Automatic rod insertion

It must be emphasized that the fast scram is in a class by itself, being the ultimate safety protecting the reactor. It is always operative and can never be vetoed by the operator. It is fast enough so that it will protect the reactor, by neutron level signal alone, against a 1/30-sec period, which is a reasonable estimate of the fastest period into which the reactor could be thrown in a start-up accident. In addition to level signals, the fast scram is at all times responsive to period signals. 

Circumstances calling for the various automatic insertions are listed in Table 5.5.A. This tabulation is to be considered somewhat tentative, particularly in regard to numerical values of limits. The last item, manual, refers to the operator. Setback and reverse, caused manually or otherwise, continue only so long as the causative condition endures. When the manual-automatic switch is on manual (servos inoperative), setback is of course 

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