He takes up the role next month and will be based in Manchester.
Longfellow was formerly vice-president of operations, european fuels with Westinghouse Electric company, a £400m revenue business manufacturing fresh nuclear fuel for reactors across Europe.
Before that he was director of Thorp Reprocessing and MOX fuel manufacturing and deputy managing director of Sellafield.
He is a chartered electrical engineer and a fellow of the Institute of Measurement and Control.