[′lin·ē·ər ik′sel·ə‚rād·ər rē′jen·ə‚rād·ər rē′ak·tər] (nucleonics) A device in which neutrons, generated by stopping a high-energy proton beam from a linear accelerator, irradiate nuclear fuel to bring it to a level of reactivity where it can be used in place in a conventional power reactor. Abbreviated LARR.