The results of neutronic stability tests performed on February 9, 1985, at the Browns Ferry Nuclear Power Plant Unit 1 under single-loop operation (SLO) conditions are documented. The main conclusions of the tests are as follows:

  1. The observed increase in neutron noise during SLO is solely due to an increase in flow noise.
  2. The Browns Ferry-1 reactor has been found to be stable in all modes of operation attained during the current tests. The most unstable test point corresponded to minimum recirculation pump speed in SLO. This operating condition has the minimum flow and maximum power-to-flow ratio. At this operating point, the estimated decay ratio of the neutron flux following an impulse perturbation of reactivity was 0.53.
  3. The decay ratio decreased as the flow was increased during SLO. This observation implies that corewide reactor stability follows the same trends in single-loop as it does in two-loop operation.
  4. Finally, no local instabilities were found in the data taken from local power range monitors. Decay ratios estimated from the local power range monitors were not significantly different from those estimated from the average power range monitors.