The Application of an On-Line Digital Computer to the Control System of the High Flux Isotope Reactor (HFIR)

A process control computer was combined with the analog control system of the HFIR to perform the function of limiting the shim-rod reactivity additions as well as direct shim-rod symmetry control. Automatic shim control is supervised by a computer program which uses the measured reactor power level to continuously compute the core reactivity requirements during the 23-day fuel cycle. The high power density (4 Mw/liter) in the HFIR requires that flux tilting be controlled to minimize the possibility of hot-spot formation. This is accomplished by limiting the difference in shim-rod positions for reactor operation above 10 Mw. The rod symmetry is controlled by a computer program that actuates rod control relays in the analog system in response to the asymmetry determined from shim-rod position sensors. The rod control algorithm was tested on-line at 10 Mw, and routine operation of the on-line programs is planned after the overall reliability of the system has been measured.