The modelling of reactors based on neutral-beam-driven plasmas confined in open-ended magnetic wells (standard mirrors) is described. Two reactors have been treated in detail: a fusion reactor producing 500 MW of electrical power and one whose main output is 2000 kg per year of fissile material. Resultant parameters for the first (fusion) reactor are: Einj = 125 keV, β⊥ = 0.8, ⟨nτ⟩ = 4 × 1013 cm−3 · s and Q = 1.1. Corresponding values for the second (hybrid) reactor are: Einj = 94 (D0) and 141 (T0) keV, β⊥ = 0.7, ⟨nτ⟩ = 2 × 1013 cm−3 · s and Q = 0.67. The low Q-values of these reactors make them unattractive as electricity producers, but of potential value as fissile-fuel producers.