Process and device for adapting new upper internal equipment to the vessel of a pressurized water nuclear reactor

Process for adapting new upper internal equipment to the vessel of a pressurized water nuclear reactor containing irradiated lower internal equipment (8) which comprises a horizontal lower plate (4), a core support shell (6) as well as the core screening (7), while the upper internal equipment (13) comprises an upper core plate (11) and a lower plate (10) which forms an upper core plate, which are held together by vertical spacer columns (12), slots (33, 28) being provided on the peripheral part of the upper plate (11) of the upper internal equipment and on the peripheral parts of the upper core plate (10), in angularly offset positions, alignment pins (20) being orovided at the upper part of the lower internal equipment (8) and centering pins (25) being fixed to the core support shell (6) which are intended to cooperate with the slots (33) in the upper plate (11) of the upper internal equipment and with the slots (28) in the upper core plate (10), respectively, for installing the upper internal equipment (3) in the vessel:

• with the vessel (1) opened and filled with water, and the core assemblies having been removed, the process comprising:
• means for measuring alignment (50) and means for measuring clearance (56, 58, 59) are mounted on the new upper internal equipment (13), together with a jig (54) corresponding to the peripheral assemblies of the core under the upper core plate (10) and skidblocks (53) under the upper plate (11) of the upper internal equipment,
• thruster devices (52) are mounted in the region of the upper part of the lower internal equipment (8) on the support flange for the vessel head and means (55) for receiving the alignment measuring devices (50) are mounted on the lower core plate (4),
• the upper internal equioment (13) is introduced into the vessel (1) so as to rest on the upper part of the lower internal equipment (8), through the intermediacy of the skid blocks (53),
• measurements of the vertical alignment of the upper internal equipment (13) and of the lower internal equipment (8) are carried out,
• the upper internal equipment (13) is moved on the lower internal equipment (8) by the use of the thruster devices (52) to correct their respective alignment, as a function of the results of the alignment measurements,
• the clearances existing between the edge of the upper core plate (10) and the opposing part of the core support shell (6) are measured at four points spaced at equal angular intervals on the periphery of the plate (10),
• if appropriate, the upper internal equipment (13) is moved again to correct the errors in the measured clearances, while a satisfactory alignment of the internal equipment (13, 8) is maintained,
• the clearances existing between, on the one hand, the alignment (20) and centering (25) pins and, on the other hand the corresponding slots (33, 28) are measured,
• the upper internal equipment (13) is withdrawn from the vessel (1),
• adapters (31, 31b, 36) machined to sizes which are determined by the measurements of clearances around the pins (21, 25) are fixed to the upper internal equipment (13), inside the slots (28, 33),
• the upper internal equipment (13) fitted with the adapters (31a, 31b, 36) and only the alignment-measuring devices (50) is reintroduced into the vessel (1),
• and the alignment of the upper internal equipment (13) relative to the lower internal equipment (8) is checked.