Assessment of Neutron Irradiation-Induced Grain Boundary Embrittlement by Phosphorous Segregation in a Reactor Pressure Vessel Steel

Kimura, A
Professor, IAE, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.

Shibata, M
Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Japan

Kasada, R
Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Japan

Fujii, K
Institute of Nuclear Safety System, Inc., Mihama, Mikata, Japan

Fukuya, K
Senior Researcher, Institute of Nuclear Safety System, Inc., 64 Sata, Mihama, Mikata, Fukui 919-1205, Japan.

Nakata, H
Institute of Nuclear Safety System, Inc., Mihama, Mikata, Japan

(Received 11 June 2004; accepted 26 October 2004)
JOURNAL JAI
Abstract
The materials used were two sorts of reactor pressure vessel steels (RPVSs), which contain different amounts of impurity phosphorous (P) and copper (Cu). The specimens for Charpy V-notch impact tests and Auger electron spectroscopy (AES) were irradiated in the Japan Materials Test Reactor (JMTR) at 290°C up to fluences of 6×10²¹ and 1×10²⁴ n/m² using a multi-division temperature control capsule which enables removal of a part of the sub-capsules during operation of the reactor.

Neutron irradiation resulted in a significant shift in the ductile-brittle transition temperature (DBTT) accompanied by a large irradiation hardening in the high P and high Cu steel. The AES measurements following the irradiations revealed that almost no phosphorous segregation occurred at grain boundaries. The DBTT shifts by neutron irradiation were reasonably interpreted in terms of a so-called hardening mechanism. The SEM observations of the fractured surface indicated that a very small amount of grain boundary fracture was induced at the irradiation conditions, and resultantly no grain boundary embrittlement was observed.

Based on the results of irradiation experiments as well as long-term thermal aging experiments beyond 16 000 h, neutron irradiation-induced grain boundary embrittlement is considered to rarely happen to the RPVS that contains 110 wppm of phosphorous.

Keywords:
DBTT shift, grain boundary fracture ratio, irradiation, non-hardening embrittlement, phosphorous segregation

Paper ID: JAI12398
DOI: 10.1520/JAI12398

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Author Kimura, A Affiliation Professor, IAE, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan. Author Shibata, M Affiliation Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Japan Author Kasada, R Affiliation Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Japan Author Fujii, K Affiliation Institute of Nuclear Safety System, Inc., Mihama, Mikata, Japan Author Fukuya, K Affiliation Senior Researcher, Institute of Nuclear Safety System, Inc., 64 Sata, Mihama, Mikata, Fukui 919-1205, Japan. Author Nakata, H Affiliation Institute of Nuclear Safety System, Inc., Mihama, Mikata, Japan Title: Assessment of Neutron Irradiation-Induced Grain Boundary Embrittlement by Phosphorous Segregation in a Reactor Pressure Vessel Steel Symposium: Effects of Radiation on Materials: 22nd International Symposium, 2004-6-10
Committee: E10 on Nuclear Technology and Applications