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24 O 02 Vapour release and particle formation from heated LWR fuel and control rod simulants
J. Aerosol Sci., Vol. 24. Suppl. 1, pp. $301-$302, 1993 Printed in Great Britain.
0021-8502/93 $6.00 + 0.00 Pergamon Press Ltd
24 O 02 VAPOUR RELEASE AND PARTICLE FORMATION FROM HEATED LWR FUEL AND CONTROL ROD SlMULANTS J. M. M~ikynen, E. I. Kauppinen I, J. K. Jokiniemi, T. M. Lind I , P. J. Bennett 2, A. M. Beard 2, J. Brunning 2, B. R. Bowsher 2
Technical Research Centre of Finland, Aerosol Technology Group, Nuclear Engineering Laboratory, mLaboratory of Heating and Ventilation, Betonimiehenkuja 5, FIN-02150 Espoo, Finland 2 AEA Technology, Reactor Chemistry Department, Winfrith Technology Centre, Dorchester, Dorset DT2 8DH, United Kingdom.
KEYWORDS aerosol formation, LWR fuel, LWR core damage
INTRODUCTION Aerosol formation mechanisms from in-vessel release in LWR core damage accidents are important when aerosol transport in the RCS is analyzed. However, currently there is only very limited information available on aerosol formation from in vessel releases. Vapour release rates and aerosol formation from heated LWR fuel and control rod simulants have been studied in the modified Falcon test facility (Beard et al, 1992). The simulant fuel samples consisted of UO 2 pellets in Zircaloy cladding. The pellets contained 8.84 mg of CsI, 56.94 mg of CsOH, 10.64 mg of Te, 21.66 mg of SrO, 34.42 mg of BaO and 55.80 mg of Mo in 18.6 g of UO 2. The composition of the control rod samples was 1.3 g 80% Ag-15% In-5% Cd in sections of 8.75 mm diameter stainless steel cladding.
EXPERIMENTAL A total of 16 tests were performed in which fuel and control rod samples were heated either separately or simultaneously in a 3%H20/He atmosphere using an induction furnace. The samples were placed in a silica vessel of height 14 cm and diameter 6 cm. The power of the induction furnace was increased in small steps according to a pre-defined heating programme. After the maximum value had been attained, the power was decreased in the same steps as used during the heatup stage. Filtered 3%H20/He carrier gas was introduced into the silica vessel below the sample at a flow rate of 5 lpm. The resulting fuel and control rod aerosols were transported along a 48 cm long, 2.5 cm diameter section of silica pipe to the aerosol analysis equipment. Four small holes were drilled through the fuel cladding in order to prevent abrupt failure of the cladding and to attain controlled and reproducible aerosol generation rates. In selected experiments an aqueous solution of boric acid was injected onto the fuel samples in order to study the effect of this species on the fuel aerosol. Aerosol instrumentation included an aerosol neutralizer, a TSI 3020 Condensation Nucleus Counter (continuous number concentration), Tapered Element Oscillating Microbalance (continuous mass concentration; time resolution 1.67 seconds), Berner Low Pressure Impactors, TSI Electrostatic Aerosol Sampler for SEM samples and necessary dilution systems. The sample temperature was monitored using a pyrometer. During the tests the TEOM and CNC were operated continuously and it was possible to collect three separate impactor samples during each test. $301
$302
1 M. M,41<',N~N et al,
The Berner low pressure impactor has 11 stages with the aerodynamic cut diameters in the particle size range of 0.03-16 lam. Particles were sampled onto Nuclepore Polycarbonate foils greased with Apiezon L vacuum grease using the method of Hillamo and Kauppinen (1991). Films were analyzed gravimetrically. In addition one quarter of the foil from each stage was washed with 25 cm 3 nitric acid and analysed using ICPOES. XPS and XRD analyses were made for selected TEOM filters.
RESULTS AND DISCUSSION Typical release from the control rod samples (Fig. 1) consisted of 2 peaks of short duration and large magnitude followed by a continuous release of much lower magnitude. It was not possible to predict the heights and occurrence times of these peaks. The release from the fuel samples
7000'
E E
CONTI~ ,3L ROD RELE.~ ~E 6000. 5000. 4000. 3000 2000 1000 0 -1000
0 10 20 30 min 40 Fig. 1: Typical TEOM result for the mass concentration of the aerosol as the function of heating time. contained no abrupt peaks, but a smooth release over a period of approximately 20 min. Cd dominated the release from the control rod simulant at the beginning of the heating period whilst later during the heating period, when the generation rate was lower, particles contained large fractions of Ag and In. In the control rod release the first peak is believed to be due to the pin holes formed in the stainless steel cladding and the second peak corresponds to the physical failure of the control rod. Cs and I dominated the release from the fuel rod simulants. This release was smooth due to the holes drilled in the Zircaloy cladding and the release was controlled by diffusion inside the fuel rod UO 2 matrix. The particle size distribution was a function of the vapour release rate. When the release rate was high, the particle mean size was larger than during low release rates.
REFERENCES Beard A. M., Bennett P. J. , Bowsher B. R. and Brunning J. (1992), J. Aerosol Sci. 23 SI pp. 831-834 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
24 O 02 VAPOUR RELEASE AND PARTICLE FORMATION FROM HEATED LWR FUEL AND CONTROL ROD SlMULANTS J. M. M~ikynen, E. I. Kauppinen I, J. K. Jokiniemi, T. M. Lind I , P. J. Bennett 2, A. M. Beard 2, J. Brunning 2, B. R. Bowsher 2
Technical Research Centre of Finland, Aerosol Technology Group, Nuclear Engineering Laboratory, mLaboratory of Heating and Ventilation, Betonimiehenkuja 5, FIN-02150 Espoo, Finland 2 AEA Technology, Reactor Chemistry Department, Winfrith Technology Centre, Dorchester, Dorset DT2 8DH, United Kingdom.
KEYWORDS aerosol formation, LWR fuel, LWR core damage
INTRODUCTION Aerosol formation mechanisms from in-vessel release in LWR core damage accidents are important when aerosol transport in the RCS is analyzed. However, currently there is only very limited information available on aerosol formation from in vessel releases. Vapour release rates and aerosol formation from heated LWR fuel and control rod simulants have been studied in the modified Falcon test facility (Beard et al, 1992). The simulant fuel samples consisted of UO 2 pellets in Zircaloy cladding. The pellets contained 8.84 mg of CsI, 56.94 mg of CsOH, 10.64 mg of Te, 21.66 mg of SrO, 34.42 mg of BaO and 55.80 mg of Mo in 18.6 g of UO 2. The composition of the control rod samples was 1.3 g 80% Ag-15% In-5% Cd in sections of 8.75 mm diameter stainless steel cladding.
EXPERIMENTAL A total of 16 tests were performed in which fuel and control rod samples were heated either separately or simultaneously in a 3%H20/He atmosphere using an induction furnace. The samples were placed in a silica vessel of height 14 cm and diameter 6 cm. The power of the induction furnace was increased in small steps according to a pre-defined heating programme. After the maximum value had been attained, the power was decreased in the same steps as used during the heatup stage. Filtered 3%H20/He carrier gas was introduced into the silica vessel below the sample at a flow rate of 5 lpm. The resulting fuel and control rod aerosols were transported along a 48 cm long, 2.5 cm diameter section of silica pipe to the aerosol analysis equipment. Four small holes were drilled through the fuel cladding in order to prevent abrupt failure of the cladding and to attain controlled and reproducible aerosol generation rates. In selected experiments an aqueous solution of boric acid was injected onto the fuel samples in order to study the effect of this species on the fuel aerosol. Aerosol instrumentation included an aerosol neutralizer, a TSI 3020 Condensation Nucleus Counter (continuous number concentration), Tapered Element Oscillating Microbalance (continuous mass concentration; time resolution 1.67 seconds), Berner Low Pressure Impactors, TSI Electrostatic Aerosol Sampler for SEM samples and necessary dilution systems. The sample temperature was monitored using a pyrometer. During the tests the TEOM and CNC were operated continuously and it was possible to collect three separate impactor samples during each test. $301
$302
1 M. M,41<',N~N et al,
The Berner low pressure impactor has 11 stages with the aerodynamic cut diameters in the particle size range of 0.03-16 lam. Particles were sampled onto Nuclepore Polycarbonate foils greased with Apiezon L vacuum grease using the method of Hillamo and Kauppinen (1991). Films were analyzed gravimetrically. In addition one quarter of the foil from each stage was washed with 25 cm 3 nitric acid and analysed using ICPOES. XPS and XRD analyses were made for selected TEOM filters.
RESULTS AND DISCUSSION Typical release from the control rod samples (Fig. 1) consisted of 2 peaks of short duration and large magnitude followed by a continuous release of much lower magnitude. It was not possible to predict the heights and occurrence times of these peaks. The release from the fuel samples
7000'
E E
CONTI~ ,3L ROD RELE.~ ~E 6000. 5000. 4000. 3000 2000 1000 0 -1000
0 10 20 30 min 40 Fig. 1: Typical TEOM result for the mass concentration of the aerosol as the function of heating time. contained no abrupt peaks, but a smooth release over a period of approximately 20 min. Cd dominated the release from the control rod simulant at the beginning of the heating period whilst later during the heating period, when the generation rate was lower, particles contained large fractions of Ag and In. In the control rod release the first peak is believed to be due to the pin holes formed in the stainless steel cladding and the second peak corresponds to the physical failure of the control rod. Cs and I dominated the release from the fuel rod simulants. This release was smooth due to the holes drilled in the Zircaloy cladding and the release was controlled by diffusion inside the fuel rod UO 2 matrix. The particle size distribution was a function of the vapour release rate. When the release rate was high, the particle mean size was larger than during low release rates.
REFERENCES Beard A. M., Bennett P. J. , Bowsher B. R. and Brunning J. (1992), J. Aerosol Sci. 23 SI pp. 831-834 Hillamo, R, E. and Kauppinen, E. I. (1991), Aerosol Sci. Technol. 14 pp. 33-47