Apros case – Dynamic testing throughout the project with plant model brought quality and savings in safety I&C renewal at Loviisa NPP

Power plants require modernization projects to keep them operational and fulfilling safety requirements over several decades. Such modernization projects are usually unique projects, where new technologies need to be coupled with older systems, and also there are time restrictions for the project execution. For such projects, digital twins are crucial tools for the engineers to verify their works before going into commission phase. Fortum carried major I&C renewal project called ELSA to Loviisa Nuclear Power Plant, where Apros dynamic simulation software was utilized extensively.

The Loviisa plant consists of two VVER-440 reactors that started producing electricity in 1977 and 1980. To ensure safe and profitable future operation of the plant, Fortum decided to renew majority of the safety related automation systems of the plant in several stages. The supplier of the new automation systems was Rolls-Royce Civil Nuclear. 

The ELSA project, which was carried out between 2014 and 2018, involved the renewal of

  • the reactor trip system
  • the preventive protection functions
  • the reactor control and power limitation system
  • the neutron flux measurement

and introduction of

  • the accident management prioritization system
  • the automatic and manual backup of reactor trip systems

Apros based simulators were extensively used during the ELSA project, with the new automation systems being validated against the simulated plant. Apros based safety analysis model was used to verify the feasibility of the safety systems functionality in concept phase and Apros based test simulator was used to verify systems functionality in design and testing phases. Simulation assisted testing made it possible to discover errors early and increased the quality in the project. System validation against the simulated plant decreased significantly the time used in factory acceptance testing phase and was one reason that no significant deficiencies were found during or after the commissioning.

The challenge

Implementing new safety automation system at NPP environment is very complex project, since the new system will interface with the existing plant systems and operations. Main challenges are that the new systems have functional interfaces with existing systems, commissioning is done during very limited time during normal outages of the plants and the functionality of the new systems shall be validated to work in plant’s all operation scenarios and verified to meet the authority requirements.

Safety automation systems have interfaces naturally to many process systems but also to existing automation systems that are not changed in the project. Project needs to ensure that interfaces are working properly and the functionality of the interfacing systems are tested together. When converting analog systems to digital the challenge is also to verify that the functionalities remain similar (i.e. control loops and measurements).
Power plant operators want minimize the length of the outages which gave the challenge that all commissioning were done during the plants normal outages. All delays have significant costs in form of lost production. In the ELSA project the commissioning was done in three consecutive outages. This requires that design quality and testing of the systems are done very extensively  and with high quality prior to the outages.

Replacing the safety automation system has effect on all main safety system functionality and accident scenario management but also to normal operation as shut down and start up processes. Challenge is to validate the new system functionality as part of plant operation in all operating scenarios. Naturally the local authority's (STUK) requirements have to be fulfilled. 

The solution

Utilizing dynamic simulation was significant part of resolving the mentioned challenges in the ELSA project. It was important to integrate simulation activities in early phase of the project and have very tight co-operation with the supplier. As part of this project, Fortum required the supplier to develop an interface between Loviisa NPP Apros plant model and the supplier I&C systems. The I&C systems we implemented as emulated systems and actual automation cabinets during this project, and both of them were connected to the Loviisa plant model. This was very crucial to be able to utilize the existing Loviisa plant models and enable virtual commissioning throughout the project lifetime. The early testing and validation of the designed systems with the Loviisa plant simulation model helped both parties to reach a successful end result.

The Apros simulation model of Loviisa NPP process was utilized in the project in concept design, basic design, detail design, V&V and factory acceptance (FAT) phases. 

Schedule for I&C  systems commissioned in 2018 outage

1. Conceptual design (safety functions)

In conceptual design phase the Loviisa NPP Apros plant model was utilized to validate safety functions. Target was to verify that the plant process systems are capable to perform the safety functions with sufficient margin compared to the allowed operating limits and that the sufficient time is available for the needed operator actions. In total about 70 different analysis cases were simulated and they included system failures and complex failure combinations. Plant owners’ own capability to do the concept phase analysis in early phase ensured effective work and enabled testing different variations to limit values and delays for the systems (i.e. steam generator liquid level and operator actions).

2. Design phase

In design phase the suppliers design was first modelled as part of the Loviisa NPP Apros plant model. The Loviisa NPP Apros plant model included all the NPP process systems, as well as the existing I&C systems and interfaces to the control room monitoring and operating systems.

Apros based simulators were extensively used to support the project

When modelling the new system to the existing power plant model the interfaces between new and existing systems were tested for the first time in the ELSA project. The co-operation between the Fortum and the supplier in this phase and onwards was very active and fruitful because the technical discussions and discussion outcomes were based on the simulation results provided by the Loviisa NPP Apros plant model. 

Very important example of modelling and simulating the conversion from analog to digital technology was the reactor power controller. Conversion is not straight forward but needs to be designed and validated so that the functionality responds to the original one. Apros Loviisa NPP model was utilized to design the new controller and based on functionality testing and tuning of the control parameters there were logic changes to initial design of the control. Simulator environment enabled the operator feedback for control design already in this phase.

Utilizing the simulation model already in the basic design phase revealed many issues in the design about the interfaces and from the logics of the new systems. These issues were reported to the supplier and the supplier corrected them before the next design phase. The plant level test scenarios for these systems were created and simulated already in the basic design phase, which gave verification that functionalities were fulfilling the defined requirements. These plant level tests were then repeated in all upcoming project phases to ensure quality of the I&C systems.

3. Validation and verification with emulations

In the detail design phase the emulation of the seven new systems was provided by the supplier. These emulated systems were tested one by one as part of the Loviisa NPP plant model. The emulations were connected to Loviisa NPP plant model as external reference model in dynamic linkable library (.dll) format. Emulated systems were tested with same testing scenarios as in the  previous test phase. In validation of emulated systems many issues were noted and corrected regarding the alarm limits, delays, controller parameters. 

Testing the emulated systems as part of plant model verified the functionality of the new systems and their interaction between existing systems. In the emulation test phase, the plant level test scenarios were extended also to include full power plant start-up and shut-down simulations. 

The emulations of the new systems were utilized and installed to the LOKS2 training simulator, which included the Loviisa NPP Apros plant model and control room replica implemented with virtual panels. This enabled the operator testing of the new systems in control room environment already in the design phase. Many observations and notes from the operators where included in the design, which resulted in good feedback from the operators after the commissioning. In the training simulator the emulations were utilized as such which assures that systems are identical between the plant and  the simulator also after the commissioning.

4. Factory acceptance test (FAT) phase

In addition to conventional I/O testing by the supplier, the simulator based I&C testing was performed during the FAT. In the FAT phase, the actual I&C cabinets were coupled to Loviisa NPP Apros plant model and this enabled the I&C testing in process transient and accident scenarios. All systems were first emulations and later replaced by actual built cabinet on the test field. The emulated systems were one by one replaced with real cabinets once cabinets were manufactured. Testing was that way restricted to only that selected system. This flexible and progressive methodology enabled early testing of each cabinet and speeded up the overall FAT schedule. 

FAT is important and last step before commissioning systems on the NPP site. Utilizing Loviisa NPP plant model  also in FAT increased the test coverage significantly, since real plant level scenarios, such as operational transients and various trip scenarios, where simulated. Test results were also compared to earlier test phases to verify the I&C system quality after the change from emulated system to real automation cabinets.

Finish authority Finnish Radiation and Nuclear Safety Authority (STUK) also participated in the FAT. Their requests and questions to the functionality of the systems in beyond-design-scenarios were answered immediately at the FAT phase by simulating additional scenarios and presenting the simulation results the authorities.

Overall the extensive utilization of simulators increased the quality of design and communication between Fortum’s technical design disciplines and between the owner and the supplier. 

Control room changes and operating instructions

In the project the main control room changes and operating instructions were validated in the training simulator. In addition the project utilized a development simulator and a virtual reality simulator, which were based on Apros Loviisa NPP model. Simulators supported development of the main control room concept and operating instructions. Extensive use of simulators increased the quality in the project.

  • Operating and emergency instructions were supported already with the concept phase simulations with Apros Loviisa NPP model
  • The development simulator supported the development of renewed and new user interfaces by providing the dynamic input to the user interfaces and enabling operators to test them in real environment. Many observations were considered and changes implemented to the user interfaces and the operating instructions.
  • Virtual reality simulator was utilized in control room and instructions development. In addition to the main control room the virtual reality simulator included the safe shutdown control room. The VR simulator enabled test cases that were not possible in the other simulators such as handing a fire in the main control room. The simulator provided additional evidence for the licensing process.

The results and benefits

Main benefits in utilization of Loviisa NPP plant model were the verification of design in early phases of the project, increasing the test coverage and decreasing the factory acceptance time needed and successful integration of operators to the testing, as well as achieving commission within the planned schedule without any delays.

System logic was verified during the design phases prior to installation. Issues in design were caught early which  saved money and increased the quality. Simulation assisted design and testing during the project ensured that commissioning was performed during the normal outages and there were no significant deficiencies were found during or after the commissioning. 

Factory acceptance test period was shortened by approximately seven months (from original, traditional IO testing approach with 18 months to 11 months) in a five year project. This was possible because testing was able to be started when first cabinets were ready. Testing setup also enabled the focus directly on the selected cabinets and systems which reduced the time on problem solving. With Apros Loviisa plant model integrations, it was possible to test the new system with real power plant transients, which is not possible with conventional testing methods. This enabled real lasting (10h) operating scenarios and repeatability of the tests which made testing process more effective. 

With Apros® based operator training simulator environment, the operators could test and familiarize themselves to the new systems during the design phase, and their feedback was then applied to the system design. This resulted as increased quality in design, decreased the resistance to the changes and increased the knowledge and adaption to the new systems before commissioning by the operators. Only positive feedback from operators was received.  The emulations were utilized at training simulator as such which assures that systems are identical between the plant and the training simulator also after the commissioning.


Decision to utilize Apros based testing simulation in the Loviisa NPP automation renewal project was one of the main drivers, which ensured that the project was successful in supplier co-operation, finished in forecasted time and budget and there were no significant deficiencies found during or after the commissioning in the systems.

Simulation aided design and testing competence is high strength for the plant owners organization / engineering departments and Apros software enables the engineers and designers to utilize their the technical competence in all phases of the project. Simulating the design and functionality with actual power plant process feedback ensures the quality of the I&C systems, highlighting the possible design issues in early phase of the project. This also has significant positive effects, such as decreasing the time used in the factory acceptance testing and commissioning phase.

Please contact us to learn more about the case and our experiences

Toni Salminen

Tel: +358 400 519 650
toni [dot] salminen [at] fortum [dot] com

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