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Neutronic and thermal estimation of blanket in-pile mockup with Li2TiO3 pebbles
Fusion Engineering and Design 58 – 59 (2001) 673– 678 www.elsevier.com/locate/fusengdes
Neutronic and thermal estimation of blanket in-pile mockup with Li2TiO3 pebbles Y. Nagao *, M. Nakamichi, K. Tsuchiya, H. Kawamura Oarai Research Establishment, Japan Atomic Energy Research Institute, Narita, Oarai-machi, Higashi-ibaraki-gun, Ibaraki-ken 311 -1394, Japan
Abstract To evaluate exactly temperature distribution in large volume of tritium breeding materials during the blanket in-pile tests with the JMTR, neutronic and thermal calculations were conducted by using Monte Carlo code ‘MCNP’ with nuclear cross section library of ‘FSXLIBJ3R2’ and the transient and steady-state distribution code ‘TRUMP’. From the results of preliminary estimation of temperature distribution in the blanket in-pile mockup, the calculated values were 24–28% higher than the measured values. One of the reasons is due to overestimation of calculated thermal neutron flux. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Li2TiO3 pebbles; Neutronic and thermal estimation; Tritium breeding materials
1. Introduction A Tritium breeding blanket, whose purposes are to breed tritium and to utilize thermal energy, is indispensable to a fusion reactor. Lithium titanate (Li2TiO3) is one of the candidates for the tritium breeding material. In general, a local temperature in small volume of the packing region with tritium breeding materials has been measured by thermocouples in various irradiation tests. However, temperature distribution in large volume of the packing region with tritium breeding materials has not been measured at the in-site irradiation tests [1]. * Corresponding author. Tel.: + 81-29-264-8756; fax: + 8129-264-8400. E-mail address: [email protected] (Y. Nagao).
On the other hand, the evaluation of temperature distribution in large volume of the packing region with tritium breeding materials is indispensable to design fusion blanket. Therefore, in order to measure temperature distribution in Li2TiO3 pebbles packing region and evaluate the effects of irradiation temperature, hydrogen content in sweep gas and sweep gas flow rate on tritium release from Li2TiO3 pebbles packing region under neutron irradiation, an integrated irradiation test of the in-pile mockup has been carried out using the JMTR (Japan Materials Testing Reactor) [2–6]. For this test, the neutronic and thermal estimation in the in-pile mockup with Li2TiO3 pebbles have been carried out with the Monte Carlo code MCNP [7] and the transient and steady-state distribution code TRUMP [8], respectively. In this
0920-3796/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 1 ) 0 0 5 2 5 - 7
674
Y. Nagao et al. / Fusion Engineering and Design 58–59 (2001) 673–678
paper, the results of comparison between measured and calculated temperature in the Li2TiO3 pebbles packing region were reported.
lium pebbles packing region. The arrangement of the thermocouples was shown in Fig. 1(b). Thirtythree thermocouples were installed inside the inpile mockup (¥ 40× 260 mm2).
2. Experiment and calculation
2.2. Irradiation test
2.1. Blanket in-pile mockup
The JMTR is a tank-in-pool type reactor with thermal power of 50 MW and both coolant and moderator are light water. The typical core configuration was shown in Fig. 2. The reactor core, which is 1560 mm in diameter and 750 mm in effective height, consists of fuel elements, control rod, reflectors and H-shaped beryllium frame. The reactor core has 204 irradiation holes. Each reflector element has irradiation hole, which is loaded with a capsule for irradiation tests or a solid plug of the same material as the reflector element. The H-shaped beryllium frame has also irradiation holes. The in-pile mock-up was loaded at L-3 and K-2 hole in JMTR, and was irradiated in the 121– 129th operating cycles (about 225 days).
The schematic of the in-pile mock-up on tritium breeding blanket of fusion reactor was shown in Fig. 1. The construction of the in-pile mock-up simulates multi-layer typed blanket. Li2TiO3 pebbles and Beryllium pebbles are packed in 1st and 2nd layer, respectively. The size of packing region is 260 mm in length, 20 mm in 1st layer diameter and 40 mm in 2nd layer diameter. The diameter and weight of Li2TiO3 pebbles were 1 mm and 134 g, respectively. The packing fraction of Li2TiO3 pebbles was about 62%. Additionally, Beryllium pebbles were packed outside the Li2TiO3 pebbles packing region. The thermocouples were installed in the Li2TiO3 and the beryl-
Fig. 1. Preliminary in-pile mockup and arrangement of thermocouples.
Y. Nagao et al. / Fusion Engineering and Design 58–59 (2001) 673–678
675
Fig. 2. Typical core configuration of JMTR.
2.3. Calculation Neutronic calculations were done in 3-D geometry with the Monte Carlo code MCNP4B using continuous energy cross section library FSXLIBJ3R2 [9] (proceeded from JENDL3.2). The code and cross section library have been used to evaluate local neutron spectral for various capsule at positions in other previously irradiation tests of the JMTR. The core configuration of 128th operating cycle was modeled and partial and whole core of the JMTR include the blanket in-pile mock-up was described in detail. For the whole core model, the distribution of neutron and gamma heating rate in the blanket in-pile mockup was calculated by using KCODE option in MCNP4B. The MCNP model of the blanket in-pile mock-up was shown in Fig. 3. For the partial core model, the heating rates were calculated by using fixed source option with the surface source, which was calculated by the whole core model. The partial core model was mainly used for parametric calculations such as radial length or vertical position in the test section.
Thermal calculations were done in 3-D geometry with the transient and steady-state distribution code TRUMP using calculated neutron and gamma heating rates, and the blanket in-pile mockup was modeled in detail. The thermal conductivity of beryllium beds was used due to Yagi and Kunii’s formula.
3. Results and discussion Measured and calculated centerline temperature are tabulated in Table 1. The measured centerline temperature of the test section were 500 °C at heater power ‘ON’ condition and 402 °C at heater power ‘OFF’ condition in L-3 hole at 50 MW operation, and the measured centerline temperature in K-2 hole was 310 °C at heater ‘OFF’ condition. The ratio of calculated value and measured one (C/M) on centerline temperature were 1.24– 1.28. The heating rate of (n, alpha) reaction in Li2TiO3 pebbles was about ten times larger than gamma heating in other structural materials (see Table 2) in the blanket in-pile mockup. The
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Y. Nagao et al. / Fusion Engineering and Design 58–59 (2001) 673–678
heating rate of (n, alpha) reaction depends on thermal neutron flux in fission reactor such as the JMTR. Fig. 4 shows comparison of measured and calculated temperature distribution in B-Section (see Fig. 1-(b)). Concerning of calculated temperature, to adjust differences of measured and calculated values by change of input data of (n, alpha) heating, calculated temperature distribution was good agreement with measured one as (n, alpha) heating values was multiplied by 0.7. In the
present status of thermal neutron flux evaluation, calculated values tend to overestimate measured values by + 30% [10,11]. Therefore, one of the reasons for overestimation of calculated centerline temperature is due to accuracy of thermal neutron flux evaluation. The neutronic calculations by Monte Carlo method have long calculation time. Therefore, modeling technique in geometry was examined. Fig. 5 shows temperature distribution by nuclear
Fig. 3. MCNP model of in-pile mock-up. Table 1 Centerline temperature of the test section Irradiation hole
L-3 L-3 K-2
Heater
ON OFF OFF
Centerline temperarture
C/M
Measurement (M)
Calculation (C)
500 402 310
642 497 390
1.28 1.24 1.26
Y. Nagao et al. / Fusion Engineering and Design 58–59 (2001) 673–678
677
Table 2 Calculation results of neutron and gamma heating (L-3 hole) Region
Heating rate [W/g]
Li2TiO3 pebbles SS316 inner container Be pebbles SS316 outer container Al thermal conducter SS316 outertube
4.37 0.40 0.17 0.41 0.32 0.42
Fig. 5. Comparison of measured and calculated temperature distribution under irradiation (L-3 hole, heater ‘ON’)— partial and whole core model.
Fig. 4. Calculation results of temperature in test section (L-3 hole, heater ‘ON’).
heating rate which were obtained by neutronic calculations with the partial and the whole core calculation models. In the partial core model, a surface source is calculated by the whole core model at first, and nuclear heating rate are calculated by using a surface source. The differences of temperature distribution between the partial and the whole core calculation models were about 55 °C. Therefore, the whole core model is necessary for nuclear design calculation of the blanket in-pile mockup.
under neutron irradiation for the first time, the calculated values were 24–28% higher than the measured values. One of the reason for overestimation of calculated temperature were due to accuracy of calculated thermal neutron flux because heating rate in Li2TiO3 pebbles packing region was higher than other structural materials in the blanket in-pile mockup. Concerning model description in between the partial and the whole core model for neutronic calculations, the differences of calculated values were very about 55 °C. Therefore, the whole core model is necessary at least for nuclear design calculation in detail. The calculated temperature depends on the input data of heating rate. Therefore, The reason of 20% (about 140 °C) of the total discrepancy between measured temperatures and calculated values with the whole core calculation model may be the neutron cross section of beryllium or the latent problem in MCNP.
References 4. Conclusion From the results of preliminary estimation of temperature distribution in large volume of the Li2TiO3 and Beryllium pebbles packing region
[1] O.D. Slagle et al., BEATRIX-II Program, PNL-7858 (1991). [2] H. Sagawa, et al., Design study of sweep gas system for fusion blanket development in the JMTR, Fusion Technology 28 (1995) 732 – 735.
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Y. Nagao et al. / Fusion Engineering and Design 58–59 (2001) 673–678
[3] M. Nakamichi et al., Design study of in-pile blanket mockup simulated neutron pulse operation of fusion reactor, 19th symposium on Fusion Technology (1996). [4] H. Kawamura et al., Status of fusion blanket irradiation study in JAERI, Proceedings of the International Tritium Workshop on Present Status and Prospect of TritiumMaterial Interaction Studies 47 –52 (1997). [5] H. Takatsu, et al., Development of ceramic breeder blankets in Japan, Fusion Eng. Des. 39-40 (1998) 645 – 650. [6] Y. Nagao et al., Neutronic design of pulse operating simulating devise for in-pile functional test of fusion blanket by MCNP, J. of Nucl. Sci. and Tech. Supplement 1 (2000). [7] J.F. Briesmeister (Ed.), MCNP-A General Monte Carlo
[8]
[9]
[10] [11]
N-Particle Transport Code, Version 4A, LA-12625-M (1993). D.C. Elrod et al., TRUMP —a program for transient and steady-state temperature distributions and multidimensional systems, UCRL-14754 (1977). K. Kosako et al., FSXLIB-J3R2: A Continuous Energy Cross Section Library for MCNP, Based on JENDL-3.2, JAERI-Data/Code 94-020 (1994). Y. Nagao, Core calculations of JMTR, JAERI-Review 98-010 128-165 (1998). Y. Nagao et al., Verification of tritium production evaluation procedure using Monte Carlo code MCNP for in-pile test of fusion blanket with JMTR, 5th International Symposium on Fusion Nuclear Technology (1999).
Neutronic and thermal estimation of blanket in-pile mockup with Li2TiO3 pebbles Y. Nagao *, M. Nakamichi, K. Tsuchiya, H. Kawamura Oarai Research Establishment, Japan Atomic Energy Research Institute, Narita, Oarai-machi, Higashi-ibaraki-gun, Ibaraki-ken 311 -1394, Japan
Abstract To evaluate exactly temperature distribution in large volume of tritium breeding materials during the blanket in-pile tests with the JMTR, neutronic and thermal calculations were conducted by using Monte Carlo code ‘MCNP’ with nuclear cross section library of ‘FSXLIBJ3R2’ and the transient and steady-state distribution code ‘TRUMP’. From the results of preliminary estimation of temperature distribution in the blanket in-pile mockup, the calculated values were 24–28% higher than the measured values. One of the reasons is due to overestimation of calculated thermal neutron flux. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Li2TiO3 pebbles; Neutronic and thermal estimation; Tritium breeding materials
1. Introduction A Tritium breeding blanket, whose purposes are to breed tritium and to utilize thermal energy, is indispensable to a fusion reactor. Lithium titanate (Li2TiO3) is one of the candidates for the tritium breeding material. In general, a local temperature in small volume of the packing region with tritium breeding materials has been measured by thermocouples in various irradiation tests. However, temperature distribution in large volume of the packing region with tritium breeding materials has not been measured at the in-site irradiation tests [1]. * Corresponding author. Tel.: + 81-29-264-8756; fax: + 8129-264-8400. E-mail address: [email protected] (Y. Nagao).
On the other hand, the evaluation of temperature distribution in large volume of the packing region with tritium breeding materials is indispensable to design fusion blanket. Therefore, in order to measure temperature distribution in Li2TiO3 pebbles packing region and evaluate the effects of irradiation temperature, hydrogen content in sweep gas and sweep gas flow rate on tritium release from Li2TiO3 pebbles packing region under neutron irradiation, an integrated irradiation test of the in-pile mockup has been carried out using the JMTR (Japan Materials Testing Reactor) [2–6]. For this test, the neutronic and thermal estimation in the in-pile mockup with Li2TiO3 pebbles have been carried out with the Monte Carlo code MCNP [7] and the transient and steady-state distribution code TRUMP [8], respectively. In this
0920-3796/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 1 ) 0 0 5 2 5 - 7
674
Y. Nagao et al. / Fusion Engineering and Design 58–59 (2001) 673–678
paper, the results of comparison between measured and calculated temperature in the Li2TiO3 pebbles packing region were reported.
lium pebbles packing region. The arrangement of the thermocouples was shown in Fig. 1(b). Thirtythree thermocouples were installed inside the inpile mockup (¥ 40× 260 mm2).
2. Experiment and calculation
2.2. Irradiation test
2.1. Blanket in-pile mockup
The JMTR is a tank-in-pool type reactor with thermal power of 50 MW and both coolant and moderator are light water. The typical core configuration was shown in Fig. 2. The reactor core, which is 1560 mm in diameter and 750 mm in effective height, consists of fuel elements, control rod, reflectors and H-shaped beryllium frame. The reactor core has 204 irradiation holes. Each reflector element has irradiation hole, which is loaded with a capsule for irradiation tests or a solid plug of the same material as the reflector element. The H-shaped beryllium frame has also irradiation holes. The in-pile mock-up was loaded at L-3 and K-2 hole in JMTR, and was irradiated in the 121– 129th operating cycles (about 225 days).
The schematic of the in-pile mock-up on tritium breeding blanket of fusion reactor was shown in Fig. 1. The construction of the in-pile mock-up simulates multi-layer typed blanket. Li2TiO3 pebbles and Beryllium pebbles are packed in 1st and 2nd layer, respectively. The size of packing region is 260 mm in length, 20 mm in 1st layer diameter and 40 mm in 2nd layer diameter. The diameter and weight of Li2TiO3 pebbles were 1 mm and 134 g, respectively. The packing fraction of Li2TiO3 pebbles was about 62%. Additionally, Beryllium pebbles were packed outside the Li2TiO3 pebbles packing region. The thermocouples were installed in the Li2TiO3 and the beryl-
Fig. 1. Preliminary in-pile mockup and arrangement of thermocouples.
Y. Nagao et al. / Fusion Engineering and Design 58–59 (2001) 673–678
675
Fig. 2. Typical core configuration of JMTR.
2.3. Calculation Neutronic calculations were done in 3-D geometry with the Monte Carlo code MCNP4B using continuous energy cross section library FSXLIBJ3R2 [9] (proceeded from JENDL3.2). The code and cross section library have been used to evaluate local neutron spectral for various capsule at positions in other previously irradiation tests of the JMTR. The core configuration of 128th operating cycle was modeled and partial and whole core of the JMTR include the blanket in-pile mock-up was described in detail. For the whole core model, the distribution of neutron and gamma heating rate in the blanket in-pile mockup was calculated by using KCODE option in MCNP4B. The MCNP model of the blanket in-pile mock-up was shown in Fig. 3. For the partial core model, the heating rates were calculated by using fixed source option with the surface source, which was calculated by the whole core model. The partial core model was mainly used for parametric calculations such as radial length or vertical position in the test section.
Thermal calculations were done in 3-D geometry with the transient and steady-state distribution code TRUMP using calculated neutron and gamma heating rates, and the blanket in-pile mockup was modeled in detail. The thermal conductivity of beryllium beds was used due to Yagi and Kunii’s formula.
3. Results and discussion Measured and calculated centerline temperature are tabulated in Table 1. The measured centerline temperature of the test section were 500 °C at heater power ‘ON’ condition and 402 °C at heater power ‘OFF’ condition in L-3 hole at 50 MW operation, and the measured centerline temperature in K-2 hole was 310 °C at heater ‘OFF’ condition. The ratio of calculated value and measured one (C/M) on centerline temperature were 1.24– 1.28. The heating rate of (n, alpha) reaction in Li2TiO3 pebbles was about ten times larger than gamma heating in other structural materials (see Table 2) in the blanket in-pile mockup. The
676
Y. Nagao et al. / Fusion Engineering and Design 58–59 (2001) 673–678
heating rate of (n, alpha) reaction depends on thermal neutron flux in fission reactor such as the JMTR. Fig. 4 shows comparison of measured and calculated temperature distribution in B-Section (see Fig. 1-(b)). Concerning of calculated temperature, to adjust differences of measured and calculated values by change of input data of (n, alpha) heating, calculated temperature distribution was good agreement with measured one as (n, alpha) heating values was multiplied by 0.7. In the
present status of thermal neutron flux evaluation, calculated values tend to overestimate measured values by + 30% [10,11]. Therefore, one of the reasons for overestimation of calculated centerline temperature is due to accuracy of thermal neutron flux evaluation. The neutronic calculations by Monte Carlo method have long calculation time. Therefore, modeling technique in geometry was examined. Fig. 5 shows temperature distribution by nuclear
Fig. 3. MCNP model of in-pile mock-up. Table 1 Centerline temperature of the test section Irradiation hole
L-3 L-3 K-2
Heater
ON OFF OFF
Centerline temperarture
C/M
Measurement (M)
Calculation (C)
500 402 310
642 497 390
1.28 1.24 1.26
Y. Nagao et al. / Fusion Engineering and Design 58–59 (2001) 673–678
677
Table 2 Calculation results of neutron and gamma heating (L-3 hole) Region
Heating rate [W/g]
Li2TiO3 pebbles SS316 inner container Be pebbles SS316 outer container Al thermal conducter SS316 outertube
4.37 0.40 0.17 0.41 0.32 0.42
Fig. 5. Comparison of measured and calculated temperature distribution under irradiation (L-3 hole, heater ‘ON’)— partial and whole core model.
Fig. 4. Calculation results of temperature in test section (L-3 hole, heater ‘ON’).
heating rate which were obtained by neutronic calculations with the partial and the whole core calculation models. In the partial core model, a surface source is calculated by the whole core model at first, and nuclear heating rate are calculated by using a surface source. The differences of temperature distribution between the partial and the whole core calculation models were about 55 °C. Therefore, the whole core model is necessary for nuclear design calculation of the blanket in-pile mockup.
under neutron irradiation for the first time, the calculated values were 24–28% higher than the measured values. One of the reason for overestimation of calculated temperature were due to accuracy of calculated thermal neutron flux because heating rate in Li2TiO3 pebbles packing region was higher than other structural materials in the blanket in-pile mockup. Concerning model description in between the partial and the whole core model for neutronic calculations, the differences of calculated values were very about 55 °C. Therefore, the whole core model is necessary at least for nuclear design calculation in detail. The calculated temperature depends on the input data of heating rate. Therefore, The reason of 20% (about 140 °C) of the total discrepancy between measured temperatures and calculated values with the whole core calculation model may be the neutron cross section of beryllium or the latent problem in MCNP.
References 4. Conclusion From the results of preliminary estimation of temperature distribution in large volume of the Li2TiO3 and Beryllium pebbles packing region
[1] O.D. Slagle et al., BEATRIX-II Program, PNL-7858 (1991). [2] H. Sagawa, et al., Design study of sweep gas system for fusion blanket development in the JMTR, Fusion Technology 28 (1995) 732 – 735.
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Y. Nagao et al. / Fusion Engineering and Design 58–59 (2001) 673–678
[3] M. Nakamichi et al., Design study of in-pile blanket mockup simulated neutron pulse operation of fusion reactor, 19th symposium on Fusion Technology (1996). [4] H. Kawamura et al., Status of fusion blanket irradiation study in JAERI, Proceedings of the International Tritium Workshop on Present Status and Prospect of TritiumMaterial Interaction Studies 47 –52 (1997). [5] H. Takatsu, et al., Development of ceramic breeder blankets in Japan, Fusion Eng. Des. 39-40 (1998) 645 – 650. [6] Y. Nagao et al., Neutronic design of pulse operating simulating devise for in-pile functional test of fusion blanket by MCNP, J. of Nucl. Sci. and Tech. Supplement 1 (2000). [7] J.F. Briesmeister (Ed.), MCNP-A General Monte Carlo
[8]
[9]
[10] [11]
N-Particle Transport Code, Version 4A, LA-12625-M (1993). D.C. Elrod et al., TRUMP —a program for transient and steady-state temperature distributions and multidimensional systems, UCRL-14754 (1977). K. Kosako et al., FSXLIB-J3R2: A Continuous Energy Cross Section Library for MCNP, Based on JENDL-3.2, JAERI-Data/Code 94-020 (1994). Y. Nagao, Core calculations of JMTR, JAERI-Review 98-010 128-165 (1998). Y. Nagao et al., Verification of tritium production evaluation procedure using Monte Carlo code MCNP for in-pile test of fusion blanket with JMTR, 5th International Symposium on Fusion Nuclear Technology (1999).