[en] This paper describes the results obtained by applying a computer assisted photoelastic technique developed by the senior author and his associates for estimating Mode 1 stress intensity factor (SIF) distributions for mathematically intractable three-dimensional problems to the reactor vessel nozzle corner crack problem. Two significantly different test programs were employed and results were compared with the literature. Frozen stress photoelastic experiments were conducted on two classes of nozzle corner cracks: (1) Researchers at the Delft University Laboratory for Nuclear Engineering have developed a nozzle-flat plate geometry which is loaded in remote uniaxial tension normal to the flaw. The transverse tension can then be included analytically. Their results indicate that such a model accurately predicts fatigue crack growth for the corresponding cracked nozzle in a pressure vessel for thin walled vessels. The test geometry identified as No. 4 in the Delft work was studied experimentally in the present work. (ii) Researchers at Oak Ridge National Laboratory developed a technique for predicting SIFs in cracked nozzles in thick walled pressure vessels from residual static strength tests on fatigue cracked plastic models of nozzle-cylinder interactions. The test geometry identified as the 'small thick walled vessel' in the Oak Ridge program was studied experimentally in the present work. (Auth.)