The Story of Apros®

Apros® is a multipurpose simulation software, which is traditionally used to design and analyse the dynamic behaviour of power plants and their control systems. It enables extensive modelling of various power plant processes, which is particularly valuable for power plant design verification and validation, evaluating new processes and control concepts, testing operational and emergency transients and for operator training.

Early history: Supporting Loviisa nuclear power plant

The story of Apros goes back to 1986, when Apros’s development started as a joint project by VTT Technical Research Centre of Finland and Fortum´s predecessor Imatran Voima (IVO). The aim of the project was to support the operations of the Loviisa nuclear power plant. As the development progressed, it soon became clear that Apros could support power plants throughout their whole life cycle: in the design phase, the commissioning phase and in training new operators and engineers.

The Loviisa model was ready for first applications in 1991, and after that, it has been constantly developed. It was an early priority for Apros, but not the only one. From the very beginning, Apros was meant to be a multipurpose software, and it has been used in various ways in many significant projects around the world.

Expansion to other nuclear and thermal applications

Alongside with the Loviisa NPP model development, both Fortum and VTT started to utilise Apros for various other applications. Some of the projects are listed below.

Haapavesi peat-fired power plant (with once through boiler configuration) was, together with the Loviisa NPP model, one of two pilot cases to be modelled and simulated with Apros to benchmark Apros code capabilities in the 1990's.
In 1993, Fortum Engineering and the nuclear plant at Kola began to cooperate in developing a simulator. The Kola NPP plant analyser and compact training simulator were developed and delivered in 1993–1998. The training simulator passed official acceptance tests in August 1999. The full set of acceptance tests covered the simulation of different steady-state operations, start-up and shut-down, and 40 failure and accident situations.
A training simulator for Vanaja combined cycle gas turbine power plant was developed in IVO to support operator training, plant modification design and marketing of operation and maintenance services in 1995.
In the HAMBO simulator project, an experimental BWR simulator based on the Forsmark 3 plant in Sweden was developed for OECD Halden. The BWR simulator development project was initiated in January 1998. The simulator model was co-developed by VTT Energy and IVO Power Engineering Ltd using Apros software, while the operator interface was developed by the Halden Project. The simulator was thoroughly tested by experienced Halden Reactor Project personnel and professional Forsmark 3 operators and accepted by the BWR utilities in June 2000. The acceptance tests consisted of 19 well-defined transients, as well as the running of the simulator from full power down to cold shutdown and back up again with the use of plant procedures.

Loviisa power upgrade and safety analyses

One of the major milestones in the history of Apros was the power uprate at the Loviisa power plant in 1995–1997, when Apros was for the first time used extensively for deterministic safety analyses calculations. The challenge was to find out exactly how the power uprate would affect the overall process behaviour and how the modified systems would work together. Naturally, the safe operation of the uprated power plant also needed to be proven to the Radiation and Nuclear Safety Authority STUK. The existing Loviisa NPP simulation model needed to be developed further to be suitable for safety analyses – meaning that every detail of the model had to be well documented and the Apros software calculations validated. It was a big effort to make the model ready for STUK´s evaluation, but in the end, it was done successfully, and the Loviisa NPP power uprate was approved.

Along with the 21st century came new challenges for Apros. Loviisa's operating licenses were expiring in 2007 and 2010, and Fortum decided to apply for a new license to continue operating both units of the power plant for another 20 years. In order to apply for the license, the safety analyses of Loviisa NPP had to be recalculated to show that it would be safe to extend the operating time. These analyses were calculated with Apros, once again successfully, and the new operating licenses were eventually granted. As part of this project, Apros was used to model and calculate reactor containment building behaviour as part of the analysis calculations, which had never been done before. Today, all deterministic safety analyses of the Loviisa power plant are calculated with Apros.

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Loviisa NPP automation renewal projects

Projects LARA and ELSA, which took place during 2005–2018, were related to the automation renewal of the Loviisa power plant. The automation of the power plant had to be modernised to ensure safe and reliable operation of the plants, and thus the automation systems needed to be renewed.

The purpose of project LARA (2005–2014) was to reform the operational and safety automation on a very large scale. Due to the tight project schedule and broad scale of the renewals, utilisation of efficient testing methods was a necessity. Finding the proper parameters for the new automation systems was a challenging task, for which Apros was able to provide an excellent solution as a comprehensive simulation tool. The Apros engineering and testing simulator as well as the Apros development simulator played important roles in supporting the control room design and I&C testing. Apros was also used as a calculating engine in the operator training simulator LOKS2 developed during this project. The demands for the new training simulator were extremely high, requiring extensive Apros software and platform development as well as necessary Apros add-on tools, such as Instructor's Station. As a result, Apros evolved extensively during the project.

Project LARA ended in 2014, but the Loviisa automation renewal project continued under the name ELSA (2014–2018), the focus of which was on renewing the safety critical I&C systems. Apros was also widely utilised in project ELSA: it was used to test the quality of Rolls Royce’s new automation system design before the actual commissioning of the automation systems at the Loviisa power plant. The testing phase, carried out in France, was expected to take up to 18 months but was completed in 11 months – a great example of the solid performance of Apros.

With an I&C system renewal project so complex as ELSA, consisting of several safety and safety related systems together with operational systems, the benefits of utilizing such a powerful tool as Apros were crucial in succeeding in such challenging time schedule. The new systems were commissioned for both plant units in three consecutive years within regular outage durations. This gradual and phased approach required effective modelling and simulation of systems in different lifecycle stages to enable smooth integration testing already at test field and minimizing errors found at plant in final commissioning phase.
- Petteri Lehtonen, Head of I＆C and Electrical Systems

From an internal tool to external business

Apros was never meant to be just an internal tool for Fortum and VTT: from the very beginning, the plan was to sell Apros products and services to external customers. At the same time, both Fortum and VTT have been continuously interested to learn more about power plants’ dynamic behaviour, increase our knowledge on different energy systems and train new engineers and scientists to become new top energy professionals in Finland. We have reached all the goals, as Apros has been a major competence development platform used in numerous Ms. Sc. thesis and Ph.D. works.

The software developers and power plant experts from both VTT and Fortum/IVO have done an extremely good job in the source code and application development work, starting from the very beginning, since Apros has been able to calculate complicated power plant processes and challenging thermohydraulic phenomena already in the 1990's. Nowadays large models and applications are easily run on regular laptops and workstations. At the same time, the software is very easy to take into use and the graphical user interface and calculation stability of Apros have been very much praised by our customers. Apros products and services have been delivered to numerous different users globally: EPC vendors, equipment manufacturers, energy utility companies, engineering companies, research institutions and universities. For example, companies such GE Power, Teollisuuden Voima, Forsmarks Kraftgrupp and Fennovoima use Apros in their daily work. Nowadays there is an ever-increasing need to simulate flexible energy production systems and to evaluate their system behaviour under different operation conditions. Apros provides an excellent simulation platform, which enables simulating all these within a single software application. - Toni Salminen, Senior Manager, Apros

Today, Apros software licenses have been sold to over 30 countries. Feedback from users around the world has been excellent. Apros has been described as an accurate, stable, user-friendly tool – one that even a newly graduated engineer can use without months of training. Also, the ongoing version development is highly appreciated: a new software release with significant improvements is published every year.

A global user community that has various practical needs and development ideas for the software is very important to us and much appreciated by the Apros developers – new ideas are always welcome.

A new application area for Apros: E2E and DigiTwin

New possibilities

While design verification and transient analysis are the key uses of Apros, operational optimisation is a very new area, and it opens plenty of new possibilities for us in the future. We have a great team behind Apros and a network of experts to support the continuing development work. With model-based optimisation, ground-breaking things can and will be done – the Digitwin project in Espoo is just the beginning.

Besides district heating applications, Apros is a very versatile tool for modelling renewable energy-based production facilities and new energy process concepts. Apros has been used to model different kinds of biomass boilers as well as Solar CSP concepts integrated with Thermal Energy Storages. Apros also provides good tools for modelling and simulating hydrogen production and P2X facilities, as has been done in the NeoCarbon project with Apros. These new system models can be integrated into the existing energy system models done with Apros, allowing evaluation of the whole performance of the energy system. Apros has also been used to model DEMO fusion balance-of-plant behaviour in the EUROfusion WPPMI project and small modular reactors in different R&D projects, showing the flexibility and usefulness of Apros as multipurpose simulation platform.

Compared to other solutions, Apros has many undeniable benefits and features that make it unique. Very extensive needs from design to tracking and online optimisation place high demands on the model or tool, and Apros can meet all these needs now and in the future.