PASSIVE CONTAINMENT COOLING SYSTEM 5.2-1
TABLE OF CONTENTS5.2PASSIVE CONTAINMENT COOLING SYSTEM . 5.2-15.2.1 Introduction . 5.2-15.2.2 System Description . 5.2-15.2.3 Component Descriptions . 5.2-35.2.3.15.2.3.2Passive Containment Cooling Water Storage Tank . 5.2-3Passive Containment Cooling Water Storage Tank IsolationValves . 5.2-45.2.3.3 Flow Control Orifices . 5.2-45.2.3.4 Water Distribution Bucket . 5.2-45.2.3.5 Water Distribution Weir System . 5.2-55.2.3.6 Containment Air Baffle . 5.2-55.2.3.7 Passive Containment Cooling Ancillary Water Storage Tank . 5.2-75.2.3.8 Chemical Addition Tank . 5.2-75.2.3.9 Recirculation Pumps . 5.2-75.2.3.10 Recirculation Heater . 5.2-75.2.4 System Performance . 5.2-75.2.4.15.2.4.2Safety Design Basis. 5.2-7System Operation . 5.2-85.2.5 Summary . 5.2-10LIST OF TABLES5.2-1 Passive Containment Cooling System Performance Parameters . 5.2-115.2-2 Component Data – Passive Containment Cooling System (Nominal) . 5.2-12LIST OF FIGURESSimplified Sketch of Passive Containment Cooling System . Fig. 5.2-1Containment and Shield Buildings with Passive Cooling Effects. Fig. 5.2-2USNRC HRTD5.2-iRev 0111
5.2PASSIVE CONTAINMENT COOLING SYSTEMLearning Objectives:1. State the purpose of the passive containment cooling system.2. Describe how the system cools the containment atmosphere.3. Describe how the following components and features contribute to thecontainment cooling function:a.b.c.d.e.f.Passive containment cooling water storage tankPassive containment cooling water storage tank isolation valvesWater distribution bucketWater distribution weir systemContainment air bafflePassive containment cooling ancillary water storage tank5.2.1 IntroductionThe passive containment cooling system (PCS) is an engineered safety featuressystem. Its functional objective is to reduce the containment temperature andpressure following a loss-of-coolant accident (LOCA) or main steam line break(MSLB) accident inside the containment by removing thermal energy from thecontainment atmosphere. The passive containment cooling system also serves asthe means of transferring heat to the safety-related ultimate heat sink for otherevents resulting in a significant increase in containment pressure and temperature.The passive containment cooling system limits releases of radioactivity (postaccident) by reducing the pressure differential between the containment atmosphereand the external environment, thereby diminishing the driving force for leakage offission products from the containment to the atmosphere. This subsection describesthe safety design bases of the safety-related containment cooling function. Nonsafety-related containment cooling is a function of the containment recirculationcooling system.The passive containment cooling system also provides a source of makeup water tothe spent fuel pool in the event of a prolonged loss of normal spent fuel pool cooling.5.2.2 System DescriptionThe passive containment cooling system is a safety-related system which is capableof transferring heat directly from the steel containment vessel to the environment.This transfer of heat prevents the containment from exceeding the design pressureand temperature following a postulated design-basis accident. The passivecontainment cooling system makes use of the steel containment vessel and theconcrete shield building surrounding the containment. The major components of thepassive containment cooling system are:USNRC HRTD5.2-1Rev 0111
The passive containment cooling water storage tank (PCCWST), which isincorporated into the shield building structure above the containment;Redundant piping with fail-open isolation valves for delivery of the PCCWSTcontents to the containment vessel;A water distribution system, mounted on the outside surface of the steelcontainment vessel, which functions to distribute water flow on thecontainment;An air baffle, located between the steel containment vessel and the concreteshield building, which defines the cooling air flowpaths; andAir inlets and an air exhaust, also incorporated into the shield buildingstructure.The air inlets, baffle, and exhaust define a natural-circulation air flow path; thecontainment vessel water film transfers energy to the circulating air via convectionand evaporation. In addition, a passive containment cooling ancillary water storagetank and two recirculation pumps are provided for onsite storage of additionalpassive containment cooling system cooling water, to transfer the inventory to thepassive containment cooling water storage tank, and to provide a backup supply tothe fire protection system (FPS) seismic standpipe system.A normally isolated, manually-opened flow path is available between the passivecontainment cooling system water storage tank and the spent fuel pool.A recirculation path is provided to control the passive containment cooling waterstorage tank water chemistry and to provide heating for freeze protection. Passivecontainment cooling water storage tank filling operations and normal makeup needsare provided by the demineralized water transfer and storage system.The safety-related portions of the passive containment cooling system are locatedwithin the shield building structure. This building (including the safety-relatedportions of the passive containment cooling system) is designed to withstand theeffects of natural phenomena such as earthquakes, winds, tornadoes, or floods.Components of the passive containment cooling system are designed to withstandthe effects of ambient temperature extremes.The portions of the passive containment cooling system which provide a long-term(post-72-hour) water supply for containment wetting are located in Seismic CategoryI or Seismic Category II structures, excluding the passive containment ancillarywater storage tank and associated valves located outside of the auxiliary building.The water storage tank and the anchorage for the associated valves are SeismicCategory II. The features of these structures which protect this function areanalyzed and designed for Category 5 hurricanes including the effects of sustainedwinds, maximum gusts, and associated wind-borne missiles.Operation of the containment cooling system is initiated automatically following thereceipt of a Hi-2 containment pressure signal. The use of this signal provides forsystem actuation during transients which result in mass and energy releases tocontainment, while avoiding unnecessary actuations. System actuation requires theopening of any of the three PCCWST isolation valves, with no other actions requiredto initiate the post-accident heat removal function since the cooling air flow path isUSNRC HRTD5.2-2Rev 0111
always open. Operation of the passive containment cooling system may also beinitiated from the main control room and from the remote shutdown workstation.The active components of the passive containment cooling system, the isolationvalves, are located in three redundant pipe lines. Failure of a component in onetrain does not affect the operability of the other mechanical train or the overallsystem performance. The fail-open, air-operated valves require no electrical powerto move to their safe (open) position. The normally open motor-operated valves arepowered from separate redundant Class 1E dc power sources.Capability is provided to periodically test actuation of the passive containmentcooling system. Active components can be tested periodically during plant operationto verify operability. The system can be inspected during unit shutdown.There are four instrument lines that penetrate containment and are required toremain functional following an accident; they are used to sense the pressure of thecontainment atmosphere and to convey it to pressure transmitters outsidecontainment. The pressure transmitters, tubing, and pressure sensors insidecontainment comprise a sealed, fluid-filled assembly forming a double barrierbetween inside and outside containment. Possible instrument line breaks do notresult in leakage of the containment atmosphere. The pressure sensors, tubing, andpressure transmitters are designed and tested for seismic Category I service.The containment pressure analyses are based on an ambient air temperature of115 F dry bulb and 86.1 F coincident wet bulb. The passive containment coolingwater storage tank water temperature basis is 120 F. Results of the analyses areprovided in subsection 5.1.System parameters are listed in Table 5.2-1. A simplified system sketch is includedas Figure 5.2-1.5.2.3 Component DescriptionsTable 5.2-2 provides component design parameters.5.2.3.1Passive Containment Cooling Water Storage TankThe passive containment cooling water storage tank is incorporated into the shieldbuilding structure above the containment vessel. The inside wetted walls of the tankare lined with stainless steel plate. It is filled with demineralized water and has theminimum required usable volume for the passive containment cooling function, asshown in Table 5.2-1. The passive containment cooling system functions as thesafety-related ultimate heat sink. The passive containment cooling water storagetank is seismically designed and missile protected.The surrounding reinforced concrete supporting structure is designed to ACI 349.The welded seams of the plates forming part of the leak-tight boundary areexamined by liquid penetrant testing after fabrication to confirm that the boundarydoes not leak.USNRC HRTD5.2-3Rev 0111
The tank also has redundant level measurement channels and alarms for monitoringthe tank water level and redundant temperature measurement channels to monitorand alarm for potential freezing. To maintain system operability, a recirculation loopthat provides chemistry and temperature control is connected to the tank.The tank is constructed to provide sufficient thermal inertia and insulation such thatdraindown can be accomplished without heater operation.In addition to its containment heat removal function, the passive containment coolingwater storage tank also serves as a source of makeup water to the spent fuel pooland as a Seismic Category I water storage reservoir for fire protection following asafe shutdown earthquake.The PCCWST suction pipe for the fire protection system is configured so thatactuation of the fire protection system will not infringe on the usable capacityallocated to the passive containment cooling function, as shown in Table 5.2-1.5.2.3.2Passive Containment Cooling Water Storage Tank IsolationValvesThe passive containment cooling system water storage tank outlet piping isequipped with three sets of redundant isolation valves. In two sets, air-operatedbutterfly valves are normally closed and open upon receipt of a Hi-2 containmentpressure signal. These valves fail open, providing a fail-safe position, on the loss ofair or the loss of Class 1E dc power. In series with these valves are normally openmotor-operated gate valves located upstream of the butterfly valves. They areprovided to allow for testing or maintenance of the butterfly valves. The third setconsists of two motor-operated gate valves in series. One valve is normally closed,and the other is normally open. Based on PRA insights, diversity requirements areadopted for these valves to minimize the probability of common-mode failure.The storage tank isolation valves, along with the passive containment cooling waterstorage tank discharge piping and associated instrumentation between the passivecontainment cooling water storage tank and the downstream side of the isolationvalves, are contained within a temperature-controlled valve room to prevent freezing.Valve room heating is provided to maintain the room temperature above 50 F.5.2.3.3Flow Control OrificesOrifices are installed in each of the four passive containment cooling water storagetank outlet pipes. They, along with the different elevations of the outlet pipes, controlthe flow of water from the passive containment cooling water storage tank as afunction of water level. The orifices are located within the temperature-controlledvalve room.5.2.3.4Water Distribution BucketA water distribution bucket is provided to deliver water to the outer surface of thecontainment dome. The redundant passive containment cooling water deliverypipes and auxiliary water source piping discharge into the bucket, below itsUSNRC HRTD5.2-4Rev 0111
operational water level, to prevent excessive splashing. A set of circumferentiallyspaced distribution slots are included around the top of the bucket. The bucket ishung from the shield building roof and suspended just above the containment domefor optimum water delivery. The structural requirements for safety-related structuralsteel apply to the water distribution bucket.5.2.3.5Water Distribution Weir SystemA weir-type water delivery system is provided to optimize the wetted coverage of thecontainment shell during passive containment cooling system operation. Water isdelivered to the center of the containment dome by the water distribution bucket,evenly distributed by slots in the distribution bucket. Vertical divider plates attachedto the containment dome originate at the distribution bucket and extend radiallyalong the surface of the dome to the first distribution weir. The divider plates limitmaldistribution of flow, which might otherwise occur due to variations in the slope ofthe containment dome. At the first distribution weir set, the water in that sector iscollected and then redistributed onto the containment utilizing channeling walls andcollection troughs equipped with distribution weirs. A second set of weirs is installedon the containment dome at a greater radius to again collect and then redistributethe cooling water to enhance shell coverage. The distribution system is capable offunctioning during extremely low or high ambient temperature conditions. Thestructural requirements for safety-related structural steel and cold-formed steelstructures apply to the water distribution weir system.5.2.3.6Containment Air BaffleAn air flow path is provided to direct air along the outside of the containment shell toprovide containment cooling. The air flow path includes a screened shield buildinginlet, an air baffle that divides the outer and inner flow annuli, and a chimney toincrease buoyancy.The containment air baffle is located within the upper annulus of the shield building,providing an air flow path for the passive containment cooling system. The air baffleseparates the downward air flow entering at the air inlets from the upward air flowthat cools the containment vessel and flows out of the discharge stack. The upperportion is supported from the shield building roof and the remainder is supportedfrom the containment vessel. The air baffle is a Seismic Category I structuredesigned to withstand wind and tornadoes. The baffle includes the followingsections: A wall supported off the shield building roof,A series of panels attached to the containment vessel cylindrical wall and theknuckle region of the dome,A sliding plate closing the gap between the wall and the panels fixed to thecontainment vessel, designed to accommodate the differential movementsbetween the containment vessel and the shield building, andFlow guides attached at the bottom of the air baffle to minimize pressuredrop.The air baffle is designed to meet the following functional requirements:USNRC HRTD5.2-5Rev 0111
The baffle and its supports are configured to minimize pressure losses as airflows through the system.The baffle and its supports have a design objective of 60 years.The baffle and its supports are configured to permit visual inspection andmaintenance of the air baffle as well as the containment vessel. Periodicvisual inspections are primarily to inspect the condition of the coatings.The baffle is designed to maintain its function during postulated design-basisaccidents. The baffle is designed to maintain its function under specifiedexternal events, including earthquakes, hurricanes and tornadoes.The portion of the air baffle attached to the containment cylinder comprises 60panels circumferentially in each of seven rows vertically, with each panel subtendingan arc of six degrees (approximately 6 ft, 11 in. wide). Each panel is supported byhorizontal beams spaced approximately 13 ft, 8 in. apart. These horizontal beamsspan the six-degree arc and are bolted to U-shaped attachments welded to thecontainment vessel. The attachment locations are established considering thecontainment vessel plate and ring assemblies. The lowest attachments are at thebottom of the middle containment ring subassembly. The upper attachments are onthe head. The attachments can be installed in the subassembly area and, therefore,should not interfere with the containment vessel erection welds. The onlypenetrations through the containment vessel above the operating deck at elevation135′ 3″ are the main equipment hatch and personnel airlock. Five panels aredeleted at the equipment hatch, and two flow guides are deleted at the personnelairlock.Two rows of panels are attached to the containment vessel above the cylindricalportion. The panels are curved to follow the curvature of the knuckle region of thehead and then become flat, forming a conical baffle that provides a transitional flowregion into the upper shield building. A vertical sliding plate is provided between thisupper row of panels and the air baffle that is attached directly to the shield buildingroof. This sliding plate rests on the 12-in.-wide horizontal top surface of the upperrow of panels. At ambient conditions the vertical sliding plate is approximatelycentered on the horizontal plate. The sliding plate is set at ambient conditions topermit relative movements from minus two in. to plus three in. radially and minusone in. to plus four in. vertically. This accommodates the differential movementbetween the containment vessel and the shield building, based on the absolute sumof the containment pressure and temperature deflections and the seismicdeflections, such that the integrity of the air baffle is maintained.The panels accommodate displacements between each panel due to containmentpressure and thermal growth. Radial and circumferential growth of the containmentvessel is accommodated by slip at the bolts between the horizontal beams and theU-shaped attachments, resulting in small gaps between adjacent panels. Verticalgrowth is accommodated by slip between the panel and the horizontal beamsupporting the top of the panel. Cover plates between the panels limit leakageduring and after occurrence of these differential displacements.USNRC HRTD5.2-6Rev 0111
5.2.3.7Passive Containment Cooling Ancillary Water Storage TankThe passive containment cooling ancillary water storage tank is a cylin
A recirculation path is provided to control the passive containment cooling water storage tank water chemistry and to provide heating for freeze protection. Passive containment cooling water storage tank filling operations and normal makeup needs are provided by the demineralized water transfer and storage system.
DIRECT-PLUMBED Containment Tanks Models 2478SQ-NA-DP 1100Lb/150Gal Containment Tank 3072-NA-DP 1500Lb/200Gal Containment Tank 4280-NA-DP 2650Lb/353Gal Containment Tank. About this manual Read this manual for the following information about inside Direct-Plumbed containment tanks:
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