COMPUTER SIMULATION IS INCREASINGLY BEING applied to the design and verification of nuclear reactor systems.

Computer integration and graphical technology can realise multi-discipline co-simulation and display calculation results and state parameters to simulation personnel. This can provide designers with quick analysis, verify working conditions and provide operators and engineers with various types of simulation training.

Virtual reality is now widely used, in industries as diverse as medicine, interior design, industrial simulation, maintenance, automobile simulation and fields in energy including nuclear power.

In nuclear power systems, virtual reality can help workers to plan, design and monitor reactors more easily and intuitively. It also provides a practical virtual simulation training system for plant operators. The professional skills and operational abilities of operators and managers are improved by this training, so virtual simulation plays an important role in improving nuclear safety.

Designing a virtual simulation system

A virtual simulation training system for a nuclear power plant can be established based on virtual reality, process modelling and visual experience equipment technology. The system architecture is shown in Figure 1.

To strengthen the sense of bringing physical objects into operation, physical objects are introduced into the system and they communicate with the simulation model through an Ethernet bus to result in a real device response. At the same time, augmented reality technology enables operators to integrate real world information and virtual world information, to achieve a sensory experience ‘beyond reality’. The real environment and virtual objects are superimposed in the same space in real time.

The nuclear power system virtual simulation training system architecture is shown in Figure 1. It includes:

1 A virtual simulation system using virtual reality technology

This establishes a three-dimensional virtual reality model of the primary loop and control system of a nuclear reactor, to intuitively reflect the structure and operating status of the primary loop and connect the virtual reality scene and the primary loop simulation.

2 Mathematical modelling of dynamic operation of the PWR system

A dynamic model of a PWR comprises at least the following models: primary loop mean temperature; neutron dynamics, temperature neutron interact dynamics, core fuel and coolant temperature; power operation temperature; zero power operation temperature; steam generator; and reactor control system.

3 Virtual simulation of operation control of PWR system

Virtual simulation for operation control is based on the high-level architecture (HLA) and analysis of the PWR’s primary loop system . The mathematical model calculation, three-dimensional view and two-dimensional situation is based on the SIMUWORKS distributed network platform. The openness of HLA and the reusability of simulation make this easy to expand to a virtual simulation of the entire system.

4 Fault simulation

The virtual training system includes the following simulation conditions and faults:

  • Normal operation and transients of operation, including frequent events during reactor power operation, shutdown, maintenance and fuel replacement.
  • Anticipated operational events that deviate from normal operation once or several times during the operating life of a reactor, such as fuel assembly damage, turbine trip or loss of external load.
  • Rare events that are likely to cause partial fuel damage and prevent the reactor from resuming operations for a considerable period of time, but will not entail loss of main systems or containment, or have radiological implications outside the public areas. Examples are a small pipe burst, the power operated relief valve remaining open by mistake, damage to the waste gas processing system, etc.

System construction

The virtual simulation training system consists of a three-dimensional model, a visual drive, process modelling, a digital simulation engine and visual experience equipment.

The 3D visual scene adopts a modular approach. The process modelling system uses Fortran to build a working process model of each item of equipment, which is the key to a real-time simulation system. The digital simulation engine uses the SIMUWORKS platform, which can simulate equipment in each function, such as operating sequence, fault setting and simulation under working conditions, The visual experience equipment includes control handles, virtual helmets and multi-channel stereo projection systems, giving personnel a sense of reality.

Developing the three-dimensional virtual reality system starts by using 3ds Max to create three-dimensional models of related structures such as virtual humans, reactor control systems, primary loop systems and integrated display platforms.

The independent model is set up using operations such as cutting and separating the structures that require interaction, while the model that does not need interaction is optimised for triangles. Finally, rendering and baking are performed to generate the final texture map.

Once the model has been made it is saved in FBX format file and imported into Unity3D. Lighting and other resources are added to build an interactive scene, design a friendly interactive interface, and implement interactive functions through scripting. After the basic interaction is completed, the helmet is connected with the Unity3D program, and an immersive visual system is developed based on the helmet. The technical route of 3D virtual reality modelling is shown in Figure 2.

The reactor primary loop system has four models: neutron dynamics; coolant and core fuel; steam generator; and coolant pipeline.

The power system comprises the primary and secondary loop subsystems.

The primary loop is composed of the nuclear reactor, main pump and pressure stabilizer. The steps are:

  • Establish and solve the mass and energy equation between the models through mathematical methods.
  • Input the temperature difference ΔTθ1 at the inlet of the fuel pipe, the temperature difference ΔTθ2 at the outlet of the fuel pipe, the core fuel temperature deviation ΔTF, the boron concentration and other parameters into the selected machine learning model.
  • Calculate the average temperature and boron concentration of the nuclear reactor coolant.
  • Analyse the stability and transient of reactor power, and evaluate the results obtained from each analysis and learning, then through the back-propagation neural network to optimising the learning.

After sufficient training, this allows for optimal control of reactor power, boron concentration and average coolant temperature. The technical route of reactor primary loop modelling is shown in Figure 3.

System operation

Before the system begins operation, it is necessary to configure the HTC head-mounted display device and the client, and deploy the operating space of the locator.

Trainees start the client program on the PC client, and enter the nuclear power virtual training system through registration or login.

They can choose training tasks and enter different scenarios. For example, after the trainee selects the nuclear power control system training task, trainees enter the nuclear power control system scene. They are integrated into the scene through the head-mounted display and they can roam the scene in a panoramic view by moving their head, or use the controller.

After selecting the fault-training task, the client loads the corresponding fault model after obtaining processing information requested by the server.

When the system development is completed, an open test is conducted for the trainees. They generally report that the head-mounted display has a stronger sense of immersion and substitution than the virtual scene in their PC terminal, and roaming is closer to the experience of the real environment. Interacting with the scene using the handheld controller is more participatory than keyboard and mouse interaction.

The overall feedback is that the system experience is ideal, but the details in some scenes need to be enhanced.

Conclusion

Using virtual reality, process modelling and visual experience equipment technology, we have established a virtual simulation training system for nuclear control equipment.

Trainees can create multiple training projects through the system, including theoretical knowledge training of various equipment, work training, troubleshooting, etc. The system can be used to train personnel, improve their knowledge of nuclear control equipment, and improve their capacity to solve problems.

Compared with the traditional physical training system, this system has the following advantages:

  • It is easy to modify, whereas it is more cumbersome to modify and replace traditional physical training.
  • It is easy to expand by increasing the training support system. For example, before roaming to a component the user can see explanatory text about it.
  • It provides a better research environment for human factors engineering research.

The authors are with the Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China, Chengdu, 610213, China