Effect of thermal cycling on the stress orientation of hydride in zircaloy
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Effect of Thermal Cycling on the Stress Orientation of Hydride in Zircaloy u
MISHIMA, T. OKUBO, AND E. SANO
A zircaloy fuel cladding tube in a water-cooled nu-
Fig. 6 - - E x t e r n a l s u r f a c e of s o d i u m - m o d i f i e d A1-Si-6 wt pet Cu alloy. Each of the white a r e a s a r e c e l l s and the g r e y
particle at the center of most ceils is a silicon crystal. Unetched. Magnification 5 times.
Fig. 7--Section t h r o u g h a white a r e a with a g r e y c e n t e r in Fig. 6. The p h o t o g r a p h s h o w s that the g r e y c e n t e r s a r e silicon ( c o n f i r m e d by e l e c t r o n p r o b e X - r a y m i c r o a n a l y s i s ) and the white a r e a s a r e c e l l s . Note the s i l i c o n f i b e r s r a d i a t i n g f r o m the s i l i c o n c r y s t a l in a s p h e r u l i t i c m a n n e r . Unetched. }Iagnification 207 t i m e s .
METALLURGICAL TRANSACTIONS
clear reactor is known to pick up hydrogen during service. I Zirconium hydride platelets will precipitate when the hydrogen concentration exceeds the terminal solid solubility. The ductility of a cladding tube will be drastically decreased when the platelets are aligned normal to the direction of tensile stress.e The zirconium fuel cladding tube must be able to accommodate the circumferential strain resulting from the diametrical expansion of the fuel pellet due to swelling or center-melting. Therefore, circumferential alignment of hydride platelets is to be preferred. The orientation of the platelets has been known to be influenced by the deformation mode during the process of fabrication as well as by the stress conditions during the process of precipitation.2-4 The terminal solid solubility at a reactor operating temperature, around 300~ is about 65 ppm and will decrease to an extremely small value at room temperature, s Therefore, repeated dissolution and reprecipitation of the hydride will occur during service due to the starting-up and shutting-down of the reactor, which may give rise to a change in the size and orientation of the hydride. It is the purpose of the present study to investigate the effect of thermal cycling under internal pressure on the orientation of hydride platelets in zircaloy-2 fuel cladding tubes. Tubes with two fabrication histories, cold rolled and cold drawn, were autoclaved in pressurized steam at 400~ for 14 days for hydriding. Through analyses, hydrogen concentrations were determined to be 30 to 40 ppm in the as-autoclaved specimens and were not changed during cycling. The tubular specimens were placed in a thermal cycling Y. MISHIMA and T. OKUBO are Professor, Department of Nuclear Engineering, and Associate Professor, Metallurgical Division, respectively, Faculty of Engineering, University of Tokyo, Hongo, Tokyo, Japan. E. SANO was sent to the University of Tokyo from the Kobe Steel Ltd. during 1967. Manuscript submitted November 2, 1970. VOLUME 2,JULY 1971-1995
Circumferential Stress (kg/mm ~)
Number of Cycles 0 (as autoclaved)
1
10
+
,'
,
: 0 (unstressed)
30
;,. +'
.
,+:
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