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Calculation of Stress Reduction for Pressure Vessel Lids in Nuclear Power Plants

This example explores the stress analysis of bolted pressure vessel lids in nuclear power plants. Given the extreme stress on the bolts subjected to high pressure from steam and pressurized water, it's essential to determine the stress criteria needed to extend the lifespan of these components. The calculations reveal that a reduction in stress to 683.2 MPa is needed to achieve 104 cycles of life, considering fatigue factors. Understanding the material properties and fatigue life is crucial for safe reactor operations and maintenance scheduling.

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Calculation of Stress Reduction for Pressure Vessel Lids in Nuclear Power Plants

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  1. ME 3180 - Mechanical Engineering Design Example #1

  2. Example #1 • Given: • The pressure vessel lids of nuclear power plants are bolted down to seal the high pressure exerted by the water vapor ( in a boiler reactor) or the pressurized water ( in a pressurized water reactor). The bolts are so heavily stressed that they are replaced after the reactors are opened 25 times. A 20% decrease in stress would give 104 cycles of life. The ultimate strength is 1080MPa. How low does the stress needs to be to give a life of 104 cycles?

  3. Example #1 • Solution: • Type of material was not given; therefore we can’t calculate Marian factors (fatigue modifying factors). • For axial load: S’e = 0.45Sut and Sf at 103 cycles = 0.75Sut • Sf = aNb (eq 7-5) : log(Sf) =log(a) + b.log(N) • Sf = (1350)(104)-0.07395 (eq 7-5) • Sf = 683.2 MPa • The stress need to be decreased to 683.2 MPa to give 104 cycles. eq 7-6

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