Verification of Warm Prestressing Effect Under a Pressurized Thermal Shock (PTS) Event

1994 ◽  
Vol 116 (3) ◽  
pp. 267-273 ◽  
Author(s):  
H. Okamura ◽  
G. Yagawa ◽  
T. Hidaka ◽  
Y. Urabe ◽  
M. Satoh ◽  
...  
Keyword(s):  
Vessel Wall ◽  
Irradiation Embrittlement ◽  
Predictive Equations ◽  
Warm Prestressing ◽  
Pressurized Thermal Shock ◽  
Reactor Steels ◽  
Fracture Tests ◽  
Integrity Analysis ◽  
Temperature Margin ◽  
Reactor Pressure

Fracture tests for the verification of WPS (warm prestressing) effect were carried out by using large flat specimens and big compact specimens with low toughness. In the case of monotonical KI increasing during cooling, the specimen broke within the scatter band of KIC. On the other hand, when KI was decreasing during cooling, the specimens did not break even if KI values were beyond the scatter band of KIC. That is, WPS effect was confirmed even for the low toughness steel like reactor pressure vessel wall under neutron irradiation. Also, KI values at fracture can be predicted by Chell’s theory. By applying WPS effect and the predictive equations for irradiation embrittlement for Japanese PWR reactor steels to the PTS integrity analysis, much more temperature margin can be expected.

Further Experimental Verification of Warm Prestressing Effect Under Pressurized Thermal Shock (PTS)

1996 ◽  
Vol 118 (2) ◽  
pp. 174-180 ◽  
Author(s):  
H. Okamura ◽  
G. Yagawa ◽  
T. Hidaka ◽  
Y. Urabe ◽  
M. Satoh ◽  
...  
Keyword(s):  
Lower Bound ◽  
Thermal Shock ◽  
Experimental Verification ◽  
Temperature Curve ◽  
Test Results ◽  
Warm Prestressing ◽  
Pressurized Thermal Shock ◽  
Bending Loads ◽  
Fracture Tests ◽  
Temperature Margin

Fracture tests for the verification of WPS (warm prestressing) effect were carried out by using large flat specimens with very low toughness. Tensile and bending loads and thermal shock were applied simultaneously to the specimens with the realistically postulated flaw and the two times larger one in order to make the maximum KI cross the lower bound of KIC data. During the tests, loading was controlled to simulate the shape of KI versus temperature curve for the postulated PTS transient. Both the specimens did not break within the scatter band of KIC when KI was decreasing during cooling. KI values at fracture by reloading were beyond the upper bound of KIC. That is, the effectiveness of WPS was directly demonstrated for the PTS transients. Also, KI values at fracture can be predicted by Chell’s theory. As the test results, Japanese PWRs have sufficient temperature margin against PTS.

Verification of Probabilistic Fracture Mechanics Analysis Code Through Benchmark Analyses

2018 ◽  
Author(s):  
Yinsheng Li ◽  
Shumpei Uno ◽  
Koichi Masaki ◽  
Jinya Katsuyama ◽  
Terry Dickson ◽  
...  
Keyword(s):  
Fracture Mechanics ◽  
The United States ◽  
Pressure Vessels ◽  
Irradiation Embrittlement ◽  
Energy Agency ◽  
Probabilistic Fracture Mechanics ◽  
Failure Frequency ◽  
Pressurized Thermal Shock ◽  
Great Confidence ◽  
Reactor Pressure

A probabilistic fracture mechanics (PFM) analysis code PASCAL has been developed by Japan Atomic Energy Agency based on Japanese methods and data to evaluate failure probabilities and failure frequencies of Japanese reactor pressure vessels (RPVs) considering pressurized thermal shock (PTS) events and neutron irradiation embrittlement. To verify PASCAL, we have been performing benchmark analyses by using a PFM code FAVOR which has been developed in the United States and utilized in nuclear regulation. Based on two-year activities, the applicability of PASCAL in failure probability and failure frequency evaluation of Japanese RPVs was confirmed with great confidence. The analysis conditions, approaches and results are given in this paper.

Probabilistic Structural Integrity Analysis of Reactor Pressure Vessels During PTS Events

2012 ◽  
Author(s):  
Kunio Onizawa ◽  
Koichi Masaki ◽  
Jinya Katsuyama
Keyword(s):  
Crack Initiation ◽  
Structural Integrity ◽  
Fracture Probability ◽  
Pressure Vessels ◽  
Sensitivity Analyses ◽  
Conditional Probabilities ◽  
Integrity Assessment ◽  
Pressurized Thermal Shock ◽  
Integrity Analysis ◽  
Reactor Pressure

In order to apply a probabilistic fracture mechanics (PFM) analysis to the structural integrity assessment of a reactor pressure vessel (RPV), PFM analysis code has been developed at JAEA. Using the PFM analysis code, PASCAL version 3, the conditional probabilities of crack initiation and fracture for an RPV during pressurized thermal shock events have been analyzed. Sensitivity analyses on some input parameters were performed to clarify the effect on the conditional fracture probability. Comparison between the conditional probabilities and temperature margin (ΔTm) from current deterministic analysis method were made for some model plant conditions of domestic typical old-type RPVs. From the analyses, a good correlation between ΔTm and the conditional probability of crack initiation was obtained.

Improved Bayesian Update Method on Flaw Distributions Reflecting Non-Destructive Inspection Result

2020 ◽  
Author(s):  
Jinya Katsuyama ◽  
Yuhei Miyamoto ◽  
Kai Lu ◽  
Akihiro Mano ◽  
Yinsheng Li
Keyword(s):  
Likelihood Function ◽  
Bayesian Updating ◽  
Pressure Vessels ◽  
Irradiation Embrittlement ◽  
Failure Frequency ◽  
Likelihood Functions ◽  
Pressurized Thermal Shock ◽  
Bayesian Update ◽  
Non Destructive ◽  
Reactor Pressure

Abstract We have developed a probabilistic fracture mechanics (PFM) analysis code named PASCAL4 for evaluating the failure frequency of reactor pressure vessels (RPVs) through consideration of neutron irradiation embrittlement and transients such as pressurized thermal shock events. It is well-known that flaw distributions, including flaw size and density, have an important role in the failure frequency calculations of a PFM analysis. NUREG-2163 report provides a methodology to obtain much more realistic flaw distributions based on a Bayesian updating approach by reflecting the non-destructive inspection (NDI) results, which is applicable for case when there are flaw indications through NDI. There may, however, be no flaw indications resulting after inspection of some RPVs. Therefore, we proposed likelihood functions applicable for both cases when flaws are detected and when there is no flaw indication as the NDI results. In the Bayesian updating method, the likelihood functions were applied to independently acquire the posterior distributions of flaw depth and density using the same NDI results. In this study, we further improve the likelihood functions to enable them to update flaw depth and density simultaneously. Based on this improved likelihood function, several application examples are presented where the flaw distributions are estimated by reflecting the NDI results through Bayesian update. In addition, PFM analyses are also performed considering those estimated flaw distributions. All the results indicate that the improved likelihood functions are useful for estimating flaw distributions.

Development of Probabilistic Fracture Mechanics Analysis Code PASCAL Version 4 for Reactor Pressure Vessels

2018 ◽  
Author(s):  
Kai Lu ◽  
Koichi Masaki ◽  
Jinya Katsuyama ◽  
Yinsheng Li ◽  
Shumpei Uno
Keyword(s):  
Structural Integrity ◽  
Prediction Method ◽  
Pressure Vessels ◽  
Stress Distributions ◽  
Irradiation Embrittlement ◽  
Energy Agency ◽  
Integrity Assessment ◽  
Failure Frequency ◽  
Pressurized Thermal Shock ◽  
Reactor Pressure

In Japan, Japan Atomic Energy Agency has developed a PFM analysis code PASCAL (PFM Analysis of Structural Components in Aging LWRs) for structural integrity assessment of Japanese reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and pressurized thermal shock transients. By reflecting the latest knowledge and findings, the PASCAL code has been continuously improved. In this paper, the development of PASCAL Version 4 (hereafter, PASCAL4) is described. Several analysis functions incorporated into PASCAL4 for evaluating the failure frequency of RPVs are introduced, for example, the evaluation function of confidence level of failure frequency considering epistemic and aleatory uncertainties in probabilistic variables, the recent stress intensity factor (KI) solutions and KI calculation methods considering complicated stress distributions, and the recent Japanese irradiation embrittlement prediction method. Finally, using PASCAL4, a PFM analysis example for a Japanese model RPV is presented.

Improvements on Evaluation Functions of a Probabilistic Fracture Mechanics Analysis Code for Reactor Pressure Vessels

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Kai Lu ◽  
Jinya Katsuyama ◽  
Yinsheng Li
Keyword(s):  
Fracture Mechanics ◽  
Structural Integrity ◽  
Evaluation Model ◽  
Pressure Vessels ◽  
Irradiation Embrittlement ◽  
Integrity Assessment ◽  
Probabilistic Fracture Mechanics ◽  
Warm Prestressing ◽  
Evaluation Functions ◽  
Reactor Pressure

Abstract In Japan, a probabilistic fracture mechanics (PFM) analysis code PASCAL was developed for structural integrity assessment of reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and pressurized thermal shock (PTS) events. By reflecting the latest knowledge and findings, the evaluation functions are continuously improved and have been incorporated into PASCAL4 which is the most recent version of the PASCAL code. In this paper, the improvements made in PASCAL4 are explained in detail, such as the evaluation model of warm prestressing (WPS) effect, evaluation function of confidence levels for PFM analysis results by considering the epistemic and aleatory uncertainties in probabilistic variables, the recent stress intensity factor (KI) solutions, and improved methods for KI calculations when considering complicated stress distributions. Moreover, using PASCAL4, PFM analysis examples considering these improvements are presented.

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