NUCLEAR REACTOR PRESSURE VESSEL

PURPOSE:To prevent a hazardous exposure to radioactivity, by providing a cylindrical housing skirt of a control rod drive mechanism enveloping a longitudinal part of the housing skirt of the control rod drive mechanism protruding downwardly from a lower end plate of a nuclear reactor pressure vessel. CONSTITUTION:A nuclear pressure vessel 1 contains a core shroud 8 enveloping a core 7 and a coolant circulating inside the pressure vessel 1. And a number of housing of control rod drive mechanisms 4 housing control rod drive mechanisms for driving control rods which controls an output of a reactor 7, penetrate through a lower end plate 2 fixed to a lower part of the pressure vessel and composing the lower part of the pressure vessel itself, and moreover the housing of the control drive mechanism 4 is fixed to the lower end plate 2 aligned with a core shroud 8 with a shop fabrication having enough working space and with well-equipped machine tools. Following this procedure, a housing support 5 of control rod drive mechanism can be assembled into the pressure vessel 1 in the shop and consequently a hazardous radioactivity exposure at cutting off the housing of the control drive mechanism is prevented.