Undervessel arrangement

In a nuclear reactor system including a pressure vessel and an undervessel support structured, a servicing arrangement located below said pressure vessel comprising;

• an undervessel servicing platform having at least two lateral extensions;
• at least two guide columns for receiving said lateral extensions of said servicing platform, said guide columns limiting the radial movement of said lateral extensions;
• a jackscrew in each of said guide columns, each penetrating an aperture in the lateral extension therein;
• a plurality of apertured plates fitted on each said jackscrew for engaging and supporting the lateral extension penetrated by the jackscrew including an upper plate formed with a raised portion surrounding the aperture therein and engaging a complementary depression in the underside of the extension, a lower plate formed with an internally threaded collar engaging the threads of said jackscrew and means for preventing rotation of said upper and lower plates with said jackscrew, the aperture in said upper plate being greater in diameter than the diameter of said jackscrew for allowing limited lateral movement between said upper and lower plates;
• means for synchronously rotating each of said jackscrews for raising and lowering said servicing platform;
• and a stabliizer mechanism for each jackscrew for restraining said jackscrew from bowing including a rod positioned parallel to said jackscrew and penetrating with sliding fit an aperture in said lateral extension;
• a stabilizer spacer secured to the lower end of said rod and having an aperture penetrated with sliding fit by said jackscrew, rollers mounted on said spacer engaging the guide column within which said jackscrew is located, and a head on the upper end of said rod for engaging said lateral extension when said servicing platform is raised a predetermined distance whereby said rod and said stabilizer spacer secured thereto are moved upward as said servicing platform is raised beyond said predetermined distance.