The present disclosure relates to a process for the preparation of polyethylene by polymerizing in a slurry ethylene and optionally one or more C3 to C10 alpha-olefins. In some embodiments, the polymerization is carried out in a cylindrical polymerization reactor equipped with an agitator for mixing the contents of the reactor and inducing a flow of the slurry, the ethylene is fed into the reactor by an ethylene injection system comprising one or more injection nozzles which project through the bottom reactor head or through the reactor wall and extend from 0.02-0.5 times the inner diameter D into the reactor, and the ethylene exits the injection nozzle with an exit velocity from 10-200 m/s.