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Satmoko, A.*;
JNC TN9400 99-035, 37 Pages, 1999/04
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 550
C 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 ...
*; *; Koakutsu, Toru; *; *
PNC TN9410 89-148, 158 Pages, 1989/10
For the purpose of the verification of the evaluation method on the sodium environmental effect on the mechanical properties of the structural materials used for the prototype LMFBR "MONJU" and the rationalization of the evaluation method for large scale LMFBRs, SUS 304 and 316 austenitic stainless steels and 2.25Cr-1Mo steel (NT) were carried out. Test specimens were exposed to a sodium loop for 10,000 hours at 400 
600C simulating the primary and secondary coolant systems of the prototype LMFBR "MONJU". After the exposure, fatigue tests were performed in sodium environment. Fatigue tests were also performed on the thermal aged material for 10.000 hours in inert gas. The results obtaind were as follows. (1)The difference between the fatigue lives of sodium exposed materials and thermal aged materials was very small for both kinds of steels and these lives were almost the same as these of as - received materials. (2)Caburization was recognized on the surface of SUS 304 and SUS 316 austenitic stainless steels in the cage tested in sodium after sodium exposed. In the case of 2.25Cr-1Mo steel (NT), some decarburization was observed at 500 C. (3)The fatigue lives didnot depend on the exposure history such as sodium exposed materials and thermal aged materials for 10,000 hours. The carburization and decarburization effects were very small on fatigue life. The fatigue lives were affected by the environment in which fatigue tests are conducted.
Seshimo, Ichiro; Ukai, Shigeharu; Nomura, Shigeo; Shikakura, Sakae
PNC TN9410 89-122, 47 Pages, 1989/08
Fuel cladding integrity must be confirmed even at the anticipated transient event in LMFBR. In case of loss of coolant accident, cladding highest temperature is limited to 830 for Monju design from a view point of preventing the cladding creep rupture failure by increasing internal gas pressure. In this study, using the recent thermal transient test results of modified SUS316 stainless steel, Larson-Miller Parameter Life Fraction method was applied for predicting the optimum failure temperature. With this method, different thermal transient data can be evaluated systematically, and the effect of irradiation on cladding failure temperature was analyzed. Through this analysis, the Monju design limit temperature of 830 for cladding failure can be changed to 966, and alternative limiting temperature of 920 defined for preventing the coolant sodium boiling becomes a critical factor. This results shows the possibility of improvement for the design limit of this event.
