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21 P 05 AHMED: Facility to study hygroscopic aerosol behaviour in LWR containment conditions
J. Aero.~ol S~'l.. Vol. 24, Suppl. I, pp. $253-$254. 1993 Printed in Great Britain.
0021-8502/93 $6.00 + 0.00 Pergamon Press Ltd
21 P 05 AHMED: F A C I L I T Y T O S T U D Y H Y G R O S C O P I C AEROSOL BEHAVIOUR IN LWR CONTAINMENT C O N D I T I O N S J. M. M~ikynen, J. K. Jokiniemi, A. Silde and E. I. Kauppinen ~ Technical Research Centre Of Finland, Aerosol Technology Group, Nuclear Engineering Laboratory, tLaboratory of Heating and Ventilation, Betonimiehenkuja 5, FIN-02150 Espoo, Finland
KEYWORDS hygroscopic particles, aerosol modelling, LWR reactor accidents
INTRODUCTION AHMED (Aerosol and H__eat Transfer Measurement Device) has been constructed to study thermal-hydraulic effects on aerosol behaviour in nuclear power station containment during a hypothetical severe reactor accident where the reactor core melts and releases radioactive aerosols into containment. In wet conditions steam condensation on particles, coupled with agglomeration, can provide much more effective particle growth mechanism than dry agglomeration alone. The growth is enhanced because the aerosol released from the core contains hygroscopic material which absorbs water under 100 % relative humidity. Under favourable conditions particles may grow to sizes larger than 10 lam. These particles will settle rapidly, after which a small fi'action of micron-sized (or smaller) particles remains airborne. Our ability to model quantitatively the effect of steam condensation on particles depends strongly on both thermal-hydraulic and aerosol modelling. It is also important to have the capability to calculate aerosol behaviour in multicompartment volumes. Large discrepancies exist between the results from aerosol model calculations and measurements obtained from large scale integral tests. More validation with small scale experiments in accurately controlled thermalhydraulic conditions is needed (Jokiniemi, 1990). The objective of this work is to understand the reasons for observed large discrepancies between the results from model calculations and measurements carried out in large scale experiments (aerosol modelling, uncertainties in thermal-hydraulic conditions or measurements errors). In the first stage aerosol behaviour in a small well insulated and instrumented vessel (1.95 m 3) will be studied. In this vessel the thermal-hydraulic conditions will be accurately controlled together with known steam and aerosol injection rates. In these experiments different timing of well defined size distribution and composition of water soluble and insoluble aerosol injection rates will be studied. At known T-H conditions it is possible to minimize the feedback from thermalhydraulics to aerosols and to validate the aerosol models separately from T-H models. By varying relevant parameters (source particle size distribution and composition, T-H conditions) and by repeating each test it is possible to validate different mechanisms affecting aerosol behaviour, which is not possible in large scale integral experiments. In the quantitative aerosol characterisation tests state-of-the-art aerosol measurement systems will be used. Aerosol number and mass concentration will be measured continuously using CNC and TEOM mass monitor after drying the aerosol in a diffusion dryer. Particle size distribution and chemical composition will be analyzed by low pressure impactors (Hillamo and Kauppinen, 1991) in wet conditions. $253
$254
,l M. MAKYNEN et al.
INSTRUMENTATION Vessel gas and surface temperatures and pressurized air and steam temperatures are measured using resistance temperature detectors (accuracy 0.2 °C at 20 °C). Relative humidity is measured using 3 Vaisala Humicap detectors. Vessel and input line pressures and steam and air flows are also monitored continuously. Input air flow is filtered and dried. Particle concentration of the input air (concentration in the vessel measured using TSI 3020 CNC) is less than 0.5 particles/cm3 and relative humidity is less than 5 % at 20 ° C . It is also possible to control the vessel surface temperature using computer controlled heating cables. Input gas mixture temperature is regulated using heat exchanger. System control and data sampling is made using computer controlled HP 3852A Data Acquisition and Control Unit.
RESULTS OF THERMAL-HYDRAULIC TESTING
L,.,i~ malil ' T30H95
.+~,+,"L
f /
!
/
tile
(min)
Fig. 1: Example of thermal-hydraulic test results. Calculated and measured relative humidity as a function of time.
Results of the thermalhydraulic tests have been compared to the theoretical calculations made using C O ~ A I N computer code. Agreement o f the theoretical and experimental results was good. At the beginning of the test the vessel surface heating cable power was disconnected and air and steam flows were closed. Heat was flowing through the insulated vessel wall and temperature was decreasing causing slow increase in RH (Fig. 1).
AEROSOL MEASUREMENTS In these experiments the behaviour of the well defined size distribution and composition of water soluble and inert aerosol will be studied at different temperatures and relative humidities. In the quantitative aerosol characterisation tests state-of-the-art aerosol measurement systems will be used. Aerosol number and mass concentration will be measured continuously using Condensation Nucleus Counter (CNC) and TEOM mass monitor. Particle size distribution and chemical composition will be analyzed by Berner 11 stage low pressure impactors in the size range 0,03 15 lam aerodynamic diameter.
REFERENCES Jokiniemi, J. (1990), OECD/CSNI Report No. 176 pp. 27-51. Hillamo R.E. and Kauppinen E.I. (1991), Aerosol Sci. Technol. 14 pp. 33-47.
0021-8502/93 $6.00 + 0.00 Pergamon Press Ltd
21 P 05 AHMED: F A C I L I T Y T O S T U D Y H Y G R O S C O P I C AEROSOL BEHAVIOUR IN LWR CONTAINMENT C O N D I T I O N S J. M. M~ikynen, J. K. Jokiniemi, A. Silde and E. I. Kauppinen ~ Technical Research Centre Of Finland, Aerosol Technology Group, Nuclear Engineering Laboratory, tLaboratory of Heating and Ventilation, Betonimiehenkuja 5, FIN-02150 Espoo, Finland
KEYWORDS hygroscopic particles, aerosol modelling, LWR reactor accidents
INTRODUCTION AHMED (Aerosol and H__eat Transfer Measurement Device) has been constructed to study thermal-hydraulic effects on aerosol behaviour in nuclear power station containment during a hypothetical severe reactor accident where the reactor core melts and releases radioactive aerosols into containment. In wet conditions steam condensation on particles, coupled with agglomeration, can provide much more effective particle growth mechanism than dry agglomeration alone. The growth is enhanced because the aerosol released from the core contains hygroscopic material which absorbs water under 100 % relative humidity. Under favourable conditions particles may grow to sizes larger than 10 lam. These particles will settle rapidly, after which a small fi'action of micron-sized (or smaller) particles remains airborne. Our ability to model quantitatively the effect of steam condensation on particles depends strongly on both thermal-hydraulic and aerosol modelling. It is also important to have the capability to calculate aerosol behaviour in multicompartment volumes. Large discrepancies exist between the results from aerosol model calculations and measurements obtained from large scale integral tests. More validation with small scale experiments in accurately controlled thermalhydraulic conditions is needed (Jokiniemi, 1990). The objective of this work is to understand the reasons for observed large discrepancies between the results from model calculations and measurements carried out in large scale experiments (aerosol modelling, uncertainties in thermal-hydraulic conditions or measurements errors). In the first stage aerosol behaviour in a small well insulated and instrumented vessel (1.95 m 3) will be studied. In this vessel the thermal-hydraulic conditions will be accurately controlled together with known steam and aerosol injection rates. In these experiments different timing of well defined size distribution and composition of water soluble and insoluble aerosol injection rates will be studied. At known T-H conditions it is possible to minimize the feedback from thermalhydraulics to aerosols and to validate the aerosol models separately from T-H models. By varying relevant parameters (source particle size distribution and composition, T-H conditions) and by repeating each test it is possible to validate different mechanisms affecting aerosol behaviour, which is not possible in large scale integral experiments. In the quantitative aerosol characterisation tests state-of-the-art aerosol measurement systems will be used. Aerosol number and mass concentration will be measured continuously using CNC and TEOM mass monitor after drying the aerosol in a diffusion dryer. Particle size distribution and chemical composition will be analyzed by low pressure impactors (Hillamo and Kauppinen, 1991) in wet conditions. $253
$254
,l M. MAKYNEN et al.
INSTRUMENTATION Vessel gas and surface temperatures and pressurized air and steam temperatures are measured using resistance temperature detectors (accuracy 0.2 °C at 20 °C). Relative humidity is measured using 3 Vaisala Humicap detectors. Vessel and input line pressures and steam and air flows are also monitored continuously. Input air flow is filtered and dried. Particle concentration of the input air (concentration in the vessel measured using TSI 3020 CNC) is less than 0.5 particles/cm3 and relative humidity is less than 5 % at 20 ° C . It is also possible to control the vessel surface temperature using computer controlled heating cables. Input gas mixture temperature is regulated using heat exchanger. System control and data sampling is made using computer controlled HP 3852A Data Acquisition and Control Unit.
RESULTS OF THERMAL-HYDRAULIC TESTING
L,.,i~ malil ' T30H95
.+~,+,"L
f /
!
/
tile
(min)
Fig. 1: Example of thermal-hydraulic test results. Calculated and measured relative humidity as a function of time.
Results of the thermalhydraulic tests have been compared to the theoretical calculations made using C O ~ A I N computer code. Agreement o f the theoretical and experimental results was good. At the beginning of the test the vessel surface heating cable power was disconnected and air and steam flows were closed. Heat was flowing through the insulated vessel wall and temperature was decreasing causing slow increase in RH (Fig. 1).
AEROSOL MEASUREMENTS In these experiments the behaviour of the well defined size distribution and composition of water soluble and inert aerosol will be studied at different temperatures and relative humidities. In the quantitative aerosol characterisation tests state-of-the-art aerosol measurement systems will be used. Aerosol number and mass concentration will be measured continuously using Condensation Nucleus Counter (CNC) and TEOM mass monitor. Particle size distribution and chemical composition will be analyzed by Berner 11 stage low pressure impactors in the size range 0,03 15 lam aerodynamic diameter.
REFERENCES Jokiniemi, J. (1990), OECD/CSNI Report No. 176 pp. 27-51. Hillamo R.E. and Kauppinen E.I. (1991), Aerosol Sci. Technol. 14 pp. 33-47.