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A measurement method for density of HTR coated fuel particles porous pyrocarbon layer
Nuclear Engineering and Design 271 (2014) 250–252
Contents lists available at ScienceDirect
Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes
A measurement method for density of HTR coated fuel particles porous pyrocarbon layer Hongsheng Zhao ∗ , Xiaoxue Liu, Ziqiang Li, Kaihong Zhang, Chunhe Tang Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, China
a r t i c l e
i n f o
Article history: Received 28 December 2012 Accepted 9 January 2013
a b s t r a c t The density of porous pyrocarbon layer of coated fuel particles is one of the important parameters of the coated fuel particles. It directly affects the performance of fuel elements. A measurement method, particle size analyzer method, to analyze the density of porous pyrocarbon was developed, and the standard uncertainty of this method was analyzed. Results showed that the particle size analyzer method has the advantages of fast measurement, large sampling number and high measurement accuracy. This method is very efficient for engineering application and is a promising candidate method to measure the density of porous pyrocarbon of coated fuel particles. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Pebble bed high temperature gas cooled reactor is one type of high temperature gas cooled reactors (HTR). It has been considered as one of the most promising advanced nuclear energy systems because of its inherent safety features (Sawa and Ueta, 2004; Ueta et al., 2011). The safety of pebble bed-type HTR is based on the quality of the spherical fuel elements each containing tens of thousands of coated fuel particles. Currently, HTGR employs TriIsotropic (TRISO) coated particles with diameter of around 1 mm. As shown in Fig. 1, TRISO fuel particles consist of a micro spherical kernel of uranium dioxide (UO2 ), coating layers of porous pyrolytic carbon (buffer), inner dense pyrolytic carbon (IPyC), silicon carbide (SiC) and outer dense pyrolytic carbon (OPyC) (Zhao et al., 2006, 2010). The principal functions of these coating layers are to retain fission products within the particles. The porous pyrolytic carbon coating layer provides the storage space for the fission gas to keep the inner pressure in a certain range, controlling the kernel expansion during the fission process and preventing the inner dense pyrolytic carbon from the damage of the nuclear fission fragments. The SiC coating layer acts as a barrier against the diffusive release of metallic fission products and provides mechanical strength for the particles. The inner and outer dense pyrolytic carbon layers protect the SiC coating layer and stop release of fission product. The parameters of coated fuel particles are very important to the safe operation of a pebble bed high temperature gas-cooled reactor. The porous pyrocarbon layer density of coated fuel particles is one of the important parameters of coated fuel particle. It directly
∗ Corresponding author. Tel.: +86 10 89796090. E-mail address: [email protected] (H. Zhao). 0029-5493/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nucengdes.2013.11.040
affects the performance of coated fuel particles and fuel elements. Therefore, it is of great significance to measure the density of each coating layer rapidly and accurately. The porous pyrocarbon layer is loose, coating on UO2 kernel with density about 10 times of buffer layer. The irregular shape, loose and porous properties of porous pyrocarbon layer determine conventional analytical methods are unavailable. In this paper, the particle size analyzer method to analyze the density of porous pyrocarbon layer is introduced. 2. The description of particle size analyzer method Particle size analyzer method is a method to measure the density of pyrocarbon by particle size analyzer and microbalance. 2.1. Instrument description The microbalance was used to weigh the mass of coating particles and kernel particles. The sensitivity of microbalance should be no more than 1 g. As shown in Fig. 2, particle size analyzer consists of light source, dispersion system, high-speed imaging system and image analysis system. Besides, a specially designed infrared counter is installed between the dispersion system and the imaging system to count the number of the particles. During measurement, samples were dispersed by the dispersion system, and then went through the counter and imaging system in sequence. The number of the particles was gained when the particles went through the counter. And images of the particles were obtained when the particles went through the imaging system. After the measurement, the particle information including mean diameter, maximum diameter, and minimum diameter would be measured from the images by the image analysis system. The
H. Zhao et al. / Nuclear Engineering and Design 271 (2014) 250–252
251
Fig. 1. Metallographic photo of TRISO fuel particle.
standard deviation was also calculated from the measurement results. Base on the number of the particles tested by the particle size analyzer and the mass of the particles weighed by microbalance, the single head weight of kernel particles and coated particles could be calculated, respectively. 2.2. Principle of method
Fig. 3. Images of kernel particles and coated particles. (a) Image of kernel particles, (b) image of coated particles.
The formula for calculating the density of coating layer is as follows:
3. Experimental
=
¯ 0) ¯ 1−m 6(m
(1)
· (ϕ ¯ 13 − ϕ ¯ 03 )
where is the coating layer density of coated particles (g cm−3 ); ¯ 0 and m ¯ 1 are the mass of each particle before and after coating, m respectively (g); ϕ ¯ 0 and ϕ ¯ 1 are the average diameters of particles before and after coating, respectively (cm). As shown in formula (1), the four key parameters to be measured are average volume and individual mass of coated particles as well as average volume and average individual mass of kernel particles. The average volume of coated particles and average volume of kernel particles are calculated from the diameter of coated particles and kernel particles measured by particle size analyzer. The individual mass of coated particles and kernel particles are respectively calculated from the numbers measured by particles size analyzer and the mass shown on the microbalance. The images of particles are automatically acquired by the image system of the particle size analyzer. The images of coated particles and kernel particles were shown in Fig. 3(a) and (b). The particle dimension information is gained through the analysis of images by the image analysis system. Using the particle size analyzer to measure the diameters of the particles has the advantages of fast and efficient measurement, large sampling number. Thousands of particles could be tested in 30 min. Thereby, the particle size analyzer method was a promising candidate method to analyze the density of porous pyrocarbon of HTR coated fuel particles.
Using the particle size analyzer to analyze the density of porous pyrocarbon, the average results of a batch of particles could be obtained. The measurement repeatability and standard uncertainty were investigated. The coated particles with ZrO2 as kernel and porous pyrocarbon as coating layer were taken as the samples. 3.1. Measurement repeatability Three groups of coated particles and ten groups of kernel particles were extracted from the same batch to evaluate measurement repeatability. And each group of samples was weighed by microbalance. Then, the samples were measured by the particles size analyzer. Finally, the individual weight and average volume were calculated by combining sample weight shown on microbalance with the other measurement results of particle size analyzer. The mean mass and volume of coated particles was average value of three groups of coated particle samples. The individual mass and volume of kernel particles were the result of each kernel sample. As shown in Table 1, both single head weigh and single head volume exhibit good reproducibility. Standard deviation of ten times measurements is very small. The average value of individual mass and diameter were 0.685 mg and 505 m, respectively. While the standard deviations of individual mass and diameter were 0.001 mg and 1 m, respectively. The calculation results of porous pyrocarbon density were also similar. The average density was
Dispersion System Imaging System Light Source
Infrared Counter
Particle Flow Fig. 2. Schematic drawing for systems of particle size analyzer.
Analysis System
252
H. Zhao et al. / Nuclear Engineering and Design 271 (2014) 250–252
Table 1 Accuracy of measurement for density of porous pyrocarbon by particle size analysis method. Series 1 2 3 4 5 6 7 8 9 10
¯ 1 (mg) m 0.8100
Average value Standard deviation
– –
ϕ ¯ 1 (m)
¯ 0 (mg) m
ϕ ¯ 0 (m)
(g cm−3 )
725
0.686 0.683 0.686 0.684 0.687 0.683 0.687 0.684 0.686 0.684
507 504 505 505 505 504 505 504 506 504
0.95 0.96 0.95 0.96 0.93 0.96 0.94 0.96 0.94 0.95
0.685 0.001
505 1
0.95 0.01
– –
Table 2 Accuracy of measurement for density of porous pyrocarbon by particle size analysis method. Series
(g cm−3 )
Standard deviation (g cm−3 )
0.95 0.94 0.93 0.84 0.93
0.01 0.02 0.02 0.01 0.01
measurement result. The less standard uncertainty means more concentrated measurement results. The result of five times measurement for the same sample was shown in Table 3. The average diameter of coated particles was 711 m, and the standard deviation was 0.4 m. While the average diameter of kernel particles was 532 m and the standard deviation was 0.5 m. Based on the accuracy of counter and microbalance, the single microsphere mass for five times measurement was the same. The calculated density values were also similar. The average density value was 0.84 g cm−3 and the standard deviation of the density was 0.004 g cm−3 . Low standard uncertainty shows good accuracy of the particle size analyzer method. 4. Conclusions The particles size analyzer method was developed to measure the density of porous pyrocarbon for HTR coated particles.
Series
ϕ ¯ 1 (m)
ϕ ¯ 0 (m)
¯ 1 (mg) m
¯ 0 (mg) m
(g cm−3 )
(1) The particle size analyzer method is a fast and efficient method. Thousands of particles could be tested in 30 min. This method can meet the requirement of online detection. (2) The particle size analyzer method has high accuracy, good measurement reproducibility and low standard uncertainty. For sample with density about 0.95 g cm−3 , the standard deviation of ten samples from the same batch was 0.01 g cm−3 . For sample with density of 0.84 g cm−3 , the standard deviation of five times repeated measurements for the same sample was 0.004 g cm−3 .
1 2 3 4 5 Average value Standard deviation
712 711 711 711 711 711 0.4
531 532 532 531 532 532 0.5
0.5047 0.5047 0.5047 0.5047 0.5047 0.5047 0
0.455 0.455 0.455 0.455 0.455 0.455 0
0.83 0.84 0.85 0.84 0.84 0.84 0.004
The particle size analyzer method is a promising candidate method to measure the density of porous pyrocarbon. This method has the advantage of fast and efficient measurement, large sampling number and high measurement accuracy. It is very efficient for engineering application.
1 2 3 4 5
Table 3 Standard uncertainty of particle size analyzer method.
0.95 g cm−3 , and the standard deviation of the above density was 0.01 g cm−3 . Thereby, the particle size analyzer method has good measurement reproducibility. For the samples with density about 0.95 g cm−3 , the standard deviation of ten samples from the same batch was 0.01 g cm−3 . For further investigation of measurement reproducibility, five batches of samples were measured by particles size analyzer method. As shown in Table 2, all of the standard deviations for 5 batches samples were no more than 0.02 g cm−3 . The smaller standard deviation data indicates good measurement reproducibility of the particle size analyzer method. 3.2. Standard uncertainty Standard uncertainty is the measurement uncertainty represented by standard deviations. It shows the dispersion of
Acknowledgement This work has been supported by the National S&T Major Project (Grant No. ZX06901). References Sawa, K., Ueta, S., 2004. Research and development on HTGR fuel in the HTTR project. Nuclear Engineering and Design 163, 233. Ueta, S., Aihara, J., Sawa, K., Yasuda, A., Honda, M., Furihata, N., 2011. Development of high temperature gas-cooled reactor (HTGR) fuel in Japan. Process in Nuclear Energy 788, 53. Zhao, H.S., Liang, T.X., Zhang, J., He, J., Zou, Y.W., Tang, C.H., 2006. Manufacture and characteristics of spherical fuel elements for HTR-10. Nuclear Engineering and Design 236 (5–6), 643. Zhao, H.S., Liu, B., Zhang, K.H., Tang, C.H., 2010. Microstructure research of zirconium carbide layer for HTR coated particle by zirconium chloride vapor method. In: 5th International Topical Meeting on High Temperature Reactor Technology, Czech Republic Prague, October 18–20.
Contents lists available at ScienceDirect
Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes
A measurement method for density of HTR coated fuel particles porous pyrocarbon layer Hongsheng Zhao ∗ , Xiaoxue Liu, Ziqiang Li, Kaihong Zhang, Chunhe Tang Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, China
a r t i c l e
i n f o
Article history: Received 28 December 2012 Accepted 9 January 2013
a b s t r a c t The density of porous pyrocarbon layer of coated fuel particles is one of the important parameters of the coated fuel particles. It directly affects the performance of fuel elements. A measurement method, particle size analyzer method, to analyze the density of porous pyrocarbon was developed, and the standard uncertainty of this method was analyzed. Results showed that the particle size analyzer method has the advantages of fast measurement, large sampling number and high measurement accuracy. This method is very efficient for engineering application and is a promising candidate method to measure the density of porous pyrocarbon of coated fuel particles. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Pebble bed high temperature gas cooled reactor is one type of high temperature gas cooled reactors (HTR). It has been considered as one of the most promising advanced nuclear energy systems because of its inherent safety features (Sawa and Ueta, 2004; Ueta et al., 2011). The safety of pebble bed-type HTR is based on the quality of the spherical fuel elements each containing tens of thousands of coated fuel particles. Currently, HTGR employs TriIsotropic (TRISO) coated particles with diameter of around 1 mm. As shown in Fig. 1, TRISO fuel particles consist of a micro spherical kernel of uranium dioxide (UO2 ), coating layers of porous pyrolytic carbon (buffer), inner dense pyrolytic carbon (IPyC), silicon carbide (SiC) and outer dense pyrolytic carbon (OPyC) (Zhao et al., 2006, 2010). The principal functions of these coating layers are to retain fission products within the particles. The porous pyrolytic carbon coating layer provides the storage space for the fission gas to keep the inner pressure in a certain range, controlling the kernel expansion during the fission process and preventing the inner dense pyrolytic carbon from the damage of the nuclear fission fragments. The SiC coating layer acts as a barrier against the diffusive release of metallic fission products and provides mechanical strength for the particles. The inner and outer dense pyrolytic carbon layers protect the SiC coating layer and stop release of fission product. The parameters of coated fuel particles are very important to the safe operation of a pebble bed high temperature gas-cooled reactor. The porous pyrocarbon layer density of coated fuel particles is one of the important parameters of coated fuel particle. It directly
∗ Corresponding author. Tel.: +86 10 89796090. E-mail address: [email protected] (H. Zhao). 0029-5493/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nucengdes.2013.11.040
affects the performance of coated fuel particles and fuel elements. Therefore, it is of great significance to measure the density of each coating layer rapidly and accurately. The porous pyrocarbon layer is loose, coating on UO2 kernel with density about 10 times of buffer layer. The irregular shape, loose and porous properties of porous pyrocarbon layer determine conventional analytical methods are unavailable. In this paper, the particle size analyzer method to analyze the density of porous pyrocarbon layer is introduced. 2. The description of particle size analyzer method Particle size analyzer method is a method to measure the density of pyrocarbon by particle size analyzer and microbalance. 2.1. Instrument description The microbalance was used to weigh the mass of coating particles and kernel particles. The sensitivity of microbalance should be no more than 1 g. As shown in Fig. 2, particle size analyzer consists of light source, dispersion system, high-speed imaging system and image analysis system. Besides, a specially designed infrared counter is installed between the dispersion system and the imaging system to count the number of the particles. During measurement, samples were dispersed by the dispersion system, and then went through the counter and imaging system in sequence. The number of the particles was gained when the particles went through the counter. And images of the particles were obtained when the particles went through the imaging system. After the measurement, the particle information including mean diameter, maximum diameter, and minimum diameter would be measured from the images by the image analysis system. The
H. Zhao et al. / Nuclear Engineering and Design 271 (2014) 250–252
251
Fig. 1. Metallographic photo of TRISO fuel particle.
standard deviation was also calculated from the measurement results. Base on the number of the particles tested by the particle size analyzer and the mass of the particles weighed by microbalance, the single head weight of kernel particles and coated particles could be calculated, respectively. 2.2. Principle of method
Fig. 3. Images of kernel particles and coated particles. (a) Image of kernel particles, (b) image of coated particles.
The formula for calculating the density of coating layer is as follows:
3. Experimental
=
¯ 0) ¯ 1−m 6(m
(1)
· (ϕ ¯ 13 − ϕ ¯ 03 )
where is the coating layer density of coated particles (g cm−3 ); ¯ 0 and m ¯ 1 are the mass of each particle before and after coating, m respectively (g); ϕ ¯ 0 and ϕ ¯ 1 are the average diameters of particles before and after coating, respectively (cm). As shown in formula (1), the four key parameters to be measured are average volume and individual mass of coated particles as well as average volume and average individual mass of kernel particles. The average volume of coated particles and average volume of kernel particles are calculated from the diameter of coated particles and kernel particles measured by particle size analyzer. The individual mass of coated particles and kernel particles are respectively calculated from the numbers measured by particles size analyzer and the mass shown on the microbalance. The images of particles are automatically acquired by the image system of the particle size analyzer. The images of coated particles and kernel particles were shown in Fig. 3(a) and (b). The particle dimension information is gained through the analysis of images by the image analysis system. Using the particle size analyzer to measure the diameters of the particles has the advantages of fast and efficient measurement, large sampling number. Thousands of particles could be tested in 30 min. Thereby, the particle size analyzer method was a promising candidate method to analyze the density of porous pyrocarbon of HTR coated fuel particles.
Using the particle size analyzer to analyze the density of porous pyrocarbon, the average results of a batch of particles could be obtained. The measurement repeatability and standard uncertainty were investigated. The coated particles with ZrO2 as kernel and porous pyrocarbon as coating layer were taken as the samples. 3.1. Measurement repeatability Three groups of coated particles and ten groups of kernel particles were extracted from the same batch to evaluate measurement repeatability. And each group of samples was weighed by microbalance. Then, the samples were measured by the particles size analyzer. Finally, the individual weight and average volume were calculated by combining sample weight shown on microbalance with the other measurement results of particle size analyzer. The mean mass and volume of coated particles was average value of three groups of coated particle samples. The individual mass and volume of kernel particles were the result of each kernel sample. As shown in Table 1, both single head weigh and single head volume exhibit good reproducibility. Standard deviation of ten times measurements is very small. The average value of individual mass and diameter were 0.685 mg and 505 m, respectively. While the standard deviations of individual mass and diameter were 0.001 mg and 1 m, respectively. The calculation results of porous pyrocarbon density were also similar. The average density was
Dispersion System Imaging System Light Source
Infrared Counter
Particle Flow Fig. 2. Schematic drawing for systems of particle size analyzer.
Analysis System
252
H. Zhao et al. / Nuclear Engineering and Design 271 (2014) 250–252
Table 1 Accuracy of measurement for density of porous pyrocarbon by particle size analysis method. Series 1 2 3 4 5 6 7 8 9 10
¯ 1 (mg) m 0.8100
Average value Standard deviation
– –
ϕ ¯ 1 (m)
¯ 0 (mg) m
ϕ ¯ 0 (m)
(g cm−3 )
725
0.686 0.683 0.686 0.684 0.687 0.683 0.687 0.684 0.686 0.684
507 504 505 505 505 504 505 504 506 504
0.95 0.96 0.95 0.96 0.93 0.96 0.94 0.96 0.94 0.95
0.685 0.001
505 1
0.95 0.01
– –
Table 2 Accuracy of measurement for density of porous pyrocarbon by particle size analysis method. Series
(g cm−3 )
Standard deviation (g cm−3 )
0.95 0.94 0.93 0.84 0.93
0.01 0.02 0.02 0.01 0.01
measurement result. The less standard uncertainty means more concentrated measurement results. The result of five times measurement for the same sample was shown in Table 3. The average diameter of coated particles was 711 m, and the standard deviation was 0.4 m. While the average diameter of kernel particles was 532 m and the standard deviation was 0.5 m. Based on the accuracy of counter and microbalance, the single microsphere mass for five times measurement was the same. The calculated density values were also similar. The average density value was 0.84 g cm−3 and the standard deviation of the density was 0.004 g cm−3 . Low standard uncertainty shows good accuracy of the particle size analyzer method. 4. Conclusions The particles size analyzer method was developed to measure the density of porous pyrocarbon for HTR coated particles.
Series
ϕ ¯ 1 (m)
ϕ ¯ 0 (m)
¯ 1 (mg) m
¯ 0 (mg) m
(g cm−3 )
(1) The particle size analyzer method is a fast and efficient method. Thousands of particles could be tested in 30 min. This method can meet the requirement of online detection. (2) The particle size analyzer method has high accuracy, good measurement reproducibility and low standard uncertainty. For sample with density about 0.95 g cm−3 , the standard deviation of ten samples from the same batch was 0.01 g cm−3 . For sample with density of 0.84 g cm−3 , the standard deviation of five times repeated measurements for the same sample was 0.004 g cm−3 .
1 2 3 4 5 Average value Standard deviation
712 711 711 711 711 711 0.4
531 532 532 531 532 532 0.5
0.5047 0.5047 0.5047 0.5047 0.5047 0.5047 0
0.455 0.455 0.455 0.455 0.455 0.455 0
0.83 0.84 0.85 0.84 0.84 0.84 0.004
The particle size analyzer method is a promising candidate method to measure the density of porous pyrocarbon. This method has the advantage of fast and efficient measurement, large sampling number and high measurement accuracy. It is very efficient for engineering application.
1 2 3 4 5
Table 3 Standard uncertainty of particle size analyzer method.
0.95 g cm−3 , and the standard deviation of the above density was 0.01 g cm−3 . Thereby, the particle size analyzer method has good measurement reproducibility. For the samples with density about 0.95 g cm−3 , the standard deviation of ten samples from the same batch was 0.01 g cm−3 . For further investigation of measurement reproducibility, five batches of samples were measured by particles size analyzer method. As shown in Table 2, all of the standard deviations for 5 batches samples were no more than 0.02 g cm−3 . The smaller standard deviation data indicates good measurement reproducibility of the particle size analyzer method. 3.2. Standard uncertainty Standard uncertainty is the measurement uncertainty represented by standard deviations. It shows the dispersion of
Acknowledgement This work has been supported by the National S&T Major Project (Grant No. ZX06901). References Sawa, K., Ueta, S., 2004. Research and development on HTGR fuel in the HTTR project. Nuclear Engineering and Design 163, 233. Ueta, S., Aihara, J., Sawa, K., Yasuda, A., Honda, M., Furihata, N., 2011. Development of high temperature gas-cooled reactor (HTGR) fuel in Japan. Process in Nuclear Energy 788, 53. Zhao, H.S., Liang, T.X., Zhang, J., He, J., Zou, Y.W., Tang, C.H., 2006. Manufacture and characteristics of spherical fuel elements for HTR-10. Nuclear Engineering and Design 236 (5–6), 643. Zhao, H.S., Liu, B., Zhang, K.H., Tang, C.H., 2010. Microstructure research of zirconium carbide layer for HTR coated particle by zirconium chloride vapor method. In: 5th International Topical Meeting on High Temperature Reactor Technology, Czech Republic Prague, October 18–20.