The present invention relates to a fuel rod for a nuclear plant and a plenum spring arranged to be provided in a fuel rod. The fuel rod (1) comprises a cladding tube (2) sealed at its ends by end plugs (3, 4), a plurality of fuel pellets (5) stacked on each other inside the cladding tube (2) such that they form a column of pellets and said plenum spring (6) arranged to hold with a spring force the column of pellets against the lower second end of the cladding tube (2) during operation. The plenum spring (6) comprises a first length variable part (8) which abuts the uppermost located fuel pellet (5) in the column of pellets with an end portion (9), a second part (10) which allows engagement of the plenum spring (6) against an inner surface of the cladding tube (2) by a radially outwardly directed pressure and a third part (11) which allows releasing of the second part (10) of the plenum spring (6) in the cladding tube (2) during operation of the nuclear plant.
A method for installing a locking retainer in a tube to maintain internal components within the tube under compression comprising the steps of: a) providing an elongated retainer spring having large and small diameter sections with the large diameter section of a size for an interference fit with the interior diameter of the tube and the smaller diameter section of a size having a clearance with the interior diameter of the tube; b) inserting a smaller diameter section of an elongated tool into the larger diameter section of the elongated retainer spring; c) engaging a transition between the smaller and larger diameter sections of the tool against a transition between the larger and smaller diameter sections of the elongated retainer spring; d) inserting the combined tool and retainer spring into an open end of the tube containing internal components with an end of the smaller diameter section of the retainer spring entering the tube first; e) advancing the combined tool and retainer spring within the tube to compress the smaller diameter spring against an adjacent internal component until an end of the tool engages the adjacent internal component enabling the spring to apply a selected axial preload on the internal components in the tube; and f) withdrawing the tool from the retainer spring.
