Patent Number: 056195460
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The NSSS of FIG. 1 includes a pressurized water nuclear reactor 1 connected by piping to steam generators 2 and 3 and pressurizer 4. The piping includes cold legs comprising: pumps 5, discharge pipes 6 from the pumps 5 to the reactor 1 and suction pipes 7 from the steam generators 2 and 3 to the pumps 5. The hot legs 8 which are shown in FIG. 1 behind discharge pipes 6, and are of slightly larger diameter than the cold leg pipes 6 and 7, run from the reactor 1 to the steam generators 2 and 3. The RTD nozzles are shown on both hot legs 8 and cold leg pipes 6 and 7 at illustrative positions in FIG. 1. The RTD nozzle 10 is hollow and contains a thermocouple type of resistance temperature detector, not shown, within its central passageway. The end of the thermocouple will, typically, extend into the interior pipe opening of a carbon steel discharge pipe 6, or other NSSS pipe, from the nozzle 10, to sense the temperature of reactor coolant fluid flowing therethrough. Originally, the nozzle 10 to pipe 6 joint is a weld. The deterioration of this weld is often the cause when there is leakage at the joint. To provide a fluid tight seal for nuclear reactor coolant system hot and cold leg RTD nozzles 10, the preferred structure of the invention is a mechanical clamp and blowout retainer as described in detail, below. The fluid tight mechanical clamp seal is generally designated by the numeral 20. It has, for sealing purposes, at the joinder of the transversely extending nozzle 10 and pipe 6, a split annular compressible graphite or similar composition seal ring or packing 22 (typically one split annular piece) commonly known in the nuclear industry as "Grafoil." The mechanical clamp seal 20 has an annular back-up split ring 24 made of plural (two or more) sections surrounding and confining the periphery of the split annular seal ring. An annular similarly split load sleeve 26 made up of plural (two or more) sections is telescopically received in the split seal ring 24 to compress axially the graphite seal ring 22 against the pipe 6, thereby also to expand radially the seal ring against the nozzle 10 and the seal confining split ring 24. A reactor plate 28 is provided which has a first surface 30 shaped to engage the pipe 6. A second and annular surface 32 of the reaction plate 28 peripherally engages and radially confines the split ring 24 and a third surface 34 of the reaction plate 28, which could be termed a flange surface, confines axially the split ring 24 against the pipe 6. Reaction plate 28 is bolted to pipe 6 by means of bolts 36 passing therethrough and threadedly secured in blind threaded holes 38 in pipe 6. The third surface or flange 34 preferable has an opening sufficiently great to allow its installation by passing down over the nozzle 10 without disassembly of the RTD or the nozzle 10 to pipe 6 joint. A load ring 40 is provided for driving the split load sleeve 26. The load ring 40 has a central opening and surround, and has a surface 42 which axially abuts against, the split load sleeve 26. Bolts 44 are threadedly connected to blind threaded holes 46 in the reaction plate 28 through holes 48 in the load ring 40 such that the ring 40 provides an axial driving and compressing force through its surface 42 axially abutting against load sleeve 26 to compress the annular seal ring 22 and provide an effective seal at the pipe 6 and nozzle 10 joint. The load ring central opening has an internally threaded portion 50 and receives a split blowout retainer 52 made up of plural (two or more) externally threaded sections secured therein. The central opening of the retainer is surrounded at its outer end by a peripheral inwardly directed flange 54 for engaging a radially directed surface 56 provided on the nozzle 10 to prevent the nozzle's ejection from the pipe in the event of a weld failure at the nozzle pipe joint. Thus is provided a fluid tight mechanical clamp seal 20 with a blowout retainer 52 according to the objects and preferred embodiments of the invention.