Reactor Coolant System System Training Guide A-1 Section 1.0 Introduction Table of Contents Section Subject/Topic Page 1.0 Introduction Table of Contents Objectives Basic Description Design Information Reference Materials 1 1 1 1 1 - 2.0 Major Components Piping Reactor Vessel Steam Generators Reactor Coolant Pumps Pressurizer Subcooling Monitor 2 2 2 2 2 2 -1 -6 -7 -8 - 10 - 11 3.0 System Operations Normal Operations Abnormal Operations Emergency Operations 3-1 3-5 3-6 4.0 Integrated Operations Limiting Specifications System Interfaces Unit Differences Major DCPP Events Industry Events 4 4 4 4 4 A1.DOC 1-1 REV 7 1 2 3 4 6 -1 -3 -7 -8 -9 Introduction Basic Description Purpose of the RCS system Obj 1 Description of the RCS system The purpose of the Reactor Coolant System (RCS) is to transfer heat generated by the fission process in the reactor core to the secondary plant steam system. Other purposes include • Provide coolant pressure boundary. • Serve as the second barrier against release of fission products. • Promote natural circulation. The RCS consists of: Four parallel heat transfer loops connected to the reactor vessel with each loop consisting of • One steam generator which serves as a heat sink, • One reactor coolant pump which circulates the loop water, • Interconnecting loop piping, and • Taps for parameters (temperature, pressure, flow). Basic flowpath Obj 2 The basic block and flow diagram of the RCS is shown here. NOTE: flow through the core is single pass from bottom to top. Steam Generator Reactor Coolant Pump Pressurizer Reactor Vessel RCS-01 A1.DOC 1-3 REV 7 Reactor Coolant System Design Information Design criteria Obj 3 The RCS design bases are tabulated below. The system is designed to ... Ensure that every penetration to containment shall have two automatic closure capability isolation barriers, one inside and one outside of containment; one barrier may be a check valve. Circulate water through the system at an optimum rate. Have a leakage detection system which detects, identifies and monitors reactor coolant leakage. This includes containment particle and radiogas monitors, sump level indicators, and Containment Fan Cooler Units water collection monitors. Handle the following load change rates: • ± 10% step change • 5%/min ramp from 15 to 100% power • -95% load rejection Importance to safety Reason Provides containment isolation of the penetration even with a single active failure. • Efficient heat transfer to the secondary system. • Prevent fuel overheating. Monitor RCS integrity. Provide reliable plant loading changes to support distribution system requirements. RCS provides a number of safety-related functions as described below. Obj 4 Function Seismic Safe shutdown Natural circulation The RCS must be able to ... withstand the design based events. • Ensure integrity during a Design Earthquake, a Double Design Earthquake (0.4g horizontal and two-thirds that vertical motion) or a Hosgri Earthquake. support the safe-shutdown analysis from either the control room or hot shutdown panel. promote natural circulation by providing a piping layout where the heat sink (steam generators) is located at a higher elevation than the heat source (reactor vessel). Continued on next page A1.DOC 1-4 REV 7 Introduction Design Information , Continued Importance to safety (continued) Function Core cooling Importance to radioactivity containment The RCS must be able to ... prevent conditions of high power, high RCS temperature, low RCS pressure or the buildup of noncondensable gases which could interfere with core cooling and lead to a DNBR of < 1.17. The RCS is important to radioactivity containment because it is the second major boundary between the fission products and the environment. Obj 4 Function RCS integrity Overpressure protection RCS venting Containment isolation A1.DOC Concern Coolant must be contained within the confines of the system. • Accommodate static and dynamic loads by a sudden reactivity insertion. • Be protected from or withstand effects of internally generated missiles. • Ensure that pressure/temperature limits have adequate safety margins for the structural integrity of the ferric components of the RCS. • Ensure that the materials are selected for a low probability of gross rupture or significant leakage. Nil ductility limits have been met. • RCS components are corrosion resistant. Ensure that overpressure protection will limit the peak system pressure to 110% of the design pressure (2485 psig, 2500 psia) under the most severe transient. • It is also protected from overpressure transients at low operating temperatures to prevent brittle fracture of the reactor vessel. Gases are vented to the Gaseous Radwaste system. Certain valves must isolate when required to ensure potential paths from the RCS are not directly connected to the environment. 1-5 REV 7 Section 2.0 Major Components Piping Purpose Obj 5 The purpose of the RCS piping is to provide a flowpath to circulate water from the reactor vessel to the S/Gs via the RCPs. Physical description The RCS piping consists of the items listed below. Obj 5 Part Hot Leg piping Piping Diagram A basic RCS piping diagram is shown below: Purpose/Description Connects the reactor vessel to the inlet of the steam generator. Piping is stainless steel and has a 29″ inside diameter. Crossover piping Connects the outlet of the steam generator to the (Intermediate leg) suction nozzle of the reactor coolant pump. Piping is stainless steel and has a 31″ inside diameter. Cold Leg piping Connects the discharge nozzle of the reactor coolant pump to the reactor vessel. Piping is stainless steel and has a 27.5″ inside diameter. Pressurizer surge line Loop 2 is connected to the pressurizer. Steam Generator Reactor Coolant Pump Crossover Leg (Intermediate Leg) Loop 1 Steam Generator Reactor Coolant Pump Crossover Leg Cold Leg Loop 2 Cold Leg PZR Hot Leg Hot Leg Rx Hot Leg Hot Leg Loop 3 Loop 4 Cold Leg Reactor Coolant Pump Steam Generator Crossover Leg Cold Leg Reactor Coolant Pump Steam Generator Crossover Leg RCS-02 Continued on next page A1.DOC 2-1 REV 7 Reactor Coolant System Piping, Continued Location Obj 6 The RCS piping is located on the 91′ elevation of the Containment inside the bioshield as shown below. North UP Pzr RCP 2 RCP 3 S/G 3 S/G 2 Reactor Vessel S/G 1 S/G 4 RCP 1 UP RCP 4 91' Containment RCS-03 Continued on next page A1.DOC 2-2 REV 7 Major Components Piping, Continued Instruments Obj 6, 5 The following drawing and tables describe instruments associated with the RCS: Reactor Coolant Pump Cold Leg Crossover Leg Steam Generator Narrow Range T-hot Narrow Range T-cold Wide Range T-cold Hot Leg Loop Flow Wide Range T-hot Reactor Vessel RCS-04 Obj 6 Instrument Narrow Range Hot Leg RTDs Purpose Provide input into: • loop ∆T circuit • Tavg circuit • indications, control and protection functions Description 3 dual element RTDs, placed in thermowell, 120° apart to minimize temperature streaming effects 3 wired up 3 spares E-21 averages Location Each loop hot leg piping has three penetrations after the piping has exited the cavity wall and prior to the S/Gs Continued on next page A1.DOC 2-3 REV 7 Reactor Coolant System Piping, Continued Instruments (continued) Instrument Narrow Range Cold Leg RTDs Purpose Provide input into: • loop ∆T circuit • Tavg circuit • indications, control and protection functions Wide Range Provide input to: Hot Leg • indication Temperature • RVLIS • Subcooling Margin Monitor Description 2 RTDs, placed in one thermowell, both wired into system. E-21 averages 1 RTD, placed in thermowell. Wide Range Provides input to: 1 RTD, placed in Cold Leg • indication thermowell Temperature • LTOP (Loop 2 & 3) Location Each loop cold leg piping has one penetration downstream of RCP discharge and prior to the piping entering the cavity wall. Each loop hot leg piping has one penetration after the piping has exited the cavity wall and prior to the S/Gs. Each loop cold leg piping has one penetration downstream of RCP discharge and prior to the piping entering the cavity wall Continued on next page A1.DOC 2-4 REV 7 Major Components Piping, Continued Instruments (continued) Instrument Purpose Wide Range Provide input to: • indication RCS • LTOP Pressure • RHR suction valve open interlock • RVLIS • Subcooling Margin Monitor RCS Flow Provide input to: • indication • reactor protection (low RCS flow reactor trip) Indicati ons Description Two separate trains that share RVLIS instrumentation piping Location Outside of containment on 85′ penetration area of Aux Bldg. 3 flow transmitters measure the ∆P between one HP tap and three LP taps Each loop cross over piping elbow prior to RCP suction. HP tap on outside elbow. LP taps on inside elbow. The following tables describes indications associated with the RCS. Obj 7, 8, 9 Indication PI-403 NR RCS Pressure Loop 4 Th PR-403 WR RCS Pressure Loop 4 Th PI-405 WR RCS Pressure Loop 3 Th FI-414, 415, 416, 424, 425, 426, 434, 435, 436, 444, 445, 446 RCS Loop Flow A1.DOC 2-5 Can be read at ... VB-2 Normal reading 0-600 range 600+ psig 2235 psig 2235 psig 100% REV 7 Reactor Coolant System Reactor Vessel Purpose Obj 5 Location Obj 6 The purpose of the Reactor Vessel in the RCS is to connect the cold and hot legs across the heat source of the primary system. The Reactor Vessel is located in the center of the containment building. See Figure RCS-03 on page 2-2. Physical description The reactor vessel is a steel cylinder with a hemispherical head welded to the bottom and a hemispherical head bolted to its top. • Reactor coolant enters the vessel from the cold leg (inlet) nozzles and flows downward between the core barrel and reactor vessel. • From the bottom of the vessel it flows upward through the fuel region to the hot leg (outlet) nozzles. Diagram A basic diagram of the Reactor Vessel is shown below. Cold Leg Inlet Hot Leg Outlet Fuel Region RCS-05 A1.DOC 2-6 REV 7 Major Components Steam Generators Purpose Obj 5 Location Obj 6 The purpose of the Steam Generators (S/G) is to provide a: • heat sink for the Reactor. • barrier between the radioactive reactor coolant and the non-radioactive secondary system. The four S/Gs are located inside Containment and are spaced at approximately 90° intervals. See Figure RCS-03 on page 2-2. Physical description Each S/G consists of a primary section (tube side) and a secondary section (shell side). • Reactor coolant flows on the primary side inside the tubes, and main feedwater flows on the secondary side which is around the tubes. • The boundary between the primary and secondary sides of the S/G is formed by the combination of the U-tubes and the tube sheet. Diagram A basic diagram of a S/G is shown below. Steam Outlet Moisture Separators Feed In Shell U-Tube Bundle Tube Sheet Hot Leg Nozzle Crossover Leg Cold Leg Nozzle RCS-06 A1.DOC 2-7 REV 7 Reactor Coolant System Reactor Coolant Pumps Purpose Obj 5 Location Obj 6 The purpose of the Reactor Coolant Pumps (RCPs) in the RCS is to provide pumped flow to support the design heat transfer rate from the core to the S/Gs. The four RCPs are located inside containment, at the 117′ elevation, inside the bioshield, next to their respective S/Gs. See Figure RCS-03 on page 2-2. Physical description The RCP is a mixed flow pump with the suction nozzle welded to the crossover piping at the bottom of the casing and discharge nozzle welded to the cold leg piping radial to the casing. • Each RCP takes suction from the crossover piping connected to its respective S/G and discharges to the reactor via the cold leg piping. Diagram A simplified drawing of an RCP is shown below. Motor Section Coupling Seal Section Pump Section Cold Leg Cross Over Leg RCS-07 A1.DOC 2-8 REV 7 Major Components Pressurizer Purpose Obj 5 Location Obj 6 Physical description The purpose of the Pressurizer in the RCS is to maintain RCS pressure during steady-state operation to prevent bulk boiling of the reactor coolant and to act as a surge volume for the RCS. The Pressurizer vessel is located in containment on the 115′ elevation. See Figure RCS-03 on page 2-2. The pressurizer is a vertical cylindrical carbon steel vessel with a hemispherical head welded to each end. • The bottom of the pressurizer is connected to Loop 2 of the RCS via surge line. • The pressurizer is normal partially filled with water. The water is maintained at saturated conditions by operation of heaters to maintain a steam bubble above the water space. ♦ Formation of a steam bubble ensures the RCS is not a hydraulically solid system and that pressure control is possible. • The pressurizer has safety and relief valves to protect the RCS from an overpressure condition. Continued on next page A1.DOC 2-9 REV 7 Reactor Coolant System Pressurizer, Continued Diagram The basic pressurizer is shown in the diagram below. Safety Valves (3) To PRT Spray Line Power Operated Relief Valve (3) Instrument Tap Support Operating Water Level Minimum Water Level Instrument Tap Surge Nozzle, Thermal Sleeve Basket Diffuser 78 Heater Elements Loop 2 Hot Leg RCS-08 A1.DOC 2 - 10 REV 7 Section 3.0 System Operations Normal Operations Significant precautions & limitations Obj 12, 13 Refer to the OP A-2 & L series of procedures for a complete listing of system precautions and limitations. The following P&Ls are considered significant: • Whenever a boration, dilution or change in RCS chemistry is in progress at least one RCP should be in operation. • Whenever RCS temperature is above 160°F*, at least one RCP should be in operation to ensure a uniform cooldown of the RCS. • During the RCS dilution it is important to maintain pressurizer boron concentration within 50 ppm of the RCS to prevent adverse reactivity changes during a pressurizer outsurge. • Maximum cooldown for the RCS must not exceed 100°F in any one hour period. This is ensured by limiting the maximum cooldown rate to 100°F/hr. • Procedural limit for RCS heatup rate is 60°F/hr. • Maximum heatup for the RCS must not exceed 100°F in any one hour period. • At all times, RCS pressure and temperature shall be maintained within the limits of the plant cooldown curve. • RCS chemistry limits shall be maintained within guidelines contained in OP F-5:I. Parameters include; Dissolved Oxygen, Chloride, and Fluoride. Dissolved oxygen limits do not apply with Tavg ≤ 250°F*. * Note: For conservatism: • the lowest Tcold should be used when the RCS needs to be greater than a given limit. • the highest Thot should be used when the RCS needs to be less than a given limit. • the highest Tavg should be used when Tavg needs to be below a given limit. Continued on next page A1.DOC 3-1 REV 7 Reactor Coolant System Normal Operations , Continued Normal operation Obj 14 Refer to OP A-2 series of procedures for the specifics of normal operation of the RCS. Equipment RCPs Pressurizer RCS piping Steam Generators Reactor Vessel Subcooling Monitor Normal operation status All four running 653°F, 2235 psig, program level Zero leakage (pressure boundary) 44% level, 780 psig, steaming 603°F exit temperature, 2235 psig, zero leakage In service The RCS system does NOT undergo lineup changes due to plant mode changes. System lineup changes are a function of testing, maintenance and RCS heat load only. Normal operation flowpath diagram Obj 15 The following diagram depicts the normal operation flowpath for the RCS. Steam Generator Reactor Coolant Pump Crossover Leg (Intermediate Leg) Loop 1 Steam Generator Reactor Coolant Pump Crossover Leg Cold Leg Loop 2 Cold Leg PZR Hot Leg Hot Leg Rx Hot Leg Hot Leg Loop 3 Loop 4 Cold Leg Reactor Coolant Pump Steam Generator Crossover Leg Cold Leg Reactor Coolant Pump Steam Generator Crossover Leg RCS-02 Continued on next page A1.DOC 3-2 REV 7 System Operations Normal Operations , Continued System startup The table below lists the procedures that are used to startup the RCS and its associated systems System RCS startup RCS Effects of operation Obj 14, 16 Procedure OP L-1 Title Plant heatup from cold shutdown to hot standby OP A-2:I RCS alignment checklist Equipment operating or evolution effects on system indications are summarized below. Although numerous possibilities exist for the initial conditions of operating a component or starting an evolution the information below assumes operation from a normal configuration. Effect of... Dilution Boration RCS pressure change RCS fatigue transient Violating RCS pressure/temperature limits Consequence Tavg increasing, inward rod motion, SCM decreasing Tavg decreasing, outward rod motion, SCM increasing Pressurizer level change, change in charging flow, SCM changing and heater operation in response to the pressure changes Results in requirement for engineering evaluation. Limit on number of transients a component is exposed to. Results in requirement for engineering evaluation to determine effects of out of limit condition on fracture toughness properties of RCS. Continued on next page A1.DOC 3-3 REV 7 Reactor Coolant System Normal Operations , Continued Effects of operation (continued) Effect of... Consequence Low or decreasing Pzr Decrease in pressurizer pressure, increased level charging flow, decrease in VCT level, SCM changing and heater operation in response to the pressure changes. Placing Excess • Large dilution or boration of the RCS would be Letdown in service very difficult so large power changes should be avoided. • With Excess Letdown in service, RCS hydrogen concentration may decrease since letdown is not being sprayed into the VCT by normal letdown. System shutdown Refer to the procedures listed below for RCS shutdown. System Procedure RCS OP L-5 shutdown A1.DOC Title Plant cooldown from minimum load to cold shutdown 3-4 REV 7 System Operations Abnormal Operations Malfunction effects The following tables describe effects of malfunctions associated with RCS system/component operation. Effects of ... Pipe leak/rupture ARPs Obj 11, 17 • • • • • Consequence Decreasing pressurizer level Increasing containment sump level Increased charging flow Frequent VCT makeup Increasing containment temperature and pressure The annunciator response procedures related to the RCS include: Procedure Title SUBCOOLING AR PK05-07 MARGIN LO SUBCOOLING MARGIN LO LO Parameter Subcooled margin Setpoint 30°F 20°F The alarms are located on PK window 05 on VB2. Alarm logic, parameters, setpoints and operator actions are included in each ARP. AOPs The abnormal operating procedures with actions related to the RCS include: Procedure AP-1 AP-24 AP-SD-2 A1.DOC Title Excessive RCS Leakage Shutdown LOCA Loss of RCS Inventory 3-5 This AOP provides direction to recover from ... RCS leakage. Loss of coolant while in mode 4. Loss of coolant while in modes 5 or 6. REV 7 Reactor Coolant System Emergency Operations Alignments Obj 15 Related EOPs The RCS does not undergo alignment changes for emergencies. • The RCPs are stopped in various emergency procedures and natural circulation or SI flow provide core cooling. The emergency operating procedures with actions related to the RCS include: EOP Procedure E-O E-1 E-0.2 A1.DOC Title Reactor Trip or Safety Injection Loss of Reactor or Secondary Coolant Natural Circulation Cooldown 3-6 This EOP provides direction to address ... diagnosing a RCS pipe rupture (LOCA). recovery from a LOCA. recovery from a reactor trip without RCPs. REV 7
