Indonesian Journal of Physics
Vol. 16 No.1, January 2005
7 MPa Commissioning of Two-phase Flow Loop for Pb-Bi Cooled Direct Contact
Boiling Water Small Fast Reactor
Yudi Pramono1,2), Minoru Takahashi1), Hiroshi Sofue1), Megumi Matsumoto1), and Fei Huang1)
1)
Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology
N1-18, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8550 Japan
E-mail: [email protected]
2)
Nuclear Energy Regulatory Agency of Indonesia
Jl. Gadjahmada 8, Jakarta, 10120 Indonesia
Abstract
One of key issues for the development of the Pb-Bi cooled direct contact boiling water small fast reactor (PBWFR) is
thermal-hydraulics. In order to solve the issues of thermal-hydraulics, Pb-Bi-water direct contact boiling two-phase flow
loop was designed and constructed, where the loop consisted of a Pb-Bi flow loop, four-heater pin bundle, a chimney, an
upper tank with a separator and a dryer, an electromagnetic flow meter, a dump tank, and water supply system, and was
operated at the pressure of 7 MPa. Pb-Bi was charged from the dump tank into the Pb-Bi flow loop. Water was circulated
by a pump through a preheater, the chimney, the upper tank, a condenser, a buffer tank, and a cooler. A subcooled water
was injected into the Pb-Bi in the chimney. Before achieving the next operation phase, commissioning stage was conducted
including obtaining of optimal condition of loop, being focused on achievement of the commissioning of the system up to 7
MPa. The experimental results show that steam pressure of 7 MPa was achieved at steam temperature of 286oC under the
saturation condition.
Keywords: Lead-bismuth, Direct contact boiling, Two-phase flow, Fast reactor
since the system would reduce the sodium subsystem and
steam generators. From seismic point of view, the FBRs
with the heavy Pb-Bi coolant must be small. However,
small Pb-Bi cooled FBRs designed so far are not
competitive economically with conventional large scale
light water reactors. A direct contact type Pb-Bi cooled
FBR (PBWR) originally proposed in Ref.[1,2] is simpler
and more economic than the conventional Pb-Bi cooled
FBRs. A supply water directly contacts with a hot Pb-Bi
flow above a core, and boiling takes place in chimneys.
Boiling bubbles serve as a gas lift pump for the
circulation of the Pb-Bi coolant. The steam generated in
the chimney goes to turbines after passing through a
separator and a dryer. Therefore, coolant circulation
pumps, intermediate heat exchangers, intermediate
circulation loops and steam generators are eliminated
from conventional Pb-Bi cooled FBRs. Here, we call it
Pb-Bi cooled direct contact boiling water small fast
reactor (PBWFR)3-6).
As the capital cost of 150MWe class-PBWFR has
been estimated to be roughly 0.35Myen/kW or
3.3kUS$/kW, the PBWFR may be competitive with large
scale LWRs taking into account the reduction of
electricity transmission cost by the installation of the
reactor near large cities and the reduction of fabrication
cost in the future.
Thus, a conceptual design and feasibility studies
have been performed for the PBWFR as an innovative
reactor concept. Key issues of thermal-hydraulics for the
development of the PBWFR are summarized as follows:
i) Start-up of reactor system,
ii) Steam lift pump performance for the circulation of
Pb-Bi,
1. Introduction
Fast breeder reactors (FBRs) are suitable not only
for an increase in efficiency of uranium utilization but
also for high proliferation resistance by means of reactors
with a long-life core. The reactors with a long-life core
may be also useful for cities and islands remote from
industrialized regions. Smaller reactors are more suitable
for transportation to un-industrialized countries or regions
after being fabricated and assembled in factories.
In conventional FBR steam generators, sodiumwater reaction accidents must be taken into account as a
design basis event. Providing countermeasures against
sodium-water reaction accidents significantly increase the
construction cost of fast reactors above that of light water
reactors (LWR).
Lead-bismuth eutectic (LBE or 45%Pb-55%Bi)
has been studied as one of primary and secondary coolant
options for a fast reactor (FR). From safety point of view,
LBE cooled FBRs are expected to be publicly-acceptable
because Pb-Bi does not react with air and water violently.
It may be possible to develop a compact steam generator
which is free of sodium-water reaction accidents by
utilizing the direct contact heat transfer between a melting
lead alloy and water1). In this concept, the melting alloy in
the steam generator is heated by the primary sodium in
the shell and tube type heat exchanger located in the
lower part of the steam generator. Water is fed into high
temperature alloy. Pre-heating, boiling, evaporation, and
superheating take place in the melting alloy. The steam
produced in the steam generator flows into a turbine
generator through mist separators.
In the present concept of advanced FBR, a low
melting point alloy (Pb-Bi) is used as reactor core coolant
7
8
iii) Steam generation performance in Pb-Bi-water direct
contact boiling heat transfer in the chimney,
iv) Possibility of vapor explosion in direct contact of
Pb-Bi and water,
v) Carry-over of mist and aerosol in the steam flow,
Carry-under of steam bubbles in the downcomer.
In order to solve the issues, Pb-Bi-water direct contact
boiling two-phase flow loop is designed and fabricated in
Tokyo Institute of Technology.
Optimal operational condition of the loop must be
achieved. In the present paper, the topic is focused on the
achievement of the commissioning operation up to 7
MPa.
2. Apparatus and Operating Procedure
Figure 1 shows a schematic diagram of the Pb-Biwater direct contact boiling two-phase flow loop which
consists of a Pb-Bi flow loop and a water-steam loop. PbBi is charged from the dump tank to the Pb-Bi flow loop,
and circulated by natural circulation force and a steam gas
lift pump through the fuel pin bundle with four electrical
heater pin, the chimney, the upper tank with the
separator-dryer, the cooler, an electromagnetic flow
meter, and a flow resistance in the Pb-Bi flow loop.
Water is circulated by the centrifugal pump from the
buffer tank through the cooler the preheater and the
chimney, and steam generated in the chimney flows
through the upper tank into the condenser. A subcooled
water is injected into the Pb-Bi in the chimney, and the
loop is operated at the pressure of 7 MPa.
A start-up technique was tested in the first
operation: a commissioning operation. The performance
of the steam lift pump and the characteristics of direct
contact boiling heat transfer were investigated in the
second operation. In the third operation, the two-phase
flow characteristics of void fractions, pressure
fluctuations and pressure drops, and heat transfer
characteristics in a Pb-Bi-boiling water two-phase flow in
the chimney will be investigated using special void
probes, pressure transducers and thin sheathed
thermocouples.
The optimal condition, or the rated operating
conditions,
could be achieved by controlling the
parameters listed in Table 1. The whole temperature
parameters and Pb-Bi circulation flow rate were
operational objective values, and it is assumed to develop
during testing (marked with *1). In practical operation,
system pressure of 7 MPa should be finally achieved.
IJP Vol. 16 No. 1, 2005
Table 1. Objective Parameter
Condition
value
Controlled
parameters
Rated operating
conditions
Heater pin
power
WIC1
132 kW
Water
injection flow
rate
HV1-1, (see
Figure 1)
250 kg/h
System
pressure
Cooling water
flow rate in
condenser
7 MPa
Pb-Bi
temperature at
inlet of heater
pins
WIC1, injected
water flow rate
308oC
*1
Pb-Bi
temperature at
outlet of
heater pins
WIC1, injected
water flow rate
458oC
*1
Injected water
temperature
Preheater
220oC
Steam outlet
temperature
WIC1
296oC
Pb-Bi
circulation
flow rate
Injected water
flow rate
6.08
Coolant outlet
temperature
Heat transfer
area, cooling
water flow rate
in condenser
220 oC * 1
*1
kg/s* 1
Some highlighted operational procedures are as
follows :
1. Preheating and baking of Pb-Bi loop
The Pb-Bi loop is heated up to clean out
unnecessary contaminants that remain on inner surfaces
of the loop. It is performed in the procedures as
− To prepare the safety control valve located in
upstream of steam assembly. It has a function to
relieve an excess pressure at the emergency condition,
− To operate the cooling water system and supply water
to a waterproof vacuum pump at a small flow rate,
− To evacuate Pb-Bi loop system, with manipulating
changeover valves in the Pb-Bi dump tank line.
During the interval of this changeover, the pressure
was controlled in atmospheric pressure with argon,
− To evacuate the water and steam system,
− To evacuate the Pb-Bi dump tank system
− To preheat the dump tank up to 200oC by monitoring
the temperature with thermocouples, and preheat the
test loop section, level tank, Pb-Bi circulation line,
and steam piping line up to 250oC, while the water
piping line is kept at ordinary temperature,
− To relieve the pressure that increases during
temperature rise by opening a valve located in dump
tank line to keep it at the atmospheric pressure.
− To confirm and keep increasing temperature condition
in each of valves and Pb-Bi loop for about 1 h and
IJP Vol. 16 No. 1, 2005
then changeover to vacuum to bake the test loop
section. The vacuum baking is continued for 1 h.
− To stop the evacuation and pressurize the Pb-Bi dump
tank line to the atmospheric pressure with argon.
2. Pb-Bi Refilling
− To refill the loop with Pb-Bi up to middle level in
level meter tank by pressurizing Ar gas pressure in the
dump tank,
− To pressurize the inner system at the atmospheric
pressure with argon.
3. Supply water quality setting
− To open and flush the water supply tank, and poure
pure water of about 80 l into the tank,
− To pressurize the Pb-Bi dump tank line at the
atmospheric pressure with argon,
− To run and stop the gas of supply water,
− To let the water pass through a hydrogen meter at
about 1 l/min for the measurement of the hydrogen
concentration by opening the valve in the pipe
between the water supply tank,
− To keep the stable condition of desire hydrogen
concentration by opening a valve to supply hydrogen,
and circulate the pure water using a pump for about
half day to have a stable condition of hydrogen
concentration.
4. Water refilling in water and steam system
− To condition the water and steam system to be stable
in vacuum,
− To fill the buffer tank with water up to middle level
using water supply pump,
− To close the cooling line valve to keep the water in
pure condition after injection.
5. General operating procedure
A) Operation of Pb-Bi loop system
− To start up Pb-Bi natural circulation by controlling a
power of the heater pins and an air cooling flow rate
at downward flow channel using compressor.
− To operate the Pb-Bi natural circulation by increasing
the heater pin power gradually while monitoring PbBi flow rate from electro-magnetic flow meter, and
achieve the assembly outlet temperature of 300oC.
− To preheat the dump tank, the upper tank, the level
tank and the steam line at 300oC, and preheat the other
loop sections and Pb-Bi circulation line at 250oC.
Meanwhile, the water piping line was is kept at
ordinary temperature,
B) Operation of water and steam system
− To start the water cooling of the water circulation
pump.
− To operate the circulation pump with opening the
valve outtake from buffer tank, and opening the valve
in water system line with condition of closing the
cooling line valve. It should not be full-opened to
prevent the circulation pump from cavitation.
− To continue the circulation; turn on the preheater, and
turn up the water system temperature moderately.
9
− To circulate the cooling water at line of water coolant
with confirming that valve of cooling line is opened to
prevent cavitation of circulation pump.
− To open the valve in the system, the valve between
the condenser and the buffer tank inline, the valves of
flow meter, and pressure gauge valves when the water
system temperature reaches 100oC.
− To increase the preheater power of water piping line,
to increase the water loop’s temperature up to 220oC
under saturation pressure of about 2.5MPa.
− To increase the power of water heaters.
− To increase the water circulation rate up to 150 kg/h
by opening the valve in water system gradually at the
condition of increased temperature of 220oC.
C) Operation of both systems
− To cool the condenser with air and water spray flow.
At the beginning, the coolant is adjusted to be less
than 1 lt./min.
− To adjust the pressure in the water loop to be 0.6 MPa
higher than pressure in Pb-Bi upper tank.
− To start the injection of water into Pb-Bi loop by
opening the intake valve to assembly at low water
flow rate, and then full-open the valve of the water
injection system.
− To increase the water injection flow rate gradually by
opening the flow control valve.
− To stop the air cooling for Pb-Bi natural circulation,
− To increase the water injection flow rate up to 85 g/h
by opening the flow control valve.
− To increase the heater pin power gradually.
− To confirm system pressure and all the temperature,
changeover the flow meter, and increase the water
injection flow rate.
− To confirm pressure temperature conditions, and
operate it at desired conditions referring to the
calibration data: Pb-Bi flow rate vs. electromotive
force of the electromagnetic flow meter; water
injection flow rate vs. pressure difference outputs of
orifice flow meters, water injection flow rate vs.
heater pin power; and voltage vs. water heater power.
3. Result
Figure 2 comprehensively shows the results of the
operation which describs the dynamics of the control
process during the operation. The final achievement was
conducted through the modification of several kinds of
regulator valves combined with an observation of
temperature, flow rate and pressure at some locations of
loop and system.
Measured operation parameters were given in
more detail in Figs. 3 through 5 which illustrate the
dynamics of temperature outlet/inlet of steam and Pb-Bi,
water and orifice flow rate during the operation and their
partial dependence on the heater pin temperature.
10
IJP Vol. 16 No. 1, 2005
PI-1
Mist
O2 Meter
Condense
Heater pin output ｋＷ
PI6
FE-2
HV1HV1-
HV
Chimney
Buffer
Void meters
280
140
240
120
kg/h
HV
Water HV
injection
tube
Heater
pin
160
PI
Warm
water
Water
supply
tan
Pre- heate
Coole
Flow rate
Coole
320
200
100
160
80
120
60
kW
80
Hydrogen
meter
Dump
40
40
Heater pin output (ｋ
Level
tan
Warm water flow rate　ｋｇ／ｈ
Electromotive force flow rate Ltr／ｍｉｎ.
Separato Drye
20
Lt./min
0
0
2.00
4.00
6.00
8.00
10.00
0.00
Operation Time (09：51：59－18：58：03）
Figure 1. Pb-Bi-water direct contact boiling two-phase
flow loop
Figure 4. Operation flow rate and heater temperature
Orifice flow rate　kg／ h
T (oC)
Assembly inlet
500
Electromotive force flow rate Ltr／ min.
Assembly outlet
End point of
commissioning
Pb-Bi outlet
450
Pb-Bi inlet
Heater pin output　kW
120
120
400
kW
100
Steam outlet
100
kg/h
300
80
Flow rate
250
200
150
TE-2　Assembly Inlet Temperatur
TE-6 PB-Bi Outlet Temperature
TE-3 Chimney Lower Section Temp
TE-4 Chimney Middle Section Temp.
TE-5 Chimney Upper Section Temp
Lt./min
40
20
20
0
0
0.00
2.00
6.00
8.00
10.00
Figure 5. Operation flow rate of orifice
TE-9 Steam outlet temperature
TE-12 Condenser outlet temperature
Steam outlet temperature-saturate pressure
Condenser outlet temperature-saturate pressure
PI-1 Pressure-Record no.1
PI-1 Pressure-Record no.2
TE-1
400
20
TE-9
350
400
o
Temperature ( C)
4.00
Operation Time (09:51:59-18:58:03)
500
450
60
40
Measurement time
Figure 2. The overall measured parameter
TE-1　Assembly Oulet Temperature
80
60
18:55:53
18:47:15
18:38:37
18:29:59
18:21:21
18:12:43
18:04:05
17:55:27
17:46:49
17:38:11
17:29:33
17:20:55
17:12:17
17:03:39
16:55:01
16:46:23
16:37:45
16:29:07
16:20:29
16:11:51
15:54:35
15:45:57
15:37:19
15:28:41
15:20:03
14:36:53
15:11:25
14:28:15
15:02:47
14:54:09
14:19:37
14:45:31
14:10:59
14:02:21
13:53:43
13:45:05
13:36:27
13:27:49
13:19:11
13:10:33
13:01:55
12:53:17
12:44:39
12:36:01
12:27:23
12:18:45
12:10:07
12:01:29
11:52:51
11:44:13
11:35:35
11:26:57
11:18:19
11:09:41
11:01:03
10:52:25
10:43:47
10:35:09
10:26:31
9:51:59
10:17:53
10:09:15
10:00:37
0
Condense
r
Warm-up
50
Achievement
region
16:03:13
100
Heater pin output　Start point of
commissioning
350
TE-6
250
TE-12
200
10
150
100
TE-2
200
0.00
250
15
5
TE-4
50
2.00
4.00
Pressure MPa
300
TE-3
TE-5
Temperature(℃
300
350
6.00
8.00
PI-1-2
10.00
Observation Time　(09:51:59-18:68:03)
Figure 3. Operation temperature of assembly inlet/outlet
0
0.00
PI-1-1
2.00
4.00
6.00
8.00
0
10.00
Operation Time (Time 09:51:59-18:58:03)
Figure 6. Correlation between pressure and temperature
during operation time
IJP Vol. 16 No. 1, 2005
11
Figure 3 shows that the temperatures at inlet and
outlet section of the assembly could be controlled stably
during initial operation after 2 hs from preheater setting
of 250-300oC, under the condition where the circulation
pump, vacuum pump, and cooling tower pump were
appropriately operated. The water flow rate during this
operation was 273 kg/s as shown in Figure 4, where the
heater pin was not turned on till about 3 h after the start
of the operation. It did not give an influence on the
electromotive force or Pb-Bi flow rate and the output of
the orifice flow meter or water flow rate as shown in
Figure 5.
During this period, water hammer occurred in
water cooling channel of the water cooler as indicated by
small ripples on the temperature gradation of steam outlet
at operation time of about 2.5-3 h. The water hammer
could be stopped by injecting air into the cooling water
flow from a compressor.
An increase in the power of the heater pins
gradually changed the other parameters during
commissioning stage at operation time of 3-8 h. During
the initial commissioning step (3-4 h), the increase of the
heater pin power caused the increase of temperatures. The
increase of the power was continued till about 8 h
operation time in order to achieve the desired pressure,
while the pressure was influenced by Pb-Bi flow rate and
water injection flow rate.
The desired pressure higher than 7 MPa was
achieved at operation time of 6-8 h as shown in Figure 6.
The system pressure was nearly equal to steam saturation
pressure at condenser outlet temperature.
The parameters achieved in the operation are listed
in Table 2 compared with the rated ones.
circulation flow rate by installing a flow resistance in the
Pb-Bi loop. The unanticipated water hammer will be
suppressed in the next improved operation.
Finally, the discussion is just emphasized on how
the 7 MPa commissioning operation can be achieved. The
dependence of the system pressure on temperature
difference between assembly inlet and outlet would be
discussed in the next papers based on the comparison of
Pb-Bi circulation flow rate with analytical data.
4. Conclusion
The commissioning experiment to obtain steam
pressure of 7 MPa was achieved at steam temperature of
285oC under the saturation condition in Pb-Bi-water
direct contact boiling loop.
There was temperature difference in Pb-Bi
assembly outlet between rated operating parameter and
achievement data. It would be possible to overcome by
installing a flow resistance in the Pb-Bi loop to decrease
the Pb-Bi circulation flow rate.
Acknowledgment
The study is a part of the Publicly Invited
Research Projects for Development of Innovative Nuclear
Technologies Adopted in FY2002 supported by the
Ministry of Education, Culture, Sport, Science and
Technology of Japan. We would like to thank Dr. H. Nei
and Mr. T. Iguchi for their helpful discussion, Mr. K.
Hata, for his assistance of experimental working, Mr. N.
Namiki, K. Hagiya, M. Komine and Mr. S. Sakai for their
set up operation.
References
1.
Table. 2 Measured-operation parameters
Test loop heater power
Intake water flow rate
Test loop pressure
Pb-Bi assembly inlet
temperature
Pb-Bi assembly outlet
temperature
Intake warm water
temperature
Steam outlet temperature
Pb-Bi circulation flow rate
Condenser outlet temperature
Rated
operating
conditions
132 kW
250 kg/h
7 MPa
308oC
Achievemen
t
458oC
371oC
220oC
227oC
296oC
6.08 kg/s
285oC
7.49-7.90
kg/s
283oC
103 kW
243kg/h
7 MPa
285oC
The experimental results show that steam pressure
of 7 MPa was achieved at steam temperature of 286oC
(559K) under the saturation condition. There was large
temperature difference in Pb-Bi assembly outlet between
rated operating conditions and achievement in the present
operation. This was caused by higher Pb-Bi circulation
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