Shimming automatic

Control of the core is affected by movable control rods which contain neutron absorbers soluble neutron absorbers ia the coolant, called chemical shim fixed burnable neutron absorbers and the intrinsic feature of negative reactivity coefficients. Gross changes ia fission reaction rates, as well as start-up and shutdown of the fission reactions, are effected by the control rods. In a typical PWR, ca 90 control rods are used. These, iaserted from the top of the core, contain strong neutron absorbers such as boron, cadmium, or hafnium, and are made up of a cadmium—iadium—silver alloy, clad ia stainless steel. The movement of the control rods is governed remotely by an operator ia the control room. Safety circuitry automatically iaserts the rods ia the event of an abnormal power or reactivity transient. 

The sample is introduced into the spectrometer, locked onto the deuter-ated solvent (here CDC13) and the homogeneity optimized by shimming as described by the instrument manufacturer (this can often be done automatically, particularly when a sample changer is used). 

The introduction of gradient shimming (that makes this procedure very easy to automate) together with the possibility of performing automatic tuning and matching (via the use of motors mounted on the probe body) has further improved the whole procedure. 

The availability of pulsed-field gradients makes it possible to automatically shim using NMR imaging techniques. In MRI we rely on the dominance of water in the human body to obtain... 

Reactor of NS 910 was frozen , all absorber rods being completely inserted. In such condition the alloy in shrouds of shim rods and automatic control rods was frozen . Cables were dismantled from all CPS actuating mechanisms. Operational time of the reactor was about 80% of its lifetime. 

Figure 3.50. Automatic deuterium gradient shimming. Spectrum (a) was acquired with all z-axis shims set to zero. After less than two minutes of gradient shimming of the z-z shims (3 iterations) spectrum (b) was obtained. The solvent was DMSO and one scan was acquired for each deuterium gradient echo collected via the probe lock coil. Automatic switching for deuterium observation was achieved with a home-built switching device.

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 withdrawn less than 7 in.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. 

After every scram be sure to turn switch S-2B (intermittent, neutral, high) to neutral.. Otherwise there may be nothing to prevent the shim rod holders, lowered automatically after rods are dropped, from picking up rods and starting (possibly even high speed) withdrawal. 

For smooth change of reactor level under servo control, keep the shim rods in step with the motor-operated rheostat. In particular, try to avoid letting the regulating rod get within 5 in. of full insertion, since at this point it automatically calls for reverse. 

Automatic - operating regime in which servo may be operative and shim rods may be affected by regulati.ng-rod limit switches. 

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