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Investigation of Neutron Irradiation on the Strength of Ferritic Steel-Steel Diffusion-Bonded at High Temperature and Pressure
- Study of Irradiation Effects on Bonding of Candidate Material for Structural Component of Fusion Blanket -


Fig. 2-15 Partial mock-up of test blanket

This mock-up was fabricated by HIP bonding using a low-activation ferritic steel F82H (candidate structural material). This example reflects the design of the first wall components of the ITER test blanket.


Fig. 2-16 Specimens from the mock-up sampled for evaluation of mechanical properties

The specimen sizes are smaller than a Japanese coin. Application of such small-size specimen evaluation techniques allowed the determination of properties of HIP bonding in the plasma-side component.


Fig. 2-17 Tensile properties of HIP bonding before irradiation

The figure shows the properties of fracture specimens from the base metal region and at the HIP bonding region. The results revealed that the HIP-bonded properties were equivalent to the properties of the base metal region.


Fig. 2-18 Strength of HIP bonding after irradiation

The figure shows the change in strength as a function of radiation damage. The strength of HIP bonding is within the range of interpolation of the strength of the base metal. This implies that HIP bonding may not be degraded by irradiation.


The blanket installed in a fusion reactor will be exposed to high-energy neutrons from plasma. A ferritic steel (F82H steel), resistant to activation and radiation damage, has been selected as a candidate structural material (e.g. blanket) for demonstration reactor. The first wall components, which are also exposed to high heat flux, will have built-in cooling channels. Fabrication by welding of such a complicated structure is impractical, so the first wall components will be fabricated by the hot isostatic pressing (HIP)-bonding method, which can strongly join structural materials using high temperature and pressure. Various radiation experiments with F82H steel have been performed that simulated the effects of the fusion reaction. The material properties after irradiation are revealed in the base metal. However, tests are needed to elucidate the properties of HIP bonding.
In this study, a mock-up (Fig. 2-15) simulating a structural portion of a test blanket to be installed in ITER was fabricated by the HIP-bonding method (at 1313K with 150 MPa for 2 h). The metallurgical and mechanical properties before irradiation were first investigated using test specimens (Fig. 2-16) sampled from the HIP-bonded mock-up. The following significant characteristics were ascertained: (1) the HIP boundary contains precipitates equivalent to carbide-precipitates seen in matrix grain boundaries, (2) the strength and elongation of HIP-bonded joints are equivalent to those in base metal (Fig. 2-17), and (3) the brittle fracture that occurred at a part of the bonds between corners of the cooling channels and plates can be eliminated by re-heat treatment to refine grains in the metal. During the neutron irradiation conducted at the Japan Materials Testing Reactor (JMTR), the tensile properties were investigated. With irradiation up to ca. 2 dpa (ca. 70% of the accumulation during the total lifetime of the test blanket) at 523K, noticeable embrittlement occurs. Finally, (4) no fractures occurred at HIP boundaries, and few changes in properties appeared at the HIP bonds following irradiation (Fig. 2-18).


Reference
K. Furuya et al., Tensile and Impact Properties of F82H Steel applied to HIP-bond Fusion Blanket Structures, Fusion. Eng. Des., 69, 385 (2003).
(http://dx.doi.org/10.1016/S0920-3796(03)00079-6)

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Persistent Quest Research Activities 2004
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