Forsmark 3 is a 1160MWe BWR that was commissioned in 1985, and was originally built by ABB Atom.
In 1996, Forsmarks Kraftgrupp and Siemens KWU-N (now Framatome ANP) began to modernise the system for control rod manoeuvre and indication (project MODS) at Forsmark 3. Before the design work began, an analysis was performed demonstrating some defects in the original system.
Taking the weak points of the original system into account, the design targets for the new system were defined as follows:
• Secure a more reliable system (reduction of probability of unintended IN manoeuvre of all rods caused by a single failure) and improved durability.
• Customise system functionality to the available operational experience.
• Improve rod positioning accuracy.
• Simplify the maintenance procedures with fewer maintenance personnel than previously, especially under the reactor vessel.
• Separate the rod control and indication functions from the existing process computer in order to achieve a clearer I&C architecture.
• Install a new digital system in order to gain experiences for later I&C upgrades based on digital technology.
• Substitute several system platforms that are becoming increasingly obsolete.
Teleperm system
The Teleperm XS system is an I&C platform that can perform functions up to the highest safety classes, and provides a basis for efficient operation during the entire plant lifetime. Systems from this platform are being implemented in several nuclear power plants of different types in Europe, the USA and China, and it has passed the licensing procedures in many countries. The scope of functions include reactor protection systems, neutron flux systems, reactor limitation and control systems, and turbine protection and control systems.
Typical benefits for plant operation are obtained in the areas of:
• Improved plant availability through the use of state-of-the-art digital equipment and software components qualified by independent experts.
• Applications can be implemented in a scalable architecture adapted to the specific requirements of each project.
• Comprehensive tools are implemented for easy-to-use design, tests, service and maintenance.
• Ease of design changes as future design optimisation occurs, through automatic documentation.
• The documentation automatically reflects the as-built configuration of the I&C system, since the
documentation is part of the engineering tool.
• Simplified testing requirements and simplified maintenance strategies due to the high degree of system self-monitoring.
Scope
In 1996, Siemens KWU-N offered a proposal to Forsmarks Kraftgrupp AB (FKA) based on a specification submitted by FKA.
The proposal included the rod control and indication system for the 169 control rods, together with the required screen-based control room equipment, switch gear for the rod drives and additional computerised equipment for rod calibration and rod specific data logging. Since the new equipment had to be integrated into the existing I&C architecture of Forsmark 3, the removal of the equipment to be substituted and the clarification of interfaces between the newly installed and already existing systems also formed part of the proposal. FKA decided to accept the proposal and exchange the control rod system. The order included system design, tests, erection and commissioning of the system as well.
Identical with the former architecture, the new system also consists of a centralised part and a local part subdivided into four redundant trains called ‘subs’. This architecture complies with the overall I&C structure of Forsmark 3.
Two central cabinets of Teleperm XS and additional equipment for the central operating and monitoring system based on Teleperm XP are located centrally. Four Teleperm XS cabinets are installed in each sub.
The central system provides the sequence controller for the selection of specific control rods according to a given sequence list and the operating mode selected by the operator. In addition, the support for operating and monitoring, including the generation of detailed alarms, has been implemented in the central system.
In general, a number of functions are performed locally in the subs, such as:
• Automatic interlocks.
• Rod specific control and monitoring functions.
• Automatic control rod insertion at shut down conditions and the automatic testing of this function.
The high requirements of positioning accuracy with non-break drives were achieved by permanent measurement of the rod inertia in every rod step via cyclic compensation calculation.
Additional earth fault monitoring has been achieved through the application of new switch gear plates.
The system can be operated via 10 operating and monitoring displays, each to be selected at four new screens in the main control room. Typical operating and monitoring tasks for the new system are:
• Selection of the control rods.
• Display of the system status.
• Automatic interlock of rod movement if the ‘manoeuvre picture’ is not selected.
• Automatic display of a specific ‘core picture’ in the case of a scram.
• Indication of neutron flux values.
• Screen-based support to calibrate the rods during maintenance.
The main display shows:
• The core section indicating rod position and rod status.
• The neutron flux in the different ranges.
• Selected alarms.
• The operation mode.
The operator has the option of selecting between two different display modes. One mode provides the information generated from the new rod control system, while the other mode displays the presentations of the existing plant computer.
Furthermore, several auxiliary systems based on conventional PCs and the SIMATIC S5 system were delivered, including a maintenance database, a workshop system and a local manoeuvre station.
These systems fulfil the following tasks:
• The maintenance database records essential rod drive specific maintenance data such as motor power and counted pulses from newly installed inductive pulse sensors.
• The workshop system is used for the pre-calibration of rod drives in the hot workshop.
The local manoeuvre station was designed on the basis of a standard notebook computer with specific software, and allows the single control of the group of rods assigned to one train (sub) in case of loss of the centralised functions.
In addition, the operator is supported by computerised maintenance equipment capable of online fault diagnosis.
The system functions were integrated in the Forsmark 3 full-scope simulator at Kärnkraftsäkerhet och Utbildning (KSU) at Studsvik for operator training. The Teleperm XS software of the main system was used directly to simulate the application software so that on both, main system and simulator, identical functionality is achieved. The operating and monitoring facilities are also identical in both main system and simulator.
Project MODS
From the start of the project, Siemens (now Framatome ANP) set out to acquire a deep understanding of Forsmark’s plant management and technology.
The original design features of the existing control rod drive mechanism, including indication units, have been analysed, verified and transferred into the application software. The specific philosophy of operation and monitoring was partly redesigned in close cooperation with the reactor operators, taking the available operational experience into account.
The application software was generated automatically with the high performance engineering tool SPACE on the basis of standardised function diagrams, ensuring consistent software for all 169 rods. The simulation-based validation tool SIVAT was applied in order to accelerate the validation process for the application software.
The project also required clarifications of interfaces between the remaining systems and the new installations, and in some cases essential modifications were needed, for example, removal of software packages from the process computer that were no longer required.
In order to get the best possible completion of the task, it was decided at an early stage to involve third parties under the global responsibility of Siemens/Framatome ANP for the following tasks:
Process computer adaptation
The removal of large software packages with the original rod control functions required detailed knowledge of the process computer. The original designer of the system was involved in this task.
Engineering of interfaces of the remaining systems
This task was performed by a local engineering company familiar with the installed I&C systems and with the document management applied at Forsmark 3.
Support of site activities
The installation, preparation and commissioning phases required daily harmonisation with Forsmark’s plant operation management and fulfilment of the binding work release procedures. These tasks were performed by experts from local companies working under the supervision of Framatome ANP’s site management.
Engineering of peripheral sub systems
The main system, composed of components of the system platforms Teleperm XS and Teleperm XP are supported by PC-based subsystems (maintenance database or workshop system). A specialised engineering company in Germany performed supply, design, tests and commissioning of these parts.
Siemens/Framatome ANP was fully responsible for all work packages, but with specific profiles of qualified companies that could best ensure that the customer requirements were met. The practice for already applied technical principles and work procedures could be observed. Language difficulties could easily be avoided by employing Swedish experts.
Due to the complexity of the system functions, including the resulting interface clarifications and the amount of integration work, the installation and commissioning activities could not be executed in the 1999 outage. Since there was only a 10-day outage planned for the 2000 outage, it was agreed between customer and supplier to bring the system into operation during the 2001 outage, which took place between 23 July and 30 August.
Until the 2001 outage, the time was used for preparatory site activities such as cable laying, erection of new cabinets and administrative work preparation.
Besides comprehensive tests in the test field in Germany, finalised by a factory acceptance test (FAT), the complete system functions were tested in advance at the Forsmark 3 plant simulator at KSU in Studsvik. This ensured the implementation of pre-tested software at the plant, and reduced the scope of tests that had to be performed during commissioning in the scheduled outage. Therefore, the site commissioning tests focused mainly on Input/Output signal tests and to integral tests of safety functions, such as scram and interlocks.
All activities planned for the 2001 outage at Forsmark were performed during the course of the outage. The only unexpected event was the detection of cracks in a few of the 169 inductive pulse sensors. Later material examinations revealed that this damage was caused by intergranular hydrogen induction. Although only seven sensors were affected and there would be no restriction of the plant operation, it was decided to exchange all sensors in the next outages for those of material not sensitive to this effect.
In addition to the comprehensive operator training at the simulator at Studsvik before system commissioning, Framatome ANP gave training courses for operating, engineering and maintenance personnel. Around 80 people were trained in the following topics:
• Basic introduction.
• Operating and monitoring.
• System design.
• Auxiliary systems.
The digital system allowed documentation which was adjusted to the existing plant documentation system to be available online. Although the documentation concept of Teleperm XS differs in detail from the previous practice at Forsmark, the personnel involved were convinced of the advantages of the new concept.
With the implementation of the new system, the goals set by the Forsmark 3 project team were achieved and were confirmed by FKA after a year’s operation. During this period, the functionality of the different system components worked according to the specifications. The only major unexpected event was caused by an interruption of communication between the central part and the operating and monitoring system, leading to confusing alarms for the operators. This disturbance was caused by a shortcoming in software management, and was quickly clarified by Framatome ANP so that any disturbance of plant operation was avoided.
As a result of the close cooperation between the Forsmark and Framatome ANP project teams, the product solution was successfully implemented, and has proven to give good operational performance. In particular, the specific needs of the rod control system were easily met.
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