Method of and drive for actuating absorber rods in pebble bed reactors

A method of actuating absorber rods in pebble bed reactors, according to which the rod is moved into or out of the ball pile with limited advancing speed in a turning or rotary manner. A feeding or advancing force is transmitted onto the rod being introduced, and this force does not exceed the appropriate maximum value of the ball strength and the rod stability. The drive provided for the foregoing procedure effects both a longitudinal shifting and rotation of a rod connected therewith, and has an axially fixed advancing spindle, the spindle nut of which is rigidly connected with the absorber rod and is journalled in a rotary pipe or tube in such a way as to be axially displaceable yet fixed against rotation, with the rotary tube being driven at a constant speed. During removal or outward travel of the rod from the ball pile, a fixed transmission ratio exists between the driving mechanism and driven end, which fixed transmission is generated with the aid of a freewheel or free-running drive. A coupling is provided between the drive motor and the spindle to limit the transferrable torque or turning moments according to a predetermined characterizing line or curve, whereby the rotary speed of the spindle is limited during introduction of the rod into the ball pile by the freewheel or free-running drive causing engagement when the driven end speed of the coupling equals the driving speed. The coupling between the drive motor and the spindle may be found by a hydraulic coupling of oil pump and oil motor, or by a Fottinger coupling.

The present invention relates to a method of actuating absorber rods in 
pebble bed reactors, according to which the rod, with limited advancing 
speed, is rotatingly moved into or out of the ball pile. The invention 
furthermore encompasses a drive adapted for this purpose, with an axially 
fixed feeding or advancing spindle, the spindle nut of which is rigidly 
connected with the absorber rod and is journalled in a rotary tube or pipe 
in such a way as to be axially displaceable yet fixed against rotation, 
with the rotary tube being driven at a constant speed. During removal of 
the rod out of the ball pile, a fixed transmission ratio exists between 
the driving mechanism and driven end, which fixed transmission is 
generated with the aid of a free-running drive or freewheel. 
Absorber rods for the control or regulation of ball-pile reactors can be 
introduced into the ball pile or fill in differing manners: for one, 
straight, smooth rods known as "lift or stroke rods or bars" can be 
pressed with high axial force into the fill to the desired depth. Another 
possibility is to introduce or move the absorber rods with a turning or 
rotating movement into the fill; the absorber rods or bars are provided 
with a threaded profile on the exterior thereof and are designated as 
"turning or rotary rods or bars". Such rotary rods have a certain 
similarity to conveyor worms. 
The rotary drive and the feeding or advancing drive of such rotary rods is 
effected by drive shafts introduced coaxially into the primary gas 
chamber. In particular, the rotary movement of a rotary pipe is 
transmitted onto the rod, which is guided in the rotary pipe so as to be 
fixed against rotation yet axially movable. The feed or advance is 
effected by an axially fixed or stationary spindle, the spindle nut of 
which moves along the spindle with the coupled-on rod. 
During the introduction of such rotary rods into the ball pile, 
considerable forces arise, on the one hand between the balls and the 
advancing or penetrating rod, and on the other hand secondarily within the 
advancing or penetrating rod itself. Furthermore, due to the outer thread 
contour of the rod, there occurs, during the movement of the rod in the 
ball pile, a mixing-through of the balls which is undesired and, with a 
given thread profile, is a function of the ratio between the rotational 
speed and the feed or advance speed. 
On the other hand, the activity of the rods occurring within the primary 
gas chamber permits no extensive switching or control elements or 
influencing measures from the outside. Therefore, attempts have been made 
to optimize the feeding or advancing speed of such rods, with a view 
toward minimal damage to the balls and the rod and to the least possible 
mixing-through of the balls. Also with such optimized, fixedly adjusted 
feeding or advancing speeds of the rod, however, considerable changing 
loads and force peaks occur at the rods which naturally also have an 
effect upon the balls. Moreover, the balls are also mixed through or 
intermixed if, for reasons of the axial force, no advancing or conveying 
effect would be necessary. 
It is therefore an object of the present invention to provide a method, and 
a drive adapted therefor, with which the aforementioned difficulties are 
substantially eliminated by the fact that especially the spindle is 
protected against bending and that breakage of the balls is avoided, while 
the conveying effect of the rod, which is undesired with respect to a ball 
intermixing, is reduced to a minimum.

The method of the present invention is characterized primarily in that an 
advancing or feeding force is transmitted onto the rod moved or introduced 
into the ball pile which does not exceed a maximum value in conformity 
with the ball strength and the rod stability. 
A drive suitable for the method of the present invention is in essence 
characterized in that a coupling is provided which limits the 
transferrable torque or turning moments according to a predetermined 
characterizing curve or line, whereby the speed of rotation of the spindle 
is limited during introduction of the rod into the ball pile by a 
free-running drive or freewheel causing engagement when the driven end 
speed of the coupling equals the driving speed, said coupling being 
provided between the drive motor and the spindle. 
With such an absorber rod drive according to the present invention, there 
is transmitted to the rod a constant advancing or feeding force or a force 
limited to a maximum value corresponding to the strength of the balls and 
the stability of the rod, with simultaneous limitation of the feeding or 
advancing speed. 
A hydrodynamic coupling according to the Fottinger principle, or a 
combination between oil pump and oil motor with a pressure limiting valve 
in the connecting line, is especially suitable as a coupling between the 
drive motor and the spindle. 
According to the present invention, accordingly, during introduction of the 
absorber rod into the ball pile there is eliminated a rigid or fixed 
transmission ratio during the feeding or advancing movement, while however 
there is assured that constantly limited feeding or advancing forces 
exist, and that a maximum speed is not exceeded. Such a wear-free torque 
or turning moment limitation can be suitably realized in a 
hydraulic-hydrodynamic manner. Under certain circumstances, however, drive 
mechanisms or couplings are also possible on an electrical basis or on the 
basis of magnetic forces. 
Referring now to the drawings in detail, according to FIG. 1, the drive 
motor 1 drives a shaft 2 which, by way of a transmission or gearing 3, 
provides the drive of the rotary pipe or tube 4. Within this rotary pipe 4 
or tube 4 is journalled a hollow shaft 6 which is axially displaceable but 
is fixed against rotation. An absorber rod 5, an end of which is shown, is 
rigidly connected with the hollow shaft 6. The spindle 7, with its spindle 
nut, provides for the advancing or feeding of the rod. The spindle 7, 
during introduction and removal of the rod, is driven by elements 8 (oil 
pump and oil motor), which are provided with a connecting line 8' having a 
pressure limiting valve, over the freewheel or free-running drive 9. The 
pressure limiting valve effects a limitation of the oil pressure, and 
accordingly of the torques of the oil motor. The oil circulation in the 
return path proceeds by way of the oil sump of the drive. 
The drive shown in FIG. 2 differs from that shown in FIG. 1 in that the 
pump and motor are combined into a Fottinger coupling (hydrodynamic 
coupling) 10. (Fottinger fluid torque converter). 
A measuring drive 11 is provided with both embodiments. It comprises an 
element connected with the rotary tube 4, and an element rigidly connected 
with the spindle 7. The differential monitoring of the two elements 
respectively provides the position of the rod at any given time, and the 
momentary drive speed of the rod. 
The present inventive drive offers the following possibilities, depending 
on the selected drive variation: 
the drive of the spindle can, during introduction of the rod into the ball 
pile, occur with constant moment or according to a predetermined torque 
characteristic line; 
the turning moment or torque limitation occurs free of wear; 
for the removal or retraction of the rod from the ball pile there can be 
selected a fixed transmission ratio with which no conveying effect arises; 
the feeding or advancing speed, during introduction of the rod, can be 
limited to a maximum value corresponding to the zero conveying effect; 
the drive requires no switch or control elements, and no external supply 
units; and 
the feeding or advancing speed of the rod is not fixed at a constant value. 
The present invention is, of course, in no way restricted to the specific 
disclosure of the specification and drawings, but also encompasses any 
modifications within the scope of the appended claims.