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CNakamura, Kinya*; Yamano, Hidemasa; Takai, Toshihide
no journal, ,
This study elucidated the phase equilibria of 14 mass% and 17 mass% B
C-SS melt mixtures below 1200C as part of investigation of the thermal stability of BC-SS multi-component system.
Kondo, Toshiki; Ogawa, Kengo*; Nakagawa, Takeshi*; Kikuchi, Shin; Seino, Hiroshi
no journal, ,
In this study, as a first step to understand the formation behaviour of gaseous iodine under Sodium-cooled fast reactor sever accident condition, gas evolution from sodium iodide (NaI) in an inert atmosphere was investigated using a Temperature Programmed Desorption-Mass Spectrometry (TPD-MS) apparatus. NaI is expected to be formed by reacting iodine as the fission product with sodium as the coolant. The result was suggested that thermal behaviour of NaI over about 660 Celsius degree was apparently phase change from solid to liquid/gas and formation of gaseous iodine was negligible in an inert atmosphere.
Kikuchi, Shin; Koga, Nobuyoshi*
no journal, ,
Sodium peroxide is one of the reaction products of sodium fire, which occurs by the reaction between liquid sodium and oxygen. Melting and evaporation behavior of these sodium oxides are key elements for evaluating plant safety and structural integrity of sodium-cooled fast reactor in relation to the influence on the ambient temperature in case of sodium fire. However, the phase change behavior of sodium oxides is not well revealed because of the experimental difficulties due to high temperature environment and significant chemical reactivity of sodium oxides. In this study, the melting behavior of sodium peroxide was investigated using differential scanning calorimetry (DSC). After careful temperature and energy calibrations of the DSC instrument, enthalpies of sodium peroxide transition and melting were obtained for validating the sodium fire analysis code.
Hirota, Noriaki; Kondo, Keietsu; Nakano, Hiroko; Fujita, Yoshitaka; Takeuchi, Tomoaki; Ide, Hiroshi; Tsuchiya, Kunihiko; Kobayashi, Yoshinao*
no journal, ,
Dynamic strain aging (DSA) has been identified in shrouds of boiling water reactors and recirculation system piping of pressurized water reactors in the nuclear field. This phenomenon increases the work hardening rate of the material and causes a reduction in ductility. Rodriguez reported that using stainless steel, this work hardening increases with grain refinement, making DSA more likely to occur. The objective of this study is to evaluate the effect of grain refinement on DSA in a high temperature pressurized water (HTPW) simulating nuclear reactor environment utilizing ultrafine grained SUS304L (UFGS). UFGS was heat treated to adjust the grain size from 0.59 
m to 68.6 m, and Hall-Petch relationship for 0.2 % yield stress was arranged. The k values obtained in this study were almost the same as the reference values previously obtained for SUS304L. Regarding the effect of grain size on fracture strain, a comparison of fracture strain between tensile test under air and slow strain rate test (SSRT) under 598 K / 15 MPa at dissolved oxygen 
1 ppb showed that the fracture strain was lower than that under air as the grain size became coarser. The micrograph after fracture in a HTPW showed that ductile fracture surfaces were observed for materials with grain sizes less than 28.4 m. However, when the grain size coarsened to 68.6 m, more than half of all fracture surfaces were brittle fractured. For the material with a grain size of 0.59 m under HTPW, many correspondence grain boundaries of {111}/
3 boundaries were observed in the fracture cross-section of the sample. But these distributions were rarely observed when the grain size was coarsened to 68.6 m. Therefore, the suppression of crack propagation by DSA to the fine grains in a HTPW can be attributed to the relaxation of dislocation accumulation by the {111}/3 boundaries.