Naoaki Akasaka

Effects of Fast Reactor Irradiation Conditions on Tensile and Transient Burst Properties of Ferritic/Martensitic Steel Claddings

The effects of fast neutron irradiation conditions have been investigated by focusing on the mechanical properties of 11Cr-0.5Mo-2W, Nb, V ferritic/martensitic (F/M) stainless steel (PNC-FMS) and 10.5Cr-1.5Mo, Nb, V F/M stainless steel (HT9M) claddings, especially tensile and transient burst properties. These two F/M claddings were irradiated at temperatures from 693 to 833K to 42.5 dpa (displacement per atom) in the experimental fast reactor JOYO using the PFB090 fuel test subassembly. Post-irradiation tensile and temperature-transient-to-burst tests were carried out for defueled cladding specimens. The results of mechanical tests for the PNC-FMS cladding showed that there was no significant degradation in tensile and transient burst strengths even after fast neutron irradiation. On the other hand, the strength of the HT9M cladding tended to shift to lower values than those of as-received specimens. The differences in tensile and transient burst strengths between the two claddings were attributed to martensite structural stability which was related to the stable solid solution elements.

Effects of Microstructural Evolution on Charpy Impact Properties of Modified Ferritic/Martensitic Steel after Neutron Irradiation

The effects of fast neutron irradiation have been investigated on Charpy impact properties and microstructural evolution of ferritic/martensitic (F/M) 11Cr-0.5Mo-2W, Nb, V stainless steel (PNC-FMS) which were developed by the Japan Atomic Energy Agency for core component applications in advanced fast reactors. One-half-size Charpy specimens were irradiated in the experimental fast reactor JOYO using the material irradiation rig to doses of 4.4 dpa at 773 K and 2.8 dpa at 923 K. Post irradiation Charpy impact tests and microstructural observations by transmission electron microscope were carried out. The results of the Charpy impact tests showed that there was no significant degradation in Charpy impact properties after neutron irradiation at 773 K to 4.4 dpa compared with the as-received specimens, but there was significant degradation in the properties after neutron irradiation at 923 K to 2.8 dpa. The Charpy impact property changes were attributed to matrix softening by recovery of martensite lath structures and to precipitate distributions.

Swelling Behaviors in a Fuel Assembly for the Wrapping Wire and Duct Made of Modified 316 Austenitic Stainless Steel

Swelling behaviors in the wrapping wire and duct made of modified type 316 austenitic stainless steel were investigated in a fuel assembly irradiated in a fast breeder reactor. The temperature dependence of volumetric swelling was measured in the wrapping wire and the duct, and the peak temperatures of swelling were evaluated. The void distribution in the material was measured by microstructure observation with electron microscopy, and it was found that the voids prefentially grew near the surface. This phenomenon seemed to be caused by a surface effect on the neutron-irradiated materials.