According to IAEA requirements the power unit project shall pass the verification process - testing on experimental models. While the physical stand is developed closer to the completion of the design of the reactor, its virtual analogue allows one to make adjustments to the design at the early stages of development. Using such stands it is possible to calculate algorithms in advance, eliminate discrepancies, which, in its turn, will increase the accuracy of work, and help reduce the time and cost of the project at all the stages. The virtual stand provides invaluable contribution for commissioning activities on new power units - initially the operation of equipment is tested in virtual mode, which will definitely increase the accuracy of work, while reducing the time and cost. One of these stands is the development of JSC “Afrikantov OKBM”, whose functions were described in detail by Igor Zotov, design engineer of the department for calculating the dynamics of systems and monitoring the automation of JSC “Afrikantov ОКBM”.
- Igor, please tell us about what is a virtual stand of nuclear power plant?
- Our development is a tool for testing the automation algorithms and modes during the design of the reactor and nuclear power plant as a whole. The use of this modeling complex allows us to quickly determine the consequences of equipment failure and make adequate decisions when designing a reactor, which is extremely important during tests with innovative reactors. Additionally, since a virtual control panel is available, this is also a computer simulator for personnel training. In other words, we have a digital prototype of a nuclear power plant.
The stand is based on a calculation code developed by OKBM specialists with participation of physicists, mathematicians, programmers, and the stand itself was designed by engineers and designers. This is a tremendous work that took about a year and brought together a huge number of people of different professions.
- What serves as idea for creation of a virtual stand ?
- The idea was born from the fact that our enterprise - JSC “Afrikantov OKBM” - designs various reactor plants. For example, for an icebreaker installation at the very early stages of design activities we wanted to work out all the control algorithms, check, how closely they are connected between themselves and whether they contradict each other. But for that one needed to have a tool. It should be noted that the calculations of a complex model of nuclear power plant are very difficult to carry out on a standard pc even with two-four monitors, because there is a control panel, automation, reactor model, steam turbine plant model. Due to these difficulties an idea came to make a stand. But initially it was planned to be in a smaller size. Eventually, during the discussion an idea was born to create such a scale tool that will help us to test all the designed reactor plants.
- Which functions are tested on that stand ?
- For our department for calculating dynamics and monitoring automation the main thing is to understand how the installation works in dynamic modes, maneuvering modes, and how good are the algorithms which were selected to control the installation, how correctly all the units allow these modes to be carried out. The first thing we have to do is to work out all the dynamic modes: startup and heating modes, power maneuvering, shut down of the plant with its cooling down. When testing the modes we also check the quality of control algorithms.
In other words, initially a designer writes algorithms on paper, where everything is prescribed in words. Programmer translates them into the text that the machine understands. And we check how the algorithms supplied to the system are interconnected with each other. Why is this needed ? Every year, installations grow more and more complicated, more and more automation is introduced, and it becomes more difficult for an appropriate specialist to take into account all the parameters when writing algorithms. There is no doubt that they need to be checked and verified with the object of control, in our case - with nuclear power unit. That is why we need a reactor model, a steam turbine plant model, a control system model and a control panel. For those purposes, a virtual stand was created on which the dynamics of the plant and its control functions are tested.
- What potential accidents and technical faults does the system take into account?
- The features of the reactor, steam turbine plant and auxiliary systems are taken into account. But such things as features of the buildings, aircraft crash and natural disasters are not taken into account. The system takes into account the processes occurring inside the nuclear power plant. At this point, accidents can include various leaks, failures of pumps and valves. We can also calculate a number of beyond design basis accidents, but we focus mainly on the normal operation of the plant, on the malfunctions in the normal operation which are caused by equipment failures. Additionally, we focus on design basis accidents.
- Is it possible at a virtual stand to test the technologies that are still at the design stage?
- Yes. It is an advantage of the virtual simulator that even at the design stage there is already a model which can be connected to the control panel. We also use this model for technical solutions to see how they affect the plant in the future. All this is closely interconnected with the way how we manage the plant. Already at an early stage, we have a fairly detailed complex model with which the personnel can begin to work. But with such a simulator it is impossible to work out some motor skills, for example, where to move the hand, where to switch the button. But it seems quite possible to get an idea of how the plant behaves in certain modes. Of course, a virtual stand can not replace a full-scale simulator, but such a conceptual simulator enables one in the early stages to begin personnel training for the maintenance service of future nuclear power station.
- Which new reactors have been already tested on the stand ?
- Reactor RITM-200 has been tested on the stand. A series of such reactors are installed on new universal nuclear icebreakers which are under construction now. For this reactor we made a full-fledged model, which includes two reactor and steam turbine units. We were visited by instructors who work on full-scale simulator, and together we worked on a virtual stand and worked out the modes which they were interested to watch. Sometimes there can be inconsistencies in the preparation documentation and that is why they were interested in learning the details firsthand.
Now we have a virtual power unit BN-1200, which we are upgrading to BN-1200M. The reactors BN-1200 are still on the design stage. Project BN-1200M is being currently upgraded. As you can see, we have already a model with which we can work, use it to work out laws and control algorithms in various modes.
- Did you have any complications during development of the stand ?
- On our order Moscow company 3V- Servis has developed an interface for our calculation code which enables us to present the input data for calculation in graphical form. In fact, now we are assembling the calculation scheme as if using a number of puzzle blocks setting the parameters for each of them. When creating a virtual interface there were many difficulties, because in order to calculate a reactor or a steam turbine plant, it is necessary to set a huge number of parameters. And we did a great deal of work, conducted all kinds of tests so that all these parameters are set correctly, and the input files for our calculation code are formed in precise way. In return for a great amount of tests done, now we have a tool in which the graphic view is not only accurate, but it is also visual.
- Is there any further development of the program? - Are its functions expanding?
- We are not wasting time, we keep working non-stop. Now we are finalizing the calculation code, which has recently been re-certified for calculating the safety of pressurized-water propulsion reactor. In addition, new closing relations are added, the numerical scheme is improved. Due to this, the stability of the program is increased, new elements for calculating the electric power system are added, the model for calculating gas systems is being improved. While our computational core is constantly improved, our colleagues from SimInTech are also upgrading the software bundle which we are using as a shell program. SimInTech programmers release new versions of the software, expanding the functionality of automation modeling and adding various functions for working with our interface. We are doing preparation works in order to incorporate Super computer in the stand. Technological development will soon create a full-fledged digital twin of a power plant and we will be able to use it at all the stages of the plant life cycle.