Testing of the TWIGL code with a reactivity transient in a large graphite-moderated reactor

As part of the effort to improve multidimensional reactivity transient analysis capability for a large graphite-moderated reactor, the TWIGL code was adapted to the Hanford N Reactor and successfully tested with some recent time- and space-dependent reactor data. The Hanford N Reactor is a large graphite-moderated light-water-cooled reactor operated by UNC Nuclear Industries for the US Dept. of Energy. The reactor is an ∼ 10.1- x 10.2- x 12.0-m graphite cuboid penetrated by 1003 horizontal Zircaloy pressure tubes, 84 horizontal control rod penetrations, 107 vertical ball backup safety system channels, 640 graphite cooling tubes parallel to the control rods, and numerous steam vent passages