Takeo Asaga

Tensile Properties of 11Cr-0.5Mo-2W, V, Nb Stainless Steel in LMFBR Environment

The tensile strength of ferritic-martensitic HCr-0.5Mo-2W, Nb, V stainless steel (PNC-FMS), which had been developed for core component applications in LMFBR by Japan Nuclear Cycle Development Institute, was evaluated for the effects of thermal aging, sodium exposure, and neutron irradiation. The tensile strength of thermal aged specimens (~1,023K, ~12,000h) decreased at aging conditions above the initial tempering parameter, and the aging effect was considerably enhanced for the wrapper tubes tempered at lower temperatures. The tensile strength of sodium exposed specimens (~973K, ~10,000h) decreased more than aged specimens due to decarburization, and the effect of decarburization was greater in thin wall cladding tubes. Evaluation of the contribution of both thermal aging and decarburization effects on the tensile strength of cladding tubes irradiated in JOYO (~1,013K, ~6,030h, ~29dpa) suggested that the radiation showed smaller effect on tensile properties than thermal aging and decarburization. By using the derived correlations for thermal aging and decarburization effects, the tensile strength decrease for PNC-FMS after long period (30,000 h) in LMFBR environment was quantitatively calculated.

An investigation of the Pu migration phenomena during irradiation in fast reactor

The phenomenon of radial plutonium migration in fast reactor MOX fuel is one of the important performance issues. In this study, mechanisms of this phenomenon were modeled for vapor transport concurrently occurring with thermal diffusion. Further improvement was modeled by accounting for the effects of the oxygen to metal ratio. Additionally, to evaluate more precisely the fuel temperature history during irradiation, the thermal conductivity in the fuel-cladding gap was evaluated by including the thermal effects of fission-product (FP) compounds. The calculated plutonium distribution in MOX fuel irradiation tests, with the linear heat rate (LHR) gradually decreasing with irradiation, agreed well with the measured data. Improvement by considering the effect of the oxygen to metal ratio was considered to be effective and indispensable for the evaluation of plutonium migration in the MOX fuel.

Demonstration Experiment of 3 BN-600 MOX Vibropac FAs Irradiation for the Excess Weapons Plutonium Disposal

The paper presents results of a demonstration experiment on conversion of 50 kg of weapon-grade plutonium in the form of metal ingots into granulated MOX-fuel to be used for manufacturing fuel pins and 3 fuel assemblies (FAs) for the fast power-generating reactor BN-600, irradiation parameters of these FAs and the data from post-irradiation examinations. It can be concluded from the PIE results that the 3FAs were successfully irradiated in BN-600 without any fuel pin failures. Therefore, disposition of weapongrade plutonium with a weight of about 20 kg was successfully done. This represents the first disposition of Russian surplus weapon-grade plutonium as an international cooperation (this experiment was performed in collaboration between RIAR and JNC). The possibility of using MOX vipac fuel as a method for weapon plutonium disposition is clearly shown.

Feasibility Study on Nitrogen-15 Enrichment and Recycling System for Innovative FR Cycle System With Nitride Fuel

Highly-isotopically-enriched nitrogen (HE-N2 ; 15 N abundance ≥ 99.9%) is indispensable for a nitride fueled fast reactor (FR) cycle to minimize the effect of carbon-14 (14 C) generated mainly by 14 N(n,p)14 C reaction in the core on environmental burden. Thus, the development of inexpensive 15 N enrichment and recycling technology is one of the key aspects for the commercialization of a nitride fueled FR cycle. Nitrogen isotope separation by the gas adsorption technique was experimentally confirmed in order to obtain its technological perspective. A conventional pressure swing adsorption technique, which is already commercialized for recovering the nitrogen gas from multi-composition gas-mixture, would be suitable for recovering in both reprocessing and fuel fabrication to recycle the HE-N2 gas. A couple of the nitride fuel cycle system concepts including the reprocessing and fuel fabrication process flow diagrams with the HE-N2 gas recycling were newly designed for both aqueous and non-aqueous (pyrochemical) nitride fuel recycle plants, and also the effect of the HE-N2 gas recycling on the economics of each concept was evaluated.Copyright

FMF-Extension Project and Post-Irradiation Examination for MONJU Fuel.

高速増殖原型炉「もんじゅ」の運転に伴い,照射された炉心燃料等の炉心構成要素が炉心より取り出されるが,これらは建設中のFMF増設施設において照射後試験を実施する。そのデータは貴重であり,照射挙動を十分に把握することは,今後の高速炉燃料開発にとって不可欠である。 本稿では,「もんじゅ」炉心構成要素等の照射後試験計画および試験実施施設,試験機の概要・特徴について解説する。