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DSAR CHAPTER 10 - STEAM AND POWER CONVERSION SYSTEM Revision 36 SECTION 10.1 Page 10.1-1 of 10.1-1 10.1 DESIGN BASIS Following the implementation of Permanently Defueled Technical Specifications, the Steam and Power Conversion System information in Chapter 10 is considered historical and does not constitute design requirements unless otherwise noted to still be applicable in the defueled condition.
The steam and power conversion system is designed to receive steam from the NSSS and convert the steam thermal energy into electrical energy. The turbine generator has an expected capacity of 845 MWe.
Components from the steam generators up to and including the main steam isolation valves and main and auxiliary feedwater header isolation check valves were designed to CP Co Design Class l requirements. The main steam piping between the main steam isolation valve and various steam takeoff block valves is designed to CP Co Design Class 2 requirements. The remainder of the components and piping is designed to CP Co Design Class 3 requirements. See Section 5.2 for a discussion of classes.
DSAR CHAPTER 10 - STEAM AND POWER CONVERSION SYSTEM Revision 36 SECTION 10.2 Page 10.2-1 of 10.2-6 10.2 SYSTEM DESCRIPTION AND OPERATION 10.2.1 SYSTEM GENERAL DESCRIPTION The main steam, extraction steam, feedwater, condensate and steam generator blowdown systems are shown on Figures 10-1, 10-2, 10-3 and 10-4.
- 1. Main Steam System (Figures 10-1 and 10-2)
Each main steam header is provided with 12 spring-loaded safety valves and 2 atmospheric dump valves upstream of the main steam isolation valves (MSIVs). The safety valves discharge to the atmosphere and are in accordance with the requirements of the ASME B&PV Code,Section III. In addition, there is a steam bypass to condenser valve downstream of the MSIVs.
- 2. Moisture Separator-Reheaters There are four moisture separator reheaters and one moisture separator drain tank.
- 3. Main Steam Dump and Bypass System (Figures 10-4 and 10-1, Respectively)
The main steam dump and bypass system consists of four atmospheric dump valves which exhaust to atmosphere and a turbine bypass valve which exhausts to the main condenser; the total capacities of the atmospheric steam dump and turbine bypass valves are 30% and 4.5%, respectively, of steam flow with reactor at full power.
The atmospheric steam dump valves have a back up nitrogen supply.
- 4. Main Steam Line Isolation One main steam isolation valve is provided on each main steam header. Each valve consists of a swing disc.
- 5. Steam Generator Blowdown System (Figures 10-3 and 10-4)
The steam generator blowdown system is designed to process steam generator blowdown water. The steam generator blowdown system is designed for continuous operation at up to 30,000 lb/h blowdown per steam generator.
The steam generator blowdown system consists of flash tank, blowdown tank, two blowdown pumps, blowdown heat exchanger,
DSAR CHAPTER 10 - STEAM AND POWER CONVERSION SYSTEM Revision 36 SECTION 10.2 Page 10.2-2 of 10.2-6 blowdown filter, three blowdown demineralizers, piping, valves and instrumentation.
A radiation monitor is located on the effluent of the blowdown tank.
10.2.2 STEAM TURBINE The turbine is an 1,800 r/min tandem compound, 3 cylinder, quadruple flow, indoor unit.
10.2.2.1 High-Pressure Turbine The high-pressure turbine element is of a double-flow design; therefore, it is inherently thrust balanced.
The reaction blading is mounted in blade rings which, in turn, are mounted in the turbine casing. The blade rings are center line supported to ensure center alignment while allowing for differential expansion between the blade ring and the casing. This design reduces casing thermal distortion and, thus, seal clearances are more readily maintained.
The high-pressure rotor is made of NiCrMoV alloy steel. The main body of the rotor weighs approximately 120,920 pounds. The approximate values of the transverse center line diameter, the maximum diameter (including blades) and the main body length (generator coupling face to extension shaft coupling face) are 36 inches, 82 inches and 301 inches, respectively.
The blade rings are made of stainless steel and the casing cover and base are made of carbon steel castings. The specified minimum mechanical properties are shown in Table 10-1.
The bend test specimen shall be capable of being bent cold through an angle of 90° and around a pin 1 inch in diameter without cracking on the outside of the bent portion.
The approximate weights of the four blade rings, the casing cover and the casing base are 97,000 pounds, 115,000 pounds and 115,000 pounds, respectively.
The casing cover and base are tied together by means of more than 100 studs. The stud material is an alloy steel having the mechanical properties shown in Table 10-2.
The studs have lengths ranging from 17 inches to 66 inches. About 90% of them have diameters ranging between 2.5 inches and 4 inches. The total stud cross-sectional area is about 900 square inches and the total stud free-length volume is about 36,000 cubic inches.
DSAR CHAPTER 10 - STEAM AND POWER CONVERSION SYSTEM Revision 36 SECTION 10.2 Page 10.2-3 of 10.2-6 10.2.2.2 Low-Pressure Turbine Each low pressure turbine is a double flow element employing reaction blading.
Each low pressure turbine consists of a fabricated outer casing. The outer casing forms the housings for the low pressure turbine bearings. The outer casing base of the No. 1 low pressure turbine provides the support for the generator end of the high pressure turbine generator end bearing. The thrust bearing is supported in the governor end of the No. 2 low pressure turbine outer casing base.
The rows of stationary blading in each end of the low pressure turbines are carried in blade rings or the inner cylinders. These blade rings and inner cylinders are each supported in the outer cylinder just below the horizontal centerline. Guide pins on the vertical centerline are supplied to maintain the position of blade rings axially.
Each low pressure turbine casing is supported by a continuous foot (or skirt) extending around the cylinder base. The foot of each casing rests on a separate seating plate which is grouted to the foundation. The location of the low pressure turbines is maintained by eight taper dowels through the foot and six keys between the foot and the seating plate.
The low pressure rotors, consisting of a series of alloy steel discs shrunk on a shaft and keyed in position, are also machined from alloy steel forgings. The outer discs are held in place by split rings, fitted in grooves in the rotor and retained by shrink rings.
All rotors are finished machined and after completely bladed, are given a running test and an accurate dynamic balance test.
Flanged, rigid type couplings are used to connect the rotors of the high pressure, No. 1 low pressure, No. 2 low pressure and the generator. The rotating element thus formed is supported by eight journal bearings and is located axially by the thrust bearing mounted at the governor end of the No. 2 low pressure turbine.
In the late 1970s, Westinghouse turbines developed a history of cracks forming in the disc bores and keyways of low-pressure turbines in nuclear plants. As a result of this generic problem, Westinghouse along with Westinghouse turbine owners and the NRC worked together to arrive at an acceptable solution. In order to minimize the possibility of disc rupture, it was necessary to periodically inspect the critical disc bore region. To arrive at a safe rational procedure for determining inspection intervals, a fracture mechanics approach for calculating the critical crack size was used. The crack's growth rate was predicted from disc yield strength and temperature using the regression equation derived from field data. Details for calculating the critical crack sizes, growth rates and criteria for inspection intervals were
DSAR CHAPTER 10 - STEAM AND POWER CONVERSION SYSTEM Revision 36 SECTION 10.2 Page 10.2-4 of 10.2-6 discussed in a proprietary Westinghouse Report MSTG-1-P, Criteria for Low Pressure Nuclear Turbine Disc Inspection, submitted to the NRC in June 1981.
The Westinghouse low pressure rotors were later replaced with Siemens Westinghouse rotors in 1999.
10.2.2.3 Electrical Generator The generator is made up of a housing, stator, rotor and shaft with sleeve bearings and ventilation blower, see Figure 10-5. The generator is a hydrogen inner cooled unit connected directly to the turbine and rated at 0.85 power factor. It is rated for 955 MVA and has the capability to accept the gross output of the turbine at rated steam conditions.
10.2.2.4 Exciter The exciter is of the brushless type and consists of a permanent magnet generator, an ac generator and a rectifier assembly mounted on a common shaft. The exciter is totally enclosed with suitable heat exchanger.
The rotor of the ac exciter is made with a multiphase winding.
10.2.3 CONDENSATE AND FEEDWATER 10.2.3.1 Condensate System The condensate/feedwater cycle (Figure 10-4) is a closed system. The main condenser originally contained 511,490 square feet of surface provided by 26,550, 1-inch, 70-foot-long Admiralty tubes, and by 1,426, 1-inch, 304 stainless steel tubes in the air cooler and impingement sections. In 1974, due to tube leakage problems, the entire Admiralty tube section was retubed with 90-10 copper-nickel tubes. In 1990, the main condenser, feedwater heaters E-5A/B & E-6A/B, and drain coolers E-7A/B were replaced to eliminate copper materials of construction in the secondary water/steam cycle. The new condenser contains 24,594 one inch, 70 ft long, 439 stainless steel tubes with an effective surface area of 449,282 square feet. The new heaters and drain coolers contain 304 stainless steel tubes.
10.2.3.2 Condensate Demineralizer System In 1973, leaks developed in the steam generator tubes. Investigations showed that the problem was tube wastage caused by using phosphates for secondary water chemistry control. In 1974, it was decided to install a full flow condensate demineralizer system and institute a program of steam generator flushing to remove phosphates, continuous steam generator blowdown, start-up recirculation and volatile secondary water chemistry control. Consumers Power Company concurred with studies and tests performed during 1979 and 1980 that the Condensate Demineralizers would
DSAR CHAPTER 10 - STEAM AND POWER CONVERSION SYSTEM Revision 36 SECTION 10.2 Page 10.2-5 of 10.2-6 be of more detriment than help. Use of the Condensate Demineralizer System ceased in 1981. This system is currently considered as "retired in place."
The Condensate Demineralizer System was isolated from the Condensate System by replacing the inlet and outlet valves with blind flanges. The Condensate Demineralizer bypass valve was removed to avoid inadvertent closures.
10.2.3.3 Deleted 10.2.4 CIRCULATING WATER SYSTEM Initially, the Plant was designed for a once-through condenser cooling Circulating Water System. In 1974, the Circulating Water System was converted to a closed cycle system (Figure 10-6) using two mechanical draft cooling towers. The system consists of two essentially independent closed loops.
10.2.4.1 Cooling Towers There are two SPX Marley induced draft cross flow cooling towers, one with 16 cells (E-30A) and on with 18 cells (E-30B). The cooling towers (Table 10-4) are designed for a 32°F range (inlet temperature minus outlet temperature). The cooling towers are erected to the south of the Plant (Figure 2-2) over concrete basins. Each tower basin supplies one-half of the condenser through a 90-inch pipe which connects to a 96-inch condenser inlet piping at the intake structure.
At the outlet of each cooling tower are screens. Cooling tower E-30A has two sets of removable screens, while cooling tower E-30B has two traveling water screens. Provisions for stop logs are also provided at the basin outlet.
The two cooling towers are located approximately 500 feet and 1,000 feet, respectively, from the Plant and 300 feet from the nearest transmission lines in order to minimize icing potential. They are spaced approximately 500 feet apart to prevent warm air recirculation between the towers.
Two half-capacity vertical wet pit cooling tower pumps (Table 10-5) are installed in the cooling tower pump building. Motor-driven butterfly valves are provided in both the pump discharge and condenser inlet piping. The valves are interlocked with their corresponding pump motor breakers.
10.2.4.2 Deleted 10.2.4.3 Deleted
DSAR CHAPTER 10 - STEAM AND POWER CONVERSION SYSTEM Revision 36 SECTION 10.2 Page 10.2-6 of 10.2-6 10.2.5 CODES AND STANDARDS All components in the system are designed and fabricated in accordance with applicable codes; eg, the moisture separators-reheaters and the closed feedwater heaters are in accordance with the ASME B&PV Code,Section VIII, and the piping and valves are to ASA B31.1-1955, Code for Pressure Piping.
The components are similar to those which have experienced extensive service in operating power plants.
DSAR CHAPTER 10 - STEAM AND POWER CONVERSION SYSTEM Revision 36 SECTION 10.4 Page 10.4-1 of 10.4-2 10.4 TESTS AND INSPECTIONS In-service inspection of ASME Class 1, 2, and 3 components is conducted in accordance with Section XI of the ASME B&PV Code.
10.4.1 PIPE WALL THINNING INSPECTION PROGRAM In response to Generic Letter 89-08, the pipe wall thinning inspection program was initiated to meet or exceed the requirements of NUREG-1344, Appendix A.
A component susceptibility ranking has been broken down into 14 systems/
subsystems for ease of tracking. These systems are:
- 1. Main steam
- 2. Condensate
- 3. Feedwater
- 4. Steam generator blowdown
- 5. Heater drain pump discharge
- 6. Reheater drain tank
- 7. Numbers 5 and 6 heater drains
- 8. Moisture separator drain tanks
- 9. Numbers 1-4 heater drains
- 10. Heater vents
- 11. Extraction steam to Number 6 heater
- 12. Extraction steam to Number 5 heater
- 13. Extraction steam to Number 3 heater
- 14. Extraction steam to Numbers 1-2 heaters
DSAR CHAPTER 10 - STEAM AND POWER CONVERSION SYSTEM Revision 36 SECTION 10.4 Page 10.4-2 of 10.4-2 Components in these systems are ranked according to projected wear rates obtained by modeling. Modeling factors for single-phase systems include piping material, fluid velocity, piping configuration, oxygen concentration, pH and temperature. Factors for two-phase systems include percent moisture, piping material, temperature, oxygen concentration, pH, piping configuration and fluid velocity.
Components were selected in a three-stage process. First, systems were selected based on material, velocity and temperature. Second, subsystem selection used temperature and velocity, water/steam quality and pH/chemistry. And last, component selection considered geometry, walkdowns and experience.
By letter dated April 19, 1990, the NRC accepted this program on the basis that it complied with NUREG-1344, Appendix A.