There are two parts to addressing a vessle nozzle: (1) nozzle stiffnesses for the stress (flexilbility) analysis, and (2) local stress evaluation after the stress analysis.

In CAESAR II there are three methods available for determining the nozzle stiffnesses on a shell (based on the type of nozzle): (1) API-650 for nozzles on API tanks, (2) WRC-297 and (3) PD-5500 for nozzles on pressure vessels. At this point, all you get here are the stiffnesses used in the stress analysis.

Following the stress analysis you must take the resulting loads on the nozzle and perform an additional evaluation to determine if these loads exceed the permitted loads at the nozzle/vessel interface. For this, you can use (depending on the nozzle type): API-650, PD-5500, WRC-107, or WRC-297. Note that WRC-107 does not provide stiffnesses. This is why in the CAESAR II documentation WRC-297 is used at the input stage, and WRC-107 was used (in this specific example) for the subsequent local evaluation.