Non-flux-trap racks

The re-racking of a pressurized water reactor (PWR) SFP includes installation of high-density storage racks and removal of the existing low-density storage racks. Two types of racks must be used in the PWR SFP flux-trap racks and non-flux-trap racks. The flux-trap racks are qualified for storage of fresh fuel and fuel which has not been fully irradiated in the reactor, whereas the non-flux-trap racks are qualified for storage of fully-irradiated fuel and therefore are used to store the majority of the fuel in the SFP. 

The non-flux-trap racks are composed of stainless steel boxes with a single fixed neutron absorber panel, attached by stainless steel sheathing centered on each side. The stainless steel boxes are arranged in an alternating pattern such that the connection of the box corners form storage cells between the stainless steel boxes. Neutron absorber panels are installed on one side between neighboring non-flux-trap racks. 

The PWR non-flux-trap style racks, as shown in Figure 13.3, are designed to accommodate tuel assemblies with a maximum initial enrichment ot 5.0 wt% which have accumulated a given minimum burnup or tuel ot initial enrichment and burnup combinations within the acceptable domain. A representative example ot the burnup versus enrichment curve tor a typical PWR non-flux-trap rack is provided in Figure 13.4. 

Additionally, accident and abnormal conditions are considered such as misplacement ot a tuel assembly outside the rack, misleading ot a tresh, unburned assembly into the center ot the non-flux trap racks, variation ot water temperature, drop ot an assembly onto the top ot the rack, and lateral rack movement during a seismic event. For accident conditions, soluble boron in the SFP may be credited to ensure that the reactivity does not exceed 0.95. 

Elevation view of a PWR non-flux-trap spent fuel storage rack. 

Typical buinup versus enrichment curve for a non-flux trap PWR storage rack. 

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