Calculations have been made to investigate the dependence of the primary neutron emission rate (the neutron source strength) of spent boiling water reactor (BWR) fuel assemblies on the irradiation parameters: initial 235U enrichment, void fraction, power density, and operation history. A BWR lattice cell calculation code, which was verified by experiments, has been used to calculate the buildup of transuranium isotopes. The neutron emission rate was split into three components: 242Cm, 244Cm, and other nuclides. The effects of the irradiation parameters have been studied for each of the three components. The energy spectra of the primary neutrons emitted by the irradiated fuel have been calculated parametrically. The calculations have elucidated the neutron emission characteristics of the spent BWR fuel assemblies and provided the basic information to be used for:1. the neutron-shielding design for spent-fuel storage facilities and transportation casks2. the feasibility study of the startup of a BWR without radioisotope neutron source3. the application of passive neutron method to the nondestructive determination of burnup and plutonium contents in spent BWR fuels.