Strain test and stress intensity assessment of a CPR1000 Nuclear Power Plant pressurizer during pre-delivery hydrostatic test

• Strain test is implemented during the hydrostatic test of a CPR1000 NPP pressurizer.
• Stress distribution in welds differs greatly according to the location, while uniform in the cylinder surface base metal.
• The stress values in cylinder surface base metal match well with the thick-walled theoretical values.
• Residual stresses and thickness non- uniformity exist at cylindrical welds and upper head welds.Hydrostatic test has little effect on the structural integrity and the total fatigue life.

Strain gages are applied to get the strain and stress of a CPR1000 Nuclear Power Plant (NPP) pressurizer during the pre-delivery hydrostatic test. The measured strain curves are discussed to find the deformation features of the cylinder. The stresses of cylindrical base metal, longitudinal welds and girth welds are calculated and compared with the theoretical values. The stresses in girth welds and upper head nozzle welds show non-uniformity at these areas. The possible reasons are discussed for this phenomenon. The stress intensity is calculated and evaluated according to the allowable limit. The fatigue usage factor is evaluated by considering the effect of internal pressure rise-and-fall cycle to pressurizer’s total fatigue life. The evaluated results show that the hydrostatic test has little effect on the integrity or fatigue life of the pressurizer. This test provides the basic deformation data of the pressurizer, which plays an important role in the ageing assessment and management during operation.