CVCS Student Text

The Letdown System

Low Pressure Letdown to CVCS Low Pressure Letdown to CVCS (Figure 20) consists of a 2-inch line from the outlet of BOTH RHR heat exchanger and taps into the letdown line upstream of the LTDN Hx. This line enables purification during cold shutdown when there is insufficient P across the letdown orifices to maintain a letdown flow. The low pressure letdown line also enables purification during refueling operations and serves as an additional means of letdown during plant heatup. The amount of letdown flow via this path is controlled by HCV-142 from the MCB. HCV-142 fails closed upon loss-of-air or loss-of-power. HCV-142 Location: AB 100' RM off charging pump hallway. Letdown Heat Exchanger The letdown heat exchanger cools the letdown to the operating temperature of the mixed bed demineralizers. The outlet letdown flow is cooled to approximately 100F. Component cooling water flowing through the shell side of the heat exchanger is the cooling medium. The outlet temperature is controlled by regulating the CCW flow through the heat exchanger via Q1/2P17TCV3083 (also called TCV-144 based on the numbering of the associated control loop, i.e. TK-144, TE-144 and TI-144) located in the CCW discharge line. A temperature sensor (TE-144) downstream of the letdown heat exchanger provides the input signal to the control circuitry for Q1/2P17TCV3083 (TCV-144). Location: AB 100' RM 170. PT-145 A pressure transmitter downstream of the letdown heat exchanger provides a control signal to the letdown pressure control valve (PCV-145). The pressure transmitter also provides local indication and a high pressure alarm on the MCB at 462 psig. Location: AB 100' RM 170. TE-143 In addition to TE-144, another temperature element TE-143 is located downstream of the letdown heat exchanger to provide various control functions. At 135F, an alarm sounds on the MCB and divert valve TCV-143 automatically shifts the letdown flow to the VCT, bypassing the demineralizers. This prevents demineralizer damage due to high temperature. Indication is also provided on the MCB. Location: AB 139' RM 303. Letdown Flow Transmitter (FT-150) Letdown flow transmitter FT-150 provides flow indication on the MCB and a high flow alarm at 140 gpm. Location: AB 100' Letdown Pressure Control Valve (PCV-145) The letdown pressure control valve automatically maintains approximately 260-450 psig of backpressure on the letdown orifices to prevent the letdown from flashing to steam downstream of the orifices. Flashing would cause excessive erosion of the orifices. This 260-450 psig band also allows the operator to maintain letdown flow ≤ 135 gpm with 2 letdown orifices in service. When the letdown exits the letdown heat exchanger, it is cooled to approximately 100F. At this temperature, the pressure can be further reduced without flashing. The pressure downstream of PCV-145 is the same as the gas pressure in the VCT plus or minus any head differences between the two components. PCV-145 receives its control signal from a pressure controller PK-145 on the MCB. In automatic, PK-145 compares upstream pressure, as measured by PT-145, with setpoint pressure indicated on the controller's potentiometer. A difference in pressure signals causes the valve to reposition to correct the difference. When PK-145 is used in manual mode, the operator controls the controller output to the valve positioner. In the solid plant condition, PCV-145 is used to maintain the desired pressure in the RCS. Low pressure letdown from RHR will be in service during solid plant pressure control. HV-142 is used in series with PCV-145 to control pressure and flow. PCV-145 fails open on loss-of-power or loss-of-air. A manual bypass line is provided so that letdown can be maintained if maintenance is required on PCV-145. Location: AB 100' RM 170. Relief Valve (8119) The pressure relief valve (8119) downstream of the letdown pressure control valve (PCV-145) protects the low pressure piping, demineralizers, and filter from overpressure when this section of the system is isolated. The overpressure may result from leakage through PCV-145. The capacity of the relief valve exceeds the maximum flow rate through all letdown orifices. The valve pressure setpoint is equal to the design pressure of the demineralizers (300 psig). The valve relieves to the VCT. The return from the gross failed fuel detector system taps in downstream of this relief valve. Letdown at Demineralizer Inlet Sample A 2-inch sample connection permits sampling of the letdown fluid prior to entering the demineralizers. Temperature Divert Valve (TCV-143) Upon receiving a high temperature signal (135°F) from TE-143 or a high temperature signal (160F) from BTRS demineralizer inlet temperature switch TIS-382 (not shown), TCV-143 diverts the letdown away from the demineralizers and directs it to the VCT. This diversion protects the letdown and BTRS demineralizer resin beds from temperatures that exceed 140F and 165F, respectively. TE-143 is downstream of the letdown heat exchanger, and TIS-382 is at the inlet to the BTRS demineralizers. TCV-143 directs flow to the VCT upon loss-of-air or loss-of-power. Location: AB 139' RM 303. Local Pressure Indicators (PI-146, PI-148, and PI-149) Local pressure indicators (not shown on Figure 3 and 21) show the P across the demineralizers and across the reactor coolant filter. Mixed Bed Demineralizers Two flushable, mixed bed demineralizers maintain reactor coolant purity by filtering action and ion exchange. The A mixed bed demineralizer is loaded with LiOH type resin and the B mixed bed demineralizer is loaded with HOH type resin when demineralizer resins are exhausted. Both forms remove fission and activation products. Only one Mixed Bed Demineralizer is placed in service at a time. Each demineralizer contains 30 cubic feet of resin and is designed for 135 gpm flow. This resin bed size is chosen to provide a decontamination factor of 10 for most fission products (except cesium, yttrium, and molybdenum). The life of a mixed bed demineralizer is one core cycle, assuming 1% failed fuel. The demineralizers are constructed from austenitic stainless steel and have connections for resin addition, replacement, flushing, and draining. The top of each demineralizer has temporary connections for connecting the resin fill tank or the demineralized water supply. In order to minimize flow channeling of the resin and to maximize resin retention, each demineralizer has an inlet flow deflector, retention screens, and mesh screens on the drain connections. Spent resins are sluiced to the spent resin storage tank via the resin sluice pump. Location: AB 139' RM 331. Access on AB 155'. Cation Bed Demineralizer A single, flushable, cation bed demineralizer is located downstream of the mixed bed demineralizers. This demineralizer can be valved in, when required, to control the concentrations of LiOH in the RCS. The cation resin bed can also remove cesium, yttrium, and molybdenum. Under normal power, shutdown, and startup conditions the mixed bed demineralizers can adequately remove all LiOH and radionuclides necessary to operate plant for one fuel cycle. The cation bed size is sufficient to maintain the cesium concentration in the reactor coolant below 1.0 μc/cc with 1% defective fuel. This resin bed is designed to accommodate 60 gpm, and a local flow instrument (FI-147) allows the proper flow setting when valving in the cation bed. AB 139' RM 331. Access on AB 155'. BTRS Divert Valve (8547) This valve diverts letdown to the BTRS. When the BTRS is placed in either the dilute or borate mode, this valve closes and diverts letdown to the BTRS. The valve fails open on loss-of-power or loss-of-air. Location: AB 139' RM 331. Return Line from BTRS (Not used) The return from the BTRS moderating heat exchanger re-enters the letdown downstream of the BTRS divert valve (8547). Letdown Sample Connection Downstream of Demineralizers This sample line is used for sampling the chemistry downstream of the demineralizers. By comparing this sample with a sample from upstream of the demineralizers, demineralizer effectiveness can be obtained. Reactor Coolant Filter A 25-micron or smaller (as low as 0.1 micron) disposable, cartridge-type filter located in the letdown stream removes particulates and resin fines from the letdown. The filter housing has a vent and drain for replacing the filter cartridge. Isolation valves on the filter inlet and outlet and a bypass line are used when replacing filters. The filter normally is replaced when the filter P reaches 30 psid as indicated by PI-148 and PI-149 (not shown) or when the radiation level on contact exceeds a predetermined limit. The maximum radiation limit is a function of the dose received when replacing the filter. AB 139' RM 303. Boron Concentration Monitoring System (Not in use) The information below is included for information only. The BCMS is powered down on both Units with no plans, at present, to restore the system to operating status. The boron concentration monitoring system (BCMS) taps across the filter bypass stop valve and utilizes the P across the filter as a driving head. An alternate sample point is just before the inlet connection to the BTRS. The BCMS uses a neutron source and a neutron detector to monitor the boron concentration in the RCS. As the letdown passes between the source and the detector, the number of neutrons detected is inversely proportional to the boron concentration (since boron is a neutron absorber). Air-operated valves (not shown) isolate inlet flow to the BCMS and are operated from the balance of plant (BOP) panel. The outlet line has two check valves in series prior to returning to the VCT. These check valves prevent backflow from the VCT and provide positive containment isolation. The system has a flushing supply from the demineralized water system. The flushing supply is used for initial system flushing prior to startup and for calibration of the boron concentration monitoring system detector. This system is discussed in more detail in the Boron Concentration Monitoring system lesson plan. AB 121' Hallway outside VCT room. VCT Level Control Valve (LCV-115A) In order to prevent overfilling the VCT, a three-way divert valve in the letdown line limits the maximum level in the VCT to 81%. LCV-115A is an air operated, modulating, three-way valve controlled by level transmitters LT-112 and LT-115 that measure the VCT level. For normal operation, LT-112 provides a varying signal to the positioner to modulate LCV-115A from fully closed at 71% to fully open at 81%. If this signal fails to function properly, LT-115 signals the valve to fully divert at an 81% level in the VCT. The letdown stream is directed to the recycle holdup tanks (RHTs). Diverting letdown to the RHTs is a normal evolution when diluting the RCS during plant heatup or late in core life when dilutions could involve hundreds of gallons of Reactor Make-up Water. Under these conditions, the modulating controller (LT-112) diverts a portion of the letdown to the RHTs and puts the remainder into the VCT, thus allowing better hydrogen control. LCV-115A fails with full flow to the VCT on loss-of-power or loss-of-air. Location: AB 139' RM 303. Reactor Makeup Control System To reduce the boron concentration of the RCS, reactor makeup water is added via the 2-inch connection to the letdown line entering the top of the VCT via FCV-114A. In addition, water may be added to the outlet of the VCT via FCV-113B. The operation of the reactor makeup system is presented in the Reactor Makeup Control and Chemical Addition system lesson plan. Volume Control Tank The VCT serves as a surge volume for the CVCS to accommodate small fluctuations in the system flow and provides suction for the charging pumps to ensure that they have a steady supply of water. It has a capacity of 300 cubic feet or approximately 2250 gallons and is constructed from austenitic stainless steel. Penetrations in the VCT include the following: 1. The normal letdown line 2. The outlet to charging pump suction header 3. The inlet from the CVCS relief valve discharge header 4. The alternate return from the seal water heat exchanger 5. The gas supply line 6. The gas return line to the WPS 7. The level taps for LT-112 and LT-115 8. The VCT drain line Location: AB 121' RM 217. Normal Letdown Line. The 3-inch normal letdown line enters the top of the vessel and terminates with a spray nozzle. Spraying the incoming letdown into the VCT increases the surface area of the liquid, thus improving the gas exchange process. Outlet to Charging Pump Suction Header The outlet from the VCT to the charging pump suction header is a 4-inch line. Located in this line is temperature element TE-116, which provides VCT outlet temperature indication on the MCB and alarms at 111F. This alarm setpoint is based on not exceeding the maximum RCP seal injection temperature of 140 F. A drain off this outlet line (not shown) is used to drain the VCT for maintenance. The VCT may be drained to the drain header or to the RHT. Inlet from CVCS Relief Valve Discharge Header. The following CVCS relief valves discharge into a common relief header that returns to the VCT: 1. Letdown line downstream of PCV-145 2. Seal water heat exchanger inlet 3. BTRS letdown reheat heat exchanger outlet The VCT relief valve is located on this common header and relieves to the RHTs. The VCT relief valve permits the tank to have a lower pressure than the upstream equipment. The valve pressure setpoint (75 psig) equals the design pressure of the VCT. At the VCT relief setpoint pressure, the valve has a relieving capacity greater than the summation of the following: 1. Maximum letdown 2. Maximum seal water return 3. Excess letdown 4. Nominal flow from one reactor makeup water pump Alternate Return from the Seal Water Heat Exchanger The alternate return for the seal water heat exchanger is also a 3-inch line which enters the top of the VCT. It too has a spray nozzle to help gas exchange. This path can be manually valved in when the excess letdown line is being used as a backup for the normal letdown line or when routing the seal return to the VCT gas space when degassing the RCS. This line is normally isolated with a lock closed manual valve. If a safety injection were to occur with this flow path aligned, Charging Pump mini-flow would cause the VCT to go solid, over-pressurize and result in lifting the VCT relief valve. Gas Supply Line The gas supply line enters a 1-inch penetration arranged so the gas bubbles up through the liquid in the VCT. This arrangement improves the gas exchange in the VCT. During normal operation, HV-8156 can supply hydrogen to the VCT. When the plant is to be shutdown, cooled down, and opened for maintenance on the RCS, the hydrogen concentration must be reduced and maintained below 5 cc/kg. In this case, nitrogen from the bulk nitrogen system (via HV-8155) is used to replace the hydrogen purge, thus reducing the hydrogen concentration in the VCT. The hydrogen and nitrogen supply valves are regulator-type valves normally set to maintain a downstream pressure of at least 18 psig, which is the minimum VCT pressure for proper RCP seal operation. The minimum pressure ensures adequate back pressure for #1 seal leak off and ensures proper coolant flow across the RCP #2 seal. Maximum VCT gas pressure is 35 psig. This limit is to ensure that in the event of a fire, which prevents the VCT outlet MOVs from closing when the RWST to the Charging Pump MOVs open, the VCT gas will not move to the Charging Pump suctions. The source of gas is selected by manual valve alignment of the respective line. VCT hydrogen pressure is adjusted as required to maintain the proper Hydrogen concentration in the RCS. The normal pressure control band is varied, based on the trend of RCS Hydrogen concentration. The Chemistry group will determine an optimum band and make the recommendation to Operations. Keep in mind that the band has to be bounded by the minimum of 18# and maximum of 35#. The following Precautions and Limitation from the SOP governing VCT operation, provides information related to At-Power VCT pressure reductions and gas accumulation in idle charging pump suctions. (Hydrogen coming out of solution) • With one orifice on service o VCT pressure reductions ≥ 7 psig can result in gas dissolution sufficient to create idle charging pump suction voiding. o Any VCT pressure reduction should be ≤ 5 psig in 4 hours to preclude void formation in charging pump suction piping. • With two orifices on service o VCT pressure reductions ≥ 15 psig can result in gas dissolution sufficient to create idle charging pump suction voiding. o Any VCT pressure reduction should be ≤ 10 psig in 4 hours to preclude void formation in charging pump suction piping. • Pressure reduction rates exceeding preceding limitations should be documented by Condition Report. • Idle Charging pump suctions should be vented when VCT pressure reduction rate has exceeded preceding limit. (not applicable to 2B Charging pump) When the waste gas decay tanks are dewatered, the condensate can be pumped to the VCT via the waste processing system (WPS) gas supply line, but is normally pumped to the waste holdup tank (WHT). Gas Return Line to WPS The gas return line to the waste gas system is a 3-inch penetration off the top of the VCT. Pressure transmitter PT-117 is connected to the gas return line and provides indication and alarms on the MCB (Hi-65 psig, Lo-12 psig). In addition, PT-117 will close PCV-1092 if low pressure in the VCT is reached. The gas return line also has a sample system tap. Detailed operation of PCV-1092 is discussed in the Waste Gas system lesson plan. However, it should be noted that the waste gas system is designed to maintain a 0.7 scfm flow of hydrogen through the VCT by controlling the discharge flow rate with a series of air-operated control valves downstream of PCV-1092. Continuous purge from the VCT is no longer in use. An alternate gas return path from the VCT to the WPS is provided by HV 8101 and regulating valve HV-8157. HV-8101 is normally closed and is controlled from the MCB and HV-8157 maintains an upstream pressure of 20 psig. This flow path can be used when venting the VCT during purge operations. Again, the operation of these valves and this alternate flow path are described in the Waste Gas system lesson plan. Level Taps The VCT has two common level taps for LT-115 and LT-112. LT-112 performs the following functions: 1. Provides one of the required inputs to shift the charging pump suction from the VCT to the RWST at 5% VCT level 2. Provides a control signal to modulate LCV-115A 3. Provides high (76%) and low (15%) VCT level alarms on MCB 4. Provides VCT level indication on the MCB 5. Provides local indication in the BTRS chiller room LT-115 performs the following functions: 1. Fully diverts LCV-115A at 81% VCT level 2. Provides one of the required inputs to shift the charging pump suction from the VCT to the RWST at 5% VCT level 3. Provides a start signal for automatic makeup at 20% VCT level 4. Provides stop signal for automatic makeup at 40% level 5. Provides VCT level indication on the MCB 6. Provides high (76%) and low (15%) VCT level alarms on MCB VCT Drain Line The VCT has one drain line that is isolated by one manual isolation valve. When draining the VCT, water is routed from the VCT to the #1 RHT via the VCT drain line.

The Letdown System

The letdown system (Figures 3 and 21) is that portion of the CVCS where the pressure and temperature of the CVCS flow are decreased to facilitate demineralization, filtration, and gas control. The temperature reduction also aids in RCP seal cooling. The letdown system consists of all the piping and components from the point of RCS letdown to the outlet of the VCT. Letdown Isolation Valves The normal letdown is taken from loop A intermediate leg at the piping low point between the steam generator and the reactor coolant pump. The following are the interlocks and/or control actuations associated with LCV-459 and LCV-460: 1. The orifice isolation valves (8149A, B, and C) must be shut in order to open or close either LCV-459 or LCV-460. 2. LCV-459 and LCV-460 fail closed on loss-of-air or loss-of-power. 3. LCV-459 and LCV-460 automatically close if pressurizer level drops to less than or equal to 15%. The first two interlocks listed above (coupled with the fact that the orifice isolation valves close if either LCV-459 or LCV-460 inadvertently closes) ensure that the hot letdown fluid will not flash to steam in the regenerative heat exchanger due to operating valves in the improper sequence. The third interlock listed above (coupled with the fact that the orifice isolation valves also close automatically when pressurizer level is less than or equal to 15%) prevents uncovering of the pressurizer heaters. Uncovering the heaters when they are still hot could result in premature heater element failure. It should be noted that on Unit 1, LCV-460 is the closest valve to the RCS loop and on Unit 2, LCV-459 is closest to the RCS. Location: CB 105' A loop inside Bioshield wall. Letdown Delay Tanks Two delay tanks located in the letdown line reduce the velocity of the letdown fluid and allow sufficient time for the decay of nitrogen-16(N16). These tanks are in series between the letdown isolation valves and the regenerative heat exchanger. They delay the coolant flow by 3.5 minutes (assuming 60 gpm), which is considerably greater than 10 half lives (7.1 seconds) of N16 decay. This permits sufficient time for N16 decay to minimize radiation levels in the auxiliary building. Location: CB 105' inside Bioshield wall. Regenerative Heat Exchanger The regenerative heat exchanger is designed to reduce unnecessary heat losses by heating the charging flow with the letdown flow. Heating the cooler charging flow also reduces the thermal shock on the charging line penetrations into the RCS piping. Letdown flows through the shell side of the heat exchanger, and the charging flows through the tubes. The shell-side inlet temperature is approximately the same as RCS temperature cold leg (TC), and the outlet temperature should be approximately 290F. TE-140, located in the letdown line immediately downstream of the regenerative heat exchanger, provides indication on the main control board (MCB) and alarms at 365F. The regenerative heat exchanger is constructed entirely from austenitic stainless steel and is an all welded construction. Location: CB 105' inside Bioshield wall. Letdown Orifices Three orifices in parallel are located downstream of the regenerative heat exchanger. The letdown flow undergoes a significant drop in pressure when passing through the orifices. With the RCS at 2235 psig, two of the orifices pass 60 gpm each, and the third orifice passes 45 gpm. As RCS pressure drops below 2235 psig, a corresponding decrease in letdown flow occurs. Location: CB 105' outside Bioshield wall. Letdown Orifice Isolation Valves (8149A, B, and C) Each orifice has its own air-operated isolation valve prior to rejoining the common letdown line. By opening different combinations of orifice isolation valves, the operator can control the amount of letdown flow. To open 8149A, B, or C, all of the following conditions must be met: 1. LCV-459 and LCV-460 must be open. 2. Pressurizer level must be greater than 15%. The orifice isolation valves automatically close if any of the following conditions exist: 1. Pressurizer level decreases to less than 15%. (defeated if in "Local" at the HSP") 2. Either LCV-459 or LCV-460 closes. (defeated if in "Local" at the HSP") 3. A Phase A containment isolation signal ("T"-signal) occurs. 4. A loss-of-power or loss-of-air occurs. Location: CB 105' outside Bioshield wall by letdown orifices. Letdown Orifice Outlet Relief Valve (8117) A pressure relief valve (8117) downstream of the letdown orifices protects low pressure piping and protects the letdown heat exchanger from over-pressurization. The capacity of the relief valve exceeds the maximum flow rate through all letdown orifices. The valve setpoint pressure is equal to the tube side design pressure of the letdown heat exchanger (600 psig). Discharge from the valve is directed to the pressurizer relief tank. A temperature sensor (TE-141) indicates on the MCB and actuates an annunciator if the temperature in the line is 165º ± 2ºF (189º on Unit 2). This is indicative of the relief valve opening or leakage past the valve. Location: CB 105' outside Bioshield wall by letdown orifices. Penetration Room Isolation Valves (8175A and B) If a break occurs in the penetration room, two air-operated valves in series isolate the letdown flow on an auxiliary building high room pressure (0.28 to .33 psig). The valves will fail closed on loss-of-power or loss-of-air. Location: CB 105' at penetration 23. Containment Isolation Valve (8152) This valve isolates containment during accident conditions. It closes upon receiving a Phase A containment isolation signal ("T"-signal), and closes on a loss-of-power or loss-of-air. Location: AB 100' Rm 184. BTRS Letdown Reheat Heat Exchanger Supply A 3-inch tap supplies approximately 290F water from the letdown system to the tube side of the BTRS letdown reheat heat exchanger. The letdown reheat heat exchanger is no longer used at FNP. Location: AB 100' Letdown Reheat Divert Valve (TCV-381B; Not in use) TCV 381B controls the amount of flow through the BTRS letdown reheat heat exchanger. This valve maintains the backpressure necessary to force the required amount of water through the letdown reheat heat exchanger tubes. By controlling flow, TCV-381B maintains the proper inlet temperature to the BTRS demineralizers. This valve fails to the open position. TCV-381B has an inlet and outlet isolation valve and also a bypass line to allow continued operation in manual in case TCV-381B becomes inoperable. Location: AB 100' RM 170. BTRS Letdown Reheat Heat Exchanger Return (Not in use) A 3-inch return line (with check valve) from the BTRS letdown reheat heat exchanger taps into the letdown line just downstream of TCV-381B and its bypass line. Location: AB 100'.

The Seal Water System

The seal water system (Figure 4) is that portion of the CVCS which provides high pressure water to the RCP controlled leakage shaft seal assembly. The components and flow paths discussed are typical of all three pumps unless otherwise stated. RCP Seal Injection Line The charging pumps supply approximately 24 gpm to the RCPs (8 gpm per RCP) to cool the lower radial bearing and supply the controlled leakage seals. If the seal water return flowpath is isolated, the Seal Injection flowrate may be reduced to approximately 2 gpm. This common supply header taps off the charging pump discharge header through MOV-8105. This valve is controlled from the MCB and powered from MCC E. MOV-8105 is normally deenergized for Appendix R considerations. Location: AB 100' RM 173 The flow rate of water to the seals is controlled by HCV-186 from the MCB. HCV-186 may also be controlled locally from the HSP via hand indicating controller HIC-186. If local control is selected at the HSP, an annunciator actuates on the MCB. This valve fails open on a loss-of-power or loss-of-air and is provided with a downstream isolation valve. A manual bypass line around 8105 and HCV-186 is provided for maintenance. HCV-186 Location: AB 100' RM 173. Seal Injection Filters Two 5-micron or smaller cartridge filters, located in a parallel flow arrangement filter out particles which might damage the RCP seal faces. Each filter has manual isolation valves, drains, and vents to allow replacement of one filter while the other is in service. In addition, each filter has a high P alarm on the MCB at 20 psid. A filter should be replaced at 20 psid or at a contact radiation level consistent with acceptable doses for filter replacement. These filters are located in the filter rooms on the 139' AB Radside. For Unit 1 only, the seal injection filter manual isolation valves are operated using a torque wrench. The torque values are provided in the SOP. Prior to use, the wrench is verified to be in calibration. (CR 2003000436 ) When operating the Unit 2 seal injection filter isolation valves, the operator hammers them shut or open using the "hammer-blow" type valve operators. Each RCP seal injection supply line taps off a header formed by the filter discharge lines. The seal injection for pump A will be described in the text with the components for pumps B and C in parentheses. Seal Flow Path (Figure 4) Prior to the seal flow path (Figure 4) entering the containment, the flow to RCP A is measured by FT-130 (FT-127, FT-124), which provides local flow indication and flow indication on the MCB. A low flow alarm annunciates at 6.7 gpm. (Normal flow is 8 gpm.) See Figure 18. A manual throttle valve outside of containment initially establishes proper seal flow. A check valve for containment isolation is provided inside containment. A manual isolation valve between the containment wall and the RCP bio-shield wall and two series check valves inside the bio-shield wall complete the isolation arrangement. The seal water injected into the RCP via a 1½-inch flanged connection on the thermal barrier flows into the cavity between the main flange and the thermal barrier. It then flows downward to the vicinity of the radial bearing where it divides into two flow paths. The upward flow travels past the radial bearing and into the seal area, while the remainder flows downward through the thermal barrier labyrinths and past the heat exchanger. At this point, the downward flow acts as a barrier to prevent reactor coolant from entering the radial bearing and seal section of the pump. The injection water lubricates both the radial bearing and seals. A local differential pressure indicator PI-131 (PI-128, PI-125) monitors the P across the labyrinth seal and thermal barrier. Temperature of the water leaving the radial bearing is measured by TE-131 (TE-128, TE-125). The water flowing up past the radial bearing passes through the No. 1 seal. The No. 1 seal bypass line allows a portion of the seal injection to bypass the No. 1 seal. Seal Bypass Line The seal bypass is a ¾-inch line with a flow restricting orifice. The line is used to pass sufficient flow for cooling the radial bearing when RCS pressure is low, thereby allowing RCP operation without bearing overheating. Low RCS pressure presents a problem to radial bearing cooling because as RCS pressure decreases, so does the discharge pressure of the running charging pump. This, in turn, causes a larger percentage of the seal injection flow to make its way downward to the area of the thermal barrier rather than upward through the radial bearing and the No. 1 seal. Opening the No. 1 seal bypass line lowers the total resistance-to-flow between the pump seal injection point and the return line to the VCT. A pressure tap upstream of the No. 1 seal bypass line orifice allows measurement of the P across No. 1 seal. Flow element FE-156 (FE-155, FE-154) provides a low seal bypass flow alarm on the MCB at 1.1 gpm flow. AOV-8142 in the No. 1 seal bypass line common header isolates the individual bypass line from the No. 1 seal return header. This valve may be open when the RCS pressure is below 1000 psig and if normal seal leakoff is below 1 gpm. This will ensure sufficient leakoff to cool the lower radial bearing. The valve must be closed when the P across No. 1 seal is less than 100 psid. This will help to detect a cocked seal during plant pressurization operations. Valve 8142 is designed to fail closed on loss-of-power or loss-of-air and is controlled from the MCB. 8142 Location: CB 105' outside Bioshield wall. No. 1 Seal Leakoff The normal No. 1 seal leakoff is a 2 inch line that has an AOV-8141A (8141B, 8141C), to allow isolation if the leakage across No. 1 seal becomes excessive. A pressure tap upstream of 8141A (8141B, 8141C) measures the No. 1 seal P. PT 156 (155, 154) measures the P across the seal and indicates locally and on the MCB. A low P alarm occurs at 210 psid. These Valves are located at CB RCP cubicles. Flow element FE 156B (155B, 154B) via dual flow transmitters FT 156B (155B, 154B) and FT 156A (155A, 154A), provides both the wide range flow recorder (FR 154A) and narrow range flow recorder (FR 154B) indication on the MCB. FT 156A (155A, 154A) also provides a high flow alarm on the MCB at 5 gpm, while FT 156B (155B, 154B) provides a low flow alarm at 0.95 gpm. Seal Return Header The seal leakoff from each pump ties into a common seal return header, which receives flow from the seal bypass header and the excess letdown header when either of these are being used. Two series MOVs (8112, 8100) are provided for seal return isolation. MOV-8112 is inside containment and has a reverse flow check valve bypass line to relieve pressure that could be built up by thermal expansion. MOV-8100 is outside containment. MOV-8100 and 8112 close upon receiving a "T"-signal. MOV-8100 and 8112 are train-oriented, powered from MCC V and U (respectively), and controlled from the MCB. 8112 located at CB 105' penetration 28. 8100 is located at AB 121' at penetration 28. Seal Water Return Line Relief Relief valve 8121, located upstream of the isolation valves, protects the seal water return piping inside containment from over-pressurization. It is designed to relieve the maximum flow from all seals and maximum excess letdown flow. The valve relieves to the PRT. The valve setpoint is 150 psig. Local temperature indicator TI 133 measures the temperature of the seal water return. Seal Water Return Filter A 25-micron or smaller cartridge filter with manual isolation valves and bypass line (not shown) filters out particulates from the excess letdown and seal return flow. Local pressure indicators PI-134 and PI-135 aid in determining the P across the filter. These filters are located in the filter rooms on the 139' AB Radside. The charging pump miniflow line taps into the flow stream downstream of the return filter. Seal Water Return Line Relief (8123) The Seal Water Return Line Relief (8123) valve (Figures 3 and 21) protects the seal water heat exchangers and its associated piping from over-pressurization. If either of the isolation valves for the seal water heat exchanger are closed and if the bypass line is closed, the piping could be overpressurized by the miniflow from the charging pumps. The valve is sized to handle full miniflow with all charging pumps running. The valve is set to relieve at 150 psig and discharges to the VCT. Seal Water Heat Exchanger The seal water heat exchanger cools the combined flows from RCP seal leakoff, excess letdown, and charging pump miniflow. This flow is through the tube side of heat exchanger. The component cooling water system passes through the shell side and is the cooling medium. Component cooling flow is manually adjusted locally. The seal water heat exchanger has manual isolation valves and a manual bypass (not shown) on the CVCS flow side. Local temperature indication on the outlet is provided by TI 136. The outlet of the seal water heat exchanger normally is routed to the charging pump suction header, but can be manually aligned to the VCT gas space for degassing operations or when excess letdown is being used in lieu of normal letdown. (This flowpath is secured by a locked closed valve in Modes 1-4.) Location: Radside AB 100' RM 170.

The Charging System

Charging Pump Lube Oil Pumps Each charging pump has an attached lube oil pump and an auxiliary lube oil pump. The auxiliary pump ensures adequate lube oil flow for startup and coastdown of the charging pumps. These auxiliary lube oil pumps are controlled from the HSP. In automatic, these pumps will turn on at 10 psig decreasing oil pressure and turn off at 20 psig oil increasing pressure. (U-166177, REA 96-1177) Charging Pump Cooling Water Component cooling water cools the charging pump oil coolers. When the swing pump is shifted from one train to the other, the valves must be manually aligned to shift the CCW supplies to the proper train. At a supply temperature of 100F, the lube oil coolers require 10 gpm, and the gear oil cooler requires 8 gpm. Service Water cools the Charging Pump Room Coolers. Each pump room has its own individual room cooler that starts automatically when the pump starts. These coolers are discussed in OPS-52107B, Aux. Bldg HVAC. Minimum Flow Lines The minimum flow (miniflow) line for each charging pump protects it from running in a shutoff head condition. Each miniflow line contains a check valve (to prevent backflow from a running pump when the pump is idle), a 60 gpm orifice, and a motor-operated isolation valve (8109A, B, or C). The individual miniflow lines join a common header, which contains a motor-operated isolation valve (8106). The combined flow then passes through the seal water heat exchanger and back to the charging pump suction header. During accident conditions the Emergency Response Procedures direct opening/closing of the pump mini flow per the foldout pages. The criteria is established to ensure sufficient cooling is provided to the charging (HHSI) pumps during periods of low pump flow and to ensure that FSAR assumed SI flow rates are delivered to the RCS during the injection phase of an accident. With RCS pressure greater than 1900 psig, the flow through the high head safety injection (HHSI) pump is relatively low, thus requiring the miniflow valves to be open to ensure proper pump heat removal. Less than 1900 psig pump flow should be sufficient to provide proper pump cooling even with the miniflow valves closed. Less than 1300 psig, the miniflow valves are closed to limit pump recirculation flow, thus maximizing pump injection flow. The 1300 to 1900 psig dead band prevents excessive valve cycling by allowing the operator a band where no action is required. An exception to this operation of the miniflow valves requires that they remain closed at all times, under accident conditions, when the charging pumps are being supplied by the RHR pumps. This requirement will eliminate a concern for a potential source for leakage external to containment should the miniflow valves be open during recirculation following a small break LOCA where pressure in the RCS could be greater than 1900 psig. 8109 A, B, C Location: AB 100' 8106 Location: AB 100' Charging Pump Discharge Header The three individual charging pumps are connected to a 4-inch discharge header. The discharge header has two sets of series isolation valves (8132A and B; 8133A and B) which serve the same function as the suction header isolation valves--to isolate the discharge header in the event of a passive failure, and provide train separation for the recirculation phase of a safety injection. The motor operators for these valves have disconnect switches in their control circuits to prevent spurious motion in the event of a fire affecting the control cables. A connection has been added to the discharge header between MOV-8132B and MOV-8133A as required to connect a portable RCS makeup pump as part of FNP's FLEX strategies. The charging pump discharge header can supply water to the following discharge paths: 1. The normal charging line 2. The line to cold leg injection (A train) 3. The line to hot leg injection 4. The line to RCP seal injection 5. The line to cold leg injection (8885) Location: AB 100' RM 181. Charging Line The normal charging line is a 3-inch line tapping off the discharge header of the charging pumps. PT-121 gives charging line pressure indication on the MCB. FT-122 Flow transmitter FT-122 provides local charging line flow indication at the HSP and MCB. FT-122 also provides charging line flow indications to the high and low flow annunciators on the MCB (125 gpm and 23 gpm, respectively), and a feedback signal for FCV-122. See Figure 16. FCV-122 An air-operated flow control valve (FCV-122) controls the charging flow rate. This valve uses a cage type trim assembly to enhance its ability to control flow at a wide range of operation. During normal operation the ΔP across the valve is low. When the plant is shut down with RCS pressure low the ΔP across the valve is high. The high ΔP can cause flow control problems and cavitation at the valve that may damage the valve. Various trim packages have been utilized to correct these problems. Efforts continue to resolve this condition. In the automatic mode, FC-122 controls FCV-122 to maintain the proper flow rate for the required pressurizer level. FC-122 receives inputs from the pressurizer level control circuit and FT-122. In automatic, the flow controller minimum demand (maximum output) corresponds to 18 gpm charging flow (ref. FNP-1/2-IMP-202.20). At ~60 gpm letdown flow, this ensures adequate cooling in the regenerative heat exchanger to prevent flashing downstream of the orifices. If a 60 and 45 gpm orifice are on service, charging flow will have to be approximately 40 gpm to prevent flashing. In manual control on the M/A station, the flow controller minimum demand (maximum output) corresponds to 0 gpm charging flow. The flow controller maximum demand in automatic (minimum output) corresponds to 130 gpm, while in manual control, charging flow can be raised to >150 GPM (off-scale on FI-122). As discussed above, FCV-122 can be controlled from the MCB via the auto-manual controller. When the RCS is at low-pressure conditions care should be taken when operating FCV-122 in manual, due to the high P that may be across the valve (OR 2-98-156). FCV-122 may also be controlled locally from the HSP via hand indicating controller HIC-122. If local control is selected at the HSP, an annunciator actuates on the MCB. FCV-122 fails open on loss-of-power or loss-of-air and has isolation valves and a bypass line for maintenance purposes. In the event of FCV-122 failure, Charging flow may be maintained with a manual bypass, location of the control and bypass valves is AB 100' RM 183. On Unit 2, CHG FLOW REGULATOR BYPASS Q2E21V606 is a Copes Vulcan 2 inch throttle valve. It contains a positioning 'Lock Nut' on the valve stem set to limit the amount of valve movement in the open direction. Attempting to open the valve further after this lock nut contacts the yoke assembly can damage the stem threads. If the lock nut does not allow sufficient valve opening maintenance should be contacted to adjust the lock nut position {CR2001000928}. On a safety injection ("S"-signal), MOV-8108 and 8107 isolate the normal charging line. This forces all injection through the A train cold leg injection path. MOV-8108 and 8107 are train-oriented. 8107 is powered from MCC U, and 8108 is powered from MCC V. They are located at AB 121' RM 223. Downstream of the containment isolation valves MOV-8108 and 8107, the charging flow passes through the tube side of the regenerative heat exchanger. Here, charging flow is heated to approximately 485F prior to its re-entry to the RCS. Temperature element TE-123 on the outlet of the regenerative heat exchanger provides indication on the MCB. The normal charging line branches into three separate flow paths: the normal charging line (which enters loop B cold leg of the RCS), the alternate charging line (which enters loop A cold leg of the RCS), and the auxiliary spray line (which enters the pressurizer via the spray connection). The flow path is selected by opening the appropriate air-operated valve (AOV-8146 for normal charging, 8147 for alternate charging, and 8145 for auxiliary pressurizer spray). Valves 8146 and 8147 fail open, valve 8145 fails closed on loss-of-power or loss-of-air. All are controlled from the MCB. 8146 and 8147 are located at CB 105' outside the Bioshield wall. 8145 is located at CB 105' outside the Bioshield wall. A spring-loaded check valve in the bypass line around the normal charging path isolation valve (AOV-8146) protects the tube side of the regenerative heat exchanger from overpressure due to thermal expansion if the charging path is blocked or isolated and letdown is continued. This check valve will open when the differential pressure across the valve reaches 200 psid. Both the normal and alternate charging lines have two series check valves and enter their respective loops via thermal sleeve connections. The pressurizer auxiliary spray line has one check valve, shares a check valve with normal pressurizer spray and enters the pressurizer via a thermal sleeve connection.

DETAILED DESCRIPTION

Design Bases The main functions of the CVCS include the following: 1. Reactor coolant purification and chemistry control 2. Reactor coolant inventory regulation 3. Reactivity control 4. Seal water injection 5. Emergency core cooling (High Head Safety Injection) Reactor Coolant Purification and Chemistry Control During power operation, the CVCS continuously removes fission and activation products from the RCS (except for tritium). It removes these contaminants whether they are in ionic or particulate form. Lowering the activity level in the RCS reduces the activity level in the associated piping and reduces the activity levels in the radiation controlled area (RCA) caused by minor leaks. As a result, the radiation exposure received by radiation workers is lowered. The CVCS is used to control RCS pH and chemistry. Adding lithium hydroxide to the CVCS initially establishes the reactor coolant pH. However, excess lithium is formed during power operation and must be removed by the CVCS in order to keep a proper pH in the RCS. In addition, radiolysis of the reactor coolant during power operation increases the oxygen concentration in the RCS and must be removed by adding hydrogen gas to the RCS via the VCT. Hydrazine is added to the RCS prior to a plant startup from a cold shutdown in order to remove large amounts of oxygen not removed by the VCT burping process. Chemical Control, Purification, and Makeup The CVCS provides the following for the chemical, purification, and makeup requirements of the RCS: 1. A means of adding and removing pH control chemicals for startup and normal operation 2. A means of controlling the oxygen concentration following system venting and for controlling oxygen produced from radiolysis 3. A means of purification to remove corrosion, activation, and fission products 4. A means of adding and removing soluble boron and makeup water in concentrations and rates compatible with all phases of plant operation pH Control The chemical control element used for pH control (Figures 3 and 21) is lithium hydroxide (LiOH). This chemical is chosen for its compatibility with the materials and water chemistry of a system that contains borated water, stainless steel, and zirconium. LiOH enters the RCS through the charging flow. It is poured into the chemical mixing tank and then flushed to the suction manifold of the charging pumps by reactor makeup water. The concentration of LiOH in the RCS is maintained between 0.2 to 4.36 ppm LiOH. As the lithium concentration increases during the early stages of core life, the nonlithiated mixed bed demineralizer or the Cation demineralizer is valved in to remove excess lithium from the letdown. Oxygen Control During plant startup from a cold shutdown condition, hydrazine is added as an oxygen scavenging agent. Hydrazine is not used at any time other than startup from the cold shutdown condition. The hydrazine solution enters the RCS in the same manner as LiOH. In order to control and scavenge oxygen produced by radiolysis of water in the core region, hydrogen from the waste processing system (plant bulk gas systems) is added to the VCT to maintain a hydrogen concentration of 25 to 50 cc/kg of reactor coolant. The pressure is regulated by adding hydrogen manually or venting the excess gas to a Gas Decay Tank. A pressure regulating valve may be used to automatically maintain a desired pressure in the VCT. Purification Three demineralizers--two mixed bed demineralizers and one cation bed demineralizer--clean up the letdown flow. They remove activation products, certain fission products, and also serve as filters. One mixed bed demineralizer is usually in continuous service for normal letdown and can be supplemented intermittently by the cation bed demineralizer to remove isotopes present due to fuel cladding defects. The on service Mixed Bed is lithiated, so as not to remove lithium from the RCS. The Cation Bed is valved in to remove lithium per chemistry instructions. Cesium and yttrium are the principal isotopes associated with cladding failure. The cation bed demineralizer has the sufficient capacity to maintain the cesium concentration in the RCS below 1.0 μc/cc with 1% defective fuel. The mixed bed resin was changed out each fuel cycle in the past. Currently, the resin is changed out based on the decontamination factor (DF) of the bed. The beds are changed out when the DF decreases below a value of 10. The "B" Mixed Bed is currently (as of October, 2006 JED) used for the crud-burst clean-up at the beginning of each unit's outage, and is not used during the course of a cycle. The design life for the cation bed demineralizer varies with plant operation. Each mixed bed demineralizer is sized to accept the maximum letdown flow (135 gpm), while the cation bed demineralizer is sized to accept 60 gpm. During residual heat removal (RHR) system operation, a portion of the RHR flow is admitted into the letdown line upstream of the letdown heat exchanger. This allows for RCS cleanup during low pressure conditions. The letdown passes through the letdown heat exchanger, a mixed bed demineralizer, the reactor coolant filter, and the VCT. (During RHR operation, the VCT has a nitrogen blanket instead of a hydrogen blanket.) The letdown then returns to the RCS via the normal charging path. The demineralizer resins are depleted or spent when the bed Decontamination Factor reaches a certain level. In order to change out the resin beds, the spent resins are flushed to the spent resin storage tank in the waste processing system. Filters in the CVCS ensure filtration of particulate and resin fines to protect the seals on the RCPs. SOP-2.5 cautions the operator to slowly valve in a demineralizer to minimize flow and pressure oscillations in the Letdown system that can cause RCS filter clogging and increased dose rates. (CR 2003003587) When changing the on-service Demineralizer, the Demineralizer must be checked for the proper Boron concentration (matches existing RCS boron.) A Demineralizer will have the same concentration of Boric Acid as the RCS when the bed was last on-service. This can cause a boration or a dilution. If the difference is too great, the Demineralizer bed must be flushed with RCS water prior to being placed on-service. Reactor Makeup and Chemical Shim The reactor makeup control system controls the normal makeup to the RCS. Reactor makeup water (from the RMWST) and boric acid solution (from the boric acid tanks) is mixed to match the current boron concentration of the RCS. In addition, the boron concentration--boration or dilution--also may be changed through the reactor makeup control system. The RMWST stores deaerated, demineralized water for normal makeup requirements. Also, 4 weight percent (w/o) boric acid solution is prepared in a batching tank and stored in the boric acid tanks (BATs). Upon demand, the reactor makeup control system initiates the following: 1. The reactor makeup water pumps deliver water from the RMWST to the suction of the charging pumps. 2. One of the two boric acid transfer pumps delivers boric acid solution from the BATs to the suction of the charging pumps. The reactor makeup water and boric acid solution combine to provide the pre-established boron concentration in the RCS. The reactor makeup control system also dilutes and borates the RCS upon demand. When dilution is required, reactor makeup water from the RMWST enters the top of the VCT. For a more rapid dilution of the RCS, reactor makeup water simultaneously enters the top of the VCT and the suction of the charging pumps. When boration is required, a pre-selected quantity of boric acid solution at a pre-selected flow rate flows directly from the BAT to the suction of the charging pumps. An emergency boration flow path sends boric acid solution from the BAT to the suction of the charging pumps via the emergency borate valve MOV (8104) or manual emergency borate valve 8439. When a Unit is in the process of shutting down the plant and cooling it down, procedural guidance exists to align the Charging Pump Suction to the RWST. This line-up allows the Pressurizer level to be controlled on program and also increases the RCS boron concentration at the same time. However, when small changes of the boron concentration are needed in the RCS at low RCS boron concentrations, the BTRS may be used. The BTRS changes the boron concentration without requiring makeup for dilution. Instead, the BTRS uses demineralizers to remove boron from the RCS. The RCS letdown flows through the BTRS demineralizers where boron is removed. Reactor makeup and the BTRS are discussed in detail in the following lesson plans: Reactor Makeup and Chemical Addition system and Boron Thermal Regeneration system. Reactor Coolant Inventory Regulation The CVCS keeps the coolant inventory in the RCS within the allowable pressurizer level range for all modes of operation including startup from cold shutdown, full power operation, and plant cooldown. The CVCS also has sufficient makeup capacity to maintain the minimum required inventory in the event of minor RCS leaks. The CVCS flow rate is based on the following requirement: that the RCS can be heated or cooled from hot standby at the design rate while maintaining the pressurizer level within the limits of its operating band. Reactivity Control The CVCS regulates the boron concentration in the reactor coolant to control reactivity changes. Reactivity changes result for a variety of reasons, such as variations in reactor coolant and fuel temperatures between cold shutdown and full power operation, burn-up of fuel and burnable poisons, and xenon transients. Seal Water Injection The CVCS continuously supplies 8gpm of filtered water to each reactor coolant pump seal. During normal operations, flow is divided at the seal package, 3gpm flows up through the #1 seal and 5gpm flows down past the thermal barrier heat exchanger into the RCS. Emergency Core Cooling The charging pumps serve as the high head safety injection pumps (HHSI) in the emergency core cooling system (ECCS). The charging pumps and their associated piping and valves, including RCP seal injection, are the only portions of the CVCS that function during a LOCA. The remaining portions of the CVCS are isolated.

GENERAL DESCRIPTION

During power operation, the RCS is continuously fed and bled. Water is bled from the RCS and flows through the regenerative heat exchanger where it gives up its heat to the water being fed to the RCS. The bleeding is referred to as letdown, and the feeding is referred to as charging. By using this regenerative process, the heat loss from the RCS is minimized. The letdown then flows through orifices, which drop the pressure of the letdown stream well below the operating pressure of the RCS. Further cooling occurs in the letdown heat exchanger, which is cooled by component cooling water (CCW). A second pressure reduction then occurs across the letdown pressure control valve. The chemistry of the letdown flow, and thus the RCS, may be improved by passing the flow through demineralizers that remove ionic impurities. The reactor coolant filter removes nonionic particulate matter, and unwanted gases are removed in the volume control tank (VCT). The water sprayed into the VCT collects temporarily in the tank before returning to the RCS. The VCT serves as a surge volume for the CVCS and accommodates small fluctuations in system flow. In doing so, it also serves as a surge volume for the RCS. The VCT provides suction for the charging pumps to ensure that they have a steady supply of water. The charging pumps take the reactor coolant from the VCT and send it along two parallel paths (1) directly to the RCS through the regenerative heat exchanger and (2) to the shaft seals of the RCPs. The major portion of the seal flow re-enters the RCS, and the seal leakage re-enters the CVCS via the seal water heat exchanger, which returns to the charging pump suction to complete the flow path. An alternate (or excess) letdown path from the RCS is provided in the event that the normal letdown path is inoperable. When the alternate letdown path is being used, it is cooled by the excess letdown heat exchanger. The excess letdown heat exchanger uses CCW as its cooling medium. The excess letdown flow normally joins the RCP seal water return and passes through the seal water heat exchanger for additional cooling. However, excess letdown flow also can be directed to the reactor coolant drain tank (RCDT). Surges from the RCS, such as when charging flow is less than letdown flow, accumulate in the VCT until a high water level causes the flow to be diverted to the on-service RHT. The RHTs are designed to store the diverted liquid for reuse or disposal. Makeup water for the CVCS, and ultimately for the RCS, comes from two sources: 1. The reactor makeup water storage tank (RMWST) 2. The refueling water storage tank (RWST) The RMWST, a demineralized and deaerated water supply, is the normal source of reactor makeup water. When demineralized water is added to the RCS, it dilutes the boron concentration in the RCS. In order to match the current boron concentration in the RCS, the demineralized water is mixed with a boric acid solution. Chemicals also can be added to the reactor makeup water via the chemical mixing tank. The boric acid tanks (BATs) also provide a source of RCS makeup via the Boric Acid Transfer System. This is done at power when plant conditions dictate the addition of negative reactivity to control reactor power and RCS temperature. The RWST contains 2300 ppm borated water and is an emergency source of reactor makeup water. When added during an emergency, the high concentration of borated water in the RWST greatly increases the boron concentration of the RCS. An additional flow path downstream of the purification demineralizers directs the letdown through the boron thermal regeneration system (BTRS) used for boron concentration changes required during late in core life boron concentration changes. The best use of BTRS is during periods of low boron concentrations such as late in core life. In the event of a LOCA, the charging pumps supply high pressure water to the RCS. The suction of the charging pumps will automatically divert from the VCT to the RWST. The discharge of the charging pumps will realign to inject flow to the RCS cold legs. Aligning the charging pumps to the RWST ensures an immediate supply of water to the RCS and a rapid establishment of adequate core shutdown margin. The major portion of the CVCS is located in the auxiliary building, and the remainder is located inside containment. Normal CVCS operating parameters are shown on Figure 2. Note the large temperature and pressure changes throughout the system.

INTRODUCTION

The CHEMICAL AND VOLUME CONTROL system (CVCS), as its name implies, provides CHEMICAL AND VOLUME CONTROL of the reactor coolant system (RCS). The main functions of the CVCS are as follows: 1. Reactor coolant purification (including removal of fission products, activation products, and impurities) and chemistry control (resulting in minimal corrosion of the RCS) 2. Reactor coolant inventory regulation through addition of reactor makeup water 3. Reactivity control by adjustment of boron concentration 4. Seal water injection 5. Emergency core cooling (High Head Safety Injection) As fission products and activation products (from corrosion and erosion of the RCS) build up, the reactor coolant contains more contamination. The CVCS keeps the RCS within acceptable limits by (1) reducing corrosion through chemical control and (2) removing radioactive products and impurities through demineralizers. Furthermore, the CVCS supplies reactor makeup water needed because of losses due to minor leaks, evaporation, and reactor coolant pump (RCP) seal injection. (The RCP seals continuously receive filtered water from the CVCS.) In addition, the CVCS adjusts the boron concentration of the RCS during all phases of plant operation and also provides an emergency boration path. A separate system, the Zinc Addition System (ZAS), adds soluble zinc to the RCS to reduce stress corrosion cracking and displace Cobalt-60. This reduces dose rates from the RCS, especially during outages. The system, like the Reactor makeup Control System, interconnects with the CVCS system (Fig. 1). Lastly, during a loss of coolant accident (LOCA), the CVCS provides an immediate source of high pressure water to keep the reactor core cooled.

The Charging System

The charging system (Figures 3 and 21) is that portion of the CVCS where the pressure and temperature of the reactor coolant are increased before returning it to the RCS. First, the pressure in the charging system is raised above RCS pressure by the charging pumps. (The charging system pressure is dependent on the flow demanded by the operator or required by the pressurizer level control system). Next, the regenerative heat exchanger returns a large portion of the heat to the charging stream that was lost to the letdown system. Charging System Makeup Line The makeup line for the charging system starts at the outlet of the boric acid blender and terminates at the VCT outlet. When in automatic or borate modes of reactor makeup control, this line sends the proper concentration of boric acid to the charging pump suction. When in alternate dilute mode of control, this line sends reactor makeup water to the charging pump suction. This makeup line is a 2-inch line. Charging Pump Suction from VCT Isolation Valves LCV-115C and LCV-115E These two valves ensure that the suction of the charging pumps from the VCT isolates on a safety injection signal. The series arrangement of the valves satisfies the design criteria for safety injection system active failures. When a Lo-Lo level in the VCT is reached as detected by both LT-112 and LT-115 or an "S"-signal is present, LCV-115C will close after the charging pump suction valve (LCV-115B) from the RWST opens. LCV-115E responds to the same control signals but must have valve 115D open before it will shut. Emergency suction from the RWST will be procedurally maintained until plant conditions meet ERG criteria, at which time realignment to the VCT is allowed. LCV-115C and LCV-115E are train-oriented and powered from MCC U and MCC V, respectively. These valves are controlled from the MCB. Location: AB 121' RM 217. Seal Water Heat Exchanger Normal Return The normal return for the seal water heat exchanger taps into the charging pump suction header downstream of LCV-115C and LCV-115E. Typically, the flow from the heat exchanger consists of the No. 1 seal water return from the RCPs and the minimum flow from the running charging pumps. When excess letdown is in service, the flow from the excess letdown heat exchanger also enters the seal water heat exchanger. Using the seal water return line, the recycle evaporator feed pumps can pump the contents of the RHTs directly to the charging pump suction header. The feed pumps discharge into the seal water return line downstream of the seal water heat exchanger. Charging Pump Suction Header The 8-inch charging pump suction header serves the three charging pumps. Two sets of motor operated valves (8130A and B; 8131A and B) isolate the header in the event of a passive failure and provide train separation for the recirculation phase of safety injection. These valves are train-oriented and are powered from MCC U and MCC V. They are controlled from the MCB. The motor operators for these valves have disconnect switches in their control circuits to prevent spurious motion in the event of a fire affecting the control cables. Location: AB 100' RM 175. Chemical Mixing Tank to Charging Pump Suction The discharge line from the chemical mixing tank to the charging pump suction provides a method of adding chemicals to the RCS for chemistry control. A check valve prevents backflow from the charging pumps when chemicals are being added to the chemical mixing tank or during emergency boration. Chemical Mixing Tank location: AB 100' RM 175. Charging Pump Suction from RWST The charging pump suction header has two separate connections from the RWST via LCV-115B and LCV-115D. These valves open on a safety injection signal or on a Lo-Lo level of 5% in the VCT as detected by both LT-115 and LT-112. These valves are train-oriented and are powered from MCC U and MCC V. They are controlled from the MCB. Location: AB 100' RM 172. Charging Pump Suction from RHR Heat Exchanger Outlet Redundant supplies to the charging pump suction header from the outlet of the RHR heat exchangers are provided for use during the recirculation phase of safety injection. The motor-operated valves (MOVs) used for this are covered in detail in the Residual Heat Removal system lesson plan. Emergency Boration Lines Two emergency boration flow paths to the charging pump suction exist. One path is through the emergency borate valve (MOV-8104), it is controlled from the MCB and is located in the charging pump hallway near the CTMT ledge. The other path is through the manual emergency borate valve (8439), it is located near the boric acid blender. FT-110 gives local and MCB flow indication for 8104, and MCB flow recorder FR-113 records flow for 8439. Charging Pumps Suction Header Relief Valves (8116A and B) These valves (not shown) protect the charging pump suction header from overpressurization. They lift at 220 psig and relieve to the pressurizer relief tank (PRT). The relief setpoint is chosen to prevent actuation during the recirculation phase of safety injection. Charging Pumps The charging pumps are dual purpose pumps. Under normal operating conditions, one pump will be running to provide direct flow to the RCS via the charging line and to provide seal water injection to the RCP seals. In the event of a safety injection signal, the charging pumps assume the role of high head safety injection pumps and inject RWST water into the RCS. During a safety injection, the charging pumps continue to supply seal water injection to the RCPs. The pumps are 11-stage pumps and rated for a flow of 150 gpm at approximately 2500 psig. They are driven by 900-hp, 4160-volt motors, which are powered as follows: Charging Pump Power Supply A 4160V F B 4160V F or G C 4160V G The charging pumps are normally controlled from the MCB and can be controlled locally from the hot shutdown panel (HSP). Each charging pump has local suction and discharge pressure indication, a minimum flow line, a discharge check valve, and manual isolation valves.