Guideline on Probabilistic Fracture Mechanics Analysis for Japanese Reactor Pressure Vessels

Abstract

In Japan, to prevent nil-ductile fracture of reactor pressure vessels (RPVs) due to neutron irradiation embrittlement, deterministic fracture mechanics evaluation in accordance with the standards developed by the Japan Electric Association is performed for assessing the structural integrity of RPVs under pressurized thermal shock (PTS) events considering neutron irradiation embrittlement. In recent years, a structural integrity assessment methodology based on probabilistic fracture mechanics (PFM) has been introduced into the regulations in the United States and a few European countries. PFM is a rational methodology for evaluating the failure frequency of important pressure boundary components by considering the statistical distributions of various influence factors related to ageing due to the long-term operation. At Japan Atomic Energy Agency (JAEA), a PFM analysis code called PASCAL has been developed to evaluate the failure frequency of RPVs considering neutron irradiation embrittlement and PTS events. In addition, JAEA has developed a guideline for the PFM based structural integrity assessment of RPVs to promote the applicability of PFM in Japan and achieve the objective that an engineer/analyst who familiar with the fracture mechanics to perform PFM analyses and evaluate through-wall cracking frequency (TWCF) of RPVs easily. The guideline consists of a main body (general requirements), explanation (guidance), and several supplements. The technical basis for PFM analysis is also provided, and the new information and better fracture mechanics models are included in the guideline. In this paper, an overview of the guideline and some typical analysis results obtained based on the guideline and the Japanese database related to PTS evaluation are presented.

Recent verification activities on probabilistic fracture mechanics analysis code PASCAL4 for reactor pressure vessel

“…This is because the input data/analysis conditions in a PFM analysis include not only the general analysis conditions but also some detailed ones. For the general analysis conditions, they have been defined in the working group based on the PFM guideline (Katsuyama et al, 2017a; however, for other detailed inputs that were not elaborated in the PFM guideline, they were set by the participants on their own discretion. For further clarification of the differed results shown in Fig.…”

“…The probabilistic variables, analysis models, and evaluation functions were verified, and the verification results have been reported previously . Along with the development of PASCAL4, a PFM guideline (Katsuyama, et al, 2017a has also been established which provides guidance to users on how to run a PFM analysis. This PFM guideline also documents the recommended analysis conditions and input data for PFM evaluation of Japanese RPVs using PASCAL4.…”

“…The analyses were planned in the following two steps:  Step-I: PFM analyses were run for a single crack and a PTS event to evaluate CPI and CPF. Here, the analysis problem was defined initially based on the discussions among all participants in the working group, and then general analysis conditions were determined on the basis of the PFM guideline (Katsuyama et al, 2017a.…”

“…Step-I, all participants discussed to define the common problem in Step-II, that is, failure frequency evaluation of an RPV by considering crack distributions and different PTS events. As in Step-I, each participant set the analysis conditions based on the PFM guideline (Katsuyama et al, 2017a, and run PFM analyses independently using PASCAL4. Afterwards, FCI and TWCF from all participants were compared.…”

“…3 The main input data and evaluation functions used in the PFM analyses of Step-I are summarized in Table 2. Most of the input data and evaluation functions were determined based on the code and data in Japan with their technical bases provided in the PFM guideline (Katsuyama et al, 2017a. Moreover, for the RPV geometries, initial RT NDT , and chemical compositions, the data of a model Japanese RPV in a three-loop pressurized water reactor were used.…”