The reactor instrumentation and control system design reflects the emphasis placed on continuity of and safety of operations. Three independent safety channels are arranged in a coincidence system that requires agreement of two of the three for safety shutdowns. This feature is complemented by an extensive "on-line" testing system that permits the safety function of any one channel to be tested at any time during operation. Additionally, three independent automatic control channels are arrayed so that failure of a single channel will not significantly disturb operation. All of these factors contribute to the continuity of operation of the HFIR.