Essential service water (ESW)

Essential Service Water System
[Name of the Writer]
[Name of the Institution]

Table of Contents
TOC o “1-5” h z u Introduction PAGEREF _Toc463978094 h 4Purpose and Function of Essential Service Water PAGEREF _Toc463978095 h 4Components of Essential Water System PAGEREF _Toc463978096 h 5The Intake Components PAGEREF _Toc463978097 h 9Travelling Screens PAGEREF _Toc463978098 h 9Screen Wash Pump PAGEREF _Toc463978099 h 10Stop Gates PAGEREF _Toc463978100 h 10Essential Service Water Pump PAGEREF _Toc463978101 h 10Bar Screens PAGEREF _Toc463978102 h 13Essential Service Water Debris Filters PAGEREF _Toc463978103 h 13Vacuum Relief Valve PAGEREF _Toc463978104 h 14Expansion Joint (Bellow) PAGEREF _Toc463978105 h 14Check Valve PAGEREF _Toc463978106 h 15Importance of Essential Service Water to Plant Safety PAGEREF _Toc463978107 h 15Significant Design Basis for the Essential Service Water PAGEREF _Toc463978108 h 18Operations of Essential Service Water System PAGEREF _Toc463978109 h 20Normal Operating Condition PAGEREF _Toc463978110 h 20Abnormal Operating Conditions PAGEREF _Toc463978111 h 21Conclusion PAGEREF _Toc463978112 h 22References PAGEREF _Toc463978113 h 24Appendix PAGEREF _Toc463978114 h 25Appendix A: Open-once Configuration (Nuclear Regulatory Commission, 1992) PAGEREF _Toc463978115 h 25Appendix B: Open-recirculating Configuration (Nuclear Regulatory Commission, 1992) PAGEREF _Toc463978116 h 26Appendix C: Closed Configuration (Nuclear Regulatory Commission, 1992) PAGEREF _Toc463978117 h 27

List of Figures
TOC h z c “Figure” Figure 1: Components of ESW (Nuclear Regulatory Commission, 1992). PAGEREF _Toc463976369 h 4Figure 2: Intake ESW System PAGEREF _Toc463976370 h 6Figure 3: Vertical Single Stage Semi-Axial Pump (Gülich, 2014). PAGEREF _Toc463976371 h 8

Essential Service Water System
IntroductionThe essential service water is a core part of the nuclear power plants as it requires massive heat load to be removed from the system. Hence, it serves as a critical safety parameter in case of plant’s equipment or process anomaly. In some literature, essential service water system is also referred to as service water system because of a vast variety of applications in system designs as well as nature of ultimate heat sink. Apart from that, it includes different types of components along with their instrumentations, lubrication, electrical power, controls, sealing and cooling water and other auxiliary equipment. However, these components are the part of a heat transfer loop of the ultimate heat sink and safety-related heat sources. Also, those components are examined as part of the paper that complies with the Nuclear Safety Class 3 having Seismic Category I. This seismic category requires that the plant systems, structures as well as components are designed for completely withstanding a DBE (Design Basis Earthquake). In addition to this feature, the essential service water is also used for other requirements pertaining to the safety-concerned cooling water loops component(s) failure. This implies that redundant components or separate trains are provided to ensure complete operations of essential water system if one of the components fails to adequate heat load that is critical to plant safety.
Purpose and Function of Essential Service WaterThe core purpose of essential service water is to provide cooling water to different safety-related types of equipment and components in case of loss of power offsite or LOCA (Loss of Coolant Accident). Another purpose is to provide a backup source of water for the auxiliary feed water along with cooling water and spent fuel pool systems. About the prior issue, the essential service water allows removing component cooling water essential and non-essential heat loads. Hence, it serves at the UHS (Ultimate Heat Sink) for the nuclear power plants during all operational modes. The heat transfer is quite commonly achieved through circulation of seawater as cold fluid against the relatively hotter component cooling water in a heat exchanger. This allows the essential service water to be used as the safety-critical system as it removes the heat loads from the primary system as well as cooling ponds of spent fuel rod. As the system draws water from a huge source of water that includes adjacent sea or river, the system is quite prone to be fouled and eroded by a marine organism, seaweed, ice, sea pollutants and debris. However, for the locations having unavailability of the massive water source, water is recirculated through the cooling tower.
The function of essential service water depends on the mode of operations. Under normal operating conditions, the essential service water is used to remove or reduce heat load from the component cooling water system. Also, it is used to supply cooled supply of water to 2-3 component cooling water heat exchangers. On the other hand, the situation having worst condition having process anomalies, the essential service water is used to facilitate the supply of cooled water for around 30 days to allow safe shutdown and subsequent cooldown operations.
Components of Essential Water SystemThe following figure is the functional definition of essential water system:

Figure SEQ Figure * ARABIC 1: Components of ESW (Nuclear Regulatory Commission, 1992).The boundary line (dashed) shows the usage of following important components:
The intake system comprising of large water-body sources along with different diversion mechanisms to filter inlet water from common environmental pollutants (debris).
The pump structure and gallery together with various water-level controls that include gates, weirs, and valves. Also, it includes different instrumentation; like, flow controllers and level controllers to name a few.
The essential water pump along with its shaft and motive source that comprises of cabling, controls, and most importantly, electrical distribution system.
The piping distribution system from different pumps towards heat exchangers. This system encompasses heat exchangers along with manifolds, valves, logic networks and instrumentations.
The service water side (circulating cooling water) on the heat exchange hot side.
The discharge valves, piping and manifolds from heat exchanger essential service water outlet to the ultimate heat sink. It also includes discharge structures, effluent channeling components, and gates.
However, these components are arranged in different manners to serve different purposes. It facilitates the division of essential water system into two broad classifications; namely, open and closed loops. The open loop systems are further subdivided into two configurations that includes, open recirculating and open once-through systems. The description of configurations, materials and environment is applicable to a broad series of applications of essential water system components. Hence, it cannot be specified for BWR (Breeder Water Reactor) or PWR (Pressurized Water Reactor).
The open once-through systems are quite commonly referred to as straight through systems and are utilized having large volume of water source available for the ultimate heat sink. This configuration is preferred because of its inherent simplicity along with lower initial investments for the utilities. Also, this layout does not require huge-capacity intermediate heat exchanger trains without any specific requirement for component cooling water system’s pumps. Lower components maintenance makes it an attractive alternative to other configurations. However, the major disadvantage of open once-through configuration is the outlook of exposing some equipment and components to aggressive and highly turbid inlet water environment. Appendix A shows a pictorial representation of open once-configuration through essential water system.
The open recirculating system is provided with a self-contained UHS (Ultimate Heat Sink) and is quite commonly achieved via cooling towers or spray cooling pond. This configuration allows the usage of components friendly water having less turbidity as compared to raw water through make-up and settling water filtration methods within low velocity areas. Apart from that, the recirculating water chemical control is achieved thereby resulting in reduction of biofouling and corrosion tendencies as per the discharge limitation proposed by Environmental Protection Agency (EPA). Appendix B shows the pictorial representation of open recirculating configuration through essential water system.
The core difference between closed and open configuration is the ability of plant personnel to control coolant chemistry that contacts with the heat exchangers in order to remove system heat load. The closed system resembles quite similarly with that of open configuration; however, it has an additional intermediate heat exchanger for preventing the exposure of local raw water environment with the heat exchangers. The closed configuration is quite commonly used in harsh, corrosive and chemically hostile environments that include ocean water sources having exceptionally high salt contents. The configuration’s open loop is designed in such a manner to allow simplicity and redundant components for swift and lower on-line plant maintenance activity. It is also facilitated with a method of mitigating different degradation stressors that includes backwashing for biofouling control. The ideal closed loop configuration comprises of pH neutral and chemically pure water having reduced preventive and corrective maintenance activities through usage of corrosion inhibitors. On the other hand, closed loop configuration is relatively expensive as compared to open loop configuration. Nevertheless, it is not susceptible to premature aging phenomenon (Nuclear Regulatory Commission, 1992). Appendix C shows the pictorial representation of closed loop configuration for essential water system.
The Intake ComponentsThe intake component comprises of different equipment that includes, traveling screens, bar screen, stop gate, ESW pump and screen wash pump.
BAR SCREENTRAVELLING SCREENSCREEN WASH PUMPESW PUMPSTOP GATE
Figure SEQ Figure * ARABIC 2: Intake ESW SystemTravelling ScreensA travelling screen is used as a water filtration mechanism having a mesh screen moving continuously and is quite commonly used to attach and remove debris from incoming raw water from ultimate thermal sink. The travelling screens are also quite usually used for wastewater purification applications. Based on water treatment and making it usable as essential service water, it is of importance to note that screening is the preliminary step in any water filtration process. Travelling screens are usually used to remove sticks, leaves, jellyfish, grass, shells, green mussels, seaweed, hydroids and other debris.
Screen Wash PumpTravelling screens become clogged with the incoming raw water debris. Hence, it is essential to clean the debris in order to enhance effectiveness of travelling screens. Screen wash pumps are used to remove debris from the travelling screens. Essential service water screen wash pumps are in operation under normal operating conditions provided that essential service water is also in operation.
Stop GatesIsolation gates are also a part of intake mechanism in essential service water system. These gates are suspended in water. However, fouling is a major factor involved in stop gates. Fouling hinders with the proper insertion of gates. Most of the panels of gates are designed with structurally supportive members that include I-beam or channel sections that are oriented horizontally. Apart from that, these structures are equipped with drain holes within the section’s web portion. The core issue arises when the drain holes become plugged with mussels thereby causing a huge amount of water to become lifted when the stop gates are raised. Under the condition of heavily fouled gates, additional load will be on the motors lifting the gates thereby causing a decrease in its efficiency. Stop gates are equipped with vertical guide channels within the supporting structure. The channels or slots are usually made up of C-channel shapes made from Carbon Steel (CS). Mussels fouling lead towards inefficient closing or opening of the gates (Mackie and Claudi, 2010).
Essential Service Water PumpESW pumps are vertical pumps that are motor driven, the single stage having semi-axial impeller. Vertical pumps are quite commonly referred to as lineshaft turbine pumps. It is a type of centrifugal pump having the dynamic head delivered through the centrifugal effect of the turbine. Hence, the vertical pumps were initially made to replace the common centrifugal pumps for the applications in which the water source is lower than that of the suction capacity of any ordinary centrifugal pumps. Turbine term is a misnomer because most of the vertical pumps make use of operational theory and equipment similar to that of centrifugal pumps. However, in this very scenario, the vertical turbine pumps are quite identical to runners that are quite commonly used in power sector. The impeller used in essential service water pump is either centrifugal or mixed flow and it depends on the specific speed, design and geometry of the impeller. Also, axial impellers are used in specific applications.
The core working principle of vertical pump is that the rotating impeller gains energy from the rotational motion through a driver and hence, transfers the required energy to the liquid. However, the transference of energy is highly dependent on the diameter, speed and design of the impeller. In the vertical pump, the moving impeller develops an energy quite commonly known as kinetic energy that is imparted to the working fluid. On the other hand, the diffuser (bowl) converts the kinetic energy to the pressure force. Semi-axial impellers have an optimum hydraulic behavior on different speeds. Hence, this feature makes it a suitable candidate for usage in wet pit installation. Apart from that, the diffuser is connected with a column pipe and it is supported by a product-lubricated bearings. Hence, for lower head requirements and subsequent higher impeller speeds, critical attention is required for the optimum hydraulic design on the discharge bend. The core reason behind it is that it causes significant pressure losses as part of significant head percentage thereby having an impact on indirect costs of the plant (Butts, 2016).

Figure SEQ Figure * ARABIC 3: Vertical Single Stage Semi-Axial Pump (Gülich, 2014).The concept of semi-axial impeller is used to reduce the outer diameter of the diffuser as compared to the radial design’s volute casing. This is one the reason of using vertical pumps for water supply economically. The diffusers are casted into stage casings that are bolted to form a single pumping unit. The water exits through the column pipe in the last stage. The assembly of pump is fitted within a tank where the water enters from a suction bell to suction impeller. In order to achieve reduction in axial thrust, annular seal and balance holes are used onto rear shroud of impeller. Volutes can have three or four channels instead of using diffuser vanes. Also, the vertical pumps of specific speeds in the range of 40 to 150 are used delivering water for irrigation and drainage as well. Semi-axial impeller vertical pumps deliver best hydraulic behavior on the above-mentioned specific speed. They are also installed within the intake water basins and hence, are suitable for wet pit installation (Gülich, 2014).
Bar ScreensBar screen are quite commonly used in almost every wastewater or effluent treatment plant. The screens are usually made up of 10-30mm opening steel bars. The core function of the bar screen is to protect the equipment or component from direct contact with large objects and debris. Apart from that, the bar screen separates the rags and large objects that could clog the intake pipes, fine screens, flow measuring instruments and most importantly, the essential service water pumps. Also, the bar screen opening or mesh size should be smaller as compared to the smallest pump or pipe installed. Bar screen is cleaned through mechanical means or by manual operations. In the case of excessive clogging of bar screens, a flow having to channel will be observed causing excessive loading on certain openings in bar screens. On the other hand, the cleaning of bar screens can also cause undesirable surge in the flow of incoming raw water (Hendricks, 2011).
Essential Service Water Debris FiltersThe essential service water debris filters are used to remove debris from the incoming water feed. It allows reduction of the high frequency of preventive and corrective maintenance. Apart from that, the filters help to avoid clogging of heat exchanger components and piping. Three debris filters are used in each train in a parallel arrangement and are located between essential service water pumps and heat exchangers. The debris filters are designed to retain particle size around 2.5mm. The differential pressure across the debris is the indicator for subsequent backwashing operation of debris filters. It can also be achieved through a timer or can be manually conducted by the onsite control panel.
Vacuum Relief ValveIt is installed on the highest point of the circulating cooling water heat exchanger outlet for avoiding water hammering and protecting piping. The vacuum relief valve is set at around -0.2 psig. Vacuum relief valves have their exceptional usage in the petroleum and petrochemical sector because of its safe working operations.
Expansion Joint (Bellow)Expansion joints are most commonly used in the piping to absorb the thermal stresses and terminal movements. They are quite applicable in areas where it is impractical or undesirable to use expansion loops. The expansion joints are also known as bellows. They are available in different material of construction depending on the application. Metallic expansion joints are used in ducts and piping system to avoid damage because of vibration, thermal growth, and mechanical thrust. In this regard, the material of construction ranges from all types of steel to nickel-based alloys. The metallic bellows are used in the following stress environments:
Thermal expansion
Movement as part of external forces (restraints)
Excessive weight of piping together with different instrumentation on pipe.
External and internal pressures
Rubber expansion joints are also used and are fabricated by synthetic or natural rubbers together with metallic composite structure. The structure facilitates effective stress relief in the piping network because of changes in thermal profiles. Rubber bellows are quite useful against lateral, angular and torsional movement in pipes. Teflon expansion joints are used for highly corrosive environments and can provide a great mix of strength and flexibility (Wermac, 2016).
Check ValveCheck valve is also called non-return valve (NRV) or one-way valve. There are different types of check valves; however, they have the similar function of avoiding backflow of the fluid. The common principle behind the working of the check valve is that the mechanism is separated by two ports. The mechanism allows water to be drawn from the first port to the second port having the inability for the fluid to travel back into the first port. A number of different check valves are used depending on the nature of fluid, process dynamics and most importantly, costing. Ball check valves are quite commonly used for moving liquids and not suitable for creating airtight seal. Swing check valve can have severe wear and tear and hence, most of the swing check valves have a considerably high pressure drop as compared to other check valves. Considering the costing, disk valves are relatively less costly and are usually used in vertical piping; however, they do not perform quite exceptionally in high pulsation flow (Empowering Valves, 2014).
Importance of Essential Service Water to Plant SafetyEssential service water is one of the most critical safety systems. During normal conditions, one train of essential service water is in operations. The flow rate of the essential service water pump is defined by the required heat load to be removed from the system for safe plant operations. Considering the plant safety outlook, the pumps are designed to withstand minimum mass flow rate under certain conditions critical to component safety. These condition include minimum level of water to avoid cavitations in pumps, inlet head losses to the pump as per full capacity plant operations, fluctuations/intermittency in supply of electricity’s frequency, increased in the roughness of pipes’ roughness because of fouling and aging, increased pressure drops in heat exchangers and most importantly, fouling in debris filters. The discharge head are determined and calculated based on the minimum/maximum level of water, dynamic pressure losses, and mechanical component related head losses at full plant capacity.
On the other hand, safety of debris filters is also quite essential. The debris filter is used to remove debris particles from the inlet of raw water. The design feature of debris filter allows backwash operation. With the increase in the fouling of filter, the differential pressure between the inlet and outlet of filter is increased thereby reaching a designated set point in the controller. As the set point is reached the backwash operation is started either manually or automatically depending on the plant instrumentation. In automatic backwash system, the signal of increased differential pressure will initiate the backwashing operations. However, in manual operations, a simpler and cost-effective pressure differential indicator is used to indicate pressure difference across filter on-site. The essential service water filters can also be cleaned through a timer after the start of the essential service water pumps. However, the disposal and discharge of the collected or removed debris must have to be treated in accordance with the state and federal regulations pertaining to the site location.
Regarding valves, piping and fittings, system’s material must have to be carefully selected that fulfill the requirements of site location, site installation and essential service water fluid properties. Also, the material of the system that comes in contact with one another must be chosen such that they inhibit galvanic corrosion. Hence, the valves, piping and fittings must be in accordance with the ASME Code Section III (Class 3).
The concept of general protection in instances of pipe failures within the essential service water system regarding flooding quite commonly relies on the very principle of limiting the very consequences. Under the circumstances of major leakage of piping or fitting within the essential service water system’s train, the motor-driven essential service water system pump’s discharge isolation valve is closed automatically. Moreover, the essential service water pump is tripped after the closure of isolation valve. Afterwards, to facilitate the availability of essential service water to the system, another train of essential service water system is brought into operation. The detection and subsequent isolation is quite commonly done considering the safety of equipment and plant personnel. Nevertheless, the electronic logics are defined such that one of the two logics from the NIDVS (Nuclear Island Drain and Vent System) level instrumentation on sump within the safeguard building’s non-controlled area will deliver a HIGH alarm in Machinery Control Room (MCR) thereby isolating the affected essential service water system train. Hence, in this regard, special action from operator is not required in the area of flooding. Two separate overpressure protection; namely, primary and secondary, are also provided for safety related issues. The primary protection on the essential service water end of circulating cooling water heat exchangers is facilitated by thermal relief valves. On the other hand, secondary protection on the essential service water is provided by manual opening and closing of the valve that is located upstream of the thermal relief valve to isolate the specific heat exchanger. Also, in order to ensure safe plant operations, it is also recommended to mechanically lock all the manually operated valves on the main line. For conducting service testing of valves, leakage rates pertaining to boundary isolation valves are required as per ASME OM Code (2004 Ed.), Subsection ITSC. For the safe operations, it is recommended that the check valves do not be less stringent as compared to the API-598 check valve (metal-seated) criterion. Apart from that, analysis of hydraulic transient has to be performed in order to confirm the very integrity and performance of the essential service water piping so that it can withstand the water hammering effects. In most of the nuclear power plants operations, butterfly valves are used for isolation of essential service water system and it is not used for throttling operations. However, in the operation in which butterfly valves are used in essential service water system, it is subjected to extensive throttling for a longer period of time. In this regard, design provisions are quite commonly considered to prevent wall thinning consequences downstream of these valves. Hence, an erosion resistant material of construction is considered together with pipes with thick wall thickness.
Significant Design Basis for the Essential Service WaterEssential service water system encompasses different systems, structures, and components vital to the safety and subsequent cooling of the safety-critical equipment in plant. Apart from that, the structure is also capable of withstanding the detrimental impacts of natural disasters that includes tornadoes, hurricanes, earthquake, floods and other external missile without any subsequent loss in the safety-related functions of the plant. Moreover, the system components as well as the structure housing the system are quite capable of withstanding the impact of earthquakes. The structures and systems are designed in compliance with the seismic design guidance of RG 1.29. Apart from that, the safety-critical portions of the essential service water systems are designed to withstand the effects of environmental conditions as well considering the normal working operations, testing, maintenance, and related postulated accidents. Similarly, it also needs to be protected against any external insurgency or missile impacts together with discharge fluids and pipe whippings as it could cause significant damage to equipment and in extreme cases, it could be a cause for equipment failure.
Another impact aspect pertaining to essential service water system includes the ability of the system to share its functions with other systems in the plant operations. It is worthwhile to be noted that the sharing of essential service water system should be such that it does not jeopardize the safety-concerned functionality of the system. Moreover, it should not also impair the ability to perform during any unforeseen events that includes, an ordered shutdown, accident in one unit of the plant or the cooldown of different units in the plant. Pertaining to the additional functions of essential service water system is to remove heat load from circulating cooling water heat exchangers, electricity diesel generator heat exchangers or essential service water pumps during normal as well as abnormal operations. The design of the system facilitates subsequent heat transfer to the ultimate heat sink.
The essential service water system is also designed to facilitate safe and swift periodic maintenance and inspection of core equipment and components that are quite essential for maintaining the overall integrity of the system. Apart from that the system is capable of permitting periodic functional and pressure testing that is quite essential for maintaining the leak-test and structure integrity of the components. The design also facilitates the safe operations and performance of the core components of the system together with the operability of the system as the whole. The essential water system is also designed and structured to make sure that the operations for reactor shutdown can be achieved in the safe environment without any mishaps. Considering the LOCA (Loss of Coolant Accident), the core operation of protected system’s applicable components together with transfer from the normal to emergency power sources is also an auxiliary function of the essential service water system.
Operations of Essential Service Water SystemEssential service water is used for two operating modes; namely, normal and abnormal operating conditions.
Normal Operating ConditionThe essential service water supply is one of the most vital systems of nuclear plant operations and it is designed to facilitate cooling water during shutdown of plant and power operations. During normal operations, two of the four essential service water pumps are operational whereas the remaining is on the standby. The four pumps are primed, filled and vented for swift operations. Under normal conditions, the essential service water pump is in operation along with the debris filter. Also, all the main line valves are in open position. However, as the differential pressure across the debris filter reaches the designated set point, automatic cleaning function of debris filter is initiated through backwashing.
During the standby condition, the train is not operational for normal conditions operations. In this aspect, manual valves in the line are open and the whole system is vented and filled. The debris filter is not operation and in standby condition. The system can be initiated either automatically or manually through machinery control room. In both the cases, the start signal must have to be actuated and in this regard, preparatory measure is not required.
Both the trains can be operational to achieve cold shutdown in the minimum time span. However, only one train can do the needful for cold shutdown as well. During refueling operation having the fuel rod completely discharged towards the fuel discharge building, one or two essential service water trains can be in operation. However, maintenance activity on only one train is possible during this time span.
On the other hand, the dedicated essential service water train is not in operations during normal operations. Hence, the essential service water side of the dedicated circulating cooling water system is isolated from the rest of system. The essential service water inlet and outlet isolation valves are in closed position and the train is filled with demineralized water to prevent the issues of corrosion. However, the rest of the essential service water system train is filled with the filtered water after bar screens and stop gates. The dedicated essential service water becomes operational only in case of any safety incident. This requires the closure of the essential service water downstream isolation valves and manually opening the dedicated essential service water upstream and downstream valves towards dedicated circulating cooling water heat exchanger and hence, starting the dedicated essential service water pump.
Abnormal Operating ConditionsThe essential service water system is also useful under the condition of LOOP (Loss of Offsite Power). In most of the times, three out of four essential service water pumps can be in operations having one in preventive maintenance.
In case of loss of offsite power condition, the dedicated essential service water system is available; however, it is in standby condition. In this case the electricity diesel generators are used to power the essential service water system components. Apart from that the STOBG (Station Blackout Diesel Generators) can also be used to supply electricity to the essential service water system. Hence, it provides an alternative in case of loss of offsite power as well as failure of all electricity diesel generators.
Considering the failure of any one of the four essential service water pumps during normal operations, a switchover is also possible to the entire train. The failure to cleaning operations of debris filter is also indicated by a HIGH alarm signal or functional alarms (Nuclear Regulatory Commission, 2016).
ConclusionAll in all, the essential service water system is the most vital part of the nuclear power plant. It is the key feature to provide safe work operation in a plant. The essential service water system comprises of a number of components including pumps, filters and most importantly, ultimate thermal sink. The core function of the essential service water is to remove heat load from the circulating cooling water through heat exchangers. However, in the abnormal plant operations that include earthquakes, torpedoes, hurricanes, and other external threats, the essential service water system provides a safety to assist in plant cooldown operation as well. The equipment and components are effective against earthquakes and provide an enhanced outlook for safe plant operations. Because of the critical nature of the system, the plant needs at least two trains for ensuring safe and versatile operation of the system. Apart from that, the electrical fluctuations and failures are also one of the issues that need to be tackled. For that, the pumps are backed up by electricity diesel generators as well as standby blackout electricity diesel generators. This feature allows operations of system and pumps with the failure of electricity as well as backup electricity diesel generators.
The essential service water system comprises of intake system to withstand the raw water chemistry. In this regard, bar screens, traveling screens, stop gates and backwash traveling filter pumps are used. Raw water (sea water) possesses floating objects and debris as part of the inlet water feed. To prevent clogging of piping, valves, and components, it is essential to inhibit the inflow of debris. For this purpose, the bar screens remove large debris and subsequently, incoming debris is further removed through traveling screens. The inlet water is then pumped towards debris filters to remove debris around 25 mm and greater. The heat exchanged essential service water is then sent to the ultimate heat sink.

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AppendixAppendix A: Open-once Configuration (Nuclear Regulatory Commission, 1992)

Appendix B: Open-recirculating Configuration (Nuclear Regulatory Commission, 1992)

Appendix C: Closed Configuration (Nuclear Regulatory Commission, 1992)