Thermo-mechanical Transient Analysis of Reactor Pressure Vessel

To demonstrate the structural integrity of a reactor pressure vessel, a detailed stress analysis is required to be carried out accounting for the transients during various operating conditions of the reactor. For thick-wall reactor pressure vessels, the temperature gradient across the vessel thickness is time-dependent during the operating transients and adds to the complexities in estimating the stress field across the vessel wall thickness. The design of such thick vessels needs to be supplemented with a detailed thermal stress analysis taking in to account the time-dependent variations. The present paper discusses the detailed thermo-mechanical stress analysis carried out for reactor pressure vessel of Tarapur Atomic Power Station-1 and 2. A complete evaluation of temperature and resulting stress distribution across the vessel wall thickness, in a non-steady state is obtained using a numerical model. In this model, the temperature of the inside surface of the vessel is considered to change according to various transients, viz., reactor startup, shutdown and emergency condition. The analysis results indicate that the most stressed location in RPV wall is clad-vessel interface and the governing transient is emergency shutdown condition. The results have been used for structural integrity assessment of reactor pressure vessel. Studies have also been carried out for re-circulation nozzle for its structural integrity assessment to preclude the possibilities of crack initiation or propagation.