Spiral reload

A Spiral load is a method of putting fuel back in the reactor vessel during a refuel outage without all control rods being inserted.

When fuel is loaded into the core with multiple control rods withdrawn, special spiral reload sequences are used to ensure that reactivity additions are minimized. Spiral reloading encompasses reloading a cell (four fuel locations immediately adjacent to a control rod) on the edge of a continuous fueled region (the cell can be loaded in any sequence). Otherwise, all control rods must be fully inserted before loading fuel. For an unloaded core the spiral reload may commence at either the core center around a "dunking type detector" or, around one of the source range monitors. Placement of the "dunking type detector" in the core cell does not violate the intent of the spiral reload pattern. Fuel assemblies may be loaded into this location when the "dunking type detector" is removed.

There are normally 4 SRMs, one in each quadrant.

Why is this needed

In a BWR control rods can not be inserted without the fuel bundles to support it because they are libel to fall over. Since not all control rods are not fully inserted the spiral pattern was developed to build the core.