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Nuclear Technology
ISSN: 0029-5450 (Print) 1943-7471 (Online) Journal homepage: http://www.tandfonline.com/loi/unct20
Aerosol Behavior Experiments on Light Water
Reactor Primary Systems
Frank J. Rahn, Jan Collén & Anthony L. Wright
To cite this article: Frank J. Rahn, Jan Collén & Anthony L. Wright (1988) Aerosol Behavior
Experiments on Light Water Reactor Primary Systems, Nuclear Technology, 81:2, 158-182, DOI:
10.13182/NT88-A34090
To link to this article: http://dx.doi.org/10.13182/NT88-A34090
Published online: 13 May 2017.
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Date: 28 October 2017, At: 21:21
AEROSOL BEHAVIOR EXPERIMENTS
ON LIGHT WATER REACTOR
PRIMARY SYSTEMS
NUCLEAR
SAFETY
FRANK J. RAHN Electric Power Research Institute
3412 Hillview Avenue, Palo Alto, California 94301
JAN COLLEN Studsvik Energiteknik AB, S-611 82 Nykoping, Sweden
ANTHONY L. WRIGHT Oak Ridge National Laboratory
P.O. BoxX, Oak Ridge, Tennessee 37381
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Received August 4, 1987
Accepted for Publication December 3, 1987
The results of three experimental programs relevant to the behavior of aerosols in the primary systems
of light water reactors (L WRs) are presented. These
are the Large-Scale Aerosol Transport Test programs
performed at the Marviken test facility in Sweden,
parts of the LWR Aerosol Containment
Experiments
(LACE) performed at the Hanford Engineering Development Laboratory, and the TRAP-MELT
validation
project performed at Oak Ridge National Laboratory.
The Marviken experiments focused on the behavior of aerosols released from fuel and structural materials in a damaged core. Data on the transport of
these aerosols and their physical characteristics were
obtained in five experiments that simulated L WR primary systems. The LACE program data include results
from the containment bypass accident tests, which
focused on aerosol transport in pipes. The TRAPMELT validation project data include results from two
types of experiments: (a) aerosol transport tests to
investigate aerosol wall plateout in a vertical pipe
geometry and (b) aerosol resuspension tests to provide
a data base from which analytical models can be developed. Typical results from these programs are presented and discussed.
INTRODUCTION
In postulated light water reactor (LWR) accidents,
meltdown of the reactor core can release substantial
quantities of fission products, initially in vapor form.
These vapors, which may include elements from structural and control materials within the core, quickly
condense to aerosol particles up to a few microns in
diameter in the cooler regions of the reactor pressure
vessel. From there, they can travel down the primary
cooling system, where they can be deposited (and perhaps subsequently resuspended or revaporized) or escape into the reactor containment building. Processes
such as thermophoresis, diffusiophoresis, gravitational
settling, and impaction may result in such deposition. In many key sequences, radioactive aerosols pass
through liquid pools, which are excellent natural filters. Since small-scale tests distort important effects,
such as the ratio of surface area to volume, the data
from large experiments are needed to develop and
improve calculational methods.
Several experimental programs have been performed in recent years to investigate the behavior of
these aerosols in the primary system. The objectives of
these programs were to provide data on (a) the nature
and chemical forms of the aerosols, (b) their deposition and resuspension inside the primary coolant system (PCS), and (c) the characteristics (i.e., quantity,
size, morphology, etc.) of the particles leaving the
PCS. The experimental work considered in this paper
are the Marviken Large-Scale Aerosol Transport Tests
(LSATT) program, those parts of the LWR Aerosol
Containment Experiments (LACE) dealing with aerosol behavior in pipes, and the TRAP-MELT validation
program. The balance of the LACE program is
reported in Ref. 1.
In the Marviken LSATT program, a multinational
project, five tests were conducted during 1983 to 1985
to provide data on the behavior of high-concentration
aerosols and volatile species in a full-scale simulated
water-cooled reactor primary circuit. Extensive experimental investigations were made of the effects of such
parameters as aerosol mass concentration, temperature, superheated steam, and water environment on
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the transport properties of aerosols and vapors. The
results constitute a data base of large-scale tests useful for the development and validation of analytical
models used to predict radionuclide transport for a
wide range of postulated accident sequences.
The LACE program, also a multinational project,
investigated inherent aerosol behavior for postulated
high-consequence accident situations. Accident situations considered are those for which high consequences
are presently calculated because either the containment
is bypassed altogether, the containment function is
impaired early in the accident, or delayed containment
failure occurs simultaneously with a large fission product release.
Two of the large-scale LACE tests focus on a
postulated containment bypass accident in a large dry
pressurized water reactor (PWR), called a V sequence
in WASH-1400 (Ref. 2). The results of these tests also
have application to the generic problem of aerosol
deposition and resuspension in pipes under other
severe accident conditions in PWRs and boiling water
reactors (BWRs). In addition to the two LACE tests
(LAI and LA3), three containment bypass scoping
tests were completed under Electric Power Research
Institute (EPRI) sponsorship while the LACE program
was being defined.
The objective of the TRAP-MELT validation
project, performed at the Oak Ridge National Laboratory (ORNL) under the sponsorship of the Division
of Accident Evaluation of the U.S. Nuclear Regulatory Commission (NRC), is to perform experiments
and analyses to aid in validation of the TRAP-MELT2
computer code. Two types of experiments have been
performed: (a) aerosol transport tests to investigate
aerosol wall plateout in a vertical pipe geometry chosen to simulate conditions in a reactor vessel upper plenum and (b) aerosol resuspension tests, which are
providing a data base of aerosol resuspension results
from which analytical models can be developed.
THE MARVIKEN TESTS
To provide such aerosol transport data in a simulated full-scale water-cooled reactor primary circuit,
the Marviken LSATT program was initiated as a multinationally financed project in 1982. The project was
supported by Ontario Hydro (Canada), Valtion Teknillinen Tutkimuskeskus (Finland), Commissariat a
1'Energie Atomique and Electricite de France (France),
Comitato Nazionale per la Ricerca e per lo Sviluppo
dell'Energia Nucleare e delle Energie Alternative (Italy),
Japanese Group (Japan), N.V. Tot Keuring Van Electrotechnische Materialen (The Netherlands), Statens
Karnkraftinspektion (Sweden), U.K. Atomic Energy
Authority (United Kingdom), EPRI and NRC (United
States), and Studsvik Energiteknik AB (Sweden). The
first test was conducted in May 1983 and the experiments were completed in March 1985.
This paper presents the LSATT program objectives, the facility and measurement system, the test
matrix, and some typical test results. The complete
data base is documented in 14 reports (see Refs. 3
through 6). The detailed information and data presented in Refs. 4, 5, and 6 are currently proprietary to
the supporting organizations only.
Objectives
The primary Marviken LSATT program objective
was to generate a data base on the behavior of highconcentration aerosols and volatile species produced
from overheated core materials in a large-scale facility representing typical water reactor primary systems
and pressure vessels. The experimental data were to be
used to verify analytical models predicting radionuclide transport for a wide range of postulated accident
sequences. A secondary objective was to provide a
large-scale demonstration of the behavior of aerosols
in water-cooled reactor primary systems.
Nonradioactive materials were to be used as fission
product simulants ("fissium") and reactor core structure simulants ("corium").
Test Facility and Measurement System
Since 1972, five international experimental programs on nuclear safety have been performed in the
Marviken facility (see Fig. 1). A total of 68 simulated
loss-of-coolant sequences were performed in the first
four projects, which studied containment response,
critical flow, and jet impingement at or near full plant
scale. The projects have utilized the full-sized pressure
vessel (425 m 3 ), connecting pipes and the pressuresuppression containment (3900 m 3 ).
LSATT
Facility
The particular components introduced for the
LSATT program were
1. reactor test vessel (140-m 3 volume)
2. reactor internals (200-m 2 surface area)
3. pressurizer (50-m 3 volume)
4. relief tank (50-m 3 volume)
5. small aerosol generators: three Metco-type 10
MB plasma-arc heaters with maximum power
of 80 kW each
6. large aerosol generators: three Westinghouse
Mark-11 plasma-arc heaters with a maximum
power of 1.65 MW each
7. piping between principal tanks
8. final filter.
The facility assembly for the various tests is shown in
Figs. 2 and 3.
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4. RELIEF TANK
5. SCRUBBER (TEST 1)
6. CONDENSATE TANK (TEST 1)
Fig. 1. The Marviken facility situated on the Baltic coast
- 1 5 0 km south of Stockholm, Sweden.
7. FINAL FILTER
8. SAMPLING STATION (TYPICAL)
Fig. 2. Test facility arrangement for tests 1, 2a, and 2b.
The small aerosol generation system consisted of
plasma-arc heaters, fissium feeders, and a vaporization
chamber. Three 80-kW Metco plasma-arc heaters
injected plasma jets into the vaporization chamber
through a face plate. Argon was used to fluidize and
feed powdered cesium iodide (Csl) and tellurium,
whereas cesium hydroxide (CsOH) was injected into
the plasma as an aqueous solution.
The large aerosol generation system included three
Westinghouse plasma-arc heaters and two vaporization
chambers as shown in Fig. 4. Each heater was rated at
1.65 M W and utilized nitrogen as the plasma gas.
Corium was fed as a mixture f r o m dual feeders to a
single plasma jet. Argon was used to fluidize the
corium powder and the feed plate was a water-cooled,
welded assembly mounted on the face of the plasmaarc heater. Fissium was added and vaporized in the
upper chamber.
The reactor test vessel was placed in the upper half
of the Marviken pressure vessel and could be externally cooled if necessary. The vessel and its internal
thermal radiation shield were made of stainless steel.
The reactor internals consisted of a support plate and
vertical tubes. A section of the internal structure,
including the attached tubes, could be lifted out of the
vessel in one piece to provide access to the internal
part of the vessel.
After leaving the reactor vessel, the flow passed
through a full-scale pressurizer to the water-filled relief
tank. Noncondensable gases then passed through the
final filter before being discharged to the atmosphere.
Measurement
System
A number of measurement stations were located
throughout the test facility as shown in Fig. 5. Direct
reading on-line instrumentation was used to obtain
1. pressures and differential pressures
2. gas and wall temperatures
3. flow rates
4. relative aerosol concentration using an optical
smoke density meter
5. gas composition using gas chromatographs, a
mass spectrometer, a carbon monoxide monitor, and a hydrogen meter.
The on-line instruments were connected to a data
recording system consisting of a process computer, a
multiplexer system, and a Pulse Code Modulation system with two tape recorders.
Extraction methods were used to take samples that
were analyzed after the test was completed. The sampling methods gave information on
1. LARGE AEROSOL GENERATORS
2. REACTOR VESSEL
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3. INTERNALS MODELING PWR
as they passed through a stainless steel tube precoated
with magnetite. Condensing vapors were collected on
the tube walls and exit filter. Flow passing the exit filter was condensed and water soluble species were
t r a p p e d . T h e remaining gas was bubbled t h r o u g h a
basic solution to t r a p any free iodine and then through
c a r b o n tetrachloride to t r a p methyl iodide.
Posttest recoverable samplers were placed in the
system t o collect material deposited at various locations during each test. The material deposited in or on
these samplers was collected a n d analyzed a f t e r the
test. R u n o f f samplers were attached to the walls of the
reactor vessel or the pressurizer, and to the pipes of
the reactor vessel internals. Several collection trays
(sedimentation trays) were placed at a number of locations such as o n the reactor vessel floor a n d internals
support plate. Stainless steel and Zircaloy deposition
c o u p o n s were placed at several positions in the reactor vessel and pressurizer. A sequential sedimentation
sampler was located in the pressurizer and consisted of
a turntable that collected samples at three levels in the
pressurizer by rotating on its axis a n d exposing collection trays at preselected times.
A n i m p o r t a n t posttest procedure was to dismantle and wash each section of the facility with water and
dilute nitric acid. Samples of the washing liquids and
slurries were then analyzed to provide a mass balance
of the corium and fissium elements, and to give a distribution pattern of these elements in the various parts
of the system.
In each test, several h u n d r e d s of samples were
taken and a substantial fraction of these was sent to
laboratories f o r chemical analysis.
Test Program and Procedure
1. total particle concentration
2. particle size distribution
3. v a p o r species
4. noncondensable gases
5. condensate composition
6. condensable t o n o n c o n d e n s a b l e gas ratio
7. vapor fission products in the relief tank off-gas.
Aerosol size characteristics were measured with
fractionating sampling trains consisting of f o u r cyclones and a filter. T o achieve isokinetic sampling,
each sampler flow was monitored using a turbine flowmeter in a temperature-controlled cabinet. A computer
p r o g r a m was used t o determine the local flow velocity f r o m the input mass flow and the local temperature
and pressure. Total aerosol samplers utilizing a filter
only were used in a similar way t o m e a s u r e aerosol
mass concentrations.
Vapor fission product samplers were used at
selected stations. The vapors were cooled t o ~ 1 1 0 ° C
Five tests were conducted in the L S A T T program.
Tests 1, 2a, 2b, a n d 7 studied the transport of fission
products that might be released during a fuel damage
process. A mixture of C s O H , Csl, and tellurium was
vaporized and f o r m e d the fissium aerosol. The first
three fissium tests used only t h e portion of the facility d o w n s t r e a m of the reactor vessel a n d were comparative tests f o r studying the effects of different
t e m p e r a t u r e ranges, superheated steam, condensing
steam, and water. Sequences with simultaneous fuel
d a m a g e a n d structural aerosol release were studied in
test 4, which simulated the general geometry of a
P W R primary circuit. The corium aerosol was produced by vaporizing silver and manganese. Fissium
was also generated in this test to study the interactions
between the various species in particle aggregates and
transport.
A s u m m a r y of the test conditions a n d specific
results is given in Table I, where aerosol and gas feed
rates, temperatures, aerosol concentrations, and gross
retention in pipes a n d vessels can be c o m p a r e d
between the tests.
MARVIKEN PRESSURE VESSEL'
REACTOR VESSEL-
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THERMAL RADIATION SHIELD •
Fig. 4. Assembly of large aerosol generation system (3 x 1.65 MW) and reactor test vessel.
Each test was preceded by a heat-up period followed by a stabilization period to achieve steady-state
conditions before the fissium/corium materials were
injected. After each test the system was cooled down
in a nitrogen atmosphere, and finally dry air was introduced when the temperatures were close to ambient.
Typical Test Results
Tests 4 and 7 are chosen to illustrate the behavior
observed. In test 4 the corium vapors were mixed with
vaporized fissium and steam in the lowest portion of
the reactor vessel to f o r m particles that were transported through the simulated large-scale primary circuit. All feeders except for the Csl feeder worked
satisfactorily throughout the test, and the desired tem-
peratures and fluid flows were attained. Some sampling problems occurred due to the very dense aerosol.
Measured aerosol mass concentrations were 30 to 120
g / m 3 at operating conditions. The deposits observed
on the walls of primary system components were
chemical admixtures of the coagglomerated fissium
and corium species, and their oxides, hydroxides, and
possibly carbonates.
The reactor vessel contained a gray-brown layer of
material at the bottom. The top layer of the deposit
was easy to remove, but under this layer there was a
hard crust that stuck to the steel surface. Deposits
below the support plate showed a radial flow pattern
(see Fig. 6). Thick gray deposits covered the upstream
parts of sampling station 2 (see Fig. 7), while almost
no deposits were found on the sheltered side. A very
Rahn et al.
AEROSOL BEHAVIOR IN PRIMARY SYSTEMS
TABLE I
Summary of Marviken LSATT Test Conditions and Specific Results*
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Test 1
(10/11/83)
Test 2a
(05/03/83)
Test 2b
(01/17/84)
Test duration (min)
138
Aerosol generation
Gross electrical power (kW)
Cesium feed rate (g/s)
Iodine feed rate (g/s)
Tellurium feed rate (g/s)
Argon feed rate (g/s)
Manganese feed rate (g/s)
Total feed (g/s)
215
6.1
0.047
1.6
0
0
7.8
204
8.8
1.1
-1.5
0
0
-11
215
9.6
0.83
1.6
0
0
12
Flow
Total [m 3 /h (101.3 kPa, 20°C)]
241
289b
235
Reactor vessel
Wall temperature (°C)
Gas temperature (°C)
Retention (%)c
Not used
Piping to pressurizer
Wall temperature (°C)
Gas temperature (°C)
Retention (%)c
Not used
115
Not used
Not used
118
Test 4
(02/27/85)
Test 7
(11/07/84)
79
69
1650
15
2a
2.3
53
3.8
73
2000
15
1.9
2.4
0
0
19
506
481
630 to 850
750 to >1200
30.3
600 to 770
-770
10.9
420 to 490
480 to 600
7. 6
400 to 450
460 to 590
2.5
Not used
Not used
Pressurizer
Wall temperature (°C)
Gas temperature (°C)
Retention (%)c
360 to 430
365 to 550
32
270 to 350
300 to 400
14
275 to 385
285 to 420
45
280 to 350
290 to 350
24.5
250 to 300
300 to 490
6.1
Piping to relief tank
Wall temperature (°C)
Gas temperature (°C)
Retention (°7o)c
255 to 330
265 to 370
4.1
95 to 280
130 to 300
0.8
70 to 300
135 to 315
4.6
125 to 290
200 to 300
10.9
120 to 220
200 to 290
19.9
Relief tank
Water volume (m3)
Fluid temperature (°C)
Wall temperature (°C)
Retention (%)c
0
180 to 200
175 to 185
20.1
20
30 to 35
37 to 44
85.3
19.6
29 to 34
25 to 30
49.0
20
24 to 32
24 to 32
26.1
20
26 to 33
26 to 33
59.2
Scrubber and condenser
Water volume (m3)
Fluid temperature (°C)
Wall temperature (°C)
Retention (%)c
Not used
Not used
7
24 to 57
20d
40
Final filter
Temperature (°C)
Retention (°7o)c
Measured aerosol concentration (g/m 3 ) e
20d
0.3
20 to 40
15d
0.1
-80
20d
0.04
40 to 50
Not used
Not used
20d
0.1
15d
0.2
30 to 120
28 to 60
'Intervals stated for temperatures and concentrations include both local variations and time variations.
a
Fed for 5 min.
b
Value uncertain due to steam leakage.
'Fraction of total amount recovered.
d
Nominal value.
e
At actual conditions. This concentration was measured in the pressurizer for tests 1, 2a, and 2b and in the reactor vessel for tests 4 and 7.
0. AEROSOL GENERATOR
1. REACTOR VESSEL BELOW INTERNALS SUPPORT PLATE
2. REACTOR VESSEL ABOVE INTERNALS SUPPORT PLATE
3. REACTOR-TO-PRESSURIZER PIPE
4. PRESSURIZER INLET
5. PRESSURIZER BULK
6. PRESSURIZER OUTLET
7. PRESSURIZER-TO-RELIEF-TANK PIPE
8. RELIEF TANK LIQUID
9. RELIEF TANK VAPOR
10. FILTER
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11. SYSTEM DISCHARGE
r"
Fig. 6. Reactor vessel internals support plate and vertical
tubes showing deposits with radial flow pattern
(test 4). At the lower left is the station 1 particle
sampler.
Fig. 5. Sampling stations, typically equipped with fractionating particle samplers, vapor fission product
samplers, temperature measurements, and deposition samplers.
Fig. 7. Station 2 sampler in horizontal exit pipe from reactor vessel (test 4). Inlet cover mechanism (top) and
first cyclone body (right) covered with heavy
corium deposit.
thick (up to 3 cm) layer of f l u f f y and easily compressed gray-black material covered the pressurizer
bottom (see Fig. 8). The horizontal piping f r o m the
pressurizer to the relief tank had a very thick layer of
gray-black material on the lower half of the pipe (see
Fig. 9), while only a light deposit was located on the
upper half of the pipe. Much solid material was found
in the relief tank, but no discoloration of the liquid in
the tank was observed.
In test 7 the vaporized fissium was mixed with
steam at the reactor vessel inlet to form particles that
were transported through the simulated large-scale primary circuit. The desired thermal-hydraulic conditions
were achieved, and the three fissium feeds (CsOH,
Csl, and tellurium) were successfully maintained. A
small water leak into the corium vaporization chamber resulted in the generation and transport of some
CO and C 0 2 through the system. No other operational problems occurred. All of the sampling equipment worked to full satisfaction, and the measured
aerosol mass concentrations were 28 to 60 g / m 3 at
operating conditions.
A very thin layer of deposited material was found
in the reactor vessel, predominantly black with some
white areas (see Fig. 10). The pressurizer surfaces were
covered with a thick layer of gray-white material containing some large fluffy white debris. The layer on the
bottom of the pressurizer was sharply subdivided into
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Fig. 10. Zirconia brick fissium chamber on the reactor vessel bottom (test 7).
Fig. 8. Deposits on station 5 sequential sedimentation
sampler and pressurizer bottom (test 4).
Fig. 11. Deposits in the first pipe bend of the pressurizerto-relief tank pipe (test 7).
Fig. 9. Deposits in horizontal pipe section of pressurizerto-relief tank pipe (test 4).
an upper black layer and a lower white layer. The piping between the pressurizer and the relief tank contained a very thick layer of deposits, especially at the
bends (see Fig. 11). The porous material varied from
black to gray-black and was layered in a similar form
to the deposit on the pressurizer bottom. The dry
fluffy nature of the deposits may be attributed to the
reaction between CsOH and C 0 2 (from steam/graphite reactions).
Conclusions of the Marviken Experiments
The LSATT program has provided the first quantitative information on the transport and deposition of
high-concentration aerosols in a simulated watercooled reactor primary system. The project met its
main objectives of obtaining a data base of large-scale
aerosol tests for development and validation of analytical models used to predict radionuclide transport
for a wide range of postulated accident sequences. The
test matrix encompassed four tests with fissium simulants only and one test with combined fissium and
corium simulants. The aerosol mass concentrations
ranged f r o m 20 to 120 g / m 3 at operating conditions
and covered temperatures f r o m 25°C to over 1200°C
using superheated steam, condensing steam, and water.
Specific conclusions and observations are as follows:
1. The transport of material during all of the tests
was dominated by aerosol phenomena even at high
temperatures.
2. Gravitational settling and inertial impaction
were the dominant deposition mechanisms observed.
This was due in part to the flow conditions and residence times in the various parts of the system.
3. The deposition rates in the reactor vessel and
pressurizer were higher at the bottom of the vessels
than at the vessel walls. Likewise, the deposition rates
were higher for horizontal than for vertical pipe sections.
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4. Aerosol particle aerodynamic mass mean diameters (AMMDs) downstream of the reactor vessel were
determined to be ~12 /tm.
5. The species were transported together in the
fissium-only tests (1, 2a, 2b, and 7). In the combined
corium-fissium test (4), there was evidence in the deposition patterns of differing transport behavior for the
different species. The measured transport times and
temperature profiles indicate that the flow patterns in
the reactor vessel and pressurizer were fairly complicated, with some indication that recirculation occurred.
6. Retention of material in the primary system
upstream of the relief tank was 36% for test 1, 15%
for test 2a (shorter residence time than test 1), 50% for
test 2b (lower temperature and flow than test 2a), 40%
in test 7 (addition of reactor vessel and higher temperatures and flow than test 2b), and 73% in test 4
(higher aerosol concentration than test 7).
7. Any aerosol remaining after passage of the dry
system parts was retained to at least 99% in the waterfilled relief tank or scrubber (at a submergence depth
of - 1 . 0 m).
The experimental data base is expected to be validated in due course by the analysis work and code
comparison exercises that are under way by the
LSATT parties. In particular, the adaption of codes to
represent interaction of aerosol behavior and prevailing thermohydraulics appears to require access to a
clearer understanding of the flow patterns in the larger
volumes of the system.
THE LACE EXPERIMENTS
Containment Bypass Tests
Two of the large-scale LACE tests focused on a
postulated containment bypass accident in a large dry
PWR, called a V sequence in Ref. 2. The results of
these tests will also have application to the generic
problem of aerosol deposition and resuspension in
pipes under other severe accident conditions in PWRs
and BWRs, such as steam generator tube rupture and
main steam isolation valve scenarios. These tests are
also of interest in systems containing pressure tubes
such as the Canada deuterium-uranium (CANDU)
reactors and certain noncommercial reactors in the
United States. Preliminary LACE results appear in
Refs. 7, 8, and 9.
In the V sequence, it is postulated that two check
valves fail in the emergency core cooling pipeline to
the reactor vessel. Following the valve failures, overpressure in a connected low-pressure pipe is assumed
to cause its rupture, allowing primary system coolant
water to discharge into an adjacent building, thus
bypassing the reactor containment building. The loss
of cooling water from this rupture eventually leads to
core overheating and the release of radioactive aerosols and gases from the reactor into the pipeline. The
pathway from the overheated core to the outside environment is tortuous so that significant deposition
and/or agglomeration of aerosols may occur. Important segments of the pathway include core region,
upper plenum, coolant pipes, steam generator (depending on system design), makeup line with valves,
transition sections and elbows, and auxiliary building.
The latter is alternatively called a safeguards or secondary building, and is assumed to fail by overpressure.
The experimental conditions of the LACE containment bypass tests deal with the pathway downstream
from the steam generator, including the makeup pipeline and auxiliary building.
In addition to the two LACE tests (LAI and
LA3), the program included three containment bypass
scoping tests. The five containment bypass tests are
characterized in Table II.
Experimental Facility and Methods —
Containment Bypass Tests
The containment bypass tests each used a test pipe
63 mm in diameter, 27 m long with five 90-deg bends,
four horizontal sections, and two vertical sections. A
schematic of the test assembly and auxiliary building
is shown in Fig. 12. The pressure drop across the pipe
was - 0 . 1 MPa and the Reynolds number of the carrier gas was - 5 x 10 5 . The test pipe terminated
within an 852-m 3 auxiliary building that was vented
to the atmosphere through a scrubber. For the three
LA3 tests, the auxiliary building shown in Fig. 12 was
not used, and the pipe discharged directly to a
scrubber.
Each test was performed in three stages: a heatup
stage to establish initial thermal-hydraulic conditions,
a 60-min period of injecting aerosol through the test
pipe to the vented auxiliary building, and a cooldown
period.
The initial thermal conditions in the test pipe and
auxiliary building were essentially the same in each
test. Approximately 20 h before time zero, steam was
injected through the test pipe into the auxiliary building. Steam feed was continued until steady-state thermal conditions were reached at ~83°C and 1-atm
pressure. At these conditions, the auxiliary building
TABLE II
LACE Aerosol and Thermal-Hydraulic Conditions at Inlet to Test Pipe
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Test
Aerosol
Soluble
Mass
Fraction
Carrier
Gas
Gas
Velocity
(m/s)
Temperature
(°C)
Auxiliary
Building
Conditions
Degrees
Superheat
(°C)
CB1
Soluble NaOH
1.00
Air-steam
100
186
88
Saturated
steam/air, 85°C
CB2
Soluble NaOH
Insoluble Al(OH)3
0.67
Air-steam
91
111
15
Saturated
steam/air, 81 °C
CB3
Insoluble Al(OH)3
0
Air-steam
97
160
66
Saturated
steam/air, 84°C
LAI
Soluble CsOH
Insoluble MnO
0.42
N2-steam
96
247
141
Superheated
steam/air, 115°C
LA3A
Soluble CsOH
Insoluble MnO
0.18
N2-steam
75
298
208
No auxiliary
building
LA3B
Soluble CsOH
Insoluble MnO
0.12
N2-steam
24
303
219
No auxiliary
building
LA3C
Soluble CsOH
Insoluble MnO
0.38
N2-steam
23
300
215
No auxiliary
building
STEAM
AIR
VENT
cr\
7
BURN
CHAMBER
MIXING
CHAMBER
SODIUM
TEST PIPE
INLET
•i/fn/t
JET PUMP
T
•nirin
Fig. 12. Schematic diagram of experimental apparatus for CB tests, LAI and LA3.
atmosphere was saturated and contained equal volumes of steam and air. The steam feed rate was then
reduced to the rate required to replenish condensation
losses caused by heat transfer to the walls.
During the latter stages of the heatup period, the
aerosol generation system was started, with the aerosol being sent to a bypass scrubber. At time zero, aerosol flow in a 50% steam/50% air carrier gas was
started through the test pipe. A constant flow velocity of - 1 0 0 m / s at the pipe inlet was maintained.
After 60 min, aerosol and carrier gas release was terminated. No steam was injected during the cooldown
period, which lasted —1 day.
The scoping tests (CB1, CB2, and CB3) used
sodium hydroxide (NaOH) and aluminum hydroxide
[Al(OH) 3 ] as the soluble and insoluble aerosol materials. The carrier gas was a 50% mixture of steam and
air and was superheated in the test pipe. The carrier
gas was 15 to 88°C above saturation at the test pipe
inlet. A schematic diagram of the aerosol generator is
given in Fig. 13.
Tests LAI and LA3 used CsOH as the soluble
aerosol species and manganese oxide (MnO) as the
insoluble aerosol species. Nitrogen/steam carrier gas
was used in these later tests in order to avoid complex
chemical reactions and oxidation of nitrogen and
MnO. The carrier gas was superheated in the test pipe.
At the test pipe inlet, the carrier gas was 141 to 219°C
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<0
a
u
60
J3
O
u.
<
u
u
iI n
<30
<3
u
43
V
o
00
60
E
Downloaded by [University of Florida] at 21:21 28 October 2017
above saturation. The most important test pipe parameters varied during the tests were the ratio of soluble
to insoluble aerosol species and carrier gas flow rate.
Aerosol characteristics measured at the test pipe
inlet and averaged over the 60-min aerosol source
period are given in Table III. Aerosol particle size distributions were determined by four cascade impactor
measurements. Approximately 14 filter samples were
taken during the source period to determine aerosol
suspended mass concentration as a function of time.
The source rates listed were calculated from aerosol
recovered from the test system. Approximately 90% of
the aerosol source was recovered in the closed material balances.
The test auxiliary building was used only in the
three CB tests and test LAI. The auxiliary building atmosphere was a 50% steam/50% air mixture at steadystate thermal conditions just prior to aerosol injection
for all four tests. The atmosphere was saturated at
80°C for the three CB tests but superheated 31°C for
test LAI. The auxiliary building was vented to a water
scrubber, and its absolute pressure was ~ 1 bar.
Test Results
than 2% of the material was vented for the liquid or
liquid/solid aerosols, although substantially more of
the material was vented for the test where only solid
aerosol was used.
The fraction of entering aerosol mass retained in
the 63-mm-diam test pipe was < 5 % in each of the
three tests. Significantly larger fractions were retained
in the short length of 300-mm-diam pipe at the downstream end of the 63-mm section: - 5 0 % for the first
two tests and 14% for test CB3. It is postulated that
a large fraction of entering aerosol was deposited on
the wall of the 63-mm pipe during transit through the
pipe, but that most of the deposited material was
resuspended or moved along the pipe as a liquid film
by shear stresses induced by the high-velocity carrier
gas. The gas velocity in the 63-mm pipe ranged from
- 1 0 0 m/s at the inlet to - 2 0 0 m / s at the outlet. Upon
entering the 300-mm-diam horizontal pipe section, the
velocity decreased to - 9 m/s, and much of the
resuspended material and liquid wall film was collected
in this section. If this enlarged section of the test pipe
had not been present, the relatively large resuspended
aerosol particles and entrained droplets of liquid wall
film would have settled quickly in the relatively quiescent atmosphere in the auxiliary building.
Several interesting phenomena were observed in
this test series. First, for the CB scoping tests where
the aerosol material was either a liquid or a dry solid,
very little material was retained in the test pipe. In
these tests, most of the material was retained in the
downstream enlarged pipe section and in the auxiliary
building where velocities were lower.
Second, for other tests, much of the material was
retained in the test pipe. For particular ratios of soluble to insoluble material, a "sticky" material was
formed. It should be noted that the three LA3 tests
had a lower soluble mass fraction and/or a lower carrier gas velocity. The higher gas superheat in these tests
probably gave less absorption of water by the soluble
aerosol than in the CB tests.
Third, even though the amount of material retained in the test pipe varied from essentially all of the
material to very little, for most cases the fraction of
material vented from the auxiliary building was quite
small based on the aerosol source to the test pipe. Less
The NaOH absorbed water from the steam atmosphere to form a liquid solution with a concentration,
calculated from vapor pressure data, of 70 wt%
NaOH in test CB1 and 30 wt% in test CB2. In test
CB2, the two aerosol materials are believed to have
coagglomerated, giving a suspension of - 1 0 vol%
Al(OH) 3 in the NaOH solution. The behavior of the
aerosol in the first two tests was similar, showing that,
for the conditions of these tests, the presence of a viscous liquid constituent dominated the behavior of the
coagglomerated liquid/solid aerosol.
A dry insoluble solid material, Al(OH) 3 , was used
for the aerosol in the third test. The particle size distribution of aerosol entering the test pipe was similar to
that in the first test. However, it behaved differently
than the liquid aerosol in the first two tests in that a
lower fraction was retained in the downstream 300-mm
pipe section and a larger fraction was suspended uniformly throughout the atmosphere of the auxiliary
building. This suggests that the physical state of the
TABLE III
LACE Measured Aerosol Characteristics at the Test Pipe Inlet
a
Property
CB1
CB2
CB3
LAI
LA3A
LA3B
LA3C
Total source rate (g/s)
Source size, AMMD (ftm)
Geometric standard deviation
Suspended mass concentration (g/m 3 ) a
3.0
3.9
2.9
9.5
0.9
3.1
2.6
3.2
2.0
4.3
2.5
6.1
1.1
1.6
1.9
3.6
0.6
1.4
2.0
6.9
0.9
2.4
2.0
22.0
0.9
1.9
2.1
30.2
At actual conditions.
NUCLEAR TECHNOLOGY
Downloaded by [University of Florida] at 21:21 28 October 2017
aerosol has an important effect on its behavior in pipe
flow. This may be related to differences in resuspension properties.
The aerosol/gas stream entered the atmosphere of
the auxiliary building at high velocity ( - 2 0 0 m/s)
horizontally near the bottom of the auxiliary building.
A large fraction of the aerosol mass leaving the test
pipe was impinged on the building wall and floor during the release and was not suspended in the atmosphere. For the first two tests, the impinged fraction
was - 0 . 8 , and for test CB3 it was - 0 . 4 . The mechanisms responsible for this effect are postulated to be
inertial impaction from the high-velocity jet and gravity settling of very large particles and droplets that had
been formed in the test pipe or at its discharge. The
significance of this effect is that the fraction of aerosol available for leakage to the environs is greatly
reduced.
Table IV summarizes the main observations and
conclusions of the CB experiments.
Results from Tests LAI and LA3
Test LAI differed from the CB tests in several
significant ways. The most important was that LAI
used a more realistic aerosol. Cesium hydroxide was
used in place of NaOH to simulate volatile, hygro-
TABLE IV
LACE CB Tests Observations and Conclusions
1. Aerosol retention in 63-mm pipe was <5%.
2. Aerosol vented from auxiliary building was —2% for
the first two tests, and -20% for test CB3.
3. Test pipe was responsible for ultimately removing
- 9 0 % of liquid aerosol of tests CB1 and CB2, and
- 5 0 % of solid aerosol of test CB3, when removal
mechanisms downstream of the test section are considered.
4. For auxiliary building, -20% of entering aerosol
mass was suspended in tests CB1 and CB2, while 60%
was suspended in CB3.
5. Physical state of aerosol was important to pipe flow
behavior and fraction suspended at outlet.
6. For the test pipe, a large fraction of the entering aerosol deposited then resuspended or flowed as a liquid
film along test pipe.
7. For auxiliary building, a large fraction of entering
aerosol mass impinged on the wall or fell out on the
floor.
8. Characteristics of aerosol passing through piping at
high velocity are changed significantly with a greatly
enhanced removal in auxiliary building.
scopic fission product species, while MnO was used in
place of Al(OH) 3 to simulate semivolatile, nonhygroscopic fission product and structural compounds. Nitrogen replaced air in the carrier gas mixture, whose
temperature (247°C) was somewhat higher than for the
scoping tests. The steam/air atmosphere in the auxiliary building was at 118°C, above the saturation temperature. Other important differences are given in
Table V. The experimental configuration for Test LAI
is given in Fig. 3, while the important experimental
parameters are summarized in Table VI. The major
conclusion of test LAI is that virtually all of the aerosol material (>98%) was retained in the 63-mm test
pipe. The reason for the high retention fraction is
attributed to the physical nature of the aerosol. Surface tension, viscosity, and melting point were some of
the important parameters affecting adhesion and
resuspension. In test LAI, a viscous, tightly adhering
film was formed on the pipe surface. This was the
result of the ratio of soluble CsOH to insoluble MnO.
As a result, < 2 % of the aerosol material reached the
auxiliary building.
The test conditions of CB2 and LAI were quite
similar, the main difference being the ratio of soluble
to insoluble components. In CB2, retention in the
63-mm pipe was < 5 % , in LAI it was > 9 8 % . It is
believed that this different behavior is the result of
physical differences of the test aerosols. Chemical differences are thought to be of secondary importance.
When soluble (and hygroscopic) aerosols were mixed
with nonsoluble ones in test CB3 and LA3, a range of
behavior was observed:
1. For purely soluble aerosols or those containing
up to - 3 0 % nonsoluble material, pressure and temperatures in the piping favored the formation of liquid droplet aerosols that picked up water of hydration
TABLE V
LACE LAI: Significant Differences from CB Tests
1. More realistic aerosol (CsOH and MnO)
2. Higher aerosol carrier gas temperature (280°C)
3. Nitrogen as noncondensible carrier gas
4. Measure aerosol flow distribution along pipe wall and
near pipe centerline
5. Improved in situ trapping of deposited aerosol
6. Superheated steam/N 2 atmosphere (115°C) in auxiliary building
7. Improved measurement of auxiliary building steam
fraction
8. Additional wall condensate collectors in auxiliary
building
TABLE VI
LACE Test LAI: Containment Bypass Test Conditions
Target
Actual
Aerosol Source at Test Pipe Inlet
1
2
3
2
CsOH rate (g/s)
MnO rate (g/s)
Source size, AMMD (/tm)
Source geometric standard deviation
Suspended concentration (g/m 3 )
CsOH
MnO
Duration (min)
2.7
5.4
60
0.48
0.65
1.64
1.91
1.8
2.3
60
Downloaded by [University of Florida] at 21:21 28 October 2017
Test Pipe Conditions
Geometry
i.d. (mm)
Length (m)
Number of 90-deg bends
Ball valves
Composition
63
30
6
4
50% steam
50% nitrogen
280
180
120
215
120
Inlet temperature (°C)
Superheat (°C)
Velocity at inlet (m/s)
Velocity at outlet (m/s)
Pressure drop (kPa)
63
29
6
4
56% steam
44% nitrogen
247
141
97
193
125 average
Auxiliary Building Conditions at Time Zero
Volume (m3)
Heat transfer
Vent
Atmosphere composition
Temperature (°C)
Superheat (°C)
Pressure (atm)
from the (dry) steam. In such cases, aerosols were carried to the pipe walls (by impaction or turbulent deposition) where liquid films formed. Some small amount
of chemical attack of the piping surfaces may have
occurred.
2. For the purely nonsoluble aerosols tested, solid
aerosols were formed prior to entering the piping.
These too were carried to the pipe walls, but were
resuspended in the flowing gas stream. Agglomeration
appears to have been negligible. Aerosols exited the
piping with about the same AMMD as they entered;
retention was small.
3. For the cases of mixed aerosols where 30 to
80% of the material was nonsoluble, the aerosols to
the walls appeared to form a thick, highly viscous
852
Approximately steady state
Open
50% air
44% air
50% steam
56% steam
115
118
33
31
1.1
1.1
layer that was immobile during the tests. Although the
aerosol components may have been slightly reactive,
chemical processes did not appear to control their
deposition behavior.
The LA3 examined the most important parameters
in containment bypass situations: aerosol composition
and flow velocity. The configuration (Fig. 14) was similar to test LAI, except the auxiliary building was not
included in the tests. Actual conditions, given in Table VII, varied in gas carrier velocity by a factor of ~ 4
(97 versus 23 m/s) and in MnO-to-CsOH ratio by a
factor of ~ 5 (7.6 versus 1.4). These conditions span a
wide range of interest. The higher velocity tests are
near critical flow conditions. The lower velocity tests
provide a link to the Marviken experiments, which also
BYPASS
TO STACK
TEST PIPE
r
STEAM AND N 2
FOR PREHEAT
STEAM
I
AEROSOL SAMPLE
AEROSOL SAMPLE
AEROSOL
GENERATOR
(SAME AS LA1)
VENTURI SCRUBBER
SUBMERGED
GRAVEL
£ SCRUBBER
DOWNSTREAM SAMPLE PIPE
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Fig. 14a. Schematic layout of experimental apparatus for test LA3.
FULL-PORT
observed significant fission product retention in pipes
at flow velocities a r o u n d 5 m / s .
LACE Conclusions
Based o n the observations of the large-scale tests,
several m a j o r conclusions are possible. First, the
a m o u n t of aerosol material retained in t h e test pipe
during the containment bypass experiments is strongly
influenced by the physical n a t u r e of the aerosol. Resuspension a n d t r a n s p o r t processes are d i f f e r e n t f o r
liquid, liquid/solid, a n d dry solid aerosol materials
a f t e r they are deposited o n the pipe wall.
LA1
— WALL SCOOP
LENGTH = 30 m
DIAMETER = 62.7 mm
CARBON STEEL
INSULATED
LA1 PIPE SECTIONS REUSED
WHERE POSSIBLE
Fig. 14b. Test pipe isometric for test LA3 showing changes
from test LAI.
Second, the passage of aerosol material t h r o u g h
the pipe changed the aerosol characteristics such as to
p r o m o t e inherent retention processes a n d minimized
the a m o u n t of aerosol material vented f r o m containm e n t . Less t h a n 2 % of liquid or liquid/solid aerosol
was vented, although approximately ten times as much
was vented in the single experiment where 100% solid
aerosol was used. Few, if any, accident scenarios are
t h o u g h t t o involve only solid aerosols.
TABLE VII
LACE LAI and LA3 Test Conditions
LAI
Gas inlet velocity (m/s)
Inlet temperature (°C)
Aerosol-to-test pipe
Average CsOH rate (g/s)
Average MnO rate (g/s)
Average MnO/CsOH ratio
Test plan ratio
Duration (min)
Test pipe length (m)
Test pipe diameter (mm)
97
247
0.48
0.65
1.4
2
60
29
63
LA3A
LA3B
LA3C
75
280
24
300
23
290
0.11
0.51
4.6
8
60
29
63
0.10
0.76
7.6
8
60
29
63
0.34
0.56
1.6
2
60
29
63
Third, it is possible that fission product deposits
m a y be leached of the soluble components, leading to
their relocation.
Fourth, other L A C E experiments have shown even
relatively simple leak paths f r o m a reactor containment building to the environment may remove a large
fraction of suspended fission products during real accidents. The d o m i n a n t removal mechanism appears to
be turbulent deposition.
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TRAP-MELT VALIDATION EXPERIMENTS
This section presents the aerosol transport test
(ATT) results, comparisons to T R A P - M E L T code predictions, preliminary aerosol resuspension test results,
a n d a discussion of resuspension modeling activities
that are under way.
Aerosol Transport Test Results
The main components of the O R N L A T T facility
are a plasma-torch aerosol generator system, a vertical test pipe, and associated temperature measurement
and aerosol sampling equipment. T o generate aerosols
in these tests, a M E T C O 9MB P l a s m a Flame Spray
Gun was used as a heat source. Figure 15 illustrates the
c o m p o n e n t s of the aerosol generator. Metal powders
(50- to 100-/xm diam) and a flow gas (either pure argon
or an a r g o n / o x y g e n mixture) were injected in the
plasma flame confined in the aerosol mixing chamber.
Metal-oxide aerosol can be produced by vaporization/oxidation of the metal powders, or metallic aerosols can be produced by direct powder vaporization in
a reducing a t m o s p h e r e .
Figure 16 shows the insulated stainless steel test
pipe section. The aerosol generator is connected to a
0.46-m-long inlet cone that provides for radial spreading of the aerosol source b e f o r e it enters the main
portion of the pipe. The cone has an inlet diameter of
0.1 m, an outlet diameter of 0.26 m, and a total
included angle of 20 deg.
The segmented, vertical test pipe sections above
the cone have a 0.26-m i.d. and a 2.63-m overall
length. Aerosol sampling was performed at three pipe
locations. Aerosols transported out of the test pipe
passed through a transition section into a large collection bag. In later discussions we will refer to the vertical test pipe in terms of a "lower" section (regions 3,
ALUMINA INSERT
Fig. 15. Main components of plasma-torch aerosol generator system.
NUCLEAR TECHNOLOGY
VOL. 81
MAY 1988
10-
12
11
91. PLASMA TORCH ASSEMBLY
-b-d, f
8 -
2. INLET CONE
3. LOWER SAMPLING STATION
a. GAS AND WALL TEMPERATURES
4. SLIDE VALVE
b. AEROSOL CONCENTRATION
5. LOWER PIPE SECTION
c. AGGLOMERATE SIZE: IMPACTORS
•b, c, f
6. CENTER SAMPLING STATION
d. PRIMARY PARTICLE SIZE:
ELECTROSTATIC PRECIPITATORS
7. CENTER PIPE SECTION
e. PRIMARY PARTICLE SIZE:
SETTLING SAMPLER
Downloaded by [University of Florida] at 21:21 28 October 2017
8. UPPER SAMPLING STATION
9. UPPER PIPE SECTION
f. METAL-FOIL DEPOSITION SAMPLES
3-D
10. TRANSITION SECTION
g
— b, e, f
11. PYREX PIPE
g. FINAL AEROSOL CONCENTRATION:
SLIDE VALVE
12. AEROSOL COLLECTION BAG
Fig. 16. Aerosol transport test section components and measurement location.
4, and 5 in Fig. 16), "center" section (regions 6 and 7),
and an " u p p e r " section (regions 8, 9, and the vertical
portion of 10).
A variety of thermal-hydraulic and aerosol transport measurements were made during the experiments.
These include (a) plasma-torch operating parameters,
(b) gas and wall temperatures at different axial locations in the pipe, (c) aerosol primary particle size
distributions, by counting particles collected on microscope grids, (d) aerosol agglomerate size distributions
using cascade impactors, (e) the mass of aerosols deposited onto the different pipe sections, and (f) plateout deposition onto thin metal coupons. To accomplish
coupon deposition, thin (0.13-mm) foil deposition
coupons, 25 m m wide x 50 mm high, were mounted
vertically midway between the pipe centerline and wall
at three aerosol sampling locations (Fig. 16). It was
calculated that only a negligible temperature gradient
existed between the gas and foil surface; this condition
would provide only minimal driving force for thermophoretic deposition on the foils. A comparison of
aerosol deposition per unit surface area on the foil and
that on the pipe walls should, then, provide information on whether thermophoresis was the dominant wall
deposition mechanism in the tests.
Results f r o m tests A105 through A108 are discussed; the m a j o r parameters for these tests are summarized in Table VIII. Iron oxide (Fe20 3 ) and
metallic zinc aerosols were used to simulate structural
material aerosols that could be produced in core-melt
accidents. The m a j o r reason for using these aerosols
was that the agglomerates produced had different
TABLE VIII
ORNL Aerosol Transport Test Parameters
Test
A105
A106
A107
A108
a
Aerosol
Material
Iron
Iron
Zinc
Zinc
oxide
oxide
metal
metal
Mean
Flow
Residence
Time
(s)
Mean
Test
Flow
Velocity
(cm/s)
56
26
54
24
4.7
10.3
4.9
11.2
Mean
Temperature
Gradient
Range 3
(°C/cm)
14 to
20 to
17 to
31 to
56
73
77
88
These values estimated from differences in temperatures
measured at pipe wall and at 13 mm from wall.
Downloaded by [University of Florida] at 21:21 28 October 2017
METALLIC ZINC AEROSOL
IRON OXIDE AEROSOL
Fig. 17. Scanning electron microscope photomicrographs of metallic zinc and iron oxide aerosols.
shapes (illustrated in Fig. 17). Chain-like iron oxide
agglomerates were produced that were made up of
submicron primary particles. Chain-like zinc agglomerates were not produced, perhaps because the zinc
aerosols were molten during part of their transport
through the pipe (inlet-cone temperatures were 600 to
700°C; zinc melts at 420°C). Agglomeration of the
original molten primary particles seems to have resulted in the spheres shown in Fig. 17.
The experimental procedure was to purge the
pipe prior to the start of each test with argon gas for
- 3 0 min. The plasma torch was then ignited and
allowed to operate for 3 to 4 min with no powder feed;
during this time the torch power was increased from
15 to 30 kW. After the preheat period, metal powder
was fed to the torch to initiate the experiment. The
aerosol generation period for each test was 10 min;
temperature and aerosol measurements were made
during this time. Dismantling of the test section was
begun on the day following the completion of each
test, and posttest analyses of test samples were initiated. Detailed data record reports were written for
each test. 10 " 13
Gas and wall temperatures were measured at the
inlet cone, lower sampling station of the pipe, and at
distances of 0.92, 1.27, 1.73, and 2.46 m above the
cone inlet. Table IX summarizes time-averaged values
(for the 10-min aerosol generation period) of centerline gas temperatures, wall temperatures, and wall
temperature gradients from tests A105 through A108
(the lower, center, and upper sections are as previously
defined). The data show that higher gas and wall temperatures were produced in the lower pipe section, as
would occur in the upper plenum in a severe accident.
Using the temperature data from Table IX and the
measured gas flow rates, ranges of Reynolds (Re) and
TABLE IX
ORNL ATT Time-Averaged Values of Centerline Gas
Temperatures, Wall Temperatures, and
Wall Temperature Gradients for
Tests A105 Through A108a
Location1"
Average
Centerline
Gas
Temperature
(°C)
Average
Wall
Temperature
Gradient
(°C/cm)
Average
Wall
Temperature
(°C)
A105
Lower
Center
Upper
237
127
77
61
39
30
56
25
14
73
31
36
73
48
20
A106
Lower
Center
Upper
309
173
103
A107
Lower
Center
Upper
299
145
81
55
31
25
'
77
39
17
A108
Lower
Center
Upper
a
374
208
129
72
36
32
88
63
31
"Average" values determined for the 10-min aerosol generation period.
b
Lower, center, and upper sections are as defined in text.
Downloaded by [University of Florida] at 21:21 28 October 2017
Grashof (Gr) numbers that characterize the test flows
were calculated and are presented in Table X. Since
the Reynolds number values were <1000, we might
expect that laminar flow conditions were produced in
the tests. However, the fact that calculated Grashof
numbers were >10 7 indicates that turbulent natural
convection flow conditions were produced. The ratio
of G r / R e 2 provides a measure of the relative importance of natural and laminar forced convection flow
in the tests. 14 Values of Gr/Re 2 » 1 indicate that free
convection dominates forced convection in these tests.
Although we have not made measurements to confirm
this, the high G r / R e 2 values imply that there is a net
downward flow of gas in the boundary layer at the
wall, with an enhanced central region gas upflow (due
to conservation of mass).
Figures 18 and 19 illustrate the aerosol deposition
and transport data (the major experimental results)
from tests A105 through A108. Figure 18 shows (as a
C7U
i
8 0
w 70
K3A106
m A107
CO
<
60
o
CO
o
cr
IZ3A105
50
ES3
A108
RESIDENCE
TIME
(s)
TOTAL AEROSOL
PRODUCED
(g)
43.6
57.1
112.0
74.7
40
L
<U 3 0
—i
<
o
20
10
rt-^r^l
TOTAL
RELEASED AIRBORNE
PLATEOUT
Fig. 18. Summary of ORNL aerosol transport test data
(mass is given as a percentage of total aerosol mass
produced).
TABLE X
ORNL ATT Calculated Average Reynolds Numbers,
Grashof Numbers, and Gr/Re 2 for Tests
A105 Through A108
Pipe
Section
Average
Reynolds
Number 3
(Re)
Average
Grashof
Number 8
(Gr)
Gr/Re 2
4.4 x 107
6.5 x 107
6.4 x 107
268
278
222
A105
Lower
Center
Upper
407
485
536
A106
Lower
Center
Upper
3.2 x 107
6.2 X 107
6.3 x 107
724
874
993
61
81
64
A107
Lower
Center
Upper
391
490
555
4.1 X 107
7.8 X 107
8.1 X 107
270
323
261
3.0 x 107
6.3 x 107
7.9 x 107
57
79
76
A108
Lower
Center
Upper
725
892
1020
"Calculated Reynolds and Grashof numbers based on pipe
diameter. The temperature difference used for Grashof
number calculations was the difference between the average gas centerline temperature and the wall temperature at
each axial location.
Fig. 19. ORNL ATT cumulative wall plateout of aerosols
versus distance from cone outlet (shown as a percentage of total mass of aerosol produced).
function of total aerosol produced) total aerosol
plateout (that deposited in the lower, center, and
upper pipe sections), aerosol release from the test pipe,
and the total amount of aerosols remaining airborne
at the end of the aerosol generation period. The figure shows that, for each aerosol material, the fractional mass transported out of the pipe was expected;
it occurred even though the measured wall temperature
gradients (which drive thermophoretic deposition)
increased with higher test flow rates.
Figure 19 shows fractional cumulative wall plateout as a function of distance from the cone outlet. In
all tests, the m a j o r fraction of the wall plateout occurred in the first 1-m length of pipe; this correlates
with the fact that measured temperature gradients were
highest in this region. For each test, the plateout data
in Fig. 19 show an exponential dependence of deposition on distance. A nonlinear fit of each data set to an
equation of the following form was performed.
Mp = A[\
10"
"l
r
TEST A106:
E
-exp(-ft)]
(1)
o
o>
— WALL DEPOSIT TEST DATA
(CURVE FIT)
where
•
cc
<
Mp = cumulative aerosol mass plated (g)
DEPOSITION FOILS
t
z
z = distance from cone outlet (m)
D
CC
UJ 1 0 "
Q-
A,B = curve-fitting constants.
The factor dMp/dS, the aerosol mass deposited per
unit surface area, can be determined by differentiating Eq. (1) with respect to z and dividing by the pipe
circumference:
3
-
Q
UJ
H
Cfl
O
0.
LU
o
Downloaded by [University of Florida] at 21:21 28 October 2017
dMp/dS
= Cexp(-5z) ,
(2)
where
C =
CO
<
</>
5
AB/(irD)
10"
0.5
D = pipe diameter.
1.0
1.5
_L
2.0
_L
2.5
3.0
DISTANCE FROM OUTLET OF CONE (m)
Using the constants A, B, and C and Eq. (2), comparisons of the aerosol deposition per unit area on the
pipe walls and that on the deposition foils for each test
can be made. The results of these comparisons are presented in Figs. 20 through 23. Remember that it was
determined by calculation that thermophoretic deposition on the foils would be negligible. The iron oxide
results in Figs. 20 and 21 show, however, that for these
10"
"i
r
TEST A105:
E
o
— WALL DEPOSIT TEST DATA
(CURVE FIT)
•
DC
<
DEPOSITION FOILS
z
D
a
io-
Fig. 21. ORNL ATT comparison of wall-deposit and
deposition-foil data for test A106, using an iron
oxide aerosol.
tests the foil deposition was essentially equal to that on
the pipe walls. Somewhat different results were obtained for the zinc experiments. For test A107 (Fig. 22),
the deposition per unit surface area on the foils was
always greater than that on the pipe walls. For test
A108 (Fig. 23), the foil deposition per unit area in the
lower pipe region was significantly greater (by a factor of ~30) than deposition on the walls. In the other
regions, the foil deposition was comparable to, but
slightly less than, that on the pipe walls. These results
overall suggest that thermophoresis was not the dominant wall deposition mechanism in our experiments,
and that it may not be the dominant wall deposition
mechanism in the reactor vessel upper plenum. At the
present time, however, we cannot explain the differences between the iron oxide and zinc deposition-foil
results.
co
o
TRAP-MELT2 Comparisons with ATT Results
0.
Ill
Q
(/)
CO
<
10"
0.5
1.0
I
_L
_L
1.5
2.0
2.5
3.0
DISTANCE FROM OUTLET OF CONE (m)
Fig. 20. ORNL ATT comparison of wall-deposit and
deposition-foil data for test A105, using an iron
oxide aerosol.
Comparisons of TRAP-MELT2 code calculations
and the results from tests A105 and A106 were performed and published in a separate report. 15 Preliminary calculations were also performed for tests A107
and A108, and the overall conclusions from these calculations are the same as for the A105-A106 comparisons. Therefore, only the results from the A105 and
A106 code comparisons are presented here.
To perform TRAP-MELT2 calculations for A105
and A106, it was assumed that the test section could
10"
TEST A t 0 8 :
<
111
a:
<
10"
z
D
Downloaded by [University of Florida] at 21:21 28 October 2017
CC
ui
Q.
O
UJ
CO
O
0.
Ui
- 3
O 10
w
CO
E
o
<
UJ
oc
<
t
z
D
cc
UJ
o.
o
— WALL DEPOSIT TEST DATA
(CURVE FIT)
•
10*
DEPOSITION FOILS
10"
w
o
a.
LU
o
co 10'
c/j
<
5
<
5
10-5|
0
'
'
I..
I
l
0.5
1.0
1.5
2.0
2.5
3.0
DISTANCE FROM OUTLET OF CONE (m)
Fig. 23. ORNL ATT comparison of wall-deposit and
deposition-foil data for test A108, using a zinc
metal aerosol.
Fig. 22. ORNL ATT comparison of wall-deposit and
deposition-foil data for test A107, using a zinc
metal aerosol.
be modeled as five control volumes: (a) the inlet cone,
(b, c, and d) the lower, center, and upper pipe sections, and (e) outflow volume. Aerosol deposition in
the inlet cone was not modeled, because some of the
deposition in the cone was due to spatter onto the surface. Therefore, in all calculations, aerosol deposition
was not allowed in the cone; however, aerosol agglomeration in the cone was allowed.
Six TRAP-MELT2 calculations were performed
for each of the tests, including a "base case" calculation and five code runs in which the influence of variations in code input parameters and code models was
investigated. The following types of inputs were used
for the base case calculations: (a) control volume
geometries, (b) measured centerline gas temperatures
and wall temperatures versus time, (c) constant aerosol source rates into the pipe (based on test massbalance data), (d) pipe section geometries, and (e)
aerosol primary particle-size distribution data determined from measurements, and all aerosol shape factors set to 1.
Parametric variations around the base case calculations were performed to determine how various
parameters influenced the calculated wall plateout
results. Figures 24 and 25 present the results of four
of the calculations performed for each test. In the
figures, the ratio of the measured-to-calculated wall
plateout for the lower, center, and upper pipe sections
is presented. The four cases correspond to the following conditions:
1. Case 1: Base case calculation.
2. Case 2: An aerosol collision shape factor of 10
was assumed.
3. Case 3: An improved correlation to calculate
the wall temperature gradient was included in
the code. In addition, the slip coefficients in the
Brock 1 6 thermophoresis model were modified
based on the work of Talbot et al. 17
4. Case 4: Instead of using a code correlation to
calculate temperature gradients, the measured
wall temperature gradients were used as code
input. In addition, the Talbot modifications to
the Brock model were used.
IZZICASE
(XSCASE
EZ3 CASE
KX) CASE
A105
Downloaded by [University of Florida] at 21:21 28 October 2017
LOWER
SECTION
CENTER
SECTION
1
2
3
4
UPPER
SECTION
Fig. 24. Selected comparisons of measured and calculated
wall plateout for ORNL ATT test A105, using an
iron oxide aerosol.
A106
E23
KS
EZ!
K3
CASE
CASE
CASE
CASE
1
2
3
4
10 was used, this choice led to a better prediction of
the airborne aerosol agglomerate size. The wall plateout predictions were worse than for the base case. This
occurred because the code calculated larger agglomerates when the collision shape factor was increased, and
the calculated thermophoretic deposition velocity tends
to decrease with increased particle size.
3. In cases 3 and 4, where improvements in the
wall temperature gradient and the thermophoresis
modeling were made, differences in measured and calculated wall plateout were reduced to a factor of ~ 8 .
The modification to the thermophoresis model accounts for a 40% increase in the calculated deposition
velocity; the additional improvement from the base
case results is due to improved values of the thermal
gradients.
The code calculations illustrate that, even with
code improvements, thermophoresis alone cannot account for the measured wall deposition. A possible
deposition mechanism that is not now included in
TRAP-MELT2 might be called "convective-turbulent
deposition." The calculated Grashof numbers for our
tests (Table X) indicate that turbulent conditions exist
near the pipe walls. Such turbulence could lead to enhanced wall deposition above that predicted by thermophoresis models. It should be noted that if a deposition
mechanism other than thermophoresis is important in
these tests, it would also be expected to be important
for aerosol behavior in the reactor vessel's upper plenum region, where strong convective currents are predicted under core-melt accident conditions.
Aerosol Resuspension Experiments
LOWER
SECTION
CENTER
SECTION
UPPER
SECTION
Fig. 25. Selected comparisons of measured and calculated
wall plateout for ORNL ATT test A106, using iron
oxide aerosol.
The overall results from the TRAP-MELT2 calculations and comparisons with experimental data are
summarized below:
1. In all cases, the dominant mechanism for predicted wall plateout in the calculations was thermophoresis.
2. In the base case calculations, where no code
model modifications were made, TRAP-MELT2 underpredicted measured wall plateout by factors of 12 to
22. For calculations where a collision shape factor of
At the present time, none of the aerosol transport
codes used for calculating aerosol behavior in the reactor coolant system includes models for aerosol resuspension from surfaces. The objective of the aerosol
resuspension work is to investigate resuspension phenomena that might occur in the reactor coolant system
(RCS) under core-melt accident conditions. The test
results will be used as a basis for developing resuspension rate correlations that will be included in the
TRAP-MELT2 code and other aerosol transport codes
in the future.
Resuspension phenomena that occur as a result of
gases flowing past a surface deposit are being investigated. In terms of the aerosol deposits, the "sticking"
forces are difficult to estimate and depend strongly on
such parameters as (a) aerosol material, (b) phase
(solid or liquid), (c) particle size, (d) system moisture
conditions, (e) concentrations of aerosol deposits on
surfaces, (f) aerosol surface roughness conditions,
and (g) the aerosol deposition mechanism. Studies of
resuspension phenomena might be classified as two
types: (a) "dry" resuspension, or the lift-off of solid
surface, and (b) "wet" resuspension, or the lift-off of
Downloaded by [University of Florida] at 21:21 28 October 2017
(a) APPARATUS FOR COLLECTING DEPOSITION SAMPLES
(WILL BE ORIENTED VERTICALLY)
(b) RESUSPENSION TEST APPARATUS
Fig. 26. Schematic for ORNL ATT Series-2 "dry resuspension" tests.
liquid or solid aerosols due to the flow of saturated or
nearly saturated steam past the surface.
In 1984 a series of aerosol and powder resuspension experiments designated as the Series-1 tests 18 was
completed; these experiments provided us with useful
information on the influence of particle size, density,
and amount of material deposited on resuspension
rates. However, they had the disadvantage that the
aerosol and powder deposits were artificially produced. The recently completed Series-2 resuspension
tests were designed to investigate resuspension of aerosols deposited onto surfaces by natural mechanisms
(for example, thermophoretic or turbulent deposition).
The results f r o m these tests are still under analysis;
however, the test procedures and conditions are described here, and an example of the test results is presented.
The Series-2 tests, which were performed in two
steps, utilized the equipment illustrated in Figs. 26 and
27. In the first step (Fig. 26a), aerosols were generated
with the plasma-torch system and deposited on the
interior of a series of 2.5-cm-diam, 7.6-cm-long stainless steel tubes. After the aerosol deposits were collected and the amount of aerosol deposited onto each
tube was determined by weighing, the tubes were
mounted into a second test section (Figs. 26b and 27).
In this test section, nitrogen was used as a flow gas,
and the amount of aerosol removal (from which rate
information can be obtained) was measured, for each
test aerosol, for varied flow velocities and sample
exposure times. The range of flow velocities used in
the experiments ranged f r o m 4 to 60 m / s ; this corresponds to flow Reynolds numbers ranging from 6000
to 90000.
Table XI summarizes the test parameters used in
the Series-2 experiments. Five different aerosols—three
oxide and two metallic —were used in the tests. The
zinc aerosols had primary particle sizes (geometric
diameters) in the range of 2 /tm; the other aerosols had
primary sizes in the range of 0.1 /xm. A key element of
the experiments was that the resuspension of "multilayer" deposits was investigated; most previous resuspension tests have investigated the resuspension of
essentially monolayer deposits. As noted in Table IV,
sample loadings per unit ~ 1 m g / c m 2 ; although these
were fairly dense deposits, they were probably at least
an order of magnitude less (per unit surface area) than
TABLE XI
ORNL ATT Test Parameters for Series-2
Aerosol Resuspension Experiments
Test
a
Aerosol Material
Sample
Mass
Loading
(mg)a
Sample
Loading
per
Unit Area
(mg/cm 2 ) a
ART-02
ART-03
ART-04
ART-05
Manganese oxide
Metallic zinc
Iron oxide
Tin oxide
63
72
82
332
1.13
1.29
1.47
5.94
ART-06
ART-07
ART-08
ART-09
Metallic manganese
Metallic zinc
Tin oxide
Iron oxide
66
114
34
11
1.18
2.04
0.61
0.20
Average for all tests performed.
Downloaded by [University of Florida] at 21:21 28 October 2017
TOTAL EXPOSURE TIME (s)
Fig. 28. Series-2 resuspension iron oxide data.
Fig. 27. Overall view of equipment for Series-2 "dry
resuspension" tests.
the deposits that might occur by plateout on RCS surfaces. Note also f r o m Table IV that the influence of
the amount of aerosol deposited, on the measured
resuspension, was investigated in the pairs of tin oxide
and iron oxide experiments.
An example of the type of data measured in the
experiments is shown in Fig. 28 for ART-04, an iron
oxide experiment. The plot illustrates that for flow
velocities <24 m / s , < 1 0 % of the aerosol initially
deposited on the sample tube was resuspended. However, for greater velocities, resuspension became significant, and at 60 m / s , nearly 90% of the initial
deposit was resuspended. The fractions resuspended
for different flow velocities differed for each of the
test aerosols. The data in Fig. 28 also illustrate that,
for each flow velocity, the amount of aerosol removed
f r o m the deposition tube varied with time; this suggests that the resuspension rate also varied with time.
In addition to evaluating the experimental data, we
are making comparisons of the results with calculations using an aerosol resuspension-rate model developed by Reeks et al. 1 9 - 2 1 This model uses a statistical
treatment to calculate particle resuspension rates due
to turbulent flows. In the model, particles are released
f r o m the surface when they receive enough energy
from the local turbulence to escape over the surface
adhesive potential barrier. 19 This is the only available
model for actually calculating resuspension rates of
deposited particles; previous resuspension models have
been of the "force balance" type that can only be used
to determine if conditions exist for resuspension. It is
hoped that a model of this type can ultimately be
implemented into the TRAP-MELT2 code.
CONCLUSION
The results from the Marviken, LACE, and TRAPMELT validation programs provide important experimental evidence needed to validate and model
aerosol behavior in LWR systems. The data obtained
are applicable not only to primary systems, but also,
in many instances, to secondary systems due to the relatively large range of experimental conditions. The
results are of high quality and show many effects not
previously modeled, including (a) chemical effects of
interacting aerosol species, (b) physical effects of liquid droplets, hygroscopic aerosols, and resuspension,
and (c) geometric effects such as pipe bends and leakage pathways. These programs have provided a sound
experimental basis for understanding these effects on
a large scale.
REFERENCES
1. W. SCHOCK et al., "Large-Scale Experiments on
Aerosol Behavior in Light Water Reactor Containments,"
Nucl. Technol., 81, 139 (1988).
2. "Reactor Safety Study: An Assessment of Accident
Risks in U.S. Commercial Nuclear Power Plants," WASH1400, NUREG 75/014, U.S. Nuclear Regulatory Commission (1975).
3. "The Marviken Large-Scale Aerosol Transport Tests.
Summary Report," MXE-301, Studsvik Energiteknik AB
(Nov. 1985).
Downloaded by [University of Florida] at 21:21 28 October 2017
4. "The Marviken Large-Scale Aerosol Transport Tests.
Test Facility," MXE-101 (Aug. 1985), "Measurement System," MXE-102 (Sep. 1985), "Data Acquisition and Computer Processing," MXE-103 (Aug. 1985), "Data Accuracy,"
MXE-104 (Nov. 1985), "Evaluation Methods," MXE-105
(Sep. 1985), and "Sample Handling and Chemical Analysis," MXE-106 (Nov. 1985), Studsvik Energiteknik AB.
NRC/LTR-86/2, Oak Ridge National Laboratory (June
1986).
13. A. L. WRIGHT and W. L. PATTISON, "Aerosol
Transport Test A108 Preliminary Data Report," ORNL/
NRC/LTR-86/10, Oak Ridge National Laboratory (Aug.
1986).
14. S. OSTRACH, "Laminar Flows with Body Forces,"
Theory of Laminar Flows, F. K. MOORE, Ed., Princeton
University Press, Princeton, New Jersey (1964).
15. A. L. WRIGHT and W. L. PATTISON, "Summary of
TRAP-MELT2 Results for Aerosol Transport Tests A105
and A106," ORNL/NRC/LTR-86/9, Oak Ridge National
Laboratory (Dec. 1986).
5. "The Marviken Large Scale Aerosol Transport Tests.
Test 1, 2a, 2b, 4, and 7 Results," MXE-201, -202a, -202b,
-204, and -207, Studsvik Energiteknik AB (Oct.-Nov. 1985).
16. J. R. BROCK, "On the Theory of Thermal Forces Acting on Aerosol Particles," J. Colloid Sci., 17, 768 (1962).
6. "The Marviken Large Scale Aerosol Transport Tests,
Report Abstracts," MXE-401 (Dec. 1985) and "Conclusions," MXE-402 (Dec. 1985), Studsvik Energiteknik AB.
17. L. TALBOT, R. K. CHENG, R. W. SCHEFER, and
D. R. WILLIS, "Thermophoresis of Particles in a Heated
Boundary Layer," J. Fluid Mech., 101, Part 4, 737 (1980).
7. "LWR Aerosol Containment Experiments, Interim
Summary Report," LACE TR-012 (Jan. 1987).
18. A. L. WRIGHT and W. L. PATTISON, "Series-1
Aerosol Resuspension Test Preliminary Data Report," Letter Report to the U.S. Nuclear Regulatory Commission
(Aug. 1984).
8. G. R. BLOOM et al., "Status of the LWR Aerosol
Containment Experiments (LACE) Program," Proc. Int.
Symp. Source Term Evaluation for Accident Conditions,
Columbus, Ohio, October 28-November 1, 1985, International Atomic Energy Agency.
9. L. MUHLESTEIN et al., "LWR Aerosol Containment
Experiments (LACE) Program," Proc. 14th Water Reactor
Safety Information Mtg., Gaithersburg, Maryland, October
27-31, 1986, U.S. Nuclear Regulatory Commission.
10. A. L. WRIGHT and W. L. PATTISON, "Aerosol
Transport Test A105 Preliminary Data Report," ORNL/
NRC/LTR-85/22, Oak Ridge National Laboratory (Sep.
1985).
11. A. L. WRIGHT and W. L. PATTISON, "Aerosol
Transport Test A106 Preliminary Data Report," ORNL/
NRC/LTR-85/30, Oak Ridge National Laboratory (Dec.
1985).
12. A. L. WRIGHT and W. L. PATTISON, "Aerosol
Transport Test A107 Preliminary Data Report," ORNL/
19. M. W. REEKS, J. REED, and D. HALL, "On the
Long Term Resuspension of Small Particles by a Turbulent
Flow Part I - A Statistical Model," TPRD/B/0638/N85,
ARPWG/P(85)35, Central Electricity Generating Board,
Technology Planning and Research Division (May 1985).
20. M. W. REEKS, J. REED, and D. HALL, "On the
Long Term Resuspension of Small Particles by a Turbulent
Flow Part II —Determination of the Resuspension Rate
Constant for an Elastic Particle on a Surface Under the
Influence of Van der Walls Forces," TPRD/B/0639/N85,
ARPWG/P(85)36, Central Electricity Generating Board,
Technology Planning and Research Division (May 1985).
21. M. W. REEKS, J. REED, and D. HALL, "On the
Long Term Resuspension of Small Particles by a Turbulent
Flow Part II —Resuspension from Rough Surfaces,"
TPRD/B/0640/N85, ARPWG/P(85)37, Central Electricity
Generating Board, Technology Planning and Research
Division (June 1985).
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