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Neutronics for equatorial and upper ports in ITER
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Neutronics for equatorial and upper ports in ITER A. Serikov a,∗ , U. Fischer a , M. Henderson b , D. Leichtle a , C.S. Pitcher b , P. Spaeh a , D. Strauss a , A. Suarez b , B. Weinhorst a a Karlsruhe Institute of Technology (KIT), Institute for Neutron Physics and Reactor Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany b ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance, France
h i g h l i g h t s • • • • •
ITER neutronics calculations for Diagnostic Equatorial Port Plug (EPP) and Electron Cyclotron Heating Upper Launcher (ECHUL). Activation and radiation shielding calculations have been performed using the MCNP5, FISPACT-2007, and R2Smesh codes. Dominant effect of radiation streaming along the port plug gaps was recognized. An optimized double labyrinth was recommended for the current EPP design. Neutronics modelling assumptions significantly affect fluxes and doses inside the ITER port interspaces.
a r t i c l e
i n f o
Article history: Received 13 September 2012 Received in revised form 6 February 2013 Accepted 11 March 2013 Available online xxx Keywords: ITER Fusion neutronics Diagnostics Equatorial port Upper port ECH launcher Shutdown dose rate MCNP R2Smesh
a b s t r a c t Specific neutronics features of the ITER equatorial and upper ports are discussed in this paper as related to the design development of Diagnostic Equatorial Port Plug (EPP) and Electron Cyclotron Heating Upper Launcher (ECHUL). The focus is on the EPP analysis. Neutronics analyses are based on new calculation results of neutron/photon fluxes, nuclear heating, neutron damage and shutdown dose rates. The results were obtained with the radiation transport code MCNP5, the activation code FISPACT-2007, and the Rigorous 2 Step mesh-based (R2Smesh) interface code which allows to provide shutdown dose rate distributions with high spatial resolution. It was revealed that neutron flux levels in the port access areas, the resulting activation of the port materials and the equivalent radiation doses imposed to work personnel after ITER shutdown are strongly dependent on the openings in the port shielding blocks. For the ECHUL in the upper port, neutron fluxes have been calculated for an updated ITER model and compared with previous results. This work reveals substantial radiation cross-talk effects between the lower, the equatorial and the upper ITER ports and provides fundamental results which can be utilized for further investigations of suitable design options of ITER ports. © 2013 Published by Elsevier B.V.
1. Introduction The ITER machine must withstand the 14 MeV neutrons generated on the D-T fusion nuclear reactions in the plasma chamber and impinged on the blanket First Wall (FW) shown in Fig. 1. The ITER machine is very large (height of 30 m, the same in diameter inside its cryostat), with a complex shaped geometry and tight mm-tolerance for components assembly. The challenges arising in the neutronics modelling of ITER are associated with the deeppenetrating radiation with ∼8 orders of magnitude of neutron fluxes attenuation from blanket FW to the bio-shield. The objective for this neutronics analysis is to guarantee the nuclear safety for maintenance personnel of the equatorial and
∗ Corresponding author. Tel.: +49 72160822157. E-mail address: [email protected] (A. Serikov).
upper ports after the ITER shutdown. To reach this goal, parametric shielding and activation analyses were performed using simple port models, then applying design improvements to them, and finally integrating them into the global ITER model for verification analyses. The ITER design target is to limit the radiation exposure of work personnel to 100 Sv/h in terms of the shutdown dose rate (SDDR) at 106 s after neutron irradiation. It was demonstrated in works [1–3] that in case of the Diagnostic Equatorial Port Plug (EPP) this SDDR limit is difficult to meet because of the neutron streaming through the gaps arranged around the EPP Diagnostic Shield Module (DSM) and along the diagnostics penetrations inside the DSM [4]. As outcome, the EPP design has been established [5] to provide radiation shielding for diagnostics and port maintenance. This paper quantifies the effect of the mutual dependence of radiation levels inside the three ITER ports (upper, equatorial, and lower) by analysing the separate SDDR contributions from the respective port interspaces. It is clear that radiation penetrates
0920-3796/$ – see front matter © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.fusengdes.2013.03.037
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3. Results of EPP neutronics analysis As outcome of the previous parametric neutronics analyses [1–3], an optimized double labyrinth configuration was devised and integrated into the ITER-global model B-lite. The schematic view of such double labyrinth is depicted in Fig. 3. The cross-talks between the interspace volumes F5 (lower port), F1 (equatorial port), and F3 (upper port) shown in Fig. 2 were quantified by opening and closing individual leakage paths in the three ITER ports. Four MCNP models have been run with the following modifications of the so-called “Ultimate Baseline Model (UBM)”:
Fig. 1. Computer Aided Design (CAD) view of the blanket First Wall (FW), Equatorial Port Plug (EPP) and its back-side interspace behind Closure Plate inside Port Extension (PE).
1. UBM with all ports and all gaps “closed” (except of blanket intermodule gaps) by filling the gaps with a steel–water mixture of 80%–20%, as shown in Fig. 4;
at some extent through all the components inside the ITER cryostat. The level of penetration, however, depends on the particular shielding configuration and radiation leakage pathways between components. In this sense, all the port interspaces in the current neutronics ITER global model are inter-connected. This paper shows how much they are connected in terms of SDDR. The radiation leakage from one port to another is called “radiation cross-talk” between the ports, and the SDDR assessments of such cross-talks are presented in Section 3. 2. Methodological approach The ITER design encompasses many engineering parts. Some of them, such as gaps and channels provide streaming paths for neutron and secondary photon radiation, and they must be explicitly modelled. Others (blanket, vacuum vessel, EPP drawers) allow the homogenization of shield materials. The Monte Carlo code MCNP5 in versions 1.40 and 1.60 [6] is used with the ITER-global MCNP5 model B-lite plotted in Fig. 2. For the SDDR analysis, the R2Smesh interface system [7] is applied which couples MCNP5 transport and FISPACT-2007 [8] activation calculations on a superimposed mesh.
Fig. 2. Vertical cut of the MCNP5 B-lite model with five interspace volumes F1–F5 to examine the cross-talk effect.
Fig. 3. Schematic view of the optimized double labyrinth EPP configuration (vertical cut).
Fig. 4. Vertical cut of the Ultimate Baseline B-lite MCNP Model (UBM) with completely blocked upper, equatorial, and lower ports. Only the inter-blanket gaps are open.
Please cite this article in press as: A. Serikov, et al., Neutronics for equatorial and upper ports in ITER, Fusion Eng. Des. (2013), http://dx.doi.org/10.1016/j.fusengdes.2013.03.037
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Table 1 Shutdown dose rate (SDDR) cross-talks between interspaces of three ports of B-lite global ITER model. Contribution to SDDR from the following ITER components
SDDR (Sv/h) F5 Lower port
SDDR (Sv/h) F1 Equatorial port
SDDR (Sv/h) F3 Upper port
1. Ultimate baseline (all ports closed) 2. Original lower port 3. Diagnostics equatorial port plug with double labyrinth and closed inter-drawer gaps 4. Original upper port
9 189 10 1
17 18 41 2
19 6 9 48
Total
209
78
82
2. Only the lower port “opened”, i.e. using the standard B-lite lower port; 3. Only the equatorial port “opened”, i.e. the Equatorial Port Plug has been replaced with the diagnostic version of the doublelabyrinth, depicted schematically in Fig. 3; 4. Only the upper port “opened”, i.e. using the standard B-lite upper port. Table 1 shows the SDDR results calculated for the four different MCNP model variants (rows 1–4) as the contributors to the designated volumes of the lower (F5), the equatorial (F1), and the upper (F3) ports. It was assumed that the voids of the blanket manifolds and the in-vessel coils of the original B-lite model have been filled with 80% steel and 20% water. Also, several ITER components are missing in this B-lite model (Port Extension bellows, thermal shield and Poloidal Field Coil supports) which will have an impact on the radiation cross talks. From the results of SDDR cross-talks presented in Table 1 it follows that half of total SDDR in the Equatorial Port interspace (78 Sv/h) is coming from other ITER parts, mainly from the original B-lite Lower Port (18 Sv/h) and general leakage of the blanket and VV of the UBM (17 Sv/h). The SDDR results are based on the generally reliable statistical quality of the MCNP5 results with less than 10% of relative statistical errors. The UBM B-lite model is depicted in Fig. 4. Fig. 5 visualizes the shutdown dose rate (SDDR) in the vicinity of the Equatorial Port Plug, assuming of additional shield for upper and lower ports. The EPP interspace SDDR is 58 Sv/h. It is assumed in this analysis that the EPP DSM drawers themselves do not include the diagnostics apertures which could contribute additionally 50 Sv/h. The DSM is homogeneous
Fig. 5. Map of shutdown dose rate (SDDR) in the vicinity of the Equatorial Port Plug (with shielded upper and lower ports) B-lite MCNP model horizontal cut.
80%–20% steel–water mixture. Therefore, taking into account these DSM apertures and thus adding 50 Sv/h to the EPP SDDR, the 100 Sv/h access limit is exceeded in the current global ITER model. Consequently, further improvements of the radiation shielding design are required. This should be done in a synergistic manner for the whole ITER device, especially its lower port. Nuclear heating distributions have been calculated for the critical locations of EPP, particularly inside the solid steel plate connected to VV which represents a part of second labyrinth shown in Fig. 3. The highest nuclear heating is at 0.23 W/cc in front of that custom-fitted VV-plate. The rate of displacements per atom (dpa) of steel located in critical positions of the EPP has been calculated using the MCNP5 code with FENDL-2.1 damage cross-section data based on the standard NRT model [6]. The damage, expressed as rate per full power year (fpy), reaches its maximum value 0.3 dpa/fpy at the same location as the nuclear heating. All the results were normalized to the nominal DT fusion power of 500 MW. The SDDR results have been provided at 106 s after shutdown in order to compare with the 100 Sv/h access limit. The ICRP74 photon-to-dose conversion factors are used to convert decay gamma spectra to SDDR at the final step of the R2Smesh scheme. The SA2 neutron irradiation scenario [9] is applied for the activation calculations performed with FISPACT as part of the R2Smesh interface; it assumes 0.3 MWa/m2 of neutron fluence on the blanket FW and D-T campaign of 0.63 fpy.
4. Results of neutron flux calculations for ECHUL Neutronics computational support for the design of Electron Cyclotron Heating Upper Launcher (ECHUL) development has been provided for a couple of years [10] and continues for the present design activities. The ECHUL design was changed due to the recession of the first wall, which also influences the position of the mirrors. Also, additional shielding blocks were introduced at positions 1 and 2 shown in Fig. 6 to protect the areas with envisaged re-welding and therefore reduce the helium production on (n, ˛) nuclear reaction. The MCNP ITER model A-lite, which was used for the helium gas production calculations, is obsolete for neutron flux calculations in the rear part of the upper launcher. Therefore, the ECHUL model was integrated into the original MCNP ITER model B-lite. During the integration a new, more realistic cut out of the blanket shield module was introduced. The new cut out takes away a significantly larger portion of the BSM because of the different position of the mirrors due to the recession of the first wall. Neutron fluxes have been calculated inside the same five interspace control volumes F1–F5 shown in Fig. 2. Table 2 gives the calculated neutron fluxes in these volumes for different MCNP models. For the original B-lite model including the ECHUL and the new cut out one finds a neutron flux of 31.8 × 107 n/cm2 /s in the interspace F3 behind the upper launcher. Compared to the B-lite model with a dummy upper port plug (80% steel and 20% water shielding block) this is 1.5 times higher. As it is given in work [11],
Please cite this article in press as: A. Serikov, et al., Neutronics for equatorial and upper ports in ITER, Fusion Eng. Des. (2013), http://dx.doi.org/10.1016/j.fusengdes.2013.03.037
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4 Table 2 Neutron fluxes for five control volumes (F1–F5). Control volume location
F1 pre-design EPP F2 pre-design EPP F3 F4 F5
Total neutron flux (107 n/cm2 /s) Original B-lite, dummy UPP
Original B-lite ECHUL old cut out
Original B-lite ECHUL new cut out
Advanced B-lite, dummy UPP
Advanced B-lite ECHUL new cut out
35 24.8 22.9 15.3 11.7
36.9 28.2 29.9 22.6 14.8
49.2 31.9 31.8 29.8 24.8
7.2 6.7 8.5 4.7 2.0
11.0 9.4 13.6 11.4 4.8
voids, e.g. the voids around the upper port plug, the voids around the blanket manifolds and in-vessel coils. There are several pieces of hardware not yet modelled in the ITER standard neutronics model (B-lite) and in order to quantify the radiation cross-talk effect discussed in this work, further modelling efforts are required. This conclusion is confirmed by analyses performed for the Electron Cyclotron Heating Upper Launcher (ECHUL) port plug model integrated into different B-lite variants. Neutronics modelling assumptions applied for the pockets of blanket manifolds and in-vessel coils were shown to significantly affect fluxes and doses in both upper and equatorial port interspaces. Acknowledgments
Fig. 6. ECHUL integrated into the MCNP ITER B-lite model. Positions 1 and 2 indicate the additional shielding blocks.
the total neutron flux at the rear side of upper launcher was estimated to be approximately 5.7 × 107 n/cm2 /s. The new results are significantly higher. This is mainly due to deficiencies of the global B-lite model, i.e. it is not due to the insertion of the ECHUL port plug in the model. In order to obtain more realistic results, the ECHUL port plug was then integrated into a more advanced B-lite model. Here again one finds an 1.5 fold increase if one compares the model with dummy upper port plug versus ECHUL, but the calculated flux is reduced to 13.6 × 107 n/cm2 /s due to the fact that the pockets of blanket manifolds and of in-vessel coils were filled with homogenized steel/water/void mixtures calculated precisely with the CATIA 3D CAD model. In the original B-lite model the pockets were empty, thus opening additional pathways for the radiation streaming. These results show the need to model these pockets accurately in accordance with the current CAD engineering design of ITER. 5. Conclusion Radiation shielding analyses have been performed for the ITER equatorial and upper ports with focus on the Diagnostic Equatorial Port Plug (EPP). A dedicated parametric analysis showed the efficiency of labyrinth type gap configurations to mitigate the effect of the radiation streaming along the gaps to the port access interspace. As a major result of the analyses performed, an optimized double labyrinth was recommended for the current EPP design. On the ITER hardware side, the designs of the systems and components could also be potentially improved by reducing gaps and
This work has been funded mainly by the ITER Organization under the ITER service contracts nos. IO/10/4300000298 and IO/12/4300000548 and partly by the European Joint Undertaking for ITER and the Development of Fusion Energy (Fusion for Energy) under contract no. F4E-2010-GRT-161 using an adaptation of the A-lite and B-lite MCNP models which were developed as a collaborative effort between the FDS team of ASIPP China, University of Wisconsin-Madison, ENEA Frascati, CCFE UK, JAEA Naka, and the ITER Organization. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization. References [1] A. Serikov, U. Fischer, D. Leichtle, C.S. Pitcher, A. Suarez, Local modeling approach for Monte Carlo parametric neutronic analysis in ITER, in: Proc. German Annual Meeting on Nuclear Technology, May 22–24, Stuttgart, Germany, 2012. [2] A. Serikov, U. Fischer, D. Leichtle, C.S. Pitcher, A. Suarez, Verification of the local Monte Carlo modelling approach for fusion neutronics applications in ITER, Transactions of the American Nuclear Society 106 (2012) 641–644. [3] A. Serikov, U. Fischer, D. Leichtle, C.S. Pitcher, Monte Carlo radiation shielding and activation analyses for the Diagnostic Equatorial Port Plug in ITER, Fusion Engineering and Design 87 (2012) 690–694. [4] F. Moro, B. Esposito, G. Brolatti, D. Marocco, R. Villari, S. Salasca, et al., Neutronic analysis of the ITER Equatorial Port Plug 1, Fusion Engineering and Design 87 (2012) 1224–1229. [5] C.S. Pitcher, R. Barnsley, L. Bertalot, A. Encheva, R. Feder, J.P. Friconneau, et al., Port-based plasma diagnostic infrastructure on ITER, in: TOFE-2012 Conference, August 27–31, Nashville, 2012. [6] X-5 Monte Carlo Team, MCNP-A General Monte Carlo N-Particle Transport Code, Version 5, Volume I, MCNP Overview and Theory, Los Alamos National Laboratory Report, LA-UR-03-1987, April 24, 2003. [7] M. Majerle, U. Fischer, D. Leichtle, A. Serikov, Verification and validation of the R2Smesh approach for the calculation of high resolution shutdown dose rate distributions, Fusion Engineering and Design 87 (2012) 443–447. [8] R.A. Forrest, et al., FISPACT 2007 user manual, UKAEA FUS 534 report, March 2007. [9] M.J. Loughlin, N.P. Taylor, Recommended plasma scenarios for activation calculations, ITER Internal Report ITER D 2V3V8G v 1.1, 28 October, 2009. [10] A. Serikov, U. Fischer, D. Grosse, P. Spaeh, D. Strauss, Evolution of shielding computations for the ITER Upper ECH Launcher, Nuclear Technology 175 (1) (2011) 238–250. [11] A. Serikov, U. Fischer, R. Heidinger, P. Spaeh, S. Stickel, H. Tsige-Tamirat, Nuclear analyses for the ITER ECRH launcher, Nuclear Fusion 48 (2008) 054016, http://dx.doi.org/10.1088/0029-5515/48/5/054016.
Please cite this article in press as: A. Serikov, et al., Neutronics for equatorial and upper ports in ITER, Fusion Eng. Des. (2013), http://dx.doi.org/10.1016/j.fusengdes.2013.03.037
ARTICLE IN PRESS Fusion Engineering and Design xxx (2013) xxx–xxx
Contents lists available at SciVerse ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Neutronics for equatorial and upper ports in ITER A. Serikov a,∗ , U. Fischer a , M. Henderson b , D. Leichtle a , C.S. Pitcher b , P. Spaeh a , D. Strauss a , A. Suarez b , B. Weinhorst a a Karlsruhe Institute of Technology (KIT), Institute for Neutron Physics and Reactor Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany b ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance, France
h i g h l i g h t s • • • • •
ITER neutronics calculations for Diagnostic Equatorial Port Plug (EPP) and Electron Cyclotron Heating Upper Launcher (ECHUL). Activation and radiation shielding calculations have been performed using the MCNP5, FISPACT-2007, and R2Smesh codes. Dominant effect of radiation streaming along the port plug gaps was recognized. An optimized double labyrinth was recommended for the current EPP design. Neutronics modelling assumptions significantly affect fluxes and doses inside the ITER port interspaces.
a r t i c l e
i n f o
Article history: Received 13 September 2012 Received in revised form 6 February 2013 Accepted 11 March 2013 Available online xxx Keywords: ITER Fusion neutronics Diagnostics Equatorial port Upper port ECH launcher Shutdown dose rate MCNP R2Smesh
a b s t r a c t Specific neutronics features of the ITER equatorial and upper ports are discussed in this paper as related to the design development of Diagnostic Equatorial Port Plug (EPP) and Electron Cyclotron Heating Upper Launcher (ECHUL). The focus is on the EPP analysis. Neutronics analyses are based on new calculation results of neutron/photon fluxes, nuclear heating, neutron damage and shutdown dose rates. The results were obtained with the radiation transport code MCNP5, the activation code FISPACT-2007, and the Rigorous 2 Step mesh-based (R2Smesh) interface code which allows to provide shutdown dose rate distributions with high spatial resolution. It was revealed that neutron flux levels in the port access areas, the resulting activation of the port materials and the equivalent radiation doses imposed to work personnel after ITER shutdown are strongly dependent on the openings in the port shielding blocks. For the ECHUL in the upper port, neutron fluxes have been calculated for an updated ITER model and compared with previous results. This work reveals substantial radiation cross-talk effects between the lower, the equatorial and the upper ITER ports and provides fundamental results which can be utilized for further investigations of suitable design options of ITER ports. © 2013 Published by Elsevier B.V.
1. Introduction The ITER machine must withstand the 14 MeV neutrons generated on the D-T fusion nuclear reactions in the plasma chamber and impinged on the blanket First Wall (FW) shown in Fig. 1. The ITER machine is very large (height of 30 m, the same in diameter inside its cryostat), with a complex shaped geometry and tight mm-tolerance for components assembly. The challenges arising in the neutronics modelling of ITER are associated with the deeppenetrating radiation with ∼8 orders of magnitude of neutron fluxes attenuation from blanket FW to the bio-shield. The objective for this neutronics analysis is to guarantee the nuclear safety for maintenance personnel of the equatorial and
∗ Corresponding author. Tel.: +49 72160822157. E-mail address: [email protected] (A. Serikov).
upper ports after the ITER shutdown. To reach this goal, parametric shielding and activation analyses were performed using simple port models, then applying design improvements to them, and finally integrating them into the global ITER model for verification analyses. The ITER design target is to limit the radiation exposure of work personnel to 100 Sv/h in terms of the shutdown dose rate (SDDR) at 106 s after neutron irradiation. It was demonstrated in works [1–3] that in case of the Diagnostic Equatorial Port Plug (EPP) this SDDR limit is difficult to meet because of the neutron streaming through the gaps arranged around the EPP Diagnostic Shield Module (DSM) and along the diagnostics penetrations inside the DSM [4]. As outcome, the EPP design has been established [5] to provide radiation shielding for diagnostics and port maintenance. This paper quantifies the effect of the mutual dependence of radiation levels inside the three ITER ports (upper, equatorial, and lower) by analysing the separate SDDR contributions from the respective port interspaces. It is clear that radiation penetrates
0920-3796/$ – see front matter © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.fusengdes.2013.03.037
Please cite this article in press as: A. Serikov, et al., Neutronics for equatorial and upper ports in ITER, Fusion Eng. Des. (2013), http://dx.doi.org/10.1016/j.fusengdes.2013.03.037
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3. Results of EPP neutronics analysis As outcome of the previous parametric neutronics analyses [1–3], an optimized double labyrinth configuration was devised and integrated into the ITER-global model B-lite. The schematic view of such double labyrinth is depicted in Fig. 3. The cross-talks between the interspace volumes F5 (lower port), F1 (equatorial port), and F3 (upper port) shown in Fig. 2 were quantified by opening and closing individual leakage paths in the three ITER ports. Four MCNP models have been run with the following modifications of the so-called “Ultimate Baseline Model (UBM)”:
Fig. 1. Computer Aided Design (CAD) view of the blanket First Wall (FW), Equatorial Port Plug (EPP) and its back-side interspace behind Closure Plate inside Port Extension (PE).
1. UBM with all ports and all gaps “closed” (except of blanket intermodule gaps) by filling the gaps with a steel–water mixture of 80%–20%, as shown in Fig. 4;
at some extent through all the components inside the ITER cryostat. The level of penetration, however, depends on the particular shielding configuration and radiation leakage pathways between components. In this sense, all the port interspaces in the current neutronics ITER global model are inter-connected. This paper shows how much they are connected in terms of SDDR. The radiation leakage from one port to another is called “radiation cross-talk” between the ports, and the SDDR assessments of such cross-talks are presented in Section 3. 2. Methodological approach The ITER design encompasses many engineering parts. Some of them, such as gaps and channels provide streaming paths for neutron and secondary photon radiation, and they must be explicitly modelled. Others (blanket, vacuum vessel, EPP drawers) allow the homogenization of shield materials. The Monte Carlo code MCNP5 in versions 1.40 and 1.60 [6] is used with the ITER-global MCNP5 model B-lite plotted in Fig. 2. For the SDDR analysis, the R2Smesh interface system [7] is applied which couples MCNP5 transport and FISPACT-2007 [8] activation calculations on a superimposed mesh.
Fig. 2. Vertical cut of the MCNP5 B-lite model with five interspace volumes F1–F5 to examine the cross-talk effect.
Fig. 3. Schematic view of the optimized double labyrinth EPP configuration (vertical cut).
Fig. 4. Vertical cut of the Ultimate Baseline B-lite MCNP Model (UBM) with completely blocked upper, equatorial, and lower ports. Only the inter-blanket gaps are open.
Please cite this article in press as: A. Serikov, et al., Neutronics for equatorial and upper ports in ITER, Fusion Eng. Des. (2013), http://dx.doi.org/10.1016/j.fusengdes.2013.03.037
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Table 1 Shutdown dose rate (SDDR) cross-talks between interspaces of three ports of B-lite global ITER model. Contribution to SDDR from the following ITER components
SDDR (Sv/h) F5 Lower port
SDDR (Sv/h) F1 Equatorial port
SDDR (Sv/h) F3 Upper port
1. Ultimate baseline (all ports closed) 2. Original lower port 3. Diagnostics equatorial port plug with double labyrinth and closed inter-drawer gaps 4. Original upper port
9 189 10 1
17 18 41 2
19 6 9 48
Total
209
78
82
2. Only the lower port “opened”, i.e. using the standard B-lite lower port; 3. Only the equatorial port “opened”, i.e. the Equatorial Port Plug has been replaced with the diagnostic version of the doublelabyrinth, depicted schematically in Fig. 3; 4. Only the upper port “opened”, i.e. using the standard B-lite upper port. Table 1 shows the SDDR results calculated for the four different MCNP model variants (rows 1–4) as the contributors to the designated volumes of the lower (F5), the equatorial (F1), and the upper (F3) ports. It was assumed that the voids of the blanket manifolds and the in-vessel coils of the original B-lite model have been filled with 80% steel and 20% water. Also, several ITER components are missing in this B-lite model (Port Extension bellows, thermal shield and Poloidal Field Coil supports) which will have an impact on the radiation cross talks. From the results of SDDR cross-talks presented in Table 1 it follows that half of total SDDR in the Equatorial Port interspace (78 Sv/h) is coming from other ITER parts, mainly from the original B-lite Lower Port (18 Sv/h) and general leakage of the blanket and VV of the UBM (17 Sv/h). The SDDR results are based on the generally reliable statistical quality of the MCNP5 results with less than 10% of relative statistical errors. The UBM B-lite model is depicted in Fig. 4. Fig. 5 visualizes the shutdown dose rate (SDDR) in the vicinity of the Equatorial Port Plug, assuming of additional shield for upper and lower ports. The EPP interspace SDDR is 58 Sv/h. It is assumed in this analysis that the EPP DSM drawers themselves do not include the diagnostics apertures which could contribute additionally 50 Sv/h. The DSM is homogeneous
Fig. 5. Map of shutdown dose rate (SDDR) in the vicinity of the Equatorial Port Plug (with shielded upper and lower ports) B-lite MCNP model horizontal cut.
80%–20% steel–water mixture. Therefore, taking into account these DSM apertures and thus adding 50 Sv/h to the EPP SDDR, the 100 Sv/h access limit is exceeded in the current global ITER model. Consequently, further improvements of the radiation shielding design are required. This should be done in a synergistic manner for the whole ITER device, especially its lower port. Nuclear heating distributions have been calculated for the critical locations of EPP, particularly inside the solid steel plate connected to VV which represents a part of second labyrinth shown in Fig. 3. The highest nuclear heating is at 0.23 W/cc in front of that custom-fitted VV-plate. The rate of displacements per atom (dpa) of steel located in critical positions of the EPP has been calculated using the MCNP5 code with FENDL-2.1 damage cross-section data based on the standard NRT model [6]. The damage, expressed as rate per full power year (fpy), reaches its maximum value 0.3 dpa/fpy at the same location as the nuclear heating. All the results were normalized to the nominal DT fusion power of 500 MW. The SDDR results have been provided at 106 s after shutdown in order to compare with the 100 Sv/h access limit. The ICRP74 photon-to-dose conversion factors are used to convert decay gamma spectra to SDDR at the final step of the R2Smesh scheme. The SA2 neutron irradiation scenario [9] is applied for the activation calculations performed with FISPACT as part of the R2Smesh interface; it assumes 0.3 MWa/m2 of neutron fluence on the blanket FW and D-T campaign of 0.63 fpy.
4. Results of neutron flux calculations for ECHUL Neutronics computational support for the design of Electron Cyclotron Heating Upper Launcher (ECHUL) development has been provided for a couple of years [10] and continues for the present design activities. The ECHUL design was changed due to the recession of the first wall, which also influences the position of the mirrors. Also, additional shielding blocks were introduced at positions 1 and 2 shown in Fig. 6 to protect the areas with envisaged re-welding and therefore reduce the helium production on (n, ˛) nuclear reaction. The MCNP ITER model A-lite, which was used for the helium gas production calculations, is obsolete for neutron flux calculations in the rear part of the upper launcher. Therefore, the ECHUL model was integrated into the original MCNP ITER model B-lite. During the integration a new, more realistic cut out of the blanket shield module was introduced. The new cut out takes away a significantly larger portion of the BSM because of the different position of the mirrors due to the recession of the first wall. Neutron fluxes have been calculated inside the same five interspace control volumes F1–F5 shown in Fig. 2. Table 2 gives the calculated neutron fluxes in these volumes for different MCNP models. For the original B-lite model including the ECHUL and the new cut out one finds a neutron flux of 31.8 × 107 n/cm2 /s in the interspace F3 behind the upper launcher. Compared to the B-lite model with a dummy upper port plug (80% steel and 20% water shielding block) this is 1.5 times higher. As it is given in work [11],
Please cite this article in press as: A. Serikov, et al., Neutronics for equatorial and upper ports in ITER, Fusion Eng. Des. (2013), http://dx.doi.org/10.1016/j.fusengdes.2013.03.037
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4 Table 2 Neutron fluxes for five control volumes (F1–F5). Control volume location
F1 pre-design EPP F2 pre-design EPP F3 F4 F5
Total neutron flux (107 n/cm2 /s) Original B-lite, dummy UPP
Original B-lite ECHUL old cut out
Original B-lite ECHUL new cut out
Advanced B-lite, dummy UPP
Advanced B-lite ECHUL new cut out
35 24.8 22.9 15.3 11.7
36.9 28.2 29.9 22.6 14.8
49.2 31.9 31.8 29.8 24.8
7.2 6.7 8.5 4.7 2.0
11.0 9.4 13.6 11.4 4.8
voids, e.g. the voids around the upper port plug, the voids around the blanket manifolds and in-vessel coils. There are several pieces of hardware not yet modelled in the ITER standard neutronics model (B-lite) and in order to quantify the radiation cross-talk effect discussed in this work, further modelling efforts are required. This conclusion is confirmed by analyses performed for the Electron Cyclotron Heating Upper Launcher (ECHUL) port plug model integrated into different B-lite variants. Neutronics modelling assumptions applied for the pockets of blanket manifolds and in-vessel coils were shown to significantly affect fluxes and doses in both upper and equatorial port interspaces. Acknowledgments
Fig. 6. ECHUL integrated into the MCNP ITER B-lite model. Positions 1 and 2 indicate the additional shielding blocks.
the total neutron flux at the rear side of upper launcher was estimated to be approximately 5.7 × 107 n/cm2 /s. The new results are significantly higher. This is mainly due to deficiencies of the global B-lite model, i.e. it is not due to the insertion of the ECHUL port plug in the model. In order to obtain more realistic results, the ECHUL port plug was then integrated into a more advanced B-lite model. Here again one finds an 1.5 fold increase if one compares the model with dummy upper port plug versus ECHUL, but the calculated flux is reduced to 13.6 × 107 n/cm2 /s due to the fact that the pockets of blanket manifolds and of in-vessel coils were filled with homogenized steel/water/void mixtures calculated precisely with the CATIA 3D CAD model. In the original B-lite model the pockets were empty, thus opening additional pathways for the radiation streaming. These results show the need to model these pockets accurately in accordance with the current CAD engineering design of ITER. 5. Conclusion Radiation shielding analyses have been performed for the ITER equatorial and upper ports with focus on the Diagnostic Equatorial Port Plug (EPP). A dedicated parametric analysis showed the efficiency of labyrinth type gap configurations to mitigate the effect of the radiation streaming along the gaps to the port access interspace. As a major result of the analyses performed, an optimized double labyrinth was recommended for the current EPP design. On the ITER hardware side, the designs of the systems and components could also be potentially improved by reducing gaps and
This work has been funded mainly by the ITER Organization under the ITER service contracts nos. IO/10/4300000298 and IO/12/4300000548 and partly by the European Joint Undertaking for ITER and the Development of Fusion Energy (Fusion for Energy) under contract no. F4E-2010-GRT-161 using an adaptation of the A-lite and B-lite MCNP models which were developed as a collaborative effort between the FDS team of ASIPP China, University of Wisconsin-Madison, ENEA Frascati, CCFE UK, JAEA Naka, and the ITER Organization. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization. References [1] A. Serikov, U. Fischer, D. Leichtle, C.S. Pitcher, A. Suarez, Local modeling approach for Monte Carlo parametric neutronic analysis in ITER, in: Proc. German Annual Meeting on Nuclear Technology, May 22–24, Stuttgart, Germany, 2012. [2] A. Serikov, U. Fischer, D. Leichtle, C.S. Pitcher, A. Suarez, Verification of the local Monte Carlo modelling approach for fusion neutronics applications in ITER, Transactions of the American Nuclear Society 106 (2012) 641–644. [3] A. Serikov, U. Fischer, D. Leichtle, C.S. Pitcher, Monte Carlo radiation shielding and activation analyses for the Diagnostic Equatorial Port Plug in ITER, Fusion Engineering and Design 87 (2012) 690–694. [4] F. Moro, B. Esposito, G. Brolatti, D. Marocco, R. Villari, S. Salasca, et al., Neutronic analysis of the ITER Equatorial Port Plug 1, Fusion Engineering and Design 87 (2012) 1224–1229. [5] C.S. Pitcher, R. Barnsley, L. Bertalot, A. Encheva, R. Feder, J.P. Friconneau, et al., Port-based plasma diagnostic infrastructure on ITER, in: TOFE-2012 Conference, August 27–31, Nashville, 2012. [6] X-5 Monte Carlo Team, MCNP-A General Monte Carlo N-Particle Transport Code, Version 5, Volume I, MCNP Overview and Theory, Los Alamos National Laboratory Report, LA-UR-03-1987, April 24, 2003. [7] M. Majerle, U. Fischer, D. Leichtle, A. Serikov, Verification and validation of the R2Smesh approach for the calculation of high resolution shutdown dose rate distributions, Fusion Engineering and Design 87 (2012) 443–447. [8] R.A. Forrest, et al., FISPACT 2007 user manual, UKAEA FUS 534 report, March 2007. [9] M.J. Loughlin, N.P. Taylor, Recommended plasma scenarios for activation calculations, ITER Internal Report ITER D 2V3V8G v 1.1, 28 October, 2009. [10] A. Serikov, U. Fischer, D. Grosse, P. Spaeh, D. Strauss, Evolution of shielding computations for the ITER Upper ECH Launcher, Nuclear Technology 175 (1) (2011) 238–250. [11] A. Serikov, U. Fischer, R. Heidinger, P. Spaeh, S. Stickel, H. Tsige-Tamirat, Nuclear analyses for the ITER ECRH launcher, Nuclear Fusion 48 (2008) 054016, http://dx.doi.org/10.1088/0029-5515/48/5/054016.
Please cite this article in press as: A. Serikov, et al., Neutronics for equatorial and upper ports in ITER, Fusion Eng. Des. (2013), http://dx.doi.org/10.1016/j.fusengdes.2013.03.037