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Research Papers: Design and Analysis

# Use of the Failure Assessment Diagram to Evaluate the Safety of the Reactor Pressure Vessel

[+] Author and Article Information
Mingya Chen

Suzhou Nuclear Power Research Institute,
No.1788, Xihuan Road,
Suzhou, Jiangsu 215004, China
e-mail: chenmingya@cgnpc.com.cn;
p134362@163.com

Feng Lu, Rongshan Wang

Suzhou Nuclear Power Research Institute,
No.1788, Xihuan Road,
Suzhou, Jiangsu 215004, China

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received May 14, 2014; final manuscript received November 17, 2014; published online February 24, 2015. Assoc. Editor: Allen C. Smith.

J. Pressure Vessel Technol 137(5), 051203 (Oct 01, 2015) (8 pages) Paper No: PVT-14-1080; doi: 10.1115/1.4029191 History: Received May 14, 2014; Revised November 17, 2014; Online February 24, 2015

## Abstract

Analysis of multiple failure modes is the key element of the integrity evaluation of the nuclear reactor pressure vessel (RPV). While the simple single-criterion failure code provides the guidance for structural integrity, the guidance ignores the interaction between fast fracture and plastic collapse. In this paper, the differences between the reserve factor (RF) in the R6 two-criteria failure procedure and the safety coefficient (SC) in the single-criterion failure code were compared. Based on 3D finite element (FE) analyses, the option 3 failure assessment diagram (FAD) of the beltline of the RPV was established according to the R6 basic route and alternative approaches, respectively. Also, the nonconservation of the secondary stress correction parameter $ρ$ was reviewed. In this paper, it was shown that the effect of crack sizes on the FAD is considered to be limited, and the influence of the thermal stress on the FAD is obvious in the transition region of the failure assessment curve (FAC). The FAD only considering the mechanical load encloses the FAD considering the thermal–mechanical load for the $Lr$ smaller than 1, but it is contrary when the $Lr$ is bigger than 1. It is not enough to just satisfy the requirement in the IWB-3612 of the ASME code because the risk of plastic-collapse failure is ignored. And in this study, the maximum nonconservation of the fracture toughness RF is more than 7% due to the approximate value of $ρ$. Accordingly, the accurate method in the R6 procedure should be used in the integrity assessment of the RPV under the faulted transient.

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## Figures

Fig. 1

Schematic diagram of the FAD

Fig. 2

Flow chart of the paper

Fig. 3

The factor ρ1

Fig. 4

Calculation of the RF

Fig. 5

Calculation the failure probability

Fig. 6

The inner surface crack model

Fig. 7

Three-dimensional mesh of the vessel containing a surface crack (a/t = 0.15)

Fig. 8

Temperature histories of the transients

Fig. 9

Plastic-collapse loads of the flawed structure

Fig. 10

The option 3 FAD

Fig. 11

The assessment points of the normal transient

Fig. 12

The assessment points of the faulted transient

Fig. 13

Comparation of Je and J

Fig. 14

The elastic hoop stress at 3600 s and 7200 s of the faulted transient

Fig. 15

FAD considering the influence of the thermal stress

Fig. 16

Comparison of the ρ parameter

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