In depth studies of cold neutron sources have been carried out at the Petersburg Nuclear Physics Institute since the early 1970's. The 18 MW WWR-M reactor has been developed to allow a cold source to produce at experimental installation a polarized cold neutron flux of 6x10(8)n/cm(2)s and an ultracold neutron flux of 6x10(3) n/cm(2)s. Experience gained with the WWR-M and other reactors has resulted in a safety strategy. That includes the hazards of operating hydrogen and also provided insight into the reactivity effects of a cold source on the reactor core.