Simulation increases effectiveness and quality in modernisation project - CASE Emergency diesel automation renewal at Loviisa NPP

The challenge in nuclear power plant modernisation projects is to ensure safe and functional connectivity between existing and new systems. Safety and functionality must be proven in advance so that the wanted changes are licensed and approved by the operator and the regulator. Dynamic simulation enables the technical concept to be verified in all design phases, and the plant's operators can be involved in functional testing and design work at the very early phase of the project.

Loviisa power plant sunset spring

The original emergency diesel automation systems at Fortum's Loviisa NPP have been modernised. The role of emergency diesels is to automatically provide power for safety-critical components during a total loss of off-site power. The emergency diesel automation consists of safety-classified I&C cabinets (analogue) and non-safety-classified I&C cabinets as well as Human-machine Interface (HMI) systems (physical controls, PLCs and touchscreen). The automation system includes many different operation and control modes, testing functions, and conditional and unconditional protection functions. The automation functionalities are too complex to evaluate with pen and paper, especially regarding fault situations, testing degraded states, and simultaneous activity of safety-classified and non-safety logics. The tight schedule of the NPP overhaul limits the available time for on-site testing of the automation. Delays in commissioning will result in large electricity production losses.

Integration of new and existing systems is extremely valuable for testing

The decision to utilise the Apros simulation software was made in the basic design phase; as a first step, the safety-classified part was modelled. Basic design functionality was tested dynamically with the model, which provided design feedback in the early phase. Then the system design proceeded to the detailed design phase. The detailed Apros simulation model was developed based on the function diagrams provided by the automation system supplier. Both safety and non-safety automation systems, together with a simplified emergency diesel model, were integrated to the same simulation model, enabling full system verification. The simulation model was found to be an efficient platform between the supplier and Fortum – not only for noting issues, but also for discussing and solving design issues.

After the detailed design phase, the Apros simulation model was used to carry out functional tests of the system. The simulation results were reviewed with NPP operators and the automation supplier. The Apros simulation model – with the simulated HMI integrated into the model – was also used to train the NPP operators in the renewed system. Training was executed before finalisation of the HMI components and automation components so that operator feedback about the new system (25 different notes in this project) could to be taken into consideration. This resulted in a more user-friendly HMI system.

In the factory acceptance tests (FAT), the simulation test results were used as a validation reference. During the site acceptance tests (SAT), the Apros simulation model was used to check changes in the operator instructions beforehand and to confirm the observations of the system behaviour.

”Most beneficial in utilising dynamic simulation was that many findings and improvements were noted and resolved already during the design phase. Simulation is really a cost-efficient way of verifying the design. Especially important is the impact it has on decreasing the risk of delays in the NPP outage schedule.”

Kristian Sjöblom Senior expert, Automation design, Fortum

The simulation model creates confidence in design decisions

The functional testing, together with simulated HMI, created confidence in the functionality and operation of the new automation system. Simulation activities were also demonstrated to the regulatory body (STUK), and positive feedback was received from them. It was beneficial that many faults and issues were found and resolved in the early phase of the project, most of them before the FAT. Solving these issues during the FAT and SAT phase would have been much more costly and time-consuming; this way, the risk of delaying the whole NPP outage schedule was decreased.

More efficient cooperation and training

The simulation model improved the cooperation in the problem-solving and design commenting work between Fortum and the automation supplier. In addition to general problem solving, the simulation model played an important part in the training of the modernised system for the NPP operators. The operators were able to complete this training independently in the control room where the laptop-based simulator was installed. This reduced travelling and training day costs, and valuable feedback was received from the NPP personnel, as using the simulation models allowed them to participate in the very early phase of the project.

Use of Apros in the diesel automation renewal project proved the value of dynamic simulation in all parts of the power plant's modernisation project. The initial investment to get value from the simulation model was only two weeks of work. The simulation model was developed throughout the project based on updated design documentation and integration of the local HMI. The utilisation of Apros simulation software enabled the validation in all the design phases, improved the communication from the suppliers to the end users, and had a positive impact on the project schedule and budget by reducing the issues in the commissioning phases.

Fortum Loviisa

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