CHAPTER 05 final Rev 8.docx

CHAPTER 5 – TABLE OF CONTENTS

List of Tables

Table 5.1: Typical Operating Parameters for the Primary Coolant System

List of Figures

Chapter 5 – Record of Revisions

5 MAIN COOLANT SYSTEMS

5.1 Summary Description

There are two main coolant systems at the NBSR facility, the Primary Coolant System and the Secondary Coolant System. The primary purposes of the coolant systems are to remove the fission and decay heat generated in the core, to dissipate that heat to the environment, and to serve as one of the barriers to prevent fission product release to the environment. The primary coolant is heavy water (D2O) and the secondary coolant is light water (H2O). Numerous auxiliary systems, described in Chapter 9, support the main coolant systems.

The coolant systems at the NBSR facility are designed to remove sufficient heat to support continuous full-power operation at a power level of 20 MW and remove the decay heat generated after shutdown from extended full-power operations. While the reactor normally operates under forced primary coolant flow, it may be operated at power levels of up to 10 kW with reduced or no flow. Below 10 kW, heat generation due to fission and decay heat is insufficient to significantly heat the existing large inventory of primary coolant in the Reactor Vessel to a temperature that would result in damage to the core.

The Primary Coolant System consists of pumps, heat exchangers, piping, and valves, and most of the system is within the reactor building confinement. While pressure throughout the system is not maintained at a constant value, the system is closed to the atmosphere. Therefore, it serves as one of the three barriers to fission product release, the other two being the fuel cladding and the reactor building confinement. Chapters 4 and 6 of this report discuss these other barriers.

The Secondary Coolant System rejects heat in the system to the atmosphere via cooling towers. Heat exchangers common to the heavy water systems and the secondary system serve as the component for transferring heat from the heavy water to the secondary water. Multiple pumps and strainers provide flow alternatives for different plant configurations that require clean water flow through the heat exchangers. Chemistry control of the towers is accomplished through the secondary piping system. The system also provides a means to detect a primary-to-secondary leak during operation at power, a system described in Chapter 9 and Chapter 11.

5.2 Primary Coolant System

5.2.1 Design Bases/Functional Requirements

The Primary Coolant System is designed to transfer 20 MW of heat from the core to the Secondary Coolant System with nominal values of: 9,000 gpm (34,000 lpm) flow, a 100 F (38 C) reactor inlet temperature, and 114 F (46 C) reactor outlet temperature. The system also has several other functions:

a. The coolant in the core region acts as the neutron moderator;

b. The coolant around and above the core region acts as the reflector;

c. The coolant over the core, together with the coolant in the D2O Emergency Cooling Tank serves as a reservoir for emergencies;

d. The coolant above the core shields the reactor top (although no credit is taken for this in accident analyses), reducing activation of the top plug;

e. The volume of coolant would retard the escape of fission products; and,

f. The coolant above the core has sufficient reactivity to serve as an alternate shutdown mechanism.

For further information see Chapter 3 and NBSR 15.

5.2.2 General System Description

Figure 5.1 shows the flow path for the Primary Coolant System.

The D2O Main Circulating Pumps pump the heated water from the Reactor Vessel to the main heat exchangers, where the water is cooled by the secondary water flowing on the opposite side of the plates comprising the heat exchange surface of the heat exchangers. The water then flows through a strainer to the two inlet plena for the Reactor Vessel. The plena direct water up through the vessel, cooling fuel and other internal vessel components, such as in-core thimbles. Heat generated by fission in the core is removed by coolant that flows up the inner plenum and then up and through the center six fuel elements, while the outer plenum directs coolant up and through the remaining twenty-four fuel elements. Approximately 4% of the incoming D2O flows around the fuel and prevents stagnation in the volume of water in which the elements are immersed. The fuel coolant exits the elements via the open top of the elements water and joins the remainder of the D2O flowing through the vessel. The total volume of water then flows to the bottom of the vessel, whence it exits through two outlet pipes that are joined to a single outlet header containing a venturi for outlet flow measurement. The outlet header joins the suction header of the main circulating pumps, completing the cooling cycle. A shutdown cooling system is provided to remove decay heat using the same cooling flow path but with different pumps.

At a reactor power of 20 MW, approximately 2,300 gpm (8,700 lpm) and 6,700 gpm (25,300 lpm) of water is pumped through the inner plenum and the outer plenum, respectively. The heavy water leaves the reactor vessel through two 12-inch (30-cm) pipes, which then join to an 18-inch (46-cm) pipe outside the sub-pile area in the Process Room. The standpipe used to maintain a minimum level in the vessel may provide a flow path for an insignificant diversion of water directly to the D2O Storage Tank.

5.2.2.1 Main Heat Exchangers

The Main Heat Exchangers, HE-1A, -1B, and -1C, each have a capacity of 35 x106 BTU/hr (10 MW). They are of plate and frame type, single pass, counter-flow heat exchangers.

A plate and frame heat exchanger uses flat plates as the heat transfer surface between the primary and secondary fluids: primary refers here to hot water at the inlet of the heat exchanger and secondary refers to cold water at the inlet of the heat exchanger. The primary and secondary flows are separated from each other by plates, welded joints, and gaskets. D2O coolant flows into the heat exchanger, nearly simultaneously to one side of all the heat transfer plates, transfers heat through the plates, and exits the heat exchanger. H2O flows on the other side of all the plates, receives the heat from the plates, and exits the heat exchanger. The design of the heat exchanger is such that a leak of the primary fluid to the secondary fluid is only feasible by a failure in a plate. The failure of a gasket surface will be revealed by water or heavy water leaking to the exterior of the heat exchanger.

Two main heat exchangers are sufficient to transfer the heat generated by the reactor at a power level of 20 MW to the secondary coolant.

5.2.2.2 Pumps

5.2.2.2.1 D2O Main Circulating Pumps

The four main circulating pumps are single-stage, shaft-sealed, centrifugal pumps operated in parallel to circulate the primary coolant from the Reactor Vessel to the Main Heat Exchangers.

The pumps can be controlled from the Main Control Panel located in the Control Room. During normal operation, three pumps are run to maintain the necessary flow, with the fourth serving as an installed spare.

5.2.2.2.2 D2O Shutdown Pumps

Two centrifugal pumps are installed in parallel with the D2O Main Circulating Pumps to provide forced cooling to the reactor during shutdown periods. Each shutdown pump has an AC motor and a DC motor mounted on a common shaft. The AC motors for SDP-1 and SDP-2 are powered from Emergency Power MCC A-5 and Emergency Power MCC B-6, respectively. The DC motors for both pumps are powered from MCC DC.

The pumps can be controlled from the Main Control Panel located in the Control Room. Only one of the two pumps is typically used to remove decay heat from the reactor.

5.2.2.3 Piping

Type 6061-T6 Aluminum is used as piping material but any material is permissible if it is compatible with the D2O used in the piping systems.

Two types of remotely operated valves are installed in the Primary Coolant System, an air-operated type and a motor-operated type.

Inlet Isolation Valve DWV-1 is a 12-inch (30.5-cm) motor-operated, diaphragm valve that controls the flow of primary coolant to the outer plenum. Inlet Isolation Valve, DWV-2, is an 8-inch (20.3-cm) motor-operated, diaphragm valve that controls the flow of primary coolant to the inner plenum. Each valve can be controlled from the Control Room to distribute the flow to the two reactor inlet plenums. Both of these valves are normally fully open.

Each valve is equipped with handwheel operators so they can be positioned manually in the Process Room. Each valve has a leak detector within the valve body, which gives a Control Room indication should a diaphragm leak. DWV-1 and DWV-2 are powered from MCC A-5 and MCC B-6, respectively.

Reactor Outlet Isolation Valve, DWV-19, is a motor-operated butterfly valve located in the piping between the vessel outlet and the D2O Main Circulating Pump suction header. Control and indication of the valve are in the Control Room, and the valve can be manually positioned with an attached handwheel. DWV-19 is powered from MCC B-6.

Air-operated diaphragm valves are provided in the vessel normal overflow line (DWV-10), in the fuel transfer overflow line (DWV-37), and in the moderator dump line (DWV-9). There are additional remote-operated valves in the Primary Coolant System with which the operator can redirect water from its normal flow path. All can be positioned from the Control Room.

Except for DWV-1, DWV-2, and DWV-19, the electrical power for all valves comes from Critical Power Panel 1 (CPP-1).

Chapter 9, Auxiliary Systems, discusses the air system from which the air needed to operate the pneumatic control valves is supplied. Control power for the solenoid valves in the Air System comes from CPP-1 and from the DC bus.

All diaphragm valves, which are 3 inches (7.6 cm) and larger, are equipped with leak detectors to annunciate any failure that could release primary coolant outside of the valve body.

5.2.2.4.2 Safety Relief Valve

A safety relief valve is installed on the 3-inch (7.6-cm) line branched from the suction line of DP-4 and on the reactor outlet piping. It can prevent over-pressurization of the primary system by relieving pressure whenever its set value is exceeded. Any primary coolant released through this relief valve returns to the D2O Storage Tank.

5.2.2.4.3 Main Heat Exchanger Isolation Valves

Four isolation valves for the two operating Main Heat Exchangers are 12-inch (30-cm) pneumatically operated triple offset butterfly valves. Each of the four valves for the two normally in-service heat exchangers is equipped with a leak detector.

5.2.2.5 Instrumentation

Instrumentation is installed to provide remote and local read-out of a number of process parameters, described below. Local gauges display pressure at various points in the system. Electrical power for the non-local instruments comes from CPP-1.

5.2.2.5.1 Flow

Two channels sense the reactor inlet flows. The Reactor Outer Plenum Flow channel FRC-3, measures the flow of primary coolant into the vessel through the outer plenum, while Reactor Inner Plenum Flow channel FRC-4, measures the flow through the inner plenum. Outer plenum flow is measured by a 12-inch (36-cm) venturi, FE-3, installed in the reactor outer plenum piping. A flow alarm unit has three on-off control signals: two to the reactor scram circuits, and one to the annunciator system. The range of the channel is 0-8,000 gpm (0-30,300 lpm). Inner plenum flow is measured by a 10-inch (25-cm) venturi, FE-4, installed in the reactor inlet plenum piping. A flow alarm unit provides three on-off control signals: two to the reactor scram circuits, and one to the annunciator system. The range of the channel is 0-4,000 gpm (0-15,000 lpm).

Reactor Vessel Outlet Flow Recorder Channel and Reactor Outlet Flow Indicator Alarm Channel measure the outlet flow for the reactor. An 18-inch (46-cm) venturi, FE-1, is common to both channels and measures the outlet flow. An electrical signal is supplied from the flow instrument to the Thermal Power BTU Recorder (BTUR). The latter supplies an electrical signal to Flow Indicator, and Flow Alarm. The alarm unit has three independent on-off outputs feeding two scram circuits and an annunciator. The range of both channels is 0-10,000 gpm (0-37,900 lpm). Section 5.2.2.5.5, Thermal Power, discusses how the flow signal is modified to produce the power signal used by the BTUR Channel.

The Reactor Vessel Overflow Channel, FIA-2, measures the flow of primary coolant in the pipe from the normal overflow standpipe in the reactor vessel with a 3-inch (7.6-cm) orifice. A flow transmitter sends an electrical signal to a flow indicator and flow alarm. The alarm unit has two independent on-off outputs that feed the reactor startup interlock relay and an annunciator. The range of the channel is 0-30 gpm (0-115 lpm).

The flow of primary coolant through the main heat exchangers is measured by ultrasonic flow elements mounted on the primary piping on the outlet side of each heat exchanger. Indication is provided in the Control Room and the range of both channels is 0-5,000 gpm (0-19,000 lpm)

5.2.2.5.2 Temperature

The differential temperature of the primary coolant across the reactor is measured by different detectors. One measurement is made with two precision four-wire platinum resistance temperature detectors (RTD) installed in the 18-inch (46-cm) primary piping on the inlet and outlet side of the reactor vessel. Temperature signal input is sent to the thermal power recorder and indication is provided in the Control Room. The range of the channel is 0-20 F (0 to 11C).

The other differential temperature measurement is made with thermocouples installed in the inlet and outlet piping. Indication is available on two meters in the Control Room and alarm units have outputs that supply a signal for reactor scram and annunciators. The range of both channels is 0-30 F (0-17 C).

The temperature of the primary coolant leaving the reactor is measured with an RTD mounted in the reactor 18 inch (46 cm) outlet piping. Indication is available in the Control Room and an alarm unit has outputs that supply a signal for a rundown and an annunciator. The range of the channel is 50-200 F (10-93 C).

The Reactor Inlet Temperature Recorder Controller Channel, TRCA-3, measures the temperature of the primary coolant entering the reactor. A temperature recorder and a temperature alarm receive inputs from the temperature detector. The temperature controller regulates the secondary coolant bypass flow around the cooling tower by controlling the position of Secondary Coolant Bypass Valve SCV-20 to maintain a constant primary coolant inlet temperature. The alarm unit has outputs that supply a signal to annunciate an abnormal temperature. The range of the channel is 50-150 F (10-66 C).

5.2.2.5.3 Level

The Reactor Vessel Level Recorder measures and records the level of the water in the reactor vessel. Indication is available in the Control Room and alarm units have six sets of contacts: two for low level reactor scram, one to permit the opening of emergency cooling valve DWV-35, one for an alarm at the NIST emergency console, one to de-energize the motors of the Main D2O Circulation Pumps, prohibit startup of the D2O Shutdown Pumps, and close the LOCA isolation valves (DWV-1, DWV-2, DWV-95A, DWV-95B, DWV-100A, and DWV-100B), if a similar signal is generated by the vessel level channel, and one for annunciation. The range of the channel is 0-200 inches (0-510 cm).

The Reactor Vessel Level Indicator Channel measures and displays the level of the primary coolant in the reactor vessel. Indication is provided in the Control Room and the Emergency Control Station. Alarm units have outputs that supply a signal for a high-level alarm, a low-level alarm, a low-level rundown, a low-level scram, and one for annunciation. They also supply a signal to permit the opening of Emergency Cooling Valve DWV-34 and another for de-energizing the motors of the D2O Main Circulating Pumps if a similar signal is generated by the vessel level recorder channel. The range of the channel is 60-200 inches (150-510 cm).

5.2.2.5.4 Pressure

The differential pressure between the primary and secondary sides of main heat exchangers are measured by a differential pressure transmitter that produces indication in the Control Room and alarms in the Control Room if differential pressure decreases below a given setpoint. The range of the channel is 0-50 psid (0-345 kPa).

5.2.2.5.5 Thermal Power

Thermal power output from the reactor is calculated and recorded by the Thermal Power Recorder Channel, BTUR. The BTUR combines a differential temperature input (see 5.2.2.5.2) with flow input (see 5.2.2.5.1) to derive the reactor power level for display and recording. The range of the channel is 0-30 MW.

There is an 18-inch (46-cm) aluminum strainer in the reactor inlet piping. The strainer has a bolted cover so that an interior stainless-steel wire #3 (approximately 1/4 inch (0.7 cm) slot) mesh basket can be removed for maintenance.

5.3 Secondary Coolant System

5.3.1 System Description

This system removes heat from the following water systems: Main Coolant System, Purification System, Thermal Shield Cooling Water System, Thermal Column Tank Cooling System, Experimental Demineralized Cooling Water System, and the Helium Compressor Secondary Cooling Water system. The heat load assumed by the secondary coolant is transferred to the atmosphere via two cooling towers.

System flow is normally generated by four main secondary pumps arranged in parallel, with three of the pumps operating. These pumps may draw cold water from the basin of the tower and heated water from the bypass piping around the cooling tower. Water from the pumps passes through discharge strainers, flows through the main heat exchangers, through a venturi for measuring the combined main and auxiliary pump flow, and then returns to the tower or directly to the pump suction header, completing the cooling cycle. When the reactor is shutdown, a single smaller pump can provide secondary flow through a dedicated strainer using a similar cooling path; the auxiliary heat exchangers are not normally supplied with flow and water typically returns directly to the basin or to the tower bypass piping.

Bypass piping around the tower allows hot water from the heat exchangers to remain uncooled by the tower, with the water flow throttled to the suction header of the main pumps. SCV-20, the tower bypass valve, receives a signal from the temperature controller (see 5.2.2.5.2) for the D2O main coolant loop. The amount of heat transferred from the main coolant loop to the secondary cooling system may be controlled by regulating the flow and/or the temperature of the secondary water flowing through the main heat exchangers. Regulating the secondary water temperature becomes the chief temperature control of the primary coolant if reactor power is maintained at a constant level, ambient temperatures and humidity remain relatively constant, the volume of water through the heat exchangers is fixed, the volume of water to the different cooling sections of the tower cells is fixed, and there is no change in tower fan speeds.

Approximately 800 gpm of cooled water is diverted from the main loop and sent through the auxiliary heat exchangers by one of two auxiliary booster pumps, returning to the main loop upstream of the venturi.

One of two dedicated pumps supplies water from the suction header of the Main Secondary Coolant Pumps to the Helium Compressor Secondary Cooling (HCSC) Heat Exchanger, the hot water inlet of which is supplied with water that has flowed through the oil cooler of a helium compressor. This helium compressor is used by the Cold Source Refrigerator to cool the hydrogen from the two cryostats located on C100. Heated secondary water from the heat exchanger returns to the tower bypass line downstream of the main secondary flow venturi.

A small flow rate of heated water from the main heat exchangers is diverted to two radiation detectors and a test-coupon station. The radiation detectors monitor the secondary water for the presence of 16N, which is produced in the D2O coolant during power operations. Detection of 16N is an indicator of a primary-to-secondary leak in the main heat exchangers. The test coupons monitor for any long-term effects that the secondary coolant might be having on the secondary piping.

One cooling tower has three cells that cool water by evaporation or by conduction in shell-and-tube heat exchangers. The second cooling tower, the basin for which is connected to the basin of the larger tower, has two cells that cool water by evaporation. Secondary coolant losses, due to evaporation, leakage, and blow down, are automatically made up from the domestic water system by valve SCV-4. There is a chemical addition system located within the Secondary Cooling Pump Building to regulate corrosion and biological growth in the secondary system. Water is continuously blown down to the sewer system to remove chlorides and concentrated solids and to maintain a low concentration of dissolved solids.

Most of the secondary components are in the Secondary Cooling Pump Building (SCPB), adjacent to the cooling towers and west of the confinement building. The 16N monitors and the secondary auxiliary cooling water pumps are in the D-wing.

Information on system design bases and functional requirements may be found in Chapter 3.

5.3.2 Components

See Section 5.2.2.1.

5.3.2.1.2 D2O Purification Heat Exchanger

HE-2 is a plate-and-frame heat exchanger which transfers heat from the Primary Coolant Purification System to the Secondary Coolant System. This heat exchanger is in the Process Room, as are three other heat exchangers described in this section.

5.3.2.1.3 Thermal Shield Heat Exchanger

HE-6 is a plate-and-frame heat exchanger which transfers heat from the Thermal Shield cooling water to the secondary cooling water.

5.3.2.1.4 Experimental Demineralized Water Heat Exchanger

HE-7 is a plate-and-frame heat exchanger, which transfers heat from the Experimental Demineralized Water cooling water to the secondary cooling water.

At present, the system is only operated to supply water pressure for the refueling cannon. Since the refueling system generates no heat, the secondary cooling water supply is not connected to the HE-7 heat exchanger; instead, the secondary water piping bypasses it.

5.3.2.1.5 Thermal Column Heat Exchanger

HE-9 is a 1.0x105 BTU/hr (0.03 MW) plate-and-frame heat exchanger which transfers heat from the Thermal Column Tank cooling water to the secondary cooling water.

5.3.2.1.6 Helium Compressor Secondary Cooling Heat Exchanger

HE-10 is a plate-and-frame heat exchanger which transfers heat from the Helium Compressor Cooling System to the Secondary Coolant System. HE-10 is in the Secondary Cooling Pump Building.

5.3.2.2 Cooling Towers

One cooling (hybrid) tower, composed of three sections (cells), uses two heat transfer mechanisms to transfer heat from the water to the atmosphere and the smaller of the towers uses a single mechanism to transfer heat.

The hybrid tower is designed to transfer 75x106 BTU/hr (22 MW) to the atmosphere without a plume and under adverse (high humidity and temperature) weather. Hybrid refers to the combination of wet and dry sections used in a cell to cool the water without producing a plume. Each cell of the hybrid tower has a two speed fan with which to draw air through the tower, a wet section and a dry section, and a vertical rolling door to vary the amount of air through the wet section. Cell 3 has two additional features, a remote operated bypass for the wet section, and a remote operated valve for the associated dry heat exchanger. Evaporation in the wet section of each cell and conductive cooling in the heat exchangers of the dry section of the cells are the two mechanisms for rejecting heat to the atmosphere.

The smaller tower, a combination of two cells, was erected to provide additional cooling capacity needed for a planned expansion of the NCNR experimental facilities, including a second cryostat. The additional heat loads from this expansion are accommodated through this increase in the cooling capacity of the secondary cooling water system, i.e. the two cell tower. This tower is designed to transfer 7.5 MW to the atmosphere through a wet section only. Each cell of the smaller tower has a two speed fan.

Evaporation of water is accomplished through a cascade of water down the internal structure of a cell. As the internal structure breaks up the water stream, fans draw air through the tower and the cascading droplets of water, evaporating some of the water and cooling the remaining water. The cooled water collects in the concrete catch basin below the tower and provides the net positive suction head for the Main Secondary Coolant Pumps. Conductive cooling is accomplished by flowing secondary water through heat exchanger tubes and drawing air through the shell of the heat exchanger mounted above each of the three cells.

Controls for fans, rolling doors, and valves are in the Control Room. Both cooling towers are constructed of wood, fiberglass, and galvanized metal and stainless steel. The materials of construction are compatible with the water chemistry of the secondary cooling system.

The four main secondary pumps circulate the secondary coolant from the cooling towers to the heat exchangers. Each pump is of the centrifugal type with the drive motor mounted above the pump. Each motor is controlled through a variable frequency drive unit, which allows the motor speed to be selected locally and the flow rate of the pump to be changed.

A Control Room operator controls the pumps from the Main Control Panel. The number of pumps in operation at any time depends on the plant heat removal requirements and the ambient conditions, e.g. temperature and humidity, at the Cooling Tower. The combined flowrate of three pumps is approximately 10,000 gpm.

5.3.2.3.2 Secondary Shutdown Pump (SD)

A single centrifugal pump of lesser flow rate capacity than a main pump may be used to circulate water through the secondary system and the tower basins.

5.3.2.3.3 Secondary Auxiliary Booster Pumps

The two pumps are single-stage, centrifugal units used to supply cooling water to the auxiliary heat exchangers. Pump #1 is powered from MCCA-7, while pump #2 is powered from MCCB-8. The units are normally operated with one running and the other in standby.

5.3.2.3.4 Helium Compressor Secondary Cooling Pumps

The two pumps are of the centrifugal type and circulate water through HE-10 and the secondary system. Each pump may be controlled from the Main Control Panel in the Control Room.

5.3.2.3.5 Piping

Piping throughout the system is carbon steel, except in the radiation detector/secondary sample loop and the chemical addition system, where it is PVC.

5.3.2.4 Non-Manual Valves

Water flow to the heat exchangers, the cooling tower cells, and cell 3 of the hybrid tower may be controlled with remotely operated or automatically controlled valves in the secondary piping system. Pneumatic positioners or electric motors are used to position the valves. These valves are:

· SCV-20 is the bypass valve for the cooling tower cells on the return, or hot, water piping to the cells and is normally throttled by a temperature controller that serves as a temperature control for the primary inlet water to the reactor vessel.

· SCV-4 is the potable water supply isolation valve for the cooling tower basin and is throttled by a level controller for the basin.

· SCV-7 can be used to bypass water around the dry and wet sections of cell 3. SCV-8 can be used to bypass the dry section of cell 3. Both valves can be operated from the Control Room.

· SCV-5 is the inlet isolation valve for the auxiliary heat exchangers and can be operated from the Control Room.

· SCV-12 is the inlet isolation valve for HE-2 and can be operated from the Control Room if a D2O storage tank pump is operating, which ensures the water pressure of the primary side of HE-2 is greater than the secondary side pressure.

· SCV-13 is the inlet isolation valve for HE-7 and is normally positioned by a signal from SCV-14 (TV-1002). That signal causes SCV-13 to move in the opposite direction of SCV-14 (TV-1002). For example, SCV-13 would be throttled in the close direction as SCV-14 (TV-1002) is throttled in the open direction.

· SCV-14 (TV-1002) is the inlet valve for HE-6 and is throttled by a temperature controller which maintains the temperature of the thermal shield cooling water on the outlet of HE-6.

· SCV-19 is the isolation valve between the shutdown pump strainer and the heat exchangers. The valve operates with the shutdown pump.

· SCV-50 is the isolation valve between the main secondary pump strainers and the main heat exchangers. The valve can be operated from the Control Room.

· The strainers for the main secondary system and the strainers for the HCSC system have inlet and outlet valves positioned by the strainer controllers.

The 100 psi (680 kPa) air to operate the pneumatic control valves is supplied by the Instrument Air System, which is described in Chapter 9, Auxiliary Systems. Air is directed to the pneumatic positioners of the control valves by solenoid valves, the power for which is 24 VDC from regulators in the rear of the Main Control Panel. Power for some of the control valves in the SCPB comes from local panels in the SCPB. It should be noted that no secondary system failure can cause an accident, so that failure of the air used to operate secondary valves has no effect on reactor safety.

5.3.2.5 Instrumentation

Necessary instrumentation is installed to remotely indicate the secondary cooling water flow, its temperature and pressure at various locations in the loop, the concentration of 16N in the water, and the level of the cooling tower basin. Local temperature and pressure indicators also are placed at various points in the system. Electrical power for the instruments is 24 VDC from the output of regulators powered from CP-1, a panel located in the Control Room.

5.3.2.5.1 Flow

The flow of secondary coolant through the main heat exchangers is measured by ultrasonic flow detectors mounted on the exterior of the inlet piping for each heat exchanger that is in service. Flow indications are in the Control Room and the range of each channel is 0-6,000 gpm (0-22,700 lpm).

The total secondary water flow, defined as main pump flow plus auxiliary pump flow, is measured by a 20-inch venturi located in the hot water piping upstream of the cooling tower. An alarm unit alerts the operator to a low flow condition. Flow indication is in the Control Room and the range of the channel is 0-12,000 gpm (0-45,400 lpm).

Total secondary water flow to the auxiliary heat exchangers is measured by a 5-inch (12.7-cm) venturi located in the common header piping on the outlet from the Secondary Auxiliary Pumps. Indication is in the Control Room and the range of the channel is 0-1,000 gpm (0-3,800 lpm).

The flow of secondary coolant through HE-2 is measured by an ultrasonic-flow element mounted on the exterior of the secondary piping to the heat exchanger. Indication is in the Control Room and the channel range is 0-300 gpm (0-1,135 lpm).

The flow of secondary coolant through HE-10 is measured by with a 6-inch (10.2 cm) orifice located in the discharge piping of the HCSC pumps. This flow transmitter supplies an electrical for local indication only and the channel range is 0-800 gpm (3,040 lpm).

5.3.2.5.2 Temperature

The temperature of the water in the cooling tower basin is measured with a thermocouple mounted in this basin. Indication is in the Control Room and the alarm unit has outputs that send a signal to annunciate a low temperature condition. The range of the channel is 30-130 °F (-1 to 54 °C).

The temperature of the secondary cooling water on the outlet of each main heat exchanger is measured with a thermocouple mounted in the 12-inch (30.5-cm) outlet piping for each heat exchanger. Indication is in the Control Room and the range of each channel is 50-150 °F (10-66 °C).

The inlet temperature of the secondary cooling water for the main heat exchangers is measured with a thermocouple mounted in the 20-inch (50.8-cm) secondary header piping. Indication is in the Control Room and the range of the channel is 50-150 °F (10-54 °C).

The temperature of the secondary cooling water to HE-6 is measured by a thermocouple mounted in the inlet piping for the heat exchanger. The temperature channel provides indication in the Control Room and the range of the channel is 50-125 °F (10-52 °C).

The outlet temperature of the secondary cooling water from the HE-2 is measured with a thermocouple mounted in the outlet piping for the heat exchanger. Indication is in the Control Room and the channel range is 50-125 °F (10-52 °C).

5.3.2.5.3 Pressure

Local pressure indications are generated with Bourdon-tube-type pressure gauges. Suction and discharge pressures of all pumps are sensed, as well as the inlet and outlet pressures of HE-2, 6, 7, and 10.

Differential pressure between the primary and secondary sides across each main heat exchanger and HE-2 is measured and an indication is provided in the Control Room. An alarm alerts the operator to a low ΔP condition across a heat exchanger. The range of each channel is 0-50 psid (0.35 MPa).

5.3.2.5.4 Radiation Monitors

The presence of 16N in the secondary coolant is indicative of a primary-to-secondary coolant leak. Secondary Cooling Radiation Monitors RM3-1 and RM3-3 provide redundant monitoring for 16N in the secondary coolant. A sample line taps off the common secondary discharge header after HE-1A and HE-1B, continuously diverting a small amount of secondary water for monitoring. Two Geiger-Mueller detectors are mounted in the piping of the 16N monitoring station located in Room D01. Local indication is provided at the monitoring station and remote indication is available in the Control Room. Alarm contacts sound an alarm when there is high activity in the secondary coolant. The range of both channels is 10-106 CPM.

5.3.2.5.5 Level

The cooling tower basin level is measured, indicated, and controlled by a level controller located which positions SCV-4, the basin makeup valve. An alarm unit has outputs that supply a signal to annunciate high-level and low-level conditions. Basin level indication is available in the Control Room and channel range is 0-80 inches (0-203 cm).

5.3.2.6 Secondary Strainer System

This subsystem uses three strainers for the main pumps, a backwash pump, a backwash assist pump, bag filter, and associated instrumentation to automatically remove debris from the secondary water. Debris collected by the strainers is flushed from the strainers by the backwash pump and to the bag filter by the backwash assist pump. The pumps cycle on after a pre-set time interval or a pressure differential across the strainer. Only one strainer can be backwashed at a time, as the others will be locked out by a signal from the strainer being backwashed. The bag filter traps the debris and an annunciator in the Control Room alarms after the bag filter inlet pressure increases to approximately 50 psig, indicating full filter bags.

The shutdown pump has a dedicated strainer and backwash pump, as does the HCSC system. Both of the backwash pumps discharge to the tower bypass piping, the debris from the strainers flowing to the suction of the main pumps and then to the strainers for the main pumps.

5.3.2.7 Make-Up Water

The local utility supplies the water used as make-up to the secondary cooling system via the domestic water system of the National Institute of Standards and Technology.

5-14 Table 5.1: Typical Operating Parameters for the Primary Coolant System

Parameter Value

Flow Rates:

Pressure:

Chemistry:

Volumes:

Figure 5.1: Primary Coolant System

Figure 5.2: Secondary Coolant System image1.emf image2.jpeg