Essentially all of the published information on frequency response testing in gas-cooled reactors comes from Britain. A great deal of excellent work has been done in Britain on testing procedures and interpretation of results as well as on actual tests.

Measurements were made on the Dragon high-temperature gas-cooled reactor at full power (200 MW). Pseudo-random binary reactivity perturba­tions were introduced using a standard control rod. The frequency range covered was approximately 0.01-0.6 rad/sec.

In the Dragon experiments, the results from the PRBS tests were also used to obtain the step response of the system. As described in Section 4.10, the cross-correlation function between input and output is approximately equal to the impulse response if the autocorrelation function of the input is approximately a delta function. Also, the step response is the integral of the impulse response. The step response for the Dragon reactor was obtained by integrating the input-output cross-correlation function obtained in a PRBS test.