Technical Meeting on Plasma Physics and Technology Aspects of the Tritium Fuel Cycle for Fusion Energy

Tritium in chamber materials, trapping and release (plasma chamber in DEMO, irradiation damage and tritium trapping)

13 Oct 2022, 11:15

35m

Board Room C (C building, 4th floor) (IAEA Headquarters)

Invited Oral Interface btw First Wall & Fuel Cycle Technology Tritium Behaviors and DEMO Fuel Cycle

Speaker

Yuji Hatano (Hydrogen Isotope Research Center, University of Toyama)

Description

Mechanisms underlying tritium retention in chamber materials can be roughly divided into two groups: trapping in deposition layers and that in bulk of materials. The contribution of trapping in the bulk to the total tritium retention could be larger in DEMO than that in existing fusion devices due to far longer discharge pulse that allows diffusion of tritium into deeper region of the materials.

Significant increase in fuel retention in W was observed after neutron irradiation to 0.01-1 dpa due to trapping effects by radiation-induced defects [1,2]. Nuclear reaction analyses of deuterium (D) profiles in neutron-irradiated D-plasma-exposed W showed that D concentration increased with decreasing temperature and reached ~1 at.% at 200 ˚C after irradiation to 0.3 dpa, Penetration depth of D into neutron-irradiated W was proportional to the square root of plasma exposure time [3,4]. The rate of penetration depends on damage level (trap concentration), temperature and hydrogen isotope flux (H/trap ratio). Penetration depth was ~50~100 micrometers after plasma exposure for 3 h at temperature of 500 ˚C and flux of ~10²¹ D m^-2s^-1 [5]. The TDS measurements for neutron-irradiated W showed broad peaks extending from plasma exposure temperature to ~1000 ˚C [2]. The apparent trapping energy was 1.4-2eV [2,5,6]. Because of the relatively large trapping energy, the fuel release at a moderately elevated temperature (~300 ˚C) was very slow [7]; the tritium removal by bake out process should be very difficult. If W monoblocks with cooling channels are used in DEMO, tritium should penetrate to cold regions around the cooling channels and be accumulated there. Nevertheless, He seeding in D plasma resulted in drastic reduction in D retention in neutron-irradiated W [8], Alloying with Re and Cr (and probably accumulation of Re by transmutation) significantly enhance annihilation of vacancy-type defects and consequently reduce fuel retention after irradiation [9,10].

Tritium trapping in deposition layers were examined via post-mortem analysis of W and Be tiles used in JET ITER-like wall experiments under the Broader Approach Activities [11]. The summary of the analyses will be given in the presentation.

[1] Y. Hatano et al 2013 Nucl. Fusion 53 073006. doi.org/10.1088/0029-5515/53/7/073006
[2] Y. Oya et al 2020 J. Nucl. Mater. 539 152323. doi.org/10.1016/j.jnucmat.2020.152323
[3] Y. Yajima et al 2019 Nucl. Mater. Energy 21 100699. doi.org/10.1016/j.nme.2019.100699
[4] Y. Yajima et al 2021 Phys. Scr. 96 124042. doi.org/10.1088/1402-4896/ac2c20
[5] Y. Hatano et al 2013 J. Nucl. Mater. 438 S114–S119. doi.org/10.1016/j.jnucmat.2013.01.018
[6] M. Shimada et al 2018 Fusion Eng. Design 136 1161-1167. doi.org/10.1016/j.fusengdes.2018.04.094
[7] V. Kh. Alimov et al 2020 Nucl. Fusion 60 096025. doi.org/10.1088/1741-4326/aba337
[8] Y. Nobuta et al 2021 Fusion Sci. Technol. 77 76–79. doi.org/10.1080/15361055.2020.1843314
[9] Y. Nobuta et al 2022 J. Nucl. Mater. 566 153774. doi.org/10.1016/j.jnucmat.2022.153774
[10] J. Wang et al 2022 J. Nucl. Mater. 559 153449. doi.org/10.1016/j.jnucmat.2021.153449
[11] S. E. Lee et al 2021 Nucl. Mater. Energy 26 100930. doi.org/10.1016/j.nme.2021.100930

Presentation materials

IAEA_2022_Hatano_for submission.pdf