1.1. The Need for Frequency Response Testing

Frequency response testing should play an important role in evaluating the performance and safety of modern power reactors. The main motiva­tions for testing are:

1. To assess the system stability margin and to detect trends in the stability margin caused by changes in operating conditions.

2. To check mathematical models and coefficients used in theoretical studies.

3. To provide information needed to optimize controller parameters.

4. To provide information that can be used to tune theoretical models so that they can be used to predict the plant response with assured confidence.

A number of frequency response measurements have been made on research reactors and some of the early central station power reactors. Most of these tests have used the oscillator method, which employs a sinusoidal reactivity input. This procedure requires special (and expensive) hardware, modification of the system design to accommodate this hardware, and interference with normal system operation during the lengthy tests. In most of the new commercial power reactors, economic and operational considera­tions have dictated that the expense and the inconvenience are too great to justify oscillator test programs. The alternatives are to forfeit the information or to develop new procedures without the disadvantages of the

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oscillator method. These new methods have been developed and are the subject of this book.

The emphasis in this book is on optimum testing procedures for measure­ments in power reactors. The criteria for suitability of tests in power reactors are:

1. The tests should make maximum use of standard system hardware and instrumentation so as to minimize costs.

2. The tests must be virtually incapable of causing a scram or a component malfunction.

3. The test must cause insignificant interference with normal power genera­tion. Dynamic testing must be done while the system continues to satisfy load demands.

4. The duration of the test must be as short as possible. The presence of test personnel in the control room, the use of system equipment (such as the on-line computer), the possible suspension of other tests, and the possible departure from normal control policies can be tolerated only briefly.

5. The results must be suitable for quick and easy interpretation. The tests should be planned and set up by specialists, but the plant engineer should be able to understand the significance of the results and their implica­tions in connection with plant operation.