Underground nuclear power station reactor grotto containment dome mounting method

The invention discloses an underground nuclear power station reactor grotto containment dome mounting method, which comprises the following steps: A, respectively mounting a containment barrel, an annular crane rail beam and a crane girder in an underground nuclear reactor grotto; B, arranging a support bottom beam on the annular crane rail beam and the crane girder in the containment barrel; C, mounting upright posts on the top surfaces of the annular crane rail beam, the crane girder and the support bottom beam, and arranging upright post inclined supports between adjacent upright posts; D, arranging a ring beam at the tops of the upright posts; E, processing a containment dome on the ground according to design sizes in a fragmentation way, then sending into the underground nuclear reactor grotto in the fragmentation way, hoisting and aligning on the ring beam by an annular construction bridge machine, and performing on-site high-altitude layered welding assembling in the fragmentation way. The method solves the technical problem that a steel lining of the containment dome cannot be integrally hoisted in the underground nuclear reactor grotto due to the limitation of the underground grotto space, and can be widely applied to the technical field of nuclear power.