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