Development of a model of the industrial circuit system of oil coolers of NPP with WCWR#

The industrial circuit of oil coolers of NPP with WCWR reactors is designed to remove heat from equipment connected to the cooling system during normal operation. The system is designed according to the intermediate circuit principle: the water in the intermediate circuit passes through the consumers, removes heat from them, and is then cooled in plate heat exchangers.

The system includes pumping equipment, pipelines, shut-off and check valves, mesh filters, plate heat exchangers and sensors. To maintain the system’s operability, backup equipment is provided: one of the pumps and one of the heat exchangers can be kept in reserve and switched on if the working equipment fails.

The developed model of the industrial circuit system of oil coolers of the NPP allows:

Set the system to the nominal operating mode;
Check the distribution of flows, pressures and temperatures;
Implement protection and blocking algorithms for pumping equipment and electric drive valves;
To study the behavior of the system when the characteristics of the filtering and heat exchange equipment deteriorate.

Gratitude

We would like to express our gratitude to the author of this guide, Aspidov Nikita Vyacheslavovich, for his contribution to the development of the REPEAT VISION platform.

1. Problem conditions#

1.1. Simulation object#

The modeling object is the industrial circuit system of oil coolers, including equipment (see Fig. 1 below):

three industrial circuit pumps: 21AP001, 22AP001, 23AP001;
three plate heat exchangers: 21AC001, 22AC001, 23AC001;
mesh filters: 81AT001, 82AT001, 83AT001;
electric drive fittings in the suction pipes and pump head: 81/82/83AA001, 81/82/83AA002;
electric drive valves at the inlet and outlet of heat exchangers: 81/82/83AA003, 81/82/83AA004;
check valves on the pump discharge: 81AA601, 82AA601, 83AA601;
pressure, differential pressure, temperature and flow sensors.

Note

Each pump is designed for 50% of the total flow rate, and each heat exchanger is designed for 50% of the heat output. In this model, the line with pump 23AP001 and heat exchanger 23AC001 serves as a backup. In nominal mode, the flow through it should be close to zero.

Fig. 1 Technological diagram of the industrial circuit system of oil coolers#

1.2. Initial data for building the model#

The parameters of the equipment, pipelines, fittings, protections and monitored sensors are given in the original tables:

System hardware characteristics

Name	Marking according to the scheme	Location mark, m	Number of wor./res.	Main technical characteristics of the equipment
Industrial circuit heat exchanger	21AC001 22AC001 23AC001	+2.5	2/1	Heat exchanger parameters: Type - plate; Mutual movement of coolants: counter-current; Number of plates: 216; Plate length: 2.3 m; Plate width: 1 m; Distance between plates: 0.006 m; Plate surface area increase coefficient: 1.25; Darcy friction coefficient (cooled medium): 1.58; Darcy friction coefficient (cooling medium): 1.35; Loss coefficient for the input and output of media: 1.5; Fouling coefficient of media surfaces: 0.1 K m²/kW
Industrial circuit pump	21AP001 22AP001 23AP001	0	2/1	Cooling water: Inlet temperature: 26 °C; Outlet temperature: 29.4 °C; Excess pressure at the inlet: 83 kPa; Nominal flow rate, l/min: 11315; Nominal pressure, m: 62.8; Nominal resistance power, W: 145300; Maximum pressure: 74.6; Maximum flow rate, l/min: 20787; Nominal shaft speed, rpm: 27.5; Minimum ratio of shaft speed to nominal: 0.01; Ratio of wheel diameter to nominal diameter: 1.0

Characteristics of the main flow pipelines of the system

Name of the main flow pipeline of the system	Dn, mm	Dout × S, mm	L, m	Environ	Material	Roughness coefficient
Common manifold on the pump suction side before the valves 81/82/83AA001	500	530×8	3.0	Desalinated water	Carbon steel	0.00004
Pipeline from valves 81/82/83AA001 to filters 81/82/83AT001	400	426×9	1.0	Desalinated water	Carbon steel	0.00004
Pipeline from filters 81/82/83AT001 to the suction of pumps 21/22/23AP001	400	426×9	5.0	Desalinated water	Carbon steel	0.00004
Pump pressure pipeline to check valves 81/82/83AA601	300	325×8	3.0	Desalinated water	Carbon steel	0.00004
Pipeline from check valves 81/82/83AA601 to valves 81/82/83AA002	300	325×8	0.1	Desalinated water	Carbon steel	0.00004
Pipeline from valves 81/82/83AA002 to the common manifold	300	325×8	5.0	Desalinated water	Carbon steel	0.00004
Common manifold for pump pressure up to valves 81/82/83AA003	500	530×8	2.0	Desalinated water	Carbon steel	0.00004
Water supply pipeline to the heat exchangers of the industrial circuit 21/22/23AC001	350	377×9	3.0	Desalinated water	Carbon steel	0.00004
Water drain pipeline from heat exchangers of industrial circuit 21/22/23AC001 to valves 81/82/83AA004	350	377×9	3.0	Desalinated water	Carbon steel	0.00004
Pipeline from valves 81/82/83AA004 to the common water drain collector from the heat exchangers of the industrial circuit 21/22/23AC001	500	530×8	5.0	Desalinated water	Carbon steel	0.00004
Common water drain manifold from heat exchangers of the 21/22/23AC001 industrial circuit	500	530×8	1.0	Desalinated water	Carbon steel	0.00004
Cooling water supply pipeline to the heat exchangers of the industrial circuit 21/22/23AC001	200	219×6	5.0	Desalinated water	Carbon steel	0.00004
Cooling water drain pipeline from heat exchangers of the 21/22/23AC001 industrial circuit	200	219×6	5.0	Desalinated water	Carbon steel	0.00004

Characteristics of the system fittings

Name	Marking	Passage diameter	Working environment	Control method
Gate valve on the suction side of the industrial circuit pumps	81AA001 82AA001 83AA001	400	Desalinated water	Electric drive
Gate valve on the discharge of industrial circuit pumps	81AA002 82AA002 83AA002	300	Desalinated water	Electric drive
Check valve on the discharge of the industrial circuit pump	81AA601 82AA601 83AA601	280	Desalinated water	-
Gate valve at the inlet to the heat exchangers of the industrial circuit	81AA003 82AA003 83AA003	500	Desalinated water	Electric drive
Gate valve at the outlet of the heat exchangers of the industrial circuit	81AA004 82AA004 83AA004	350	Desalinated water	Electric drive

List of system protections and blockings

Protection №, blocking	Name and KKS of the equipment	Conditions for blocking to occur
1	Cooling water pump 21AP001	Shutting down pump 21AP001 when the following events coincide: 1) pump 21AP001 is in operation; 2) the pressure in the pump discharge manifold (sensor pos. 80CP001) is greater than 0.6 MPa
2	Cooling water pump 22AP001	Shutting down pump 22AP001 when the following events coincide: 1) pump 22AP001 is in operation; 2) the pressure in the pump discharge manifold (sensor pos. 80CP001) is greater than 0.6 MPa
3	Cooling water pump 23AP001	Shutting down pump 23AP001 when the following events coincide: 1) pump 23AP001 is in operation; 2) the pressure in the pump discharge manifold (sensor pos. 80CP001) is greater than 0.6 MPa
4	Cooling water pump 21AP001	Shutting down pump 21AP001 when one or more events occur: 1) the pressure at the discharge of pump 21AP001 is more than 0.66 MPa (sensor pos. 81CP002); 2) the pressure at the suction of pump 21AP001 is less than 0.117 MPa (sensor pos. 81CP001)
5	Cooling water pump 22AP001	Shutting down pump 22AP001 when one or more events occur: 1) the pressure at the discharge of pump 22AP001 is more than 0.66 MPa (sensor pos. 82CP002); 2) the pressure at the suction of pump 22AP001 is less than 0.117 MPa (sensor pos. 82CP001)
6	Cooling water pump 23AP001	Shutting down pump 23AP001 when one or more events occur: 1) the pressure at the discharge of pump 23AP001 is more than 0.66 MPa (sensor pos. 83CP002); 2) the pressure at the suction of pump 23AP001 is less than 0.117 MPa (sensor pos. 83CP001)
7	Electric drive fittings 82AA002 on pump pressure 22AP001	Opening of valve 82AA002 at the pressure of pump 22AP001 10 seconds after its switching on
8	Electric drive fittings 83AA002 on pump pressure 23AP001	Opening of valve 83AA002 at the pressure of pump 23AP001 10 seconds after its switching on
9	Electric drive fittings 81AA002 on pump pressure 21AP001	Closing valve 81AA002 at the pressure of pump 21AP001 after its shutdown
10	Electric drive fittings 82AA002 on pump pressure 22AP001	Closing valve 82AA002 at the pressure of pump 22AP001 after its shutdown
11	Cooling water pump 21AP001	Ensure that the backup pump 23AP001 starts when the working pump 21AP001 stops
12	Cooling water pump 22AP001	Ensure that the backup pump 23AP001 starts when the working pump 22AP001 stops

Readings of controlled parameters in the nominal operating mode

№	KKS sensor	Sensor description	Value nom.	Min/max value	Units of measurement
1	80CT001	Temperature at the discharge manifold of the industrial circuit pumps of the oil coolers	32.15	23/60	°C
2	80CP001	Pressure in the discharge manifold of the oil cooler circuit pumps	0.594	0/0.75	MPa
3	81CP003	Pressure drop across the filter mesh	10.3	0/15.0	kPa
4	82CP003	Pressure drop across the filter mesh	10.3	0/15.0	kPa
5	83CP003	Pressure drop across the filter mesh	0.0	0/15.0	kPa
6	81CP004	Pressure drop on heat exchanger 21AC001 (industrial circuit water)	13.8	0/0.50	kPa
7	82CP004	Pressure drop on heat exchanger 22AC001 (industrial circuit water)	14.0	0/0.50	kPa
8	83CP004	Pressure drop on heat exchanger 23AC001 (industrial circuit water)	0.0	0/0.50	kPa
9	81CP001	Suction pressure of the oil cooler circuit pump 21AP001	0.154	0/0.5	MPa
10	82CP001	Suction pressure of the oil cooler circuit pump 22AP001	0.154	0/0.5	MPa
11	83CP001	Suction pressure of the intermediate circuit pump of oil coolers 23AP001	0.166	0/0.5	MPa
12	81CP002	Pressure at the discharge of the pump of the industrial circuit of oil coolers 21AP001	0.636	0/0.75	MPa
13	82CP002	Pressure at the discharge of the pump of the industrial circuit of oil coolers 22AP001	0.636	0/0.75	MPa
14	81CT002	Temperature at the outlet of the heat exchanger 21AC001	27.9	23/60	°C
15	82CT002	Temperature at the outlet of the heat exchanger 22AC001	27.9	23/60	°C
16	83CT002	Temperature at the outlet of the heat exchanger 23AC001	29.9	23/60	°C
17	84CT001	Temperature at the outlet manifold of the heat exchangers	27.9	23/60	°C
18	84CF001	Flow rate at the outlet manifold of heat exchangers	326.6	0/2600	kg/s
19	31CP001	Pressure drop across heat exchanger 21AC001 (cooling water)	44.0	0/65.0	kPa
20	32CP001	Pressure drop across heat exchanger 22AC001 (cooling water)	44.0	0/65.0	kPa
21	33CP001	Pressure drop across heat exchanger 23AC001 (cooling water)	0.0	0/65.0	kPa

Note

In the tables, Dn refers to the nominal bore of the pipeline, and Dout × S refers to the outside diameter and wall thickness. When specifying the diameter in model blocks, the inside diameter is used. For example, for a pipe 530×8 mm, the inside diameter is 530 - 2·8 = 514 mm.

1.3. Statement of the problem#

It is necessary to develop a model of the industrial circuit of oil coolers, configure it for the nominal operating mode and check the system’s behavior when protections, interlocks and failure scenarios are in operation.

The work consists of four stages:

Assembling the system’s thermal-hydraulic diagram. This involves setting the parameters for pipelines, valves, pumps, and heat exchangers.
Setting the nominal operating mode. The rotation speed of the operating pumps is determined by solving an optimization problem. The flow rate at the outlet manifold should be close to 326.6 kg/s, and the sensor readings should correspond to the nominal values from the original tables.
Implementation of protection and interlocks for pumping equipment and motorized valves. For motorized valves, a valve position change pattern is specified, such as linear or exponential. For pumps, a soft start and soft stop are implemented to prevent abrupt transitions in the model.
Execution of equipment failure scenarios associated with deterioration of filter and heat exchanger performance:

for the 81AT001 filter, the increase in hydraulic resistance is simulated. The local resistance coefficient increases by a factor of 10 according to a linear or exponential law. Based on the calculation results, it is necessary to show the operation of the automation on the pump 21AP001, and also to plot graphs of the change in pressure drop on the filter and the local resistance coefficient;
for the 22AC001 heat exchanger, plate fouling is simulated. The fouling coefficient for both media increases to 0.005 m²·K/W. After the calculation, it is necessary to determine the change in the intermediate circuit water temperature at the heat exchanger outlet and at the outlet manifold.

1.4. Initial and boundary conditions#

Parameter	Value
Temperature of industrial circuit water at the inlet to the system	32.15 °C
Excessive water pressure of the industrial circuit at the entrance to the system	0.166 MPa
Temperature of the industrial circuit water at the outlet of the system	27.9 °C
Excessive water pressure of the industrial circuit at the outlet of the system	0.58 MPa
Water consumption in a closed system	326.6 kg/s
Heat exchange with the environment	not taken into account

Note

Demineralized water is used as the working medium. The thermal properties of water are defined according to IAPWS-95 or IAPWS-97.

2. I Assembling the model#

At the first stage, it is necessary to assemble the thermo-hydraulic part of the model.

Below is shown a general view of the circuit that needs to be assembled, Fig. 2 :

Схема промконтура маслоохладителей — Fig. 2 General view of the industrial circuit diagram of oil coolers#

2.1. Setting boundary conditions, water properties and connecting sensors#

Boundary and initial conditions are specified using Reservoir (TH) blocks. One reservoir is used at the system inlet, the second one at the system outlet.
Thermophysical properties of water are specified using the Liquid properties (TH) block.
To connect sensors and combine flows, Node (TH) blocks are used.

Note

When setting the parameters of fittings, pumps and filters, the cross-sectional area of the ports is calculated based on the diameter of the pipeline connected to the inlet port of the corresponding block.

2.2. Sales of pumps#

Pumps 21AP001, 22AP001 and 23AP001 are implemented by the blocks Centrifugal pump (TH) and Angular velocity source, Fig. 3 :

Схема насоса — Fig. 3 Pump implementation#

For the backup pump 23AP001, the value 0 is set in the nominal mode, since it does not participate in the operation of the system.

For working pumps 21AP001 and 22AP001, the value of the global variable w is fed to the angular velocity source input. This is necessary for subsequent changes in its value when solving the optimization problem.

Variable	Value	Description
w	152	Initial value of the angular velocity of the pump, [rad/s]

2.3. Implementation of electric valves#

Electric-driven valves are implemented by the block Gate valve (TH). The position of the valve is set by the opening control signal, Fig. 4 :

Схема арматуры — Fig. 4 Implementation of the valve#

In normal operation, the valves on the working lines are open. In the backup line, the valve at the pump discharge 23AP001 and the valve at the heat exchanger outlet 23AC001 are closed. This prevents flow through the backup equipment in normal operation.

2.4. Implementation of mesh filters and selection of the resistance coefficient#

The mesh filters 81AT001, 82AT001 and 83AT001 are represented in the model by the block Local resistance (TH). This approach is used because the filter primarily affects the hydraulic resistance of the branch and creates a pressure drop when water passes through it.

The resistance coefficient of the block must be selected so that the pressure drop across the working filter is close to the nominal value of 10.3 [kPa].

The selection can be performed manually: change the coefficient value in the block properties, run the calculation and compare the resulting pressure drop with the required one. However, this method is inconvenient, since after each change of the parameter it is necessary to re-perform the calculation and check the sensor readings.

To speed up the setup, the local resistance coefficient is selected using the Jython block. The calculated pressure drop across the filter is transmitted to the input of the block, and a new resistance coefficient value is generated at the output.

The Jython block uses an iterative fitting of the local resistance coefficient. If the calculated pressure drop across the filter (see Fig. 5 below) differs from the required one, the coefficient is recalculated using the ratio of the nominal drop to the calculated one (1) :

(1)#\[ \xi_{\text{нов}} = \xi_{\text{тек}} \cdot \frac{\Delta p_{\text{ном}}}{\Delta p_{\text{расч}}} \]

Схема фильтра — Fig. 5 Filter implementation#

Note

Automatic selection of the resistance coefficient allows maintaining the pressure drop across the working filter close to 10.3 [kPa] when the flow rate in the working line changes. Therefore, to set the nominal mode, it remains to select the value of the global variable w.

2.5. Implementation of heat exchangers#

Heat exchangers 21AC001, 22AC001 and 23AC001 are implemented by the block Plate heat exchanger (TH-TH), Fig. 6 :

Схема подбора давления на выходе охлаждающей воды — Fig. 6 Selection of pressure at the cooling water outlet#

Two thermal-hydraulic media are connected to the block: industrial circuit water and cooling water. The water side of the industrial circuit is connected to the main circuit of the model, and the cooling water side is connected to a separate branch with boundary conditions.

For the cooling water side, the inlet boundary condition and the nominal pressure drop across the heat exchanger are known. Therefore, the cooling water outlet pressure can be conveniently selected using a PID controller.

PID controller varies the outlet limit pressure until the calculated pressure drop on the cooling water side becomes close to the nominal value.

3. II Setting the nominal mode#

After assembling the thermal-hydraulic circuit, the model is configured for nominal operation. The main adjustable parameter is the shaft speed of the working pumps 21AP001 and 22AP001.

The rotation speed is selected so that the flow rate at the outlet manifold is close to the nominal value of 326.6 [kg/s].

Since the angular velocity of the working pumps is specified via the global variable w, to configure the mode it is sufficient to change the value of this variable.

The value of w can be selected manually. Increasing the pump angular velocity increases the flow rate at the outlet manifold, which is monitored by the 84CF001 sensor. However, to speed up the setup, it is convenient to solve an optimization problem in which the objective function shows the deviation of the calculated flow rate from the nominal (2) :

(2)#\[ F(w) = \left| G_{\text{расч}}(w) - G_{\text{ном}} \right| \]

where:

\(G_{calc(w)}\) — calculated flow rate at the outlet manifold at the current value of w;

\(G_{nom}\) is the nominal flow rate, equal to 326.6 [kg/s].

Note

More details on solving this optimization problem are described in the tutorial Optimization of working fluid flow rate in the industrial circuit of NPP oil coolers based on pump rotation frequency.

The resulting value is w ≈ 152.5075 [rad/s].

Hint

For independent study of the model under consideration, you can download file with an assembled thermal-hydraulic circuit and a configured nominal mode.

3.1. Nominal mode check#

When the value of w is found, the main calculated readings of the sensors should be close to the nominal values.

KKS sensor	Controlled parameter	Received value
`80CT001`	Temperature at the discharge manifold of the pumps	32.15 °C
`80CP001`	Pressure in the discharge manifold of the pumps	0.594 MPa
`81CP003`	Pressure drop across filter `81AT001`	10.3 kPa
`82CP003`	Pressure drop across filter `82AT001`	10.3 kPa
`83CP003`	Pressure drop across filter `83AT001`	`0.0 kPa`
`81CP004`	Pressure drop across heat exchanger `21AC001`	13.8 kPa
`82CP004`	Pressure drop across heat exchanger `22AC001`	14.0 kPa
`83CP004`	Pressure drop across heat exchanger `23AC001`	0.0 kPa
`81CT002`	Temperature at the outlet of the heat exchanger `21AC001`	27.9 °C
`82CT002`	Temperature at the outlet of the heat exchanger `22AC001`	27.9 °C
`84CT001`	Temperature at the outlet manifold of the heat exchangers	27.9 °C
`84CF001`	Flow rate at the outlet manifold of heat exchangers	326.6 kg/s

Note

Nominal values are used as a guide for model tuning. Depending on the selected model level of detail, minor deviations are allowed as long as they do not interfere with the physical operation of the system.

4. Preparing the model for automation implementation#

Before implementing automation, the model configured for the nominal mode must be simplified and converted to a form convenient for connecting control signals.

To do this, the following changes are made (see Fig. 7 below):

The filter resistance coefficient values are fixed. For this purpose, the Jython blocks used for automatic selection are deleted, and constant loss coefficient values obtained during the nominal mode setup stage are specified in the Local resistance (TH) blocks.
The PID controller used to select the cooling water outlet pressure is removed. The resulting boundary condition value is set directly in the tank block as a constant.
Continuous control signals are removed from the valves on the pump head and from the pump angular velocity sources. At the next stage, the position of the valves and the rotation frequency of the pump shafts will be determined by automation algorithms.

Fig. 7 Changes in the model before implementing automation#

For convenient visual connection of automation, we will use the blocks GO TO and GO FROM. They allow signals to be transmitted between remote sections of a circuit without long connecting lines, Fig. 8 :

Схема модели для подключения автоматики — Fig. 8 Model diagram prepared for connecting automation#

5. III Implementation of automation#

At the third stage, protection and blocking algorithms for pumping equipment and electric drive valves are added to the model. Automation is implemented in separate groups for pumps 21AP001, 22AP001 and 23AP001, Fig. 9 :

Each automation group receives signals from pressure sensors and generates control actions:

signal to the pump angular velocity source
pump pressure valve opening signal
pump status signal used in the backup equipment start logic

Next, let us consider the operation of the automation using the example of the pump group 21AP001.

5.1. Pump automation 21AP001#

The automation group of pump 21AP001 generates a control signal to the source of the angular velocity of the pump and a control signal to the valve 81AA002 on its pressure, Fig. 10 :

The input signals for the group are the pressure sensor readings and the pump angular velocity signal:

80CP001 — pressure in the discharge manifold of pumps
81CP001 — pressure in the suction pipe of pump 21AP001
81CP002 — pressure at the discharge of pump 21AP001
pump angular velocity signal - used to check the condition that the pump is in operation

The pump is considered to be in operation if a non-zero value is supplied to the angular velocity source.

Pump 21AP001 switches off when one of the following conditions is met:

The pressure in the discharge manifold 80CP001 is greater than 0.6 [MPa] if the pump is in operation
The discharge pressure of pump 81CP002 is greater than 0.66 [MPa]
The pressure in the suction pipe of the pump 81CP001 is less than 0.117 [MPa]

To check the conditions, the Compare to Constant blocks are used. They specify the protection settings: 0.60 [MPa], 0.66 [MPa] and 0.117 [MPa].

Logical signals are combined by blocks Logical AND, Logical OR.

The protection triggering is detected by the SR latch block. When a shutdown signal appears, the trigger transitions from 0 to 1 and maintains this state. This prevents the pump from restarting immediately after the short-term protection signal disappears.

After the SR latch there is a Logical NOT block, which inverts the trigger signal.

The signal is then multiplied by the value of the global variable w using the Multiplication block. As a result, the following is supplied to the angular velocity source:

w if protection failed;
0 if the protection worked.

For smooth starting and stopping, the Inertia block block is used. Thanks to this, the shaft rotation speed changes gradually, without a jump.

The valve 81AA002 on the pump discharge closes after the pump is switched off. Its position also changes smoothly with the help of an inertial link.

Note

To protect against low pressure in the pump suction pipe, it is additionally checked that 81CP001 > 0. This eliminates false alarms during the first calculation iteration, when the sensor signal may still be zero.

5.2. Pump automation 22AP001#

The automation of the pump 22AP001 is built on the same principle as the automation of the pump 21AP001, Fig. 11 :

The difference between the 22AP001 automation group and the 82AA002 valve is related to its control. After the pump is turned on, the valve opens at its pressure with a delay of 10 [s].

5.3. Pump automation 23AP001#

Pump 23AP001 is used as a backup pump, so its automation system additionally receives signals to turn off the working pumps 21AP001 and 22AP001, Fig. 12 :

When one of the working pumps is switched off and the backup pump protections are not triggered, the start command 23AP001 is generated.

The control logic of the pressure valve 83AA002 is similar to the logic for 82AA002.

Hint

For independent study of the implemented automation, you can download the finished model.

6. IV Failure scenarios#

At the fourth stage, failure scenarios associated with deterioration of the characteristics of filtering and heat exchange equipment are carried out.

6.1. Increase in hydraulic resistance of filter 81AT001#

The local resistance coefficient of the filter is increased linearly using the Piecewise-linear function block, Fig. 13 :

The increase begins 30 [s] after the start of the calculation and lasts 10 [s]. During this time, the drag coefficient increases by 10 times (see Fig. 14 below). The delay before the increase is needed to allow the working branches to reach a steady state after the model is launched.

График 1 — Fig. 14. Increase in resistance of filter 81AT001 and activation of low pressure protection in the suction pipe of pump 21AP001#

The graphs show that after the resistance coefficient begins to increase, the pressure drop across the 81AT001 filter increases, and the pressure in the suction pipe of the 21AP001 pump decreases. When the setpoint of 0.117 [MPa] is reached, the low pressure protection condition in the pump suction pipe is triggered, Fig. 15 :

График 2 — Fig. 15 Shutting down pump 21AP001 and starting the backup pump 23AP001#

After the protection is triggered, pump 21AP001 gradually stops, and valve 81AA002 closes at its pressure. The automation then generates a command to start the backup pump 23AP001. Its rotational speed gradually increases, and valve 83AA002 opens with a delay.

Hint

To independently study the failure scenario, you can download the model with the implemented increase in the hydraulic resistance of the filter 81AT001 and the automatic start of the backup pump.

6.2. Contamination of heat exchanger plates 22AC001#

In the second failure scenario, the contamination coefficient of the heat exchanger surfaces 22AC001 increases to 0.005 [m²·K/W] = 5 [m²·K/kW] for both environments. After the calculation, the temperatures of the industrial circuit water before and after the failure are compared.

Controlled parameter	Before pollution	After contamination	Change
Temperature of industrial circuit water at the outlet of `22AC001`	27.9 °C	31.5 °C	+3.6 °C
Temperature of the industrial circuit water at the outlet manifold	27.9 °C	29.7 °C	+1.8 °C

According to the table, contamination of the plates of the heat exchanger 22AC001 leads to an increase in the temperature of the water in the industrial circuit after this heat exchanger and on the outlet manifold.

Hint

To independently study the failure scenario, you can download the model with realized fouling of the heat exchanger plates 22AC001.

7. Conclusions#

Within the framework of this practical guide, you managed to master the basic principles of developing a one-dimensional thermal-hydraulic model of the industrial circuit of oil coolers of NPP with WCWR: assembling the circuit, setting the nominal mode, implementing automation and analyzing failure scenarios.

The developed model allows us to check the distribution of flow rates, pressures and temperatures, evaluate the operation of pumping equipment protections and interlocks, and also study the system’s behavior when the performance of filtering and heat exchange equipment deteriorates.

This approach helps to verify adopted technical solutions and assess the impact of failures before conducting more detailed calculations or tests.