Evaluation of crack growth rates and microstructures near the crack tip of neutron-irradiated austenitic stainless steels in simulated BWR environment

Chimi, Yasuhiro; Kasahara, Shigeki; Seto, Hitoshi*; Kitsunai, Yuji*; Koshiishi, Masato*; Nishiyama, Yutaka

Proceedings of the 18th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, Vol.2, p.1039 - 1054, 2018/00

https://doi.org/10.1007/978-3-319-68454-3_76

In order to understand irradiation-assisted stress corrosion cracking (IASCC) growth behavior, crack growth rate (CGR) tests have been performed in simulated Boiling Water Reactor water conditions at 288C on neutron-irradiated 316L stainless steels (SSs) at 12-14 dpa. After the tests, the microstructures near the crack tip of the specimens are examined with scanning transmission electron microscope (FE-STEM). In comparison with a previous study at 2 dpa, this result shows a less benefit of low electrochemical corrosion potential (ECP) conditions on CGR. A crack tip immersed over 1000 hours was filled with oxides, while almost no oxide film was observed near the crack front in the low-ECP conditions. In addition, a high density of deformation twins and dislocations were found near the fracture surface of the crack front. It is considered that both localized deformation and oxidation are possible dominant factors for the SCC growth in highly irradiated SSs.

Evaluation on strength of reinforced concrete slabs in Bituminization Demonstraion Facility

Yamada, Toshiro*; Morikawa, Hiroshi*; Ishida, Masatoshi*; Seto, Yutaka*; Yamamoto, Yoshifumi*; Sawamoto, Yoshikazu*

JNC TJ8410 98-002, 124 Pages, 1998/11

JNC-TJ8410-98-002.pdf:3.82MB

On the 11st of March 1997, a fire and explosion occurred in a Bituminization Demonstraion Facility. It subsequently became necessary to estimate the explosive force of this event. To this end, this report evaluates the static yield and ultimate strength of the main structural walls and floors of this facility. A simple method and a Finite Element Method (FEM) were considered to evaluate the yield and ultimate strength of reinforced concrete (RC) slabs. Using the simple method, the yield strength can be estimated effectively by solution of fundamental differential equations. The ultimate strength of RC slabs is tried to estimate using a modified yield line theory which is taken an arch effect created within RC slabs into account. However, this method is difficult to apply to slabs with complicated boundary conditions. In this case, FEM is necessary. The validity of the simple method is verified by analyzing some slabs using both methods and comparing the results. Previous experimental results and some RC slabs in the Asphalt Bituminization Facility were evaluated on the basis of yield and ultimate strength using both methods, and the validity of both methods were verified. Especially, in simulating previous experiments, the error in the estimated values of the ultimate strength using simple method to experimental values were within 30%. The estimated values of the ultimate strength using the FEM were 15% larger than the experimental values. As a result, the simple method taking arch effect into account was verified to some extent.

Effects of environmental mitigation and water radiolysis on crack growth in simulated BWR environment in highly irradiated 316L stainless steel

Chimi, Yasuhiro; Kasahara, Shigeki; Hata, Kuniki; Nishiyama, Yutaka; Seto, Hitoshi*; Chatani, Kazuhiro*; Kitsunai, Yuji*; Koshiishi, Masato*

no journal, , 

In order to investigate effects of environmental mitigation and water radiolysis caused by -rays from radioactive material on irradiation-assisted stress corrosion cracking (IASCC) growth behavior for highly irradiated material, crack growth tests in simulated BWR water conditions (at 563 K) are performed. The specimens made of 316L stainless steels are irradiated with neutrons up to 12 dpa in the Japan Materials Testing Reactor (JMTR). One of the specimens is annealed at 973 K for 1 hour to show almost recovered mechanical and micro-chemical properties corresponding to the unirradiated material. For low electrochemical corrosion potential (ECP) condition, the crack growth rate (CGR) is suppressed by about one order of magnitude in high stress intensity factor (K) condition. This result indicates that environmental mitigation for crack growth can be found even under severe conditions on material and stress factors. The effects of water radiolysis on the CGRs are discussed.

Relationship between crack growth rates and locally deformed structures in irradiated 316L stainless steels

Chimi, Yasuhiro; Kasahara, Shigeki; Nishiyama, Yutaka; Seto, Hitoshi*; Kitsunai, Yuji*; Koshiishi, Masato*

no journal, , 

In order to understand irradiation-assisted stress corrosion cracking (IASCC) growth behavior, crack growth tests using compact tension (CT) specimens made of neutron-irradiated 316L stainless steels (SSs) were performed in simulated BWR environments (at 288C). Moreover, microstructures of deformed areas were observed by transmission electron microscope (TEM) after straining tensile specimens made of neutron-irradiated 316L SSs. As a result, for lower neutron dose than 1.9 dpa, the crack growth rates (CGRs) show effective environmental mitigation and the deformed structures show tangling of dislocations. On the other hand, for higher neutron dose than 2.7 dpa, the CGRs show small environmental mitigation and the deformed structures consist mainly of dislocation channels. From the relationship between CGRs and deformed structures, mechanisms on IASCC growth will be discussed.