METHOD FOR DISMOUNTING SPENT DEFECTIVE FUEL ASSEMBLIES Russian patent published in 2005 - IPC

FIELD: nuclear power engineering; handling radioactive wastes and spent nuclear fuel assemblies disposed in floating or coastal stores.

SUBSTANCE: proposed method used in particular for dismounting spent defective fuel assemblies disposed in store of floating technical depot includes removal of shielding plug from charging port of swivel slab combined with one of concentrically arranged rows of subchannels in tube plate holding fuel assemblies and detection of all defective fuel assemblies in this row. Upon removal of shielding plug swivel stab is rotated, charging port is aligned with head of box holding defective fuel assembly, and annular drilling is made in tube plate body through this port through depth exceeding weld penetration in tube plate, inner diameter of this drilling being slightly greater than outer diameter of bushing. After that box holding defective fuel assembly is separated from tube plate by blasting through its thickness value followed by its lifting from subchannel together with bushing over height of about 0.8 m from bottom edge of box bushing to top plane of swivel slab. Then auxiliary snap ring is fitted onto cylindrical surface of box, outer diameter of this ring being slightly greater than that of bushing, whereupon box is moved back downward and placed in same subchannel of tube plate. After that charging port of swivel slab is sequentially placed above each box holding defective fuel assembly in this row, and all above-described operations are resumed. Upon completion of all these operations all disrupted boxes are extracted one after the other together with bushings and auxiliary snap rings through charging port. Such method takes minimal time for extracting all defective fuel assemblies from floating technical deport store and ensures essential (by several times) reduction in gamma-ray dose absorbed by personnel and reduced escape of radionuclides into environment due to reduced time taken for auxiliary operations associated with specific process equipment installation on, alignment, and removal from working position.

EFFECT: reduced process time, enhanced safety for personnel.

2 cl, 8 dwg