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 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.

Stable and Unstable Crack Growth of A508 Class 3 Plates Subjected to Combined Force of Thermal Shock and Tension

1989 ◽  
Vol 111 (3) ◽  
pp. 234-240 ◽  
Author(s):  
G. Yagawa ◽  
Y. Ando ◽  
K. Ishihara ◽  
T. Iwadate ◽  
Y. Tanaka
Keyword(s):  
Thermal Shock ◽  
Nuclear Power ◽  
Power Plants ◽  
Fracture Behavior ◽  
Structural Integrity ◽  
Three Dimensional ◽  
Test Results ◽  
Unstable Crack ◽  
Pressurized Thermal Shock ◽  
Series Of Experiments

An urgent problem for nuclear power plants is to assess the structural integrity of the reactor pressure vessel under pressurized thermal shock. In order to estimate crack behavior under combined force of thermal shock and tension simulating pressurized thermal shock, two series of experiments are demonstrated: one to study the effect of material deterioration due to neutron irradiation on the fracture behavior, and the other to study the effect of system compliance on fracture behavior. The test results are discussed with the three-dimensional elastic-plastic fracture parameters, J and Jˆ integrals.

Further Predictions of Fracture Experiments of a Pre-Cracked Pressurised Thermal Shock Disk (PTS-D) Specimen Under Warm Prestressing Loading Cycles

2012 ◽  
Author(s):  
H. Teng ◽  
J. K. Sharples ◽  
P. J. Budden
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Thermal Shock ◽  
Local Stress ◽  
Superposition Method ◽  
Warm Prestressing ◽  
Disk Specimen ◽  
Pressurized Thermal Shock ◽  
Different Levels ◽  
Good Agreement

Finite element analyses have been performed to investigate the effects of warm prestressing (WPS) of a pre-cracked PTS-D (Pressurized Thermal Shock Disk) specimen. Three basic types of WPS loading cycles were used in the analyses: LUCF (Load-Unload-Cool-Fracture) cycle; LCF (Load-Cool-Fracture) cycle; and LCTF (Load-Cool-Transient-Fracture) cycle. The analyses aimed to predict the fracture toughness enhancements due to WPS using different analysis methods and to make comparisons with the experimental work conducted by the Belgium SCK-CEN organisation under the European NESC VII project. The finite element results were used to derive the enhanced fracture toughness by three different engineering methods: (1) Chell’s displacement superposition method; (2) the local stress matching method; and (3) Wallin’s empirical formula. The enhanced fracture toughness was evaluated at the deepest point of the semi-elliptical crack based on three different levels of as-received fracture toughness of 43.96, 65.94, and 86.23 MPam1/2, which correspond to probabilities of failure of 5%, 50% and 95%, respectively. The predicted fracture loads were compared with the experimental fracture loads for the three WPS loadings cycles. The results show good agreement.

Methodology and Warm Prestressing Effect for Pressurized Thermal Shock Analysis in Nuclear Power Plant

2015 ◽  
Vol 750 ◽  
pp. 104-113
Author(s):  
Gui An Qian ◽  
Markus Niffenegger
Keyword(s):  
Thermal Shock ◽  
Nuclear Power ◽  
Structural Integrity ◽  
Pressurized Water Reactor ◽  
Local Approach ◽  
Pressurized Water ◽  
Warm Prestressing ◽  
Load Paths ◽  
Pressurized Thermal Shock ◽  
Integrity Analysis

One potential challenge to the integrity of the reactor pressure vessel (RPV) in a pressurized water reactor is posed by pressurized thermal shock (PTS). Therefore, the safety of the RPV with regard to neutron embrittlement has to be analyzed. In this paper, the procedure and method for the structural integrity analysis of RPV subjected to PTS is presented. The FAVOR code is applied to calculate the probabilities for crack initiation and failure by considering crack distributions based on cracks observed in the Shoreham and PVRUF RPVs in the U.S. A local approach to fracture, i.e. the σ*-A* model is used to predict the warm prestressing (WPS) effect on the RPV integrity. The results show that the remaining stress contributes to the WPS effect, whereas the increase of fracture toughness is not completely attributed to the remaining stress. The modeled load paths predict a material toughness increase of 30-100%.

Consequence evaluation for pressurized thermal shock

1985 ◽  
Vol 89 (1) ◽  
pp. 173-179
Author(s):  
Richard J. Barrett ◽  
Edward D. Throm
Keyword(s):  
Thermal Shock ◽  
Pressurized Thermal Shock

The Impact of an Improved Flaw Model on a Pressurized Thermal Shock Evaluation

2002 ◽  
Author(s):  
T. L. Dickson ◽  
F. A. Simonen
Keyword(s):  
Thermal Shock ◽  
Computational Models ◽  
The United States ◽  
Pressure Vessels ◽  
Pressurized Water ◽  
Evaluation Program ◽  
Pressurized Thermal Shock ◽  
Computational Methodology ◽  
The Impact ◽  
Flaw Characterization

The current regulations for pressurized thermal shock (PTS) were derived from computational models that were developed in the early-mid 1980s. The computational models utilized in the 1980s conservatively postulated that all fabrication flaws in reactor pressure vessels (RPVs) were inner-surface breaking flaws. It was recognized at that time that flaw-related data had the greatest level of uncertainty of the inputs required for the probabilistic-based PTS evaluations. To reduce this uncertainty, the United States Nuclear Regulatory Commission (USNRC) has in the past few years supported research at Pacific Northwest National Laboratory (PNNL) to perform extensive nondestructive and destructive examination of actual RPV materials. Such measurements have been used to characterize the number, size, and location of flaws in various types of welds and the base metal used to fabricate RPVs. The USNRC initiated a comprehensive project in 1999 to re-evaluate the current PTS regulations. The objective of the PTS Re-evaluation program has been to incorporate advancements and refinements in relevant technologies (associated with the physics of PTS events) that have been developed since the current regulations were derived. There have been significant improvements in the computational models for thermal hydraulics, probabilistic risk assessment (PRA), human reliability analysis (HRA), materials embrittlement effects on fracture toughness, and fracture mechanics methodology. However, the single largest advancement has been the development of a technical basis for the characterization of fabrication-induced flaws. The USNRC PTS-Revaluation program is ongoing and is expected to be completed in 2002. As part of the PTS Re-evaluation program, the updated risk-informed computational methodology as implemented into the FAVOR (Fracture Analysis of Vessels: Oak Ridge) computer code, including the improved PNNL flaw characterization, was recently applied to a domestic commercial pressurized water reactor (PWR). The objective of this paper is to apply the same updated computational methodology to the same PWR, except utilizing the 1980s flaw model, to isolate the impact of the improved PNNL flaw characterization on the PTS analysis results. For this particular PWR, the improved PNNL flaw characterization significantly reduced the frequency of RPV failure, i.e., by between one and two orders of magnitude.

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