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JAEA Reports

Report of Examination of the Samples from Primary Loop Recirculation Piping (K1-PLR) at Kashiwazaki-Kariwa Nuclear Power Station Unit-1 (Contract Research)

The Working Team for Examination of the Sample from Core Shrouds and Primary Loop Recirculation Pipi

JAERI-Tech 2004-049, 44 Pages, 2004/06

JAERI-Tech-2004-049.pdf:7.21MB

At the Kashiwazaki-Kariwa Nuclear Power Station Unit-1, indications of cracks were identified in a weld joint portion of the primary loop recirculation piping. To investigate the cause of cracks, TEPCO conducted a material examination on the specimen including the cracks. The present investigation was carried out to ensure transparency of the examination by providing JAERI's own evaluation report as a third party organization. The following findings were made; (1) A crack was observed near the weld region. (2) Intergranular cracking was observed at almost whole fracture surface. (3) Transgranular cracking was observed at the crack opening region. Increases of hardness by cold work were observed and the crack was initiated near the region where hardness value showed the highest. (4) Content of Cr was very slightly depleted in the vicinity of grain boundary. Based on the above results with the presence of tensile residual stress near the crack generated by welding process and dissolved oxygen contents in cooling water, the observed cracks were concluded to be stress corrosion cracking.

JAEA Reports

Report of Examination of the Sample from Core Shroud (2F2-H3) at Fukushima Dai-ni Power Station Unit-2 (Contract research)

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.

JAEA Reports

Report of Examination of the Sample from Core Shroud (O1-H2) at Onagawa Nuclear Power Station Unit-1 (Contract research)

The Working Team for Examination of the Sample from Core Shrouds and Primary Loop Recirculation Pipi

JAERI-Tech 2004-012, 62 Pages, 2004/02

JAERI-Tech-2004-012.pdf:16.4MB

At Onagawa Nuclear Power Station Unit-1 of the Tohoku Electric Power co., inc., cracks were confirmed near welded joints of core shroud in 15th periodical inspection. Tohoku Electric Power co., inc. has conducted a material examination with Nippon Nuclear Fuel Development Co., Ltd.. To investigate independently, a JAERI's own evaluation report was provided. The results are as follows; (1) Hardening layer was detected at the depth of about 150-250$$mu$$m from outer surface of the sample. (2) Corrosion products were observed on inner surface of the cracks and some of them penetrated into grains. (3) Transgranular cracking and intergranular cracking were observed at the region within about 100$$mu$$m and the deeper region more than about 200$$mu$$m in depth from outer surface of the sample, respectively. (4) Distinct chromium depletion was not detected at the grain boundaries. (5) Chemical compositions of the sample corresponded to type 304L stainless steel in Japanese Industrial Standard. From the above, it is concluded that the cracks are stress corrosion cracking.

JAEA Reports

Report of Examination of the Sample from Core Shroud (K1-H4) at the Kashiwazaki-Kariwa Nuclear Power Station Unit-1 (Contract research)

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.

JAEA Reports

Report of Examination of the Sample from Core Shroud (1F4-H4) at Fukushima Dai-ichi Nuclear Power Station Unit-4 (Contract research)

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).

JAEA Reports

Report of Examination of the Sample from Core Shrouds (K3-H7a) at Kashiwazaki-Kariwa Nuclear Power Station Unit-3 (Contract research)

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

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