Improvements in or relating to fuelling machine input drives

Abstract

This invention provides an improved method to modify the input drives of a PHWR fueling machine to ensure their operability so to minimize the potential of a fueling machine becoming stuck on a nuclear reactor fuel channel. During the life cycle of a PHWR fueling machine it is possible for the fueling machine input drives bearings to become damaged or seized due to particulate, magnetite, and CRUD (chalk river unidentified deposit) build up on the bearings. These deposits can cause the fueling machine to become stuck on a reactor fuel channel necessitating a reactor shut down to remove the fueling machine. A modification to the input drive assemblies to allow for the installation of bearing holders, sleeve bearings, mechanical fuse and a modified labyrinth seal holder to allow for the ability to recover the fueling machine from the nuclear reactor fuel channel in the event of seized bearings.

Description

Improvements in or relating to fueling machine input drives of fueling machines developed and built by Canadian General Electric Company Limited, patent CA 1015470 and fueling machines developed from the original design. This invention provides an improved method to modify Fueling Machine (FM) input drives of a Pressurized Heavy Water Reactors (PHWR) to ensure their operability so to minimize the potential of the FM becoming stuck on a fuel channel. During the life cycle of the PHWR it is possible for the FM input drive bearings to become damaged or seized due to particulate, magnetite, and CRUD build up on the bearings. These deposits can cause the FM to become stuck on the fuel channel necessitating a PHWR shut down to remove the FM from the fuel channel. A modification to the FM input drive assemblies comprising of; the installation of bearing holders, sleeve bearings, mechanical fuse and a modified labyrinth seal holder will provide the opportunity to recover the FM from the fuel channel in the event of seized bearings and thus avoiding a PHWR shutdown. TECHNICAL FIELD OF THE INVENTION This invention is for the input drives of fueling machine developed by General Electric Canada Limited, patent CA 105470 for use with a PHWR, pressurized heavy water reactors and reactors developed from existing CANDU reactors. Background of the Invention: In the PHWR style reactors, the fueling machines are subject to operations that can cause the possibility of particulate, magnetite, and CRUD to enter the fueling machine causing a reduction in internal clearances and an increase of friction between the internal parts of the fueling machine input drive bearings. This can cause damage to the fueling input drives and interfere with on power fueling operations. MODIFICATION A method by installing a modification for an input drive housing, that includes machining to fit bearing holders and sleeve bearings, holes drilled and tapped for installation of mechanical fuses, a modified labyrinth seal holder, that will allow recovery of a fueling machine, so that seized input drive bearings can be bypassed, by providing a higher input torque that will shear a mechanical fuse and allow rotation of a roller bearing holder within an outer bearing sleeve to obtain shaft rotation, yet still allows for limited operation of the input drives, utilized as part of operating a Pressurized Heavy Water Reactor (PHWR). OPERATION To recover the fueling machine from the fuel channel if the bearings become seized once standard operating procedures are declared ineffective of providing shaft rotation. Upon approval, a non- standard operating procedure is executed to provide a higher input torque that will shear a mechanical fuse and allow for the bearing holders to rotate inside of the sleeve bearing. This would then allow the shaft to rotate to allow for the recovery of the fueling machine from the fuel channel. Once the recovery has been completed and the fueling machine is back in its maintenance area. The affected input drive would have to be removed and repaired with new bearings and new mechanical fuses. BRIEF DESCRIPTION OF THE DRAWINGS: In PHWR style reactors the fueling machine has input drives that provide motion to the fueling machine charge tube and ram assemblies. The input drives contain bearings that support the required shaft and gear movements. The input drive housing schematic (Fig 1) identify items 1 to 9. This modification requires installation of sleeve bearings (item 2 and item 5) and the roller bearing holders (item 6 and item 8). The sleeve bearings will be held in a radial position by a mechanical fuse (item 4 and item 7) during normal operation. A larger labyrinth seal holder (item 1) will be required to accommodate this modification. The input drive shaft (item 9) and seal assembly (item 3) are shown for reference. These modifications will keep the input drive poised for recovery from a roller bearing failure event. The onset of roller bearing failure requires increased torque values to rotate the input drive shaft. Torque values are incrementally increased within a standard operating envelope. If unable to recover operation of the input drive, based on suspected bearing failure, a nonstandard higher torque value may be applied. This increase of torque will activate the calibrated mechanical fuse allowing radial rotation of the bearing holder within the sleeve allowing recovery of input drive and exiting the roller bearing failure event returning to standard operating envelope. 1. Figure 2 shows the cross-section locations. DETAILED DESCRIPTION: 2. Figure 1: is a schematic of the fueling machine input drive showing all of the components of the input drive and components required to modify the input drive. item 1; enlarged labyrinth seal holder, item 2; sleeve bearing item 3; seal assembly; item 4; mechanical fuse; item 5; sleeve bearing; item 6; roller bearing holder; item 7; mechanical fuse; item 8; roller bearing holder; item 9; input drive shaft; 3. The embodiment, figure 1 shows all of the individual parts of the input drive assembly. 4. The embodiment, Figure 2 shows the cross-section locations. 5. The embodiment, Figure 3: shows Cross section AA, at the enlarged labyrinth seal holder. 6. The embodiment, Figure 4: shows Cross section BB, at the outer housing, sleeve bearing, a roller bearing holder, a roller bearing, and input drive shaft. 7. The embodiment, Figure 5: shows Cross section CC, at the outer housing, mechanical fuse, sleeve bearing, a roller bearing holder, a roller bearing, and input drive shaft. 8. The embodiment, Figure 6: shows Cross section DD, at the outer housing, mechanical fuse, sleeve bearing, roller bearing holder, a roller bearing, and input drive shaft. 9. The embodiment, Figure 7: shows Cross section EE, at the outer housing, sleeve bearing, a roller bearing holder, a roller bearing, and a drive shaft.

Claims

1. A method by installing a modification for an input drive housing, that includes machining to fit bearing holders and sleeve bearings, holes drilled and tapped for installation of mechanical fuses, a modified labyrinth seal holder, that will allow recovery of a fueling machine, so that seized input drive bearings can be bypassed, by providing a higher input torque that will shear a mechanical fuse and allow rotation of a roller bearing holder within an outer bearing sleeve to obtain shaft rotation, yet still allows for limited operation of the input drives, utilized as part of operating a Pressurized Heavy Water Reactor (PHWR).