  By operating an antineutrino detector of simple design during several fuel
cycles, we have observed long term changes in antineutrino flux that result
from the isotopic evolution of a commercial Pressurized Water Reactor (PWR).
Measurements made with simple antineutrino detectors of this kind offer an
alternative means for verifying fissile inventories at reactors, as part of
International Atomic Energy Agency (IAEA) and other reactor safeguards regimes.
