Historically the rod-oscillator measurement of the zero-power transfer function is one of the oldest reactor — dynamics measurements,4 dating back to CP-2 Since then it has been repeated many times on many reactors with the techniques detailed below

Basically, a sinusoidal reactivity excitation provided by a rotating or reciprocating control rod causes a power oscillation that is detected by ion chambers. The purpose of these measurements may be any of the following

l. To determine j3/1 for a particular reactor by fitting the measurement to a formula in Table 6.4.

2. To verify experimental techniques on a known transfer function.

3 To compare reactivity effects of small samples by the amplitude of the resulting power oscillation.

A considerable number of methods in addition to the rod oscillator have proved useful in obtaining dynamics information, і e., in determining quantities closely related to the reactor transfer function. These methods are listed and classified in Table 6.5. Methods having no reactor excitation by external equipment depend on the random fluctuations or noise in the neutron population, as detected by counters or ion chambers, to provide information about

reactor characteristics The following incentives for applying such methods differ slightly from those for the rod oscillator

1. To determine specific reactor parameters, such as (3// at critical, the subcntical reactivity, or the absolute reactor power.

2 To verify experimental techniques on a known system

3 To investigate spatial neutron effects

Experiments on the dynamic behavior of zero-power reactors have been numerous and also somewhat repetitious owing to similarities among the reactors and kinds of equipment used. The particular reactors studied along with the classes of information obtained are given in Table 6.6. It will suffice here to point out that the quantities being measured are the constant parameters appearing in the neutron kinetics equations and the transfer function. (The numerous cases in which samples have been oscillated to make reactivity measurements are omitted since the emphasis here is on transfer functions.)

Section 6-3, Methods of Measurement, summarizes the features of the various methods and how the results in Table 6.6 are obtained

Although neutron detectors have been used in virtually all the zero-power dynamics studies to date, there has been some theoretical732 and experimental2 3,69a work in­volving gamma detectors. Cerenkov detectors and liquid scintillators have been found suitable for monitoring the fluctuations of prompt gammas from fission. The emission of these gammas, like the neutrons, exhibits statistical fluctuations that depend on the reactor’s zero-power transfer function. Since gammas travel farther than neu­trons in a reactor, the prompt gammas offer a means of using peripheral detectors to monitor deep into the core of a large reactor In one novel application693 two widely separated gamma detectors were pointed in collimated fashion at various fuel elements, and relative local power values were obtained by cross correlation.