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Radiation level analysis for the port cell of the ITER electron cyclotron-heating upper launcher
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Radiation level analysis for the port cell of the ITER electron cyclotron-heating upper launcher Bastian Weinhorst a,∗ , Ulrich Fischer a , Lei Lu a , Dirk Strauss b , Peter Spaeh b , Theo Scherer b , Dieter Leichtle c a
KIT, Institute for Neutron Physics and Reactor Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany KIT, Institute for Applied Materials, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany c F4E, Analysis & Codes/Technical Support Services, Josep Pla 2, Torres Diagonal Litoral B3, 08019 Barcelona, Spain b
h i g h l i g h t s • First detailed neutronic modelling of the ECHUL port cell with ECHUL equipment (including beam lines with diamond windows, the beam lines mounting • • • •
box, conduit boxes and rails). Three different bioshield port plug configurations and two different neutron source configurations are investigated. Radiation Levels are calculated in the port cell, focusing on the position of the diamond window. The dose rate in the port cell is below the limit for maintenance in the port cell. The radiation level at the diamond window is very low and should not influence its performance.
a r t i c l e
i n f o
Article history: Received 31 August 2015 Accepted 2 December 2015 Available online xxx Keywords: ITER ECHUL MCNP Port cell Dose rate
a b s t r a c t The electron cyclotron-heating upper launcher (ECHUL) will be installed in four upper ports of the ITER tokamak thermonuclear fusion reactor. Each ECHUL is able to deposit 8 MW power into the plasma for plasma mode stabilization via microwave beam lines. An essential part of these beam lines are the diamond windows. They are located in the upper port cell behind the bioshield to reduce the radiation levels to a minimum. The paper describes the first detailed neutronic modelling of the ECHUL port cell with ECHUL equipment. The bioshield plug is modelled including passageways for the microwave beam lines, piping and cables looms as well as rails and openings for ventilation. The port cell is equipped with the beam lines including the diamond windows, the beam lines mounting box, conduit boxes and rails. The neutrons are transported into the port cell starting from a surface source in front of the bioshield. Neutronic results are obtained for radiation levels in the port cell at different positions, mainly focusing on the diamond windows position. It is shown that the radiation level is below the limit for maintenance in the port cell. The radiation level at the diamond window is very low and should not influence its performance. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The electron cyclotron-heating upper launcher (ECHUL) [1] will be installed in four of the 18 upper ports of the ITER tokamak thermonuclear fusion reactor (see Fig. 1) which is classified by French authority as a Nuclear Facility INB-174. Each ECHUL aims to suppress plasma instabilities which could cause severe loads on the components close to the plasma by depositing 8 MW power into
∗ Corresponding author. Tel.: +49 72160823760. E-mail address: [email protected] (B. Weinhorst).
the plasma via microwave beam lines. An essential part of these beam lines are the CVD diamond windows [2] located in the upper port cell behind the bioshield. The diamond window reacts very sensible to radiation and shows deterioration signs from radiation damage as early as 10E − 4 dpa [3]. The port cell is equipped with rails for installing/removing the upper launcher, conduit boxes and a beamline mounting box holding the beam lines including the diamond window (see Fig. 3). The port cell is separated from the port interspace by the bioshield plug which includes passageways for the beam lines, piping and cable looms as well as rails and openings for ventilation. The bioshield plug is the most important component for preventing radiation to enter from the interspaces into the port
http://dx.doi.org/10.1016/j.fusengdes.2015.12.003 0920-3796/© 2015 Elsevier B.V. All rights reserved.
Please cite this article in press as: B. Weinhorst, et al., Radiation level analysis for the port cell of the ITER electron cyclotron-heating upper launcher, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.003
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Fig. 1. Vertical cut through the ITER B-lite model with integrated ECH upper launcher. The cylindrical surface for which the neutron flux and spectra was calculated is superimposed over the geometry.
cell. It is therefore essential to check the current design for its shielding properties. The obtained results are therefore discussed in the light of ITER’s dose rate design limit for maintenance in the port cell of 10 Sv/h at 1 day after shut-down [4]. The most sensible component of the microwave system is the diamond window. In this work the methodology of the performed analyses is introduced in Section 2, including the used programs, codes and data as well as a description of the used model. The results of the radiation calculations are presented in Section 3 and a conclusion is given in Section 4. 2. Methodology Neutronics calculations for the ECHUL port cell were performed using MCNP6 Monte Carlo code [5]. The Monte Carlo method is well suited to handle such complex 3D geometry like the ITER tokamak (see Fig. 1) or ITER port cells. The ECHUL port cell was modelled by using the port cells structure (Sector 15) from the ITER complex model (see Fig. 2) [6] and integrating the ECHUL port cell environment (Fig. 3) into this model (see Fig. 4). For the neutron source a cylindrical surface source in front of the bioshield at radial position of 1400 cm was used. As a conservative approach all neutrons start with velocity vectors perpendicular to the cylindrical surface which lead to larger streaming effects and head-on wall penetrations. For comparison a less conservative approach was used with an isotropic distribution of the starting velocity vector (only positive side of the cylindrical surface). To obtain the necessary neutron flux and spectra at this position the ITER MCNP B-lite model version 2 with integrated ECHUL (see
Fig. 2. Vertical cut through the model of the ITER building. The ITER tokamak, which is not shown in the model, is indicated in the centre of the figure. Only the upper three levels surrounding the tokamak are used for the port cell neutronic analyses.
Fig. 3. The ECHUL port cell environment with rails for installing/removing the upper launcher, conduit boxes with cable looms and a beamline mounting box holding the beam lines into which the diamond window is integrated. The bioshield with ventilation holes and pathways for the beam lines.
Fig. 1) was used. The bioshield in this model was voided in order to calculate only the neutron flux without neutrons reflected at the bioshield. In the port cell model several configurations of the bioshield were investigated. These are the bioshield as obtained from the ECHUL environment model including ventilation holes (10 holes, 706 cm2 each), a model with closed ventilation holes and one model with closed ventilation holes but with gaps around the waveguides (8 holes, 74.6 cm2 each) which are necessary for the waveguides installation. The ECHUL port cell MCNP geometry was generated by conversion of the simplified CAD model using the CAD Interface Program McCad [7]. The shut-down dose rate analysis was performed employing the Rigorous 2-Step (R2Smesh [8]) methodology which includes Monte Carlo MCNP5 transport calculations using FENDL-2.1 nuclear data [9] and activation calculations with the FISPACT inventory code [10] using EAF-2007 activation data [11]. In the first step of the R2Smesh method the neutron flux and spectra (175 energy bins, vitamin-J) are calculated on a fine and coarse rectangular mesh, respectively. The shape of the spectra is assumed to be the same over the coarse mesh size (100 × 100 × 100 cm3 ). This normalized spectra is multiplied by the neutron flux for every fine mesh (10 × 10 × 10 cm3 ) in order to obtain an individual spectra for each fine mesh. The statistical relative errors associated with the calculated neutron flux are less than 10% for most of the fine meshes. Exceptional cases are e.g. the interior of backside concrete walls which are negligible for
Fig. 4. The ECHUL and 5 adjacent port cells. The whole model includes a third level of rooms above the upper port level which is not shown here.
Please cite this article in press as: B. Weinhorst, et al., Radiation level analysis for the port cell of the ITER electron cyclotron-heating upper launcher, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.003
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Table 1 Neutron heating in diamond windows for the three models with two different neutron source configurations (perpendicular and isotropic). Model
Neutron heating [W/cm3 ]
Bioshield with ventilation holes
perp: 1.77E − 9 ± 0.1E − 9 iso: 2.25E − 10 ± 0.2E − 10 perp: 1.12E − 9 ± 0.5E − 10 iso: 6.50E − 11 ± 0.3E − 11 perp: 1.20E − 9 ± 0.9E − 10 iso: 6.78E − 11 ± 0.3E − 11
Bioshield without ventilation holes Bioshield with wave guide gaps
the performed analysis. The spectra are calculated over 1000 times bigger volumes (coarse mesh) and therefore provide good statistics for each energy bin. In the second step of the R2Smesh method the obtained fluxes and spectra are used to perform activation calculations for the materials in every fine mesh. Following the ITER SA2 radiation scenario [12] the materials are subjected to radiation over 20 years according to the scheduled ITER operation. The activation is calculated for 1 day after reactor shut-down. From this a decay gamma source is obtained which is used for the dose rate calculations by performing gamma transport calculations with MCNP.
Fig. 5. Vertical cut through the dose-rate distribution in the ECHUL port cell 1 day after shut-down. The yellow lines indicate surfaces with equal dose rates. In this model the bioshield has open ventilation holes and the perpendicular source configuration was used. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
3. Results In order to assess the radiation levels inside the ECHUL port cell and at the position of the diamond window several nuclear responses have been calculated. 3.1. Radiation levels at diamond window The window is subject to high intensity microwaves which deposite a large amount of heat into the diamond. The heat deposited by neutronic radiation is less than 2 nW/cm3 and can be completely neglected in cooling considerations (see Table 1). The results for the perpendicular source configuration are more than one order of magnitude larger than the results for the isotropic source configuration which is mainly due to less absorption of the neutrons in the bioshield plug. Gaps around the waveguides also increase the neutron flux at the position of the diamond windows resulting in a slightly higher heating compared to the bioshield without these gaps. Due to the large openings for the ventilation lots of neutrons stream into the port cell which results in higher heat deposition into the diamond window for this model. The diamond window reacts very sensible to radiation damage which is one reason why it will be installed behind the bioshield. With only 3E − 9 dpa during ITER lifetime (0.54 fpy [13]) for the model with open ventilation holes the radiation damage is well below the value of 1E − 4 dpa at which the thermal conductivity of the diamond window is reduced (see Table 2). Again, as already seen for the nuclear heating results, the obtained result for the model with open ventilation holes is by a factor of two higher compared to the other two models. This effect results from the neutrons streaming through the gaps in the bioshield. Therefore, holes inside Table 2 Neutron damage in diamond windows per full power year for the three models and two different neutron source configurations (perpendicular and isotropic). Model
Neutron damage [dpa/fpy]
Bioshield with ventilation holes
perp: 5.55E − 9 ± 0.2E − 9 iso: 7.39E − 10 ± 0.4E − 10 perp: 2.94E − 9 ± 0.2E − 9 iso: 1.70E − 10 ± 0.1E − 10 perp: 3.21E − 9 ± 0.1E − 9 iso: 1–79E − 10 ± 0.1E − 10
Bioshield without ventilation holes Bioshield with wave guide gaps
Fig. 6. Vertical cut through the dose-rate distribution in the ECHUL port cell 1 day after shut-down. The yellow lines indicate surfaces with equal dose rates. In this model the bioshield has closed ventilation holes and the perpendicular source configuration was used. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 7. Vertical cut through the dose-rate distribution in the ECHUL port cell 1 day after shut-down. The yellow lines indicate surfaces with equal dose rates. In this model the bioshield has closed ventilation holes but includes gaps around the waveguides. The perpendicular source configuration was used. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
the bioshield should be as small as possible and streaming should be mitigated by labyrinths if possible. 3.2. SDDR in port cell The obtained results for the dose rates for each model one day after reactor shut-down are shown in Figs. 5–10 in a vertical cut through the dose rate distribution and ECHUL port cell geometry. The distributions for the three models resemble each other very closely but show big differences for the two source configurations. The concrete of the bioshield is activated strongest because it shields the port cells from the neutron radiation coming from
Please cite this article in press as: B. Weinhorst, et al., Radiation level analysis for the port cell of the ITER electron cyclotron-heating upper launcher, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.003
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ARTICLE IN PRESS B. Weinhorst et al. / Fusion Engineering and Design xxx (2015) xxx–xxx Table 3 Shut-down dose rate 1 day after reactor shut down in ECHUL port cell. Dose rates are given for the three models with two different neutron source configurations (perpendicular and isotropic).
Fig. 8. Vertical cut through the dose-rate distribution in the ECHUL port cell 1 day after shut-down. The yellow lines indicate surfaces with equal dose rates. In this model the bioshield has open ventilation holes and the isotropic source configuration was used. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Model
Max [Sv/h]
Mean [Sv/h]
Bioshield with ventialtion holes Bioshield without ventilation holes Bioshield with wave guide gaps
perp: 14.9 ± 0.4 iso: 6.6 ± 0.2 perp: 11.3 ± 0.3 iso: 5.5 ± 0.2 perp: 13.6 ± 0.3 iso: 4.7 ± 0.2
perp: 2.0 ± 0.06 iso: 0.89 ± 0.03 perp: 0.83 ± 0.03 iso: 0.43 ± 0.01 perp: 0.89 ± 0.03 iso: 0.44 ± 0.01
With 14.9 Sv/h the highest dose rate is found for the model with open ventilation holes (mean 2 Sv/h) and perpendicular source configuration. For all results obtained with this conservative source configuration the maximum dose rate in the port cell is slightly above the 10 Sv/h ITER limit. Nevertheless, the mean value for the dose rates in the port cell is below 2 Sv/h for all models and therefore satisfying the ITER design limit. 4. Conclusions
Fig. 9. Vertical cut through the dose-rate distribution in the ECHUL port cell 1 day after shut-down. The yellow lines indicate surfaces with equal dose rates. In this model the bioshield has closed ventilation holes and the isotropic source configuration was used. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 10. Vertical cut through the dose-rate distribution in the ECHUL port cell 1 day after shut-down. The yellow lines indicate surfaces with equal dose rates. In this model the bioshield has closed ventilation holes but includes gaps around the wave-guides. The isotropic source configuration was used. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
the plasma. Yellow contour lines for 0.1, 1 and 10 Sv/h are superimposed on the distribution to give a better understanding. For the two models with closed ventilation holes the dose rate does reach the 10 Sv/h limit only in very small areas inside the port cell which shows the good shielding of the bioshield. In the case of the model with open ventilation holes high dose rates are found close to the openings. Gaps around waveguides result in a small increase in dose-rates close to the beginning of the waveguides for the perpendicular source configuration. This is due to the activation of the beamline mounting box which is directly behind the gaps around the waveguides. Table 3 gives maximal and mean values for the ECHUL port cell for all models and source configurations.
The first neutronic analysis of the ECHUL port cell was performed in order to identify weaknesses and to verify compliance of the radiation level inside the port cell with ITER dose rate limits for maintenance. Furthermore, special focus was put on the radiation which could influence the performance of the diamond window. For this analysis the model of the ECHUL port cell environment was integrated into the model of the ITER upper port cell. A neutron source in front of the bioshield was created in a conservative way in order to have a safety margin. In addition, a less conservative configuration was used to be able to classify this safety margin. The radiation damage and heating analyses performed for the diamond windows show that the neutron radiation during reactor operation will not affect the performance of the window. With 3E − 9 dpa per ITER lifetime the neutron damage is orders of magnitude lower than the limit at which the thermal conductivity of the diamond will be affected. Its location behind the bioshield is therefore well chosen from the neutronics point of view. For maintenance the port cell needs to be accessible for humans and therefore the dose rate 1 day after reactor shutdown needs to be lower than 10 Sv/h. The performed analysis shows that the mean dose rate inside the port cell satisfies this limit for all investigated models/source configurations. In the conservative case the dose rate exceeds the 10 Sv/h limit in small areas in the port cell. As the exact configuration of the port cell environment and bioshield is not yet determined and including the safety margin resulting from the conservative approach the radiation levels in the ECHUL port cell seem to comply with all relevant neutronic limits. Nevertheless, small changes in the geometry of the bioshield like introducing gaps around the waveguides have a large impact on the calculated dose rate. Minimizing the openings in the bioshield is therefore essential to maintain the good shielding of the port cell. If the necessity for further openings arises the integration of labyrinths could become necessary. Future analyses in this regard will show if labyrinths or inclined pathways through the bioshield are needed to sati. Acknowledgments This work was supported by Fusion for Energy under the grant contract No. F4E-2014-GRT-615. The views and opinions expressed herein reflect only the author’s views. Fusion for Energy is not liable for any use that may be made of the information contained therein.
Please cite this article in press as: B. Weinhorst, et al., Radiation level analysis for the port cell of the ITER electron cyclotron-heating upper launcher, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.003
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References [1] D. Strauss, G. Aiello, R. Chavan, S. Cirant, M. deBaar, D. Farina, et al., Preliminary design of the ITER ECH upper launcher, Fusion Eng. Des. 88 (11) (2013) 2761–2766. [2] K. Sakamoto, A. Kasugai, et al., Chemical vapor deposition diamond window for high-power and long pulse millimeter wave transmission, Rev. Sci. Instrum. 69 (1998) 2160–2165 (ECHUL port cell environment). [3] R. Heidinger, M. Rohde, R. Spörl, Neutron irradiation studies on window materials for EC wave systems, Fusion Eng. Des. 56–57 (October) (2001) 471–476 (ISSN 0920-3796). [4] H. Iida, V. Khripunov, L. Petrizzi, G. Federici, Nuclear analysis group, nuclear analysis report (NAR), ITER Naka & Garching Joint Work Sites, in: Internal Report G 73 DDD 2 W 0.2, Version, July, 2004. [5] J.T. Goorley, et al., Initial MCNP6 Release Overview MCNP6 Version 1.0, in: LANL Report LA-UR-13-22934, 2013. [6] M. Loughlin, ITER Analysis Model: STL model-Tokamak, Diagnostic and Tritium buildings, private communication.
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[7] L. Lu, U. Fischer, P. Pereslavtsev, Improved algorithm and advanced features for the CAD to MC conversion tool McCad, Fusion Eng. Des. 89 (October (9–10)) (2014) 1885–1888. [8] P. Pereslavtsev, U. Fischer, D. Leichtle, R. Villari, Novel approach for efficient mesh based Monte Carlo shutdown dose rate calculations, Fusion Eng. Des. 88 (October (9–10)) (2013) 2719–2722 (ISSN 0920-3796). [9] D. Lopez Aldama, A. Trkov, FENDL-2.1 Library, Update of an Evaluated Nuclear Data Library for Fusion Applications, International Atomic Energy Agency, Vienna, Austria, 2004, http://www-nds.iaea.org/fendl21/, December. [10] R.A. Forrest, et al., FISPACT 2007 user manual, in: UKAEA FUS 534 Report, March 2007. [11] R.A. Forrest, J. Kopecky, J.-C. Sublet, The European activation file: EAF-2007 neutron-induced cross section library, in: UKAEA FUS 535 Report, 2007. [12] M.J. Loughlin, N.P. Taylor, Recommended plasma scenarios for activation calculations, in: ITER Internal Report ITER D 2V3V8G v 1.1, October 2009. [13] E. Polunovskiy, Nuclear responses in vicinity of blanket module #4, private communication.
Please cite this article in press as: B. Weinhorst, et al., Radiation level analysis for the port cell of the ITER electron cyclotron-heating upper launcher, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.003
ARTICLE IN PRESS
FUSION-8373; No. of Pages 5
Fusion Engineering and Design xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Radiation level analysis for the port cell of the ITER electron cyclotron-heating upper launcher Bastian Weinhorst a,∗ , Ulrich Fischer a , Lei Lu a , Dirk Strauss b , Peter Spaeh b , Theo Scherer b , Dieter Leichtle c a
KIT, Institute for Neutron Physics and Reactor Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany KIT, Institute for Applied Materials, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany c F4E, Analysis & Codes/Technical Support Services, Josep Pla 2, Torres Diagonal Litoral B3, 08019 Barcelona, Spain b
h i g h l i g h t s • First detailed neutronic modelling of the ECHUL port cell with ECHUL equipment (including beam lines with diamond windows, the beam lines mounting • • • •
box, conduit boxes and rails). Three different bioshield port plug configurations and two different neutron source configurations are investigated. Radiation Levels are calculated in the port cell, focusing on the position of the diamond window. The dose rate in the port cell is below the limit for maintenance in the port cell. The radiation level at the diamond window is very low and should not influence its performance.
a r t i c l e
i n f o
Article history: Received 31 August 2015 Accepted 2 December 2015 Available online xxx Keywords: ITER ECHUL MCNP Port cell Dose rate
a b s t r a c t The electron cyclotron-heating upper launcher (ECHUL) will be installed in four upper ports of the ITER tokamak thermonuclear fusion reactor. Each ECHUL is able to deposit 8 MW power into the plasma for plasma mode stabilization via microwave beam lines. An essential part of these beam lines are the diamond windows. They are located in the upper port cell behind the bioshield to reduce the radiation levels to a minimum. The paper describes the first detailed neutronic modelling of the ECHUL port cell with ECHUL equipment. The bioshield plug is modelled including passageways for the microwave beam lines, piping and cables looms as well as rails and openings for ventilation. The port cell is equipped with the beam lines including the diamond windows, the beam lines mounting box, conduit boxes and rails. The neutrons are transported into the port cell starting from a surface source in front of the bioshield. Neutronic results are obtained for radiation levels in the port cell at different positions, mainly focusing on the diamond windows position. It is shown that the radiation level is below the limit for maintenance in the port cell. The radiation level at the diamond window is very low and should not influence its performance. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The electron cyclotron-heating upper launcher (ECHUL) [1] will be installed in four of the 18 upper ports of the ITER tokamak thermonuclear fusion reactor (see Fig. 1) which is classified by French authority as a Nuclear Facility INB-174. Each ECHUL aims to suppress plasma instabilities which could cause severe loads on the components close to the plasma by depositing 8 MW power into
∗ Corresponding author. Tel.: +49 72160823760. E-mail address: [email protected] (B. Weinhorst).
the plasma via microwave beam lines. An essential part of these beam lines are the CVD diamond windows [2] located in the upper port cell behind the bioshield. The diamond window reacts very sensible to radiation and shows deterioration signs from radiation damage as early as 10E − 4 dpa [3]. The port cell is equipped with rails for installing/removing the upper launcher, conduit boxes and a beamline mounting box holding the beam lines including the diamond window (see Fig. 3). The port cell is separated from the port interspace by the bioshield plug which includes passageways for the beam lines, piping and cable looms as well as rails and openings for ventilation. The bioshield plug is the most important component for preventing radiation to enter from the interspaces into the port
http://dx.doi.org/10.1016/j.fusengdes.2015.12.003 0920-3796/© 2015 Elsevier B.V. All rights reserved.
Please cite this article in press as: B. Weinhorst, et al., Radiation level analysis for the port cell of the ITER electron cyclotron-heating upper launcher, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.003
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Fig. 1. Vertical cut through the ITER B-lite model with integrated ECH upper launcher. The cylindrical surface for which the neutron flux and spectra was calculated is superimposed over the geometry.
cell. It is therefore essential to check the current design for its shielding properties. The obtained results are therefore discussed in the light of ITER’s dose rate design limit for maintenance in the port cell of 10 Sv/h at 1 day after shut-down [4]. The most sensible component of the microwave system is the diamond window. In this work the methodology of the performed analyses is introduced in Section 2, including the used programs, codes and data as well as a description of the used model. The results of the radiation calculations are presented in Section 3 and a conclusion is given in Section 4. 2. Methodology Neutronics calculations for the ECHUL port cell were performed using MCNP6 Monte Carlo code [5]. The Monte Carlo method is well suited to handle such complex 3D geometry like the ITER tokamak (see Fig. 1) or ITER port cells. The ECHUL port cell was modelled by using the port cells structure (Sector 15) from the ITER complex model (see Fig. 2) [6] and integrating the ECHUL port cell environment (Fig. 3) into this model (see Fig. 4). For the neutron source a cylindrical surface source in front of the bioshield at radial position of 1400 cm was used. As a conservative approach all neutrons start with velocity vectors perpendicular to the cylindrical surface which lead to larger streaming effects and head-on wall penetrations. For comparison a less conservative approach was used with an isotropic distribution of the starting velocity vector (only positive side of the cylindrical surface). To obtain the necessary neutron flux and spectra at this position the ITER MCNP B-lite model version 2 with integrated ECHUL (see
Fig. 2. Vertical cut through the model of the ITER building. The ITER tokamak, which is not shown in the model, is indicated in the centre of the figure. Only the upper three levels surrounding the tokamak are used for the port cell neutronic analyses.
Fig. 3. The ECHUL port cell environment with rails for installing/removing the upper launcher, conduit boxes with cable looms and a beamline mounting box holding the beam lines into which the diamond window is integrated. The bioshield with ventilation holes and pathways for the beam lines.
Fig. 1) was used. The bioshield in this model was voided in order to calculate only the neutron flux without neutrons reflected at the bioshield. In the port cell model several configurations of the bioshield were investigated. These are the bioshield as obtained from the ECHUL environment model including ventilation holes (10 holes, 706 cm2 each), a model with closed ventilation holes and one model with closed ventilation holes but with gaps around the waveguides (8 holes, 74.6 cm2 each) which are necessary for the waveguides installation. The ECHUL port cell MCNP geometry was generated by conversion of the simplified CAD model using the CAD Interface Program McCad [7]. The shut-down dose rate analysis was performed employing the Rigorous 2-Step (R2Smesh [8]) methodology which includes Monte Carlo MCNP5 transport calculations using FENDL-2.1 nuclear data [9] and activation calculations with the FISPACT inventory code [10] using EAF-2007 activation data [11]. In the first step of the R2Smesh method the neutron flux and spectra (175 energy bins, vitamin-J) are calculated on a fine and coarse rectangular mesh, respectively. The shape of the spectra is assumed to be the same over the coarse mesh size (100 × 100 × 100 cm3 ). This normalized spectra is multiplied by the neutron flux for every fine mesh (10 × 10 × 10 cm3 ) in order to obtain an individual spectra for each fine mesh. The statistical relative errors associated with the calculated neutron flux are less than 10% for most of the fine meshes. Exceptional cases are e.g. the interior of backside concrete walls which are negligible for
Fig. 4. The ECHUL and 5 adjacent port cells. The whole model includes a third level of rooms above the upper port level which is not shown here.
Please cite this article in press as: B. Weinhorst, et al., Radiation level analysis for the port cell of the ITER electron cyclotron-heating upper launcher, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.003
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Table 1 Neutron heating in diamond windows for the three models with two different neutron source configurations (perpendicular and isotropic). Model
Neutron heating [W/cm3 ]
Bioshield with ventilation holes
perp: 1.77E − 9 ± 0.1E − 9 iso: 2.25E − 10 ± 0.2E − 10 perp: 1.12E − 9 ± 0.5E − 10 iso: 6.50E − 11 ± 0.3E − 11 perp: 1.20E − 9 ± 0.9E − 10 iso: 6.78E − 11 ± 0.3E − 11
Bioshield without ventilation holes Bioshield with wave guide gaps
the performed analysis. The spectra are calculated over 1000 times bigger volumes (coarse mesh) and therefore provide good statistics for each energy bin. In the second step of the R2Smesh method the obtained fluxes and spectra are used to perform activation calculations for the materials in every fine mesh. Following the ITER SA2 radiation scenario [12] the materials are subjected to radiation over 20 years according to the scheduled ITER operation. The activation is calculated for 1 day after reactor shut-down. From this a decay gamma source is obtained which is used for the dose rate calculations by performing gamma transport calculations with MCNP.
Fig. 5. Vertical cut through the dose-rate distribution in the ECHUL port cell 1 day after shut-down. The yellow lines indicate surfaces with equal dose rates. In this model the bioshield has open ventilation holes and the perpendicular source configuration was used. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
3. Results In order to assess the radiation levels inside the ECHUL port cell and at the position of the diamond window several nuclear responses have been calculated. 3.1. Radiation levels at diamond window The window is subject to high intensity microwaves which deposite a large amount of heat into the diamond. The heat deposited by neutronic radiation is less than 2 nW/cm3 and can be completely neglected in cooling considerations (see Table 1). The results for the perpendicular source configuration are more than one order of magnitude larger than the results for the isotropic source configuration which is mainly due to less absorption of the neutrons in the bioshield plug. Gaps around the waveguides also increase the neutron flux at the position of the diamond windows resulting in a slightly higher heating compared to the bioshield without these gaps. Due to the large openings for the ventilation lots of neutrons stream into the port cell which results in higher heat deposition into the diamond window for this model. The diamond window reacts very sensible to radiation damage which is one reason why it will be installed behind the bioshield. With only 3E − 9 dpa during ITER lifetime (0.54 fpy [13]) for the model with open ventilation holes the radiation damage is well below the value of 1E − 4 dpa at which the thermal conductivity of the diamond window is reduced (see Table 2). Again, as already seen for the nuclear heating results, the obtained result for the model with open ventilation holes is by a factor of two higher compared to the other two models. This effect results from the neutrons streaming through the gaps in the bioshield. Therefore, holes inside Table 2 Neutron damage in diamond windows per full power year for the three models and two different neutron source configurations (perpendicular and isotropic). Model
Neutron damage [dpa/fpy]
Bioshield with ventilation holes
perp: 5.55E − 9 ± 0.2E − 9 iso: 7.39E − 10 ± 0.4E − 10 perp: 2.94E − 9 ± 0.2E − 9 iso: 1.70E − 10 ± 0.1E − 10 perp: 3.21E − 9 ± 0.1E − 9 iso: 1–79E − 10 ± 0.1E − 10
Bioshield without ventilation holes Bioshield with wave guide gaps
Fig. 6. Vertical cut through the dose-rate distribution in the ECHUL port cell 1 day after shut-down. The yellow lines indicate surfaces with equal dose rates. In this model the bioshield has closed ventilation holes and the perpendicular source configuration was used. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 7. Vertical cut through the dose-rate distribution in the ECHUL port cell 1 day after shut-down. The yellow lines indicate surfaces with equal dose rates. In this model the bioshield has closed ventilation holes but includes gaps around the waveguides. The perpendicular source configuration was used. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
the bioshield should be as small as possible and streaming should be mitigated by labyrinths if possible. 3.2. SDDR in port cell The obtained results for the dose rates for each model one day after reactor shut-down are shown in Figs. 5–10 in a vertical cut through the dose rate distribution and ECHUL port cell geometry. The distributions for the three models resemble each other very closely but show big differences for the two source configurations. The concrete of the bioshield is activated strongest because it shields the port cells from the neutron radiation coming from
Please cite this article in press as: B. Weinhorst, et al., Radiation level analysis for the port cell of the ITER electron cyclotron-heating upper launcher, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.003
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ARTICLE IN PRESS B. Weinhorst et al. / Fusion Engineering and Design xxx (2015) xxx–xxx Table 3 Shut-down dose rate 1 day after reactor shut down in ECHUL port cell. Dose rates are given for the three models with two different neutron source configurations (perpendicular and isotropic).
Fig. 8. Vertical cut through the dose-rate distribution in the ECHUL port cell 1 day after shut-down. The yellow lines indicate surfaces with equal dose rates. In this model the bioshield has open ventilation holes and the isotropic source configuration was used. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Model
Max [Sv/h]
Mean [Sv/h]
Bioshield with ventialtion holes Bioshield without ventilation holes Bioshield with wave guide gaps
perp: 14.9 ± 0.4 iso: 6.6 ± 0.2 perp: 11.3 ± 0.3 iso: 5.5 ± 0.2 perp: 13.6 ± 0.3 iso: 4.7 ± 0.2
perp: 2.0 ± 0.06 iso: 0.89 ± 0.03 perp: 0.83 ± 0.03 iso: 0.43 ± 0.01 perp: 0.89 ± 0.03 iso: 0.44 ± 0.01
With 14.9 Sv/h the highest dose rate is found for the model with open ventilation holes (mean 2 Sv/h) and perpendicular source configuration. For all results obtained with this conservative source configuration the maximum dose rate in the port cell is slightly above the 10 Sv/h ITER limit. Nevertheless, the mean value for the dose rates in the port cell is below 2 Sv/h for all models and therefore satisfying the ITER design limit. 4. Conclusions
Fig. 9. Vertical cut through the dose-rate distribution in the ECHUL port cell 1 day after shut-down. The yellow lines indicate surfaces with equal dose rates. In this model the bioshield has closed ventilation holes and the isotropic source configuration was used. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 10. Vertical cut through the dose-rate distribution in the ECHUL port cell 1 day after shut-down. The yellow lines indicate surfaces with equal dose rates. In this model the bioshield has closed ventilation holes but includes gaps around the wave-guides. The isotropic source configuration was used. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
the plasma. Yellow contour lines for 0.1, 1 and 10 Sv/h are superimposed on the distribution to give a better understanding. For the two models with closed ventilation holes the dose rate does reach the 10 Sv/h limit only in very small areas inside the port cell which shows the good shielding of the bioshield. In the case of the model with open ventilation holes high dose rates are found close to the openings. Gaps around waveguides result in a small increase in dose-rates close to the beginning of the waveguides for the perpendicular source configuration. This is due to the activation of the beamline mounting box which is directly behind the gaps around the waveguides. Table 3 gives maximal and mean values for the ECHUL port cell for all models and source configurations.
The first neutronic analysis of the ECHUL port cell was performed in order to identify weaknesses and to verify compliance of the radiation level inside the port cell with ITER dose rate limits for maintenance. Furthermore, special focus was put on the radiation which could influence the performance of the diamond window. For this analysis the model of the ECHUL port cell environment was integrated into the model of the ITER upper port cell. A neutron source in front of the bioshield was created in a conservative way in order to have a safety margin. In addition, a less conservative configuration was used to be able to classify this safety margin. The radiation damage and heating analyses performed for the diamond windows show that the neutron radiation during reactor operation will not affect the performance of the window. With 3E − 9 dpa per ITER lifetime the neutron damage is orders of magnitude lower than the limit at which the thermal conductivity of the diamond will be affected. Its location behind the bioshield is therefore well chosen from the neutronics point of view. For maintenance the port cell needs to be accessible for humans and therefore the dose rate 1 day after reactor shutdown needs to be lower than 10 Sv/h. The performed analysis shows that the mean dose rate inside the port cell satisfies this limit for all investigated models/source configurations. In the conservative case the dose rate exceeds the 10 Sv/h limit in small areas in the port cell. As the exact configuration of the port cell environment and bioshield is not yet determined and including the safety margin resulting from the conservative approach the radiation levels in the ECHUL port cell seem to comply with all relevant neutronic limits. Nevertheless, small changes in the geometry of the bioshield like introducing gaps around the waveguides have a large impact on the calculated dose rate. Minimizing the openings in the bioshield is therefore essential to maintain the good shielding of the port cell. If the necessity for further openings arises the integration of labyrinths could become necessary. Future analyses in this regard will show if labyrinths or inclined pathways through the bioshield are needed to sati. Acknowledgments This work was supported by Fusion for Energy under the grant contract No. F4E-2014-GRT-615. The views and opinions expressed herein reflect only the author’s views. Fusion for Energy is not liable for any use that may be made of the information contained therein.
Please cite this article in press as: B. Weinhorst, et al., Radiation level analysis for the port cell of the ITER electron cyclotron-heating upper launcher, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.003
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Please cite this article in press as: B. Weinhorst, et al., Radiation level analysis for the port cell of the ITER electron cyclotron-heating upper launcher, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.003