Regulating rods

Z Begulatlng Rods. The regulating rods are designed to provide Continuous control of the reactor. White four location s are provided for these rods in the beryllium reflector (see Fig. 2.4.A), normally only one will be used for control with one more as a stand-by. The remaining two locations can then be used for hydraulic rabbit tubes. 

When connected to its support shaft, each regulating rod is driven by a low inertia electric motor through a pinion and rack integral with the shaft. The motor will be driven by an amplidyne as described in Chap. S. 

When disconnected the.regulating rod rests on the top of the upper bearing grid. In this position the lower tip of the regulating rod and the loner tip of the Cadmium section are 60 and 12 in., respectively, below the center of the pile lattice. Table 2.3.B summarizes the pertinent data for the regulating 

Weight of regulating rod Weight of drive rod Weight of water in drive rod Total weight of conbined rods Buoyant-force of regulating rod Buoyant force of drive rod Total buoyant force 

Resistance force of rod through pile section (friction) 

---

The MTR control rods are of two main classes, the shim-safety rods and the regulating rods. All of them are designed to lower the reactivity of the reactor when they are inserted, and when fully in, i.e., resting in their shock absorbers, they will Overcome ah excess reactivity of greater than 40X. It will be shown in Chap. 6 that it is necessary to have approximately 19% excess reactivity built into the reactor hence the control rods provide an adequate margin of safety. 

The lower rack housing, attached to the undersurface of the top plug platform, functions as a seal for the regulating-rod drive shaft and as a means of support for the lower shock absorber. 

The regulating-rod primary indicators at the top plug platform consist of a double-disk dial operated by means of suitable gearing.. The outer disk shows the position of the rod in inches while the inner disk indicates to hundredths of an inch. One complete revolution of the outer disk provides indication for 30 in. of travel of the rod, while the inner disk makes one revolution for each inch of travel of the rod. 

The secondary position indicator at the console consists of a dial pointer which moves 240° for 12 in., of travel of the regulating rod. This provides 20° of rotation of the pointer for each inch of rod travel. 

The secondary indicator in both cases is operated by means of a receiver selsyn. The regulating-rod-driver sclsyns are located at the., regulating-rod driver, while those for the, shim rods are located under the - top, plug platform. All are driven by means of suitable gearing,. and in all cases either the primary or secondary indicators may be removed for servicing without affecting the other. 

REGULATING ROD PASSAGES VERTICAL HYDRAULICS FACILITY /DISCHARGE PLUG... 

Instantaneous velocity of regulating rods is measured by tachometers... 

An important feature of this outpp.t circuit is the limit-switch action. These switches operate at extremes of regulating-rod travel of 12 inv in the uniform-sensitivity region at tHe middle of the reactor. The action of the limit-switch circuit, mentioned in Section 5.2.2, is to keep a light,load on the shock absorbers in the limited direction while leaving the possibility of full torque in the opposite direction. 

Two complete servo channels are provided. The operator chooses the channel to be activated by a manual selector switch. Amplidyne motor power is cut off on the inactive channel, and during this stand-by condition a spring-action brake guards the inactive regulating rod against accidental insertion. When the channel is activated (amplidyne motor on), the brake is released by magnetic action. 

Next is panel P, carrying the, selsyn receivers for the regulating rods and also a regulating-rod selector switch. These selsyn dials are also calibrated in inches with clockwise pointer rotation indicating withdrawal. The 22 in. of possible rod motion is spread out for extra sensitivity over one and a quarter pointer revolutions so that the first few inches- and the last few overlap. Amber lights mounted under the scale come on to indicate actuation of the regulating-rod limit switches. 

Preferred shim rods are. also inserted automatically by regulating-rod limit switches., If. the regulating rod is. withdrawn less than 7 in. (,R9)., preferred rods are inserted, and,. if the withdrawal, is less.than 5 in. (RIO), all rods are inserted. This simultaneous insertion of. all rods is called "reverse." It may at,all times.be initiated manually on S-1 or.by a level of 20iX. above Nf, Reverse, may also. be. caused by. certain period or level signals. If, the run auxiliary r,elay, R-3,.-is not picked-up, a., level greater than... 

Shatdowm. For,a normal intentional shutdown the operator has the choice of a variety of procedures. For-example, he could set all shim rod switches (S-21 through 28) On "jpg and leave them there. This would run all the shim rods completely in. If the manual-automatic switch is on automatic, the operative servo will be left with its regulating rod completely withdrawn and its rheostat completely lowered. Since this procedure leaves all the shim rods at the bottom of their travel, it is suitable for a relatively permanent (e.g., maintenance) shutdown but would not be advisable if the plan was to raise the level back up in a short time. In such a case, lowering of the control point, followed by careful insertion of preferred rods, would be a better plan. 

---