دانلود رایگان مقاله آزمون کرنش و تنش شدت محفظه تنظیم فشار نیروگاه هسته ای CPR 1000

abstract

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.

Conclusions

In this paper, actual strain of a CPR1000 unit’s pressurizer during the pre-delivery hydrostatic test is acquired. The strain and stress data acquired can be used as the basic data for the pressurizer ageing condition assessment or structural integrity assessment during its long-term operation. The conclusions of this study are summarized as below: (1) The longitudinal and hoop strains of base metal in the cylinder are very uniform, and the stress values match well with the thick-walled theoretical values. However, the strains of girth and longitudinal welds vary with location. The strains decrease from lower head to upper head, and have the same trend with the circumference deformation variation. (2) The longitudinal and hoop stresses near the centerline of cylinder middle longitudinal weld are much lower than the stresses at other locations. This indicates the possibility of compressive residual stresses at both longitudinal and circumferential directions. (3) The principal stresses of symmetrical locations in upper head welds vary a lot. There is possibility that the weld thickness is not uniform along the weld circumference. Also, residual stresses may have contribution to this phenomenon. The principal stresses of symmetrical locations in the surge line nozzle weld agree well. It indicates a good geometric uniformity of this weld. (4) The maximum general primary membrane stress is at the spray nozzle weld in upper head. The stress value is lower than the allowable value. So the structural integrity is maintained at the highest hydrostatic test pressure. The fatigue usage factor is far less than one, which indicates that a single hydrostatic test cycle has little effect on the total pressurizer fatigue life.