In the entire nuclear power industry, equipment suppliers are withdrawing from the nuclear market. Utilities and component manufacturers are adopting innovative methods to replace obsolete components that cannot be purchased as safety-related or cannot be certified by the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) Part III.
Investments in outdated management are common, and the focus is on the development of a wider range of reverse engineering and commercial-grade special procedures to ensure access to component replacement. Original equipment manufacturers have the additional ability to evaluate component design and service history to make technical design changes to overcome procurement barriers and improve all aspects of in-service operations.
This case study examined the reconfiguration of the system to eliminate the problematic solenoid valve in the basic service water (ESW) pump bearing lubrication system. The elimination of the solenoid valve solved the procurement problem (the valve could not be purchased from the 10CFR50 Appendix B supplier) and the valve clogging problem that caused the end user to shorten the maintenance interval.
The ESW pump is a single-stage vertical turbo pump that can continuously supply seawater to the tube side of the cooling water heat exchanger of the component cooling water heat exchanger in the pressurized water reactor (PWR) system-28,000 gallons per minute (gpm). ESW pumps operate under all plant conditions, including design basis events, to cool plant equipment required for safe shutdown.
Each ESW pump has a closed spool bearing and uses an integral bearing lubrication system to cool and lubricate the six bearings along the length of the pump. The system provides a pressurized lubrication flow to the bearings before the pump starts, and continues to supply it during the entire operation. The lubricating fluid is injected into the stuffing box below the gland packing and is also the source of gland leakage.
The bearing lubrication system has two operating modes: external oil supply and internal oil supply. During external water supply, this is the normal operating mode, and clean water is supplied from an external source. The return flow through the internal supply line is initially blocked by a solenoid valve activated by the flow. The internal water supply is a backup operating mode that is only activated when the external water source fails. During the internal oil supply, the lubricating fluid is discharged from the pump discharge port and allowed to enter the system. The original system used an electric flow switch to open the solenoid valve in this mode of operation. The side stream is filtered through a cyclone abrasive separator before being injected into the bearing. Check the return flow through the external supply line. The schematic diagram of the original system is shown in Figure 2.
When reviewing the order for the replacement of the bearing lubrication system, it was determined that the solenoid valve and the corresponding electronic flow switch could not be purchased as safety-related or certified by ASME BPVC Section III; there was no viable 10CFR50 Appendix B supplier for the original components. Purchased as a commercial grade and through a commercial grade dedicated upgrade, the process usually implemented in these scenarios proves to be impractical because the original component manufacturer lacks sufficient design information.
In addition to the procurement problem, a clogging problem of the solenoid valve was also found in the technical discussion with the end user. The ESW pump operates in a particularly harsh seawater environment; the pump suction chamber contains a large amount of suspended particles and sediments. Even after being filtered by the abrasive separator, particles in the process fluid will accumulate in the solenoid valve over time. Blocked valves result in shortened service intervals for end users and unplanned system maintenance. Valve cleaning requires the ESW pump to be shut down completely.
After a thorough review of the bearing lubrication system, a redesign and reconfiguration were implemented, and the solenoid valve and flow switch were completely eliminated while maintaining the original system functions. In the modified configuration, the drain check valve is repositioned to the filtered water discharge port of the abrasive separator, replacing the solenoid valve. The schematic diagram of the reconfigured system is shown in Figure 2.
The original system uses a flow-controlled solenoid valve to be electrically driven, which switches from external lubrication to internal lubrication when the external supply fails. When the cleaning flow drops below the minimum lubrication flow of 3 gpm, the solenoid valve is activated by the flow switch to allow self-lubricating to flow to the bearing; the internal supply will continue until the external flow is restored, at which time the solenoid valve will be deactivated and the injection process into the bearing will be stopped fluid.
In contrast, the reconfigured system is a passive system that uses pressure control using only check valves. The lubrication method is selected according to the pressure of the internal and external oil supply pipelines. The source with the highest pressure at any given time dictates and lubricates the bearing without the need for external power or signals between components. During normal operation, the external supply pressure is maintained above the pump discharge pressure to achieve constant clean water lubrication. When the external supply pressure is lost, the system automatically switches to self-lubrication.
The separator drain check valve was considered unimportant to system operation and was reused as an internal supply valve. The drain valve was originally designed to prevent backflow into the system, but backflow pollution requires that the sea level above the pump floor is unlikely to rise.
If this happens while the pump is running, the part of the water flow leaving the separator drain pipe through the bypass line will prevent the entry of unprocessed seawater. If both the pump and the external water supply are turned off, the total inflow through the cyclone separator will be insignificant, and the original seawater will be washed away from the closed pipe when the pump is started, and the impact on bearing life will be negligible.
Due to the removal of the separator discharge check valve, the reconfiguration resulted in a decrease in the discharge line resistance, and the internal supply line resistance was increased due to the lower flow coefficient (higher flow resistance) of the internal supply valve; the flow rate of the internal supply check valve The coefficient is 1.9 (Cv = 1.9), while the flow coefficient of the original solenoid valve is 4.0 (Cv = 4.0).
In order to verify that the internal lubrication flow is still sufficient in the modified configuration, an iterative flow analysis is performed to determine the flow of the bearing. The new and original system configurations were analyzed, and the expected self-lubricating flow was compared based on the pump's rated head (133 feet, 59 psi). The results showed that the internal supply flow of the bearings in the reconfigured system remained above the minimum 3 gpm flow rate specified in the original design.
Elimination of solenoid valves and flow switches, eliminating procurement problems, so that orders can be completed, while minimizing the impact of obsolescence on suppliers and end users. The check valve used in the modified system is easy to purchase; the valve body is manufactured in-house, and special valve trims are purchased through material analysis and functional testing. Reconfiguration eliminates clogging problems associated with solenoid valves, thereby reducing system maintenance.
The update reduces the complexity of the system while maintaining the dual power requirements of the original system. The reconfigured system is passively self-regulating and uses fewer components, thereby reducing potential points of failure. The result is that a more robust design has the added benefit of directly reducing overall system cost.
Jake Fragnoli is an aftermarket design engineer for Hayward Tyler, Inc. His contact information is jake.fragnoli@haywardtyler.com. For more information, please visit www.haywardtyler.com.