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problem6 - and the radial displacement o f the outer...

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22.31411.5612.084113.14 Fall 2006 Problem Set VI Due 10126106 his problem i l l u s t r a t e s a mechanism by which clad stresses can be reduced during up-power ramps by approaching f u l l power a t a slower rate. 1. Geometry (20°C) The clad outside diameter i s 11.2 nun; and the clad thickness i s 0.7 mm. 2. Clad Material Properties (assumed constant) Young's Modulus = 76 GPa; Poisson's Ratio = 0.25; Coefficient o f Thermal Expansion = 6.7 m1m.K; and ; = clad creep rate (sl.) = (1 x 10-9)ag; 9 . . where a has the units MPa. 9 3. Operating Conditions - A t hot zero power, the clad i s a t 280°C. the coolant pressure i s 15.5 MPa, the gas pressure inside the rod i s 5.4 MPa, and the clad i s touching the fuel with zero contact pressure. A t hot f u l l power the coolant and gas pressures are unchanged, the average clad temperature i s 375'C,
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Unformatted text preview: and the radial displacement o f the outer surface o f the fuel has increased by 35 run. Consider two cases: - An up-power ramp from zero t o f u l l power i n 30 minutes; - An up-power r i i p from zero t o f u l l power i n 30 hours. 4. Calculational Basis - Use a single r i n g to represent the clad - Consider that the radial deflection a t the fuel outer surface and the clad average temperature vary l i n e a r l y with time during each up-power ramp. - Use only elastic, thermal, and creep strains. Let the creep strains equal zero a t hot zero power. - Use zero axial force from fuel-clad contact. 5. Questions Obtain the following quantities upon reaching f u l l power i n each up- power ramp: . , - clad stress; - clad strain; and - r a d i a l displacement a t the clad outer surface....
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