f UNCLASSIFIED ORNL DWG 64-648OA
I POWER SUPPLY
RANGE CHANGER b
CONSOLE CHANNEL SELECTOR SWITCH
TO SHIM- REGULATING
COMPENSATED ION CHAMBER
MSRE Nuclear Instrumentation -Linear Flux Level Channels.
Figure 10 i s a diagram of a control rod drive. The articulated cont r o l rod i s suspended from a sprocket chain driven by a gear-reduced ac servamotor. The three drives are identical; they include coarse and fine synchros t o transmit rod position, an irreversible worm and gear s e t , and a potentiometer f o r the position input signal t o the safety system. You w i l l note t h a t two p a r a l l e l power transmission paths have been provided to the sprocket chain. O n e is via the electromagnetic clutch; the alternate drive path i s through an overrunning I! clutch. The l a t t e r always provides a positive drive i n the insert" direction, and a l s o maintains a positive connection t o the drive, so t h a t reverse torque a t the output sprocket cannot produce accidental rod withdrawal. Any one of the three rods i s capable of being used as the servo-controlled shim-regulating rod, by merely changing the e l e c t r i c a l interconnections.
The shock absorber (shown i n Fig. 11) used with t h i s drive u n i t i s somewhat unusual. It consists of a cylinder and a piston or lunger with the unique feature t h a t the working "fluid" i s composed of 3 32-in.-diam s t e e l balls. The shock absorber assembly moves up and down with the rod. When the rod i s scrammed, the cylinder h a l t s a t the stop blocks a t the bottom of the housing. The rod and the plunger continue t o move downwards, and the kinetic energy of the rod i s absorbed a s the s t e e l b a l l s are forced through the narrow annulus around the plunger i n t o the upper part of the cylinder. This device i s a development of the Vard Corporation, who are building the rod drives.
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