Analysis of Godiva-IV delayed-critical and static super-prompt-critical conditions Page: 3 of 13
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Mosteller and Goda
experiments, the excursion was terminated by thermal expansion of the core. Thermal expansion
also caused the bottom central part of the core known as the safety block to disengage from the
electromagnet that held it in place and drop out of the core, ensuring that the assembly remained
subcritical thereafter.
The core of the Godiva-IV assembly contained six stacked rings, an inner subassembly plate
with two components, a central spindle, an alignment pin, a shim ring, two control rods, a burst
rod, the safety block, and a base for the safety block. Two thermocouples to measure the
temperature rise during the excursion also were present. The stacked rings enclosed the inner
subassembly plate, the safety block, and the safety-block base. Hollow cylinders within the
rings permitted passage of the control and safety rods, which were in symmetric locations, 120
apart. The rings, the inner subassembly plate, the control rods, the burst rod, and the safety
block all were made from an alloy of highly enriched uranium (HEU) and molybdenum. The
spindle, the alignment pins, the shim ring, and the base for the safety block were made from
various types of steel.
Since the control and burst rods contained mostly HEU, they increased reactivity as they were
inserted and reduced reactivity as they were withdrawn. When the assembly was not in
operation, the safety block and its base were withdrawn to a position such that the top of the
safety block was only slightly higher than the bottom of the mounting plate of the assembly
machine, and the control and burst rods were fully withdrawn. However, even when the control
and burst rods were fully withdrawn, the tops of those rods still were inside the bottom fuel ring.
Restraints for the core included three clamps, three clamp supports, a circular belly band, a
subassembly cover plate, a loading ring, three support pads, and several nuts and bolts. The
restraints were made from various types of steel. The loading ring fitted into the top of the top
fuel ring, and the support pads fitted into the bottom of the bottom fuel ring. The subassembly
cover plate sat above the inner subassembly plate, inside the loading ring and enclosing a section
of the spindle. Each clamp had top and bottom prongs that fitted onto the top of the loading ring
and the bottom of one of the support pads, respectively. The central portion of each clamp fitted
into notches in the outer edges of the fuel rings. Each of the three clamps fitted into a slot in its
clamp support and was bolted to it. The tops of the clamp supports were held in place by the
belly band, and the bottoms of the clamp supports were bolted to the mounting plate. Figures 1
and 2 provide top and side views, respectively, of the Godiva-IV core and its restraints, and a
schematic of the core and its restraints is presented in Figure 3. Restraints and core components
that were made from the same type of steel appear in the same color in Figure 3.
The core and its restraints were enclosed inside a thin cylindrical core cover that was made of
aluminum. Similarly, a contamination shield made of steel and plastic was attached to the
bottom of the mounting plate, enclosing the safety block and the bottoms of the control rods and
the burst rod when they were withdrawn.
The four delayed-critical configurations and the static super-prompt-critical configuration
discussed herein differed only in the positions of the two control rods and the burst rod. A
summary of the positions of those rods is presented in Table I. The full stroke of the burst rod
2009 International Conference on Mathematics, Computational 2/12
Methods & Reactor Physics (M&C 2009), Saratoga Springs, NY, 2009
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Mosteller, Russell D & Goda, Joetta M. Analysis of Godiva-IV delayed-critical and static super-prompt-critical conditions, article, January 1, 2009; [New Mexico]. (https://digital.library.unt.edu/ark:/67531/metadc929028/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.