Post-Irradiation Evaluation of Eurofer97 Fracture Toughness Using Miniature Multinotch Bend Bar Specimens

In this study, we performed fracture toughness characterization of ten neutron-irradiated Eurofer97 variants using precracked miniature multi-notch bend bar (M4CVN) specimens based on the Master Curve method in the ASTM E1921 standard. The neutron irradiation was performed in the flux trap position of the High Flux Isotope Reactor (HFIR) of the Oak Ridge National Laboratory (ORNL) with the nominal irradiation temperature of 300°C and irradiation dose of 2.5 displacements per atom (dpa). Depending on the irradiation temperature and materials, we observed different degrees of irradiation hardening and embrittlement for ten Eurofer97 variants. The upper shift in the Master Curve reference temperature T0Q vs. the increase in Vickers microhardness values showed a liner relationship for only a few materials indicating different irradiation responses of the Eurofer97 variants.

Evaluation of Quasi-Static and Dynamic Fracture Toughness on the Low-Alloy Reactor Pressure Vessel Steel JRQ in the Transition Region

Three point bending and impact tests with sub-sized Charpy specimens were performed on the JRQ reference steel for reactor pressure vessels. Quasi-static and dynamic fracture toughness data were calculated and the fracture behavior in the ductile to brittle transition region was evaluated within the frame of the master curve method (ASTM E1921). Specimens with shallow and deep cracks were studied and the respective influence of crack length and loading rate on the reference transition temperature was determined. The force-time curves of specimens with shallow cracks presented significantly smaller oscillations with respect to the absolute force, making the fracture toughness evaluation more accurate.

PTS Evaluation Case Study Considering Actual Through-Wall Fracture Toughness Distribution

The surveillance test specified in JEAC4201 requires the fracture toughness evaluation of base metal at 1/4-T thickness and T-L orientation, where the initial fracture toughness generally is the minimum in whole thickness at any orientation. In the present study, actual through-wall fracture toughness distribution from a commercial RPV base metal on both of T-L and L-S (actual through crack orientation) orientations were evaluated from Zion Unit 1, which was decommissioned after 25 years (15EFPY) commercial operation. A base metal block of 40mm(T) × 216mm(L) × 216mm(S) was retrieved from belt line region by effort of ORNL and provided to CRIEPI under the USA - Japan collaborative agreement on civil nuclear research framework called CNWG. Through-wall fracture toughness distribution was characterized by means of the Master Curve method utilized by 4mm thickness C(T) “Mini-C(T)” specimens. Near surface material possessed significantly high fracture toughness at amount of 40 degrees Celsius lower reference temperature (To) than those in center thickness locations, despite of higher neutron fluence gained during service operation. Pressurized thermal shock evaluation by probabilistic fracture mechanics code PASCAL4 demonstrated that through-wall fracture probability can be remarkably lowered by considering through-wall fracture toughness distribution.

Master Curve Fracture Toughness Characterization of Eurofer97 Steel Variants Using Miniature Multi-Notch Bend Bar Specimens for Fusion Applications

In this study, we performed fracture toughness testing of ten Eurofer97 steel variants using precracked miniature multi-notch bend bar (M4CVN) specimens based on the Master Curve method in the ASTM E1921 standard. Additional Vickers microhardness and room temperature tensile testing complemented the fracture toughness testing. Compared with standard Eurofer97, the ten variants didn’t show a comprehensive improvement of mechanical properties. The Master Curve method was found to yield a reasonable prediction of fracture toughness results obtained from M4CVN specimens with most valid fracture toughness data within the 2% and 98% tolerance boundaries of the Master Curve. The three-parameter Weibull distribution with Weibull exponent b = 4 also yielded excellent prediction of the relationship between fracture toughness results KJc and the cumulative probability for failure pf for one steel variant.

Influence of Microstructural Variation in Thick Section Steels on the Characterisation of Fracture Toughness Using Sub-Size Specimens

The challenges of performing full-thickness fracture toughness tests on steel plates of 100mm thickness and greater means that the use of sub-size specimens is desirable. In this work, 100mm thick parent plate of S690 high strength steel was characterised using SENB fracture toughness specimens with thickness of 12mm, 25mm, 50mm and 100mm. Sub-size specimens were extracted at two different locations through the plate thickness; mid-wall and quarter wall. Sufficient specimens were tested to apply the Master Curve method in ASTM E1921 to predict the behaviour of 100mm thick material from each set of sub-size specimens. The through-thickness microstructural variation in these heavy-wall steel plates meant that significantly different predictions of full-thickness fracture toughness were obtained from the two sampling locations. However, when sampled from the mid-wall location, sub-size specimens down to 25mm thick were able to conservatively predict full-thickness fracture toughness using Master Curve methods.

Investigation of Mechanical Properties and Ductile-Brittle Transition Behaviors of SA738Gr.B Steel Used as Reactor Containment

The low temperature tensile properties, Charpy-V notch impact performance and fracture toughness of SA738Gr.B steel plate for domestic CAP1400 containment vessel were tested. On this basis, the reference temperature T0 of the master curve method was obtained. The fracture toughness distribution of the steel in the whole ductile-brittle transition zone is predicted and its applicability is verified by the theoretical basis of the master curve method. The results show that the reference temperature of SA738Gr.B steel master curve method is-123.6 °C. The master curve method is appropriate for SA738Gr.B steel with domestic nuclear containment vessel.

Evaluation of Through Wall Fracture Toughness Distribution of IAEA Reference Material JRQ by Mini-C(T) Specimens and the Master Curve Method

The load and temperature history during pressurized thermal shock (PTS) event is highly depending on the crack edge location in wall thickness direction of a reactor pressure vessel (RPV) beltline region. Therefore, the consideration of plant specific through-wall fracture toughness distribution, which is not considered in the current codes and regulations [1,2], may improve the structural integrity assessment for PTS event. The Master Curve (MC) method [3,4] is one of the methods, which can directory evaluate the fracture toughness of ferritic materials with relatively low number of any size of specimens. CRIEPI has proposed the use of very small C(T) (Mini-C(T)) specimens for the MC method. The appropriateness of Mini-C(T) technology has been demonstrated through a series of researches and round robin activities [5, 6, 7, 8, 9]. The present study evaluated the through-wall fracture toughness distribution of irradiated IAEA reference material (JRQ) by means of combination of MC method and Mini-C(T) specimens. Four thickness locations between inner surface to 1/4-T was selected. Those four layers were separately subjected to the Mini-C(T) MC evaluation in two different laboratories. Both laboratories could separately obtain valid and consistent reference temperature, To, from all the tested layers. Inner most layer exhibits 80 °C lower To compared to the 1/4-T location even though the layer has the highest fluence of 5.38 × 1019 n/cm2, while that in 1/4-T location is 2.54 × 1019 n/cm2. The results demonstrate that initial toughness distribution is dominant in the general trend of fracture toughness distribution even after the material was highly irradiated.