Microstructural assessment of damaged materials in FBR assessment of creep damage in weldment

Momma, Yoshio*; *; ; ; ; Aoto, Kazumi

JNC TN9400 2000-044, 22 Pages, 2000/03

JNC-TN9400-2000-044.pdf:1.37MB

ln the past the microstructural observation was mostly applied to understand the materials behavior qualitatively in R&D of the new materials and the life prediction for the fast breeder reactor components. However, the correlation between the changes in properties and microstrutures must be clarified to ensure the structural integrity. Particularly we are interested in the method to correlate the long-term properties and microstructural changes at high temperatures. The current research is to quantify the changes in microstructure of the weld metal for the welded structure of the reactor vessel. ln this research we have conducted creep testing of the weld metals at 823 and 873K up to 37,000h. Two types of the weld metals (16Cr-8Ni-2Mo and 18Cr-12Ni-Mo) were subjected to the creep testing. Based on the areas of the precipitates, the microstructural characterization with time and creep damage was attempted. The creep strength of the 16Cr-8Ni-2Mo weld metal is lower than that of the 18Cr-12Ni-Mo one at higher stresses, shorter times. But there is a trend toward to become similar strength with lower stresses and increasing times. The creep-rupture ductility of the 16Cr-8Ni-2Mo weld metal is superior to that of the 18Cr-12Ni-Mo one. The creep-rupture takes place at the interface of the sigma () phases precipitated in the delta () ferrites at 823K lower stresses and 873K. The amount of precipitates in the 16Cr-8Ni-2Mo weld metal is smaller than that in the 18Cr-12Ni-Mo one at each temperature and stress. Also it is apparent that the amount of the precipitates is primarily responsible to the decomposition of the phase, because the amount of the residual ferrites measured by the Magne-Gauge reduces with times. Using the Larson-Miller parameter it was possible to correlate the amount of the precipitates linearly with the LMP values.

Simulation of creep test on 316FR stainless steel in sodium environment at 550

Satmoko, A.*;

JNC TN9400 99-035, 37 Pages, 1999/04

JNC-TN9400-99-035.pdf:1.54MB

In sodium environment, materia1 316FR stainless steel risks to suffer from carburization. In this study, an analysis using a Fortran program is conducted to evaluate the carbon influence on the creep behavior of 316FR based on experimental results from uni-axial creep test that had been performed at temperature 550C in sodium environment simulating Fast Breeder Reactor condition. As performed in experiments, two parts are distinguished. At first, elastic-plastic behavior is used to simulate the fact that just before the beginning of creep test, specimen suffers from load or stress much higher than initial yield stress. In second part, creep condition occurs in which the applied load is kept constant. The plastic component should be included, since stresses increase due to section area reduction. For this reason, elastic-plastic-creep behavior is considered. Through time carbon penetration occurs and its concentration is evaluated empirically. This carburization phenomena are assumed to affect in increasing yield stress, decreasing creep strain rate, and increasing creep rupture strength of material. The model is capable of simulating creep test in sodium environment. Material near from surface risks to be carburized. Its material properties change leading to non-uniform distribution of stresses. Those layers of material suffer from stress concentration, and are subject to damage. By introducing a damage criteria, crack initialization can thus be predicted. And even, crack growth can be evaluated. For high stress levels, tensile strength criterion is more important than creep damage criterion. But in low stress levels, the latter gives more influence in fracture. Under high stress, time to rupture of a specimen in sodium environment is shorter than in air. But for stresses lower than 26 kgfmm, the time to rupture of creep in sodium environment is the same or little longer than in air. Quantitatively, the carburization effect at ...

Characteristics and experimental evaluation of super-heat-resisting Nb-based and Mo-based Alloys

Morinaga, Masahiko*; *; *; *

PNC TJ9603 97-001, 95 Pages, 1997/03

PNC-TJ9603-97-001.pdf:3.95MB

[PURPOSE] Nb-based and Mo-basd alloys have been investigated in order to develop the frontiers of matelials technique which will be utililized in the environment of high-temperature liquid alkali metals. In this study, both mechanical properties and corrosion resistance to liquid Li were evaluated for two designed Mo-based alloys, Mo-15Re-0.1Zr and Mo-15Re-0.1Zr-0.1Ti. In addition, a series of corrosion test was performed with provisionally designed Nb-based alloys, Nb-(1-4)Hf. [EXPERIMENTAL METHODS] (1)High-temperature tensile test : A tensile test in the Ar atmosphere was carried out at 1473K for the designed Mo-based alloys. Commercial TZM alloy was also tested as a reference. (2)High-temperature creep test : A Creep test in the Ar atmosphere was performed at 1473K under the several applied stress levels for the designed Mo-based alloys. (3)Workability test : A three-point bend test was carried out at room temperature to evaluate the workability of the designed Mo-based alloys. (4)Corrosion resistance to liquid Li : Both the provisionally desingned Nb-based alloys and the designed Mo-based alloys were immersed in the liquid Li at 1473K. The weight change was measured as an indication of the corrosion resistance. Also, the Auger electron spectroscopy analysis was performed with several specimens to examine the surface state of them after corrosion tests. [RESULTS AND DISCUSSIONS] (1)High-temperature tensile properties : The designed Mo-based alloys were superior in the tensile properties at 1473K to the commercial TZM alloy. In fact, both the tensile and yield strengths of them were about 1.5 and 2.3 times higher than the TZM alloy, respectively. (2)High-temperature creep properties : The creep rate of the designed Mo-based alloys at 1473K was lower, compared to other solid solution hardening Mo-based alloys, but higher than the precipitation hardening TZM alloy. (3)Workability : The workability of the designed Mo-based alloys was satisfactory regardless ...

Development of creep-fatigue evaluation method for welde structures considering metallurgical and geometrical discontinuities; Application of elastic follow-up model to welded joints

kasahara, Naoto

PNC TN9410 95-213, 38 Pages, 1995/08

PNC-TN9410-95-213.pdf:1.72MB

In order to evaluate thermal transient strength of welded components in nuclear plants, conventional structural design codes provide conservative strength reduction factors, which are desired to be rationalized. Author extended the generalized clastic follow-up model to evaluate main causes of strength reduction of welded joints. As main causes of strength reduction of welded joints subjected to cyclic thermal transients, attention was given to (1)Metallurgical discontinuity in which the different deformation response between base metal and weld metal can result in nonuniform stresses and strain across the weldment, (2)Structural discontinuity at penetration beads of welded joints, and (3)Degradation of Weld Metal. In order to evaluate (1) and (2) of above factors, an elastic follow-up model was successfully applied. Thermal transient strength test results provide further substantiation of the validity of the elastic follow-up model for ensuring adequate life in elevated temperature component weldments. Author applied the creep-fatigue life prediction methods based on the elastic follow-up model to evaluate test results of a welded vessel model. Proposed method was proved to be adequate through comparison of predicted damagc with observed cracks data.

Crack growth properties of FBR structural materials at elevated temperature

Koi, Mamoru

PNC TN9410 90-105, 163 Pages, 1990/07

PNC-TN9410-90-105.pdf:2.32MB

Fatigue and creep crack growth data of SUS304 stainless steel, 2.25Cr-1Mo steel and Mod.9Cr-1Mo steel, which were accumulated in PNC in last several years, were treated as a data base. Average trend equations of crack growth rate were proposed and also statistical analysis was carried out. Finite Elements analysis of center cracked tensioned plate was performed and simplified prediction method of modified J-integral J'(C ) was developed. 0btained results are summerized as follows: (1)In all tested materials, fatigue crack growth rate and creep crack growth rate were successfully represented using cyclic J-integral range J and modified J-integral J', respectivery. (2)In all tested materials, meaningful difference of crack growth rate could not be detected between hot rolled plate and forged material, and also between base metal and welded material. (3)Averaged trend equations of fatigue crack growth rate and creep crack growth rate of all tested materials were proposed on the basis of power low with cyclic J-integral range and modified J-integral, respectively. (4)Assuming that the coefficient and exponent of the above power low obey joint normal distribution, statistical analysis of crack growth rate was carried out and relationship between variance and J, J' were obtained. (5)Simplified method was developed to predict modified J-integral of center cracked tensioned plate. Prediction results show good agreement with experimental results, and this fact suggests that J-integral evaluation method of 3-dimensional surface crack, which has been developed in PNC, has good prediction accuracy.

Key technology design study of large FBR; Study of crack opening area for LBB

; *; Furuhashi, Ichiro*

PNC TN9410 88-147, 215 Pages, 1988/09

PNC-TN9410-88-147.pdf:10.23MB

The present study includes the analytical work for of the stable crack growth of the finite plate with semi-elliptical surface defect by creep-fatigue loadings, and of the crack opening area for presumed leakage of cloolant to be considered in safety assessment. The objective of this study is to develop the basic inelastic fracture mechanics to the level in which the integrity of basic components, plate, vessel, piping, and so on, with crack would be able to be assessed analytically. CANIS code developed last year was used to analize the J integral for fatigue crack growth and J' integral for creep crack growth of SUS 304 plates with various shapes of semi-elliptical surface cracks at 500 C, then those distributions were arranged from the view point of crack growth assessment. An appricable range of these data is 1.5 Sm of fatigue cycle and hold time of 108,000 hr creep. 0nly secondary stress including membrane, bending and combination of these stresses were considered in the data base. Evaluation of elbow with 42 diameter and 20.6mm thickness considered in the design of large loop type FBR were achieved based on the data base. Then calculated through wall crack lengths were applied to the calculation of opening areas of 42 elbow subjected of internal pressure of 2 atg and in plane bending moment corresponding to stress level of 1.5Sm. The results are (1)A numbers of cycles at penetration are 6,250 for membrane stress and 30,520 for bending stress in the case of fatigue, and 303 for memberane and 1,534 for bending in the case of creep-fatigue. (2)opening area against internal pressure is larger than that against bending moment, and is about 0.5mm. (3)maximum leak rate from the opening area is about 23 /hr. The level up of analytical method for stable crack growth was almost accomplished. In the near future, the experimental study would be needed for validation of this method.

Creep Strength of the Uranium Monocarbide Containing Small Quantity of Uranium Monosulfide

;

JAERI-M 5675, 14 Pages, 1974/04

JAERI-M-5675.pdf:0.53MB

no abstracts in English

Current status and issues on ODS tempered martensitic steel development for performance enhancement of advanced nuclear power system

Otsuka, Satoshi; Tanno, Takashi; Yano, Yasuhide; Fujita, Koji; Shizukawa, Yuta; Hashidate, Ryuta; Onizawa, Takashi; Kaito, Takeji; Ito, Chikara

no journal, , 

Implementation of fusion energy system and fast reactor cycle system requires the development of advanced materials resistant to the severe core environment where high-temperature and high-dose neutron irradiation are superposed. A lot of efforts have been made worldwide for research and development of oxide dispersion strengthened (ODS) steels with a variety of specification; Japan Atomic Energy Agency (JAEA) has focused on the development of 9Cr,11Cr-ODS tempered martensitic steel (TMS) for high-burnup fuel cladding tube of sodium-cooled fast reactor (SFR). This paper overviews the current status on 9Cr,11Cr-ODS TMS cladding tube development in JAEA, and discusses the cross-cutting issues in material development for advanced nuclear power systems.