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Akita, Koichi; Suzuki, Hiroshi; Nishikawa, Satoru*; Okita, Shigeru*
Nihon Zairyo Gakkai Dai-61-Ki Tsujo Sokai, Gakujutsu Koenkai Rombunshu (USB Flash Drive), 2 Pages, 2012/05
Residual stresses on the surface and inside of ultrasonic shot peened dissimilar weld joint were measured using X-ray and neutron diffraction before and after thermal loading. Mechanism of residual stress relaxation due to thermal loading was discussed.
The Working Team for Examination of the Sample from Core Shrouds and Primary Loop Recirculation Pipi; Nakajima, Hajime*; Shibata, Katsuyuki; Tsukada, Takashi; Suzuki, Masahide; Kiuchi, Kiyoshi; Kaji, Yoshiyuki; Kikuchi, Masahiko; Ueno, Fumiyoshi; Nakano, Junichi; et al.
JAERI-Tech 2004-015, 114 Pages, 2004/03
JAERI-Tech-2004-015.pdf:38.06MB
The Tokyo Electric Power Company (TEPCO) visually inspected the weld joint of core shroud at Fukushima Dai-ni Nuclear Power Station Unit-2 by a direction of the Nuclear and Industrial Agency, cracks were observed at outer side of the ring weld joint (H3) between a core shroud middle trunk and a middle ring. TEPCO has conducted a material examination with Nippon Nuclear Fuel Development Co. Ltd. (NFD) on the specimen including cracks sampled from the core shroud. The present examination has been performed with the objective to independently investigate and evaluate the materials by jointly attending the examination with NFD from the planning stage. Based on results of the present examination, the probable presence of tensile residual stress by welding process and dissolved oxygen contents in the cooling water, it was shown that the cracks were considered to be stress corrosion cracking (SCC). However, the cause of the cracks needs more consideration on the way of shroud construction.
The Working Team for Examination of the Sample from Core Shrouds and Primary Loop Recirculation Pipi
JAERI-Tech 2004-011, 64 Pages, 2004/02
JAERI-Tech-2004-011.pdf:14.65MB
At the Kashiwazaki-Kariwa Nuclear Power Station Unit-1 of the TEPCO, cracks were confirmed at the weld joint (H4) in the middle of core shroud, by the visual inspection test for the weld joint of core shroud during the 13th periodic examination by a direction of the Nuclear and Industrial Agency. TEPCO has conducted a material examination with NFD on the specimen including cracks sampled from the core shroud. The present research has been performed with the objective to independently investigate and evaluate the materials by jointly attending the examination with NFD from the planning stage, receiving the final data given by the examination and providing JAERI's own evaluation report as a third-party organization for assuring the transparency. As a result, the consideration of residual stress induced with welding process and dissolved oxygen concentration in core cooling water, it was concluded that the cracks were initiated by SCC and propagated three-dimensionally through grains, and some cracks reached weld metal.
The Working Team for Examination of the Sample from Core Shrouds and Primary Loop Recirculation Pipi
JAERI-Tech 2004-004, 74 Pages, 2004/02
JAERI-Tech-2004-004.pdf:31.62MB
During the 12th periodical inspection in Fukushima Dai-ichi Nuclear Power Station Unit-4 (BWR, 784MW) of Tokyo Electric Power Company (TEPCO), which has been held from September 1993 to February 1994, cracks were found at welded joints No.H4 in the core shroud middle shell. TEPCO has conducted a material examination with Nippon Nuclear Fuel Development Co. Ltd. (NFD) on the SUS304L specimen including cracks sampled from the inner surface of welded joints (H4) of the middle shell of the core shroud. The present examination has been performed with the objective to independently investigate and evaluate the materials by jointly attending the examination with NFD, receiving the final data given by the examination and providing a JAERI's own evaluation report as a third-party organization for assuring the transparency. Based on the research results described above, presence of tensile residual stress by welding and relatively high dissolved oxygen contents in core coolant, it is concluded that the cracks observed were caused by the stress corrosion cracking (SCC).
The Working Team for Examination Operation of Samples from Primary Loop Recirculation Piping at Onag
JAERI-Tech 2004-003, 74 Pages, 2004/02
JAERI-Tech-2004-003.pdf:30.08MB
The present examination has been performed with the objective to provide technical basis for identifying causes of cracking through the examination of the samples, which was conducted at the post irradiation examinations facilities of JAERI, taken from the cracked region of the recirculation pipe at the Onagawa Nuclear Power Station Unit-1. The following findings were obtained from this examination result. (1) Cracks were observed near the weld region of inner surface of the pipe and depth of the crack was about 5 to 7mm. (2) Intergranular crackings were observed in the almost whole fracture surface. Partially transgranular cracking was observed at the surface layer with the depth of about 100
m. Microstructure formed by cold work and increase of hardness were observed in these surface layers. Cracks initiated near the region where hardness value was the highest. Based on the examination results described above concerning presence of tensile residual stress by welding and relatively high dissolved oxygen contents in core coolant and so on, it is concluded that these cracks were initiated in the cold work layer of inner surface by stress corrosion cracking (SCC) and propagated along the grain boundaries.
The Working Team for Examination of the Sample from Core Shrouds and Primary Loop Recirculation Pipi
JAERI-Tech 2004-002, 58 Pages, 2004/02
JAERI-Tech-2004-002.pdf:15.44MB
no abstracts in English
Akita, Koichi; Suzuki, Hiroshi; Moriai, Atsushi; Harjo, S.; Nishikawa, Satoru*
no journal, ,
To clarify the relaxation process on dissimilar metal weld joints, 
stress measurements during thermal cycles from RT to 593 K were conducted using a neutron engineering diffractometer, TAKUMI in J-PARC. The effects of the difference in thermal expansion coefficient of the materials and the temperature dependence of the yield strength on the residual stress relaxation were discussed based on the experimental results.
Akita, Koichi; Suzuki, Hiroshi; Nishikawa, Satoru*; Moriai, Atsushi; Harjo, S.; Vladimir, L.*
no journal, ,
The materials used for the dissimilar weld joint were a SUS316L stainless steel and a NCF600 nickel alloy for the base plates, and an Alloy82 nickel alloy for the weld metal. The ultrasonic shot peening (USP) was applied to the sample surface after welding. The residual stress mappings of the as-peened and heat treated (593 K, 2 h) samples were measured at room temperature using KOWARI in ANSTO. In the results, the reduction of the tensile residual stress was observed near the interface of the weld metal and the nickel base plate. To clarify the relaxation process, the in-situ stress measurements during thermal cycles from RT to 593 K were conducted using TAKUMI in J-PARC. The effects of the difference in thermal expansion coefficient of the materials and the temperature dependence of the yield strength on the residual stress relaxation were disscussed based on the experimental results.
Akita, Koichi; Moriai, Atsushi; Suzuki, Hiroshi; Harjo, S.; Nishikawa, Satoru*; Shibahara, Masakazu*; Ikushima, Kazuki*
no journal, ,
Internal residual stresses of a dissimilar weld joint under cyclic thermal aging were measured using neutron diffraction technique and the residual stress relaxation process was investigated.