- Email: [email protected]
Measurement and analysis of neutron flux spectra in a neutronics mock-up of the HCLL test blanket module
Fusion Engineering and Design 85 (2010) 1803–1806
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Measurement and analysis of neutron flux spectra in a neutronics mock-up of the HCLL test blanket module A. Klix a,∗ , P. Batistoni b , R. Böttger c , D. Lebrun-Grandie a , U. Fischer a , J. Henniger d , D. Leichtle a , R. Villari b a
Association FZK-Euratom, Karlsruhe Institute for Technology, D-76344 Eggenstein-Leopoldshafen, Germany ENEA Frascati, Via E. Fermi 45, I-00044 Frascati, Italy PTB Braunschweig, Bundesallee 100, D-38116 Braunschweig, Germany d Technische Universität Dresden, D-01062 Dresden, Germany b c
a r t i c l e
i n f o
Keywords: HCLL-TBM Mock-up Fast neutron flux Time-of-arrival spectrum Lithium lead
a b s t r a c t Fast neutron and gamma-ray flux spectra and time-of-arrival spectra of slow neutrons have been measured in a neutronics mock-up of the European Helium-Cooled Lithium–Lead Test Blanket Module with the aim to validate nuclear cross-section data. The mock-up was irradiated with fusion peak neutrons from the DT neutron generator of the Technical University of Dresden. A well characterized cylindrical NE-213 scintillator was inserted into two positions in the LiPb/EUROFER assembly. Pulse height spectra from neutrons and gamma-rays were recorded from the NE-213 output. The spectra were then unfolded with experimentally obtained response matrices of the NE-213 detector. Time-of-arrival spectra of slow neutrons were measured with a 3 He counter placed in the mock-up, and the neutron generator was operated in pulsed mode. Monte Carlo calculations using the MCNP code and nuclear cross-section data from the JEFF-3.1.1 and FENDL-2.1 libraries were performed and the results are compared with the experimental results. A good agreement of measurement and calculation was found with some deviations in certain energy intervals. © 2010 Published by Elsevier B.V. All rights reserved.
1. Introduction In the frame of the European Fusion Technology Programme, a series of neutronics benchmark experiments are performed. In these experiments, mock-ups of the two European Test Blanket Modules (TBM) lines for ITER are irradiated and nuclear responses such as the tritium production rate, neutron and gamma-ray spectra are measured. The measurements provide a database to check and validate the capability of the neutronics tools and nuclear data libraries for the design of breeding blankets and especially the TBMs developed for testing in ITER. While previous experiments were devoted to the Helium-Cooled Pebble Bed (HCPB) TBM concept, the current focus is on experiments on a mock-up of the Helium-Cooled Lithium Lead (HCLL) breeder blanket module [1] which employs the eutectic alloy LiPb as breeder/multiplier and Eurofer as structural material. The experiments were performed in two campaigns. Firstly, a series of irradiations had been conducted with the aim to measure the tritium production by various techniques and detectors, and
∗ Corresponding author at: Institute for Neutron Physics and Reactor Technology, Karlsruhe Institute for Technology, 76344 Eggenstein-Leopoldshafen, Germany. Tel.: +49 7247 82 3768; fax: +49 7247 82 3718. E-mail address: [email protected] (A. Klix). 0920-3796/$ – see front matter © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2010.05.038
dosimetry foil activation rates at the Frascati neutron generator [2]. In the second campaign, these experiments were complemented by measurements of neutron and gamma-ray flux spectra at the 14 MeV neutron generator of the Technical University of Dresden (TUD). Such measurements are not only essential for validating the shielding efficiency of the HCLL-TBM but also for identifying deficiencies in the available cross-section database. In the present work, we report on the measurements of fast neutron and gammaray spectra with a NE-213 detector and time-of-arrival spectra of slow neutrons with a 3 He counter in two positions inside the mock-up and compare them with spectra based on Monte Carlo calculations with a detailed geometry description of the mock-up. 2. Experiment The mock-up was made of layers of lithium–lead which were separated by Eurofer sheets with a thickness of 0.9 cm. The entire assembly was at room temperature for this neutronics experiment. The lithium–lead layers were made of bricks of the size 9.0 cm by 3.6 cm by 17.3 cm. A sketch of the mock-up and its composition is shown in Fig. 1 and a photograph of the experimental set-up can be seen in Fig. 2. The mock-up is the same as used before for the measurement of the tritium production rate at FNG of ENEA/Frascati [2], however, in this case the central channel which accommodated the
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Fig. 1. Sketch of the mock-up with sizes in mm. Fig. 3. Block diagram of the fast neutron spectrometer used in this experiment.
tritium detectors (see Ref. [2]) was replaced by solid bricks of LiPb. A special channel with squared cross-section of 5 cm × 5 cm was prepared perpendicular to the central axis of the mock-up (as defined by the deuteron beam of the neutron generator) from five bricks of the LiPb. This channel served to accommodate the NE213 detector and 3 He proportional counter. By changing the rear bricks with the front bricks of the middle LiPb layer, two separate measurement positions were realized. The neutron generator is a deuteron accelerator with a terminal deuteron energy of 320 keV bombarding a water-cooled tritiumloaded titanium (Ti-T) target. For the experiments described here, the neutron source was monitored with a silicon detector for the alpha particle associated with the DT fusion reaction. The source strength of the DT neutron source for this measurement was typically 1.4 × 108 n/s. The mock-up was placed in front of the Ti-T target of the neutron generator at a distance of 32.7 cm. Fast neutron spectra were obtained by means of a cylindrical NE-213 scintillator with 3.75 cm diameter and thickness. The scintillator was coupled to a photomultiplier with a 50 cm long light
guide. Pulse shape discrimination techniques with a Canberra PSD 2160 and a CFD 2128 together with a multi-parameter acquisition system was used to separate recorded neutron events from events caused by gamma-rays. A sketch of the electronic circuit is shown in Fig. 3. The obtained raw pulse height spectra where unfolded with the MAXED code [3] and experimentally obtained response matrices for this detector [4]. Figs. 4 and 5 show the resulting fast neutron and gamma-ray flux spectra in comparison with calculated ones. Time-of-arrival spectra were measured with a Canberra 24NH15 proportional counter filled with 3 He in both measurement positions. This counter tube has a helium pressure of 4 bar and was operated at a bias voltage of 950 V. The counter tube was connected to an ORTEC 142 preamplifier and the output signal was amplified with an ORTEC 470 and further processed with a multi channel scaler. The scaler was operated in sweeping mode. Each sweep was started with the synchronization signal from the neutron generator and run for 900 s. The neutron generator was set to produce DT neutron pulses with a width of 10 s and a repetition rate of 1 kHz.
Fig. 2. The lithium–lead mock-up arranged for the fast neutron flux measurement at the neutron generator of TUD. The TiT target with the deuteron beam line is to the right, and the photomultiplier housing and light guide to the NE-213 scintillator in the Position B is to the left.
Fig. 4. Fast neutron spectra measured with the NE-213 spectrometer in comparison with calculated spectra based on MCNP and cross-section mostly from JEFF-3.1.1 and FENDL-2.1, respectively.
A. Klix et al. / Fusion Engineering and Design 85 (2010) 1803–1806
Fig. 5. Gamma-ray spectra measured with the NE-213 spectrometer in comparison with calculated spectra based on MCNP and cross-section mostly from JEFF-3.1.1 and FENDL-2.1, respectively.
The resulting time-of-arrival spectrum after accumulating sweeps over a period of approximately 30 min is shown in Fig. 5. The spectrum was normalized to the sensitive volume and the number of produced DT neutrons as recorded with the silicon detector for the associated alpha particle from the DT reaction. 3. Calculation Calculations have been performed with the Monte Carlo Code MCNP5 [5] and transport cross-sections from JEFF-3.1.1 [6] and FENDL-2.1 [7]. Details of the mock-up materials are described in Ref. [2]. The neutron source of the DT neutron generator was modeled in the MCNP input using source card energy distribution tables and a geometry and material description of the target assembly of the neutron generator. The distribution tables have been prepared with the help of the DROSG code [8]. Prior to this experiment, the correct description of the neutron spectrum has been verified experimentally at different angles with respect to the deuteron beam by the activation of a set of Zr/Nb foils following Ref. [9]. Fast neutron and gamma-ray flux spectra at the location of the detectors were obtained by track length estimator tallies. The NE213 detector and the helium proportional counter were described in detail in the MCNP input. In case of the helium proportional counter, the response was obtained by multiplying the neutron flux spectra from the track length estimator tally with the reaction cross-section for the (n,p) reaction on 3 He using also data from JEFF-3.1.1. The effective geometry of the 3 He counter was investigated previously in the thermal neutron beam of the FRG-1 research reactor of GKSS Geesthacht and it was verified that the length of the sensitive volume was 15.0 cm and the volume itself 67.9 cm3 . 4. Discussion The fast neutron flux in this mock-up is expected to be determined mostly by interactions with lead nuclei due to their abundance in the mock-up. Slow neutrons, however, are at the end of a cascade of interactions and the slow neutron flux will finally be determined by absorption on 6 Li, which is the strongest absorber in terms of the macroscopic absorption cross-section in the LiPb. Measured and calculated fast neutron spectra for the two detector positions chosen for this experiment are presented in Fig. 4. The
1805
Fig. 6. Time-of-arrival spectral measured with the 3 He counter in the back position (Position A). “sn” means source neutron, the original DT neutron.
measured neutron spectrum was calibrated adjusting the 14 MeV peaks. The calculated fast neutron spectra based on FENDL-2.1 and JEFF-3.1.1 show only minor differences, but there is an underestimation of the calculated values in the energy range 11–13 MeV in Position B while the calculated values between 5 and 11 MeV are slightly higher than the measured ones. Fig. 5 shows the measured and calculated gamma-ray flux spectra for the same measurement positions. There is a good agreement of experiment and calculation values in both positions with some overestimation between 1 and 2 MeV. Since both, the gamma-ray and fast neutron flux, in the Position A (back position) is described rather well by the calculation with JEFF-3.1.1 and FENDL-2.1 with a small overestimation of the calculation in some energy intervals, it can be concluded from this analysis that shielding calculations will be quite reliable with a tendency to be conservative. However, one should not forget that the real blanket structure will be much more complicated and contain more chemical elements with influence on the neutron balance than can be considered in these mock-up experiments. Therefore one should see this experiment as part of a series of validation experiments which will also include similar measurements on the real TBMs in ITER during DD and DT phases. Time-of-arrival spectra of slow neutrons are shown in Figs. 5 and 6. Again, the two cross-section evaluations used for the calculation yield very similar results. The calculations show that the response of the He counter to neutrons between 0 and 1 eV is already one order of magnitude larger than in all higher energy intervals 45 s after the DT neutron pulse’s rising edge. From this time to the decay of the disappearance of the slow neutron population around 250 s after the DT neutron pulse the He measurement is completely dominated by slow neutrons. It is therefore sensitive to the absorption cross-section in the assembly which is mostly due to the 6 Li concentration in the LiPb. A lithium concentration of 0.28 wt.% had been used in the present calculations which was deduced from the results of the measurements in the mock-up at FNG [2]. Fig. 7 shows the effect of a 10% change in the Li concentration on the time-of-arrival spectrum for illustration. Since the reaction cross-section for the 6 Li(n,a)T reaction which determines the absorption cross-section of 6 Li in the energy range considered here is well known, it is concluded that the measurements with the He counter confirm an effective Li content of 0.28 wt.% in the LiPb (Fig. 8).
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state-of-the-art evaluated cross-section data and neutron/gamma transport codes for the design of the TBMs. Here we report on measurements of the fast and slow neutron and gamma-ray fluxes which were conducted at the neutron laboratory of the Technical University of Dresden. Comparisons of the fast neutron and gammaray fluxes with calculated values based on the JEFF-3.1.1 library and the reference library for ITER, FENDL-2.1, showed some discrepancies in some energy intervals but agreed rather well in general. The slow neutron flux tested with the time-of-arrival method is in very good agreement with the calculations assuming a Li content of 0.28 wt.% in the LiPb which is half of the nominal value of 0.61 wt.%. This conforms the activation foil and tritium production rate measurements conducted earlier with this mock-up at FNG. The reason for the discrepancy in the Li or 6 Li concentration is still under investigation. Acknowledgements
Fig. 7. Time-of-arrival spectral measured with the 3 He counter in the front position (Position B).
This work, supported by the European Communities under the contracts of Association with EURATOM, was carried out within the framework of the European Fusion Development Agreement. The views and opinions expressed herein do not necessarily reflect those of the European Commission. References
Fig. 8. Influence on changes of the lithium content on the time-of-arrival spectrum. A change of approximately 10% is clearly visible.
5. Conclusions Neutronics experiments with a mock-up of the European HCLL-TBM are currently underway with the aim to validate
[1] G. Rampal, D. Gatelet, L. Giancarli, G. Laffont, A. Li-Puma, J.F. Salavy, E. Rigal, Design approach for the main ITER test blanket modules for the EU helium cooled lithium–lead blankets, Fusion Eng. Des. 81 (2006) 695. [2] P. Batistoni, M. Angelone, P. Carconi, U. Fischer, K. Kondo, A. Klix, et al., Neutronics experiments on HCPB and HCLL TBM mock-ups in preparation of nuclear measurement in ITER, in: Proceedings of 9th International Symposium on Fusion Nuclear Technology, Dalian, China, October 11–16, 2009. [3] M. Reginatto, P. Goldhagen, S. Neumann, Spectrum unfolding, sensitivity analysis and propagation of uncertainties with the maximum entropy deconvolution code MAXED, Nucl. Instrum. Methods A 476 (2002) 242. [4] S. Guldbakke, H. Klein, A. Meister, J. Pulpan, U. Scheler, M. Tichy, S. Unholzer, in: H. Farrar, et al. (Eds.), Response Matrices of NE213 Scintillation Detectors for Neutrons, Reactor Dosimetry ASTM STP 1228, American Society for Testing Materials, 1995, pp. 310–322. [5] MCNP—A General Monte Carlo N-Particle Transport code, Version 5, Report LAUR-03-1987, Los Alamos, 2003. [6] A. Santamarina, D. Bernard, Y. Rugama (Eds.), The JEFF-3.1.1 Nuclear Data Library, JEFF Report 22, Validation Results from JEF-2.2 to JEFF-3.1.1, NEA Data Bank (2009), ISBN:978-92-64r-r99074-6. [7] D.L. Aldama, A. Trkov, FENDL-2.1—Update of an Evaluated Nuclear Data Library for Fusion Application, INDC(NDS)-467, IAEA, 2004. [8] M. Drosg, DROSG-2000: Neutron Source Reactions, IAEA-NDS-87, IAEA Nuclear Data Section, May 2005. [9] V.E. Lewis, K.J. Zieba, A transfer standard for d + T neutron fluence and energy, Nucl. Instrum. Methods 174 (1980) 141–144.
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Measurement and analysis of neutron flux spectra in a neutronics mock-up of the HCLL test blanket module A. Klix a,∗ , P. Batistoni b , R. Böttger c , D. Lebrun-Grandie a , U. Fischer a , J. Henniger d , D. Leichtle a , R. Villari b a
Association FZK-Euratom, Karlsruhe Institute for Technology, D-76344 Eggenstein-Leopoldshafen, Germany ENEA Frascati, Via E. Fermi 45, I-00044 Frascati, Italy PTB Braunschweig, Bundesallee 100, D-38116 Braunschweig, Germany d Technische Universität Dresden, D-01062 Dresden, Germany b c
a r t i c l e
i n f o
Keywords: HCLL-TBM Mock-up Fast neutron flux Time-of-arrival spectrum Lithium lead
a b s t r a c t Fast neutron and gamma-ray flux spectra and time-of-arrival spectra of slow neutrons have been measured in a neutronics mock-up of the European Helium-Cooled Lithium–Lead Test Blanket Module with the aim to validate nuclear cross-section data. The mock-up was irradiated with fusion peak neutrons from the DT neutron generator of the Technical University of Dresden. A well characterized cylindrical NE-213 scintillator was inserted into two positions in the LiPb/EUROFER assembly. Pulse height spectra from neutrons and gamma-rays were recorded from the NE-213 output. The spectra were then unfolded with experimentally obtained response matrices of the NE-213 detector. Time-of-arrival spectra of slow neutrons were measured with a 3 He counter placed in the mock-up, and the neutron generator was operated in pulsed mode. Monte Carlo calculations using the MCNP code and nuclear cross-section data from the JEFF-3.1.1 and FENDL-2.1 libraries were performed and the results are compared with the experimental results. A good agreement of measurement and calculation was found with some deviations in certain energy intervals. © 2010 Published by Elsevier B.V. All rights reserved.
1. Introduction In the frame of the European Fusion Technology Programme, a series of neutronics benchmark experiments are performed. In these experiments, mock-ups of the two European Test Blanket Modules (TBM) lines for ITER are irradiated and nuclear responses such as the tritium production rate, neutron and gamma-ray spectra are measured. The measurements provide a database to check and validate the capability of the neutronics tools and nuclear data libraries for the design of breeding blankets and especially the TBMs developed for testing in ITER. While previous experiments were devoted to the Helium-Cooled Pebble Bed (HCPB) TBM concept, the current focus is on experiments on a mock-up of the Helium-Cooled Lithium Lead (HCLL) breeder blanket module [1] which employs the eutectic alloy LiPb as breeder/multiplier and Eurofer as structural material. The experiments were performed in two campaigns. Firstly, a series of irradiations had been conducted with the aim to measure the tritium production by various techniques and detectors, and
∗ Corresponding author at: Institute for Neutron Physics and Reactor Technology, Karlsruhe Institute for Technology, 76344 Eggenstein-Leopoldshafen, Germany. Tel.: +49 7247 82 3768; fax: +49 7247 82 3718. E-mail address: [email protected] (A. Klix). 0920-3796/$ – see front matter © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2010.05.038
dosimetry foil activation rates at the Frascati neutron generator [2]. In the second campaign, these experiments were complemented by measurements of neutron and gamma-ray flux spectra at the 14 MeV neutron generator of the Technical University of Dresden (TUD). Such measurements are not only essential for validating the shielding efficiency of the HCLL-TBM but also for identifying deficiencies in the available cross-section database. In the present work, we report on the measurements of fast neutron and gammaray spectra with a NE-213 detector and time-of-arrival spectra of slow neutrons with a 3 He counter in two positions inside the mock-up and compare them with spectra based on Monte Carlo calculations with a detailed geometry description of the mock-up. 2. Experiment The mock-up was made of layers of lithium–lead which were separated by Eurofer sheets with a thickness of 0.9 cm. The entire assembly was at room temperature for this neutronics experiment. The lithium–lead layers were made of bricks of the size 9.0 cm by 3.6 cm by 17.3 cm. A sketch of the mock-up and its composition is shown in Fig. 1 and a photograph of the experimental set-up can be seen in Fig. 2. The mock-up is the same as used before for the measurement of the tritium production rate at FNG of ENEA/Frascati [2], however, in this case the central channel which accommodated the
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A. Klix et al. / Fusion Engineering and Design 85 (2010) 1803–1806
Fig. 1. Sketch of the mock-up with sizes in mm. Fig. 3. Block diagram of the fast neutron spectrometer used in this experiment.
tritium detectors (see Ref. [2]) was replaced by solid bricks of LiPb. A special channel with squared cross-section of 5 cm × 5 cm was prepared perpendicular to the central axis of the mock-up (as defined by the deuteron beam of the neutron generator) from five bricks of the LiPb. This channel served to accommodate the NE213 detector and 3 He proportional counter. By changing the rear bricks with the front bricks of the middle LiPb layer, two separate measurement positions were realized. The neutron generator is a deuteron accelerator with a terminal deuteron energy of 320 keV bombarding a water-cooled tritiumloaded titanium (Ti-T) target. For the experiments described here, the neutron source was monitored with a silicon detector for the alpha particle associated with the DT fusion reaction. The source strength of the DT neutron source for this measurement was typically 1.4 × 108 n/s. The mock-up was placed in front of the Ti-T target of the neutron generator at a distance of 32.7 cm. Fast neutron spectra were obtained by means of a cylindrical NE-213 scintillator with 3.75 cm diameter and thickness. The scintillator was coupled to a photomultiplier with a 50 cm long light
guide. Pulse shape discrimination techniques with a Canberra PSD 2160 and a CFD 2128 together with a multi-parameter acquisition system was used to separate recorded neutron events from events caused by gamma-rays. A sketch of the electronic circuit is shown in Fig. 3. The obtained raw pulse height spectra where unfolded with the MAXED code [3] and experimentally obtained response matrices for this detector [4]. Figs. 4 and 5 show the resulting fast neutron and gamma-ray flux spectra in comparison with calculated ones. Time-of-arrival spectra were measured with a Canberra 24NH15 proportional counter filled with 3 He in both measurement positions. This counter tube has a helium pressure of 4 bar and was operated at a bias voltage of 950 V. The counter tube was connected to an ORTEC 142 preamplifier and the output signal was amplified with an ORTEC 470 and further processed with a multi channel scaler. The scaler was operated in sweeping mode. Each sweep was started with the synchronization signal from the neutron generator and run for 900 s. The neutron generator was set to produce DT neutron pulses with a width of 10 s and a repetition rate of 1 kHz.
Fig. 2. The lithium–lead mock-up arranged for the fast neutron flux measurement at the neutron generator of TUD. The TiT target with the deuteron beam line is to the right, and the photomultiplier housing and light guide to the NE-213 scintillator in the Position B is to the left.
Fig. 4. Fast neutron spectra measured with the NE-213 spectrometer in comparison with calculated spectra based on MCNP and cross-section mostly from JEFF-3.1.1 and FENDL-2.1, respectively.
A. Klix et al. / Fusion Engineering and Design 85 (2010) 1803–1806
Fig. 5. Gamma-ray spectra measured with the NE-213 spectrometer in comparison with calculated spectra based on MCNP and cross-section mostly from JEFF-3.1.1 and FENDL-2.1, respectively.
The resulting time-of-arrival spectrum after accumulating sweeps over a period of approximately 30 min is shown in Fig. 5. The spectrum was normalized to the sensitive volume and the number of produced DT neutrons as recorded with the silicon detector for the associated alpha particle from the DT reaction. 3. Calculation Calculations have been performed with the Monte Carlo Code MCNP5 [5] and transport cross-sections from JEFF-3.1.1 [6] and FENDL-2.1 [7]. Details of the mock-up materials are described in Ref. [2]. The neutron source of the DT neutron generator was modeled in the MCNP input using source card energy distribution tables and a geometry and material description of the target assembly of the neutron generator. The distribution tables have been prepared with the help of the DROSG code [8]. Prior to this experiment, the correct description of the neutron spectrum has been verified experimentally at different angles with respect to the deuteron beam by the activation of a set of Zr/Nb foils following Ref. [9]. Fast neutron and gamma-ray flux spectra at the location of the detectors were obtained by track length estimator tallies. The NE213 detector and the helium proportional counter were described in detail in the MCNP input. In case of the helium proportional counter, the response was obtained by multiplying the neutron flux spectra from the track length estimator tally with the reaction cross-section for the (n,p) reaction on 3 He using also data from JEFF-3.1.1. The effective geometry of the 3 He counter was investigated previously in the thermal neutron beam of the FRG-1 research reactor of GKSS Geesthacht and it was verified that the length of the sensitive volume was 15.0 cm and the volume itself 67.9 cm3 . 4. Discussion The fast neutron flux in this mock-up is expected to be determined mostly by interactions with lead nuclei due to their abundance in the mock-up. Slow neutrons, however, are at the end of a cascade of interactions and the slow neutron flux will finally be determined by absorption on 6 Li, which is the strongest absorber in terms of the macroscopic absorption cross-section in the LiPb. Measured and calculated fast neutron spectra for the two detector positions chosen for this experiment are presented in Fig. 4. The
1805
Fig. 6. Time-of-arrival spectral measured with the 3 He counter in the back position (Position A). “sn” means source neutron, the original DT neutron.
measured neutron spectrum was calibrated adjusting the 14 MeV peaks. The calculated fast neutron spectra based on FENDL-2.1 and JEFF-3.1.1 show only minor differences, but there is an underestimation of the calculated values in the energy range 11–13 MeV in Position B while the calculated values between 5 and 11 MeV are slightly higher than the measured ones. Fig. 5 shows the measured and calculated gamma-ray flux spectra for the same measurement positions. There is a good agreement of experiment and calculation values in both positions with some overestimation between 1 and 2 MeV. Since both, the gamma-ray and fast neutron flux, in the Position A (back position) is described rather well by the calculation with JEFF-3.1.1 and FENDL-2.1 with a small overestimation of the calculation in some energy intervals, it can be concluded from this analysis that shielding calculations will be quite reliable with a tendency to be conservative. However, one should not forget that the real blanket structure will be much more complicated and contain more chemical elements with influence on the neutron balance than can be considered in these mock-up experiments. Therefore one should see this experiment as part of a series of validation experiments which will also include similar measurements on the real TBMs in ITER during DD and DT phases. Time-of-arrival spectra of slow neutrons are shown in Figs. 5 and 6. Again, the two cross-section evaluations used for the calculation yield very similar results. The calculations show that the response of the He counter to neutrons between 0 and 1 eV is already one order of magnitude larger than in all higher energy intervals 45 s after the DT neutron pulse’s rising edge. From this time to the decay of the disappearance of the slow neutron population around 250 s after the DT neutron pulse the He measurement is completely dominated by slow neutrons. It is therefore sensitive to the absorption cross-section in the assembly which is mostly due to the 6 Li concentration in the LiPb. A lithium concentration of 0.28 wt.% had been used in the present calculations which was deduced from the results of the measurements in the mock-up at FNG [2]. Fig. 7 shows the effect of a 10% change in the Li concentration on the time-of-arrival spectrum for illustration. Since the reaction cross-section for the 6 Li(n,a)T reaction which determines the absorption cross-section of 6 Li in the energy range considered here is well known, it is concluded that the measurements with the He counter confirm an effective Li content of 0.28 wt.% in the LiPb (Fig. 8).
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state-of-the-art evaluated cross-section data and neutron/gamma transport codes for the design of the TBMs. Here we report on measurements of the fast and slow neutron and gamma-ray fluxes which were conducted at the neutron laboratory of the Technical University of Dresden. Comparisons of the fast neutron and gammaray fluxes with calculated values based on the JEFF-3.1.1 library and the reference library for ITER, FENDL-2.1, showed some discrepancies in some energy intervals but agreed rather well in general. The slow neutron flux tested with the time-of-arrival method is in very good agreement with the calculations assuming a Li content of 0.28 wt.% in the LiPb which is half of the nominal value of 0.61 wt.%. This conforms the activation foil and tritium production rate measurements conducted earlier with this mock-up at FNG. The reason for the discrepancy in the Li or 6 Li concentration is still under investigation. Acknowledgements
Fig. 7. Time-of-arrival spectral measured with the 3 He counter in the front position (Position B).
This work, supported by the European Communities under the contracts of Association with EURATOM, was carried out within the framework of the European Fusion Development Agreement. The views and opinions expressed herein do not necessarily reflect those of the European Commission. References
Fig. 8. Influence on changes of the lithium content on the time-of-arrival spectrum. A change of approximately 10% is clearly visible.
5. Conclusions Neutronics experiments with a mock-up of the European HCLL-TBM are currently underway with the aim to validate
[1] G. Rampal, D. Gatelet, L. Giancarli, G. Laffont, A. Li-Puma, J.F. Salavy, E. Rigal, Design approach for the main ITER test blanket modules for the EU helium cooled lithium–lead blankets, Fusion Eng. Des. 81 (2006) 695. [2] P. Batistoni, M. Angelone, P. Carconi, U. Fischer, K. Kondo, A. Klix, et al., Neutronics experiments on HCPB and HCLL TBM mock-ups in preparation of nuclear measurement in ITER, in: Proceedings of 9th International Symposium on Fusion Nuclear Technology, Dalian, China, October 11–16, 2009. [3] M. Reginatto, P. Goldhagen, S. Neumann, Spectrum unfolding, sensitivity analysis and propagation of uncertainties with the maximum entropy deconvolution code MAXED, Nucl. Instrum. Methods A 476 (2002) 242. [4] S. Guldbakke, H. Klein, A. Meister, J. Pulpan, U. Scheler, M. Tichy, S. Unholzer, in: H. Farrar, et al. (Eds.), Response Matrices of NE213 Scintillation Detectors for Neutrons, Reactor Dosimetry ASTM STP 1228, American Society for Testing Materials, 1995, pp. 310–322. [5] MCNP—A General Monte Carlo N-Particle Transport code, Version 5, Report LAUR-03-1987, Los Alamos, 2003. [6] A. Santamarina, D. Bernard, Y. Rugama (Eds.), The JEFF-3.1.1 Nuclear Data Library, JEFF Report 22, Validation Results from JEF-2.2 to JEFF-3.1.1, NEA Data Bank (2009), ISBN:978-92-64r-r99074-6. [7] D.L. Aldama, A. Trkov, FENDL-2.1—Update of an Evaluated Nuclear Data Library for Fusion Application, INDC(NDS)-467, IAEA, 2004. [8] M. Drosg, DROSG-2000: Neutron Source Reactions, IAEA-NDS-87, IAEA Nuclear Data Section, May 2005. [9] V.E. Lewis, K.J. Zieba, A transfer standard for d + T neutron fluence and energy, Nucl. Instrum. Methods 174 (1980) 141–144.