Transient and stability tests at Peach Bottom Atomic Power Station Unit 2 at end of Cycle 2

Turbine trip transient and low flow stability tests were performed at the Peach Bottom-2 BWR/4 nuclear power plant prior to shutdown for refueling at end of Cycle 2 in April 1977. The results of the turbine trip transient tests showed that the fundamental mode of the acoustical pressure oscillation generated in the main steam piping propagates with relatively little attenuation into the reactor core. The magnitude of the neutron flux transient taking place in the BWR core was found to be strongly affected by the initial rate of pressure rise caused by the pressure oscillation. The measured neutron flux transients showed a strong spatial variation along the axis of the reactor core. Very little radial variation in the neutron flux transient was observed. The low-flow stability tests demonstrated that the Peach Bottom-2 Cycle 2 core exhibited a high degree of stability at the limiting test condition above the rated power-flow control line. The measured reactor stability margins showed the expected sensitivity to core power changes at minimum reactor core flow. The tests showed that the small pressure perturbation stability testing offers a useful and practical method of measuring core stability margins. The actual core stability margin was determined from the measured closed-loop pressure to average neutron flux transfer function data based on maximum likelihood estimates of the parameters in a relatively simple transfer function model determined from nonlinear regression analysis. Both static and dynamic error estimates were taken into consideration in evaluating the test results