The objective of this paper is to assess the lower head of nuclear reactor under the in-vessel vapor explosion load. Firstly, the calculated explosion pressure loads are applied on the lower head inner wall for 2-D model and 3-D model, respectively, to calculate the equivalent strain and membrane stress intensity secondly, both calculated explosion pressure loads and thermal loads are imposed on the 2-D model of the lower head to calculate the equivalent stain, membrane stress intensity, and total mechanical and thermal strain. Then, the calculated strain and stress results are compared with the reference standard values of failure criteria to determine the failure probability of the lower head. All the stain and stress calculations are performed by ANSYS 11.0 Program.
The structure analysis results show that the lower head failure does not exist under the pressure value up to 118.5 MPa in vessel explosion.
The thermo-mechanical results show that the lower head failure under the pressure value up to 118.5 MPa and temperature value up to 700℃ in-vessel explosion also does
not exist. During this analysis process, the nucleate boiling crisis will not occur when the
outside wall of lower head is cooled by the saturation water at 100℃ and 0.1 MPa.