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Research Papers: Nuclear Power

Industry Practice for the Neutron Irradiation Embrittlement of Reactor Pressure Vessels in Japan

[+] Author and Article Information
Norimichi Yamashita1

 Tokyo Electric Power Company, Chiyoda-ku, Tokyo 100-8560, Japan

Masanobu Iwasaki

 Kansai Electric Power Company, Mikata-gun, Fukui 919-1141, Japan

Koji Dozaki

 Japan Atomic Power Company, Chiyoda-ku, Tokyo 101-0053, Japan

Naoki Soneda

 Central Research Institute of Electric Power Industry, Komae, Tokyo 201–8511, Japan

1

Corresponding author.

J. Eng. Gas Turbines Power 132(10), 102919 (Jul 09, 2010) (8 pages) doi:10.1115/1.4001057 History: Received August 12, 2009; Revised November 11, 2009; Published July 09, 2010; Online July 09, 2010

Neutron irradiation embrittlement of reactor pressure vessel steels (RPVs) is one of the important material aging issues. In Japan, almost 40 years have past since the first plant started its commercial operation, and several plants are expected to become beyond 40 years old in the near future. Thus, the safe operation, based on the appropriate recognition of the neutron irradiation embrittlement, is inevitable to ensure the structural integrity of RPVs. The amount of the neutron irradiation embrittlement of RPV steels has been monitored and predicted by the complemental use of the surveillance program and embrittlement correlation method. Recent surveillance data suggest some discrepancies between the measurements and predictions of the embrittlement in some old boiling water reactor (BWR) RPV steels with high impurity content. Some discrepancies of pressurized water reactor (PWR) RPV surveillance data from the predictions have also been recognized in the embrittlement trend. Although such discrepancies are basically within a scatter band, the increasing necessity of the improvement of the predictive capability of the embrittlement correlation method has been emphasized to be prepared for the future long term operation. Regarding the surveillance program, on the other hand, only one original surveillance capsule, except for the reloaded capsules containing Charpy broken halves, is available in some BWR plants. This situation strongly pushed establishing a new code for a new surveillance program, where the use of the reloading and reconstitution of the tested specimens is specified. The Japan Electric Association Code, JEAC 4201-2007 “Method of Surveillance Tests for Structural Materials of Nuclear Reactors,” was revised in December 2007, in order to address these issues. A new mechanism-guided embrittlement correlation method was adopted. The surveillance program was modified for the long term operation of nuclear plants by introducing the “long term surveillance program,” which is to be applied for the operation beyond 40 years. The use of the reloading, reirradiation, and reconstitution of the tested Charpy/fracture toughness specimens is also specified in the new revision. This paper reports the application and practice of the JEAC4201-2007 in terms of the prediction of embrittlement and the use of tested surveillance specimens in Japan.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Historical change in Cu content in Japanese RPV steels

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Figure 2

Relationship between Cu and Ni contents

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Figure 3

Relationship between Cu and P contents

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Figure 4

Relationship between neutron fluence and flux

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Figure 5

Transition temperature shifts of BWR and PWR plants with neutron fluence

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Figure 6

Surveillance data and predicted trend curves of Tsuruga Power Station Unit 1

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Figure 7

Surveillance data and predicted trend curves of Fukushima Daiichi Unit 1

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Figure 8

Surveillance data and predicted trend curves of Mihama Unit 1

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Figure 9

Surveillance data and adjusted trend curves of the base metal of Tsuruga Power Station Unit 1

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Figure 10

Surveillance data and adjusted correlations of the base metal of Fukushima Daiichi Unit 1

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Figure 11

Surveillance data and adjusted correlations of the weld metal of Mihama Unit 1

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Figure 12

Surveillance data and predictions of the plate metal with 0.05 wt % Cu and 0.58 wt % Ni

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Figure 13

Surveillance data and predictions of the plate metal with 0.036 wt % Cu and 0.75 wt % Ni

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Figure 14

Comparison of the predictions and measurements of the Japanese surveillance data

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Figure 15

Reconstitution of the Charpy broken halves

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