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<p>Mono-energetic fusion neutrons produced by the primary deuterium–tritium fuel reactions in tokamaks play a critical role in the performance and safety of the first wall and the blanket system. Through energy deposition and the generation of secondary particles and photons, these neutrons can directly influence first-wall design. Moreover, after penetrating the first wall and entering the breeding region, they become increasingly important due to the requirement for achieving a sufficiently high tritium breeding ratio (TBR). Therefore, a systematic investigation of the interaction of 14.1&#xa0;MeV fusion neutrons with the first wall, particularly considering structural modifications, is of significant importance. This work provides a systematic, thickness-dependent assessment. In this study, Monte Carlo simulations were employed to investigate the interaction of mono-energetic fusion neutrons with a tungsten first wall. The effects of varying the tungsten layer thickness, as well as the addition of a water-cooling layer and changes in its thickness, on energy deposition, the energy spectra of outgoing neutrons and photons, TBR, and the production of secondary reaction products were analyzed. The results indicate that increasing the tungsten thickness leads to higher energy deposition and an increased probability of neutron-induced reactions, with (n,2n) reactions becoming more dominant. The introduction of a water layer reduces neutron energies, broadens the photon energy spectrum, and activates (n,γ) reactions, resulting in enhanced energy deposition. The maximum TBR was obtained for a tungsten thickness of 20&#xa0;mm, whereas in water-cooled configurations, TBR decreases significantly with increasing cooling layer thickness. Analysis of neutron energy profiles shows that thermal neutrons are nearly absent in the absence of water; however, in the presence of water, both thermal and epithermal neutron populations increase, accompanied by a reduction in the fraction of 14.1&#xa0;MeV neutrons. Nevertheless, in all investigated configurations, a portion of high-energy neutrons penetrates the tungsten wall and may cause damage to components located behind it. In addition, the production of secondary products, including photons, outgoing neutrons, and the elements Re, H, He, Hf, and Ta were examined. The results demonstrate that the production of these elements increases with tungsten thickness, although their variation ranges differ due to the distinct reaction cross sections involved. Overall, the findings highlight an important trade-off between the neutron energy distribution and the number of neutrons entering the breeding zone production, which should be carefully considered in the optimal design of tokamak first-wall and blanket systems.</p>

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Thickness-driven optimization of tungsten first walls for tritium breeding with 14.1 MeV fusion neutron irradiation

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年8月5日

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  • Zahra Moravveji,
  • Hassan Mehdian,
  • Chapar Rasouli,
  • Banafsheh Pourshahab,
  • Kamal Hajisharifi

摘要

Mono-energetic fusion neutrons produced by the primary deuterium–tritium fuel reactions in tokamaks play a critical role in the performance and safety of the first wall and the blanket system. Through energy deposition and the generation of secondary particles and photons, these neutrons can directly influence first-wall design. Moreover, after penetrating the first wall and entering the breeding region, they become increasingly important due to the requirement for achieving a sufficiently high tritium breeding ratio (TBR). Therefore, a systematic investigation of the interaction of 14.1 MeV fusion neutrons with the first wall, particularly considering structural modifications, is of significant importance. This work provides a systematic, thickness-dependent assessment. In this study, Monte Carlo simulations were employed to investigate the interaction of mono-energetic fusion neutrons with a tungsten first wall. The effects of varying the tungsten layer thickness, as well as the addition of a water-cooling layer and changes in its thickness, on energy deposition, the energy spectra of outgoing neutrons and photons, TBR, and the production of secondary reaction products were analyzed. The results indicate that increasing the tungsten thickness leads to higher energy deposition and an increased probability of neutron-induced reactions, with (n,2n) reactions becoming more dominant. The introduction of a water layer reduces neutron energies, broadens the photon energy spectrum, and activates (n,γ) reactions, resulting in enhanced energy deposition. The maximum TBR was obtained for a tungsten thickness of 20 mm, whereas in water-cooled configurations, TBR decreases significantly with increasing cooling layer thickness. Analysis of neutron energy profiles shows that thermal neutrons are nearly absent in the absence of water; however, in the presence of water, both thermal and epithermal neutron populations increase, accompanied by a reduction in the fraction of 14.1 MeV neutrons. Nevertheless, in all investigated configurations, a portion of high-energy neutrons penetrates the tungsten wall and may cause damage to components located behind it. In addition, the production of secondary products, including photons, outgoing neutrons, and the elements Re, H, He, Hf, and Ta were examined. The results demonstrate that the production of these elements increases with tungsten thickness, although their variation ranges differ due to the distinct reaction cross sections involved. Overall, the findings highlight an important trade-off between the neutron energy distribution and the number of neutrons entering the breeding zone production, which should be carefully considered in the optimal design of tokamak first-wall and blanket systems.