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.Ktd Lentral rile AWU/ RES CHRON/ CIRC CPRyder:mir ASTP0 Subject File 08/SO/84 CPRyder Dr. Simon L. Goren 201 F Gilman Department of Chemical Engineering University of California Berkeley, CA 95720
Dear Dr. Goren:
You wanted to know about experimental research projects on source tenn projects; the information should emphasize aerosol science.
Enclosed is a report on each of the subjects that you asked about.
Experimental research on aerosols in an ice bed (condenser) has not been done; I did not report on this subject. However, I included a report about aerosols from the ejection of carium melt simulants.
I compiled the collection of reports as follows. Some of the reports were written by NRC contractors; I edited a couple of these reports, usually by rearranging paragraphs, so that the collection has a single format. Some reports I wrote to summarize many papers.
The delays in sending the reports to you is due to editing.
This is the format that I used:
Purpose (Objective)
Relationship to the Source Term Research Experimental System and Instrumentation Experimental Results t
Comparison with Codes and Theory
, Future Plans In addition to the reports, I have attached a list of the authors and how they can be reached.
I urge you to contact them for additional information as you need it.
I believe that the reports are satisfactory and fulfill your request.
If you find deficiencies, please call me immediately.
Sincerely, Christopher P. Ryder Accident Source Term Program Office Office of Nuclear Regulatory Research (301) 427-4337 l
Enclosures:
As stated l
/
ALVAREZ85-110 PDR
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LIST OF AUTHORS
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Subject Author / Affiliation Telephone Number.
'i
- 1. Aerosol Release and Transport A.L. Wright, ORNL (615)574-6878 (2 reports)
R.E. Adams, ORNL (615)574-0556
- 2. Fission Product Interaction with Aerosols R.D. Spence, ORNL (615)574-6782
- 3. Power Burst R.R. Hobbins, EG&G (208)583-9796,
-9545
- 4. LACE C.P. Ryder, U.S. NRC (301)427-4337
- 5. MARVIKEN C.P. Ryder, U.S. NRC (301) 427-4337
- 6. DEMONA C.P. Ryder, U.S. NRC (301) 427-4337
- 7. Core Concrete Interaction D. Powers, SNL (505)844-4392
- 8. Ice Condenser No experimental data. Analysis is done using classical aerosol mechanics.
l
- 9. Suppression Pool C.P. Ryder, U.S. NRC (301)427-4337
- 10. High Pressure Ejection D. Powers, SNL (505)844-4392
- 11. Code Comparison J. Gieseke, BCL (614)424-4864 i
-e.
STATUS OF REPORTS Experiments Status i
1.
Aerosol Relea'se and Transport Enclosed (2 reports)
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j 2.
Fission Product Interaction with Aerosols Enclosed 3.
Power Burst Facility Enclosed 4.
LACE Enclosed 5.
MARVIKEN Enclosed i
'6.
DEMONA Enclosed 7.
Core Concret,e Interaction Enclosed 8.
Ice Condenser No experimental data. Analysis is done using classical aerosol mechanics.
9.
Suppression Pool Delayed
- 10. High Pressure Ejection Enclosed
- 11. Code Comparison Enclosed 1
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i AEROSOL RELEASE AND TRANSPORT Study of Aerosol Release Within Containment; Nuclear Safety Pilot Plant (NSPP) Experiments R. E. Adams, A. W. Longest, M. L. Tobias Oak Ridge National Laboratories s
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g STUDY OF AEROSOL BEHAVIOR WITHIN CONTAINMENT; NUCLEAR SAFETY PILOT PLANT (NSPP) EXPERIMENTS R. E. Adams, A. E Iongest, M. L. Tobias In the event of a core-melt accident, the quantity of fission pro-ducts (source term) reaching the environment surrounding a nuclear reac-tor plant will, in part, depend upon the aerosol processes taking place j
within the final barrier which limits the release, i.e., the outer con-l-
tainment.
If this containment volume does not leak, or fail, then the i
mass of fission products (aerosols) released will be minimal.
If the barrier is breached, then the mass of fission products (aerosols) re-leased will depend upon the mass concentration of fission products (aerosols) existing in the containment volume at the time of failure 1
and the volumetric leak rate through the breach.
In order that ptoper
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safety assessments can be made, it is necessary that the behavior of various aerosols within containment, and under the atmospheric condi-tions existing in containment, be studied as a function of time and, 1
further, that processes which influence the removal rate of aerosols from the containment volume be identified.
The behavior of aerosols assumed to be characteristic of those gen-i-
erated during light water reactor (LWR) accident sequences and released into containment is being studied in the Nuclear Safety. Pilot Plant (NSPP) which is located at the Oak Ridge National Laboratory (ORNL).
This project, which is part of the ORNL Aerosol Release and Transport (ART) Program, is sponsored by the Division of Accident Evaluation, Nu-clear Regulatory Commission, and the purpose is to provide experimental qualification for LWR aerosol behavior codes under development.
The program plan for the NSPP aerosol project provides for the
- study of the behavior, within containment, of simulated LWR accident aerosols emanating from fuel, reactor core structural materials, and from concrete-molten core materials interactions.
The aerodynamic be-j havior of each of these aerosols was studied individually to establish its characteristics; current experiments involve mixtures of these aero-sols to establish their interaction and collective behav?or within con-tainment. Tests have been conducted with U308 aerosols, fe203 aerosols, and concrete aerosols in an environment of either dry air (relative j
humidity (RH) less than 20%] or steam-air (relative humidity (RH) ap-proximately 100%] with aerosol mass concentration being the primary ex-perimental variable.
-Experiments are underway involving mixtures of thes; aerosols, and, to date, the test aerosol mixtures have been Fe203
+ concrete and Fe203 + U308; in these tests the primary experimental variables have been aerosol mass concentration and aerosol mass ratio.
EXPERIMENTAL FACILITY, INSTRUMENTATION, AND PROCEDURES The NSPP facility, shown schematically in Fig.
1, includes a test containment vessel, aerosol generating equipment, analytical sampling and system parameter measuring equipment, and an in-vessel liquid spray decontamination system.
The NSPP vessel is a stainless steel cylinder
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with dished ends having a diameter of 3 m, a total height of 5.5 m, and 3
a volume of 38.3 m.
The floor area is 7.7 m2 and the internal surface area (including top, bottom, and structural items) is 68.9 m,2 Aerosols are generated with a plasma torch system equipped with a special water-cooled adapter head through which metal powder (or con-
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crete powder) and oxygen gas are added to the argon plasma flame.
The resulting vaporized material combines with oxygen and condenses to form an oxide aerosol as it is propelled into the vessel.
Equipment for the measurement of aerosol parameters includes filter samplers for measuring the aerosol mass concentration and composition, coupon samplers for aerosol fallout and plateout rate measurements, I
total fallout and plateout collectors, cascade impactors and a centri-
,i fuge sampler for determining the aerodynamic particle size distribution of the aerosol, and devices for collecting samples for electron micro-J scopy to obtain qualitative information on the shape and appearance of the aerosol.
Seven filter samplers are used to obtain aerosol mass concentra-tions; four are the in-vessel type and three are the wall sampler type indicated in Fig.
1.
The in-vessel sampler is a self-contained unit with 12 filter tubes, a sequential valve, and a stepping motor; mechani-cal operation of this sampler is remote from the control room.
The other type, the wall aerosol sampler (so-called because the sampler penetrates the vessel wall through a ball valve and flange arrangement),
is inserted and retrieved manually.
The sampling procedure for either type of sampler requires drawing a measured volume of containment vessel atmosphere through a sampling pack that contains four membrane filters in series.
Most of the aerodynamic particle size measurements are made with a cascade impactor (Andersen Mark III Particle Sizing Stack ~ Sampler).
This is an eight-stage impactor, operating at a gas flow of 2.36 x 10-4 3m /s (0.5 cfm), and covers the aerodynamic particle diameter range from 0.54 to.13.6 um.
The system parameters measured include inlet steam conditions of temperature, pressure, velocity (flow rate), moisture content of the vessel atmosphere, steam condensation rates on the vessel wall, heat flux through the wall, temperature of the vessel atmosphere, temperature gradients near the vessel wall, and pressure of the vessel atmosphere.
For the dry aerosol tests the vessel atmosphere is dry air (RH
<20%) and the temperature and pressure are slightly above ambient. The slight elevations in temperature and pressure result from the heat p ro-duced and gases injected by the plasma torch aerosol generator.
The steam-air aerosol tests are conducted under quasi-steady-state steam conditions.
The test atmosphere is prepared by injecting steam into the vessel (initially at subatmospheric pressure) to form a steam-air mixture at elevated temperature and pressure (around 380 K and at an absolute pressure of about 0.2 MPa); upon achieving this condition the rate of steam injection is reduced and the accumulated steam condensate.
removed from the vessel.
The test aerosol is then introduced and steam injection is continued for six hours at a low rate to balance steam los-ses by wall condensation and assure maintenance of the quasi-steady-state conditions. At the end of the six hour period the steam injection
is terminated and the vessel, and its contents, is allowed to cool un-
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disturbed (except for sampling operations) for the remainder of the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> test period.
EXPERIMENTAL RESULTS A number of single-component aerosol tests have been conducted under both dry air and steam-air test environments. Table I lists these tests.
Under dry conditions the three aerosols, U308, Fe2O3, and concrete, exhibit different rates of removal (decrease in aerosol mass concentra-tion) from the vessel atmosphere. Figure 2 compares the behavior of the three aerosols. (Note that the aerosol mass concentration is normalized 7
with respect to maximum concentration and that time is measured from the time of termination of aerosol generation for the pt.rpose of compari-son.)
Scanning electron microphotography (SEM) shows these aerosols to be agglomerated in the form of branched-chains.
The presence of steam in the test environment causes a change in both the aerodynamic behavior and the physical shape of these aero-sols.
The aerodynamic behavior of the aerosols is compared in Fig. 3.
The most obvious effect of steam is an enhanced rate of aerosol removal from the vessel atmosphere in the case of U308 and Fe2O3 aerosols. For example, in Fig. 2 under dry conditions, the time required for 99% of the Fe203 aerosol to disappear from the vessel atmosphere is about 350 min.; under steam-air conditions this time is about 100 min. A similar comparison can be. made for U308 aerosol.
The shape of these two aero-sols is changed from chain-agglomerate to almost spherical by the pres-er.w of steam.
Concrete aerosol does not seem to be affected by the presence of steam in the same manner as U308 or Fe203 aerosol. This lack of influ-ence is illustrated in Fig. 4 where the rates of removal of concrete aerosol under dry and under steam-air conditions are compared. -
This aerosol was generated by passing powdered limestone-aggregate concrete through the plasma torch aerosol generator. The concrete aerosol is not
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a simple, single-component, aerosol such as U308 or Fe203; it is actu-ally a complex mixture of Al203, SiO2, Ca0, Mgo, Fe203, and various sil-icates with A1, Ca, Mg, and Fe as the cations.
Steam also affects the
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physical shape of concrete aerosols (possibly to a slightly lesser de-gree than for U308 or Fe2O3) producing some spherical agglomerates.
Recent activities in the NSPP involve the study of the behavior of
-multi-component (mixed) aerosols in both dry air and steam-air environ-
^
ments.
Details of these tests are contained in Table II.
The first mixed aerosol to be studied in detail is U308 + Fe 2O 3 This mixture simulates those aerosols emanating from molten fuel and molten-core sup-port and structural materials.
Experimental procedures are essentially the same as for the single-component aerosol tests. The principal dif-ference is in aerosol generation; the U 08 and Fe2O3 aerosols are pro-3 duced with separate plasma torch generators and allowed to mix within the vessel.
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Four mixed aerosol experiments involving various mixtures of Fe2O3 and U308 aerosols have been completed; three were conducted in a steam-air envi ronment and one in a dry air (RH <20%) environment.
The be-havior of the mixed aerosol (Fe2O3 + U308) in a steam-air environment has been similar in the three experiments conducted, although the mass ratio of Fe2O3 to U308 has been different in each case.
The aerosol mass fraction airborne (C/Ci$$!s)trated as a function of time after termination of aerosol generation is in Fig. 5 for these experiments.
Although the rate of aerosol removal during the first 30 min is somewhat larger in Exps. 611 and 613 as compared to Exp. 612, the time required for 99% removal of aerosol mass from the volume of the vessel is about 60 min in all three experiments.
SEM photographs of the mixed aerosol showed almost spherical clumps of aerosol in each case.
To illustrate the effect of steam on the behavior of the mixed aerosol, the results from Experiment 631 are compared with those of Nos.
611-613 in Fig. 5.
Under dry air conditions, the mixed aerosol tends to remain airborne longer than under steam-air conditions.
Note that the time required for 99% of this aerosol to be removed from the vessel is about 400 min as compared with 60 min for the aerosol in the steam-air environment.
SEM photographs show the aerosol in Exp. 631 to be in the form of chain-agglomerates (also observed in previous experiments with Fe2O3 or U308 aerosol in dry air) rather than in spherical clumps as in Nos. 611-613.
It appears, based upon limited data, that the influence of one aerosol component on the other, in a mixed aerosol, can be signifi-The behavior of the mixed Fe203-U308 aerosol is more like that of cant.
Fe203 aerosol than U308 aerosol. Data are available which permit a com-parison of the influence of concrete aerosol and U308 aerosol in a mix-ture with Fe2O3 aerosol.
Figure 6 compares the behavior of a Fe2O3 +
concrete aerosol with a Fe2O3 + U308 aerosol in a steam-air environ-Fe203 + concrete aerosol at a mass ratio of 0.45 to 1 (Fe2O3 to ment.
concrete) behaves more like a concrete aerosol: Fe2O3 + U308 aerosol at a mass ratio of 1.4 to 1 (Fe203 to U308) behaves more like a Fe2O3 aero-sol. Future tests on mixed aerosols will permit a more definitive exam-ination of the influence of one component on another in mixed aerosols.
General statements may be made on the behavior of single-component and multi-component aerosols in the NSPP vessel.
The removal processes for U308, Fe2O3, and U308 + Fe2O3 aerosols are enhanced in a steam-air atmosphere.
Steam-air seems to have little effect on removal of con-crete aerosol or Fe2O3 + concrete aerosol from the vessel atmosphere. A steam-air environment causes a change in aerosol shape from chain-agglomerate to basically spherical for U308, Fe203, and U308 + Fe 20 3 aerosol; for concrete and Fe203 + concrete aerosol the change in aerosol shape is from chain-agglomerate to partially spherical. The mass ratio, as well as the identity, of the individual components of a multi-component aerosol seems to have an observable influence on the resultant behavior of these aerosols in steam.
The enhanced rate of removal of the U308, the Fe203, and the mixed U308 + Fe2O3 aerosols from the atmosphere of the NSPP vessel by steam-air is probably caused by the change in aerosol shape and the condensa-tion of steam onto the aerosol surfaces combining to increase the effect of gravitational settling.
The apparent lack of an effect by steam-air i
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1 on the removal rate of concrete aerosol is not yet understood but could result from a differing physical / chemical response of the surfaces of this aerosol to condensing steam.
COMPARISON OF EXPERIMENTAL OBSERVATION TO AEROSOL CODE PREDICTIONS Code predictions of aerosol behavior are being compared with the observed aerosol behavior in the NSPP experiments.
To date, this'com-parison for the behavior of aerosols in a steam-air environment has been limited.
Codes that are now operational on the ORNL computers include HAARM-3 and NAUA-Mod 4; MAEROS (Sandia Labs.) is in the final process of being made operational.
Copies of the latest versions of QUICKM (Battelle-Columbus) and AEROMECH (Univ. of Missouri-Columbia) were a
received this month and are not yet operational.
HAARM-3 has been used for comparison with the results for non-steam aerosol experiments and NAUA for those experiments when the possibility i
exists for condensation of steam onto aerosol surfaces. HAARM-3 assumes
-that the particle size distribution is lognormal.
This enables trans-formation of the basic aerosol equations into a set of simultaneous first-order differential equations which can be solved by standard methods.
The NAUA code treats the equations by dividing the size dis-tribution range into monodisperse size groups.
In addition to the ag-glomeration and deposition processes treated by ' HAARM, the NAUA code i
also permits condensation of moisture onto the solid particles from a i
supersaturated steam-air atmosphere.
The condensation rate is deter-i mined by the Mason equation (developed originally for analysis of meteorological phenomena) which includes the effects of surface tempera-1 ture and particle size.
HAARM-3 can treat only one solid component.
NAUA permits consideration of sources of aerosols of different materials and size distributions, but these are homogenized immediately.
There-l fore, possibility of analysis of multi-component aerosol behavior phe-i, nomena are quite limited.
Use of HAARM-3 in analyzing dry aerosol experiments has shown that it ~ is often dif ficult to obtain good comparisons because the code requires data which may not be readily available or not accurately 4
known.
Examples of such items are the size distribution of the aerosol source, the shape factors which account for the influence of non-spherical particle shape on particle mobility and particle collisions, and the temperature gradient at the vessel wall which would control thermophoretic deposition.
NAUA avoids the shape factor problem for I'
steam-aerosol analysis, since there is experimental evidence that the particles are more or less spherical so that all shape factors can be set to unity.
(NAUA, however, permits the use of shape factors if desired.) On the other hand, the user of NAUA must provide input defin-1 ing the amount of steam available for deposition onto the aerosol sur-face.
The version of the code that we have (Mod 4) does not treat J
thermophoretic or diffusiophoretic deposition, but the code does con-sider diffusional deposition.
Many of these problems do not represent actual deficiencies in the codes but rather indicate the need for addi-tional experimental information; efforts are being made to more i
accurately define the behavior of steam in the NSPP experiments, and J
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studies will begin shortly to evaluate the influence of steam on aerosol shape factors.
The NAUA code (Mod 4 version) has 'been used for comparisons with some of the uranium oxide / steam experiments as well as the some of the iron oxide / steam experiments.
No comparisons have been made. with the concrete aerosol / steam tests. The fit between the code predictions and experimentally observed data is fairly good. in some cases but not in others.
Efforts continue to be made to improve understanding of code application.
FUTURE PLANS A meeting was held in June with developers of some of the LWR aero-sol codes and the needs for experimental data were discussed.
As a result the scope of aerosol studies at ORNL was modified. The NSPP test plan was enlarged to include additional two-and three-component aerosol tests in dry air and steam-air environments over the next three years.
In addition, efforts will be directed toward obtaining more detailed in-formation on (1) influence of humidity on aerosol shape factors, (2) aerosol mass generation rates for the plasma torch aerosol generators, and (3) thermo-hydraulic conditions during NSPP steam-air tests.
Table I.
Details of single-component aerosol tests est Aerosol conc.
Test Nos.
Aerosol 3
tests environment range (pg/cm )
201-7, 209 U308 8
Air (dry) 0.05-9.0 208, 210 Usos 2
Air (moist) 7.1, 12.5 401-4, 406-7 U308 6
Air-steam 5.8-28.0 511 Fe2O3 1
Air (dry) 2.4 501-2 Fe2O3 5
. Air-steam 1.0-8.5 531 Concrete 1
Air (dry) 1.5 521-2 concrete 2
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Details of multi-component aerosol tests Test Mixed Test Max. aerosol Mass ratio No.
aerosol environment cone. (pg/cm )
(Fe2 3O /U 0s) 3 3
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+ Fe203 2.5 611 U308 +
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p Report lb Aerosol Release and Transpert Experiments TRAPMELT Validation Tests A.L. Wright Oak Ridge National Laboratory O
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purpose Recent calculational results published as part of the Battelle-Columbus EMI-2104 source term study indicate that, for some LWR accident sequences, aerosol deposition in the reactor primary coolant system (PCS) can lead to significant reductions in the radionuclide source term. Aerosol transport and deposition in the PCS has been calculated in this study using the TRAP-MELT 2 computer code, which was developed at Battelle-Columbus. The objective of the ORNL TRAP-MELT Validation project is to conduct simulated reactor-vessel upper plenum aerosol deposition and transport tests.
Relationship to the Source Term Research The project consists of two experimental subtasks:
the Aerosol Transport Tests and the Aerosol Resuspension Tests.
In the Aerosol Transport Tests, aerosol transport in a vertical pipe is being studied; this geometry was chosen to simulate aerosol deposition and transport in the reactor vessel upper plenum.
l The Aerosol Resuspension Tests are being performed to provide a data base for developing aerosol resuspension-rate models that can be included in TRAP-MELT 2 and other aerosol transport codes. None of the presently-used aerosol codes i
include resuspension models; however, the potential exists in the PCS and the secondary containment for aerosol resuspension to occur. The results from these tests will be used in the on going effort to validate the aerosol dynamics portion of TRAP-MELT 2.
Exoerimental System and Instrumentation Transoort Tests. The tests are performed in a 2.95 m long, 0.26 m diameter, segmented vertical pipe; the test configuration is illustrated in Figure 1.
Aerosols are generated by feeding metal powder to a plasma torch aerosol genera-tor. Tests are performed by generating aerosols in the pipe for a period of roughly 10 minutes. The generated aerosols can agglomerate, settle on the horizontal floor at the bottom of the pipe, deposit on the pipe sidewalls, or be transported out of the pipe into an aerosol collection bag. During the aerosol generation period measurements are made of pipe-wall and gas tempera -
tures, airborne aerosol mass concentrations (by filter sampling), and aerodynamic i
size distributions (by cascade-impactor sampling) in the pipe. At the end of an experiment the slide valve at the bottom of the pipe is closed; based on the mass collected on the slide-valve plate, the amount of aerosol airborne at 1
the end of the aerosol generation period can be estimated. One to two days after the test is completed, the test section is dismantled, and the amounts of aerosol deposited on the three pipe sections, settled on the floor, and transported out of the pipe are determined.
Aerosol transport in the reactor-vessel upper plenum can be influenced by a number of factors; among these are the upper plenum gas flow rates (residence times) and flow fields, aerosol release rates and aerosol materials, magnitudes of wall temperature gradients, and moisture conditions in the plenum. Table 1 illustrates the test matrix for the present Aerosol Transport Test series.
1
The main variables in the present series are the flew residence time and the aerosol material used. The range of residence times spans a factor of six and is reasonably representative of those expected in the upper plenum in core-melt accidents. The choice of aerosol materials was made not to directly simulate core-melt aerosols but to determine if metal and oxide aerosols (both metals and oxide aerosols are expected to be produced in core-melt accidents) behave differently.
Resuspension Test. The test series recently completed was performed in the test section illustrated in Figure 2.
The main portion of the test section consisted of a 1.83-m long, 0.076-m diameter pyrex pipe and a 1.83-m long, O.051-m wide deposition surface that could be inserted into the pipe (with the deposition surface in the pipe, the effective pipe hydraulic diameter was i
0.072 m).
In an experiment, aerosols or powders were artificially deposited by pouring them through a 100-mesh screen and allowing them to settle onto the i
deposition surface (the deposition surface was 302 stainless steel). Materials were deposited on a 0.41-m length of the deposition surface such that the gas flow entrance length to the deposit region was 1.22 m.
Air flows through the test section of up to.094 m"*3/s (200 SCFM) could be achieved; this meant that maximum plug-flow velocities of greater than 20 m/s or flow Reynold's numbers of greater than 100,000 could be achieved.
)
A typical experiment was performed by first measuring the amount of material deposited on the deposition surface and then inserting the surface into the pyrex pipe. A steady air flow would be produced, measured, and maintained for a time of less than 300 seconds. After the flow was turned off, the deposition surface was removed from the test section and the amount of material remaining on the surface was removed and measured.
Parameters that can influence the hydrodynamic resuspension of aerosols from surfaces include aerosol material and particle size, the concentration of the aerosol deposits on the surface, system moisture condition, aerosol deposition mechanism, and the aerosol deposition-surface roughness.
Table 3 summarizes the test conditions for the test results presented here.
In this study, forty-nine experiments were performed for the nine sets of conditions illustrated in Table 3.
Parameters varied were the deposited material, particle size and density, and the mass deposited.
In evaluating the resuspension literature, we found that few experiments have been done using materials with particle sizes representative of aerosols produced in reactor accidents (0<10 microns).
In addition, we found that few experiments had been performed at the deposit concentrations that might exist in reactor accidents. Hand calculations indicated that the deposit concentrations in the upper plenum and the secondary containment could range from 0.01 to 0.1 g/cm""2; this range was covered in the experiments.
Results Transoort tests. A summary of the aerosol deoosition results from tests A101 through A104 is presented in Table 2; details for eacn test can be found in pre-liminary data record reports [1-4]. The following comments can be made related to the results presented in Table 2:
1.
In each test, aerosol plateout was largest in the lower pipe section (nearest 4
to the aerosol generator) and least in the upper section. This was expected 2
since wall temperature gradients and aerosol concentrations were largest in i
the lower section.
2.
Although results from tests A101 and A102 are presented, it is not appro-4 priate to model these two tests with TRAP-MELT 2.
In test A101, there was an uncertainty as to whether the airborne material was pure aerosol or simply small~ powder dispersed by the plasma torch.
In test A101 and A102, a significant fraction of the heat lost to.the pipe walls was due to radia-tion heat loss from the aerosol generator plasma; because of this, we could not reliably estimate thermal gradients in the first two tests. The test configuration was modified for tests A103 and A104 to eliminate radiation heat loss to the pipe walls.
4 3.
Tests A103 and A104 were performed with the same aerosol material but had different residence times; the A103 residence time was roughly half that for A104. The results that the fractional aerosol transport out of the pipe in A103 was greater than in A104, and that the total aerosol settling in A104 was greater than in A103, were consistent with test A103 having a shorter residence time.
j Resusoension tests. Preliminary results for the tests summarized in Table 3 are presented in Figures 3 and 4.
Data for measured resuspension rates as a f
function of the average test flow velocity are presented, where the resuspension rate was determined from:
I Resuspension Rate = A = (M /M )/( At) 7 g M = mass resuspended; p
Mg = initial mass deposited; and At = total flow time.
The data in Figure 3 are for tets where the deposited mass was in the 1-2 gram
- a range, while the data in Figure 4 are for tests where the deposited mass was in the 10-20 gram range. The following comments can be made related to these results:
1.
The measured resuspension rates and the mechar: ism for resuspension of the i
deposited materials varied as the mass loading on the surface was increased.
For the low-loading tests summarized in Figure 3, individual particles seemed to be stripped from the surface in a continuous manner. For the high-loading
'l test results shown in Figure 4 (except for test group W-3), however, resuspen-sion was characterized by " layer-stripping" or bursts of particle removal from the surface. We believe that in the low-loading tests, particle-surface forces were the major ones resisting resuspension, while in the high-loading tests, particle particle forces were dominant.
i*
2.
Test groups W-2 and W-3 were performed with the same mass loading but with different size tungsten powders. Figure 4 illustrates that powder size had a large influence on the measured tungsten powder resuspension rates.
In addition, the larger tungsten powder did not resuspend by " layer-stripping" but by the mechanism exhibited in the low-loading tests.
3
_ - _ _, - _. _. _ ~ _
3.
Results in both figures indicate a possible influence of particle density on resuspension rate, but the data for tin-oxide aerosols (Sn0 ) and for 2
manganese powder did not follow this trend.
4.
The results for the 10-micron manganese and tungsten powders were quite different and illustrate that resuspension rates can be influenced by the material deposited.
Comoarison with Theory and Codes Transoort tests. We are now in the process of performing and analyzing results from TRAP-MELT 2 calculations for tests A103 and A104.
Resuspension tests. This series of experiments was completed two months ago, and test analysis is just starting. At present we feel that there are no theories
~
available that the results-could be compared against.
Future plans Transport tests. The present test series will be completed in January 1985.
Future plans presently include a series of two-component aerosol transport tests; these will begin in mid-1985.
Resusoension tests. Future plans in this area include a second series of experiments in wnich reuspension rates of true aerosol deposits (deposited by thermophoresis, for example) will be measured.
References:
1.
A. L. Wright and W. L. Pattison, " Aerosol Transport Test A101 ' Quick-Look' Data Report," letter report to the U.S. NRC (September 1983).
2.
A. L. Wright and W. L. Pattison, " Aerosol Transport Test A102 Preliminary Data Report," letter report to the U.S. NRC (February 1984).
3.
A. L. Wright and W. L. Pattison, " Aerosol Transport Test A103 Preliminary Data Report," letter report to the U.S. NRC (May 1984).
4.
A. L. Wright and W. L. Pattison, " Aerosol Transport Test A104 Preliminary l
Data Report," letter report to the U.S. NRC (July 1984).
i e
4
Table 1.
Aerosol Transport Test Matrix Test Flow Residence Aerosol Number Time (sec)*
Material A101 80 Zine metal A102 50 Iron oxide A103 25 Iron oxide A104 50 Iron oxide A105 80 Zine metal A106 40 Zine metal A107 13 Iron oxide A108 20 Zine metal
- At estimated average gas temperature.
Table 2.
Summary of Aerosol Deposition Results for Tests A101-A104 Parameter A101 A102 A103 A104 1.
Aerosol Material Zinc Iron-oxide Iron-Oxide Iron-Oxide 2.
Aerosol Generation 11 12.5 9*
11 Time (min) 3.
Total Aerosol 126.9 253.96 92.57 189.14 Produced (g) 4.
Aerosol Plateout, 43.0 59.0 23.8 26.7 Lower Section (%)
5.
Aerosol Plateout, 2.8 9.8 13.5 13.1 Center Section (%)
6.
Aerosol Plateout, 1.7 4.2 8.8 11.8 Upper -Section (%)
7.
Aerosol Settling (2) 11.4 19.1 1.6 29.3 8.
Aerosol Transported 41.1 8.0 52.3 19.1 Out of Pipe (%)
- Total test time was 10 minutes:
9 minutes with aerosol generation and 1 minute without.
Table 3.
Summary of Aerosol Resuspension Test Conditions Average Test Material Particle Particle Mass Designation Type Diameter Density De posited (microns)
(g/cm**3)
(g)
W-1 Tungsten 0.5 19.4 2.4 Powder W-2 Tungsten 0.5 19.4 20.3 Powder W-3 hngsten 10 19.4 20.1 Powder Ni-1 Nickel 2.5 8.9
- 7. 2 19.9 Powder i
Fe O -1 Ir on-oxida
<0.2 5.2 1.6 23 Aerosol Fe 0 -2 Iron-oxide
<0.2 5.2
- 9. 6 23 Aerosol Sn0 -1 Tin-oxide
<0.2 7.0 1.1 2
.hrosol I
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Aerosol Transport Test Section Schematic L
(9.4 x10-2 3
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AIR INLET N
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AEROSOL j
g OUTLET TO HEPA FILTER 7.6 -Cm-01AMETER AEROSOLS DEPOSITED ON PYREX PIPE 40.6-cm LENGTH OF 5.1-cm W10E,183-cm LONG COLLEC-e TION FOIL Figure 2.
Aerosol Resuspension Test Section Schematic
CRNL OWG S4-73o 0
10 s
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w_j A Ni-t Fe2O3 -1 a
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8 to 12 14 16 18 AVERAGE TEST SECTICN AIR FLOW VELCCITY (m/s)
Figure 3.
Asrosol Resuspension Test Data, Test Groups W-1, Ni-1, Fe2 3-1, and Sn0 -1.
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ORNL CWG 84-791 0
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Figure 4.
Aerosol Resuspension Test Data, Test Groups W-2, W-3, Ni-2, Fe2O -2, and Mn-1.
3 4
t
s Report 2 I
Fission Product Interaction with Aerosols R. D. Spence and F. F. Oyer Oak Ridp National Laboratory a
e e
FISSION PRODUCT INTERACTION WITH AEROSOLS (FIN NO. B0815)
R. D. Spence and F. F. Dyer 1.
OBJECTIVES 1.
Measure ' the sorptive capacity of LWR aerosol materials for fission product vapors.
2.
Determine the rate of sorption, if possible, i.e., the rate as applied to reactor vessel accident conditions.
3.
Measure the sorption of fission product vapors on the aerosols and walls in a concurrent flow reactor.
2.
RELATIONSHIP TO SOURCE TERM RESEARCH Current LWR accident consequence evaluations indicate that a principal mode of fission product movement in both the primary reactor vessel and in the contain-ment system (in the gas phase) occurs by aerosol transport. Consequently, the rate of sorption of fission products onto aerosols and the sorption capacity of aerosol particles for fission products are key factors in accident consequence assessment.
A number of sorptive mechanisms are possible (e.g., condensation, chemisorp-tion) depending on the temperature regime, chemical environment, and chemical makeup of the aerosol and the fission product species. These lead to a range of possible deposition rates and also a range of sorptive capacities of aerosol par-ticles for fission products. Review of published work in this area has revealed a very small data base.
This work provides required information for NRC programs relating to LWR accident source term evaluation. For example, input data are provided to the TRAP-MELT code and should be useful in understanding the results of the PBF Severe Fuel Damage experiments and the Marviken experiments. Programs which relate to PRA methods and application require this type of data to allow soundly-based acci-dent consequence determinations. The Severe Accident Sequences Analysis Program (SASA) will be aided by providing data to improve accident consequence evaluations.
3.
DESCRIPTION OF EXPERIMENTAL SYSTEM Two experimental approaches are being used in this project -- static tests and dynamic tests. In the static tests, samples of aerosols will be collected or deposited on substrates and the adsorption / desorption isotherms of these samples will be measured.
In the dynamic tests, an aerosol and fission product vapor will flow concurrently down a tube held at constant temperature. The aerosol will be analyzed to determine how much vapor interacted while passing through the tube and the tube will be analyzed to determine how much vapor and aerosol deposited on it.
Both experimental approaches depend on radioisotope tagging and gamma spectrometry to monitor the interactions with only the fission product vapor tagged in the static tests and both aerosol and vapor tagged in the dynamic tests.
The scope of this experimental work has been limited to vapor-solid inter-actions, which does mean some potentially important interactions will not be
2 investigated (e.g., Cs0H-B 0 ).
Based on this limitation and a simple thermo-23 dynamic estimate of the aerosols produced in an LWR core heatup accident,2 seven aerosols - silver, chromium oxide, manganese oxide, iron, iron oxide, tin oxide, and nickel - and three vapors - cesium hydroxide, cesium iodide, and tellurium --
have been selected for investigation. Since this many interactions cannot be studied in this program in detail, screening tests are performed in the static test apparatus for each vapor species to identify the more important interactions for static tests and dynamic tests.
3.1 STATIC TESTS Figure 1 illustrates the static test apparatus. The Cs0H or CsI is added to the vapor generator as a solution. After precipitating the Cs0H or CsI, the CaOH or Cs1 is dehydrated by heating above 400*C for a few hours. In general, samples are placed in the adsorption chamber on two types of holders:
(1) loose powder dumped into a chamber (e.g., Pt boat) and (2) thin layer deposited on the inside of a PC cylinde r.
The sample is weighed, placed in the apparatus, pretreated for several hours at temperature, and finally exposed to Cs0H vapors.
The Cs0H or CsI is tagged with 137CsC1 prior to placement in the vapor genera-tor. Equilibrium adsorption and desorption on the sample at a given vapor pressure is determined by in situ monitering via a NaI gamma detector. The Cs0H vapor is trapped by reaction with quartz and the Cal is trapped by condensation at a low temperature. The vapor concentration is determined by the rate of increase of the trap activity and the carrier gas flowrate. After an experiment is over, the activity of the sample, the trap, and the platinum sleeve (used to insert and retrieve the samples) are measured with a Ge/Li detector and multichannel analyzer system (TP 5000).
Changing the fission product vapor pressure of the carrier gas can approact a step change by changing the temperature of the vapor generator. This is possible because an infrared lamp furnace is used which gives essentially a step change in temperature on the outside wall of the vapor generator. Thus, once equilibrium at one vapor pressure has been established, the vapor pressure can be step changed and the kinetics of approach to the next equilibrium observed. The utility of these kinetics to actual reactor accident conditions remains to be determined.
Three carrier gases will be utilized in the static test apparatus: (1) He, (2) He-H, and (3) He-H -H O (H /H O = 0.1 to 10).
2 2 2 2 2 3.2 DYNAMIC TESTS Figure 2 illustrates the dynamic test apparatus concept. The aerosol is con-tinuously produced from a commercial plasma gun using a helium plasma and matallic a
powder. Oxidic aerosols are produced by burning the metallic powder in an excess of oxygen. Metallic aerosols are produced by vaporizing the powder with the plasma under reducing conditions followed by nucleation and condensation.
The plasma flame and aerosol are injected into an empty tack which serves to damp minor fluctuations in the aerosol generation rate. Most (>90%) of the aero-sol generated will be deposited inside the tank or filtered out of the vent flow.
A controlled flowrate of gas, including aerosols, will be pulled continuously from the tank and down the reactor tube. The bulk aerosol concentration (aass/ volume)
~
i 3
of the gas flowing to the reactor tube will be measured. In addition, charac-terization tests will identify the typical particle size distribution produced for each aerosol material and how this distribution is affected on passing through the reactor tube.
Fission product vapor will be produced as in the static tests and introduced into the reactor tube via a carrier gas. Thus, the aerosol and fission product vapor will flow concurrently down the reactor tube. The proposed concept is to discard the initial material flowing through the reactor tube and then redirect -
l the flow through a filter where the aerosol will be separated from the gas stream.
Once enough aerosol has been collected on the filter, the flow will be shif ted back to its original route and the sample leg purged of fission product vapor.
Irt situ monitoring will detect desorption during this purge phase.
Both the aerosol and vapor will be tagged with a radioisotope. Thus, gamma
?
spectroscopy will identify the amount of aerosol collected on the filter, the amount of vapor deposited on the aerosols, and the amount of vapor in the vapor trap. Also, the amount of aerosol and vapor deposited on the reactor walls will be measured.
(A test without an aerosol will determine the affinity of the walls for the vapor.)
4.
EXPERIMENTAL RESULTS TO DATE q
4.1 SCREENING TEST t
4.1.1 Cesium Hydroxide The Cs0H vapor reacted extensively with both an Fe2 3 and a Fe sample at O
700*C for 2 x 10-3 bar CaOH. The three Ag samples demonstrated a range of inter-actions (0.4, 20, and 96 mg Cs0H/g Ag), but wat still more than an order of magni-tude less than the Fe and Fe2 3 interactions' (~2000 mg Cs0H/g). The remaining O
materials -- Cr2 3, Mn2 3, Sn0, and Ni -- showed much lower interactions (<10 mg 0
0 2
Cs0H/g). The interactions were also compared on a BET surface area basis, which does change the relative rankings of the wedcar interactions.
The amount of interaction observed for the Fe species is not inconsistent with the formation of a Cs-Fe-O species - CsFe02 or Cs2 e02 -- proposed by Lindemer F
et al.2 Thermodynamic calculations demonstrated that these species could not only form in our experiments, but also in the reactor vessel during an accident.
Silver appears to be activated by passing through the plasma torch since the Ag powder interacted only 0.4 mg Cs0H/g Ag (2 mg Cs0H/m2) while the two samples of aerosol collected interacted 20 and 96 mg/g (51 and 240 mg/m ).
Although reforma-2 tion of the surface could account for this activation, so could contamination of the surface (e.g., tungsten from the plasma electrode; or, Ag20 on the' surface, x-ray diffraction demonstrated the bulk sample was Ag).
l To rank the materials, the observed interactions were weighted according to
.the expected prevalence of each material in the aerosol cloud of the reactor J
i vessel during an accident. Considering an aerosol cloud made up of only these seven materials, Fe or Fe2 3 makes up a little over 1% (wt.) of the aerosols, but O
could account for 60% or more of the Cs activity found on the aerosols. Even based on the weakest Ag interaction, Ag can account for twice the Cs activity in the aerosol cloud of any other component (except Fe'and Fe2 3) because Ag makes up O
92% of this cloud (other estimates claim run-off and alloying of' the molten silver
4 control rods lower the Ag content of the aerosol cloud). Based on the interme-diate value (20 mg Cs0H/g Ag), 39% of the Cs activity would be associated with Ag.
The remaining Cs contributions are Cr2 3 (0.5%), Mn2 3 (0.2%), Sn02 (0.02%), and 0
0 Ni (0.006%).
4.1.2 Cesium Iodide The CsI vapor reacted extensively with Cr2 3 at 800*C for 6 x 10-4 bar CsI to 0
form Cs2 r0. In addition, about half of the Ag disappeared during the test, C 4 leading us to believe that volatile AgI was formed. The remaining materials --
Mn3 g,
0 Mn2 3, Fe, Fe2 3, Sn0, and Ni - interacted weakly (<5 mg CsI/g).
0 O
2 All of the screening tests were performed using a carrier gas of helium pretreated in a titanium. sponge bed at 510*C which gives an equilibrium oxygen potential of -831 kJ/mol. However, to form Cs2 rou in our test required an oxygen
~
C potential of -82 kJ/mol aroichiometrically and -43 kJ/mol thermodynamically. (The
~
oxygen potential in the reactor vessel during an accident is estimated to be -250 to -450 kJ/mol.) Thus, we must have had oxygen contamination for this screening The CsI-Cr2 3 reaction to form Cs2 rog has been observed previously, but test.
0 C
only under oxidizing conditions.3 Thermodynamics also indicates that a CsI-Ag reaction to form AgI vapor did not take place in our test. A more likely explanation is that the I2 released from the CsI-Cr2 3 reaction reacted with the Ag to form AgI vapor (even though the 0
Ag was located upstream of the Cr2 3 and 70% of the I2 released would be required 0
to react with the Ag.)
Weighting the observed interactions as before, Cr2 3 dominates (~>80%) the 0
pickup of Cs activity with only 2% of the aerosol mass. The Ag interaction is confused by the apparent strong interaction with I2 released from the CsI-Cr2 3 0
reaction, but the large mass fraction of Ag in the aerosol result. in as much as 20% of the aerosol activity. The remaining activity contributions are negligible
(<0.05%) compared to these two.
However, the oxygen potential during a reactor accident will preclude the strong interactions observed in this screening test and the relative importance of the weak interactions should increase significantly.
4.2 STATIC TESTS The kinetics of the static test apparatus was characterized by using a quartz cylinder in place of a sample (baseline tests). The quartz essentially reacts instantaneously on contact with the Cs0H vapor. Thus, by monitoring the pickup of activity of the quartz cylinder after a step change in the vapor generator, we can measure how long before any change is noticeable and how quickly a steady-state mass transfer is established to the cylinder. This not only measures the time response of the vapor generator and transport line, but also the time response of the gas phase diffusion resistance.
The response showed a time delay followed by an oscillatory (quickly damped) approach to a linear increase in activity. All of the Cs0R in the carrier gas reacted in the first 10 to 25% of the quartz cylinder. This means that gas phase diffusion resistance was not a significant barrier to transport to the cylinder surface, but our monitoring system cannot accurately measure the gas phase dif-fusivity (i.e., the limit to the mass transfer rate for our test was the limit in transport from the vapor generator). If the mass transfer rate is not so limited in transport to a thin sample layer deposited inside a cylinder, then a measurable
5 mass trans(er resistance exists in the sample layer (e.g., pore diffusion, adsorp-tion, solid diffusion).
. The sorption / desorption isotherm for Cr2 3 has been measured at 700*C for 0
10-3 to 10-3 bar Cs0H with a He-0.5% H2 carrier gas. The sorption rate was measurably slower than the mass transfer rate demonstrated in the baseline test, but a large bed of Cr2 3 was needed rather than a thin deposit and the mass trans-0 fer resistances are different for such a bed as opposed to the thin deposit.
Another static test using the He carrier gas resulted in complete reaction of the Cr2 3 to form Ca2 rog, unlike the weak interaction observed in the screening 0
C tests. Thermodynamics demonstrate that this reaction is quite sensitive to te=-
perature and oxygen potential.
4.3 DYNAMIC TESTS This test concept is still under development. The aerosol generator is operational and has made both oxidic and metallic aerosols. Several concepts described in Sect. 3.2 remain to be proven oat.
5.
COMPARISON OF EXPERIMENTS TO THEORY Our theoretical concepts have not been completely worked out and we have little experimental data for comparative purposes as yet.
The theoretical approach is best described in Levenspiel's section on heterogeneous. reactions.4 The aerosols are viewed as nonporous primary spheres agglomerated into a loose spheroidal structure. In general, the vapor species must diffuse through a gas boundary layer, through the loose agglomerate structure (for interior particles),
adsorb onto the primary particle, diffuse through a layer of reacted material, and finally react with the unreacted material. Starting with this general overall
.model, different approaches can be taken and various controlling steps proposed to make simpler models. The most common practice is to view the mass transfer pro-cess as a series of first order processes so that the law of additive resistances will apply. Experiments measure overall rates and hence overall resistances. By changing experimental conditions, one resistance can be eliminated or singled out in one particular measurement.
6.
FUTURE PLANS 6.1 CESIUM HYDROXIDE The sorption / desorption isotherms and kinetics for Cr2 3 and Ag will be 0
measured at different temperatures. In addition, the strong interactions of Fe2 3, Fe, and Cr2 3 will be investigated as a function of 02 potential and 0
0 temperature.
6.2 CESIUM IODIDE
[
The sorption / desorption isotherms and kinetics for Mn2 3 and Fe will be 0
measured at different temperatures.
In addition, the strong interactions of Cr2 3 and Ag will be investigated as a function of 02 potential and temperature.
0 6
o 6.3 TELLURIUM-Once the tests have been completed for Cs0H and CsI, the apparatus can be
~
modified to study Te vapor interactions. First, screening tests will identify the more important interactions. Then, sorption isotherms and strong interactions can
'be studied at different temperatures. The sorption and reaction rates will also be measured.
6.4 DYNAMIC TESTS The dynamic test concept will be proven out using Cs0H vapor. Once the limi-tations of the system have been determined, dynamic tests will be done for an oxidic and a metallic aerosol at different temperatures and mixing times for Cs0H, CsI, and Te vcpors.
7.
REFERENCES 1.
R. P. Wichner and R. D. Spence,. Quantity and Nature of LWR Aerosols Produced in the Pressure Vessel During Core Heatup Accidents -- A Chemical Equilibrium Estimate, NUREG/CR-3181 (ORNL/TM-8683), March 1984 2.
T. B. Lindemer, T. M. Besmann, and C. E. Johnson, " Thermodynamic Review and Calculations -- Alkali-Metal Oxide Systems with Nuclear Fuels, Fission Products, end Structural Materials," J. Nucl. Mater. 100, 178-226 (1981).
3.
S. Aronson, M Friedlander, I. N. Tang, and H. R. Munkelwitz, "The Interaction of CsI with High-Chronium Alloys in the Presence of Oxygen," J. Inorg. Nucl.
Chem. 4],, 1209-11 (1979).
4 O. Levenspiel, Chemical Reaction Engineering, John Wiley & Sons, 1962, pp. 338-357 and pp. 426-465.
-n.
Fig. 1 a
ORNL DWG 83-886 ADD CsOH SOLUTION p
He + H2+HO 2
m 6
700 - 1000 *C 300 - 700 *C He 700 - tOOO *C r-SAMPLE
~II)UARTZ WOOLl
+
=
- - r - ~ ~ ~ ~~ ~ ~ ~ ~ ~ ~ ~ 1 I 7g/
l gf l
7..
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Report 3
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PBF Aerosol Research in the PBF (Power Burst Facility)
Severe Fuel Damage Program R. R. Hobbins EG&G, Idaho Editor: Christopher Ryder, U.S. NRC
purpose Aerosol benavior during a severe reactor accident is being investigated in part within the Severe Fuel Damage (SFD) Program at the Power Burst Facility (PBF).
Four SFD in pile tests are included in the program. Test 3 and Test 4 are designed to collect aerosol deposition data. Test 4 is specifically instru-mented to measure on-line aerosol releases.
Relationshio to the Source Term Research The information from the PBF SFD program will supplement the NRC data base on fission product behavior during reactor accidents.
It will serve as an impor-tant benchmark for assessino both fission product release calculations and source term estimates.
Exoerimental System and Instrumentation The first two tests, the SFD Scoping Test (SFD-ST) and the Test SFD 1-1, were done using a 32-rod bundle of previously unirradiated fuel rods. The third test was conducted with a bundle of 26 highly irradiated (~40 GWd/TV) fuel rods, two instrumented fresh rods and four empty control rod guide tubes. The last test (SFD 1-4) 1s designed to use a bundle of 26 highly irradiated fuel rods, two instrumented fresh rods and four Ag/In/Cd control rods in guide tubes.
The design of the test trains (in pile fuel bundle assemblies) is different for the last two tests. A scaled plenum region is included in Test SFD 1-3 and in Test 1-4 just above the fuel bundle region, and a deposition rod is located along the axis of this plenum to collect aerosol and fission product deposits during a high temperature transient. The deposition rod includes twenty removable coupons that will be kept dry and subjected to detailed surface examination and fission product analyses after each test.
The temperature of the plenum region is controlled to provide a surface temperature gradient from 1500 K at the inlet to 700'K at the outlet. The deposition rod is kept dry after the transient by a nitrogen pressurization system and the rod is removed from the test train shortly after each test.
After removal of the deposition rod, the test bundle is flushed with water.
A fission' product sampling and monitoring system is used to characterize the effluent downstream of the plenum. The effluent lines are subjected to gamma scanning after a test and again after flushing.
{
Experimental Results The principal conclusions reached thus far in the pBF program are summarized below:
1.
Fission product release during severe reactor accidents in strangly dependent on fuel morphology, not just the fuel temperature.
[
1 l
l
2.
Fission product transport away from the fuel region is strongly dependent on thermochemical conditions in the effluent stream. Steam-hydrogen ratios and effluent flow rate play important roles in fission product chemistry and transport.
High steam flow (as occurred in the SFD-ST) promotes atomic iodine and HI formation; coupled to the short transport time, transport efficiency of iodine out of the core (bundle) region is increased.
A low effluent flowrate and a high hydrogen concentration (as occurred in the SFD 1-1 and 1-3 tests) increase Csl formation and plateout because the effluent is exposed for a long time to cold walls during trans-Tellurium is held up by metallic zircaloy (SFD 1-1) and released by port.
zircaloy oxidation (SFD-ST).
Most fission products are reversibly deposited and easily washed off surfaces by flowing liquid water. The dependence of fission product transport on aerosol behavior is not well understood and additional experimental data (e.g. SFD 1-4 results) are needed to improve source term calculations.
3.
Fission product source terms for different reactor accidents can vary greatly, depending on the fuel morphology and thermochemical conditions.
The rate of core heatup, the zircaloy oxidation, the aerosol generation, the effluent chemistry, and the effluent flow rate can vary greatly, depending on accident scenario.
Each of these parameters affects fission product release or transport.
Comoarison with Theory and Codes Fresh fuel, as it was used in the first two PBF tests, released fission product vapors at much slower rates than predicted by current models (e.g., CORSOR) until the fuel structure changed by high temperatures (>2000*K), by dissolution in molten zircaloy (T > 2170*K), or by fuel fracturing (e.g., by rapid quench).
Highly irradiated fuel, used in the third and fourth pBF tests and the tests that contributed data to the CORSOR model, had a significantly different fuel structure; this resulted in high fission product release rates up to a tempera-ture of approximately 2000*K.
The data analysis and reporting schedule for the program is comprehensive and will include comparison of test results with code calculations such as SCDAP, TRAP-MELT, CORSOR. New models for aerosol generation and fission product l
chemical behavior will also be compared.
i Future Plans During the SFD 1-4 test, additional instrumentation will be used on the sampling and the monitoring system.
the affluent closer to the plenum exit.A fourth gamma spectrometer will be added to monitor Six additional gas samples with particle i
filters will be added and an on-line aerosol monitor will be included. This combination of instruments is intended to (1) characterize the aerosol behavior during the SFD 1-4 test, (2) provide data on the interrelationship of fission.
product and aerosol release, and (3) show the dependence of the release on fuel behavior.
The principal aerosol data will be provided by Test SFD 1-4.
2
Fission Product & Aerosol Measurements
- i Instrument Data 1.
On-line Gamma Spectrometers:
Isotopic release rates versus time.
3 on SFD-ST, 1-1, and 1-3 Corrolation to fuel and aerosol 4 on SFD 1-4.
behavior.
2.
On-line Aerosol Monitor.
Aerosol particle number concentraticn (SFD 1-4 only) versus time. Qualitative size distri-bution history. Corro1ation to fission product and fuel behavior.
3.
Aerosol Filter Samples Electron micrographs of aerosol samples.
(SFD 1-4 only)
-Primary particle size, shape and elemental i
composition. Association of selected fission product species with aerosol materials. Aerosol mass concentration at six discrete points in time and correla-tion to fuel and fission product behavior.
4.
Deposition Coupons Fission product, aerosol and vapor
~
SFD 1-3 and 1-4 only deposition along vertical thermal gradient. Micrographs of deposition.
Primary particle size distribution, shape and composition. Fission product chemical fo rms. Aerosol particle chemical forms.
5.
Steam Grab Samples:
Fission product release rates at six (6 on SFD ST, 1-1 and 1-3.
times (long lived and trace isotopes).
12 on SFD 1-4)
Hydrogen release rate at six (or 12) discrete times. Corrolation to fuel and aerosol behavior.
6.
Liquid Grab. Samples Fission product release rates without 6 samples noble gases at six disdrete times (long lived and trace isotopes).
7.
Liquid Line Filter Sample Solid material mass released during test.
Fission product and elemental make up of filtered mass. Fissile content of mass.
Particle size distribution of filtered mass.
-i 8.
Collection Tank Monitoring Total isotopic release fractions before and Grab Samples and after bundle and sample line flushing.
Total hydrogen release.
Iodide partitioning before and after flushing.
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SEWEDS refers to microscopy with energy dispersive x-ray spectroscopy to identify key elemental make up of particles.
- c. MEE/FLl10R. refers to micro-raman spectroscopy and fluorescence spectroscopy to identify chemical species, d.
Meta 11ography is coeducted on selected filter derts specimens to investigate metallic forms (e.g. oxidized zircaloy).
- c. Ph analysis is done on selected samples of condensed steau containing fission products.
f.
60EES refers to Gas Chramstography Microwave Emissfon Spectroscopy for identification of hydrides, hydrogen todide and certain other' chemical forms in pas samples.'
g.
Electrochen gamma is a technigee for measuring tonic species in salution.
...i
1 PBF SEVERE FUEL DAMAGE TEST PROGRAN Sup0MRY Heating Rate (K/g Inlet Bundle Test fuel Test Date Initial Final Cooling Rate (K/s)
Flow (q/s)
Configuration Burnup (MWD /iU)
Quench-SFD-ST 10-29-82 0.13 10
-200 20.0 32 Fresh Rods 100 SFD-1-1 9-8-83 0.45 30
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-2.45 0.7 44 Guide Tubes 40,000 i
Scheduled 26 HBU+2 Fresh SFD-I-4 2-15-85 4.5 30
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Report 4 t
LWR AEROSOL CONTAINMENT EXPERIMENTS (LACE) f F. J. Rahn Electric Power Research Institute This paper is a summary of the original report (HEDL-SA 3099)
Editor: Christopher P. Ryder, U.S. NRC i
e 4
4
Objective The overall objective of the LACE experiments is to characterize the aerosol re-tention processes in the pipes and the large volumes of a nuclear power plant.
These experiments will be used to collect data where the current knowledge of aerosol deposition and resuspension is deficient. The data will be used to validate the computer codes that extimate the aerosol behavior and thermal hydraulic conditions during a severe accident.
The LACE experiments consist of two sections, a support program and a base program. The three objectives of the support program are as follows:
(1) Develop and implement techniques to generate aerosols, calculate thermal hydraulic ocnditions, understand chemistry, and build instruments.
(2) Study, in small scale experiments, the individual aerosol phenomena such as altered behavior due to burning hydrogen, flow through cracked concrete, and resuspended aerosols.
(3) Make estimates both before testing to design experiments and after testing to analyze data.
The objective of the base program is to simulate the conditions expected during a high consequence accident. These experiments are large scale integrated experiments. The accident conditions that are studied include a bypass of a containment, an early leak or failure to isolate a containment, and a delayed failure of a containment.
Relationship to the Source Term Research Early experiments into source terms were done to elucidate the mechanisms for the transport and for the retention of aerosols. However, these experiments failed to account for highly concentrated aerosols, for transient thermal con-ditions, and for intercompartment flow. Thus, the knowledge of source terms was incomplete.
The LACE experiments were initiated to study aerosol behavior in areas where knowledge is deficient. The behavior of aerosols in pipes and in vessels are being investigated to collect data to analyze a postulated sequence with a high consequence.
"High consequence" is defined as a degraded containment, either by a structural failure or by an isolation failure.
The LACE experiments relate to the source term research that the NRC is sponsoring. Some of the sequences choosen by the NRC to analyze are also high consequence accident sequences:
The V sequence is a failure of a check valve in the low pressure injection system. This opens a release pathway that bypasses a containment.
A sequence labeled with a " beta" is a failure to isolate a containment.
Experimental System The Containment System Test Facility (CSTF) is a large scale system for experimenting with aerosols in pipes an'd large vessels. The test pipe has an.
inner diameter of 63 millimeters and is 27 meters long with 5 elbows. The large (CSTF) vessel has a volume of 850 meters; this is the test vessel that receives aerosols through the test pioe.
An aerosol mixture is made in a mixing tank. This tank receives sodium and aluminum hydroxide through feeder pipes. Also, nitrogen, air, and steam enter into the mixing tank. The flow of materials entering the tank is regu-lated.
The aerosol mixture exits the mixing tank through a 30 centimeter diameter pipe that leads to the 63 millimeter diameter test pipe through a reducing joint. The aerosols exit the test pipe through an inverted reducing joint that feeds another 30 centimeter diameter pipe. This large bore pipe' leads to the CSFT vessel through a reducing joint.
The CSFT vessel is equipt with water sprays and collectors. The watcr sprays are located in the top head and the bottom head. Condensation is collected at both the mid-section and at the lower section of the tank by wall condensate collectors. A venturi scrubber connects to the vessel through a gravel scrub-ber near the upper head. The sump condensate is collected in the lower head.
The aerosols can be routed passed the CSFT vessel via a 50 millimeter diameter aerosol bypass line.
The system is instrumented with flow meters and with Anderson impactors. The flow ceters are located on pipes such as the air feed and the steam feed.
Five Anderson impactors are used. One impactor is at the outlet of the aerosol mixing tank. The second impactor is at the outlet of the test pipe.
The remaining three impactors are in the CSFT vessel.
The fission product aerosols are simulated with nonradioactive substances.
Sodium hyroxide simulates the soluble fission products such as cesium hydroxide. Aluminum hydroxide simulates the insoluble aerosols such as structural materials. Condensing water and hydrating water is simulated using superheated steam.
n.
The aerosols are generated in two ways, with burning sodium and with aluminum hydroxide powder. The sodium is burned in the mixing tank where it oxidizes in the steam to form sodium hydroxide vapors. The vapors rapidly condense to form particles with a mass mean diameter of 2 to 3 microns. The aluminum hydroxide powder particles have an initial diameter of 1 micron; the 1 micron particles agglomerated to form particles with a mass m'an diameter of 2 to 3 microns.
Experimental Results i
Three tests have been conducted. The atmospheric condition in the vessel was.
held constant. The vessel atmosphere was saturated with water. When the aero-i sol was first injected into the vessel, some water condensed onto the walls.
~
While the aerosols was injected, the vessel atmosphere became slightly super-saturated.
The condition in the test pipe was varied. During two tests, the pipe wall was relatively cool such that water condensed. During one test, the pipe wall was relatively hot such that no water condensed. Each test used a super-saturated carrier gas of steam-nitrogen-air and the aerosol composition was varied from test to test.
In the first test, a sodium hydroxide aerosol was used; this ia a hydrophobic aerosol.
In the second test, a mixed aerosol consisting of sodium hydroxide and aluminum hydroxide was used.
In the third test,an aluminum hydroxide aerosol will be used (the test is in complete); this is a hydrophilic aerosol.
The results for Test 1 and Test 2 are as indicated below. Test 3, using alumimum hydroxide, with no condensation in the test pipe and some condensation in the vessel, is incomplete at this time.
Parameter Test 1 Test 2 Aerosol NaOH NaOH/Al(OH)}cn Aerosol water Hydrated Some hydrat Pipe conditions No condensation Condensation Vessel conditions Some condensation Some condensation NaOH source rate to test pipe (g/s) 3.8 0.6 Al(OH)3 source rate to test pipe (g/s) 0 0.4 Source size, AMMD (microns) 3.9 3.2 i
Source geometric standard deviation 3.0 2.5 Suspended Concentration at Pipe Inlet 3
Na0H (g/m ) 3 12 2
Al(OH)3 (g/m )
0 1
The average total aerosol source rate and the suspended concentration were greater for a hydrophobic aerosol in a non-condensing atmosphere than for a hydrophilic aerosol in a condensing atmosphere. A large fraction of the aerosols accumulated in the large bore pipe after the test pipe and in the CSFT vessel; less than 3% of the aerosols were vented from the vessel.
. )
Comparison with Theories and Codes The particle size and the standard deviation ~of the aerosols were as expected from the estimates made before testing.
The results from the LACE experiments have not yet been compared to the ccmputer codes used to predict aerosol behavior.
l Future Plans Other experiments are planned for the CSFT facility. A plasma torch may be fitted to the system so that a variety of materials can be vaporized. The results will be used to validate the computer codes used to predict aerosol behavior.
}
1; j
i 1
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SIMPLIFIED LACE TEST MATRIX Number Of Tests Simulated Accident Failure Mode
' Phenomena Studied 5
Containment bypass through cold leg interface piping Aerosol retention in pipe, auxiliary building, and leak path 1
4 2
Late containment leakage due to overpressure Aerosol containment behavior, resuspension 1
Failure to isolate containment Aerosol containment behavior, leak path retention 1
Early containment leakage due to overpressure Isentropic expansion effects 1
Failure to isolate containment Aerosol behavior in inter-compartment flow, leak path retention 4
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TEST CONDITIONS CONTAINMENT BfPA55 -5 COPING TESTS Test Test Test Parameter CB-1 CB-2 CB-3 1
_ Aerosol Species NaOH MaOH A1(OH)3 A1(OH)3 Duration (min) 60 60 60 j
Test Pipe Inlet
--Carrier Gas Inermal Hydraulics Steam mass flow rate (kg/s) 0.14 0.14 0.14 Air mass flow rate (kg/s) 0.19 0.23 0.26 Nitrogen mass flow rate (kg/sj/s) 0.08 0
0 Totalvojumetricflowrate(m 0.38 0.35 0.37 (at 0 C,101 kPa)
Gas velocity (m/s 100 91 97 Gastemperature(j)
C 186 111 160 Pressure (kPa) 210 179 181 Volumetric fracti Steam superheat (gn steam 0.45 0.48 -
0.46 C) 88 N
5 15 66 5
5 gg 4x10 4x10 SX10 Test Pipe Diameter, 10 (mm) 63 63 63 Length (m) 27 27 27 No. of elbows 5
5 5
AP (Clean) (MPa) 0.1 0.08 0.1 Test Auxiliary Building Conditions volume (m-)
850 850 850 Initialgastemp.(f*C)
Initial wall temp.
85 81 84 C) 85 81 84 Pressure (atm) 1 1
1 Vented YES YES YES 0
4--
6 Report 6 s
.3 DEMONA (DEMONSTRATION OF NUCLEAR AEROSOL BEHAVIOR) EXPERIMENTS J. P. Hoseman, KfK, Germany i
This paper is a summary of the original report.
Editor: Christopher Ryder, U. S. NRC O
e Objective The objectives of the OEMONA aerosol removal experiments are as follows:
(1) To demonstrate the efficiency of the natural aercsol removal proc-ess using large-scale tests.
(2) To demonstrate the predictive power of the NAUA code >hich describes the behavior of aerosols in a reactor containi.ent).
.i (3) To demonstrate the predictive power of the COCMEL code (which f
describes the atmospheric conditions in a post accident containment).
l Computer codes that accurately predict the behavior of an aerosol are essential j
for accurately predicting source terms.
l The reactor containment has a stronger influence on reducing a fission product release from the core than does the reactor coolant system. The relative importance of the coagulating and the condensing processes is seen when surface areas are compared. The surface area of an aerosol is much larger than the surface area of a reactor coolant system; therefore, particles should coagulate and condense more than they should adhere to the reactor coolant system sur-faces. This has been confirmed by the SASCHA experiments.
In a containment, volitile elements condense on particles and small particles coagulate, espe-cially when an aerosol is concentrated.
All existing aerosol codes predict the behavior of an aerosol that has a homogeneous concentration. This is reasonable because persisting heterogeneous conditions are unlikely. Also, an aerosol with a heterogeneous concentration is expected to coagulate more rapidly than an aerosol with a homogeneous con-centration. Because the NAUA code simulates a homogeneous aerosol concentra-tion, its results should be conservative. This conclusion will be demonstrated by the DEMONA experiments.
Experiments are needed to illustrate the aerosol behavior in an air / steam atmosphere that represents the expected containment atmosphere composition i
during a severe accident. The results would be used to verify both the NAUA code and the C0CMEL code for both the scientific community and the general public.
Relationshio to Source Term Research In Gennany, an accepted notion is that the design basis accident (DBA) is suf-ficient to limit doses during an accident to the limits discussed in the nuclear regulatory codes. Together, the regulatory codes and the plant design mean that a DBA cannot proceed beyond a core damage of more than about a 1000 fuel rods carrying the highest heat load. Only noble gases, iodine, and some cesium can be released to keep a dose within the required limits. By this standard, radioactive aerosols need not be investigated for a DBA.
3
2-But during a LOCA where the water level in the reactor vessel has reached the top of the core, a time period of about 15 to 20 minutes exists in which the ECCS can be operated to prevent melting. A conservative notion is to as-sume that the ECCS will be operated unsuccessfully during the time period.
In this case, a core will melt and produce an aerosol. Within the context of the German reactor safety research program, it seems reasonable to study aerosols in addition to noble gases, iodine, and cesium releases.
A definition of a severe accident in a German reactor is that a core completely melts and the containment maintains its integrity for 4 to 5 days with a leak-rate of 10 times the design leakage (0.25%/ day). The containment fails when the i
internal pressure reaches 9 bars (130 psi). This is called an FK-6 type
. i accident.
If a core melt occurs in a PWR, the probability that it is an FK-6 accident is 99.6%. The 4 to 5 day period for the containment failure to occur suggests that the aerosol behavior is a major factor in determining the fission prcduct release to the environment.
Experimental System 4
The Battelle-Frankfurt (BF) containment is used for the OEMONA experiments.
The main advantage of the BF containment is that it has a 1:4 linear scale simular to the German PWR containment. The total volume of the BF containment is 640 cubic meters and,-to a certain extent, its internal geometry can be al tered. Both electricity and water are readily available. Thermodynamic instruments and data acquisition systems come installed and satisfy most of the equipment needs for the DEMONA experiments. The leak rate of the containment is 70% to 100% volume per day at a pressure of 3 bars and at a g
temperature of 130 C; this was determined by measuring the change in concentration of methylen, the change in concentration of nitrogen and oxygen, and the partial pressure of steam and air.
To measure an aerosol concentration, simple instruments are used inside of the containment and sophisticated instruments are used outside of the containment.
The types of instruments to measure an aerosol are as follows - filters, impactors, light transmission meters, and an optical droplet spectrometer.
o The filters are located in four different locations. To determine the concentration and the particle size, the filters will be analyzed by conventional weighing, neutron activation, and electron microscopy.
l 0
Five inertial impactors will be at one location. Detailed spectral information on the particle size will be obtained at different times.
Ten light transmission meters will be used to continuously monitor the o
concentration of an aerosol.
The laser light scattering spectrometer will measure the time-dependent o
variations of particle size and droplet size spectra at one location.
w
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. An aerosol will be conducted out of the containment into an auxiliary tank o
where,the particle concentration can be determined using Beta-absorption techniques and particle size spectra using impactors. An aerosol is con-ducted into this tank from the containment by two electronically control-led gate values. The temperature in the auxiliary tank will be adjusted such that no condensation occurs.
The auxiliary tank is instrumented with a prodi/ impactor and an " aerosol o
particle analyzer" (APA) as well as an INSPEC-impactor. Filters and an absorption dust analyzer are used. A gate will be developed through which instruments can be inserted into the containment.
~'
A droplet size analyzer is used to determine the size of the ~ drops and o
the amount of suspended water in the containment atmosphere, Instruments are installed to continuously monitor the temperature, the o
total pressure, and the partial pressure of water.
The SASCHA experiments suggest that the following amounts of fission products will be released from a core-melt accident.
Element Mass (Kg)
Commment Ag 1600 160 Kg of inactive FP Fe 750 100 Kg of active FP U
490 Sn 300 Zr 80 An aerosol of this composition would be desirable but impractical. The behavior of an aerosol and the accuracy of the NAUA code can be determined using another aerosol, such as gold, iron, or tin. The use of cesium, as a substitute of uranium, is being investigated.
Iron is the element of choice.
Tin is considered as an alternate source if an iron aerosol is insoluble.
Three plasma torches generate a multi-chemical aerosol. The carrier gas is argon.
Experimental Results The containment-leak rate was determined to be 70% to 100% volume / day. The BF containment is considered acceptable for the remaining DEMONA experiments. No other experiments have been completed.
Carparison of Results with Codes and Theory The experiments have not been done to validate the NAUA code or to validate i
both the NAVA code and the C0 CME code operating together.
O m-.
Future Plans The OEMONA program consists of seven experiments. These experiments are listed below:
Experiment 1 - Steam, without an aerosol, is injected into the containment to determine the containment leak rate (this experiment has been completed).
Experiment 2 - An aerosol, without steam, is injected into the containment.
The data describes an aerosol behavior lacking condensation and diffusionphoresis.
~
Experiment 3 - An overpressure failure of a containment is simulated. A maximum aerosol concentration is used.
Experiment 4 - An overpressure containment failure, with large leakage is sim-ulated. A reduced aerosol concentration (relative to Experiment 3) is used.
Experiment 5 - Non-stationary thermodynamic conditions are established in a containment.
Experiment 6 - An overpressure containment failure is simulated. A maximum aerosol concentration is usad. Multicompartment geometry is created by isolating subcompartments.
Experiment 7 - Standby experiment.
t Experiment 8 - Standby experiment.
Experiment 9 - Standby experiment.
Experiment 10 - An overpressure containment failure is simulated. A maximum aerosol concentration is used. Multicompartment geometry l
is created by isolating subcompartments. This experiment differs from Experiment 6 in that here, additional video recording l
equipment is used.
The experiments are designed to test the flexibility of the NAUA code and the interaction of the NAUA code with the C0CMEL code' The experiments are expected to be completed and documented by 1985.
e
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cerosol concentration U
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9 Report 7 Summary Report on the Tests of Aerosol Production During Core Debris / Concrete Interactions D. A. Powers Sandia National Laboratories Albuquerque, NM Editor:
Christopher Ryder, U.S. NRC
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SUMMARY
REPORT ON TESTS OF AEROSOL PRODUCTION OURING CORE DEBRIS / CONCRETE INTERACTIONS D.A. Powers Sandia National Laboratories Albuquerque, NM Objectives of the Tests The USNRC has sponsored at Sandia National Laboratories an experimental program to characterize the nature of core debris interactions with concrete. These I
interactions would be expected to occur in an uninterruped core meltdown accident should a melt escape the reactor vessel. The experimental efforts are directed toward providing data on the loading of containment produced by the core debris interactions. Thus, the emphasis is on data concerning non-condensible gas generation, flammable gas generation, heat partitioning between the concrete and the ambient atmosphere from the molten debris, and concrete ablation. Midway through the experimental work it was recognized that aerosol generation was endemic to the core debris interactions with concrete.
Some efforts have been made to characterize this source term to the containment.
Quite a few experimental series have been conducted.
In this summary, three test series will be described:
Test Series Objectives NSS Transient interaction of corium melts with concrete.
BURN Visualization of melt behavior on concrete by x-ray image enhancement.
COIL Sustained, large-scale, steel melts interacting with concrete.
In the concluding section of the document, forthcoming tests with strong source term components - the SWISS, TURC, and SURC test series - will be mentioned.
Relationship to Source Term Research Release of radionuclides during ex-vessel interactions of core debris has been recognized as a substantive phenomenon of severe reactor accidents since the time of the Reactor Safety Study. A model of the radionuclide release ex-ves-sel was formulated in the Reactor Safety Study despite the absence of any substantive data.
Releases hypothesized in the Reactor Safety Study tave been used in all reactor accident analyses since that time until the NRC's source term reassessment effort (BMI-2104).
1
,,_--n,_
d The plan for the BMI-2104 work was to take advantage of the technical develop-ments that had occurred since the time of the Reactor Safety Study and to formulate a consistent, mechanistically-based, best estimate of the source term specific to an accident and plant in question.
For the ex-vessel release of radionuclides this meant using the CORCON model of core debris interactions with concrete and a conceptual model being formulated to rationalize releases observed in the NSS test series.
The conceptual model was implemented in a crash effort and became known as the VANESA model of release during ex-vessel core debris interactions. The genesis of the VANESA model was not just from the experience with the tests described here. Substantive portions of the model arose from technology available from the ferrous metal industry.
Description of the Experimental Systems
~
(A) NSS Tests The NSS tests used melts weighing 15 to 35 kg.
The melts had the nominal "corium" composition-30 w/o stainless steel, 54 w/o U0 and 16 2
w/o Zr0. They were formulated by metallothermic reactions. Once formed, no 2
further heat was supplied to the melts save that arising because of gases evolved from concrete reacting with melt constituents.
The melts were formed within a concrete crucible.
Intense core debris attack on the concrete lasted for 1-2 minutes. Variables in the tests were concrete composition and the shape of the concrete cavity.
A variety of materials were added to the melts to simulate fission products.
The concrete crucibles used in the tests were capped by a highly instrumented a
" top hat" to monitor the release of the fission product simulants as well as gas generation and gas compositions. Aerosol instrumentation consisted of cascade impactors and an optical turbidity monitor.
Samples collected in the tests were analyzed by x-ray powder diffraction, spark source mass spectroscopy, and thermal gravimetric analysis.
1 (B) BURN Test This test was similar to but smaller than the NSS tests (2 kg melt).
The melt, produced by metallothermic reaction, had the nominal composi-tion of 55 w/o Fe and 45 w/o A1 0. Visualization of the melt behavior was 2 3 done with x-rays. A Linatron source provided 7.5 Mev x-rays at a rate of about 500 rads / minute. X rays that passed through the test fixture and impinged on a neutron sensitive screen. The screen image was enhanced with a Decalix image-enhancement system.
(C) COIL Tests For the COIL tests melts of type 304 stainless steel weighing about 200 kg were prepared in an induction furnace. When the melt reached 1573*k, it was teemed into a concrete crucible.
The cavity in the crucible was about 30 cm in depth and diameter. The crucible was equipped with embedded induction coils so that once the melt was in place heat could be provided to sustain the melt. A typical time-temperature history of a test is shown in i
Figure 1.
The crucible was capped by an instrumentation tower for sampling aerosols, gases, and measuring the gas generation rate, and upward heat flux.
The primary aerosol diagnostics were cascade impactors. No simulants of fission products were included in the melts. The COIL tests provided an 2
indication of the release of non-radioactive species from the concrete and steel constituents of core debris during melt / concrete interactions.
Results to Date (A) NSS Tests The NSS tests yielded quite a lot of quantitative data not all of which has been exmained to date.
Some of the important conclusions obtained from the tests concerning aerosol generation include the following:
(1) Intense aerosol generation was observed.
Concentrations of aerosols reached peaks of 150 g/m -STP in the gases evolved from the concrete.
3 As the melt temperatures fell toward the freezing point of the metallic phase, concentrations of aerosol in the evolved gas were 3
about 20 g/m -STP.
(2)- The integrals of aerosol generation in tests with siliceous concrete were less than the integrals in tests with limestone concretes.
(3) The mean size (AMMO) of aerosols evolved from the melt were about 1.3 pm.
There were variations in size that seemed to correlate with aerosol concentration, but this correlation could not be firmly established because of sampler overloading in many tests.
(4) Except for obvious discrepancies caused by differences in the con-crete compositions, the aerosols produced in the NSS tests had remarkably similar compositions (see Table 2).
(5) Most of the aerosol was from sources that would not be radioactive in an accident concrete and steel.
(6) There was a tendency for the aerosol composition to be size-dependent (see Table 3). More volatile species were concentrated in the smaller size fractions of tne cascade impactors and the more refrac-tory species were concentrated in the larger size fractions. Again overloading may have affected this observation.
(7) Aerosol concentrations seemed to correlate linearly with the super-ficial gas velocity through the melt.
(8) -Speciation of the aerosol by x-ray diffraction was difficult because of both the complexity of the material and its fine particle size.
Evidence could be found for sulphides, chlorides and fluorides in the aerosol. The sources of sulfur and halogens was the concrete.
(B) BURN Test The BURN test established that after an initial transient when the melt first contacted concrete, the gas bubbles passing through the melt were discrete and had shapes of wobbly-ellipsoids or nearly spherical caps.
That is, the bubbles were consistent with predictions of bubble theory and the experiences during carbon "Olows" in steel making.
These findings constituted the base for quantitative predictions of release kinetics.
3 i
(C) COIL Tests The COIL tests established the following:
(1) Copious quantities of aerosol would be evolved from the concrete and the melt event if no radionuclides were present.
(2) Aerosol emissions were continuous and not a peculiarity of metallo-thermic melts.
(3) Aerosol emissions at low temperatures were primarily from the con-crete and especially potassium in the concrete. Again, chlorides were detected in the aerosol samples.
Results obtained in the NSS and the COIL tests were used to formulate an
~
empirical correlation of the total aerosol concentration in gases evolved during core debris attack on concrete:
i
[A] = Kexp-(E/RT) (Vs + B) where [A] = aerosol concentration (g/m -STP) 3 T =, absolute temperature of the melt R = gas constant Vs = superficial gas velocity through the melt.
Comparison of Experimental Results to Model Predictions Comparison of the results of the NSS, BURN, and COIL tests to models used in the Reactor Safety Study reveals a familiar litany of discrepencies with regard to core. debris / concrete interactions; experimental gas production is higher and more flammable; concrete erosion is by ablation with little spalla-tion; upward heat fluxes are higher; and melt temperatures are more variable.
With regard to aerosol release, the most substantive findings are listed below:
(1) Most of the aerosol mass is composed of materials that would not be radioactive in an accident.
Release of these mattrials was~ neglected in the Reactor Safety Study.
(2) Release of aerosols is dependent on temperature and gas generation and does not abate in time as hypothesized in the Reactor Safety Study.
Direct extrapolation of the NSS test results to a reactor accident yields much higher release fractions of radionuclides such as isotopes of La, Ce, 8a and S r.
Comparison of the test results to predictions of the CORCON code indicate the CORCON tends to underpredict melt temperatures and overpredict radial erosion of the concrete. ' Predictions of the VANESA code have been compared to the results of the empirical correlation of integral releases observed in the tests.
(By doing the comparison this way, discrepancies in the modeling of core debris interactions used in the VANESA model are eliminated from the 4
comparison.) In general, predictions of the correlation and the VANESA model agree well.
If large quantities of metallic zirconium are not present in the melts, then the VANESA model and the correlation predictions of integral mass release agree to within a factor of.two. When metallic zirconium is in the melt, the VANESA model predicts high releases.
The tests upon which the correlation we'e based had a low metallic zirconium content.
r Little has been done to validate VANESA predictions of the release of specific elements.
The mode? correctly predicts the important contribution of potas-sium to the aerosol observed in the COIL tests.
It predicts the dominant influence of non-radioactive species to the aerosol throughout melt / concrete interactions. The order of predicted species volatility is correct.
It does not predict the observed chlorides, sulphides, and fluorides.
It may under-predict Mo release though data obtained on Mo release in the NSS tests may have been affected by the way Mo was incorporated in the melts. VANESA may overpredict nickel release.
Future plans Several tests are planned with the specific objective of validating predic-tions of the VANESA model of aerosol generation during core debris / concrete interactions:
(1) Separate effects tests - a series of small, well-controlled tests to measure mechanical aerosol generation by bubble-bursting and validate predictions of low-level Te release as well as other radionuclides.
(2) Large-scale integral tests - a series of sustained tests of about 200kg of UO /Zr0 /Zr melt interacting with concrete will be conducted.
Fission 2
2 products will be incorporated in these melts and their release will be monitored.
(3) Effects of coolant - tests of steel melts and UO /Zr2/Zr melts inter-2 acting with concrete in the presence of a water pool are planned. The effects of a coolant layer on aerosol production will be determined. The VANESA model predicts a sharp mitigation of release by an overlying water pool.
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UO2 51.73%
Zr02 15.14%
Fe 20.87%
Ni 2.26%
Cr 5.08%
Mo 0.71%
(La) 0.80%
(Ce) 0.76%
l (Cs) 0.44%
(Sr) 0.21%
(Sn) 0.74%
Table 1 Melt Composition Rb, Sb, and rare earths were impurities in the materials added to melt to simulate radionuclides.
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Element Concentration (PPM) in Aerosol Test with Test with 4 -
Basaltic Concrete Limestone Concrete U
> 5000
> 5000.
j Zr 7
14 Cr
> 10000
> 10000 Fe
> 10000 I 10000 Ca 130
- 250 Si
> 10000
> 10000 K
> 10000 I 10000 Na
> 5000 1600 Al 250 250 Cs
> 5000
> 5000 Rb 2900 1500 Sn
> 10000
> 10000 Sb 3700 5000 Sr 25 38 Ca 15 31 La 1100 910 MO 1100 910 Table 2 Compositions of aerosols obtained in the NSS tests l
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Element Concentration (PPM) 25 - 15 pm
> 0.6 pm U
> 104 150 Ce I 5000 3
La I 5000 8
Zr I 104 2100
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> 103 2100
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> 5000 Mo 1700 I 104 Sn 2900
[5000 Table 3 Aerosol composition as a function of particle size from the NSS test results
In Mn03 Cr-0 solid solution 2
Fe 0s Nacl Cscr p7 2
SiO2 Sb 2
Fe Sj7 3
Cr Ss KCi 2
InFe 04 KSbS2 Mnci2 3
KFe (Cr04)2(OH)s CsFeF*
Table 4 Some chemical species identified in aerosol produced by melt / concrete interactions charging the NSS tests 9
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t, Report 9 Suppression Pool Experiments
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This paper is a summary of three papers:
Scrubbing of Radionuclide Aerosol in Water Pools A. T. Wassel, M. 5. Hoseyni, J. L. Furr, Jr., Science Applications, Inc.,
Hermosa Beach, CA.
R. N. Oehlberg, Electric Power Research Institute, Palo Alto, CA.
Radionuclide Scrubbing in Water Pools--Gas-Liouid Hydrodynamic D. D. Paul, L. J. Flanigan, J. C. Cunnane, R. A. Cudnik, R. P. Collier, Battelle Columbus Laboratories Columbus, OH.
R. N. Oehlberg, Electric Power Research Institute, Palo Alto, CA.
Scrubbing of Fission Product Aerosols in LWR Water Pools Under Severe Accident Conditions - Experimental Results J. C. Cunnane, M. R. Kulhman, Battelle Columbus Laboratories, Columbus, OH.
R. N. Oehlberg, Electric Power Research Institute, Palo Also, CA.
o The summary was written by Christopher Ryder, U.S. NRC 1
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-Purpose The effect of a suppression pool on the steam /noncondensable gas mixtures and entrained radionuclides must be known to analyze the fission product transport.
A typical steam quencher may contain hundreds of holes for gas injection. The i
focus of this study is the hydrodynamic response of a single hole.
Tests have been conducted using superheated steam as the condensable gas and either air, helium, or hydrogen as the noncondensable gas.
Relation to the Source Term Research e
i In the Reactor Safety Study (WASH-1400), an assumed decontamination factor of
,i 100 was used for subcooled pools and I was used for steam saturated pools. But the water pool scrubbing process might be significantly more effective. The problem is ' hat data are sparse.
The os pool scrubbing DFs seem to be sensitive to the test conditions.
The cont an in a water pool changes significantly when steam and noncondens-able gas mixtures with entrained fission product aerosols are injected. The best estimate of pool scrubbing performance is an estimate that is a function of time.
Experimental Systems A.
Gas-liquid hydrodynamics study System. Two different size water holding tanks are used for the experi-ments. The small tank is 1.8 meters in diameter and 2.4 meters high. The large tank is 3.0 meters in diameter and 5.0 meters high. During testing, the tanks are filled wigh tap water. The tanks have three vertical' sets of Lexan windows, located 90 apart, to observe and photograph the gas-liquid hydro-dynamics.
Heaters on the noncondensable gas lines change the gas temperature.
Condensable and noncondensable gas streams mix far enough upstream of the injector outlet to insure a homogeneous mixture.
The discharge end of the injection probe is fitted with a removable orifice.
Two orifice diameters are used, 9.9 mm. and 12.7 m.
The entire injector assembly is centered in the water tank, 0.30 meters from the bottom, and can be adjusted to discharge in any direction. The nonconden-sable gas flow rate is monitored using a rotometer at low flow rates and either a turbine meter or a critical flow nozzle at high flow rates. Condensable gas (superheated steam) is supplied from the boilers. Orifice meters are used to monitor the steam flow rate. Gas temperature and pressure measurements are made to determine the gas flow rate and to determine the conditions near the injector outlet.
B.
Aerosol Removal System The scrubbing facility and associated process irstruments consist of an aerosol generator, a sampling system, and a scrubbing taak.
Two types of aerosol generators are used in the test. An evaporation-reconden-sation generator produces Cs! and Te0 aerosols in a penetrating size range.
2 A powder feeder and fluidizing system generates a tin powder aerosol with an aerodynamic mass median diameter of about 3 mm.
The ev3poration-recondensation generator is a flange vessel which contains a stainless steel pan into which dried Csl and Te powder are fed from a supply i
vessel at a controlled rate by an electronically driven auger. The pan is supported in and heated by water cooled copper coils supplying an RF field. A Pt-Rh thermoccuple is spot welded to the bottom of the pan to monitor its tem-perature. An aerosol is generated when a molten material in the pan evapor-ates, then condenses when the vapors become supersaturated in a cooler nitrogen purge gas stream. The stream transports the aerosols away from the molten pool surface. The relative standard deviation of the mass output rate is about 20%.
The tin powder aerosol is produced using a hopper that feeds the powder into a mixing chamber. A fluidizing carrier gas suspends the powder and transports the aerosol into the scrubbing system. The relative standard deviation for the mass output rate is about 40%.
The scrubbing tank has a diameter of 1.8 meters and a height of 2.6 meters.
The tank has a small entry hatch and penetrations for sampling ports and electrical power for an internal mixing fan. An exhaust duct is valved so that the air space above the water surface in the tank can be isolated. For the hot pool tests, electrical resistant blanket heaters are on the tank. Except for the bottom, the tank is insulated. All tests are conducted using a 1.27 cm orifice oriented horizontally at the center of the tank and located 0.27 m above the tank floor.
Instruments. A sampling system pulls grab samples of the injected aerosol and the escaping aerosol for determining the injected mass, the escaped mass, and the particle size distribution. Where only noncondensable gas is injected, a 5-inch diameter glass fiber filter collects the aerosol. For tests where a steam-noncondensable gas mixture is injected, the sampling train is a condensing coil, two impingers, and a glass fiber filter in sequence.
The sampling system for the escaped mass measurements is as follows. For the ambient temperature pool, 47 mm filter holders containing millipore type HA filters are inserted directly into the above pool air space and used to sample a known volume of the gas. For the hot pool tests, the sampling train that is used is similar to the injection line sampling system.
I
l i
i 4 The experiments are designed to establish and maintain constant conditions.
Calibrated rotometers are used to monitor the volumetric flow rate into the
]
system. The steam metering syste:n is a pair of orifices whose pressure drop i
is monitored with an oil gauge or mercury manometer. Chromal-alumel therno-couples monitor the wall and the fluid temperatures.
The methods selected for aerosol size distribution measurements are dictated 1
^
by the size range of the particles. For the size distributions of tin powder particles in the supermicron aerodynamic diameter range, cascade impactors collect size segregated samples of the aerosol fo. chemical analyses. An Active Scattering Aerosol Spectrometer (ASAS) System compiles size distri-bution data from the grab samples obtained for the Cs! and the Te0, tests. The instrument has the capability to measure particles in the 0.09 um to 3.0 um range and classify the data into 60 discrete size intervals.
It is calibrated j
using monodisperse polystyrene lates (PSL) spheres of 0.167, 0.26, 0.62, 1.09, and 2.02 um. The particles are spheres; the aerodynamic diameters are directly l
determined from their geometric diameter and density. The ASAS size distribu-tion oata is compared to data from an impactor with cut points for the stages of 7.2, 3.6,1.8, 0.9, and 0.45 um aerodynamic diameter. The impactor data agrees with the ASAS data.
Independent measurements of the injected mass, scrubbed mass, and escaped mass are made. They are determined from chemical analysis of the grab samples at the injection line, the post test tank water, and the post-test atmosphere above the pool.
All of.the samples (solutions, glass and millipore filters) are analyzed using 1'
atomic absorption spectrophotometry (AAS) to measure elemental concentrations.
For Csl in solution, the samples are first concentrated by a factor of 10 be-fore measuring; it is analyzed using AAS, after leaching the Cs! from the fil-ters using a solution of 1% HC1. For the Te0, and Sn powder analyses, the aerosol material is dissolved using concentrated hcl and HNO, respectively. A 3
Perkin-Elmer Model 5000 Atomic Absorption Spectrophotometer Ts used for the absorbance meansurements. The procedure detects greater than 1 ppm levels with a precision of about 5% RSD.
Experimental Results A.
Gas-liquid hydrodynamics study Three distinct zones of gas-liquid hydrodynamic behavior have been identified.
Zone I is the injection zone where discrete vapor globules are formed as a gas is injected into the water pool. Zone II is the vapor globule breakup zone where hydrodynamically unstable vapor globules break up into bubbles. Zone III is the bubble rise zone where the size of the bubbles becomes stable.
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Injection Zone. Depending on the flow conditions, a gas injected into a water pool causes either the periodic formation of vapor globules at the in-jector outlet or causes a continuous jet of gas to penetrate a finite distance into the water before forming vapor globules.
In either case, the initial glo-bule volume has been determined from high speed films by measuring the major and minor axes of an oblate spheroid that most closely approximates the globule shape. Previous studies comparing circular and noncircular openings have shown that equal globule volumes are produced with injectors having the same cross-sectional areas.
I The gas injector Weber number describes the gas injection.
2 p D
)
W U
=
t Where W Weber number
=
U gas velocity
=
p density of gas at the injector
=
D diameter of the injector
=
gas-liquid interfacial surface t =
tension 5
When W < 10, discrete vapog globules are periodically formed at the in-jector outlet. When W > 10, a jet of gas penetrates into the liquid be-fore vapor globules are formed.
Zone II: The Vapor Globules Breakup Zone. The initial vapor globules generated in the injection zone are nyorodynamically unstable; they break up as they rise in the water pool. The larger the vapor globule, the longer the distance traveled before complete break up. Based upon visual flow studies, i
the length traveled before complete break up is approximately 10 initial globule diameters from the injector outlet.
Zone III: The Bubble Rise Zone. The bubble rise zone corresponds to the par-tion of the water pool located about 10 initial globule diameters from the injector outlet. In this region, the bubble size distributions have been studied using photographs. The bubble volumes are determined by measuring the major and minor axes of an oblate spheroid that most closely approximates the bubble shape.
Experimental data are for air, helium, and hydrogen gas injected horizontally through orifices 9.9.12.7, or 20.2 m in diameter. Data have been taken at
- ambient temperatures and pressures. Bubble size distributions have been meas-ured at elevations in the water pool of 0.46,1.22,1.98, or 3.50 meters above the injector outlet. These data show that the bubble size distributions do not change significantly with the gas injection rate or with increasing elevation in the pool.
l.
Subble size distributions for mixtures of condensable and noncondensable gasec injected into a water pool have been determined.
In all cases, the superheated l
steam has been used as the condensable gas. The gas mixtures ( 420'K) are m-j jecged through a 9.9 mm diameter orifice into a water pool with a subcooling of 99 X.
The total gas mixture volumetric flow rate is held at a constant value of 2 1/s. At low steam fractions, the mean diameter of gas bubbles asymptoti-cally increases to the value of 5.6 mm for noncondensable gases. As the steam fraction increases, the mean diameter of the gas bubbles slowly decreases until the steam fraction exceeds 0.90.
This implies that most of the steam is con-densing before the vapor globule has completely broken up into small bubbles.
When steam is injected into the water pool, the steam completely condenses within the two initial globule diameters of the injector outlet.
B.
Aerosol removal study For hot and saturated pool conditions, the above-pool aerosol concentration is significantly attenuated because of diffusiophoretic deposition on the tank walls or particle growth and subsequent sedimentation on the water pool surface. To study minimum diffusiophoretic deposition, the tank walls and top are insulated and heated.
In addition, a trough collects the wall condensate from a quarter of the wall surface.
The diffusiophoretic deposition effects are small.
Csl sedimentation measurements for hot pool test conditions show that the Cs!
particles reach particle sizes in the range of a few microns.
The two param-eters which dominate the overall behavior of the subcooled pool are the aerosol particle size and the carrier gas steam mass fraction. Varying the steam mass fraction has a large effect on the the Csl and Te0,3 aerosol material which have an AMMO of 0.4 mm.
The effect is less apparent foF the tin powder aerosol which has an Aff0 of 2.7 m; apparently the DF for this material is large even when the carrier gas contains no steam. Although the value cited for the Cs!
test (low submergence, ambient pool, high steam content, high flow) appears anomalous, the relatively low 0F is probably caused by a very low submergence (0.15 m) test.
When the aerosol particle size is increased from 0.4 to 2.7 mm Aft 0, a signifi-cant increase in DF for all steam mass fractions occurs. This increase seems to be relatively lower at the lower submergences.
Submergence has its most apparent effects on the DF values in the tests on tin powder with a low steam mass fraction. The effect for the 0.4 AMMO Cs! and Te0 aerosol is less dramatic, although a significant trend appears for the low steal $1 mass fraction.
The gas mass flow rate has a relatively weak effect on the DF values. Entrance impaction effects also occur. The Cs! growth and subsequent sedimentation in the above-pool volume may result in a significant contribution to the experi-mentally observed DF for the hot pool tests.
Comoarison With Theory and Codes A.
Gas-liouid hydrodynamics study The bubble sizes are adequately described using a log-normal distribution func-tion, with < log D) = 0.750 and log w = 0.173, where:
average of parameters enclosed,
=
D bubble diameter,
=
b log w standard deviation
=
The average skewness coefficient (Y
-0.07)forthesedistributiobsarec.11)andkurtosiscoefficient 0
~.
=
(Y lose enough to ze.ro to show that the
=
loj-normal distribution function represents the experimental data. The standard deviations of the log-normal bubble size distribution for mixtures of condens-able and noncondensable gases (log w 0.174) are approximately equal to the
=
value for noncondensable gases. Therefore, the primary effect of injecting a condensable gas together_with a noncondensable gas is to shift the center of the log-normal bubble size distribution toward smaller mean diameters.
8.
Aerosol removal study Data from the hot pool tests show that the experimental 0Fs are higher than ex-pected from theoretical calculations. However, it appears that the Csl growth and subsequent sedimentation in the above-pool volume may result in a signiff-cant contribution to the experimental 0Fs.
For steam mass fractions less than 0.15, the DF's are slightly higher than those for pure noncondensables. For mass fractions of steam greater than 0.5, the DFs are markedly increased. The difference betgeen the experimental value of 0F = 2500 and the predicted value of 0F = 5 X 10 is due to a change of less than 0.04% in the scrubbed mass ; for a DF of 2500, 0.996 of the mass is re-4 tained; for a DF of 5 X 10, 0.999 of the mass is retained.
The comparisons between the predicted and calculated mass of scrubbed aerosol were done for subcooled pools using steam-air mixtures. The differences be-tween the predicted DFs and measured DFs are between 0.0 and 37% of the experi-mental values.
To assess the effect of particle size distribution on the total aerosol integral 0F, a test was done whose conditions are as follows:
Mass of gas phase 2.33 X 10-3 g jg g
Mass of steam 00 0
Temperature of gas 283 K Temperature of liquid phase 279 K Special variable at orifice 1.65 m Duration of injection 9 minutes
I The experimentally inferred factor is DF = 5.0 : 1.1.
A cesium iodide size distribution with a mass mean radius of 0.1 mm gives a predicted factor of DF = 3.2.
Using a different size distribution with a mass mean radius on the order of 0.2 mm gives a predicted factor of 0F = 6.5.
In general, it is found that reasonable _ variations in an aerosol particle size distribution result in variations in the predicted DF between a factor of 1.1 and 4.5.
Future Plans The experiments done at EPRI use a sparger ring to disperse bubbles. Future experiments will be done with a vent (down comer).
The research at EPRI is comprehensive. The suppression pool program is nearly complete. The NRC will review the EPRI experiments when they are completed.
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Submergence 0.152 - 1.6E m (6 - 65 in. )
Pool Temme"..ture 293 - 373 K (70 - 210*F)
Gas Temperature 293 - 395 K (70 - 250 F)
Orifice Diameter Fixed (1.27 cm) (0.5 in.)
Injector Orientation Fixed (horizontal)
Condensible/Noncondensible Ratio 0- 0.95 (mass fraction)
Aerosol Density 4.5 - 6.0 g/cc
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Aerosol size (mass mean diameter) 0.2 - 3.0 pm (mmd)
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Report 10 4
J High Pressure Melt Ejection Summary Report on the Test Of Aerosol Production During Pressurized Melt Ejection D. A. Powers Sandia National Laboratories Albuquerque, NM I
I 1
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SUMMARY
REPORT ON TESTS OF AEROSOL PRODUCTION DURING PRESSURIZED MELT EJECTION D. A. Powers Sandia National Laboratories Albuquerque, NM Objectives of the Tests Two series of tests of the phenomena of high pressure melt ejection have been conducted - the HIPS and the SPIT tests.
The primary objective of the tests was to confirm predictions made in the Zion Probabilistic Safety Study that core debris expelled from pressurized reactor vessels during the risk dominant accidents would be dispersed from the reactor cavity and could be both quenched
~
easily and permanently cooled. The HIPS and SPIT tests were at two size scales - 1:10 linear scaling with 80 kg of melt and 1:20 linear scaling with 10 kg of melt, respectively. This was done to confirm the scale up of the test results to reactor dimensions. Finally, the tests were instrumented for the detection and collection of aerosols because of a suspicion that pressurized ejection might produce aerosols.
Relationship to Source Term Research The studies of high pressure melt ejection are directed primarily at the definition of loads placed on reactor containments during severe accidents.
These loads may threaten the structural integrity of the containments.
Some source term consequences of pressurized melt ejection were envisaged at the start of the test program.
If core debris were dispersed as hypothesized in the Zion Probabilistic Safety Study, then there would be no long-term release of radionuclides and non-radioactive material caused by core debris interactions with concrete.
If pressurized melt ejection generated aerosols, then a mechanism for radionuclide release was available that had not been considered in either the Zion Probabilistic Safety Study or the Reactor Safety Study.
The work in the effort came too late for inclusion in the source term reassess-ment effort (BMI-2104).
Results of the test program and models derived from these tests would be applicable to several sequences considered in the source term reassessment effort.
Since the Zion reactor was modeled in the hardware for the tests, the test results are particularly applicable to pressurized sequences such as the S 0 and TMLB which were considered in source term 2
reassessment.
Pressurized sequences such as $ 0 and TMLB sequences at Surry 2
and the TC sequence at Grand Gulf could be analyzed using the data.
Preliminary data on aerosol generation were used for the uncertainty study (QUEST) of the Surry TMLB sequence.
Pressurization data and aerosol generation data from the test program are being used in the uncertainty study of the Grand Gulf TC sequence.
Description of the Exoerimental System The experimental system in both the HIPS and SPIT tests was based on the generation of a melt within a vessel pressurized at 15 to 170 atmospheres with 1
either nitrogen or carbon dioxide.
The melts were formed by the metallothermic reaction of aluminum metal with magnetite.
The nominal composition of the product melt is 55 w/o Fe and 45 w/o A1 0.
To the melt were added about 2 3 1 w/o of nickel, barium oxide, lanthanum oxide and molybdenum to simulate the presence of fission products.
Once a melt' formed within the pressure vessel, it contacted a brass plug at the base of the vessel. When the plug melted, molten material was expelled from the vessel.
In the case of the HIPS tests, 80 kg of melt was available for expulsion.
For most of the SPIT tests, the melt weighed 10 kg, though in the earliest tests, only 2.3 kg were used.
The tests differed in the level of pressurization of the reactor vessel, the gas used to pressurize the melt, and the fixtures into which melt was expelled.
The first SPIT tests involved melt expulsion onto a refractory plate or catcher.
The objective of these tests was to characterize the apparatus and the melt stream that emerged from the vessel.
Primary diagnostics for these early tests were photographic coverage, flash x-rays of the melt jet, heat flux monitors in the refractory plate, and cascade impactors or filter samplers for aerosol collection.
Later tests in the spit series and all the tests in the HIPS series involved melt expulsion into scaled models of reactor cavities:
Test Fixture Comment SPIT 15 water filled plexiglass box open to air SPIT 17 aluminum model (1:20 scale) of open to air the Zion reactor cavity filled with water SPIT 18 dry, refractory model (1:20 enclosed in a scale) of the Zion cavity 45 m3 building SPIT 19 dry, concrete model (1:20 enclosed in a scale of the Zion cavity 45 ma building Test Fixture Comment HIPS 2C dry, concrete model (1:10 scale) open to air of the Zion cavity HIPS 4W water-filled, concrete model open to air (1:10 scale) of the Zion cavity Primary diagnostics for the tests with cavity models included pressure trans-ducers, temperature detectors in the fixtures, photographic and flash x-ray imaging of the melt emerging from the fixture.
The building that enclosed the tests SPIT 18 and SPIT 19 was instrumented for pressure, gas composition, gas temperature and aerosol detection and collection.
The enclosed tests also allowed post-test collection of the dispersed debris.
This debris was sized by screening.
2
. _ =.
5 Results Quite a lot of data has been obtained from the tests for the quantitative j
analyses that are now underway. Qualitative conclusions that can be drawn from the tests are summarized below:
Test Conclusions & Observations SPIT 1-14
-Aerosols with multimodal size distributions are formed during melt expulsion.
Size distribution data suggests several mechanisms of aerosol l
formation operative.
-The melt jet is not a coherent stream if pressur-izing gas is soluble in the melt as would be expected in a reactor accident.
-Heat fluxes to impact area of the melt stream are consistent with models for a stagnated jet.
SPIT -15
-No energetic melt / coolant interaction was observed.
SPIT 17
-A violent explosion was observed which may be due to phenomena peculiar to aluminum and not the result of melt / coolant interactions.
i
-Prior to the explosion a coherent slug of water I,
was expelled from the cavity model.
4 SPIT 18
-58% of the ejected melt was expelled from the cavity model. The remainder of the melt was retained as a frozen film on cavity surfaces.
Melt was expelled from the cavity as droplets rather than as a coherent flow,' Post-test sieving of debris showed a log-normal size distribution with a mean of about 0.76 mm.
l
-The enclosing building was pressurized more than would be expected.
-Aerosols were more abundant and finer than would be expected from free jet test results.
SPIT 19
-More than 90% of ejected melt expelled from the cavity model.
3-
-Again, the melt was expelled as droplets. The size distribution of the droplets was log-normal with a mean of about 0.43 mm.
-The enclosing building ruptured and was torn i
loose from its foundation. Pressurization of the building was far in excess of expectations.
-Aerosol generation was extensive.
['
HIPS 2C
-96% of expelled melt dispersed from the cavity j
as droplets and aerosol.
Expelled melt followed i,
a ballistic trajectory, t
6 3
4
Test Conclusions & Observation
-Melt droplets remained molten throughout their flight from the cavity model.
The cloud of particles expanded several fold during flight.
-Maximum pressure in cavity was 10 psig.
HIPS 4W
-Cavity pressurized to 500 psig and ruptured.
Pressurization appears too slow to be a steam explosion.
-Just prior to fixture rupture, a coherent slug of water and a could of quenched particulate was expelled from the cavity model.
Comparison of Results to Theory and Models There are no formal models of the pressurized ejection process. Only plausi-bility arguments were formulated in the Zion Probabilistic Safety Study. The results of the tests can be compared to the assumptions and conclusions of these arguments.
Results can also be used to define areas needing modeling.
A clear conclusion of the tests is that, indeed, melts can be' dispersed from the reactor cavity when ejected from pressurized vessels. Any retention of debris is caused by the formation of a frozen film on surfaces in the cavity.
Based on the experimental data, this film will contain negligible amounts of material in a reactor accident.
The dispersal of debris is quite different than hypothesized in the Zion Probabilistic Safety Study.
The debris is expelled as droplets lofted into the atmosphere rather than as a coherent film flowing up out of the cavity and across the containment floor. The lofted particles can react exothermically with the ambient atmosphere.
These reactions and the heat they impart to the atmosphere can pose a significant danger of containment overpressurization.
The Zion Probabilistic Safety Study hypothesized that water in the reactor cavity would be promptly expelled and would not interfere with debris dispersal.
Tests to date support but do not prove this hypothesis.
Aerosol generation is extensive in the tests. Aerosol data support three types of generation mechanisms:
(1) aerosol formation by condensation of vapors, (2) aerosol formation by mechanical processes, and (3) aerosol genera-tion by chemical reactions of expelled debris particles with the ambient atmosphere.
Several mechanical aerosol formation mechanisms can be hypothesized.
Interesting among these are (1) processes initiated by the effervescence of gas dissolved in the melt, and (2) simultaneous expulsion of gas and melt through the breach in the reactor vessel.
Direct scaling of the test results suggests aerosol generation from pressurized melt ejection will introduce more material into the containment atmosphere than will in vessel core degradation.
This source term has not been considered in reactor analyses to date aside from the QUEST uncertainty study.
~
4
1 l
l FUTURE PLANS Future activities in the study of pressurized melt ejection are to be focused on questions of loads placed on containment.
In particular, the load caused by heat transfer and chemical heat generation from debris particles expelled from the cavity are of primary interest.
Enclosed tests scaled to reactor dimensions at a linear ratio of 1:10 will be done to determine the following:
(1) the effects of structures above the opening of the reactor cavity on debris dispersal, (2) the effects of water films on structures and water pools on containment i
- heating, (3) the effects of vessel pressure, gas solubility, and debris temperature on dispersal and subsequent behavior of the debris, (4) quantitative evaluation of heat transfer from expelled debris to an inert atmospheres, l
(5) quantitative evaluation of debris reaction rates with steam and air, and (6) the possibility that debris expelled from the cavity can trigger hydrogen burns or recombination.
Aerosol generation data can be obtained from these tests without affecting the primary objectives of the tests. Aerosol data will be collected to provide a basis for quantitative estimation of the various generation mechanisms and scaling of the results to reactor dimensions.
Mathematic models of all stages of the ejection process are now being formulated.
These models, including models of aerosol generation, will be refined and validated by comparison to the test results.
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