A simple test method for measuring ?valid? JIc fracture toughness in Charpy-size surveillance specimens of nuclear pressure vessel steel

1978 ◽  
Vol 14 (6) ◽  
pp. R329-R334 ◽  
Author(s):  
R. O. Ritchie ◽  
W. L. Server ◽  
R. A. Wullaert
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Test Method ◽  
Pressure Vessel Steel ◽  
Simple Test ◽  
Vessel Steel ◽  
Surveillance Specimens

Reconstitution of Compact Specimen for Irradiated Reactor Pressure Vessel Steel

2006 ◽  
Author(s):  
Toru Osaki ◽  
Hiroshi Matsuzawa
Keyword(s):  
Fracture Toughness ◽  
Plastic Deformation ◽  
Crack Opening ◽  
Crack Tip ◽  
Reactor Vessel ◽  
Compact Specimen ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Original Size ◽  
Surveillance Specimens

Reconstitution in this paper means to constitute the original size compact specimen, which is made of the insert cut out from tested specimen and tubs welded to the insert. It is a promising technique to secure an adequate number of surveillance specimens for long-term operation of nuclear power plants. The fracture toughness of each reactor vessel of pressurized water reactors in Japan is measured periodically by 1/2T compact surveillance specimens, and is applied to assess the structural integrity of the reactor vessel under pressurized thermal shock loads. [1] This practice should be continued and enhanced if possible, after the full use of originally installed specimens, because its fracture toughness is lower than before. Reconstitution of irradiated 1/2T compact specimens to the original size was studied and demonstrated. Reconstituted specimens were composed of an irradiated material called an insert and un-irradiated tabs welded to the insert. It was demonstrated that the central part of the insert near the crack tip was not annealed by the thermal transient during welding if properly adjusted YAG laser welding was applied. Crack-tip opening and compliance before and after reconstitution were investigated by testing and analysis. Testing and analysis of un-irradiated specimens before reconstitution showed that the plastic deformation expanded to an area wider than 6 mm, the half width of the insert if it was a reconstituted specimen. The material had medium fracture toughness. The reconstituted specimen of the same material showed almost the same fracture toughness, although the weld could not be yielded as the insert, which could affect the crack opening. The crack opening was immune to the change of the deformation far from the crack tip. Correlation between J at 2.5 mm crack extension and plastic deformation width, and the effects of short time annealing of the insert far from the crack tip during welding were studied. Integrating the results, the conditions for reconstituting the 1/2T compact specimen were settled. The reconstituted specimen with irradiated insert designed to meet the conditions showed little change in fracture toughness.

Fracture Toughness Characterization of Midland Beltline Weld After High Dose of Irradiation

2006 ◽  
Author(s):  
Mikhail A. Sokolov ◽  
Randy K. Nanstad
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Neutron Fluence ◽  
National Laboratory ◽  
Reactor Pressure Vessel ◽  
High Dose ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Oak Ridge ◽  
Reactor Pressure

The Heavy-Section Steel Irradiation (HSSI) Program at Oak Ridge National Laboratory includes a task to investigate the shape of the fracture toughness master curve for reactor pressure vessel steel highly embrittled as a consequence of irradiation exposure, and to examine the ability of the Charpy 41-J shift to predict the fracture toughness shift. As part of this task, a low upper-shelf WF-70 weld obtained from the beltline region of the Midland Unit 1 reactor pressure vessel was characterized in terms of static initiation and Charpy impact toughness in the unirradiated and irradiated conditions. Irradiation of this weld was performed at the University of Michigan Ford Reactor at 288°C to neutron fluence of 3.4×1019 neutron/cm2 in the HSSI irradiation-anneal-reirradiation facility. This reusable facility allowed the irradiation of either virgin or previously irradiated material in a well-controlled temperature regime, including the ability to perform in-situ annealing. This was the last capsule irradiated in this facility before reactor shut down. Thus, the Midland beltline weld was irradiated within the HSSI Program to three fluences — 0.5×1019; 1.0×1019; and 3.4×1019 neutron/cm2. It was anticipated that it would provide an opportunity to address fracture toughness curve shape and Charpy 41-J shift compatibility issues at different levels of embrittlement, including the highest dose considered to be in the range of the current end of life fluence. It was found that the Charpy 41-J shift practically saturated after neutron fluence of 1.0×1019 neutron/cm2. The transition fracture toughness shift after 3.4×1019 neutron/cm2 was only slightly higher than that after 1.0×1019 neutron/cm2. In all cases, transition fracture toughness shifts were lower than predicted by the Regulatory Guide 1.99, Rev. 2 equation.

Assessment of Pressure Vessel Steel Irradiation Embrittlement Up to 40 Years Using Local Approach to Fracture Modelling: Application to the French Surveillance Program

2011 ◽  
Author(s):  
B. Tanguy ◽  
A. Parrot ◽  
F. Cle´mendot ◽  
G. Chas
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Chemical Elements ◽  
Experimental Results ◽  
Physical Models ◽  
Surveillance Program ◽  
Pressure Vessel Steel ◽  
Irradiation Embrittlement ◽  
Vessel Steel ◽  
Different Levels

For western pressure vessel reactors, assessment of pressure vessel steels irradiation embrittlement due to neutron irradiation is based on a semi-empirical formulae which predicts the shift of a reference lower bound fracture toughness curve as a function of fluence and embrittlement-involved chemical elements. Periodically, in order to monitor the embrittlement of each RPV, the predictions of the formulae is confronted to experimental results obtained from Charpy specimens located in surveillance capsules irradiated with a higher fluence level than the pressure vessel itself. Historically only the shift of the temperature index defined for a given level of energy, e.g. 56J in the French surveillance program, is used. In support to the French surveillance program methodology, for some of the French RPVs, physical models of fracture (for both cleavage and ductile fracture) are used to analyse in details the whole experimental basis available at different levels of fluence. This study presents the methodology developed in order to analyse the experimental results of a RPV steel from the french surveillance program, including Charpy and fracture toughness tests at different levels of fluence i.e. of embrittlement. The methodology applied aims to use the numerous Charpy tests results available in order to assess, at the same fluence levels, the fracture toughness embrittlement. The results are then compared to available fracture toughness results for a given level of embrittlement.

Fracture Toughness of a Highly Irradiated Pressure Vessel Steel in Warm Pre-Stress Loading Conditions (WPS)

2011 ◽  
Author(s):  
Guillaume Chas ◽  
Eric Molinie´ ◽  
Eric Garbay ◽  
Francois Cle´mendot ◽  
Dominique Moinereau ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Load Level ◽  
Experimental Program ◽  
Favourable Effect ◽  
Surveillance Program ◽  
Pressure Vessel Steel ◽  
Loading Conditions ◽  
Load History ◽  
Vessel Steel

The warm pre-stress (WPS) of a flawed structure occurs when it is pre-loaded at high temperature in the ductile domain then cooled and loaded up to fracture in the brittle to ductile transition temperature domain. This load history is a feature of RPV accidental transients of LOCA type. Numerous tests on non irradiated specimens and structures have shown the favourable effect of WPS on fracture behaviour. Theorical knowledge let expect that the WPS effect occurs by the same way on irradiated material, but experimental approach had to be completed in such conditions. The experimental program presented in the present article consists in fracture toughness tests under WPS loading conditions performed on two RPV steels irradiated up to a fluence of 6,5.1019 n/cm2. The CT12.5 specimens used for these tests had been irradiated in the capsules of the pressure vessel surveillance program of two french reactors. Different types of WPS load history have been applied to cover typical accidental transients. All the results obtained confirmed for an irradiated steel the two assumptions generally made about the WPS effect: no fracture occurred during the cooling step of the loading even at high load level and the mean fracture toughness value is higher than that measured with conventional mono-temperature tests.

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