and 70 atg, the inlet sub-cooling between 2 and 16 °C and the .liquid level between 563 5 and 593 5 mm above
the reference level.
Throttling of the flow before the test section was achieved by
means of the throttle valve in the downcomer: 5 positions of this
valve were employed.
‘ Throttling of the flow after the test section was obtained by
reducing the number of 8 mm holes in the riser exit. 2, 3, 4 and
96 holes were used. In addition, a few runs were made with both
inlet and outlet throttling.
In order to reduce the number of runs, the effect of inlet sub
cooling, liquid level and throttling were only studied at a pressure
of 50 atg. The total research program consisted then of 30 runs.
Some preliminary runs obtained before the steam separator
was installed are also included in the present report. These runs
comprised measurements with a section of 10 mm inner diameter
of 4980 mm heated length.
For the runs without steam separator it was difficult to keep
the water level constant during a complete test. As the power was
increased and more cooling capacity was required, the liquid level
in the cooler moved downwards. Further it was very difficult to
operate at low sub -cooling temperatures, so that the measurements
were performed in the sub-cooling temperature range from about 80 to 250 °C.
- 11 -
5.0 Results of Preliminary Runs Without Steam Separator
In figures 5 and 6 the measured mass velocities are plotted
versus the surface heat flux. The figures cover data between 10
and 60 atg obtained with a 10 mm tube, and the inlet temperatures were 20 and 100 °C respectively for the two sets of data given in
the figures. One should note that the inlet temperature knd not the
inlet sub-cooling is constant so that the sub-cooling varies with the
pressure.
The end point on each curve represents the last measurement
of the series. A further increase of the power caused the burnout
detector to react, indicating that burnout conditions had been ob
tained in the test section. For all the runs shown in figures 5 and
6 the flow was stable until the last power increase. Then diverging
oscillations with a frequency of about l/4 sec developed and
after a period varying between 10 and 45 seconds the burnout de
tector reacted. The oscillations were observed as fluctuations on
the mass flow rate, the inlet temperature and the test section
pressure drop measurements.
The figures reveal that the stability of the loop increases with
the pressure. Concerning the effect of inlet sub-cooling a compa
rison of the data in figures 5 and 6 indicate that the critical power
increases as the inlet sub-cooling increases. This, however,
should not lead to any general conclusion that the stability of the
flow increases as the inlet sub-cooling increases. One should note
that in the present case where the inlet temperatures for the two 'sets of data are 20 and 100 °C respectively, a substantial part of
the power is used for heating the water up to the saturation temp
erature, A more correct measure of the effect of inlet sub-cooling
on the stability is obtained by considering the exit steam qualities
which are plotted in figure 7 versus the static pressure. One ob- .
serves that the exit steam quality at the onset of instability increas
es with both the pressure and the inlet temperature, indicating that
the flow becomes more stable at higher pressures and at lower in
- 12 -
let sub-coolings. Actually, one might expect the flow to become
completely stable when the pressure approaches the critical pressu
re since no flow oscillations of the kind studied in the present work
can exist at the critical pressure.
6, 0 Results with Steam Separator
The main and most important part of the present study dealt
with measurements obtained when the steam separator was mount
ed in the1 loop. The performance of the loop was now much better,
compared with the earlier case, as it was easier to control the
pressure and the inlet temperature, and the data obtained under
these conditions were therefore more accurate and possessed an
excellent reproducibility. ,
The effects of pressure, inlet sub-cooling, liquid .level, in
let throttling and outlet throttling were studied separately. In the
Sallowing paragraphs the measurements dealing with each of these
variables will be discussed.
6.1 Effect of pressure
The effect of pressure was studied for the case where the inlet sub-cooling was approximately 2 °C, and where the liquid sur
face was 5835 mm above the reference level. The reults are shown
in figure 8, where the measured mass velocities are plotted versus
the surface heat flux. The power density,or the power per litre test
section, is also indicated along the horizontal axis, since perhaps
this parameter is of greater significance for the stability than the
surface heat flux. Curves representing the threshold of instability
and the burnout values are also given. Concerning the measurement
of mass velocity after the onset of instability, there may be slight
errors in the measured values, due to the effects of fluid accelera
tion on the venturimeter readings. Only dotted curves are therefore
shown in the oscillating flow regime.
- 13
One observes that as the pressure increases the threshold
of instability increases and approaches the burnout curve with
which it coincides at approximately 65 atg. For higher pressures
burnout is obtained directly without the,..flow passing through the
oscillating regime.
The flow oscillations were studied by recording the output from
the venturimeter and its D.P. cell. Figures 9 and 10 show traces
obtained at different pressures just before burnout. Although the
absolute values may possess serious errors, the figures show
that as the pressure increases the amplitude of the oscillations
becomes smaller, indicating less violent oscillations and more
stable flow.
Figure 11 shows the frequencies of the oscillations discuss
ed in the previous diagrams. A slight increase in frequency from -1 -10. 55 sec to 0. 62 sec is found as the pressure increases from
10 to 50 atg.
Figure 12 shows traces of mass velocity oscillations obtain
ed at a pressure of 20 atg. As the heat flux increases and burnout
conditions are approached, the amplitude of the oscillations in
creases while the frequency remains almost constant.
Reverting to figure 8, one observes that the burnout heat flux
has a maximum value at a pressure of 65 atg. This is in agreement
with the available information for steady state forced convection
burnout where the maximum heat flux occurs at a pressure between
40 and 7 5 atg (9).
In order to compare the measured burnout values with forced cir
culation burnout conditions, the test section was, on completion of
the measurements, mounted in a forced circulation loop. This loop
had a pump with a pressure head of 8 atg. It was therefore possible
to apply heavy throttling of the flow before the test section, securing
- 14 -
stable operation of the loop. Unfortunately the forced circulation
loop had only a maximum, operating pressure of 40 atg, so that the
comparison could only be established up to this pressure.
The comparison in question is given in figure 13 in terms of
the burnout steam qualities and the data are summarized in table
I on page 21. One should note that the forced circulation data were
obtained by extrapolating from the measurements to the same heat
fluxes as the natural circulation data. The comparison reveals that
the forced circulation data are higher by a factor of about 1.3 . This
seems to be the case even at the highest pressures where no flow
oscillations were observed. No satisfactory explanation has been
found for this discrepancy.
However, this could be attributed to the fact that the ampli
fication of the signals from the flow measuring device has not been
adequate to indicate minor oscillations in the natural circulation
flow at high pressures.
6. 2 _ Effect^ of Jnlet Sub-cooling
The effect of inlet sub-cooling was studied at a pressure of 50
atg and a liquid level, H, of 5835 mm in the steam separator. The
mass velocity versus heat flux curves are given in figure 14, and in
figure 15 the heat fluxes at the onset of oscillations and at burnout
are plotted versus the inlet sub-cooling. It is observed that the sta
bility of the flow is strongly reduced as the inlet sub-cooling increases. At 16 °C inlet'sub-cooling a critical heat flux of 24 W/cm^
was obtained compared with 73 W/cm^ at 2 °C sub-cooling.
However, at very large sub-cooling temperatures it is possible,
as discussed in section 5.0, that the critical power will start to in
crease with a further increase of the inlet sub-cooling, since a re
latively large portion of the power is then used for just heating the
water up to the saturation temperature. This behaviour is demonstrat-
- 15 -
ed in figure 16, where the critical power density at a pressure of
50 atg is plotted versus the inlet sub-cooling. In the figure are also included the data obtained at 1 64 °C and 244 °C inlet sub - cooling
with the 10 mm diameter test section before the steam separator
was installed. A very large increase of the critical power density
is observed at the highest sub-coolings, so that the values obtained at 244 °C inlet sub-cooling, is actually higher than the value
corresponding to 2 °C sub-cooling.
Our loop is now being modified with the purpose of being
able to study the flow in the whole range of sub-cooling tempera
tures.
6.3 Effect of Liquid Level
The effect of the liquid level in the steam separator was studied for the case of 2.0 °C inlet sub -cooling and 50 atg pressu
re. The maximum possible variation was 300 mm, and since this
value is small compared with the length of the test section with
the riser, only small variations of the measured critical and burn
out heat fluxes may be expected. The conclusions reached should
therefore be treated with caution.
The measured mass velocities versus surfase heat flux are
shown in figure 17. One observes that the burnout heat flux increas
es slightly with increasing liquid level, while the critical heat flux
remains constant. The corresponding steam qualities, however,
which are indicated in figure 18, decrease with increasing liquid
level, suggesting that the loop stability decreases with increasing
liquid level.
f),_4 Effect^of J-nlet Th_rottling_
The effect of throttling before the. test section was studied for the cases of 50 atg pressure, 583 5 mm liquid level and 2, 0 °C
and ~ 11.0 °C respectively inlet sub-cooling. The measured mass
-16-
velocities are given in figures 19 and 20. The throttling of the flow
through the throttle valve is indicated by means of the E, values de
fined by the equation
APi= EiDii
where v is the velocity of saturated water through the test section.
One observes that as the throttling increases, the stability of
the loop also increases and one reaches a point where the flow is so
stable that burnout is obtained directly without preceding flow
oscillations. With regard to the burnout heat fluxes, these also in
crease with increasing inlet throttling until they reach a maximum
whereafter they decrease with further throttling due to the high
steam qualities which are now encountered in the test section.
This is more clearly demonstrated in figure 21, where the
burnout steam qualities are plotted versus the inlet throttling. The
corresponding values for forced circulation are also indicated in
the figure. The forced circulation points were obtained by extra
polation to 50 atg from,the measured values, which were obtained
between 10 and 40 atg. As the pressure drop over the throttle valve
increases, the measured burnout steam qualities rapidly approach
the values for forced circulation, indicating the absence of flow
instabilities.
6. 5 Effect of Outlet Throttling
The outlet throttling was varied by changing the number of 8
mm holes at the end of the riser. For all the measurements in the
previous paragraphs 96 hole's were used corresponding to a valueof 16.15 of the ratio Fq/F, where F is the cross sectional area
of the test section and F is the area of the riser outlet. The flowowas throttled by reducing the number of holes to 2, 3 and 4 corre
sponding to area ratios of 0.328, 0. 492 and 0. 656. For these runs„ o
the pressure was fixed at 50 atg, the inlet sub -cooling at « 2 C and
the liquid level at 583 5 mm.
17
The results arc shown in figure 22. As the outlet throttling of the
flow increases, the critical and the burnout heat fluxes decrease
sharply, indicating that outlet throttling renders the flow more
unstable. The burnout steam qualities, which are also indicated,
first approach the forced circulation value of 0. 80, but the value
for the highest throttling is only 0.48. No satisfactory explanation
has been found for this fact.
6. 6 Measurements with Simultaneous Inlet an Outlet Throttling
Finally one test series was obtained using a riser with three
8 mm holes and varying the inlet throttling. This test series was performed at a pressure of 50 atg, 2 °C inlet sub -cooling and a
liquid level of 583 5 mm. The results are shown in figure 23. One
observes that the burnout heat flux first increases, reaches a maxi
mum value and thereafter decreases with the inlet throttling. Further,
it is seen that the flow becomes more stable as the inlet throttling in
creases and reaches a condition where burnout is obtained directly
without preceding flow oscillations.
The burnout steam qualities for the runs in figure 23 varied
between 0. 82 and 0. 93, which is well above the forced circulation
value of 0. 80. This inconsistency is probably due to an error in the
mass flow rate measurements at burnout.
7.0 Comparison with Analytical Results
Simultaneously with the measurements described in the present
report, an analytical study of the problem was undertaken by Jahnberg
(7) with the aim of developing a model which later could be used for
predictions of reactor stability. The first phase of that study consist
ed of developing a model describing the flow during steady state. Du
ring the second phase small perturbations were added to the steady
flow, and a model for predicting when the perturbations would grow
- 18 -
or decay was established. The details of the analysis are given in
the reference mentioned above.
Figures 24 and 25 show a comparison between the predicted and the measured mass velocities for the case of 2 °C inlet sub
cooling and no throttling. In the pressure range from 20 to 50 atg
the agreement between theoretical and measured mass velocities is
rather good, the discrepancy being a maximum of 10 per cent and on
the average only 3-4 per cent. For 10 atg the theoretical values
are about 15 per cent higher than those measured, but at 7 0 atg the
theoretical are about 15 per cent lower. The measured and the pre
dicted thresholds of instability are also indicated in the figure. One
should note that for the case of 70 atg burnout was obtained without
observing any oscillations. In this case the analysis predicts stable
flow up to a steam quality of 1.0.
The thresholds of instability are more clearly demonstrated
in figure 25, where the surface heat fluxes at the onset of oscillations
are plotted versus the pressure. The measured values compare
excellently with the predictions, the difference between the two sets
of values being always less than 10 ner cent.
The data obtained at 50 atg inlet sub-cooling temperatures of 7, 11 and 16 °C were also analyzed by Jahnberg. Figure 26 shows
the predicted and the measured stability limits. The agreement
between experimental and analytical results is excellent also for these
cases.
As regards the cases with inlet or .outlet throttling, these are
now being analyzed and the results will be given in a later report.
- 19 -
Nomenclature
Symbol Definition Units
d Diameter . m
F Cross section of heated duct2m
F o Outlet area of riser2m
f F requency -isec r
H Liquid level m
L bleated length m
rh/F Mass velocity kg/ m sec
P Pressure atg
AP Pressure drop over test section mm H^O
APi Pressure drop over throttle valve
mm H-,0
Q Power input kW
q/A Surface heat flux W/cm^
(q/A)CR Critical surface heat flux W/cm^
(q/^Bo Burnout heat flux W / cm^
t Temperature °C
^ sub Inlet sub -cooling °c
V Volume of test section ' 3m
V Fluid velocity . m/ sec
X Steam quality Dimens ionles s
XCR Critical steam quality Dimensionless
XBO Burnout steam quality Dimensionless
P . Density kg/m^
ii Resistance factor for throttle Dimens ionles svalve
- 20 -
Bibliography
4. KM Becker, G Hernborg and M BodeAn Experimental Study of Pressure Gradients for Flow of Boiling Water in a Vertical Round Duct ( Part 4, 2, 3 and 4), Reports AE-69, AE-70, AE-85 and AE-86, AlctiebolagetAtomenergi, Stockholm, Sweden.
2. S Z Rouhani and K M BeckerMeasurements of Void Fractions for Flow of Boiling Heavy Water in a Vertical Round Duct, Report AE-108, Aktiebola- get Atomenergi, Studsvik, Sweden.
3. KM Becker ct al. , lMeasurements of Burnout Conditions for Flow of Boiling Water in Vertical Round Ducts (Part 4 and 2), Reports AE - 87 and AE-114, Aktiebolaget Atomenergi, Studsvik, Sweden.
4. KM Becker and P PerssonAn Analysis of Burnout Conditions for Flow of Boiling Water in Vertical Round Ducts, Report AE-443, Aktiebolaget Atomenergi, Studsvik, Sweden.
5. KM Becker and G Hernborg -Measurements of Burnout Conditions for Flow of Boiling Water in a Vertical Annulus, Trans. ASME Paper 63-HT-25
6. KM BeckerBurnout Conditions for Flow of Boiling Water in Vertical Rod Clusters, AICHE Journal, March 1963
7„ S JahnbergA One-dimensional Model for Calculation of Non-Steady Two- Phase Flow, Paper presented at EAES-Symposium, Studsvik October 1-962.
8. R P Mathisen, G Hernborg and L ValkingNatural Circulation Experiment. Description of the Loop and its Behaviour, Including Some Test Results, Report R4-472/ RPL-641, Aktiebolaget Atomenergi, Studsvik, Sweden. 9
9. • J G CollierHeat Transfer and Fluid Dynamic Research as Applied to Fog Cooled Power Reactors, Report AECL-1 631, June 1962.
- 21
Table I. Burnout Data
Natural Circulation
p Atsub m/F q/A XBO
eg/ cm2 °C2
kg/m s TA/cna2 %
20 4.1 500 51.5 52.6
30 3.2 563 58.8 56.2
40 2.8 630 67.0 60.0
50 2.1 732 75.7 60.9
60 2.2 805 80. 5 61.4
70 2.4 900 79.0 51.7
Forced Circulation
20 70 310 51. 5 0.70
30 70 350 58. 8 0.75
40 115 350 67. 0 0. 80
AIR COOLED CONDENCER
LEGENDH-RISER HEIGHT I - INDICATOR P-PRESSURE R-RECORDER T-TEMPERATURE
FIG 1 NATURAL CIRCULATION LOOP
. Upper part of natural circulation loop.Fig. 2
TO CONDENSER
RISER
LIQUIDSURFACE
CONDENSATE FROM CONDENSER
TO INLET OF TEST SECTION
FROM TEST SECTION
Fig. 3, Steam separator.
LIQUIDLEVELINDICATORTO DRAIN AIR COOLED
CONDENSER
MANOMETER
OUTLET TEMPERATURETHERMOCOUPLE
ELECTRODE
i-16-THERMOCOUPLES
ELECTRODE
ELECTRODE
INLET TEMPERATURETHERMOCOUPLE
----- TURBINEMETER ORVENTURIMETER
Mj MANOMETER
[PUMPJ
Fig. 4. Flow diagram for loop without steam separator
'THRESHOLD OF INSTABILITY AND BURNOUT
INLET TEMPERATURE , t„ = 20‘C INNER DIAMETER,d = 10mm HEATED LENGTH, L = 4890
5E200
SURFACE HEAT FLUX, q}A, wjcm:
Fig. 5. Measured mass velocities.
INLET TEMPERATURE, t„ =100*C INNER DIAMETER,d=10mm HEATED LENGTH, L*4890
THRESHOLD OF INSTABILITY AND BURNOUT
SURFACE HEAT FLUX, qjA,wjcm3
Fig. 6. Measured mass velocities
ma
ss vel
oc
ity,
0.5
INNER DIAMETER,d =10mm *" HEATED LENGTH . L=4890
o 20
0 10 20 30 40 50 60 70PRESSURE, p, kg/cm2
Fig. 7. Exit steam quality at onset of oscillations.
H = 5835 mm
ONSET OF INSTABILITY.
5.0 i 0.5
BURNOUT3.2 i 0.32.8 i 0.32.1 i 0.32.2 1 1.02.4 ± 0.5
SURFACE HEAT FLUX, wjcrrV
120 140 160POWER DENSITY, ojv.kw/liter
Fig. 8. Effect of pressure
q)A= 51. s w|<
TIME, T, sec.
Fig. 9. Traces of oscillations.
rtfF-SeakgJrrfsxv
mjF»732kg|irfs
*lFeS3° ^ -qfA=sto wjcm1
P=>30otg <^A= S*.B wjcnf
PaSO otg q|A=75.7 wjcW*
10TIME, T, sec.
Fig. 10. Traces of oscillations.
FREQ
UEN
CY,
f, sec
0.7
0.4
0.3 ---------------------- ----------------------- ----------------------- ----------------------- ----------------------- -----------------------
0.2---------------------------------------------------------------------------------------------------------------------------- -
0.1-------------------------------------------------------------------------------------------------------------------------------
0|......................... .......................... ............... ........................ .......................... .................. ........0 10 20 30 40 50 60
PRESSURE,p, kgjcm2
Fig. 11. Measured frequencies.
BURNOUT q(A=51.S w|i
at =3.5 t
TIME, T, sec.
Fig. 1 2. Traces of oscillations.
1.0
• -
"
r ■
-
•/
/
1
^ •
-o N/
PCJURAL
Ptfil:iRCULAlCP #1
'ION (q/A ro BE TAt<EN
■ -o FORCED CIRCULATION (THE q/A-VALUES ARE
EQUAL TO THE CORRESPONDING NATURAL *CIRCULATION VALUES). . .
Sx>'
00
tSo.5h(Z)
o0
110 20 30 40 50 60 70 80
PRESSURE, p, kgjcm2
Fig. 13. Comparison between naural and forced circulation burnout data.
p*SO otg
7,2 *C
2.1 *CONSET OF INSTABILITY
BURNOUT
o 2.1 S 0.3» 7.2 i 0.2
a 16.0 i 0.2
0 10 2 0 30 40 5 0 60 7 0 6 0SURFACE HEAT FLUX, W cm2
4- ......... . I ......... ..4,. I ........ ■■■■*............................ I
60 60 100 120 U0 160POWER DENSITY, ojv, kw/liter
Fig. 14, Effect of inlet subcooling.
u0 20 40
p a 50 atgH * 5835 mm
BURNOUT
ONSET OF INSTABILITY
0 2 4 6 8 10 12 14 16 18 20INLET SUBCOOLING TEMPERATURE, Atgub/ °C
Fig. 15, Effect of inlet subcooling on critical and burnout heat fluxes.
200
c15Q
p= 50 otg
V / .
\\ m ID, WITH STEAM SEP
m ID,WITHOUT STEAM
APATDR —- <-
a 10 m SEPARATOR.
>a
100
1
$ 50
50 100 150 200INLET SUBC00UNG TEMPERATURE, At$ub ,°C,
250
Fig. 16. Effect of inlet subcooling on critical power density.
1500
<P,fotg) H, (mm)
Q 50 2.0 ±0.3 5635A 50 1.9 ±0.3 5735O 50 2.1 +0.3 5835V 50 2.0+0.3 5935
0 10 20 30 40 50 60 70 , 80SURFACE HEAT FLUX,W|cm2
*.......-...... * * .......... » —....- '............................ .. ■ «-.....-....................... ‘ - ■.......... ............... ‘ ■
0 20 40 60 80 100 120 140 160POWER DENSITY, 0/V, kw/liter
Fig. 17. Effect of liquid level.
0.7 ---------—-------------
p= 50 a
AtsulT 2-(
....... ........................
tg
3 t 0.1
A
A '—-___BUR!vjOUT
nwsFT n
------------^
F INSTABILITY
__
ro'
>-t—I<3O
Z < UJ i—to
as
0.55600 5700 5800 5900 6000
LIQUID LEVEL,H,mmFig. 18. Effect of liquid level on critical and burnout
steam qualities.
FULLY OPEN VALVE 0.27 t 0.03 1.68 t 0.08 4.30 ± 0.07
12.5 ±0.6o 2.4 ±0.4» 3.3 ±0.5
.ONSET OF INSTABILITY
-BURNOUT
SURFACE HEAT FLUX, wjcm1
0 20 60 60 80 100 120 140 150POWER DENSITY, ojv, kW^litef
Fig. 19. Effect of inlet throttling.
H — 5835 mm
O 11 ±0.2 FULLY OPEN VALVE 0.61 ± 0.06 1.38 ± 0.07 3.2' i 0.2
o 11 ± 0.2X 11 ± 0 2
ONSET OF INSTABILITY
BURNOUT
60 70 8SURFACE HEAT FLUX, W cm'
POWER DENSITY, o/v, kw/liter
Fig. 20. Effect of inlet throttling.
MA
SS VEL
OC
ITY,
mjF, ker
n's
BU
RN
OU
T STE
AM
QU
ALI
TY,
1.0
i—o- -O—D-— «r
CL
p* 50 atg H= 5835 mm
-6-
Q5z t^Crfr '1 45< alA< 78 wjcm2
lsub 1 v- >
■ NATURAL CIRCULATION, a - NATURAL CIRCULATION, a l$ub
FORCED CIRCULATION (THE qjA-VALUES ARE EQUAL TO THE CORRESPONDING NATURAL CIRCULATION VALUES).
500 1000 1500 2000PRESSURE DROP OVER THROTTLE VALVE FOR NATURAL CIRCULATION, *P; , mm HjO,
Fig. 21. Effect of inlet throttling on burnout.
o 2.1 ±0.3v 3.1 10.4
a 3.2 ± 0.4
ONSET OF INSTABILITY.
SURFACE HEAT FLUX, W cm'
120 140 ISOPOWER DENSITY, o|v, kW/liter
Fig. 22. Effect of outlet throttling
MA
SS VEL
OC
ITY,
m F, kgm
2s
p— 50 atgo 3.0 1 0.6 FULLY OPEN VALVE
o 3.4 ± 0.4 i 0.3± 0.6
v 4.5 t 0.5 -52.81000 h
ONSET OF INSTABILITY
BURNOUT
SURFACE HEAT FLUX, W cm
POWER DENSITY, o|v,kW/liter
FIG.23. EFFECT OF INLET AND OUTLET THROTTLING.
p*10 otgPREDICTED
•MEASURED
ONSET OF INSTABILITY
SURFACE HEAT FLUX,
MEASUREDONSET OF INSTABILITY
SURFACE HEAT FLUX, ^w/cm2
•MEASURED
PREDICTED
>ON5ET OF INSTABILITY
0 20 40 SO SURFACE HEAT FLUX,
Fig. 24. Comparison between analytical andexperimental results.
[ONSET OF U STABILITY
*60 SURFACE HEAT FLUX, qjA, Wjenf
IEASUREO
ONSET OF INSTABILITY-
SURFACE HEAT FLUX.sjA.Wj
•MEASURED
•BURNOUT
60 SURFACE HEAT^FLUX^qjAiwjcrf?
Fig. 25. Comparison between analytical andexperimental results.
100
<tuxUi
gcrs
40
20
BURNOUT WITHOUT OSCILLAT IONS.
i> '
o FREE>ENT ME.YTICAL
ASUREMERESULTS
NTS __a ANAL
0 10 20 30 40 50 60 70 80PRESSURE, p, kg|cm2
Fig. 26. Comparison between experimental and analytical results.
Fig. 27. Comparison between experimental and analytical results.
LIST OF PUBLISHED AE-REPORTS
1—60. (See the back cover earlier reports.)61. Comparative and absolute measurements of 11 inorganic constituents of
38 human tooth samples with gamma-ray spectrometry. By K. Samsahl and R. Soremark. 19 p. 1961. Sw. cr. 6:—.
62. A Monte Carlo sampling technique for multi-phonon processes. By Thure Hogberg. 10 p. 1961. Sw. cr. 6:—.
63. Numerical integration of the transport equation for infinite homogeneous media. By Rune Hdkanssan. 1962. 15 p. Sw. cr. 6:—.
64. Modified Sucksmith balances for ferromagnetic and paramagnetic measurements. By N. Lundquist and H. P. Myers. 1962. 9 p. Sw. cr. 6:—.
65. Irradiation effects in strain aged pressure vessel steel. By M. Grounes and H. P. Myers. 1962. 8 p. Sw. cr. 6:—.
66. Critical and exponential experiments on 19-rod clusters (R3-fuel) in heavy water. By R. Persson, C-E. Wikdahl and Z. Zadwdrski. 1962. 34 p. Sw. cr. 6:*—.
67. On the calibration and accuracy of the Guinier camera for the determination of interplanar spacings. By M. Moller. 1962. 21 p. Sw. cr. 6:—.
68. Quantitative determination of pole figures with a texture goniometer by the reflection method. By M. Moller. 1962. 16 p. Sw. cr. 6i—.
69. An experimental study of pressure gradients for flow of boiling water in a vertical round duct. Part I. By K. M, Becker, G. Hernborg ond M. Bode. 1962. 46 p. Sw. cr. 6:—.
70. An experimental study of pressure gradients for flow of boiling water in a vertical round duct. Part II. By K.M, Becker, G. Hernborg and M. Bode. 1962. 32 p. Sw. cr. 6r—•.
71. The space-, time- and energy-distribution of neutrons from a pulsed plane source. By A. Claesson. 1962. 16 p. Sw. cr. 6:—.
72. One-group perturbation theory applied to substitution measurements with void. By R. Persson. 1962. 21 p. Sw. cr. 6:—.
73. Conversion factors. By A. Amberntson and S-E. Larsson. 1962. 15 p. Sw. cr. 10:—.
74. Burnout conditions for flow of boiling water in vertical rod clusters. By Kurt M. Becker. 1962. 44 p. Sw. cr. 6:—.
75. Two-group current-equivalent parameters for control rod cells. Autocode programme CRCC. By O. Norinder and K. Nyman. 1962. 18 p. Sw. cr. 6:—.
76. On the electronic structure of MnB. By N. Lundquist. 1962. 16 p. Sw. cr. 6;—'.
77. The resonance absorption of uranium metal and oxide. By E. Hellstrand and G. Lundgren. 1962. 17 p. Sw. cr. 6:—.
78. Half-life measurements of *He, "N, "O, 20F, 28AI, 77Sem and 110Ag. By J. Konijn and S. Malmskog. 1962. 34 p. Sw. cr. 6:—.
79. Progress report for period ending December 1961. Department for Reactor Physics. 1962. 53 p. Sw. cr 6:—.
80. Investigation of the 800 keV peak in the gamma spectrum of Swedish Laplanders. By I. O. Andersson, I. Nilsson and K. Eckerstig. 1962. 8 p. Sw. cr. 6,:—.
81. The resonance integral of niobium. By E. Hellstrand and G. Lundgren. 1962. 14 p. Sw. cr. 6:—.
82. Some chemical group separations of radioactive trace elements. By K. Samsahl. 1962. 18 p. Sw. cr. 6:—.
83. Void measurement by the (y, n) reactions. By S. Z. Rouhoni. 1962. 17 p. Sw. cr. 6,:—.
84. Investigation of the pulse height distribution of boron trifluoride proportional counters. By I. O. Andersson and S. Malmskog. 1962. 16 p. Sw. cr. 6,:—.
85. An experimental study of pressure gradients for flow of boiling water in vertical round ducts. (Part 3). By K. M. Becker, G. Hernborg and M. Bode. 1962. 29 p. Sw. cr. 6:—.
86. An experimental study of pressure gradients for flow of boiling water in vertical round ducts. (Part 4). By K. M. Becker, G. Hernborg and M. Bode. 1962. 19 p. Sw. cr 6:—.
87. Measurements of burnout conditions for flow of boiling water in vertical round ducts. By K. M. Becker. 1962. 38 p. Sw. cr. 6:—.
88. Cross sections for neutron inelastic scattering and (n, 2n) processes. By M. Leimdorfer, E. Bock and L. Arkeryd. 1962. 225 p. Sw. cr. 10:—%
89. On the solution of the neutron transport equation. By S. Depken. 1962. 43 p. Sw. cr. 6:—.
90. Swedish studies on Irradiation effects in structural materials. By M. Grounes and H. P. Myers. 1962. 11 p. Sw. cr. 6:—.
91. The energy variation of the sensitivity of a polyethylene moderated BF3 proportional counter. By R. Fraki, M. Leimdorfer and S. Malmskog. 1962. 12. Sw. cr. 6:—.
92. The backscaftering of gamma radiation from plane concrete walls. By M. Leimdorfer. 1962. 20 p. Sw. cr. 6:—.
93. The backscaftering of gamma radiation from spherical concrete walls. By M. Leimdorfer. 1962. 16 p. Sw. cr. 6:—.
94. Multiple scattering of gamma radiation in a spherical concrete wall room. By m. Leimdorfer. 1962. 18 p. Sw. cr. 6r—.
95. The paramagnetism of Mn dissolved in a end R brasses. By H. P. Myersand R. Westm. 1962. 13 p. Sw. cr. 6:—. "
96. Isomorphic substitutions of calcium by strontium In calcium hydroxyapatite. By H. Christensen. 1962. 9 p. Sw. cr. 6:—.
97. A fast lime-to-pulse height converter. By O. Aspelund. 1962. 21 p. Sw. cr.
98. Neutron streaming in D2O pipes. By J. Braun and K. Rand6n. 1962 41 p. Sw. cr. 6:—.
99. The effective resonance integral of thorium oxide rods. By J. Weitman.1962. 41 p. Sw. cr. 6:—.
ICO. Measurements of burnout conditions for flow of boiling water in vertical annuli. By K. M. Becker and G. Hernborg. 1962. 41 p. Sw. cr. 6:—.
101. Solid angle computations for a circular radiator and a circular detector. By J. Konijn and B. Tollander. 1963. 6 p. Sw. cr. 8:—.
102. A selective neutron detector in the keV region utilizing the i9F(n, y)20Freaction. By J. Konijn. 1963. 21 p. Sw. cr. 8:—. *
103. Anian-exchange studies of radioactive trace elements in sulphuric acid solutions. By K. Samsahl. 1963. 12 p. Sw. cr. 8:—.
104. Problems in pressure vessel design and manufacture. By O. Hellstrom and R. Nilson. 1963. 44 p. Sw. cr. 8:—.
105. Flame photometric determination of lithium contents down to 10-3 ppm in woter samples. By G. Jonsson. 1963. 9 p. Sw. cr. 8:—.
106. Measurements of void fractions for flow of boiling heavy water in a vertical round duct. By S. Z. Rouhani and K. M. Becker. 1963. 2nd rev. ed. 32 p. Sw. cr. 8:—.
107. Measurements of convective heat transfer from a horizontal cylinder rotating in a pool of water. K. M. Becker. 1963. 20 p. Sw. cr. 8:—.
108. Two-group analysis of xenon stability in slab geometry by modal expansion. O. Norinder. 1963. 50 p. Sw. cr. 8:—.
109. The prooerties of CaSOjMn thermoluminescence dosimeters. B. Bjarn- gard. 1963. 27 p. Sw. cr. 8:—.
110. Semianalytical and seminumerical calculations of ootlmum material distributions. By C. 1. G. Andersson. 1963. 26 p. Sw. cr. 8:—.
111. The paramagnetism of small amounts of Mn dissolved in Cu-AI and Cu-Ge alloys. By H. P. Myers and R. Westin. 1963. 7 p. Sw. cr. 8;—.
112. Determination of the absolute disintegration rate of Cs137-sources by the tracer method. S. Hellstrom and D. Brune. 1963. 17 p. Sw. cr. 8:—.
113. An analysis of burnout conditions for flow of boiling water in vertical round ducts. By K.M. Becker and P. Persson. 1963. 28 p. Sw. cr 8r—.
114. Measurements of burnout conditions for flow of boiling water in vertical round ducts (Part 2). By K. M. Becker, et al. 1963 . 29 p. Sw. cr. 8:—.
115. Cross section measurements of the MNifn, p)58Co and **Si(n, a)26Mg reactions in the energy range 22 to 3.8 MeV. By J. Konijn and A. Lauber1963. 30 p. Sw. cr. 8:—%
116. Calculations of total and differential solid angles for a proton recoil solid state detector. By J. Konijn, A. Lauber ana B. Tollander. 1963. 31 p. Sw. cr. 8:—.
117. Neutron cross sections for aluminium. By L. Forsberg. 1963. 32 p. Sw. cr. 8:—.
118. Measurements of small exposures of gamma radiation with CaSO<:Mn radiothermoluminescence. By B. Bjarngard. 1963. 18 p. Sw. cr. 8:—.
119. Measurement of gamma radioactivity in a group of control subjects from the Stockholm area during 1959—1963. By I. t? Andersson, I. Nilsson and Eckerstig. 1963. 19 p. Sw. cr. 8:—.
120. The thermox process. By O. Tjalldin. 1963. 38 p. Sw. cr. 8:—,121. The transistor as low level switch. By A. Lyd6n. 1963. 47 p. Sw. cr. 8:—.122. The planning of a small pilot plant for development work on aqueous
reprocessing of nuclear fuels. By T. U. Sjoborg, E. Haeffner and Hult- gren. 1963. 20 p. Sw. cr. 8:—.
123. The neutron spectrum in a uranium tube. By E. Johansson, E. Jonsson, M. Lindberg and J. Mednis. 1963. 36 p. Sw. cr. 8:—.
124. Simultaneous determination of 30 trace elements in cancerous and non- cancerous human tissue samples with gamma-ray spectrometry. K. Samsahl, D. Brune and P. O. Wester. 1963. 23 p. Sw. cr. 8:—.
125. Measurement of the slowing-down and thermalization time of neutrons in water. By E. Moller and N. G. Sjostrand. 1963. 42 p. Sw. cr. 8:—.
126. Report on the personnel dosimetry at AB Atomenergi during 1962. By K-A. Edvardsson and S. Hagsgdrd. 1963. 12 p. Sw. cr. 8:—.
127. A gas target with a tritium gas handling system. By B. Holmqvist and T. Wiedling. 1963. 12 p. Sw. cr. 8:—.
128. Optimization in activation analysis by means of epithermal Neutrons. Determination of molybdenum in steel. By D. Brune and K. Jirlow. 1963. 11 p. Sw. cr. 8:—.
129. The Pi-approximation for the distribution of neutrons from a pulsed source in hydrogen. By A. Claesson. 1963. 18 p. Sw. cr. 8:—,
130. Dislocation arrangements in deformed and neutron irradiated zirconium and zircaloy-2. By R. B. Roy. 1963. 18 p. Sw. cr. 8:—.
131. Measurements of hydrodynamic instabilities, flow oscillations and burnout in a natural circulation loop. By K. M. Becker, R. P. Mathisen, O. Eklind and B. Norman. 1964. 21 p. Sw. cr. 8:—.
Forteckning over publlcerade AES-rapporter
1. Analys medelst gamma-spektrometri. Av D. Brune. 1961. 10 s. Kr 6:—%2. Bestrdlningsforandringar och neutronatmosfar 1 reaktortrycktankar —
ndgra synpunkter. Av M. Grounes. 1962. 33 s. Kr 6:—.3. Studium av strackgransen 1 mjukt stdl. G. Ostberg, R. Attermo. 1963. 17 s,
Kr 6:—.4. Teknisk upphandling inom reakloromrtidet. Erik Jonson. 1963.64 s. Kr. 8r—.
Additional copies available at the library of AB Atomenergi, Studsvik, Nyhoping, Sweden. Transport microcards of the reports are obtainable through the International Documentation Center, Tumba, Sweden.
EOS-tryckerierna, Stockholm 1964
