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Core configuration of a gas-cooled reactor as a tritium production device for fusion reactor
Nuclear Engineering and Design 271 (2014) 505–509
Contents lists available at ScienceDirect
Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes
Core configuration of a gas-cooled reactor as a tritium production device for fusion reactor H. Nakaya a,∗ , H. Matsuura a , Y. Nakao a , S. Shimakawa b , M. Goto b , S. Nakagawa b , M. Nishikawa c a
Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, 744 Motooka, Fukuoka 8190395, Japan Japan Atomic Energy Agency, 4002 Oarai, Ibaraki, Japan c Malaysia-Japan International Institute of Technology, UTM, Kuala Lumpur 54100, Malaysia b
a b s t r a c t The performance of a high-temperature gas-cooled reactor as a tritium production device is examined, assuming the compound LiAlO2 as the tritiumproducing material. A gas turbine high-temperature reactor of 300 MWe nominal capacity (GTHTR300) is assumed as the calculation target, and using the continuous-energy Monte Carlo transport code MVP-BURN, burn-up simulations are carried out. To load sufficient Li into the core, LiAlO2 is loaded into the removable reflectors that surround the ring-shaped fuel blocks in addition to the burnable poison insertion holes. It is shown that module high-temperature gas-cooled reactors with a total thermal output power of 3 GW can produce almost 8 kg of tritium in a year. © 2013 Elsevier B.V. All rights reserved.
1. Introduction The fusion reactor, as a power generator, is expected to provide a substantial amount of energy in the future. Deuterium and tritium are considered to be the main fuels for the first generation of fusion reactors. Deuterium is obtained from water, but tritium does not exist in nature; it must be artificially produced. When many fusion reactors begin to operate, the initial inventory of the next reactor is co-operatively supplied from several fusion reactors. However, this process needs an outside tritium source to supply a sufficient amount of tritium to the initial and subsequent fusion reactors. The requirement for the initial tritium inventory is estimated to be 23 kg (Nishikawa et al., 2012), and it can be effective with an outside tritium supply having an annual tritium production rate of 5–10 kg/year (Nishikawa et al., 2012). The present tritium source is 2.2–2.3 kg/year (Gierszewski, 1989) from the Ontario Hydro Darlington facility, but the requirements for tritium exceed the amounts that can be supplied by the Ontario Hydro Darlington facility. It is necessary to consider some other methods to supply tritium for fusion reactors. We have proposed the use of a high-temperature gas-cooled reactor as a tritium production device (Matsuura et al., 2012a). It is known that the 6 Li(n,˛)T reaction has a large crosssection around the thermal neutron energy range. Tritium can be efficiently produced by the 6 Li(n,˛)T reaction using thermal neutrons in a high-temperature gas-cooled reactor. The design of a high-temperature gas-cooled reactor is advantageous for tritium
∗ Corresponding author. Tel.: +81 92 802 3503. E-mail address: [email protected] (H. Nakaya). 0029-5493/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nucengdes.2013.12.023
production. First, main core structures and coolant are composed of materials with relatively low-neutron-absorbing characteristics, i.e., graphite and helium gas. This enables efficient tritium production by avoiding the consumption of thermal neutrons by structural materials, excluding fuel and transmutable nuclides. Second, to confine fission products in the reactor core, a unique fuel-pellet configuration, i.e., ceramic-coated fuel particles (Fig. 1), is adopted as the fuel-pellet component. It is known that the ceramic-coated particle structure provides a secure containment of tritium. To confine produced tritium, it is necessary to use ceramic-coated Li compound particles. A large amount of space is needed to load ceramic-coated Li compound particles, and the unique fuel-pellet configuration provides sufficient space to load a large amount of ceramic-coated Li compound particles close to the 235 U-fuel region with a large surface area per unit volume. In our previous study (Matsuura et al., 2012a), we assumed the use of a gas turbine high-temperature reactor of 300 MWe nominal capacity (GTHTR300) (Nakata et al., 2002; Yan et al., 2003) as a high-temperature gas-cooled reactor. The GTHTR300 had insertion holes for loading B4 C as a burnable poison (BP). Tritium can be produced in the GTHTR300 reactor by loading Li compound into the BP insertion holes instead of B4 C, without changing the original GTHTR300 core design. When Li compounds, i.e., Li2 O, Li4 SiO4 , and Li2 TiO3 , were loaded into the BP insertion holes, it was shown that module high-temperature gas-cooled reactors with a total thermal output power of 3 GW could produce 4–7 kg of tritium in a year, depending on the loaded Li compounds. These Li compounds have excellent physical and chemical properties as tritium breeders (Futamura et al., 1999), but LiAlO2 also is thermally and chemically stable (Roux et al., 1992). Li density in LiAlO2 , however, is less than one-third of the Li2 O compound. When
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H. Nakaya et al. / Nuclear Engineering and Design 271 (2014) 505–509
Fig. 1. Schematic view of a typical fuel compact of a high-temperature gas-cooled reactor.
LiAlO2 is loaded only into the BP insertion holes, tritium production substantially decreased compared with that of other Li compounds. To produce the same amount of tritium as that produced with other Li compounds, a method for loading more LiAlO2 into the reactor core should be considered. Several methods are used to load sufficient Li into the core. The first method involves loading low Li density compound enriched in 6 Li into the BP insertion holes. In this case, changing the original GTHTR300 core design is not necessary to produce tritium, but the cost of tritium production is increased with the cost of enriching Li compound. The second method involves loading low Li density compound into the removable reflector blocks in addition to the BP insertion holes. In this case, thermal neutrons around the reflector blocks can be used to produce tritium, but the GTHTR300 core design must be changed. The third method involves loading a sufficient amount of low Li density compound only into the BP insertion holes by using Li compound pebbles without secure multiple coatings (Matsuura et al., 2012b). In this case, tritium is continuously recovered from the reactor core by the helium-gas coolant, but a system to recover tritium is needed; therefore, the configuration of the reactor becomes complex. In this study, the performance of a high-temperature gas-cooled reactor with loading low Li density compound as a tritium production device is examined, and it is shown that the same amount of tritium as that shown in previous study can be produced by loading low Li density compound into the removable reflector blocks in addition to the burnable insertion holes. 2. Calculation model We also assume the use of the GTHTR300 as a high-temperature gas-cooled reactor in this study. The burn-up calculations for the whole core region of the GTHTR300 were performed using the continuous-energy Monte Carlo transport code MVP-BURN (Nagaya et al., 2005) to evaluate the efficiency of the GTHTR300 for tritium production. 2.1. Reactor core configuration The horizontal cross-section of the GTHTR300 core is shown in Fig. 2. The core consists of 90 fuel columns arranged in an annular ring, 55 inner and 36 outer removable reflector columns, 18 inner and 12 outer control-rod guide columns, and 18 outer permanent reflector sectors. Each fuel column consists of eight layers of hexagonal fuel blocks, with upper and lower reflector blocks vertically arranged. Each hexagonal block is 407 mm wide across the flats, including 1 mm gaps at both sides, and 1000 mm high (Fig. 3a). A fuel block contains 57 fuel channels and three BP insertion holes. The diameter of the fuel channel in the fuel blocks is 39 mm. A fuel rod consists of 12 hollow fuel compacts with an inner diameter of 9 mm and an outer diameter of 26 mm (Fig. 3b). The fuel rod is 1000 mm in height, including the upper and lower covers. The
Fig. 2. Horizontal cross-section of the GTHTR300 core.
Fig. 3. Schematic views of (a) the fuel block and (b) the fuel rod.
Fig. 4. Schematic view of the ceramic-coated fuel particle.
diameter of the BP rod is 44 mm. Fuel compacts are covered with graphite at a thickness of 1 mm. Helium gas flows as a coolant in the space between the wall and the fuel rod. A ceramic-coated particle is incorporated into the fuel compacts with a graphite matrix. Each ceramic-coated fuel particle consists of a micro sphere of UO2 with a tri-isotropic coating (Fig. 4). A fuel kernel composed of UO2 resides in the center and is coated with four layers of three isotopic materials: low-density pyrolitic carbon (low-density PyC), pyrolitic carbon (PyC), and silicon carbide (SiC). The volume ratio of the ceramic-coated particles filling a compact to the fuel compact is assumed to be 33%. The diameter of a ceramic-coated fuel particle is 1.01 mm and that of the UO2 kernel is 0.55 mm. The LiAlO2 kernel is also coated with four layers of three isotopic materials (Fig. 5), and the volume ratio of the ceramic-coated particles filling a compact to a LiAlO2 compact is assumed to be 33%.
Fig. 5. Schematic view of the ceramic-coated LiAlO2 particle.
H. Nakaya et al. / Nuclear Engineering and Design 271 (2014) 505–509 Table 1 Typical calculation parameters in the present system of GTHTR300.
800
1.3 LiAlO2
600 MW 14 wt.% 1360 K 1190 K
Li2TiO3
Li4SiO4 600
keff
1.2
The original operation parameters of the GTHTR300 are indicated in Table 1. Throughout the calculations, all control rods were assumed to be pulled out of the core.
1.1
400
1.0
200
Tritium Production [g]
Thermal output power 235 U enrichment Fuel temperature Moderator temperature
507
Thermal output : 600 MW
0.9
2.2. Calculation of 6 Li burn-up In the MVP-BURN code system 6 Li is not incorporated into the default burn-up chains (the transmutation from 6 Li to T is not accounted in the default code system). Therefore, we manually calculated transmutation from 6 Li to T. We first obtain neutron flux g (r, t0 ) of energy group g in the 6 Li-loading position at a time t0 by using the code system. We next evaluate reduction of the 6 Li number density n6Li (r, t) due to transmutation during a time interval from t0 to t0 + t by using the neutron flux g (r, t0 ) at t0 as: dn6Li (r, t) dt
=−
g
n6Li (r, t)(n,T) g (r, t)
0
30
60
90
120
150
0 180
Time [day] Fig. 6. The amount of produced tritium and the effective multiplication factor when LiAlO2 is loaded into the BP insertion holes.
(1)
g
g Here (n,T) represents the group constant for cross section of 6 Li(n,˛)T reaction. The reduction in the number density of 6 Li nuclei
in the time interval t is reflected back to the subsequent transport calculation to evaluate the neutron flux at next time step. Transmutation of 7 Li during the operation, beta decay of tritium and interactions between neutron and tritium were ignored. To validate our calculation method for 6 Li transmutation, reduction of 10 B number density due to 10 B(n,˛)7 Li reaction was evaluated by above method. Reduction of 10 B number density obtained by above method and the MVP-BURN code system are agreed within 1% error. Throughout the calculations nuclear data was taken from JENDL-3.3. Detailed information for the calculation model is given by Matsuura et al. (2012a). 3. Simulations when LiAlO2 is loaded into the BP insertion holes We first discuss the simulation when LiAlO2 , Li2 TiO3 , and Li4 SiO4 are loaded into the BP insertion holes without changing the original GTHTR300 core configuration design. Time evaluations of the cumulative weight of the produced tritium and the effective multiplication factor for Li2 O, Li2 TiO3 , and Li4 SiO4 were previously evaluated and discussed by Matsuura et al. (2012a). In this paper, the simulation for LiAlO2 is newly carried out and the results are shown in Fig. 6 on the same plane with the previous evaluations for Li2 TiO3 and Li4 SiO4 . Time evolutions of the cumulative weight of the produced tritium and the effective multiplication factor for each Li compound are shown in Fig. 6. When LiAlO2 is used, the amount of tritium production decreases, compared with that of other Li compounds, because the number of 6 Li nuclei contained in the unit volume of the LiAlO2 is smaller than that of other Li compounds. Throughout the calculations, the 6 Li densities are considered as 0.035, 0.028, and 0.017 g/cm3 for Li4 SiO4 , Li2 TiO3 and LiAlO2 , respectively (85% of the theoretical densities are assumed) (Yan et al., 2003; Riberio et al., 2001). When LiAlO2 is used as the tritium-producing material, 280 g of tritium is produced in a 180-day operation using a high-temperature gas-cooled reactor with 600 MW thermal output power. When considering reactors with a total of 3 GW thermal output power, the amount of tritium produced in a year is evaluated as 2.8 kg. The minimum effective multiplication factor during the 180-day operation is estimated as
Fig. 7. Core configuration when Li blocks are loaded into the outside area of the permanent reflector. Li blocks are covered with graphite.
∼1.15, and it is found that we can load more 6 Li into the reactor and increase the amount of tritium produced during the same operation period. 4. Simulations when LiAlO2 is loaded into the removable reflectors In this section, we consider loading LiAlO2 into the removable reflector blocks and evaluate the amount of tritium produced in the high-temperature gas-cooled reactor. Loading LiAlO2 into the reflector blocks can secure a large space for loading LiAlO2 and makes it possible to use thermal neutrons stagnating in the region outside the permanent reflector. Throughout the calculations, the natural abundance of 6 Li, i.e., 7.5%, was assumed. 4.1. Loading LiAlO2 into the outside area of the permanent reflector At first, the burn-up simulation is carried out assuming that the LiAlO2 compound is loaded only into the outside area of the permanent reflector region (Fig. 7). The 66 Li blocks are placed such that they surround the core region. Each Li block contains 60 Li
Fig. 8. Schematic views of (a) the Li block and (b) the Li rod.
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H. Nakaya et al. / Nuclear Engineering and Design 271 (2014) 505–509
1.7
100 loading LiAlO into the outside area of permanent reflector region without loading LiAlO
80
1.5
60
1.4
40
1.3
20
Tritium Production [g]
keff
1.6
Thermal output : 600 MW
1.2
0
30
60
90
120
150
Fig. 11. Position of the loaded Li compound.
0 180
Time [day] Fig. 9. The produced tritium and effective multiplication factor when Li blocks are placed outside the permanent reflector.
rod insertion holes with a diameter of 44 mm (Fig. 8a). A Li rod is 950 mm in height and consists of 12 Li compacts with a 44 mm diameter (Fig. 8b). The time evolutions of the cumulative weight of the tritium produced by the 6 Li(n,˛)T reaction and the effective multiplication factor are shown in Fig. 9. The dotted line represents the effective multiplication factor when the LiAlO2 compound is not loaded at all into the reactor core (in this case, there is no tritium production), and the solid line represents the result when LiAlO2 is loaded only into the outside area of the permanent reflector. In this case, 80 g of tritium is produced during a 180-day operation. When considering reactors with a total of 3 GW of thermal output power, the amount of tritium produced in a year is evaluated as 0.8 kg. The time evolutions of the effective multiplication factors when LiAlO2 is loaded and not loaded are almost the same. This implies that in the present loading pattern of LiAlO2 , there are no influences on the effective multiplication factor. This is because tritium is produced by the thermal neutrons stagnating in the region outside the permanent reflector. It is shown that loading LiAlO2 outside the ring-shaped fuel region is effective to increase the tritium production. 4.2. Loading LiAlO2 into the BP insertion holes in fuel blocks and removable reflectors
• Case 1: LiAlO2 is loaded only into BP insertion holes. • Case 2: LiAlO2 is loaded into the outer reflector blocks in addition to BP insertion holes. • Case 3: LiAlO2 is loaded into both outer and inner reflector blocks in addition to the BP insertion holes. The time evolutions of the cumulative weight of the tritium produced by the 6 Li(n,˛)T reaction and the effective multiplication factor are shown in Fig. 12 for three loading patterns, i.e., Case 1, Case 2, and Case 3. The results for Case 1 correspond to the one shown in Fig. 6. As Li loading weight increased, the amount of tritium produced in the reactor core also increased. To utilize the thermal neutrons outside the ring-shaped fuel region, more LiAlO2 is loaded into the outer reflector blocks than in the inner reflector blocks. In this case, the amount of tritium produced in the reactor core increased more than twice compared with the case when LiAlO2 was loaded only into the BP insertion holes. When we additionally loaded LiAlO2 into the inner reflector blocks, 800 g of tritium could be produced during the 180-day operation. When considering the 3 GW thermal output power operation in a year, the amount of tritium produced in the high-temperature gas-cooled reactor is almost 8 kg.
1000
1.4
800
1.2
600
1.1
400 200
1.0
Tritium Production [g]
1. loading into the BP holes 2. BP holes +outer reflector 3. BP holes +outer and inner reflector
1.3
keff
We next carried out the simulation assuming that LiAlO2 is loaded into the removable reflector blocks in addition to the BP insertion holes. We prepared two types of Li blocks, as shown in Fig. 10: (a) Li block in which 57 Li rods with a diameter of 37 mm and three Li rods with a diameter of 44 mm and (b) a Li block containing three Li rods with a diameter of 37 mm and three Li rods with a diameter of 44 mm. 36 outer and 12 inner reflector blocks were arranged as shown in Fig. 11. When we assume that LiAlO2 is loaded into the reflector blocks in addition to the BP insertion holes in the fuel blocks, about 20 kg of 6 Li can be loaded into
the reactor core (when we assumed that LiAlO2 is loaded only into the BP insertion holes in the fuel blocks, about 3 kg of 6 Li can be loaded into the reactor core). In addition, as discussed in the previous section, when the Li compound is loaded outside the ring-shaped fuel region, we can efficiently use the thermal neutrons. Next, we discuss the results of burn-up simulations, assuming three types of Li loading patterns:
Thermal output : 600 MW
0.9
0
30
60
90
120
150
0 180
Time [day]
Fig. 10. (a) Outer and (b) inner reflector blocks loaded of Li rods.
Fig. 12. The produced tritium and effective multiplication factor for several LiAlO2 loading patterns.
H. Nakaya et al. / Nuclear Engineering and Design 271 (2014) 505–509
509
5. Conclusion
Acknowledgment
We showed that the almost same amount of tritium as that shown in previous study can be produced by loading LiAlO2 into the removable reflector blocks in addition to the BP insertion holes. Utilizing the thermal neutrons in the area outside the ring-shaped fuel region can increase the amount of tritium produced. In this case, almost 8 kg of tritium can be produced in a year using module high-temperature gas-cooled reactors with a total of 3 GW thermal output power. Even if low Li density compound is used as the tritium-producing material, sufficient Li can be loaded into the reactor core. In this study, we assumed a 180-day operation period to monitor the performance of a high-temperature gas-cooled reactor as a tritium production device. The amount of tritium produced in a year is represented by doubling the amount of tritium produced in six months. Considering the fuel exchange period, the amount of tritium produced in a year changed according to the operation period. As the operation period become shorter, more Li compound was loaded into the reactor core, and the amount of tritium produced in a year became larger. On the other hand, when the operation period was too short, the number of fuel exchanges increased and the annual tritium production decreased. In addition, the fuel cost rises because many fuels are burned up. It is necessary to optimize operation period. Throughout our calculations, the temperature of the LiAlO2 region was fixed at 1190 K, which is the average temperature specified in the GTHTR300 design. To produce tritium by confining it in the ceramic-coated particles, it is necessary to reduce the temperature. The influence of reduced temperature on tritium production must be examined.
This research was supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for challenging Exploratory Research, 23656574. References Nishikawa, M., Yamasaki, H., Kashimura, H., Matsuda, S., 2012. Effect of outside tritium source on tritium balance of D-T fusion reactor. Fusion Eng. Des. 87 (466-470). Gierszewski, P., 1989. Tritium supply for near-term fusion devise. Fusion Eng. Des. 10, 399–403. Matsuura, H., Kouchi, S., Nakaya, H., Yasumoto, T., Nakao, Y., Shimakawa, S., Goto, M., Nakagawa, S., Nishikawa, M., 2012a. Performance of high-temperature gascooled reactor as a tritium production device for fusion reactors. Nucl. Eng. Des. 243, 95. Nakata, T., Katanishi, S., Takada, S., Yan, X., Kunitomi, K., 2002. Nuclear Design of the Gas Turbine High Temperature Reactor (GTHTR300). JAERI-Tech (in Japanese). Yan, X., Kunitomi, K., Nakata, T., Shiozawa, S., 2003. GTHTR300 design and development. Nucl. Eng. Des. 222, 247–262. Futamura, Y., Kawamura, H., Tsuchiya, K., 1999. Tritium breeding materials date base for fusion reactor blankets (4) (Li2 O, Li2 TiO3 , Li2 ZrO3 , Li4 SiO4 Solid Breeding Materials). Ann. Rep. Hydrogen Isotope Res. Center 19, 65. Roux, N., Johnson, C., Noda, K., 1992. Properties and performance of tritium breeding ceramics. J. Nucl. Mater. 191-194, 15–22. Matsuura, H., Nakaya, H., Nakao, Y., Shimakawa, S., Goto, M., Nakagawa, S., Nishikawa, M., 2012b. Performance of gas-cooled reactor as a tritium production and continuous tritium recovery system for fusion reactors. In: Presented at SOFT 2012, Liége, Belgium. Nagaya, Y., Okumura, K., Mori, T., Nakagawa, M., 2005. MVP/GMVP: General Purpose Monte Carlo for Neutron and Photon Transport Calculation based on Continuous Energy and Multigroup Method. JAERI-Japan Atomic Energy Research Institute. Riberio, R.A., Silve, G.G., Mohallem, N.D.S., 2001. The influence of heat treatment on the structural properties of lithium aluminates. J. Phys. Chem. Solids 62, 857–864.
Contents lists available at ScienceDirect
Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes
Core configuration of a gas-cooled reactor as a tritium production device for fusion reactor H. Nakaya a,∗ , H. Matsuura a , Y. Nakao a , S. Shimakawa b , M. Goto b , S. Nakagawa b , M. Nishikawa c a
Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, 744 Motooka, Fukuoka 8190395, Japan Japan Atomic Energy Agency, 4002 Oarai, Ibaraki, Japan c Malaysia-Japan International Institute of Technology, UTM, Kuala Lumpur 54100, Malaysia b
a b s t r a c t The performance of a high-temperature gas-cooled reactor as a tritium production device is examined, assuming the compound LiAlO2 as the tritiumproducing material. A gas turbine high-temperature reactor of 300 MWe nominal capacity (GTHTR300) is assumed as the calculation target, and using the continuous-energy Monte Carlo transport code MVP-BURN, burn-up simulations are carried out. To load sufficient Li into the core, LiAlO2 is loaded into the removable reflectors that surround the ring-shaped fuel blocks in addition to the burnable poison insertion holes. It is shown that module high-temperature gas-cooled reactors with a total thermal output power of 3 GW can produce almost 8 kg of tritium in a year. © 2013 Elsevier B.V. All rights reserved.
1. Introduction The fusion reactor, as a power generator, is expected to provide a substantial amount of energy in the future. Deuterium and tritium are considered to be the main fuels for the first generation of fusion reactors. Deuterium is obtained from water, but tritium does not exist in nature; it must be artificially produced. When many fusion reactors begin to operate, the initial inventory of the next reactor is co-operatively supplied from several fusion reactors. However, this process needs an outside tritium source to supply a sufficient amount of tritium to the initial and subsequent fusion reactors. The requirement for the initial tritium inventory is estimated to be 23 kg (Nishikawa et al., 2012), and it can be effective with an outside tritium supply having an annual tritium production rate of 5–10 kg/year (Nishikawa et al., 2012). The present tritium source is 2.2–2.3 kg/year (Gierszewski, 1989) from the Ontario Hydro Darlington facility, but the requirements for tritium exceed the amounts that can be supplied by the Ontario Hydro Darlington facility. It is necessary to consider some other methods to supply tritium for fusion reactors. We have proposed the use of a high-temperature gas-cooled reactor as a tritium production device (Matsuura et al., 2012a). It is known that the 6 Li(n,˛)T reaction has a large crosssection around the thermal neutron energy range. Tritium can be efficiently produced by the 6 Li(n,˛)T reaction using thermal neutrons in a high-temperature gas-cooled reactor. The design of a high-temperature gas-cooled reactor is advantageous for tritium
∗ Corresponding author. Tel.: +81 92 802 3503. E-mail address: [email protected] (H. Nakaya). 0029-5493/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nucengdes.2013.12.023
production. First, main core structures and coolant are composed of materials with relatively low-neutron-absorbing characteristics, i.e., graphite and helium gas. This enables efficient tritium production by avoiding the consumption of thermal neutrons by structural materials, excluding fuel and transmutable nuclides. Second, to confine fission products in the reactor core, a unique fuel-pellet configuration, i.e., ceramic-coated fuel particles (Fig. 1), is adopted as the fuel-pellet component. It is known that the ceramic-coated particle structure provides a secure containment of tritium. To confine produced tritium, it is necessary to use ceramic-coated Li compound particles. A large amount of space is needed to load ceramic-coated Li compound particles, and the unique fuel-pellet configuration provides sufficient space to load a large amount of ceramic-coated Li compound particles close to the 235 U-fuel region with a large surface area per unit volume. In our previous study (Matsuura et al., 2012a), we assumed the use of a gas turbine high-temperature reactor of 300 MWe nominal capacity (GTHTR300) (Nakata et al., 2002; Yan et al., 2003) as a high-temperature gas-cooled reactor. The GTHTR300 had insertion holes for loading B4 C as a burnable poison (BP). Tritium can be produced in the GTHTR300 reactor by loading Li compound into the BP insertion holes instead of B4 C, without changing the original GTHTR300 core design. When Li compounds, i.e., Li2 O, Li4 SiO4 , and Li2 TiO3 , were loaded into the BP insertion holes, it was shown that module high-temperature gas-cooled reactors with a total thermal output power of 3 GW could produce 4–7 kg of tritium in a year, depending on the loaded Li compounds. These Li compounds have excellent physical and chemical properties as tritium breeders (Futamura et al., 1999), but LiAlO2 also is thermally and chemically stable (Roux et al., 1992). Li density in LiAlO2 , however, is less than one-third of the Li2 O compound. When
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H. Nakaya et al. / Nuclear Engineering and Design 271 (2014) 505–509
Fig. 1. Schematic view of a typical fuel compact of a high-temperature gas-cooled reactor.
LiAlO2 is loaded only into the BP insertion holes, tritium production substantially decreased compared with that of other Li compounds. To produce the same amount of tritium as that produced with other Li compounds, a method for loading more LiAlO2 into the reactor core should be considered. Several methods are used to load sufficient Li into the core. The first method involves loading low Li density compound enriched in 6 Li into the BP insertion holes. In this case, changing the original GTHTR300 core design is not necessary to produce tritium, but the cost of tritium production is increased with the cost of enriching Li compound. The second method involves loading low Li density compound into the removable reflector blocks in addition to the BP insertion holes. In this case, thermal neutrons around the reflector blocks can be used to produce tritium, but the GTHTR300 core design must be changed. The third method involves loading a sufficient amount of low Li density compound only into the BP insertion holes by using Li compound pebbles without secure multiple coatings (Matsuura et al., 2012b). In this case, tritium is continuously recovered from the reactor core by the helium-gas coolant, but a system to recover tritium is needed; therefore, the configuration of the reactor becomes complex. In this study, the performance of a high-temperature gas-cooled reactor with loading low Li density compound as a tritium production device is examined, and it is shown that the same amount of tritium as that shown in previous study can be produced by loading low Li density compound into the removable reflector blocks in addition to the burnable insertion holes. 2. Calculation model We also assume the use of the GTHTR300 as a high-temperature gas-cooled reactor in this study. The burn-up calculations for the whole core region of the GTHTR300 were performed using the continuous-energy Monte Carlo transport code MVP-BURN (Nagaya et al., 2005) to evaluate the efficiency of the GTHTR300 for tritium production. 2.1. Reactor core configuration The horizontal cross-section of the GTHTR300 core is shown in Fig. 2. The core consists of 90 fuel columns arranged in an annular ring, 55 inner and 36 outer removable reflector columns, 18 inner and 12 outer control-rod guide columns, and 18 outer permanent reflector sectors. Each fuel column consists of eight layers of hexagonal fuel blocks, with upper and lower reflector blocks vertically arranged. Each hexagonal block is 407 mm wide across the flats, including 1 mm gaps at both sides, and 1000 mm high (Fig. 3a). A fuel block contains 57 fuel channels and three BP insertion holes. The diameter of the fuel channel in the fuel blocks is 39 mm. A fuel rod consists of 12 hollow fuel compacts with an inner diameter of 9 mm and an outer diameter of 26 mm (Fig. 3b). The fuel rod is 1000 mm in height, including the upper and lower covers. The
Fig. 2. Horizontal cross-section of the GTHTR300 core.
Fig. 3. Schematic views of (a) the fuel block and (b) the fuel rod.
Fig. 4. Schematic view of the ceramic-coated fuel particle.
diameter of the BP rod is 44 mm. Fuel compacts are covered with graphite at a thickness of 1 mm. Helium gas flows as a coolant in the space between the wall and the fuel rod. A ceramic-coated particle is incorporated into the fuel compacts with a graphite matrix. Each ceramic-coated fuel particle consists of a micro sphere of UO2 with a tri-isotropic coating (Fig. 4). A fuel kernel composed of UO2 resides in the center and is coated with four layers of three isotopic materials: low-density pyrolitic carbon (low-density PyC), pyrolitic carbon (PyC), and silicon carbide (SiC). The volume ratio of the ceramic-coated particles filling a compact to the fuel compact is assumed to be 33%. The diameter of a ceramic-coated fuel particle is 1.01 mm and that of the UO2 kernel is 0.55 mm. The LiAlO2 kernel is also coated with four layers of three isotopic materials (Fig. 5), and the volume ratio of the ceramic-coated particles filling a compact to a LiAlO2 compact is assumed to be 33%.
Fig. 5. Schematic view of the ceramic-coated LiAlO2 particle.
H. Nakaya et al. / Nuclear Engineering and Design 271 (2014) 505–509 Table 1 Typical calculation parameters in the present system of GTHTR300.
800
1.3 LiAlO2
600 MW 14 wt.% 1360 K 1190 K
Li2TiO3
Li4SiO4 600
keff
1.2
The original operation parameters of the GTHTR300 are indicated in Table 1. Throughout the calculations, all control rods were assumed to be pulled out of the core.
1.1
400
1.0
200
Tritium Production [g]
Thermal output power 235 U enrichment Fuel temperature Moderator temperature
507
Thermal output : 600 MW
0.9
2.2. Calculation of 6 Li burn-up In the MVP-BURN code system 6 Li is not incorporated into the default burn-up chains (the transmutation from 6 Li to T is not accounted in the default code system). Therefore, we manually calculated transmutation from 6 Li to T. We first obtain neutron flux g (r, t0 ) of energy group g in the 6 Li-loading position at a time t0 by using the code system. We next evaluate reduction of the 6 Li number density n6Li (r, t) due to transmutation during a time interval from t0 to t0 + t by using the neutron flux g (r, t0 ) at t0 as: dn6Li (r, t) dt
=−
g
n6Li (r, t)(n,T) g (r, t)
0
30
60
90
120
150
0 180
Time [day] Fig. 6. The amount of produced tritium and the effective multiplication factor when LiAlO2 is loaded into the BP insertion holes.
(1)
g
g Here (n,T) represents the group constant for cross section of 6 Li(n,˛)T reaction. The reduction in the number density of 6 Li nuclei
in the time interval t is reflected back to the subsequent transport calculation to evaluate the neutron flux at next time step. Transmutation of 7 Li during the operation, beta decay of tritium and interactions between neutron and tritium were ignored. To validate our calculation method for 6 Li transmutation, reduction of 10 B number density due to 10 B(n,˛)7 Li reaction was evaluated by above method. Reduction of 10 B number density obtained by above method and the MVP-BURN code system are agreed within 1% error. Throughout the calculations nuclear data was taken from JENDL-3.3. Detailed information for the calculation model is given by Matsuura et al. (2012a). 3. Simulations when LiAlO2 is loaded into the BP insertion holes We first discuss the simulation when LiAlO2 , Li2 TiO3 , and Li4 SiO4 are loaded into the BP insertion holes without changing the original GTHTR300 core configuration design. Time evaluations of the cumulative weight of the produced tritium and the effective multiplication factor for Li2 O, Li2 TiO3 , and Li4 SiO4 were previously evaluated and discussed by Matsuura et al. (2012a). In this paper, the simulation for LiAlO2 is newly carried out and the results are shown in Fig. 6 on the same plane with the previous evaluations for Li2 TiO3 and Li4 SiO4 . Time evolutions of the cumulative weight of the produced tritium and the effective multiplication factor for each Li compound are shown in Fig. 6. When LiAlO2 is used, the amount of tritium production decreases, compared with that of other Li compounds, because the number of 6 Li nuclei contained in the unit volume of the LiAlO2 is smaller than that of other Li compounds. Throughout the calculations, the 6 Li densities are considered as 0.035, 0.028, and 0.017 g/cm3 for Li4 SiO4 , Li2 TiO3 and LiAlO2 , respectively (85% of the theoretical densities are assumed) (Yan et al., 2003; Riberio et al., 2001). When LiAlO2 is used as the tritium-producing material, 280 g of tritium is produced in a 180-day operation using a high-temperature gas-cooled reactor with 600 MW thermal output power. When considering reactors with a total of 3 GW thermal output power, the amount of tritium produced in a year is evaluated as 2.8 kg. The minimum effective multiplication factor during the 180-day operation is estimated as
Fig. 7. Core configuration when Li blocks are loaded into the outside area of the permanent reflector. Li blocks are covered with graphite.
∼1.15, and it is found that we can load more 6 Li into the reactor and increase the amount of tritium produced during the same operation period. 4. Simulations when LiAlO2 is loaded into the removable reflectors In this section, we consider loading LiAlO2 into the removable reflector blocks and evaluate the amount of tritium produced in the high-temperature gas-cooled reactor. Loading LiAlO2 into the reflector blocks can secure a large space for loading LiAlO2 and makes it possible to use thermal neutrons stagnating in the region outside the permanent reflector. Throughout the calculations, the natural abundance of 6 Li, i.e., 7.5%, was assumed. 4.1. Loading LiAlO2 into the outside area of the permanent reflector At first, the burn-up simulation is carried out assuming that the LiAlO2 compound is loaded only into the outside area of the permanent reflector region (Fig. 7). The 66 Li blocks are placed such that they surround the core region. Each Li block contains 60 Li
Fig. 8. Schematic views of (a) the Li block and (b) the Li rod.
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1.7
100 loading LiAlO into the outside area of permanent reflector region without loading LiAlO
80
1.5
60
1.4
40
1.3
20
Tritium Production [g]
keff
1.6
Thermal output : 600 MW
1.2
0
30
60
90
120
150
Fig. 11. Position of the loaded Li compound.
0 180
Time [day] Fig. 9. The produced tritium and effective multiplication factor when Li blocks are placed outside the permanent reflector.
rod insertion holes with a diameter of 44 mm (Fig. 8a). A Li rod is 950 mm in height and consists of 12 Li compacts with a 44 mm diameter (Fig. 8b). The time evolutions of the cumulative weight of the tritium produced by the 6 Li(n,˛)T reaction and the effective multiplication factor are shown in Fig. 9. The dotted line represents the effective multiplication factor when the LiAlO2 compound is not loaded at all into the reactor core (in this case, there is no tritium production), and the solid line represents the result when LiAlO2 is loaded only into the outside area of the permanent reflector. In this case, 80 g of tritium is produced during a 180-day operation. When considering reactors with a total of 3 GW of thermal output power, the amount of tritium produced in a year is evaluated as 0.8 kg. The time evolutions of the effective multiplication factors when LiAlO2 is loaded and not loaded are almost the same. This implies that in the present loading pattern of LiAlO2 , there are no influences on the effective multiplication factor. This is because tritium is produced by the thermal neutrons stagnating in the region outside the permanent reflector. It is shown that loading LiAlO2 outside the ring-shaped fuel region is effective to increase the tritium production. 4.2. Loading LiAlO2 into the BP insertion holes in fuel blocks and removable reflectors
• Case 1: LiAlO2 is loaded only into BP insertion holes. • Case 2: LiAlO2 is loaded into the outer reflector blocks in addition to BP insertion holes. • Case 3: LiAlO2 is loaded into both outer and inner reflector blocks in addition to the BP insertion holes. The time evolutions of the cumulative weight of the tritium produced by the 6 Li(n,˛)T reaction and the effective multiplication factor are shown in Fig. 12 for three loading patterns, i.e., Case 1, Case 2, and Case 3. The results for Case 1 correspond to the one shown in Fig. 6. As Li loading weight increased, the amount of tritium produced in the reactor core also increased. To utilize the thermal neutrons outside the ring-shaped fuel region, more LiAlO2 is loaded into the outer reflector blocks than in the inner reflector blocks. In this case, the amount of tritium produced in the reactor core increased more than twice compared with the case when LiAlO2 was loaded only into the BP insertion holes. When we additionally loaded LiAlO2 into the inner reflector blocks, 800 g of tritium could be produced during the 180-day operation. When considering the 3 GW thermal output power operation in a year, the amount of tritium produced in the high-temperature gas-cooled reactor is almost 8 kg.
1000
1.4
800
1.2
600
1.1
400 200
1.0
Tritium Production [g]
1. loading into the BP holes 2. BP holes +outer reflector 3. BP holes +outer and inner reflector
1.3
keff
We next carried out the simulation assuming that LiAlO2 is loaded into the removable reflector blocks in addition to the BP insertion holes. We prepared two types of Li blocks, as shown in Fig. 10: (a) Li block in which 57 Li rods with a diameter of 37 mm and three Li rods with a diameter of 44 mm and (b) a Li block containing three Li rods with a diameter of 37 mm and three Li rods with a diameter of 44 mm. 36 outer and 12 inner reflector blocks were arranged as shown in Fig. 11. When we assume that LiAlO2 is loaded into the reflector blocks in addition to the BP insertion holes in the fuel blocks, about 20 kg of 6 Li can be loaded into
the reactor core (when we assumed that LiAlO2 is loaded only into the BP insertion holes in the fuel blocks, about 3 kg of 6 Li can be loaded into the reactor core). In addition, as discussed in the previous section, when the Li compound is loaded outside the ring-shaped fuel region, we can efficiently use the thermal neutrons. Next, we discuss the results of burn-up simulations, assuming three types of Li loading patterns:
Thermal output : 600 MW
0.9
0
30
60
90
120
150
0 180
Time [day]
Fig. 10. (a) Outer and (b) inner reflector blocks loaded of Li rods.
Fig. 12. The produced tritium and effective multiplication factor for several LiAlO2 loading patterns.
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5. Conclusion
Acknowledgment
We showed that the almost same amount of tritium as that shown in previous study can be produced by loading LiAlO2 into the removable reflector blocks in addition to the BP insertion holes. Utilizing the thermal neutrons in the area outside the ring-shaped fuel region can increase the amount of tritium produced. In this case, almost 8 kg of tritium can be produced in a year using module high-temperature gas-cooled reactors with a total of 3 GW thermal output power. Even if low Li density compound is used as the tritium-producing material, sufficient Li can be loaded into the reactor core. In this study, we assumed a 180-day operation period to monitor the performance of a high-temperature gas-cooled reactor as a tritium production device. The amount of tritium produced in a year is represented by doubling the amount of tritium produced in six months. Considering the fuel exchange period, the amount of tritium produced in a year changed according to the operation period. As the operation period become shorter, more Li compound was loaded into the reactor core, and the amount of tritium produced in a year became larger. On the other hand, when the operation period was too short, the number of fuel exchanges increased and the annual tritium production decreased. In addition, the fuel cost rises because many fuels are burned up. It is necessary to optimize operation period. Throughout our calculations, the temperature of the LiAlO2 region was fixed at 1190 K, which is the average temperature specified in the GTHTR300 design. To produce tritium by confining it in the ceramic-coated particles, it is necessary to reduce the temperature. The influence of reduced temperature on tritium production must be examined.
This research was supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for challenging Exploratory Research, 23656574. References Nishikawa, M., Yamasaki, H., Kashimura, H., Matsuda, S., 2012. Effect of outside tritium source on tritium balance of D-T fusion reactor. Fusion Eng. Des. 87 (466-470). Gierszewski, P., 1989. Tritium supply for near-term fusion devise. Fusion Eng. Des. 10, 399–403. Matsuura, H., Kouchi, S., Nakaya, H., Yasumoto, T., Nakao, Y., Shimakawa, S., Goto, M., Nakagawa, S., Nishikawa, M., 2012a. Performance of high-temperature gascooled reactor as a tritium production device for fusion reactors. Nucl. Eng. Des. 243, 95. Nakata, T., Katanishi, S., Takada, S., Yan, X., Kunitomi, K., 2002. Nuclear Design of the Gas Turbine High Temperature Reactor (GTHTR300). JAERI-Tech (in Japanese). Yan, X., Kunitomi, K., Nakata, T., Shiozawa, S., 2003. GTHTR300 design and development. Nucl. Eng. Des. 222, 247–262. Futamura, Y., Kawamura, H., Tsuchiya, K., 1999. Tritium breeding materials date base for fusion reactor blankets (4) (Li2 O, Li2 TiO3 , Li2 ZrO3 , Li4 SiO4 Solid Breeding Materials). Ann. Rep. Hydrogen Isotope Res. Center 19, 65. Roux, N., Johnson, C., Noda, K., 1992. Properties and performance of tritium breeding ceramics. J. Nucl. Mater. 191-194, 15–22. Matsuura, H., Nakaya, H., Nakao, Y., Shimakawa, S., Goto, M., Nakagawa, S., Nishikawa, M., 2012b. Performance of gas-cooled reactor as a tritium production and continuous tritium recovery system for fusion reactors. In: Presented at SOFT 2012, Liége, Belgium. Nagaya, Y., Okumura, K., Mori, T., Nakagawa, M., 2005. MVP/GMVP: General Purpose Monte Carlo for Neutron and Photon Transport Calculation based on Continuous Energy and Multigroup Method. JAERI-Japan Atomic Energy Research Institute. Riberio, R.A., Silve, G.G., Mohallem, N.D.S., 2001. The influence of heat treatment on the structural properties of lithium aluminates. J. Phys. Chem. Solids 62, 857–864.