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EVEDA accelerator building
Fusion Engineering and Design 87 (2012) 1235–1238
Contents lists available at SciVerse ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Evaluation of gamma-ray and neutron energy for area monitoring system in the IFMIF/EVEDA accelerator building Hiroki Takahashi a,∗ , Sunao Maebara a , Hironao Sakaki b , Keiichi Hirabayashi c , Kosuke Hidaka c , Nobuhiro Shigyo c , Yukinobu Watanabe d , Kenshi Sagara e a
Directorates of Fusion Energy Research, Japan Atomic Energy Agency (JAEA), Rokkasho, Aomori, 039-3212, Japan Photo Medical Research Center, JAEA, Kizugawa, Kyoto, 619-0215, Japan c Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Motooka, Fukuoka, 819-0395, Japan d Department of Advanced Energy Engineering Science, Kyushu University, Kasuga, Fukuoka, 816-8580, Japan e Department of Physics, Kyushu University, Hakozaki, Fukuoka, 812-8581, Japan b
a r t i c l e
i n f o
Article history: Available online 30 March 2012 Keywords: IFMIF/EVEDA prototype accelerator Deuteron Area monitoring system PHITS code
a b s t r a c t The engineering validation of the IFMIF/EVEDA prototype accelerator, up to 9 MeV by supplying the deuteron beam of 125 mA, will be performed at the BA site in Rokkasho. A design of this area monitoring system, comprising of Si semiconductors and ionization chambers for covering wide energy spectrum of gamma-rays and 3 He counters for neutrons, is now in progress. To establish an applicability of this monitoring system, photon and neutron energies have to be suppressed to the detector ranges of 1.5 MeV and 15 MeV, respectively. For this purpose, the reduction of neutron and photon energies throughout shield of water in a beam dump and concrete layer is evaluated by PHITS code, using the experimental data of neutron source spectra. In this article, a similar model using the beam dump structure and the position with a degree of leaning for concrete wall in the accelerator vault is used, and their energy reduction including the air is evaluated. It is found that the neutron and photon flux are decreased by 104 -order by employing the local shields using concrete and polyethylene around beam dump, and the photon energy can be suppressed in the low energy. © 2012 Elsevier B.V. All rights reserved.
1. Introduction International Fusion Materials Irradiation Facility (IFMIF) [1–3] is an accelerator-based neutron irradiation facility to develop materials for a demonstration fusion reactor next to ITER. For preparing the necessary information to make a decision of the IFMIF construction, Engineering Validation and Engineering Design Activities (EVEDA) have been started. IFMIF/EVEDA prototype accelerator consists of an injector (output energy: 100 keV), a 175 MHz RFQ linac (0.1–5.0 MeV), a medium energy beam transport, the first section of superconducting RF linac (5.0–9.0 MeV), a high energy beam transport line and a beam dump (9 MeV–125 mA CW) [4]. In the accelerator building, an accelerator vault is surrounded by the concrete wall with thickness of 1.5 m. For the radiation controlled area (with no possibility of RI contamination), the effective dose rate has to be suppressed to less than 12.5 Sv/h with no neutron leakage. For Personal Protection System (PPS) in the prototype accelerator, a design study of the area monitoring system, comprising of Si semiconductors and ioniza-
∗ Corresponding author. Tel.: +81 175 71 6623. E-mail address: [email protected] (H. Takahashi). 0920-3796/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2012.02.109
tion chambers for covering wide energy spectrum of gamma-rays and 3 He counters for neutrons, is now in progress. In this system, the upper limits of detectable photon and neutron energies are set to be 1.5 MeV and 15 MeV, respectively. In the previous works done for the spherical model of “water: 750 mm, iron: 250 mm, concrete: 2000 mm”, the numbers of neutron and photon, which fall below the 101 -order level, were evaluated by using PHITS code. However, it was found the maximum photon energy reached up to 8 MeV, and shielding capability is not enough for achieving the required level of gamma-ray intensity [5,6]. To fit the measurable range of monitoring detectors, shielding configurations using the local concrete and polyethylene are evaluated.
2. IFMIF/EVEDA prototype accelerator 2.1. Accelerator building A schematic drawing of the prototype accelerator is shown in Fig. 1. The IFMIF/EVEDA accelerator building in Rokkasho site has the total area of 2019.5 m2 , and the accelerator vault has the inside area of W: 8.0 m × D: 41.5 m × H: 7.0 m. The vault is surrounded by concrete shield of 1.5 m thickness.
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Fig. 1. IFMIF/EVEDA accelerator building and area monitor layout.
2.2. Area monitoring system As indicated in Fig. 1, area monitoring system consists of two types; gamma-ray monitors and neutron monitor. The detectable energy range of the neutron monitor is from 0.025 eV to 15 MeV and the directional angular range is −60 to +240◦ along a vertical direction. For the gamma-ray monitor energy range is 80 keV–1.5 MeV and horizontal/vertical angular range is −90 to +90◦ /−60 to +240◦ . 3. Analysis 3.1. Nuclear data Deuteron induced thick target neutron yield at 9 MeV was measured in collaboration with Kyushu University because there was no experimental data for Cu(d,nx) reaction in the range of 5–9 MeV [7]. The experimental data which is neutron generation in case of 1 C irradiated to cupper is used as a source term in neutron transportation, and the energy reduction of photon are evaluated by PHITS code. The JENDL 4.0 is used for nuclear cross-section library.
3.2. Beam dump Schematic drawing of a beam dump is shown in Fig. 2. For the target cone made of copper, an axial length of 2500 mm, the bore diameter of 290 mm and the thickness of 5 mm are designed. On surface area, thirty-five source terms are distributed in equal. In these analyses, the hydrogen concentration in the concrete is assumed to be 0.56 wt%, and the concrete density of 2.1 g/cm3 is used to consider a safety margin for required environmental assessment. As showing Fig. 3(2), the beam dump (BD) is installed in accelerator vault and the flux of outside of accelerator vault was evaluated. Normalized neutron flux around the beam dump is indicated in Fig. 3(1). The fluxes at front and back side are 10−6 -level and 10−9 -level, respectively, and the difference is due to back streaming neutrons through the target entrance bore.
By the concrete thickness of 150 cm surrounding accelerator vault, the neutron flux is decreased to 104 or 105 as shown in Fig. 3(2). In case that deuteron beam of 125 mA is injected to the BD, the fluxes at detector 1 (D1) and detector 2 (D2) are indicated in Fig. 3(3) and (4), respectively. The maximum number of neutrons at D1 is calculated to 103 [n] level, while that of D2 is 104 [n] level. Therefore, the neutron flux has to be decreased by 104 in order to avoid neutron leakage at the outside of accelerator vault. In addition, the maximum photon energy of both detectors is about 9 MeV which is beyond the measurable range for gamma-ray. 3.3. Local shield of concrete and polyethylene Shielding characteristics changes due to additions of concrete and polyethylene material are evaluated using a spherical model as shown in Fig. 3(1) for no shield case. The neutron flux is decreased with factor of 103 for a 120 cmthickness of concrete shield (Fig. 4(1)) and factor of 101 for a 20 cmthickness of polyethylene shield (Fig. 4(2)). From these results, it is decided to employ the local shield using a 60 cm-thickness (H: 400 cm, W: 600 cm) and two 30 cm-thickness (H: 200 cm [50 cm above the floor], W: 700 cm) of concrete blocks and three 20 cm-thickness of polyethylene boards. Two polyethylene boards (H: 300 cm, W: 200 cm) are located in the front and
Fig. 2. Beam dump model.
H. Takahashi et al. / Fusion Engineering and Design 87 (2012) 1235–1238
1237
Fig. 3. BD + accelerator vault.
at the both sides (right and left) of beam dump, and another (H: 200 cm [50 cm above the floor], W: 700 cm) is located between two 30 cm-thickness of concrete blocks. For these usages of polyethylene material, we will check the embrittlement while accelerator commissioning and the operation by monitoring neutron and gamma-ray, and these boards will be replaced if necessary. As shown Fig. 5(1) and (2), the reduction of about 104 -order is obtained by the local shield for the neutron flux. At the D2
position, neutron and photon leakage has to be suppressed as low as possible. As shown in Fig. 5(3), at the D1, the photon number of 2.0 × 102 [n] are calculated at the energy of 0.5 MeV, and the number of 1.5 × 102 [n] and 5.0 × 101 [n] are also calculated at the energy of 5 MeV and 3 MeV. But, the 5 MeV and 3 MeV energy is beyond the gamma-ray detector range, these signals are evaluated to be total about 10−1 Sv/h level for the effective dose rate. Since this dose rate is smaller than the limit value of radiation
Fig. 4. Decay effect.
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H. Takahashi et al. / Fusion Engineering and Design 87 (2012) 1235–1238
Fig. 5. BD + local shield + accelerator vault.
safety (12.5 Sv/h) by two orders, the effect by signals at the D1 is small. From these calculation results, it is concluded that these proposed local shield have enough shielding characteristics for this area monitoring system. 4. Conclusion Photon and neutron energy have to be suppressed to 1.5 MeV and 15 MeV for matching to their detector range, respectively. For this purpose, using a current beam dump design model, accelerator vault and proposed local shield is evaluated by PHITS code using the experimental data of neutron spectra. In order to reduce neutron and photon fluxes, a 60 cm-thickness and two 30 cm-thickness of concrete blocks and three 20 cmthickness of polyethylene boards are employed for the local shield. At the outside of accelerator vault (D1 position), neutron is not calculated and photon flux is decreased to 102 -level. The maximum photon energy is decreased to 5 MeV. Since the effective dose rate is about 10−1 Sv/h, the effect by the photon of 5 MeV energy
seems to be small. The proposed local shield has enough shielding characteristics for this area monitoring system. Acknowledgments The authors would like to express their thanks to Dr. T. Sato of Nuclear Science and Engineering Directorate in JAEA and Dr. K. Niita, Director of Research Center of Research Organization for Information Science & Technology (RIST), for their continuous support for PHITS code usage. References [1] M. Martone (Ed.), ENEA Frascati Report, IFMIF-CDA Team, RT/ERG/FUS/96/17, 1996. [2] T. Kondo, et al., J. Nucl. Mater. 47 (1998) 258–263. [3] T.E. Shannon, et al., J. Nucl. Mater. (1998) 106. [4] A. Mosnier, et al., MOPEC056, in: Proceedings of the 1st International Particle Accelerator Conference, 2010. [5] H. Takahashi, et al., Fusion Eng. Design 86 (2011) 2795–2798. [6] H. Takahashi et al., JAEA-Conf. 2011-002, 205–209. [7] N. Shigyo, Measurement of deuteron induced thick target neutron yields at 9 MeV, J. Korean Phys. Soc. 59 (2) (2011) 1725–1728.
Contents lists available at SciVerse ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Evaluation of gamma-ray and neutron energy for area monitoring system in the IFMIF/EVEDA accelerator building Hiroki Takahashi a,∗ , Sunao Maebara a , Hironao Sakaki b , Keiichi Hirabayashi c , Kosuke Hidaka c , Nobuhiro Shigyo c , Yukinobu Watanabe d , Kenshi Sagara e a
Directorates of Fusion Energy Research, Japan Atomic Energy Agency (JAEA), Rokkasho, Aomori, 039-3212, Japan Photo Medical Research Center, JAEA, Kizugawa, Kyoto, 619-0215, Japan c Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Motooka, Fukuoka, 819-0395, Japan d Department of Advanced Energy Engineering Science, Kyushu University, Kasuga, Fukuoka, 816-8580, Japan e Department of Physics, Kyushu University, Hakozaki, Fukuoka, 812-8581, Japan b
a r t i c l e
i n f o
Article history: Available online 30 March 2012 Keywords: IFMIF/EVEDA prototype accelerator Deuteron Area monitoring system PHITS code
a b s t r a c t The engineering validation of the IFMIF/EVEDA prototype accelerator, up to 9 MeV by supplying the deuteron beam of 125 mA, will be performed at the BA site in Rokkasho. A design of this area monitoring system, comprising of Si semiconductors and ionization chambers for covering wide energy spectrum of gamma-rays and 3 He counters for neutrons, is now in progress. To establish an applicability of this monitoring system, photon and neutron energies have to be suppressed to the detector ranges of 1.5 MeV and 15 MeV, respectively. For this purpose, the reduction of neutron and photon energies throughout shield of water in a beam dump and concrete layer is evaluated by PHITS code, using the experimental data of neutron source spectra. In this article, a similar model using the beam dump structure and the position with a degree of leaning for concrete wall in the accelerator vault is used, and their energy reduction including the air is evaluated. It is found that the neutron and photon flux are decreased by 104 -order by employing the local shields using concrete and polyethylene around beam dump, and the photon energy can be suppressed in the low energy. © 2012 Elsevier B.V. All rights reserved.
1. Introduction International Fusion Materials Irradiation Facility (IFMIF) [1–3] is an accelerator-based neutron irradiation facility to develop materials for a demonstration fusion reactor next to ITER. For preparing the necessary information to make a decision of the IFMIF construction, Engineering Validation and Engineering Design Activities (EVEDA) have been started. IFMIF/EVEDA prototype accelerator consists of an injector (output energy: 100 keV), a 175 MHz RFQ linac (0.1–5.0 MeV), a medium energy beam transport, the first section of superconducting RF linac (5.0–9.0 MeV), a high energy beam transport line and a beam dump (9 MeV–125 mA CW) [4]. In the accelerator building, an accelerator vault is surrounded by the concrete wall with thickness of 1.5 m. For the radiation controlled area (with no possibility of RI contamination), the effective dose rate has to be suppressed to less than 12.5 Sv/h with no neutron leakage. For Personal Protection System (PPS) in the prototype accelerator, a design study of the area monitoring system, comprising of Si semiconductors and ioniza-
∗ Corresponding author. Tel.: +81 175 71 6623. E-mail address: [email protected] (H. Takahashi). 0920-3796/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2012.02.109
tion chambers for covering wide energy spectrum of gamma-rays and 3 He counters for neutrons, is now in progress. In this system, the upper limits of detectable photon and neutron energies are set to be 1.5 MeV and 15 MeV, respectively. In the previous works done for the spherical model of “water: 750 mm, iron: 250 mm, concrete: 2000 mm”, the numbers of neutron and photon, which fall below the 101 -order level, were evaluated by using PHITS code. However, it was found the maximum photon energy reached up to 8 MeV, and shielding capability is not enough for achieving the required level of gamma-ray intensity [5,6]. To fit the measurable range of monitoring detectors, shielding configurations using the local concrete and polyethylene are evaluated.
2. IFMIF/EVEDA prototype accelerator 2.1. Accelerator building A schematic drawing of the prototype accelerator is shown in Fig. 1. The IFMIF/EVEDA accelerator building in Rokkasho site has the total area of 2019.5 m2 , and the accelerator vault has the inside area of W: 8.0 m × D: 41.5 m × H: 7.0 m. The vault is surrounded by concrete shield of 1.5 m thickness.
1236
H. Takahashi et al. / Fusion Engineering and Design 87 (2012) 1235–1238
Fig. 1. IFMIF/EVEDA accelerator building and area monitor layout.
2.2. Area monitoring system As indicated in Fig. 1, area monitoring system consists of two types; gamma-ray monitors and neutron monitor. The detectable energy range of the neutron monitor is from 0.025 eV to 15 MeV and the directional angular range is −60 to +240◦ along a vertical direction. For the gamma-ray monitor energy range is 80 keV–1.5 MeV and horizontal/vertical angular range is −90 to +90◦ /−60 to +240◦ . 3. Analysis 3.1. Nuclear data Deuteron induced thick target neutron yield at 9 MeV was measured in collaboration with Kyushu University because there was no experimental data for Cu(d,nx) reaction in the range of 5–9 MeV [7]. The experimental data which is neutron generation in case of 1 C irradiated to cupper is used as a source term in neutron transportation, and the energy reduction of photon are evaluated by PHITS code. The JENDL 4.0 is used for nuclear cross-section library.
3.2. Beam dump Schematic drawing of a beam dump is shown in Fig. 2. For the target cone made of copper, an axial length of 2500 mm, the bore diameter of 290 mm and the thickness of 5 mm are designed. On surface area, thirty-five source terms are distributed in equal. In these analyses, the hydrogen concentration in the concrete is assumed to be 0.56 wt%, and the concrete density of 2.1 g/cm3 is used to consider a safety margin for required environmental assessment. As showing Fig. 3(2), the beam dump (BD) is installed in accelerator vault and the flux of outside of accelerator vault was evaluated. Normalized neutron flux around the beam dump is indicated in Fig. 3(1). The fluxes at front and back side are 10−6 -level and 10−9 -level, respectively, and the difference is due to back streaming neutrons through the target entrance bore.
By the concrete thickness of 150 cm surrounding accelerator vault, the neutron flux is decreased to 104 or 105 as shown in Fig. 3(2). In case that deuteron beam of 125 mA is injected to the BD, the fluxes at detector 1 (D1) and detector 2 (D2) are indicated in Fig. 3(3) and (4), respectively. The maximum number of neutrons at D1 is calculated to 103 [n] level, while that of D2 is 104 [n] level. Therefore, the neutron flux has to be decreased by 104 in order to avoid neutron leakage at the outside of accelerator vault. In addition, the maximum photon energy of both detectors is about 9 MeV which is beyond the measurable range for gamma-ray. 3.3. Local shield of concrete and polyethylene Shielding characteristics changes due to additions of concrete and polyethylene material are evaluated using a spherical model as shown in Fig. 3(1) for no shield case. The neutron flux is decreased with factor of 103 for a 120 cmthickness of concrete shield (Fig. 4(1)) and factor of 101 for a 20 cmthickness of polyethylene shield (Fig. 4(2)). From these results, it is decided to employ the local shield using a 60 cm-thickness (H: 400 cm, W: 600 cm) and two 30 cm-thickness (H: 200 cm [50 cm above the floor], W: 700 cm) of concrete blocks and three 20 cm-thickness of polyethylene boards. Two polyethylene boards (H: 300 cm, W: 200 cm) are located in the front and
Fig. 2. Beam dump model.
H. Takahashi et al. / Fusion Engineering and Design 87 (2012) 1235–1238
1237
Fig. 3. BD + accelerator vault.
at the both sides (right and left) of beam dump, and another (H: 200 cm [50 cm above the floor], W: 700 cm) is located between two 30 cm-thickness of concrete blocks. For these usages of polyethylene material, we will check the embrittlement while accelerator commissioning and the operation by monitoring neutron and gamma-ray, and these boards will be replaced if necessary. As shown Fig. 5(1) and (2), the reduction of about 104 -order is obtained by the local shield for the neutron flux. At the D2
position, neutron and photon leakage has to be suppressed as low as possible. As shown in Fig. 5(3), at the D1, the photon number of 2.0 × 102 [n] are calculated at the energy of 0.5 MeV, and the number of 1.5 × 102 [n] and 5.0 × 101 [n] are also calculated at the energy of 5 MeV and 3 MeV. But, the 5 MeV and 3 MeV energy is beyond the gamma-ray detector range, these signals are evaluated to be total about 10−1 Sv/h level for the effective dose rate. Since this dose rate is smaller than the limit value of radiation
Fig. 4. Decay effect.
1238
H. Takahashi et al. / Fusion Engineering and Design 87 (2012) 1235–1238
Fig. 5. BD + local shield + accelerator vault.
safety (12.5 Sv/h) by two orders, the effect by signals at the D1 is small. From these calculation results, it is concluded that these proposed local shield have enough shielding characteristics for this area monitoring system. 4. Conclusion Photon and neutron energy have to be suppressed to 1.5 MeV and 15 MeV for matching to their detector range, respectively. For this purpose, using a current beam dump design model, accelerator vault and proposed local shield is evaluated by PHITS code using the experimental data of neutron spectra. In order to reduce neutron and photon fluxes, a 60 cm-thickness and two 30 cm-thickness of concrete blocks and three 20 cmthickness of polyethylene boards are employed for the local shield. At the outside of accelerator vault (D1 position), neutron is not calculated and photon flux is decreased to 102 -level. The maximum photon energy is decreased to 5 MeV. Since the effective dose rate is about 10−1 Sv/h, the effect by the photon of 5 MeV energy
seems to be small. The proposed local shield has enough shielding characteristics for this area monitoring system. Acknowledgments The authors would like to express their thanks to Dr. T. Sato of Nuclear Science and Engineering Directorate in JAEA and Dr. K. Niita, Director of Research Center of Research Organization for Information Science & Technology (RIST), for their continuous support for PHITS code usage. References [1] M. Martone (Ed.), ENEA Frascati Report, IFMIF-CDA Team, RT/ERG/FUS/96/17, 1996. [2] T. Kondo, et al., J. Nucl. Mater. 47 (1998) 258–263. [3] T.E. Shannon, et al., J. Nucl. Mater. (1998) 106. [4] A. Mosnier, et al., MOPEC056, in: Proceedings of the 1st International Particle Accelerator Conference, 2010. [5] H. Takahashi, et al., Fusion Eng. Design 86 (2011) 2795–2798. [6] H. Takahashi et al., JAEA-Conf. 2011-002, 205–209. [7] N. Shigyo, Measurement of deuteron induced thick target neutron yields at 9 MeV, J. Korean Phys. Soc. 59 (2) (2011) 1725–1728.