Microstructural characterization and density change of 304 stainless steel reflector blocks after long-term irradiation in EBR-II

Microchemical and microstructural evolution of AISI 304 stainless steel irradiated in EBR-II at PWR-relevant dpa rates

“…There were also variations in temperature arising from the local sodium coolant temperature and the local gamma heating rate, the latter serving to elevate the temperature inside the block. These blocks have been used in a series of studies involving dimensional distortion, internal swelling profiles, microstructural evolution, density change, mechanical properties and ultrasonic velocity changes [26][27][28][29][30][31][32][33]. This study is the most recent in the series and used specimens taken from block #3 in the middle of the stack and from block #5, the highest in the stack.…”

“…The starting state of the blocks was somewhat unknown, since the original 50 year-old purchase order did not specify the final condition, but only the steel and its required dimensions. From previous work in this series, however, it was determined from microstructural examination that the archived material was ~5% cold worked in the block interior and ~10% cold worked near the block surfaces [26]. The alloy composition was measured in a previous study on an archive block by inductively coupled plasma atomic emission spectroscopy (ICP-AES) [27] and is listed in Table 1.…”

“…We have confidence in the calculated temperature of this plate to only ±10°C. The plate used in this study was archived as #3D1C1C, which was adjacent (within 0.08 cm) to one of the plates used by Huang [26], so the irradiation conditions are expected to be essentially the same as those cited by her. The estimated irradiation temperature and dose for specimens from block #5 are 416°C and 0.4 dpa, accumulated at 4.4x10 -9 dpa/s.…”

“…The estimated irradiation temperature and dose for specimens from block #5 are 416°C and 0.4 dpa, accumulated at 4.4x10 -9 dpa/s. The plate used in this study was archived as #5D1C1B, which was immediately adjacent (within 0.04 cm) to one of the plates used by Huang [26], so the irradiation conditions are also expected to be essentially the same. We have confidence in the temperature assignment to ±2-3°C since the gamma heating rates are very low so far above the core and the coolant temperature is well known at that elevation.…”

“…In this report we have chosen to examine AISI 304 irradiated at low dose rates in two reactor locations: within and far above the reflector region of EBR-II. A recently published study by H uang involving the same material at very closely adjacent locations to those used in our studies focused primarily on the microstructural evolution using conventional transmission electron microscopy on typical 3 mm disks [26]. Unfortunately, the intense radioactivity of the relatively large specimens precluded reliable microchemical analysis.…”