Kenji Kako

Development of new ferritic steels as cladding material for metallic fuel fast breeder reactor

The excellent thermal, chemical and neutronic properties of metallic fuel (U-Pu-Zr alloy) will lead to drastic improvements in fast reactor safety and the related fuel cycle economy. Some new high molybdenum 12Cr ferritic stainless steel candidate cladding alloys have been designed to achieve the mechanical properties required for high performance metallic fuel elements. These candidate claddings were irradiated by ion bombardment and tested to determine their strength and creep rupture properties. A 12Cr-8Mo and a 12Cr-8Mo-0.1Y2O3 steel were fabricated into cladding via a powder metallurgy process and by a mechanical alloying process, respectively. These claddings had two and three times the creep rupture strength (pressurized at 650°C for 10000 h) of a conventional 12Cr ferritic steel (HT-9). These two steels also showed no void formation up to 350 dpa by Ni3+ irradiation. A zircaloy-2 lined steel cladding tube has also been fabricated for the purpose of reducing fuel-cladding interdiffusion and chemical interaction.

Corrosion Behavior of High-Purity Fe-Cr-Ni Alloys in the Transpassive Condition

Abstract The corrosion behavior of high-purity (99.99%) Fe-Cr-Ni alloys was investigated in 13 kmol/m3 [0.36 kmol/ft3] nitric acid (HNO3) with and without ceric (Ce4+) ions to clarify the effect of...

Hardness of 12Cr8Mo ferritic steels irradiated by Ni ions

Abstract 12Cr Mo and 12Cr 8Mo 0.1Y2O3 ferritic steels were irradiated with 4-MeV Ni+ ions up to 300 dpa at 525°C. Microstructural evolution was examined by transmission electron microscopy (TEM) and mechanical properties were evaluated with a depth-sensing ultra-low load indentation hardness tester at room temperature with a maximum load of 1 gf. Effects of aging at 650°C for 115 h and heat treatment at 525°C for 50 h were also investigated. TEM observations reveal that these steels exhibit no void swelling in the present irradiation condition. Aging and heat treatment induces precipitation of Laves phase and ion-irradiation enhances precipitation. The induction and enhancement of precipitation strengthened the specimens.

Effect of various impurities on the transpassive corrosion of high-purity Fe-18%Cr-14%Ni alloys

Abstract Effects of C, P, S, and N on the transpassive corrosion of high-purity (HP) Fe-18%Cr-14%Ni alloys were studied in 13 kmol/m3 (13 N) nitric acid (HNO3) and 13 kmol/m3 HNO3 containing Ce4+ i...

Behavior of Stress Corrosion Cracking for Type 316L Stainless Steel With Controlled Distribution of Surface Work Hardened Layer in Simulated Boiling Water Reactors Environment

Stress corrosion cracking (SCC) of Type 316L stainless steels with controlled surface hardness distribution was investigated under simulated boiling water reactor (BWR) condition by creviced bent beam (CBB) tests. Intergranular microcracks having a depth of less than 50 μm are observed in 50 hours. Until 250 hours, depths of the microcracks are not increased. After 500 hours, cracks with depths of more than 50 μm are observed. SCC is initiated preferentially in a steep hardness gradient area.

Effect of Silicon and Manganese Additions on the Transpassive Corrosion of High-Purity Fe-18% Cr-14% Ni Alloys

Abstract Effects of Si and Mn on the transpassive corrosion of high-purity Fe-18% Cr-14% Ni alloys were studied in 13 kmol/m3 (0.36 kmol/ft3) nitric acid (HNO3) and 13 kmol/m3 HNO3 containing Ce4+ ...

Synergistic effect of impurities on the corrosion behavior of Fe-18%Cr-14%Ni alloys in concentrated nitric acid

Abstract Synergistic effect of Si, Mn, C, P, and S on the transpassive corrosion of high-purity (HP) Fe-18%Cr-14%Ni (HP18%Cr-14%Ni) alloys was studied in boiling 13 kmol/m3 nitric acid (HNO3). The specimens were fabricated by a cold crucible method in a high-vacuum chamber to reduce contamination. The addition of Si < 1% and Mn < 2% had no effect on the corrosion rate of HP18%Cr-14%Ni alloys, and the addition of Si < 1% also had no effect on the corrosion rate of HP18%Cr-14%Ni-1%Mn alloys, although 1% Si induced intergranular corrosion in both alloys. Thus, HP18%Cr-14%Ni-1%Mn-0.5%Si alloys were selected to evaluate the effect of minor impurities such as C, P, and S. The addition of 100 ppm P, or co-addition of 100 ppm C, 100 ppm P, and 100 ppm S, induced intergranular corrosion of the same degree in solution-annealed HP18%Cr-14%Ni-1%Mn-0.5%Si alloys. This result suggested a synergistic effect of Si and P to induce intergranular corrosion, since a single addition of 0.5% Si or 100 ppm P did not induce inte...